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Cerebellar injury: clinical relevance and potential in traumatic brain injury research
Weber & Maas (Eds.) Progress in Brain Research, Vol. 161 ISSN 0079-6123 Copyright r 2007 Elsevier B.V. All rights reserved
CHAPTER 23
Cerebellar injury: clinical relevance and potential in traumatic brain injury research Eugene Park1,2, Jinglu Ai1 and Andrew J. Baker1,2, 1 St. Michael’s Hospital, Trauma Research, Toronto, ON, M5B 1W8, Canada University of Toronto, Institute of Medical Sciences, Toronto, ON, M5S 1A, Canada
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Abstract: A treatment for traumatic brain injury (TBI) remains elusive despite compelling evidence from animal models for a variety of therapeutic targets. Numerous animal models have been developed to address the wide spectrum of mechanisms involved in the progression of secondary injury after TBI. Evidence from well-established models such as the fluid percussion injury (FPI) device, cortical impact model, and the impact acceleration model has demonstrated diffuse pathophysiological mechanisms throughout various brain structures. More specifically, we have recently extended characterization of the FPI model to include pathophysiological changes in the cerebellum following unilateral fluid percussion. Data suggest that the cerebellum is susceptible to selective Purkinje cell loss as well as white matter dysfunction. Despite the cerebellum’s low profile in TBI research, there is evidence to warrant further study of the cerebellum to examine mechanisms of neuronal death and traumatic axonal injury. Furthermore, evidence from clinical literature and basic science suggests that some components of TBI pathophysiology have a basis in cerebellar dysfunction. This review highlights some of the recent findings in cerebellar trauma and builds an argument for including the cerebellum as a model to assess mechanisms of secondary injury and its potential contribution to the pathology of TBI. Keywords: animal models; cerebellum; electrophysiology; FPI; TAI; TBI injury mechanisms exists in variety of injured axon subpopulations (reviewed by Buki and Povlishock (2006)). These data support a need for in-depth scrutiny of mechanisms encompassing all regions susceptible to traumatic brain injury (TBI) in order to formulate an accurate and thorough description of pathophysiologic processes. The cerebellum’s role in TBI has received relatively limited scrutiny and characterization as other structures including the brain stem, hippocampus, and cerebral cortex. It is becoming increasingly evident that general mechanistic descriptions of cell death and axonal injury are overly simplistic and do not accurately reflect the full spectrum of events occurring after TBI. Clinical cases of TBI and parallel research in animal
Introduction Intense scrutiny of neuronal cell death and traumatic axonal injury (TAI) has clarified numerous molecular and cellular events contributing to the progression of secondary injury cascades. As our understanding of molecular events continues to increase, our description of these events have become increasingly complex. For example, all traumatically injured axons were previously thought to undergo a series of pathophysiological events leading to disconnection and bulb formation. However, it has become evident that a spectrum of Corresponding author. Tel.: +1-416-864-5510; Fax: +1-416864-5512; E-mail: [email protected] DOI: 10.1016/S0079-6123(06)61023-6
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models have confirmed that the mechanisms of injury extend to the cerebellum thus building a case for its relevance in neurotrauma. A thorough characterization of all affected structures throughout the brain, including the cerebellum, would provide a better framework with which to optimize treatments for TBI. Furthermore, the potential for discovering or elucidating mechanisms of injury not yet described would also add to our existing knowledge of secondary injury mechanisms. It may be argued that cerebellar trauma is of limited clinical importance; however, recent studies have begun to elucidate roles in higher order cognitive function not previously appreciated in cerebellar processing (Petrosini et al., 1998; Ramnani, 2006). These higher order functions as well as other neurological processing functions not previously known may account for some of the observed behavioral abnormalities in people afflicted by TBI. In the present discussion we propose several lines of evidence to support the role of cerebellar injury as an important component of TBI, and also several unique features that render the cerebellum a potentially useful structure in which to assess mechanisms of secondary injury after trauma.
Clinical evidence of cerebellar trauma Clinical manifestation of cerebellar dysfunction include perturbations to stance and gait, characterized by a loss of equilibrium, a wide-based stance, irregular steps, and lateral veering (Mariotti et al., 2005). Cerebellar deficits can also give rise to tremors (e.g., Parkinsonian), alterations to speech resulting in slowed or slurred vocalization, as well as cerebellar mutism (Gordon, 1996). Recent studies have also indicated an important contribution of cerebellar function to visuo-motor control (Glickstein, 2000). Patients with cerebellar ataxias exhibit ocular motor defects in target fixation and coordinating head movements (Mariotti et al., 2005). Although these deficits are generally not described in the context of trauma, it is not unreasonable to draw inference to traumatic cerebellar injury which could result in similar pathological impairments, particularly since
many of the motor, cognitive, and speech impairments described above are also observed in TBI patients. There are many reviews on diagnoses, mechanisms, outcome, epidemiology, cost analysis, rehabilitation, etc., and specific case studies in TBI involving cerebral injury. However there is limited clinical literature with direct emphasis on cerebellar trauma. In 1917, Gordon Holmes described observations of World War I soldiers who had sustained gunshot wounds to the cerebellum. He described a drunken-sailor type gait, as well as the postural disturbances commonly associated with cerebellar dysfunction (Holmes, 1917). A recent report of 26 patients who had sustained infratentorial injuries is the only clinical study to date to specifically address the issue of direct trauma to the cerebellum (Nathoo et al., 2002). This particular type of injury, although rare in the civilian population, has been documented predominantly in military literature (Rish et al., 1983; Brandvold et al., 1990). Moreover, the authors of this study note that cerebellar injury had no effect on outcome. It should be noted however, that the five point Glasgow Outcome Scale (GOS) used in this particular study might not be an adequately sensitive measure of functional and behavioral deficits to detect cerebellar dysfunction. Furthermore, the GOS is primarily a measure of global outcome and does not factor in the consequences of motor, speech, and cognitive impacts on daily living. Despite limited literature on direct cerebellar trauma there is a varied collection of literature in which the cerebellum has been referenced as exhibiting pathological changes including selective cell loss, altered metabolism, and white matter injury after focal and diffuse TBI. For example, Purkinje cell loss has been noted in the brains of boxers and implicated as a significant contributor to ataxias and Parkinsonian tremors (Guterman and Smith, 1987; Unterharnscheidt, 1995a, b). Another report cites hypertrophic olivary and Purkinje cell degeneration following chronic TBI (Anderson and Treip, 1973). Post-traumatic intracerebellar hemorrhage, though an unusual clinical occurrence, has been observed after head trauma and is an important clinical entity with respect to
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neurological outcome (Bostrom et al., 1992; D’Avella et al., 2001). There have also been several reports of cerebellar atrophy following TBI (Krauss et al., 1995; Soto-Ares et al., 2001; Gale et al., 2005). Furthermore, a subgroup of ataxic TBI patients may have etiologic basis in cerebellar dysfunction after injury (Chester and Reznick, 1987; Mysiw et al., 1990). Crossed cerebellar diaschisis (CCD), a well-documented phenomenon of altered or depressed metabolic flow and activity in the hemisphere of the cerebellum contralateral to the side of cortical lesion or injury, has also been documented after TBI (Alavi et al., 1997). Ipsilateral metabolic changes as well as hypermetabolic changes have also been documented (Shamoto and Chugani, 1997; Niimura et al., 1999). A loss of afferent inputs from the cortico-ponto-cerebellar pathway is believed to result in deactivation of the targets in the cerebellum, although the exact physiological mechanism is not entirely understood (Feeney and Baron, 1986). The occurrence of CCD underscores the importance of synaptic connectivity between the cerebrum and the cerebellum. This would suggest TBI resulting in a loss of cortical synaptic input to the cerebellum that results in an unknown volume of information processing that is not taking place. The relationship between ischemia and cerebellar injury is also of significance as Purkinje cells are highly susceptible to ischemic injury (Bhatia et al., 1995; Welsh et al., 2002). Ischemia is a common component of non-penetrating head injuries and an important contributor to secondary injury mechanisms (Graham et al., 1978, 1989). Examination of 151 cases of fatal head injury revealed that the majority of ischemic damage occurred in the hippocampus (81% of patients); however, there was also a significant proportion of patients with evidence of ischemic injury in the cerebellum (44%; Graham et al., 1978). Furthermore, TBI, including multisystem trauma patients, often present with hypoxichypotensive or hemorrhagic complications (Miller et al., 1978, 1981; The Brain Trauma Foundation, 2000) increasing the likelihood of global brain ischemia and subsequent cerebellar injury.
Cerebellar injury in animal models Purkinje cell vulnerability Several studies in animal models of TBI have documented vulnerability of Purkinje cells following forebrain injury. Both midline and unilateral forebrain FPI have been shown to result in significant and delayed cell death of Purkinje neurons accompanied by the presence of activated microglia (Fukuda et al., 1996; Mautes et al., 1996). Other studies have supported these findings by demonstrating the presence of FluorojadeB positive cells in the cerebellum, consistent with the morphology of Purkinje neurons (Sato et al., 2001; Hallam et al., 2004). Using double label fluorescent immunohistochemistry, we recently demonstrated selective vulnerability of Purkinje neurons in the posterior regions of the cerebellum following unilateral FPI in the cerebrum (Park et al., 2006b). In this study we demonstrated that the majority of Purkinje neurons were lost in the acute phase of injury (24 h) while delayed cell loss occurred in the middle and anterior regions of the cerebellum at 7 and 14 days post-injury at higher grades of injury severity (Fig. 1). Examination of the coronal plane cerebellar sections following forebrain FPI indicates no evidence of medio-lateral banding (unpublished observations). Others, however, have reported parasagittal banding patterns of Purkinje cell loss using the CCI model of trauma (Weber, J., personal communication), perhaps indicative of variations in injury biomechanics to the cerebellum. Although the mechanisms of Purkinje cell loss following trauma are still unknown, there are several potential explanations to consider with relevance to neurotrauma research. Presynaptic hyperexcitability, differential gene expression, pre- and post-synaptic cell survival, and neuronal–glial interactions are several possible avenues to be explored. The cerebellum offers several unique features to address these mechanisms as contributors to secondary injury. Furthermore, these areas have a broad range of application to the study of TBI in general and are not limited to analysis of cerebellum specific effects.
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Fig. 1. Double label immunohistochemistry indicates selective Purkinje cell death in the cerebellum following forebrain fluid percussion trauma: (a) Sham, (b) 1 day post-injury, (c) 14 days post-injury. Scale bar ¼ 50 mm. (d) Quantification of surviving Purkinje cells from the posterior cerebellum following four grades of fluid percussion trauma indicates a dose–response effect at 1 day postinjury (red asterisk). A significant decline in Purkinje cell numbers relative to sham animals is observed as early as 1 day post-injury in the 2–2.5 atm injury groups (*). The cartoon (left) indicates the area of fluid percussion trauma (red arrow) and the region of Purkinje cell quantification (red circle). (Adapted with permission from Park et al., 2006b.)
Presynaptic hyperexcitability The synaptic architecture of the Purkinje cells, consisting of glutamatergic inputs from climbing and parallel fibers, creates an environment in which the potential for synaptic mediated excitotoxicity is high (for review see Slemmer et al., 2005). Our laboratory has demonstrated that direct cerebellar trauma results in delayed
presynaptic hyperexcitability in parallel fiberPurkinje cell synaptic connections (Ai and Baker, 2002). Given that a single Purkinje cell receives input from 200,000 parallel fibers (Fox and Barnard, 1957), the potential for a presynaptic excitotoxic event is high. In addition, a single climbing fiber, originating from the inferior olive, forms up to 1500 synaptic connections on the proximal dendrite of a Purkinje cell (Strata and
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Rossi, 1998). Excitation of this afferent pathway with ibogaine administration results in excitotoxic Purkinje cell death while ablation with 3-AP is protective to Purkinje cells (O’Hearn and Molliver, 1997). The pattern of cell death from climbing fiber depolarization results in very distinct medio-lateral banding pattern of cell death likely corresponding to the terminal afferent projections of the climbing fibers. However, there are factors beyond simple afferent targets to consider in this discussion of Purkinje cell vulnerability.
Gene expression Despite a seemingly homogeneous and redundant arrangement of cellular architecture throughout the cerebellum (Voogd and Glickstein, 1998; Ramnani, 2006), there exist subtle differences within cell populations that can give rise to vastly different pathologies. In particular, differential expression of genes involved in metabolism and cell signaling have been demonstrated within subsets of Purkinje neurons with both medio-lateral and anterior–posterior patterns of expression (reviewed by Herrup and Kuemerle (1997) and Sarna and Hawkes (2003)) (Fig. 2). Furthermore patterned gene expression in Purkinje neurons occurs independently of afferent synaptic organization. The effectiveness of neuroprotective strategies targeting these differentially expressed gene products can be readily ascertained through histological examination for the presence or absence of banding patterns (see O’Hearn and Molliver, 1997). There are numerous candidate proteins that are expressed in distinct patterns within the cerebellum that are of interest to neurotrauma research including heat shock proteins, zebrin expression, calcium binding proteins, and amino acid transporters (Herrup and Kuemerle, 1997). There may also be others that have not yet been characterized to date. Also of importance is the maintenance of the compartmentalized expression of these gene products across mammalian species permitting for a degree of consistency in crossspecies comparisons of mechanism and role in TBI.
Pre- and post-synaptic cell survival The cerebellum is a potentially useful structure in which to assess the effects of neuronal cell loss in pre- and post-synaptic targets following TBI. For example, the lurcher mouse phenotype resulting from a mutation of the Grid2 gene for the d2-glutamate receptor (d2-GluR) results in chronic depolarization and loss of Purkinje cells (Zuo et al., 1997). Subsequent to Purkinje neuron death is the loss of granule cells as well as retrograde loss of inferior olive input (Heckroth and Eisenman, 1991; Heckroth, 1992; Zanjani et al., 1998). Anterograde effects manifest as a loss of deep cerebellar nuclei (Heckroth, 1994). Whether these effects are specific to the mutation of the d2-GluR or are a common response to Purkinje cell loss has not been elucidated but may be a valuable area of research to pursue. The extensive literature describing afferent tracing to the cerebellum as well as its relatively simple synaptic organization makes it a suitable model in which to evaluate retrograde and anterograde fates of injured or dying neurons. These studies could add to our understanding of how focal injuries affect distal targets through retrograde or anterograde signaling dysfunction or cell loss.
Neuronal– glial cell communication The role of neuronal–glial communication following neurotrauma remains a controversial issue with evidence to supporting glial scarring as inhibitor of endogenous repair mechanisms along with compelling evidence to indicate neuroprotective roles as well (reviewed by Sofroniew (2005)). In the cerebellum, Bergmann glia residing in the molecular layer form a complex functional and structural relationship with Purkinje cells (reviewed by Bellamy (2006)). These specialized astrocytes form a sheath around the Purkinje neuron soma and synapses. This physical interaction has functional implications as stimulation of climbing and parallel fibers have been shown to activate inward currents in Bergmann glia (Bergles et al., 1997; Clark and Barbour, 1997; Bellamy and Ogden, 2005). These currents are in part
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Fig. 2. Cartoon representation of cerebellar compartmentation in the mouse, as revealed by the expression of zebrin II in subsets of Purkinje cells (Adapted with permission from Sillitoe and Hawkes, 2002): anterior, dorsal and posterior views are shown. The cerebellar vermis is divided into 10 lobules (I–X). However, a more fundamental parcellation is into four transverse zones — anterior (AZ), central (CZ), posterior (PZ), and nodular (NZ). The AZ and PZ are striped — all Purkinje cells in the CZ and NZ express zebrin II uniformly (although stripes can be revealed here by using other markers, such as the small heat shock protein, HSP25 (Armstrong et al., 2000)). Complementary views of a cerebellum whole mount immunoperoxidase stained for zebrin II are shown on the right. (Adapted with permission from Sarna and Hawkes, 2003.)
contributed to by glial-expressed alpha-amino-3hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors, GluR1 and GluR4, as well as glial glutamate transporters, GLAST and GLT-1 (Bellamy, 2006). Although the Bergmann glia
represent a specialized form of astrocyte, they maintain the characteristic reactive astrocyte response to injury following trauma. We have demonstrated the presence of reactive astrocytes in regions of Purkinje cell loss following forebrain
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Fig. 3. (a) Confocal image of sham tissue expression of GFAP in Bergmann glia astrocytes, in red, in close proximity to Purkinje cells, labeled in green. (b) Following forebrain fluid percussion trauma there is a marked increased in GFAP immunoreactivity in regions of cerebellar injury indicated by the loss of Purkinje cells and increase in GFAP immunoreactivity. Scale bar ¼ 50 mm. (Adapted with permission from Park et al., 2006b.)
trauma as indicated by increased GFAP expression (Fig. 3). The close anatomical coupling and functional relationship between Purkinje cells and Bergman glia presents an excellent opportunity to examine the changes in neuronal and glial communication following TBI. Specifically, the cerebellum is an ideal system in which to perform patch-clamping experiments in brain slices, which permits maintenance of cellular architecture and synaptic connectivity. These features may be helpful in elucidating the changes in communication and synaptic plasticity between glial cells and neurons in pathophysiological states. Cerebellar white matter injury Numerous animal models of TBI have reported evidence of TAI in the cerebellum (Lighthall et al., 1990; Shima and Marmarou, 1991; Foda and Marmarou, 1994; Hoshino et al., 2003). Information regarding the functional consequences of such injuries, however, is limited. We recently characterized functional and structural changes in cerebellar white matter following forebrain FPI and demonstrated significant and persistent deficits and pathological changes in the cerebellum (Park et al., 2006a). Early neurofilament degradation and
parallel accumulation in a subset of axons was observed at 1 day post-injury while persistent calpainmediated degradation of aII-spectrin was observed up to 14 days post-injury. The acute degradation of heavy neurofilament chain (NF200) and prolonged degradation of calpain-mediated aII-spectrin would suggest temporally preferential targeting of calpain substrates, NF200 and aII-spectrin, in the cerebellum. Another possibility is that proteolysis of these substrates occurred in subsets of axons with different modes of axonal injury progression. The observations of NF200 and aII-spectrin degradation are not novel concepts in the study of TAI. However, the results reveal a further level of complexity in TAI with respect to calpain’s temporal substrate specificity. Compound action potential recordings from cerebellar white matter have also demonstrated the usefulness of electrophysiological techniques in assessment of white matter function after TBI. The results indicate a consistent CAP response within selected regions. Interestingly, recordings from the middle cerebellar lobe produce a primarily fast conducting myelinated response whereas the posterior and anterior cerebellar lobes exhibit a two-peaked response including both fast and slow myelinated and unmyelinated responses, respectively (Fig. 4). This
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Fig. 4. (a) Compound action potentials were recorded from three regions of cerebellar white matter as indicated by the black-boxed regions. (b) CAP waveforms were dependent on location of recording. Anterior and posterior waveforms consisted of distinct fast and slow components. The middle cerebellar CAP response was primarily a fast myelinated signal. (c) CAP values from cerebellar white matter following forebrain fluid percussion trauma indicated a significant decline in electrophysiological function (*) in the posterior and middle regions of the cerebellum which persisted at 14 days post-injury. (Adapted with permission from Park et al., 2006a.)
presents an opportunity to examine the effects of TBI and potential therapeutic interventions on both myelinated and demyelinated axon populations. A recent study demonstrated varying electrophysiological susceptibilities of these two axonal populations in the corpus callosum (Reeves et al., 2005).
Given the relative lack of electrophysiological data available for TBI white matter injury studies, a comparison of results between the cerebellum and the corpus callosum may reveal whether these susceptibilities are structure specific or are a general principle of injured axons throughout the brain.
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The cerebellum as a model of neurotrauma A key question in the discussion of cerebellar injury and its application in neurotrauma research is ultimately whether it is clinically relevant. We would argue ‘yes’ for the following reasons. There is sufficient evidence of clinical manifestation of cerebellar injury following TBI. In addition to the role in motor coordination, the role of the cerebellum in multiple higher order function is becoming more appreciated and hence a recognition of its potential importance if injured. The traumatized cerebellum offers numerous technical opportunities to examine relevant areas of research related to mechanisms of cellular injury, neuronal–glial pathophysiological interactions, TAI, post-injury synaptic plasticity, selective neuronal vulnerability, and mechanisms of diffuse injury remote from the location of initial trauma. From an anatomical perspective, there are notable differences in human and rodent cerebellar placement that is likely to result in differences on the production of injury biomechanics between these two species. However, there are structural similarities in the cerebellum, such as the cellular organization and foliated segments that are maintained throughout all mammalian species (Voogd and Glickstein, 1998). This gyrencephalic property is not maintained in the cerebral cortex between species and represents an area in which the biomechanics of injury production may differ significantly between higher and lower order species. Despite the pros and cons of anatomical similarity between species, the intent of this discussion is to provide a rationale for inclusion of the cerebellum not only for its clinical and functional importance in TBI pathophysiology, but also as a structure in which to examine the mechanistic phenomena of TBI mechanisms in general. We propose that comparison and complement of studies across various injury models will not only validate but also elucidate novel mechanism of secondary injury.
Conclusion Traumatic brain injury continues to be a health care issue of epidemic proportions as a leading
cause of morbidity and mortality in young adults. Despite the prevalence of this silent epidemic, there is little therapeutic benefit that has translated from the neuroprotective strategies developed in animal models of TBI (Bullock et al., 1999; Faden, 2001; Narayan et al., 2002; Tolias and Bullock, 2004). The failure of clinical trials highlights a lack of complete understanding of the complexity of TBI pathophysiology. This includes optimizing therapeutic time windows and clarifying the multiple pathways leading to cell death. Addressing these issues will require multifaceted approaches and balancing the inhibition of secondary injury mechanisms while not adversely affecting normal physiologic function (Faden, 2002; Ikonomidou and Turski, 2002). We believe that this will be best achieved through complementation and comparisons between existing and novel injury paradigms. The cerebellum is one such novel area that remains to be fully appreciated and described in the context of TBI. Abbreviations AMPA CCD FPI GluR GOS NF200 TAI TBI
alpha-amino-3-hydroxy-5methyl-4-isoxazole propionic acid crossed cerebellar diaschisis fluid percussion injury glutamate receptor Glasgow outcome scale heavy neurofilament chain traumatic axonal injury traumatic brain injury
Acknowledgment We thank the Ontario Neurotrauma Foundation for its funding support. References Ai, J. and Baker, A. (2002) Presynaptic hyperexcitability at cerebellar synapses in traumatic injury rat. Neurosci. Lett., 332: 155–158. Alavi, A., Mirot, A., Newberg, A., Alves, W., Gosfield, T., Berlin, J., Reivich, M. and Gennarelli, T. (1997) Fluorine-18FDG evaluation of crossed cerebellar diaschisis in head injury. J. Nucl. Med., 38: 1717–1720.
336 Anderson, J.R. and Treip, C.S. (1973) Hypertrophic olivary degeneration and Purkinje cell degeneration in a case of longstanding head injury. J. Neurol. Neurosurg. Psychiatry, 36: 826–832. Armstrong, C.L., Krueger-Naug, A.M., Currie, R.W. and Hawkes, R. (2000) Constitutive expression of the 25-kDa heat shock protein Hsp25 reveals novel parasagittal bands of purkinje cells in the adult mouse cerebellar cortex. J. Comp. Neurol., 416: 383–397. Bellamy, T.C. (2006) Interactions between Purkinje neurones and Bergmann glia. Cerebellum, 5: 116–126. Bellamy, T.C. and Ogden, D. (2005) Short-term plasticity of Bergmann glial cell extrasynaptic currents during parallel fiber stimulation in rat cerebellum. Glia, 52: 325–335. Bergles, D.E., Dzubay, J.A. and Jahr, C.E. (1997) Glutamate transporter currents in bergmann glial cells follow the time course of extrasynaptic glutamate. Proc. Natl. Acad. Sci. U.S.A., 94: 14821–14825. Bhatia, K.P., Brown, P., Gregory, R., Lennox, G.G., Manji, H., Thompson, P.D., Ellison, D.W. and Marsden, C.D. (1995) Progressive myoclonic ataxia associated with coeliac disease. The myoclonus is of cortical origin, but the pathology is in the cerebellum. Brain, 118(Pt 5): 1087–1093. Bostrom, K., Helander, C.G. and Lindgren, S. (1992) Blunt basal head trauma: aspects of unconsciousness. Acta Neurochir. Suppl. (Wien.), 55: 25–28. Brandvold, B., Levi, L., Feinsod, M. and George, E.D. (1990) Penetrating craniocerebral injuries in the Israeli involvement in the Lebanese conflict, 1982–1985: analysis of a less aggressive surgical approach. J. Neurosurg., 72: 15–21. Buki, A. and Povlishock, J.T. (2006) All roads lead to disconnection? Traumatic axonal injury revisited. Acta Neurochir. (Wien.), 148: 181–194. Bullock, M.R., Lyeth, B.G. and Muizelaar, J.P. (1999) Current status of neuroprotection trials for traumatic brain injury: lessons from animal models and clinical studies. Neurosurgery, 45: 207–220. Chester, C.S. and Reznick, B.R. (1987) Ataxia after severe head injury: the pathological substrate. Ann. Neurol., 22: 77–79. Clark, B.A. and Barbour, B. (1997) Currents evoked in Bergmann glial cells by parallel fibre stimulation in rat cerebellar slices. J. Physiol., 502(Pt 2): 335–350. D’avella, D., Cacciola, F., Angileri, F.F., Cardali, S., La Rosa, G., Germano, A. and Tomasello, F. (2001) Traumatic intracerebellar hemorrhagic contusions and hematomas. J. Neurosurg. Sci., 45: 29–37. Faden, A.I. (2001) Neuroprotection and traumatic brain injury: the search continues. Arch. Neurol., 58: 1553–1555. Faden, A.I. (2002) Neuroprotection and traumatic brain injury: theoretical option or realistic proposition. Curr. Opin. Neurol., 15: 707–712. Feeney, D.M. and Baron, J.C. (1986) Diaschisis. Stroke, 17: 817–830. Foda, M.A. and Marmarou, A. (1994) A new model of diffuse brain injury in rats. Part II: morphological characterization. J. Neurosurg., 80: 301–313.
Fox, C.A. and Barnard, J.W. (1957) A quantitative study of the Purkinje cell dendritic branchlets and their relationship to afferent fibres. J. Anat., 91: 299–313. Fukuda, K., Aihara, N., Sagar, S.M., Sharp, F.R., Pitts, L.H., Honkaniemi, J. and Noble, L.J. (1996) Purkinje cell vulnerability to mild traumatic brain injury. J. Neurotrauma, 13: 255–266. Gale, S.D., Baxter, L., Roundy, N. and Johnson, S.C. (2005) Traumatic brain injury and grey matter concentration: a preliminary voxel based morphometry study. J. Neurol. Neurosurg. Psychiatry, 76: 984–988. Glickstein, M. (2000) How are visual areas of the brain connected to motor areas for the sensory guidance of movement? Trends Neurosci., 23: 613–617. Gordon, N. (1996) Speech, language, and the cerebellum. Eur. J. Disord. Commun., 31: 359–367. Graham, D.I., Adams, J.H. and Doyle, D. (1978) Ischaemic brain damage in fatal non-missile head injuries. J. Neurol. Sci., 39: 213–234. Graham, D.I., Ford, I., Adams, J.H., Doyle, D., Teasdale, G.M., Lawrence, A.E. and Mclellan, D.R. (1989) Ischaemic brain damage is still common in fatal non-missile head injury. J. Neurol. Neurosurg. Psychiatry, 52: 346–350. Guterman, A. and Smith, R.W. (1987) Neurological sequelae of boxing. Sports Med., 4: 194–210. Hallam, T.M., Floyd, C.L., Folkerts, M.M., Lee, L.L., Gong, Q.Z., Lyeth, B.G., Muizelaar, J.P. and Berman, R.F. (2004) Comparison of behavioral deficits and acute neuronal degeneration in rat lateral fluid percussion and weight-drop brain injury models. J. Neurotrauma, 21: 521–539. Heckroth, J.A. (1992) Development of glutamic acid decarboxylase-immunoreactive elements in the cerebellar cortex of normal and lurcher mutant mice. J. Comp. Neurol., 315: 85–97. Heckroth, J.A. (1994) Quantitative morphological analysis of the cerebellar nuclei in normal and lurcher mutant mice. I: morphology and cell number. J. Comp. Neurol., 343: 173–182. Heckroth, J.A. and Eisenman, L.M. (1991) Olivary morphology and olivocerebellar topography in adult lurcher mutant mice. J. Comp. Neurol., 312: 641–651. Herrup, K. and Kuemerle, B. (1997) The compartmentalization of the cerebellum. Annu. Rev. Neurosci., 20: 61–90. Holmes, G. (1917) The symptoms of acute cerebellar injuries due to gunshot wounds. Brain, 40: 461–535. Hoshino, S., Kobayashi, S., Furukawa, T., Asakura, T. and Teramoto, A. (2003) Multiple immunostaining methods to detect traumatic axonal injury in the rat fluid-percussion brain injury model. Neurol. Med. Chir. (Tokyo), 43: 165–174. Ikonomidou, C. and Turski, L. (2002) Why did NMDA receptor antagonists fail clinical trials for stroke and traumatic brain injury? Lancet Neurol., 1: 383–386. Krauss, J.K., Wakhloo, A.K., Nobbe, F., Trankle, R., Mundinger, F. and Seeger, W. (1995) Lesion of
337 dentatothalamic pathways in severe post-traumatic tremor. Neurol. Res., 17: 409–416. Lighthall, J.W., Goshgarian, H.G. and Pinderski, C.R. (1990) Characterization of axonal injury produced by controlled cortical impact. J. Neurotrauma, 7: 65–76. Mariotti, C., Fancellu, R. and Di Donato, S. (2005) An overview of the patient with ataxia. J. Neurol., 252: 511–518. Mautes, A.E., Fukuda, K. and Noble, L.J. (1996) Cellular response in the cerebellum after midline traumatic brain injury in the rat. Neurosci. Lett., 214: 95–98. Miller, J.D., Butterworth, J.F., Gudeman, S.K., Faulkner, J.E., Choi, S.C., Selhorst, J.B., Harbison, J.W., Lutz, H.A., Young, H.F. and Becker, D.P. (1981) Further experience in the management of severe head injury. J. Neurosurg., 54: 289–299. Miller, J.D., Sweet, R.C., Narayan, R. and Becker, D.P. (1978) Early insults to the injured brain. JAMA, 240: 439–442. Mysiw, W.J., Corrigan, J.D. and Gribble, M.W. (1990) The ataxic subgroup: a discrete outcome after traumatic brain injury. Brain Inj., 4: 247–255. Narayan, R.K., Michel, M.E., Ansell, B., Baethmann, A., Biegon, A., Bracken, M.B., Bullock, M.R., Choi, S.C., Clifton, G.L., Contant, C.F., Coplin, W.M., Dietrich, W.D., Ghajar, J., Grady, S.M., Grossman, R.G., Hall, E.D., Heetderks, W., Hovda, D.A., Jallo, J., Katz, R.L., Knoller, N., Kochanek, P.M., Maas, A.I., Majde, J., Marion, D.W., Marmarou, A., Marshall, L.F., McIntosh, T.K., Miller, E., Mohberg, N., Muizelaar, J.P., Pitts, L.H., Quinn, P., Riesenfeld, G., Robertson, C.S., Strauss, K.I., Teasdale, G., Temkin, N., Tuma, R., Wade, C., Walker, M.D., Weinrich, M., Whyte, J., Wilberger, J., Young, A.B. and Yurkewicz, L. (2002) Clinical trials in head injury. J. Neurotrauma, 19: 503–557. Nathoo, N., Chite, S.H., Edwards, P.J. and van Dellen, J.R. (2002) Civilian infratentorial gunshot injuries: outcome analysis of 26 patients. Surg. Neurol., 58: 225–233. Niimura, K., Chugani, D.C., Muzik, O. and Chugani, H.T. (1999) Cerebellar reorganization following cortical injury in humans: effects of lesion size and age. Neurology, 52: 792–797. O’Hearn, E. and Molliver, M.E. (1997) The olivocerebellar projection mediates ibogaine-induced degeneration of Purkinje cells: a model of indirect, trans-synaptic excitotoxicity. J. Neurosci., 17: 8828–8841. Park, E., Liu, E., Shek, M., Park, A. and Baker, A. (2006a) Heavy neurofilament accumulation and alpha-spectrin degradation accompanies cerebellar white matter functional deficits following forebrain fluid percussion injury. Exp. Neurol., in press, Oct. 26, Epub ahead of print. Park, E., McKnight, S., Ai, J. and Baker, A.J. (2006b) Purkinje cell vulnerability to mild and severe forebrain head trauma. J. Neuropathol. Exp. Neurol., 65: 226–234. Petrosini, L., Leggio, M.G. and Molinari, M. (1998) The cerebellum in the spatial problem solving: a co-star or a guest star? Prog. Neurobiol., 56: 191–210.
Ramnani, N. (2006) The primate cortico-cerebellar system: anatomy and function. Nat. Rev. Neurosci., 7: 511–522. Reeves, T.M., Phillips, L.L. and Povlishock, J.T. (2005) Myelinated and unmyelinated axons of the corpus callosum differ in vulnerability and functional recovery following traumatic brain injury. Exp. Neurol., 196: 126–137. Rish, B.L., Dillon, J.D. and Weiss, G.H. (1983) Mortality following penetrating craniocerebral injuries: an analysis of the deaths in the Vietnam Head Injury Registry population. J. Neurosurg., 59: 775–780. Sarna, J.R. and Hawkes, R. (2003) Patterned Purkinje cell death in the cerebellum. Prog. Neurobiol., 70: 473–507. Sato, M., Chang, E., Igarashi, T. and Noble, L.J. (2001) Neuronal injury and loss after traumatic brain injury: time course and regional variability. Brain Res., 917: 45–54. Shamoto, H. and Chugani, H.T. (1997) Glucose metabolism in the human cerebellum: an analysis of crossed cerebellar diaschisis in children with unilateral cerebral injury. J. Child. Neurol., 12: 407–414. Shima, K. and Marmarou, A. (1991) Evaluation of brain-stem dysfunction following severe fluid-percussion head injury to the cat. J. Neurosurg., 74: 270–277. Sillitoe, R.V. and Hawkes, R. (2002) Whole-mount immunohistochemistry: a high-throughput screen for patterning defects in the mouse cerebellum. J. Histochem. Cytochem., 50: 235–244. Slemmer, J.E., De Zeeuw, C.I. and Weber, J.T. (2005) Don’t get too excited: mechanisms of glutamate-mediated Purkinje cell death. Prog. Brain Res., 148: 367–390. Sofroniew, M.V. (2005) Reactive astrocytes in neural repair and protection. Neuroscientist, 11: 400–407. Soto-Ares, G., Vinchon, M., Delmaire, C., Abecidan, E., Dhellemes, P. and Pruvo, J.P. (2001) Cerebellar atrophy after severe traumatic head injury in children. Child’s Nerv. Syst., 17: 263–269. Strata, P. and Rossi, F. (1998) Plasticity of the olivocerebellar pathway. Trends Neurosci., 21: 407–413. The Brain Trauma Foundation. The American Association of Neurological Surgeons. The Joint Section on Neurotrauma and Critical Care. (2000) Resuscitation of blood pressure and oxygenation. J. Neurotrauma, 17: 471–478. Tolias, C.M. and Bullock, M.R. (2004) Critical appraisal of neuroprotection trials in head injury: what have we learned? NeuroRx, 1: 71–79. Unterharnscheidt, F. (1995a) A neurologist’s reflections on boxing. I: impact mechanics in boxing and injuries other than central nervous system damage. Rev. Neurol., 23: 661–674. Unterharnscheidt, F. (1995b) A neurologist’s reflections on boxing. V: Concluding remarks. Rev. Neurol., 23: 1027–1032. Voogd, J. and Glickstein, M. (1998) The anatomy of the cerebellum. Trends Neurosci., 21: 370–375. Welsh, J.P., Yuen, G., Placantonakis, D.G., Vu, T.Q., Haiss, F., O’Hearn, E., Molliver, M.E. and Aicher, S.A. (2002) Why do Purkinje cells die so easily after global brain
338 ischemia? Aldolase C, EAAT4, and the cerebellar contribution to posthypoxic myoclonus. Adv. Neurol., 89: 331–359. Zanjani, H.S., Vogel, M.W., Martinou, J.C., Delhaye-Bouchaud, N. and Mariani, J. (1998) Postnatal expression of Hu-bcl-2 gene in Lurcher mutant mice fails to rescue Purkinje
cells but protects inferior olivary neurons from target-related cell death. J. Neurosci., 18: 319–327. Zuo, J., De Jager, P.L., Takahashi, K.A., Jiang, W., Linden, D.J. and Heintz, N. (1997) Neurodegeneration in Lurcher mice caused by mutation in delta2 glutamate receptor gene. Nature, 388: 769–773.
CHAPTER 23
Cerebellar injury: clinical relevance and potential in traumatic brain injury research Eugene Park1,2, Jinglu Ai1 and Andrew J. Baker1,2, 1 St. Michael’s Hospital, Trauma Research, Toronto, ON, M5B 1W8, Canada University of Toronto, Institute of Medical Sciences, Toronto, ON, M5S 1A, Canada
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Abstract: A treatment for traumatic brain injury (TBI) remains elusive despite compelling evidence from animal models for a variety of therapeutic targets. Numerous animal models have been developed to address the wide spectrum of mechanisms involved in the progression of secondary injury after TBI. Evidence from well-established models such as the fluid percussion injury (FPI) device, cortical impact model, and the impact acceleration model has demonstrated diffuse pathophysiological mechanisms throughout various brain structures. More specifically, we have recently extended characterization of the FPI model to include pathophysiological changes in the cerebellum following unilateral fluid percussion. Data suggest that the cerebellum is susceptible to selective Purkinje cell loss as well as white matter dysfunction. Despite the cerebellum’s low profile in TBI research, there is evidence to warrant further study of the cerebellum to examine mechanisms of neuronal death and traumatic axonal injury. Furthermore, evidence from clinical literature and basic science suggests that some components of TBI pathophysiology have a basis in cerebellar dysfunction. This review highlights some of the recent findings in cerebellar trauma and builds an argument for including the cerebellum as a model to assess mechanisms of secondary injury and its potential contribution to the pathology of TBI. Keywords: animal models; cerebellum; electrophysiology; FPI; TAI; TBI injury mechanisms exists in variety of injured axon subpopulations (reviewed by Buki and Povlishock (2006)). These data support a need for in-depth scrutiny of mechanisms encompassing all regions susceptible to traumatic brain injury (TBI) in order to formulate an accurate and thorough description of pathophysiologic processes. The cerebellum’s role in TBI has received relatively limited scrutiny and characterization as other structures including the brain stem, hippocampus, and cerebral cortex. It is becoming increasingly evident that general mechanistic descriptions of cell death and axonal injury are overly simplistic and do not accurately reflect the full spectrum of events occurring after TBI. Clinical cases of TBI and parallel research in animal
Introduction Intense scrutiny of neuronal cell death and traumatic axonal injury (TAI) has clarified numerous molecular and cellular events contributing to the progression of secondary injury cascades. As our understanding of molecular events continues to increase, our description of these events have become increasingly complex. For example, all traumatically injured axons were previously thought to undergo a series of pathophysiological events leading to disconnection and bulb formation. However, it has become evident that a spectrum of Corresponding author. Tel.: +1-416-864-5510; Fax: +1-416864-5512; E-mail: [email protected] DOI: 10.1016/S0079-6123(06)61023-6
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models have confirmed that the mechanisms of injury extend to the cerebellum thus building a case for its relevance in neurotrauma. A thorough characterization of all affected structures throughout the brain, including the cerebellum, would provide a better framework with which to optimize treatments for TBI. Furthermore, the potential for discovering or elucidating mechanisms of injury not yet described would also add to our existing knowledge of secondary injury mechanisms. It may be argued that cerebellar trauma is of limited clinical importance; however, recent studies have begun to elucidate roles in higher order cognitive function not previously appreciated in cerebellar processing (Petrosini et al., 1998; Ramnani, 2006). These higher order functions as well as other neurological processing functions not previously known may account for some of the observed behavioral abnormalities in people afflicted by TBI. In the present discussion we propose several lines of evidence to support the role of cerebellar injury as an important component of TBI, and also several unique features that render the cerebellum a potentially useful structure in which to assess mechanisms of secondary injury after trauma.
Clinical evidence of cerebellar trauma Clinical manifestation of cerebellar dysfunction include perturbations to stance and gait, characterized by a loss of equilibrium, a wide-based stance, irregular steps, and lateral veering (Mariotti et al., 2005). Cerebellar deficits can also give rise to tremors (e.g., Parkinsonian), alterations to speech resulting in slowed or slurred vocalization, as well as cerebellar mutism (Gordon, 1996). Recent studies have also indicated an important contribution of cerebellar function to visuo-motor control (Glickstein, 2000). Patients with cerebellar ataxias exhibit ocular motor defects in target fixation and coordinating head movements (Mariotti et al., 2005). Although these deficits are generally not described in the context of trauma, it is not unreasonable to draw inference to traumatic cerebellar injury which could result in similar pathological impairments, particularly since
many of the motor, cognitive, and speech impairments described above are also observed in TBI patients. There are many reviews on diagnoses, mechanisms, outcome, epidemiology, cost analysis, rehabilitation, etc., and specific case studies in TBI involving cerebral injury. However there is limited clinical literature with direct emphasis on cerebellar trauma. In 1917, Gordon Holmes described observations of World War I soldiers who had sustained gunshot wounds to the cerebellum. He described a drunken-sailor type gait, as well as the postural disturbances commonly associated with cerebellar dysfunction (Holmes, 1917). A recent report of 26 patients who had sustained infratentorial injuries is the only clinical study to date to specifically address the issue of direct trauma to the cerebellum (Nathoo et al., 2002). This particular type of injury, although rare in the civilian population, has been documented predominantly in military literature (Rish et al., 1983; Brandvold et al., 1990). Moreover, the authors of this study note that cerebellar injury had no effect on outcome. It should be noted however, that the five point Glasgow Outcome Scale (GOS) used in this particular study might not be an adequately sensitive measure of functional and behavioral deficits to detect cerebellar dysfunction. Furthermore, the GOS is primarily a measure of global outcome and does not factor in the consequences of motor, speech, and cognitive impacts on daily living. Despite limited literature on direct cerebellar trauma there is a varied collection of literature in which the cerebellum has been referenced as exhibiting pathological changes including selective cell loss, altered metabolism, and white matter injury after focal and diffuse TBI. For example, Purkinje cell loss has been noted in the brains of boxers and implicated as a significant contributor to ataxias and Parkinsonian tremors (Guterman and Smith, 1987; Unterharnscheidt, 1995a, b). Another report cites hypertrophic olivary and Purkinje cell degeneration following chronic TBI (Anderson and Treip, 1973). Post-traumatic intracerebellar hemorrhage, though an unusual clinical occurrence, has been observed after head trauma and is an important clinical entity with respect to
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neurological outcome (Bostrom et al., 1992; D’Avella et al., 2001). There have also been several reports of cerebellar atrophy following TBI (Krauss et al., 1995; Soto-Ares et al., 2001; Gale et al., 2005). Furthermore, a subgroup of ataxic TBI patients may have etiologic basis in cerebellar dysfunction after injury (Chester and Reznick, 1987; Mysiw et al., 1990). Crossed cerebellar diaschisis (CCD), a well-documented phenomenon of altered or depressed metabolic flow and activity in the hemisphere of the cerebellum contralateral to the side of cortical lesion or injury, has also been documented after TBI (Alavi et al., 1997). Ipsilateral metabolic changes as well as hypermetabolic changes have also been documented (Shamoto and Chugani, 1997; Niimura et al., 1999). A loss of afferent inputs from the cortico-ponto-cerebellar pathway is believed to result in deactivation of the targets in the cerebellum, although the exact physiological mechanism is not entirely understood (Feeney and Baron, 1986). The occurrence of CCD underscores the importance of synaptic connectivity between the cerebrum and the cerebellum. This would suggest TBI resulting in a loss of cortical synaptic input to the cerebellum that results in an unknown volume of information processing that is not taking place. The relationship between ischemia and cerebellar injury is also of significance as Purkinje cells are highly susceptible to ischemic injury (Bhatia et al., 1995; Welsh et al., 2002). Ischemia is a common component of non-penetrating head injuries and an important contributor to secondary injury mechanisms (Graham et al., 1978, 1989). Examination of 151 cases of fatal head injury revealed that the majority of ischemic damage occurred in the hippocampus (81% of patients); however, there was also a significant proportion of patients with evidence of ischemic injury in the cerebellum (44%; Graham et al., 1978). Furthermore, TBI, including multisystem trauma patients, often present with hypoxichypotensive or hemorrhagic complications (Miller et al., 1978, 1981; The Brain Trauma Foundation, 2000) increasing the likelihood of global brain ischemia and subsequent cerebellar injury.
Cerebellar injury in animal models Purkinje cell vulnerability Several studies in animal models of TBI have documented vulnerability of Purkinje cells following forebrain injury. Both midline and unilateral forebrain FPI have been shown to result in significant and delayed cell death of Purkinje neurons accompanied by the presence of activated microglia (Fukuda et al., 1996; Mautes et al., 1996). Other studies have supported these findings by demonstrating the presence of FluorojadeB positive cells in the cerebellum, consistent with the morphology of Purkinje neurons (Sato et al., 2001; Hallam et al., 2004). Using double label fluorescent immunohistochemistry, we recently demonstrated selective vulnerability of Purkinje neurons in the posterior regions of the cerebellum following unilateral FPI in the cerebrum (Park et al., 2006b). In this study we demonstrated that the majority of Purkinje neurons were lost in the acute phase of injury (24 h) while delayed cell loss occurred in the middle and anterior regions of the cerebellum at 7 and 14 days post-injury at higher grades of injury severity (Fig. 1). Examination of the coronal plane cerebellar sections following forebrain FPI indicates no evidence of medio-lateral banding (unpublished observations). Others, however, have reported parasagittal banding patterns of Purkinje cell loss using the CCI model of trauma (Weber, J., personal communication), perhaps indicative of variations in injury biomechanics to the cerebellum. Although the mechanisms of Purkinje cell loss following trauma are still unknown, there are several potential explanations to consider with relevance to neurotrauma research. Presynaptic hyperexcitability, differential gene expression, pre- and post-synaptic cell survival, and neuronal–glial interactions are several possible avenues to be explored. The cerebellum offers several unique features to address these mechanisms as contributors to secondary injury. Furthermore, these areas have a broad range of application to the study of TBI in general and are not limited to analysis of cerebellum specific effects.
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Fig. 1. Double label immunohistochemistry indicates selective Purkinje cell death in the cerebellum following forebrain fluid percussion trauma: (a) Sham, (b) 1 day post-injury, (c) 14 days post-injury. Scale bar ¼ 50 mm. (d) Quantification of surviving Purkinje cells from the posterior cerebellum following four grades of fluid percussion trauma indicates a dose–response effect at 1 day postinjury (red asterisk). A significant decline in Purkinje cell numbers relative to sham animals is observed as early as 1 day post-injury in the 2–2.5 atm injury groups (*). The cartoon (left) indicates the area of fluid percussion trauma (red arrow) and the region of Purkinje cell quantification (red circle). (Adapted with permission from Park et al., 2006b.)
Presynaptic hyperexcitability The synaptic architecture of the Purkinje cells, consisting of glutamatergic inputs from climbing and parallel fibers, creates an environment in which the potential for synaptic mediated excitotoxicity is high (for review see Slemmer et al., 2005). Our laboratory has demonstrated that direct cerebellar trauma results in delayed
presynaptic hyperexcitability in parallel fiberPurkinje cell synaptic connections (Ai and Baker, 2002). Given that a single Purkinje cell receives input from 200,000 parallel fibers (Fox and Barnard, 1957), the potential for a presynaptic excitotoxic event is high. In addition, a single climbing fiber, originating from the inferior olive, forms up to 1500 synaptic connections on the proximal dendrite of a Purkinje cell (Strata and
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Rossi, 1998). Excitation of this afferent pathway with ibogaine administration results in excitotoxic Purkinje cell death while ablation with 3-AP is protective to Purkinje cells (O’Hearn and Molliver, 1997). The pattern of cell death from climbing fiber depolarization results in very distinct medio-lateral banding pattern of cell death likely corresponding to the terminal afferent projections of the climbing fibers. However, there are factors beyond simple afferent targets to consider in this discussion of Purkinje cell vulnerability.
Gene expression Despite a seemingly homogeneous and redundant arrangement of cellular architecture throughout the cerebellum (Voogd and Glickstein, 1998; Ramnani, 2006), there exist subtle differences within cell populations that can give rise to vastly different pathologies. In particular, differential expression of genes involved in metabolism and cell signaling have been demonstrated within subsets of Purkinje neurons with both medio-lateral and anterior–posterior patterns of expression (reviewed by Herrup and Kuemerle (1997) and Sarna and Hawkes (2003)) (Fig. 2). Furthermore patterned gene expression in Purkinje neurons occurs independently of afferent synaptic organization. The effectiveness of neuroprotective strategies targeting these differentially expressed gene products can be readily ascertained through histological examination for the presence or absence of banding patterns (see O’Hearn and Molliver, 1997). There are numerous candidate proteins that are expressed in distinct patterns within the cerebellum that are of interest to neurotrauma research including heat shock proteins, zebrin expression, calcium binding proteins, and amino acid transporters (Herrup and Kuemerle, 1997). There may also be others that have not yet been characterized to date. Also of importance is the maintenance of the compartmentalized expression of these gene products across mammalian species permitting for a degree of consistency in crossspecies comparisons of mechanism and role in TBI.
Pre- and post-synaptic cell survival The cerebellum is a potentially useful structure in which to assess the effects of neuronal cell loss in pre- and post-synaptic targets following TBI. For example, the lurcher mouse phenotype resulting from a mutation of the Grid2 gene for the d2-glutamate receptor (d2-GluR) results in chronic depolarization and loss of Purkinje cells (Zuo et al., 1997). Subsequent to Purkinje neuron death is the loss of granule cells as well as retrograde loss of inferior olive input (Heckroth and Eisenman, 1991; Heckroth, 1992; Zanjani et al., 1998). Anterograde effects manifest as a loss of deep cerebellar nuclei (Heckroth, 1994). Whether these effects are specific to the mutation of the d2-GluR or are a common response to Purkinje cell loss has not been elucidated but may be a valuable area of research to pursue. The extensive literature describing afferent tracing to the cerebellum as well as its relatively simple synaptic organization makes it a suitable model in which to evaluate retrograde and anterograde fates of injured or dying neurons. These studies could add to our understanding of how focal injuries affect distal targets through retrograde or anterograde signaling dysfunction or cell loss.
Neuronal– glial cell communication The role of neuronal–glial communication following neurotrauma remains a controversial issue with evidence to supporting glial scarring as inhibitor of endogenous repair mechanisms along with compelling evidence to indicate neuroprotective roles as well (reviewed by Sofroniew (2005)). In the cerebellum, Bergmann glia residing in the molecular layer form a complex functional and structural relationship with Purkinje cells (reviewed by Bellamy (2006)). These specialized astrocytes form a sheath around the Purkinje neuron soma and synapses. This physical interaction has functional implications as stimulation of climbing and parallel fibers have been shown to activate inward currents in Bergmann glia (Bergles et al., 1997; Clark and Barbour, 1997; Bellamy and Ogden, 2005). These currents are in part
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Fig. 2. Cartoon representation of cerebellar compartmentation in the mouse, as revealed by the expression of zebrin II in subsets of Purkinje cells (Adapted with permission from Sillitoe and Hawkes, 2002): anterior, dorsal and posterior views are shown. The cerebellar vermis is divided into 10 lobules (I–X). However, a more fundamental parcellation is into four transverse zones — anterior (AZ), central (CZ), posterior (PZ), and nodular (NZ). The AZ and PZ are striped — all Purkinje cells in the CZ and NZ express zebrin II uniformly (although stripes can be revealed here by using other markers, such as the small heat shock protein, HSP25 (Armstrong et al., 2000)). Complementary views of a cerebellum whole mount immunoperoxidase stained for zebrin II are shown on the right. (Adapted with permission from Sarna and Hawkes, 2003.)
contributed to by glial-expressed alpha-amino-3hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors, GluR1 and GluR4, as well as glial glutamate transporters, GLAST and GLT-1 (Bellamy, 2006). Although the Bergmann glia
represent a specialized form of astrocyte, they maintain the characteristic reactive astrocyte response to injury following trauma. We have demonstrated the presence of reactive astrocytes in regions of Purkinje cell loss following forebrain
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Fig. 3. (a) Confocal image of sham tissue expression of GFAP in Bergmann glia astrocytes, in red, in close proximity to Purkinje cells, labeled in green. (b) Following forebrain fluid percussion trauma there is a marked increased in GFAP immunoreactivity in regions of cerebellar injury indicated by the loss of Purkinje cells and increase in GFAP immunoreactivity. Scale bar ¼ 50 mm. (Adapted with permission from Park et al., 2006b.)
trauma as indicated by increased GFAP expression (Fig. 3). The close anatomical coupling and functional relationship between Purkinje cells and Bergman glia presents an excellent opportunity to examine the changes in neuronal and glial communication following TBI. Specifically, the cerebellum is an ideal system in which to perform patch-clamping experiments in brain slices, which permits maintenance of cellular architecture and synaptic connectivity. These features may be helpful in elucidating the changes in communication and synaptic plasticity between glial cells and neurons in pathophysiological states. Cerebellar white matter injury Numerous animal models of TBI have reported evidence of TAI in the cerebellum (Lighthall et al., 1990; Shima and Marmarou, 1991; Foda and Marmarou, 1994; Hoshino et al., 2003). Information regarding the functional consequences of such injuries, however, is limited. We recently characterized functional and structural changes in cerebellar white matter following forebrain FPI and demonstrated significant and persistent deficits and pathological changes in the cerebellum (Park et al., 2006a). Early neurofilament degradation and
parallel accumulation in a subset of axons was observed at 1 day post-injury while persistent calpainmediated degradation of aII-spectrin was observed up to 14 days post-injury. The acute degradation of heavy neurofilament chain (NF200) and prolonged degradation of calpain-mediated aII-spectrin would suggest temporally preferential targeting of calpain substrates, NF200 and aII-spectrin, in the cerebellum. Another possibility is that proteolysis of these substrates occurred in subsets of axons with different modes of axonal injury progression. The observations of NF200 and aII-spectrin degradation are not novel concepts in the study of TAI. However, the results reveal a further level of complexity in TAI with respect to calpain’s temporal substrate specificity. Compound action potential recordings from cerebellar white matter have also demonstrated the usefulness of electrophysiological techniques in assessment of white matter function after TBI. The results indicate a consistent CAP response within selected regions. Interestingly, recordings from the middle cerebellar lobe produce a primarily fast conducting myelinated response whereas the posterior and anterior cerebellar lobes exhibit a two-peaked response including both fast and slow myelinated and unmyelinated responses, respectively (Fig. 4). This
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Fig. 4. (a) Compound action potentials were recorded from three regions of cerebellar white matter as indicated by the black-boxed regions. (b) CAP waveforms were dependent on location of recording. Anterior and posterior waveforms consisted of distinct fast and slow components. The middle cerebellar CAP response was primarily a fast myelinated signal. (c) CAP values from cerebellar white matter following forebrain fluid percussion trauma indicated a significant decline in electrophysiological function (*) in the posterior and middle regions of the cerebellum which persisted at 14 days post-injury. (Adapted with permission from Park et al., 2006a.)
presents an opportunity to examine the effects of TBI and potential therapeutic interventions on both myelinated and demyelinated axon populations. A recent study demonstrated varying electrophysiological susceptibilities of these two axonal populations in the corpus callosum (Reeves et al., 2005).
Given the relative lack of electrophysiological data available for TBI white matter injury studies, a comparison of results between the cerebellum and the corpus callosum may reveal whether these susceptibilities are structure specific or are a general principle of injured axons throughout the brain.
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The cerebellum as a model of neurotrauma A key question in the discussion of cerebellar injury and its application in neurotrauma research is ultimately whether it is clinically relevant. We would argue ‘yes’ for the following reasons. There is sufficient evidence of clinical manifestation of cerebellar injury following TBI. In addition to the role in motor coordination, the role of the cerebellum in multiple higher order function is becoming more appreciated and hence a recognition of its potential importance if injured. The traumatized cerebellum offers numerous technical opportunities to examine relevant areas of research related to mechanisms of cellular injury, neuronal–glial pathophysiological interactions, TAI, post-injury synaptic plasticity, selective neuronal vulnerability, and mechanisms of diffuse injury remote from the location of initial trauma. From an anatomical perspective, there are notable differences in human and rodent cerebellar placement that is likely to result in differences on the production of injury biomechanics between these two species. However, there are structural similarities in the cerebellum, such as the cellular organization and foliated segments that are maintained throughout all mammalian species (Voogd and Glickstein, 1998). This gyrencephalic property is not maintained in the cerebral cortex between species and represents an area in which the biomechanics of injury production may differ significantly between higher and lower order species. Despite the pros and cons of anatomical similarity between species, the intent of this discussion is to provide a rationale for inclusion of the cerebellum not only for its clinical and functional importance in TBI pathophysiology, but also as a structure in which to examine the mechanistic phenomena of TBI mechanisms in general. We propose that comparison and complement of studies across various injury models will not only validate but also elucidate novel mechanism of secondary injury.
Conclusion Traumatic brain injury continues to be a health care issue of epidemic proportions as a leading
cause of morbidity and mortality in young adults. Despite the prevalence of this silent epidemic, there is little therapeutic benefit that has translated from the neuroprotective strategies developed in animal models of TBI (Bullock et al., 1999; Faden, 2001; Narayan et al., 2002; Tolias and Bullock, 2004). The failure of clinical trials highlights a lack of complete understanding of the complexity of TBI pathophysiology. This includes optimizing therapeutic time windows and clarifying the multiple pathways leading to cell death. Addressing these issues will require multifaceted approaches and balancing the inhibition of secondary injury mechanisms while not adversely affecting normal physiologic function (Faden, 2002; Ikonomidou and Turski, 2002). We believe that this will be best achieved through complementation and comparisons between existing and novel injury paradigms. The cerebellum is one such novel area that remains to be fully appreciated and described in the context of TBI. Abbreviations AMPA CCD FPI GluR GOS NF200 TAI TBI
alpha-amino-3-hydroxy-5methyl-4-isoxazole propionic acid crossed cerebellar diaschisis fluid percussion injury glutamate receptor Glasgow outcome scale heavy neurofilament chain traumatic axonal injury traumatic brain injury
Acknowledgment We thank the Ontario Neurotrauma Foundation for its funding support. References Ai, J. and Baker, A. (2002) Presynaptic hyperexcitability at cerebellar synapses in traumatic injury rat. Neurosci. Lett., 332: 155–158. Alavi, A., Mirot, A., Newberg, A., Alves, W., Gosfield, T., Berlin, J., Reivich, M. and Gennarelli, T. (1997) Fluorine-18FDG evaluation of crossed cerebellar diaschisis in head injury. J. Nucl. Med., 38: 1717–1720.
336 Anderson, J.R. and Treip, C.S. (1973) Hypertrophic olivary degeneration and Purkinje cell degeneration in a case of longstanding head injury. J. Neurol. Neurosurg. Psychiatry, 36: 826–832. Armstrong, C.L., Krueger-Naug, A.M., Currie, R.W. and Hawkes, R. (2000) Constitutive expression of the 25-kDa heat shock protein Hsp25 reveals novel parasagittal bands of purkinje cells in the adult mouse cerebellar cortex. J. Comp. Neurol., 416: 383–397. Bellamy, T.C. (2006) Interactions between Purkinje neurones and Bergmann glia. Cerebellum, 5: 116–126. Bellamy, T.C. and Ogden, D. (2005) Short-term plasticity of Bergmann glial cell extrasynaptic currents during parallel fiber stimulation in rat cerebellum. Glia, 52: 325–335. Bergles, D.E., Dzubay, J.A. and Jahr, C.E. (1997) Glutamate transporter currents in bergmann glial cells follow the time course of extrasynaptic glutamate. Proc. Natl. Acad. Sci. U.S.A., 94: 14821–14825. Bhatia, K.P., Brown, P., Gregory, R., Lennox, G.G., Manji, H., Thompson, P.D., Ellison, D.W. and Marsden, C.D. (1995) Progressive myoclonic ataxia associated with coeliac disease. The myoclonus is of cortical origin, but the pathology is in the cerebellum. Brain, 118(Pt 5): 1087–1093. Bostrom, K., Helander, C.G. and Lindgren, S. (1992) Blunt basal head trauma: aspects of unconsciousness. Acta Neurochir. Suppl. (Wien.), 55: 25–28. Brandvold, B., Levi, L., Feinsod, M. and George, E.D. (1990) Penetrating craniocerebral injuries in the Israeli involvement in the Lebanese conflict, 1982–1985: analysis of a less aggressive surgical approach. J. Neurosurg., 72: 15–21. Buki, A. and Povlishock, J.T. (2006) All roads lead to disconnection? Traumatic axonal injury revisited. Acta Neurochir. (Wien.), 148: 181–194. Bullock, M.R., Lyeth, B.G. and Muizelaar, J.P. (1999) Current status of neuroprotection trials for traumatic brain injury: lessons from animal models and clinical studies. Neurosurgery, 45: 207–220. Chester, C.S. and Reznick, B.R. (1987) Ataxia after severe head injury: the pathological substrate. Ann. Neurol., 22: 77–79. Clark, B.A. and Barbour, B. (1997) Currents evoked in Bergmann glial cells by parallel fibre stimulation in rat cerebellar slices. J. Physiol., 502(Pt 2): 335–350. D’avella, D., Cacciola, F., Angileri, F.F., Cardali, S., La Rosa, G., Germano, A. and Tomasello, F. (2001) Traumatic intracerebellar hemorrhagic contusions and hematomas. J. Neurosurg. Sci., 45: 29–37. Faden, A.I. (2001) Neuroprotection and traumatic brain injury: the search continues. Arch. Neurol., 58: 1553–1555. Faden, A.I. (2002) Neuroprotection and traumatic brain injury: theoretical option or realistic proposition. Curr. Opin. Neurol., 15: 707–712. Feeney, D.M. and Baron, J.C. (1986) Diaschisis. Stroke, 17: 817–830. Foda, M.A. and Marmarou, A. (1994) A new model of diffuse brain injury in rats. Part II: morphological characterization. J. Neurosurg., 80: 301–313.
Fox, C.A. and Barnard, J.W. (1957) A quantitative study of the Purkinje cell dendritic branchlets and their relationship to afferent fibres. J. Anat., 91: 299–313. Fukuda, K., Aihara, N., Sagar, S.M., Sharp, F.R., Pitts, L.H., Honkaniemi, J. and Noble, L.J. (1996) Purkinje cell vulnerability to mild traumatic brain injury. J. Neurotrauma, 13: 255–266. Gale, S.D., Baxter, L., Roundy, N. and Johnson, S.C. (2005) Traumatic brain injury and grey matter concentration: a preliminary voxel based morphometry study. J. Neurol. Neurosurg. Psychiatry, 76: 984–988. Glickstein, M. (2000) How are visual areas of the brain connected to motor areas for the sensory guidance of movement? Trends Neurosci., 23: 613–617. Gordon, N. (1996) Speech, language, and the cerebellum. Eur. J. Disord. Commun., 31: 359–367. Graham, D.I., Adams, J.H. and Doyle, D. (1978) Ischaemic brain damage in fatal non-missile head injuries. J. Neurol. Sci., 39: 213–234. Graham, D.I., Ford, I., Adams, J.H., Doyle, D., Teasdale, G.M., Lawrence, A.E. and Mclellan, D.R. (1989) Ischaemic brain damage is still common in fatal non-missile head injury. J. Neurol. Neurosurg. Psychiatry, 52: 346–350. Guterman, A. and Smith, R.W. (1987) Neurological sequelae of boxing. Sports Med., 4: 194–210. Hallam, T.M., Floyd, C.L., Folkerts, M.M., Lee, L.L., Gong, Q.Z., Lyeth, B.G., Muizelaar, J.P. and Berman, R.F. (2004) Comparison of behavioral deficits and acute neuronal degeneration in rat lateral fluid percussion and weight-drop brain injury models. J. Neurotrauma, 21: 521–539. Heckroth, J.A. (1992) Development of glutamic acid decarboxylase-immunoreactive elements in the cerebellar cortex of normal and lurcher mutant mice. J. Comp. Neurol., 315: 85–97. Heckroth, J.A. (1994) Quantitative morphological analysis of the cerebellar nuclei in normal and lurcher mutant mice. I: morphology and cell number. J. Comp. Neurol., 343: 173–182. Heckroth, J.A. and Eisenman, L.M. (1991) Olivary morphology and olivocerebellar topography in adult lurcher mutant mice. J. Comp. Neurol., 312: 641–651. Herrup, K. and Kuemerle, B. (1997) The compartmentalization of the cerebellum. Annu. Rev. Neurosci., 20: 61–90. Holmes, G. (1917) The symptoms of acute cerebellar injuries due to gunshot wounds. Brain, 40: 461–535. Hoshino, S., Kobayashi, S., Furukawa, T., Asakura, T. and Teramoto, A. (2003) Multiple immunostaining methods to detect traumatic axonal injury in the rat fluid-percussion brain injury model. Neurol. Med. Chir. (Tokyo), 43: 165–174. Ikonomidou, C. and Turski, L. (2002) Why did NMDA receptor antagonists fail clinical trials for stroke and traumatic brain injury? Lancet Neurol., 1: 383–386. Krauss, J.K., Wakhloo, A.K., Nobbe, F., Trankle, R., Mundinger, F. and Seeger, W. (1995) Lesion of
337 dentatothalamic pathways in severe post-traumatic tremor. Neurol. Res., 17: 409–416. Lighthall, J.W., Goshgarian, H.G. and Pinderski, C.R. (1990) Characterization of axonal injury produced by controlled cortical impact. J. Neurotrauma, 7: 65–76. Mariotti, C., Fancellu, R. and Di Donato, S. (2005) An overview of the patient with ataxia. J. Neurol., 252: 511–518. Mautes, A.E., Fukuda, K. and Noble, L.J. (1996) Cellular response in the cerebellum after midline traumatic brain injury in the rat. Neurosci. Lett., 214: 95–98. Miller, J.D., Butterworth, J.F., Gudeman, S.K., Faulkner, J.E., Choi, S.C., Selhorst, J.B., Harbison, J.W., Lutz, H.A., Young, H.F. and Becker, D.P. (1981) Further experience in the management of severe head injury. J. Neurosurg., 54: 289–299. Miller, J.D., Sweet, R.C., Narayan, R. and Becker, D.P. (1978) Early insults to the injured brain. JAMA, 240: 439–442. Mysiw, W.J., Corrigan, J.D. and Gribble, M.W. (1990) The ataxic subgroup: a discrete outcome after traumatic brain injury. Brain Inj., 4: 247–255. Narayan, R.K., Michel, M.E., Ansell, B., Baethmann, A., Biegon, A., Bracken, M.B., Bullock, M.R., Choi, S.C., Clifton, G.L., Contant, C.F., Coplin, W.M., Dietrich, W.D., Ghajar, J., Grady, S.M., Grossman, R.G., Hall, E.D., Heetderks, W., Hovda, D.A., Jallo, J., Katz, R.L., Knoller, N., Kochanek, P.M., Maas, A.I., Majde, J., Marion, D.W., Marmarou, A., Marshall, L.F., McIntosh, T.K., Miller, E., Mohberg, N., Muizelaar, J.P., Pitts, L.H., Quinn, P., Riesenfeld, G., Robertson, C.S., Strauss, K.I., Teasdale, G., Temkin, N., Tuma, R., Wade, C., Walker, M.D., Weinrich, M., Whyte, J., Wilberger, J., Young, A.B. and Yurkewicz, L. (2002) Clinical trials in head injury. J. Neurotrauma, 19: 503–557. Nathoo, N., Chite, S.H., Edwards, P.J. and van Dellen, J.R. (2002) Civilian infratentorial gunshot injuries: outcome analysis of 26 patients. Surg. Neurol., 58: 225–233. Niimura, K., Chugani, D.C., Muzik, O. and Chugani, H.T. (1999) Cerebellar reorganization following cortical injury in humans: effects of lesion size and age. Neurology, 52: 792–797. O’Hearn, E. and Molliver, M.E. (1997) The olivocerebellar projection mediates ibogaine-induced degeneration of Purkinje cells: a model of indirect, trans-synaptic excitotoxicity. J. Neurosci., 17: 8828–8841. Park, E., Liu, E., Shek, M., Park, A. and Baker, A. (2006a) Heavy neurofilament accumulation and alpha-spectrin degradation accompanies cerebellar white matter functional deficits following forebrain fluid percussion injury. Exp. Neurol., in press, Oct. 26, Epub ahead of print. Park, E., McKnight, S., Ai, J. and Baker, A.J. (2006b) Purkinje cell vulnerability to mild and severe forebrain head trauma. J. Neuropathol. Exp. Neurol., 65: 226–234. Petrosini, L., Leggio, M.G. and Molinari, M. (1998) The cerebellum in the spatial problem solving: a co-star or a guest star? Prog. Neurobiol., 56: 191–210.
Ramnani, N. (2006) The primate cortico-cerebellar system: anatomy and function. Nat. Rev. Neurosci., 7: 511–522. Reeves, T.M., Phillips, L.L. and Povlishock, J.T. (2005) Myelinated and unmyelinated axons of the corpus callosum differ in vulnerability and functional recovery following traumatic brain injury. Exp. Neurol., 196: 126–137. Rish, B.L., Dillon, J.D. and Weiss, G.H. (1983) Mortality following penetrating craniocerebral injuries: an analysis of the deaths in the Vietnam Head Injury Registry population. J. Neurosurg., 59: 775–780. Sarna, J.R. and Hawkes, R. (2003) Patterned Purkinje cell death in the cerebellum. Prog. Neurobiol., 70: 473–507. Sato, M., Chang, E., Igarashi, T. and Noble, L.J. (2001) Neuronal injury and loss after traumatic brain injury: time course and regional variability. Brain Res., 917: 45–54. Shamoto, H. and Chugani, H.T. (1997) Glucose metabolism in the human cerebellum: an analysis of crossed cerebellar diaschisis in children with unilateral cerebral injury. J. Child. Neurol., 12: 407–414. Shima, K. and Marmarou, A. (1991) Evaluation of brain-stem dysfunction following severe fluid-percussion head injury to the cat. J. Neurosurg., 74: 270–277. Sillitoe, R.V. and Hawkes, R. (2002) Whole-mount immunohistochemistry: a high-throughput screen for patterning defects in the mouse cerebellum. J. Histochem. Cytochem., 50: 235–244. Slemmer, J.E., De Zeeuw, C.I. and Weber, J.T. (2005) Don’t get too excited: mechanisms of glutamate-mediated Purkinje cell death. Prog. Brain Res., 148: 367–390. Sofroniew, M.V. (2005) Reactive astrocytes in neural repair and protection. Neuroscientist, 11: 400–407. Soto-Ares, G., Vinchon, M., Delmaire, C., Abecidan, E., Dhellemes, P. and Pruvo, J.P. (2001) Cerebellar atrophy after severe traumatic head injury in children. Child’s Nerv. Syst., 17: 263–269. Strata, P. and Rossi, F. (1998) Plasticity of the olivocerebellar pathway. Trends Neurosci., 21: 407–413. The Brain Trauma Foundation. The American Association of Neurological Surgeons. The Joint Section on Neurotrauma and Critical Care. (2000) Resuscitation of blood pressure and oxygenation. J. Neurotrauma, 17: 471–478. Tolias, C.M. and Bullock, M.R. (2004) Critical appraisal of neuroprotection trials in head injury: what have we learned? NeuroRx, 1: 71–79. Unterharnscheidt, F. (1995a) A neurologist’s reflections on boxing. I: impact mechanics in boxing and injuries other than central nervous system damage. Rev. Neurol., 23: 661–674. Unterharnscheidt, F. (1995b) A neurologist’s reflections on boxing. V: Concluding remarks. Rev. Neurol., 23: 1027–1032. Voogd, J. and Glickstein, M. (1998) The anatomy of the cerebellum. Trends Neurosci., 21: 370–375. Welsh, J.P., Yuen, G., Placantonakis, D.G., Vu, T.Q., Haiss, F., O’Hearn, E., Molliver, M.E. and Aicher, S.A. (2002) Why do Purkinje cells die so easily after global brain
338 ischemia? Aldolase C, EAAT4, and the cerebellar contribution to posthypoxic myoclonus. Adv. Neurol., 89: 331–359. Zanjani, H.S., Vogel, M.W., Martinou, J.C., Delhaye-Bouchaud, N. and Mariani, J. (1998) Postnatal expression of Hu-bcl-2 gene in Lurcher mutant mice fails to rescue Purkinje
cells but protects inferior olivary neurons from target-related cell death. J. Neurosci., 18: 319–327. Zuo, J., De Jager, P.L., Takahashi, K.A., Jiang, W., Linden, D.J. and Heintz, N. (1997) Neurodegeneration in Lurcher mice caused by mutation in delta2 glutamate receptor gene. Nature, 388: 769–773.