Anatomic connections of the fastigial nucleus to the rostral forebrain in the cat

EXPERIMENTAL

NEUROLOGY

Anatomic

39,

285-292 (1973)

Connections of the Fastigial Nucleus Rostra1 Forebrain in the Cat JON W. HARPER AND ROBERT G. HEATH

Dcpartmerct

of Psychiatry

awd Ncwology, New Orlcam, Rrccived

Tulane Louisiana

November

Unizwsity

to the

1

School

of Medicine,

7011-7

16,1972

Unilateral electrolytic lesions of the fastigial nucleus of the cerebellum were made in six cats with a cauterizing current to a stereotaxically implanted electrode. Cats were perfused at days 6, 7, or 8 after this procedure, and their brains were serially sectioned at 300-pm intervals for staining by the NautaGygax, Fink-Heimer procedure I, and cresylechtviolet methods. Lesions affected more than 80% of the fastigial nucleusin three cats and about 407% of the nucleus in one cat. The lesion did not involve the nucleus in two cats. Brains of the cats with the extensive lesions showed degenerating fibers into the hypothalamus, the central nuclei of the thalamus, and into several sites of the septal region, including nucleus accumbens septi, nucleus of the diagonal band (Broca), the dorsal anterior and medial septal nuclei, and more rostra1 into sites of the orbital gyri and into the gyrus rectus. Degenerating fibers to the more rostra1 sites traversed the internal capsule into the cingulum before coursing rostra1 ventrally. Although degeneration was noted bilaterally, ipsilateral degeneration was heavier at all sites. No ascending degenerating fibers were seen in the brains of the cats in which the nucleus was spared. Fink-Heimer preparations showed terminal degeneration in nuclei at the sites noted above. The rostra1 projections of the fastigial nucleus demonstrated by anatomic technics for the first time in this study correspond with those we previously demonstrated by electrically evoked potentials.

IIKTRODUCTION The fastigial nuclei, an integral part of the vestibular system, are considered part of the phylogenetically oldest cerebellum. The most rostra1 connections that have been described anatomically are to the thalamic nuclei. Most authorities consider the fastigial nuclei to be without significant influence on higher centers, but studies using technics other than 1 This study was supported in part by funds from the Ittleson New York, N. Y. 285 Copyright All rights

1973 by Academic Press, reproduction in any form

IX. reserved.

Family

Foundation,

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direct demonstrations of anatomic connections have suggested labyrinthine influences on higher centers. Mettler and Mettler (lit), in 1940, reported disregard of labyrinthine stimulation after removal of the heads of both caudate nuclei in cats. In our laboratories, labyrinthine stimulation in rhesus monkeys which had been raised in isolation induced electroencephalographic changes in the septal region (6), caudate nucleus, and hippocampus (8). In another study, in which evoked potential and mirror (distal) focus technics were used in rhesus monkeys, we demonstrated direct back-and-forth connections between the fastigial nucleus and several rostra1 subcortical sites, including the septal region, hippocampus, thalamus, and amygdala (9). Using evoked potential technics, we have also demonstrated that the fastigial nucleus projects bilaterally into the septal region of both the rhesus monkey and the cat (13). These same technics substantiated the direct connections of the thalamus that had been described previously by Carpenter (2). The short latencies for response in these rostra1 subcortical

FIG. 1. (A) lesion of the violet. (D) nodulus. (13 lesion of the

A thick section (30 right fastigial nucleus nucleus dentatus, (F) X). (B) A similarly right fastigial nucleus

bm) through the caudal part of a nearly complete (Cat LQ). Stain 1.5% silver nitrate and cresylechtnucleus fastigius, (I) nucleus interpositus, (N) stained thick section (30 pm), showing the anterior (Cat LQ). (17 X).

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FIG. 2. A schematic representation of the pattern of fiber and terminal degeneration in the forebrain, as seen in Nauta and Fink-Heimer stained sagittal sections. Sites of terminal degeneration are indicated by stippling. Numbered squares indicate the locations from which micrographs were taken for Figs. 3A-D. Abbreviations: (AC) anterior commissure ; (CC) corpus callosum ; (DA) dorsal anterior septal nucleus ; (F) fornix; (MED) media1 septal nucleus ; (MFB) media1 forebrain bundle; (NAc) nucleus accumbens septi; (OT) optic tract; (RC) rostra1 neuron cluster ; (SCP) supracallosal projections ; (SMT) stria medullaris thalami ; (TP) thalamic projections ; (VDB) ventral component-diagonal band nucleus. nuclei to stimulation of the fast&al nucleus suggested direct monosynapitic connections and led us to efforts to demonstrate the existence of such pathways by neuroanatomic methods. The present report, based on studies of axonal and synaptic terminal degeneration after placement of unilateral electrolytic lesions in the fastigial nuclei of cats, describes pathways from the fastigial nucleus rostrally into the diencephalon, thalamus, and rostra1 forebrain structures. Our previous studies have indicated that these rostra1 connections are clinically significant and descending pathways are well docu(7, l&12). Th e intracerebellar mented in the literature (2, 3, 18).

MATERIAL

AND

METHOD

In six adult male cats an attempt was made to destroy the right fastigial nucleus completely with a fulgerating continuous unidirectional current of 4 ma applied for 30 set at two sites within the nucleus. The lesion-producing electrode was implanted stereotaxically, with use of coordinates in accordance with the atlas of Snider and Lee (17). On each of days 6, 7, and 8 after the surgical procedure, two cats were killed by perfusion with heparinized Ringer-Locke’s solution for 30 set followed by perfusion with a lOc;l, solution of buffered formalin for 1 hr. The cranium of each cat was

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FIG. 3. (A) An example of Fink-Heimer stained degenerating axons in the medial (B) An example of terminal degeneration seen in Finkseptal nucleus. (400 X). Heimer preparations of the medial septal nucleus. (720 X). (C) A Nauta-stained version of the supracallosal projection. Abbreviations : (SW) supracallosal projection; (CC) corpus callosum. (300 X). (D) A Nauta-stained section showing a welldefined fasciculus of degenerating axons in the sagittal plane of the gyrus rectus.

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then partly opened and, with the brain in sitzl, the head was immersed in a similar formalin solution overnight. The next day the brain was removed from the skull and placed in 10% solution of buffered formalin, where it remained for at least 2 weeks before it was sectioned. At successive 300 pm intervals, serial section sets consisting of four sections each M:ere cut in the frontal and sagittal planes on a freezing microtome. The first two of these sections were cut at 10 and 30 pm, respectively, and were stained by the Nauta-Gygas (16) method for degenerating axons. The third section of each set was cut at 10 pm and processed according to the Fink-Heimer (5) procedure I for degenerating axoplasm and synaptic terminals. The fourth section was cut at 10 ~111and stained with cresylechtviolet to clarify cytoarchitectural details. RE.SUI,TS In three of the sis cats, the lesion in the fastigial nucleus encompassed more than SO(J of the nuclear mass (Fig. 1A and B), and in one cat the lesion encompassedahout 4076 of the nucleus. In two cats the nucleus was spared completely, having been confined to the subcortical white matter dorsal to the nucleus in one and tlorsolateral to the nucleus in the other. Degeneration Follozeity Complete Fnsfiginl hrlrclcnfs L&on. Figure 2 is a simplified schematic drawing, lmed on a camera lucida tracing, of one representative sag&al section of a lesion-contaitlillg brain stained by the Nauta-Gygax method. The section has been cut through the lower right aspect of the forebrain and thalamus at an approximate lateral stereotaxic coordinate of 1.5 mm. This section, as lye11as all others from this location, shows two separate and extensive tributaries of degenerating fibers extending into the forebrain rostra1 to the anterior commissure. At the junction of the diencephalon with the telencephalon, the degenerating fibers becomedistributed heavily into the fimbria, fornix proper, and septal nuclei. More laterally, in sections at this anterior-posterior level, degenerating fibers from both the internal and external capsules enter the septal region, terminating at several sites within this relatively broad but specifically defined region (6). Moderate-to-heavy fiber argyrophilia is seenin certain of the ipsilateral septal nuclei, including the dorsal anterior and medial nuclei (Fig. 3A), as well as in the ventral component of the diagonal band nucleus and medial aspects of the nucleus accumbenssepti. Degeneration is evident bilaterally in these nuclei. The intensity of the staining, however, appears to be less on the contralateral side than in the nuclei ipsilateral to the lesion. Synaptic terminal degeneration is present in the various ipsi(R) rostral, (C) caudal. (700 X). (E) A cresylechtvioletcounterstainedNauta preparationshowingfibers which appearto terminatein layer four of the cingulate gyrus. (130X >.

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lateral septal nuclei into which the degenerating fibers are distributed (Fig. 3B), as indicated by the stippled areas in Fig. 2. Contralateral dispersion of involved terminals is somewhat diminished by comparison. Degenerating fibers and terminals are seenin the head of the caudate nucleus but, as elsewhere, are more abundant on the ipsilateral side. Figure 2 also depicts a well-defined bundle of strongly argyrophilic fibers sweeping rostrally above the dorsal aspect of the corpus callosum (Fig. 3C). This supracallosal projection is a continuation of degenerating fibers which exit the brain stem in more caudal regions of the diencephalon to intermingle with the thalamocortical radiation. Many of the fibers, after traversing the internal capsule, enter the cingulum; someterminate in layer 4, but most course forward in a rostroventrally-directed arc into the frontal pole where they disperse in large part to various parts of the orbital gyri. A cluster of neurons on the rostromedial wall of the gyrus rectus is seento receive several well-defined small fasciculi of fibers from this projection (.Fig. 3D). Terminal degeneration is seen in light-to-moderate density throughout a great part of the gyrus rectus. It is particularly heavy, however, i? an area surrounding the heretofore mentioned cell cluster on the rostra1 medial gyrus rectus. Both fiber and terminal argyrophilia are observed in similar loci in the contralateral brain half, but neither appears as pronounced in density as the ipsilateral pattern. The sagittal and frontal sections through the thalamus showed many degenerating fibers streaming diffusely into and through the midline thalamus, as well as ventrally along the course of the medial forebrain bundle. Terminating fibers are noted in the centromedian nuclei, parafasicular nuclei, posteroventrolateral nuclei, and posterolateral nuclei of the thalamus. Argyrophylic axons have also been observed in several cortical areas, including the primary motor and sensory areas, in portions of the temporal gyri, and in the cingulate gyrus (Fig. 3E). These axons are seen to terminate mainly in layer four of these various cortical loci when observed in counter-stained Fink-Heimer preparations. Degeneration After Incomplete Fastigial Nuclezcs Lesion. Sections of the brain of the cat with a partial lesion showed notably fewer degenerative fibers and terminals. In the two cats with lesions that did not involve the fastigial nucleus, degeneration did not occur at rostra1 sites. DISCUSSION Some questions concerning the cerebellofugal projections-in particular, the exact course and final termination of descending pathways-are still being debated (1,4, 19). There is, however, agreement that the fastigial nucleus is richly interconnected with the vestibular system and that it receives

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fibers conveying proprioception from the dorsal colums of the spinal cord. Publications are sparser regarding the fate of the ascending efferents of the fastigial nucleus. The demonstration by degeneration studies of pathways from the fastigial nucleus to the hypothalamus, the several sites within the septal region, and the numerous cortical sites presented here have not been previously described. Terminations of the ascending fastigial efferents have been described in the nucleus of the lateral lemniscus, the nucleus of the posterior commissure, and in thalamic nuclei-specifically, the centromedian and the parafasicular (3). The ascending fastigial nucleus efferent pathways, demonstrated by histologic technics, closely correspond with the connections elicited by evoked potential studies (9). The very short latency response in the septal region after stimulation of the fastigial nucleus in the earlier study indicated a monosynaptic connection. In that study, latency responses at various cortical sites were considerably longer, suggesting multiple synapses. Data presented here of degeneration studies showed the fibers terminating in layer four at cortical sites. Involvement of several additional synapses apparently occurred before the response was elicited on the surface of the cortex. Rostra1 forebrain structures, including the septal region and media1 forebrain bundle, have long been implicated in basic behavioral mechanisms. Mettler and Mettler (15) reported that extensive bilateral lesions of the head of the caudate nucleus resulted in profound behavioral decrement in cats. Correlations of septal region function and behavior (normal and pathologic) in both human subjects and animals have been extensively described (7, 10-12). The connections into the rostra1 forebrain substantiate earlier findings with evoked potentials and provide additional evidence regarding the mechanism by which these particular functional systems, vestibular and proprioceptive. are involved in emotional expression and in behavior. REFERENCES 1.

A., and G. SZIKLA. 1972.The terminationof the brachiumconjunctivum descendens in the nucleusreticularistegmentipontis.An experimentalanatomical study in the cat. Brain Res. 39: 337-351. 2. CARPENTER, M. B. 1959.Lesionsof the fastigial nuclei in the rhesusmonkey. ‘4wer. J. Awat. 194: l-34. 3. CARPENTER, M. B., G. M. BRITTIN, and J. PINES. 1958.Isolatedlesionsof the fastigialnucleiin the cat. J. Camp.Ne~ol. 109: 65-W. 4. CARPENTER, M. B., and H. R. NOVA. 1960.Descendingdivision of the branchium conjunctivumin the cat: A cerebella-reticularsystem.J. Coup. Neztrol. 114: BRODAL,

295-305. R. P., and L.

HEIMER. 1967.Two methodsfor selectivesilver impregnation of degeneratingaxons and their synapticendingsin the central nervous system.Brain Res. 4: 369-374.

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6. HEATH, R. G. 1954. Definition of the septal region, pp. 3-5, In “Studies in Schizophrenia,” Tulane University Department of Psychiatry and Neurology. Harvard University Press, Cambridge. 7. HEATH, R. G. 1966. Schizophrenia: Biochemical and physiologic aberrations. Znt. J. Neuropsychiat. 2: 597-610. 8. HEATH, R. G. 1971. Cerebellar activity in emotional behavior. Presented at the Society of Neuroscience, Washington, D. C., October 1971. In preparation for publication. 9. HEATH, R. G. 1972. Physiologic basis of emotional expression: Evoked potential and mirror focus studies in rhesus monkeys. Bioloy. Psychiat. 5: 1531. 10. HEATH, R. G. 1972. Pleasure and brain activity in man: deep and surface electroencephalograms during orgasm. J. New. Merit. Dis. 154: 3-18. 11. HEATH, R. G. 1972. Electroencephalographic studies in isolation-raised monkeys with behavioral impairment. Dis. New. System. 33: 157-163. 12. HEATH, R. G. 1972. Marihuana : Effects on deep and surface electroencephalograms of man. Arch. Gen. Psychiat. 26: 577-584. 13. HEATH, R. G. 1973. Fastigial nucleus connections to the septal region in monkey and cat: A demonstration with evoked potentials of a bilateral pathway. Biolog. Psychiat. 6: 193-196. 14. METTLER, F. A., and C. C. METTLER. 1940. Labyrinthine disregard after removal of the caudate. Proc. Sot. Exp. Biol. Med. 45: 473-475. 15. METTLER, F. A., and C. C. METTLER. 1942. Effects of striatal injury. Brain 65: 242-255. 16. NAUTA, W. J. H., and P. A. GYGAX. 1954. Silver impregnation of degenerating axons in the central nervous system: a modified technique. Stain. Technol. 29: 91-93.

17. SNIDER, R. S., and J. C. LEE. 1961. “A Stereotaxic Atlas of the Monkey Brain (Macaca Mulatta) .” University of Chicago Press, Chicago. 18. TRUEX, R. C., and M. B. CARPENTER. 1969. “Human Neuroanatomy,” Sixth Edition, Williams & Wilkins, Baltimore. 19. WALBERG, F., 0. POMPEIANO, L. E. WESTRUM, and E. HAUGLIE-HANSSEN. 1962. Fastigioreticular fibers in the cat. An experimental study with silver methods. J. Camp. Neural. 119: 187-199.