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Compartmental Organization of the Mammalian Striatum
Compartmental Organization of the Mammalian Striatum A N N M. GRAYBIEL
Department of Psychology and Brain Science, Massachusetts Institute of Technology, Cambridge. M A 02139 (U.S.A.)
By far the most striking architectural characteristic of the mammalian cerebral hemisphere is its division into tissue of cortical and subcortical types. This distinction has dominated views about the level of sophistication and neural processing in different parts of the telencephalon, and has also influenced ideas about the evolution of the cerebral hemispheres from an apparently more primitive striatal type to the exquisitely differentiated neocortical type found in higher mammals, especially man (Herrick, 1926, 1956; Romer, 1962). Because the cerebral cortex is the largest subdivision of the human brain, and disproportionately so by comparison with other species, the view naturally arose that the specialized structure of cortex somehow forms a necessary prerequisite for the complex mental capacities unique to the human. The fact that there is very little cortical tissue in the telencephalon of non-mammalian vertebrates, but instead a large noncortical “striatal” mass, led to the parallel assumption that the striatum is the highest integrative subdivision in these forms. Thus for years it was thought that the great development of the striatum in birds was related to their highly evolved instinctive patterns of behavior. The term, striatum, was applied to this non-cortical mass in birds and other non-mammals mainly because the tissue looked like the striatum (caudate-putamen) of mammalian species. With rough equivalence of the striatum in these different forms assumed, the cortical rind of mammals thus appeared to be a new and greatly modified form of telencephalic tissue overlying a more primitive core. The final link in the reasoning was that in mammals, sophisticated forms of behavior come to be under the control of the neocortex, while the striatum is left in charge of simpler generalized functions, for example, the control of tone. Three lines of evidence have led to major modifications in this view. First, it became possible to define the mammalian striatum by its histochemistry: it is rich in dopamine and in acetylcholinesterase (Dahlstrom and Fuxe, 1964; Jacobowitz and Palkovits, 1974). When histochemical methods were applied to the non-mammalian forebrain, it turned out that only a small part of the entire striatal mass is equivalent, in terms of its histochemistry, to the mammalian caudate nucleus and putamen (Fig. 1; see Parent and Olivier, 1970; Karten and Dubbeldam, 1973). Second, with the development of reliable methods for tracing central nervous pathways, Karten and other comparative neuroanatomists were able to show that much of the large remaining part of the non-mammalian striatum has fiber connections very much like those of the neocortex (Karten, 1969). The implication of these findings was that the uniqueness of the neocortex cannot simply lie in its connections, for example, its connections with the thalamus. This raised a fundamental question, still unanswered, about how the
248
Fig. 1. Transverse sections through the forebrain of rat (A) and pigeon (B) stained for acetylcholinesterase activity. Note relatively small size of the acetylcholinesterase-positiveregion in the bird’s brain; this region (the paleostriatum augmentatum, PA) is the only part of the avian striatum histochemically indentifiable as the counterpart of the mammalian striatum (caudoputamen, C-P). Bars = 2 mm.
architecture of a tissue is related to the connections it is allowed and not allowed to make. Finally, and most recently, it has become clear that the striatum of mammals has a more complex structure than was evident before. As reviewed below, the caudoputamen has a compartmental organization reflected in the patterning both of its
249 histochemistry and its input-output connections. Apparently, just as we had distinguished too sharply between the mammalian and non-mammalian forebrain, so we may also have overdrawn the contrast between neocortex and striatum in mammals. The first hints of compartmental ordering in the striatum of adult mammals were given already in comments on the cytoarchitecture of the striatum: though lacking distinguishable layers, the caudate nucleus and putamen were described by Papez (1929), for example, as being “composed of tubular clusters of large quantities of small radiating cells with short axon cylinders. . . [and] within the clusters, large branching cells”. Recent work by Mensah (1977), Goldman-Rakic (1982), and our own group (see Fig. 2 and Graybiel and Hickey, 1982; Graybiel, 1982) has confirmed the occurrence of such cluster patterns. However, as Goldman-Rakic (1981) has emphasized (see also Graybiel and Ragsdale, 1980, and Fig. 2A), it is only in fetal and neonatal brains that the clustering of cell bodies of striatal neurons is as obvious as inhomogeneities in the distributions of neurotransmitter-related compounds and receptors described below. It was in the immature striatum that a striking histochemical differentiation of the caudoputamen was first demonstrated. Two groups of investigators showed that formaldehyde-induced catecholamine fluorescence, mainly attributable t o dopamine, was organized in patches in the striatum of young animals and only become uniform later in development (Olson et al., 1972; Tennyson et al., 1972).The other characteristic histochemical marker for striatal tissue, acetylcholinesterase, was also shown to occur in patches in the caudoputamen of neonates (Butcher and Hodge, 1976). Recently we have shown that there is an exact spatial correspondence between the dopaminergic and acetylcholinesterase-containing patches (Fig. 3), so that the acetylcholinesterase and dopamine likely coexist in the same mesostriatal fibers (Graybiel et al., 1981a).
Fig. 2. A: clustering of neurons in the developing striatum; Nissl-stained transverse section through caudate nucleus of an E63 kitten fetus. B: Nissl-stained transverse section through the caudate nucleus of adult cat; typical lack of striking cytoarchitectural differentiation is evident but some cluster-patterns(e.g. asterisk) are visible nonetheless. Bars = 2 mm.
250
Fig. 3. A: demonstration by the glyoxylic acid histofluorescence method of the so-called dopamine islands in the caudate nucleus of an E54 kitten fetus. B: same section photographed a second time following post-fixation and staining for acetylcholinesterase activity. Note precise correspondence of patches in A and B. Refer to Graybiel et al. (1981a). Bar = 1 mm.
The compartmental ordering in the immature striatum was assumed to reflect developmental processes finally leading to uniformity or near uniformity of tissue organization in the adult, because not only dopamine and acetylcholinesterase activity, but also afferent fibers and projection neurons, were thought to have a homogeneous distribution in the mature caudoputamen. A series of findings in the past ten years have made it clear, however, that this view is incorrect. For the dopaminergic innervation, Fuxe and colleagues showed that the apparent homogeneity of histofluorescence in Falck-Hillarp preparations of adult caudoputamen could be changed to a patch pattern resembling that in the neonate by pretreatment with a tyrosine hydroxylase inhibitor (Olson et al., 1972). For the acetylcholinesterase activity, we found that with brief incubation times a mosaic of small zones of low acetylcholinesterase activity appeared in the otherwise acetylcholinesterase-rich striatal tissue (Fig. 4);we came to call these “stnosomes” (Graybiel and Ragsdale, 1978, 1979). When the afferent connections of the striatum were studied by means of the autoradiographic technique, corticostriatal (Kunzle, 1975; Goldman and Nauta, 1977; Jones et al., 1977)and thalamostriatal (Kalil, 1978; Royce, 1978) fibers and, very recently, amygdalostriatal fibers (Kelly and Nauta, 1981) were found to terminate in clusters and patches or to avoid small patches of striatum. Similarly, with retrograde tracers, we found that striatal projection neurons are distributed in mosaic patterns (Graybiel et al., 1979). Finally, when techniques were developed to demonstrate opiate receptors in histological material, one of the most striking findings reported was of the patchy distribution of receptors in the caudoputamen (Pert et al., 1976; Young and Kuhar, 1979). We have made the corresponding
251
Fig. 4. Acetylcholinesterase-poorzones (called striosomes) visible in a thiocholine-stained transverse section through the caudate nucleus (CN) of adult cat. Note branching patterns of the zones, e.g., at asterisk. P, putamen; NA, nucleus accumbens septi. Bar = 2 nun.
observation that enkephalin-like immunoreactivity follows a comparable organization into patch-patterns (Graybiel et al., 1981b). With such overwhelming evidence for compartmentalization in the striatum, the question clearly becomes one of how the different patchworks are related to one another, and what the functional consequences of the compartmental ordering might be. We have approached the matter of correlations by comparing the histochemical and immunohistochemical patterns in the striatum to patterns of afferent and efferent fiber distribution visible after appropriate injections of anterograde or retrograde tracer substances (Graybiel et al., 1979, 1981b; Ragsdale and Graybiel, 1981; Graybiel, 1981). The findings suggest that in the adult striatum of the cat acetylcholinesterase-poor striosomes are related in a systematic way t o each of the other distributions: afferent fibers just fill or just avoid the striosomes (Fig. 5A);HRP-labeled projection neurons mainly (though not necessarily exclusively) avoid them (Fig. 5B);and Met-enkephalinlike immunoreactivity (and, for some striosomes, substance P-like immunoreactivity) is richest in these zones (Fig. 5C). In a related correlative study in the rat, Herkenham and Pert (1981) have reported that opiate receptor patches also just match the acetylcholinesterase-poor striosomes. We have a great deal still to learn about this compartmental organization at the anatomical level. We do not know, for example, whether there are multiple striosomal organizations of which we have clearly identified only one, the acetylcholinesterasepoor striosomes. We do not know how the large neurons and various classes of medium
252
253 sized neurons are arranged with respect to the striosomes, nor the rules governing which afferents are engaged or kept apart from striatal interneurons or projection neurons by means of the striosomal ordering. The ultrastructural characteristics of the striosomes also remain to be defined. Nevertheless, the correlational work already done suggests that the striosomes comprise a key architectural unit of the striatum by means of which afferent and efferent connections are separated or brought together and within which modulation of transmission by particular neuropeptides can occur. A study of the physiological properties of these regions would clearly be of great interest. If this compartmental ordering of the striatum is compared to that of the neocortex, a formal similarity is apparent (Fig. 6). In the neocortex (see, e.g., Lund, 1981; Gilbert and Wiesel, 1981; Jones, 1981; Emson and Hunt, 1981), afferent fibers of a particular type terminate only in certain cortical layers (and sometimes only in certain columns or slabs within these layers). Each cortical efferent projection pathway originates from cells within similarly restricted layers or sublayers. And at least some layers (and certain patches within layers) are characterized by distinctive histochemistries. For the striatum there apparently are comparable specifications: input fibers either terminate in the striosomes or just avoid them (Fig. 6 ) ;the output cells and probably interneurons are organized with respect to the striosomes; and the histochemistry of the striosomes is distinctive. Thus, at the macroscopic level, at least, the striosomes in the caudoputamen and the layers and columns of the neocortex appear to share a significance in representing structural counterparts of an ordered channeling of information through each tissue. It is not yet clear whether the analogy should be extended to the functional level, with striosomes representing intrinsic processing units of the striatum in the manner of the physiologically defined columns of the neocortex. The striatum lacks the apical dendritic organization of the neocortex and, at the functional level, this may well be a crucial difference between striatum and cortex in terms of the relative functional potential and evolutionary advantage of their tissue arrangements. For these apical dendrites may represent a mechanism for coordinated sampling across multiple compartments that gives the cortex a computational capacity superior to that of any other part of the brain.
Fig. 5. Examples from correlational studies demonstrating correspondence, in the cat’s caudate nucleus, of acetylcholinesterase-pr striosomes and (A) figures formed by corticostriatal afferent-fiber terminations, (B) regions of weak retrograde labeling after injection of horseradish peroxidase into the pallidum, and (C) regions of high Met-enkephalin-like immunoreactivity. For each pair, serially adjoining sections are shown with the acetylcholinesterase-stained section on the left. On the right, A shows autoradiogram of the contralateral frontocaudate projection (see Ragsdale and Graybiel, 1981); B shows tetramethylbenzidine staining (Mesulam, 1978) of striatal neurons sending axons to (or through) the ipsilateral internal pallidum (entopeduncular nucleus) (see Graybiel et al., 1979; Graybiel and Ragsdale, 1979); and C shows peroxidase-antiperoxidase immunohistochemical preparation (Sternberger, 1979), following incubation with antiserum raised against the neuropeptide, Met-enkephalin (see Graybiel et al., 1981b). Photomicrographs at same scale. Bar = 1 mm.
254
Fig. 6. Three schematic drawings comparing the compartmental organizations of the neocortex (above) and striatum (below). A: patterns of afferent-fiber termination in relation to layers and “columns” in neocortex, and in relation to striosornes in caudoputamen. B: patterns of efferent-cell organization in the two structures. In C, functional subdivisions (columns, slabs) are shown for the neocortex, but the functional subdivisions drawn for the striaturn are hypothetical. Note presence of apical dendrites orientated along columns in the neocortex, and the absence of an apical dendritic organization in the striaturn.
255 ACKNOWLEDGEMENTS The work described was supported by the National Science Foundation (BNS 78-10549 and BNS 81-12125), the National Institutes of Health (Biomedical Research Support Grant 5-S07-RR07047-14)and the Scottish Rite Foundation. It is a pleasure to aknowledge the help of Mr. Henry F. Hall, who made the photographs.
REFERENCES Butcher, L.L. and Hodge, G.K. (1976)Postnatal development of acetylcholinesterase in the caudate-putamen and substantia nigra of rats. Brain Res., 106: 223-240. Dahlstrom, A. and Fuxe, K. (1964) Evidence for the existence of monoamine-containing neurons in the central nervous system. Acra physiol. scand., 62, Suppl. 232: 1-55. Emson, P.C. and Hunt, S.P. (1981)Anatomical chemistry of thecerebral cortex In F.O. Schmitt, F.G. Worden and F. Dennis (Eds.), "he Organization of the Cerebral Cortex., MIT Press, Cambridge, MA, pp. 325345. Gilbert, C.D. and Wiesel, T.N. (1981) Laminar specialization and intracortical connections in cat primary visual cortex. In F.O. Schmitt, F.G. Worden and F. Dennis (Eds.), "he Organizah'on of the Cerebral Correx, MIT Press, Cambridge, MA, pp. 163-191. Goldman, P.S. and Nauta, W.J.H. (1977) An intricately patterned prefronto-caudate projection in the rhesus monkey. J. comp. Neurol., 171: 369-386. Goldman-Rakic, P.S. (1981) Prenatal formation of cortical input and development of cytoarchitectonic compartments in the neostriatum of the rhesus monkey. J. Neurosci., 1: 721-735. Graybiel, A.M. (1982) Correlative studies of histochemistry and fiber connections in the central nervous system. In S.L. Palay and V. Chan-Palay (Eds.), Cytochemical Methods in Neuronnatomy, Alan Liss, New York, pp. 4.S47. Graybiel, A.M. and Hickey, T.L. (1981) Chemospecificity of ontogenetic units in the striaturn demonstrated by combining [3H]thymidine neuronography and histochemical staining, Roc. nut. Acad. Sci. U.S.A., 79: 198-202. Graybiel, A.M. and Ragsdale, C.W. (1978) Histochemically distinct compartments in the striaturn of human, monkey and cat demonstrated by acetylthiocholinesterasestaining. Proc. nut. Acad. Sci. U.S.A.,75: 572S5726. Graybiel, A.M. and Ragsdale, C.W. (1979) Fiber connections of the basal ganglia. In M. CuCnod, G.W. Kreutzberg and F.E. Bloom (Eds.), Developmenr and Chemical Specificity of Neurons, Progr. Brain Rex, Vol. -51, Elsevier/North-Holland, Amsterdam, pp. 239283. Graybiel, A.M. and Ragsdale, C.W. (1980) Clumping of acetylcholinesterase activity in the developing striaturn of the human fetus and young infant. Proc. nut. Acad. Sci. U.S.A., 77: 1214-1218. Graybiel, A.M., Ragsdale, C.W. and Edley, S.M. (1979)Compartments in the striaturn of the cat observed by retrograde cell labeling. Exp. Brian Res., 34: 1%195. Graybiel, A.M., Pickel, V.M., Joh, T.H., Reis, D.J. and Ragsdale, C.W. (1981a) Direct demonstration of a correspondence between the dopamine islands and cholinesterase patches in the developing striatum. Roc. nat. Acad. Scr. U.S.A.,78: 5871-5875. Graybiel, A.M., Ragsdale, C.W., Yoneoka, E.S. and Elde, R.P. (1981b) A n immunohistochemical study of enkephalins and other neuropeptides in the striaturn of the cat with evidence that the opiate peptides are arranged to form mosaic patterns in register with the striosomal compartments visible by acetylcholinesterase staining. Neuroscience, 6: 377-397. Herkenham, M. and Pert, C.B. (1981) Mosaic distribution of opiate receptors, parafascicular projections and acetylcholinesterase in rat striaturn. Narure (Lond.), 291: 415-418. Hemck, C.J. (1926) Brains of Rats and Men. Univ. of Chicago Press, Chicago. Hemck, C.J. (1956) The Evolution of Human Nature. Univ. of Texas PresdHarper Brothers, New York. Jacobowitz, D.M. and Palkovits, M. (1974) Topographic atlas of catecholamine and acetylcholinesterasecontaining neurons in the rat brain. I. Forebrain (telencephalon, diencephalon). J. comp. Neurol., 157: 13-28.
256 Jones, E.G. (1981) Anatomy of cerebral cortex: columnar input-output organization. In F.O. Schmitt, F.G. Worden and F. Dennis (Eds.), The Organization of the Cerebral Cortex, MIT Press, Cambridge, MA, pp. 199-235. Jones, E.G., Coulter, J.D., Burton, H. and Porter, R. (1977) Cells of origin and terminal distribution of corticostriatal fibers arising in the sensory-motor cortex of monkeys. J. comp. Neurol., 173: 53-80. Kalil, K. (1978) Patch-like termination of thalamic fibers in the putamen of the rhesus monkey: an autoradiographic study. Brain Res., 140: 333-339. Karten, H.J. (1969) The organization of the avian telencephalon and some speculations on the phylogeny of the amniotic telencephalon. Ann. N. Y. Acad. Sci., 167: 164-179. Karten, H.J. and Dubbledam, J.L. (1973)The organization and projections of the paleostriatal complex in the pigeon (Columbia livia). J. comp. Neurol., 148: 61-90. Kelly, A.E., Domesick, V.B. and Nauta, W.J.H. (1981) The amygdalostriatal projection in the rat. Anat. Rec., 199: 134A. Kiinzle, H. (1975) Bilateral projections from precentral motor cortex to the putamen and other parts of the basal ganglia. Brain Res., 88: 195-210. Lund, S.J. (1981) Intrinsic organization of the primate visual cortex, area 17, as seen in Golgi preparations. In F.O. Schmitt, F.G. Worden and F. Dennis @is.), The Organization ofrhe Cerebral Cortex,MIT Press, Cambridge, MA, pp. 105-124. Mensah, P.L. (1977) The internal organization of the mouse caudate nucleus: evidence for cell clustering and regional variation. Brain Res., 137: 53-66. Mesulam, M.-M. (1978) Tetramethyl benzidine for horseradish peroxidase neurohistochemistry: a non-carcinogenic blue reaction-product with superior sensitivity for visualizing neural afferents and efferents. J.oHistochem.Cytochem., 26: 106-117. Olson, L., Seiger, A. and Fuxe, K. (1972) Heterogeneity of striatal and limbic dopamine innervation: highly fluorescent islands in developing and adult rats. Brain Res., 44: 283-288. Papez, J.W. (1929) Comparative Neurology, Thomas Y. Crowell Co., New York, p. 319. Parent, A. and Olivier, A. (1970) Comparative histochemical study of the corpus striatum. J. Himforsch., 12: 73-81. Pert, C.B., Kuhar, M.J. and Snyder, S.H. (1976) Opiate receptor: autoradiographic localization in rat brain. Roc. nat. Acad. Sci. U.S.A.,73: 3729-3733. Ragsdale, C.W. and Graybiel, A.M. (1981) The fronto-striatal projection in the cat and monkey and its relationship to inhomogeneities established by acetylcholinesterase histochemistry . Brain Res., 208: 259-266. Romer, A S . (1%2) The Vertebrate Body, W.B. Saunders Co., Philadelphia. Royce, G.J. (1978) Autoradiographic evidence for a discontinuous projection to the caudate nucleus from the centromedian nucleus in the cat. Brain Res., 146: 145-150. Stemberger, L.A. (1979) Zmmunocytochemisfry,Wiley and Sons, New York. Tennyson, V.M., Barrett, R.E., Cohen, G., CBC, L., Heikkila, R.and Mytilineou, C. (1972) The developing neostriatum of the rabbit: correlation of fluorescence histochemistry, electron microscopy, endogenous dopamine levels, and [3qdopamine uptake. Brain Res., 46: 251-285. Young, W.S. and Kuhar, M.J. (1979) A new method for receptor autoradiography: [3H]opioid receptors in rat brain. Brain Res., 179: 255-270.
Department of Psychology and Brain Science, Massachusetts Institute of Technology, Cambridge. M A 02139 (U.S.A.)
By far the most striking architectural characteristic of the mammalian cerebral hemisphere is its division into tissue of cortical and subcortical types. This distinction has dominated views about the level of sophistication and neural processing in different parts of the telencephalon, and has also influenced ideas about the evolution of the cerebral hemispheres from an apparently more primitive striatal type to the exquisitely differentiated neocortical type found in higher mammals, especially man (Herrick, 1926, 1956; Romer, 1962). Because the cerebral cortex is the largest subdivision of the human brain, and disproportionately so by comparison with other species, the view naturally arose that the specialized structure of cortex somehow forms a necessary prerequisite for the complex mental capacities unique to the human. The fact that there is very little cortical tissue in the telencephalon of non-mammalian vertebrates, but instead a large noncortical “striatal” mass, led to the parallel assumption that the striatum is the highest integrative subdivision in these forms. Thus for years it was thought that the great development of the striatum in birds was related to their highly evolved instinctive patterns of behavior. The term, striatum, was applied to this non-cortical mass in birds and other non-mammals mainly because the tissue looked like the striatum (caudate-putamen) of mammalian species. With rough equivalence of the striatum in these different forms assumed, the cortical rind of mammals thus appeared to be a new and greatly modified form of telencephalic tissue overlying a more primitive core. The final link in the reasoning was that in mammals, sophisticated forms of behavior come to be under the control of the neocortex, while the striatum is left in charge of simpler generalized functions, for example, the control of tone. Three lines of evidence have led to major modifications in this view. First, it became possible to define the mammalian striatum by its histochemistry: it is rich in dopamine and in acetylcholinesterase (Dahlstrom and Fuxe, 1964; Jacobowitz and Palkovits, 1974). When histochemical methods were applied to the non-mammalian forebrain, it turned out that only a small part of the entire striatal mass is equivalent, in terms of its histochemistry, to the mammalian caudate nucleus and putamen (Fig. 1; see Parent and Olivier, 1970; Karten and Dubbeldam, 1973). Second, with the development of reliable methods for tracing central nervous pathways, Karten and other comparative neuroanatomists were able to show that much of the large remaining part of the non-mammalian striatum has fiber connections very much like those of the neocortex (Karten, 1969). The implication of these findings was that the uniqueness of the neocortex cannot simply lie in its connections, for example, its connections with the thalamus. This raised a fundamental question, still unanswered, about how the
248
Fig. 1. Transverse sections through the forebrain of rat (A) and pigeon (B) stained for acetylcholinesterase activity. Note relatively small size of the acetylcholinesterase-positiveregion in the bird’s brain; this region (the paleostriatum augmentatum, PA) is the only part of the avian striatum histochemically indentifiable as the counterpart of the mammalian striatum (caudoputamen, C-P). Bars = 2 mm.
architecture of a tissue is related to the connections it is allowed and not allowed to make. Finally, and most recently, it has become clear that the striatum of mammals has a more complex structure than was evident before. As reviewed below, the caudoputamen has a compartmental organization reflected in the patterning both of its
249 histochemistry and its input-output connections. Apparently, just as we had distinguished too sharply between the mammalian and non-mammalian forebrain, so we may also have overdrawn the contrast between neocortex and striatum in mammals. The first hints of compartmental ordering in the striatum of adult mammals were given already in comments on the cytoarchitecture of the striatum: though lacking distinguishable layers, the caudate nucleus and putamen were described by Papez (1929), for example, as being “composed of tubular clusters of large quantities of small radiating cells with short axon cylinders. . . [and] within the clusters, large branching cells”. Recent work by Mensah (1977), Goldman-Rakic (1982), and our own group (see Fig. 2 and Graybiel and Hickey, 1982; Graybiel, 1982) has confirmed the occurrence of such cluster patterns. However, as Goldman-Rakic (1981) has emphasized (see also Graybiel and Ragsdale, 1980, and Fig. 2A), it is only in fetal and neonatal brains that the clustering of cell bodies of striatal neurons is as obvious as inhomogeneities in the distributions of neurotransmitter-related compounds and receptors described below. It was in the immature striatum that a striking histochemical differentiation of the caudoputamen was first demonstrated. Two groups of investigators showed that formaldehyde-induced catecholamine fluorescence, mainly attributable t o dopamine, was organized in patches in the striatum of young animals and only become uniform later in development (Olson et al., 1972; Tennyson et al., 1972).The other characteristic histochemical marker for striatal tissue, acetylcholinesterase, was also shown to occur in patches in the caudoputamen of neonates (Butcher and Hodge, 1976). Recently we have shown that there is an exact spatial correspondence between the dopaminergic and acetylcholinesterase-containing patches (Fig. 3), so that the acetylcholinesterase and dopamine likely coexist in the same mesostriatal fibers (Graybiel et al., 1981a).
Fig. 2. A: clustering of neurons in the developing striatum; Nissl-stained transverse section through caudate nucleus of an E63 kitten fetus. B: Nissl-stained transverse section through the caudate nucleus of adult cat; typical lack of striking cytoarchitectural differentiation is evident but some cluster-patterns(e.g. asterisk) are visible nonetheless. Bars = 2 mm.
250
Fig. 3. A: demonstration by the glyoxylic acid histofluorescence method of the so-called dopamine islands in the caudate nucleus of an E54 kitten fetus. B: same section photographed a second time following post-fixation and staining for acetylcholinesterase activity. Note precise correspondence of patches in A and B. Refer to Graybiel et al. (1981a). Bar = 1 mm.
The compartmental ordering in the immature striatum was assumed to reflect developmental processes finally leading to uniformity or near uniformity of tissue organization in the adult, because not only dopamine and acetylcholinesterase activity, but also afferent fibers and projection neurons, were thought to have a homogeneous distribution in the mature caudoputamen. A series of findings in the past ten years have made it clear, however, that this view is incorrect. For the dopaminergic innervation, Fuxe and colleagues showed that the apparent homogeneity of histofluorescence in Falck-Hillarp preparations of adult caudoputamen could be changed to a patch pattern resembling that in the neonate by pretreatment with a tyrosine hydroxylase inhibitor (Olson et al., 1972). For the acetylcholinesterase activity, we found that with brief incubation times a mosaic of small zones of low acetylcholinesterase activity appeared in the otherwise acetylcholinesterase-rich striatal tissue (Fig. 4);we came to call these “stnosomes” (Graybiel and Ragsdale, 1978, 1979). When the afferent connections of the striatum were studied by means of the autoradiographic technique, corticostriatal (Kunzle, 1975; Goldman and Nauta, 1977; Jones et al., 1977)and thalamostriatal (Kalil, 1978; Royce, 1978) fibers and, very recently, amygdalostriatal fibers (Kelly and Nauta, 1981) were found to terminate in clusters and patches or to avoid small patches of striatum. Similarly, with retrograde tracers, we found that striatal projection neurons are distributed in mosaic patterns (Graybiel et al., 1979). Finally, when techniques were developed to demonstrate opiate receptors in histological material, one of the most striking findings reported was of the patchy distribution of receptors in the caudoputamen (Pert et al., 1976; Young and Kuhar, 1979). We have made the corresponding
251
Fig. 4. Acetylcholinesterase-poorzones (called striosomes) visible in a thiocholine-stained transverse section through the caudate nucleus (CN) of adult cat. Note branching patterns of the zones, e.g., at asterisk. P, putamen; NA, nucleus accumbens septi. Bar = 2 nun.
observation that enkephalin-like immunoreactivity follows a comparable organization into patch-patterns (Graybiel et al., 1981b). With such overwhelming evidence for compartmentalization in the striatum, the question clearly becomes one of how the different patchworks are related to one another, and what the functional consequences of the compartmental ordering might be. We have approached the matter of correlations by comparing the histochemical and immunohistochemical patterns in the striatum to patterns of afferent and efferent fiber distribution visible after appropriate injections of anterograde or retrograde tracer substances (Graybiel et al., 1979, 1981b; Ragsdale and Graybiel, 1981; Graybiel, 1981). The findings suggest that in the adult striatum of the cat acetylcholinesterase-poor striosomes are related in a systematic way t o each of the other distributions: afferent fibers just fill or just avoid the striosomes (Fig. 5A);HRP-labeled projection neurons mainly (though not necessarily exclusively) avoid them (Fig. 5B);and Met-enkephalinlike immunoreactivity (and, for some striosomes, substance P-like immunoreactivity) is richest in these zones (Fig. 5C). In a related correlative study in the rat, Herkenham and Pert (1981) have reported that opiate receptor patches also just match the acetylcholinesterase-poor striosomes. We have a great deal still to learn about this compartmental organization at the anatomical level. We do not know, for example, whether there are multiple striosomal organizations of which we have clearly identified only one, the acetylcholinesterasepoor striosomes. We do not know how the large neurons and various classes of medium
252
253 sized neurons are arranged with respect to the striosomes, nor the rules governing which afferents are engaged or kept apart from striatal interneurons or projection neurons by means of the striosomal ordering. The ultrastructural characteristics of the striosomes also remain to be defined. Nevertheless, the correlational work already done suggests that the striosomes comprise a key architectural unit of the striatum by means of which afferent and efferent connections are separated or brought together and within which modulation of transmission by particular neuropeptides can occur. A study of the physiological properties of these regions would clearly be of great interest. If this compartmental ordering of the striatum is compared to that of the neocortex, a formal similarity is apparent (Fig. 6). In the neocortex (see, e.g., Lund, 1981; Gilbert and Wiesel, 1981; Jones, 1981; Emson and Hunt, 1981), afferent fibers of a particular type terminate only in certain cortical layers (and sometimes only in certain columns or slabs within these layers). Each cortical efferent projection pathway originates from cells within similarly restricted layers or sublayers. And at least some layers (and certain patches within layers) are characterized by distinctive histochemistries. For the striatum there apparently are comparable specifications: input fibers either terminate in the striosomes or just avoid them (Fig. 6 ) ;the output cells and probably interneurons are organized with respect to the striosomes; and the histochemistry of the striosomes is distinctive. Thus, at the macroscopic level, at least, the striosomes in the caudoputamen and the layers and columns of the neocortex appear to share a significance in representing structural counterparts of an ordered channeling of information through each tissue. It is not yet clear whether the analogy should be extended to the functional level, with striosomes representing intrinsic processing units of the striatum in the manner of the physiologically defined columns of the neocortex. The striatum lacks the apical dendritic organization of the neocortex and, at the functional level, this may well be a crucial difference between striatum and cortex in terms of the relative functional potential and evolutionary advantage of their tissue arrangements. For these apical dendrites may represent a mechanism for coordinated sampling across multiple compartments that gives the cortex a computational capacity superior to that of any other part of the brain.
Fig. 5. Examples from correlational studies demonstrating correspondence, in the cat’s caudate nucleus, of acetylcholinesterase-pr striosomes and (A) figures formed by corticostriatal afferent-fiber terminations, (B) regions of weak retrograde labeling after injection of horseradish peroxidase into the pallidum, and (C) regions of high Met-enkephalin-like immunoreactivity. For each pair, serially adjoining sections are shown with the acetylcholinesterase-stained section on the left. On the right, A shows autoradiogram of the contralateral frontocaudate projection (see Ragsdale and Graybiel, 1981); B shows tetramethylbenzidine staining (Mesulam, 1978) of striatal neurons sending axons to (or through) the ipsilateral internal pallidum (entopeduncular nucleus) (see Graybiel et al., 1979; Graybiel and Ragsdale, 1979); and C shows peroxidase-antiperoxidase immunohistochemical preparation (Sternberger, 1979), following incubation with antiserum raised against the neuropeptide, Met-enkephalin (see Graybiel et al., 1981b). Photomicrographs at same scale. Bar = 1 mm.
254
Fig. 6. Three schematic drawings comparing the compartmental organizations of the neocortex (above) and striatum (below). A: patterns of afferent-fiber termination in relation to layers and “columns” in neocortex, and in relation to striosornes in caudoputamen. B: patterns of efferent-cell organization in the two structures. In C, functional subdivisions (columns, slabs) are shown for the neocortex, but the functional subdivisions drawn for the striaturn are hypothetical. Note presence of apical dendrites orientated along columns in the neocortex, and the absence of an apical dendritic organization in the striaturn.
255 ACKNOWLEDGEMENTS The work described was supported by the National Science Foundation (BNS 78-10549 and BNS 81-12125), the National Institutes of Health (Biomedical Research Support Grant 5-S07-RR07047-14)and the Scottish Rite Foundation. It is a pleasure to aknowledge the help of Mr. Henry F. Hall, who made the photographs.
REFERENCES Butcher, L.L. and Hodge, G.K. (1976)Postnatal development of acetylcholinesterase in the caudate-putamen and substantia nigra of rats. Brain Res., 106: 223-240. Dahlstrom, A. and Fuxe, K. (1964) Evidence for the existence of monoamine-containing neurons in the central nervous system. Acra physiol. scand., 62, Suppl. 232: 1-55. Emson, P.C. and Hunt, S.P. (1981)Anatomical chemistry of thecerebral cortex In F.O. Schmitt, F.G. Worden and F. Dennis (Eds.), "he Organization of the Cerebral Cortex., MIT Press, Cambridge, MA, pp. 325345. Gilbert, C.D. and Wiesel, T.N. (1981) Laminar specialization and intracortical connections in cat primary visual cortex. In F.O. Schmitt, F.G. Worden and F. Dennis (Eds.), "he Organizah'on of the Cerebral Correx, MIT Press, Cambridge, MA, pp. 163-191. Goldman, P.S. and Nauta, W.J.H. (1977) An intricately patterned prefronto-caudate projection in the rhesus monkey. J. comp. Neurol., 171: 369-386. Goldman-Rakic, P.S. (1981) Prenatal formation of cortical input and development of cytoarchitectonic compartments in the neostriatum of the rhesus monkey. J. Neurosci., 1: 721-735. Graybiel, A.M. (1982) Correlative studies of histochemistry and fiber connections in the central nervous system. In S.L. Palay and V. Chan-Palay (Eds.), Cytochemical Methods in Neuronnatomy, Alan Liss, New York, pp. 4.S47. Graybiel, A.M. and Hickey, T.L. (1981) Chemospecificity of ontogenetic units in the striaturn demonstrated by combining [3H]thymidine neuronography and histochemical staining, Roc. nut. Acad. Sci. U.S.A., 79: 198-202. Graybiel, A.M. and Ragsdale, C.W. (1978) Histochemically distinct compartments in the striaturn of human, monkey and cat demonstrated by acetylthiocholinesterasestaining. Proc. nut. Acad. Sci. U.S.A.,75: 572S5726. Graybiel, A.M. and Ragsdale, C.W. (1979) Fiber connections of the basal ganglia. In M. CuCnod, G.W. Kreutzberg and F.E. Bloom (Eds.), Developmenr and Chemical Specificity of Neurons, Progr. Brain Rex, Vol. -51, Elsevier/North-Holland, Amsterdam, pp. 239283. Graybiel, A.M. and Ragsdale, C.W. (1980) Clumping of acetylcholinesterase activity in the developing striaturn of the human fetus and young infant. Proc. nut. Acad. Sci. U.S.A., 77: 1214-1218. Graybiel, A.M., Ragsdale, C.W. and Edley, S.M. (1979)Compartments in the striaturn of the cat observed by retrograde cell labeling. Exp. Brian Res., 34: 1%195. Graybiel, A.M., Pickel, V.M., Joh, T.H., Reis, D.J. and Ragsdale, C.W. (1981a) Direct demonstration of a correspondence between the dopamine islands and cholinesterase patches in the developing striatum. Roc. nat. Acad. Scr. U.S.A.,78: 5871-5875. Graybiel, A.M., Ragsdale, C.W., Yoneoka, E.S. and Elde, R.P. (1981b) A n immunohistochemical study of enkephalins and other neuropeptides in the striaturn of the cat with evidence that the opiate peptides are arranged to form mosaic patterns in register with the striosomal compartments visible by acetylcholinesterase staining. Neuroscience, 6: 377-397. Herkenham, M. and Pert, C.B. (1981) Mosaic distribution of opiate receptors, parafascicular projections and acetylcholinesterase in rat striaturn. Narure (Lond.), 291: 415-418. Hemck, C.J. (1926) Brains of Rats and Men. Univ. of Chicago Press, Chicago. Hemck, C.J. (1956) The Evolution of Human Nature. Univ. of Texas PresdHarper Brothers, New York. Jacobowitz, D.M. and Palkovits, M. (1974) Topographic atlas of catecholamine and acetylcholinesterasecontaining neurons in the rat brain. I. Forebrain (telencephalon, diencephalon). J. comp. Neurol., 157: 13-28.
256 Jones, E.G. (1981) Anatomy of cerebral cortex: columnar input-output organization. In F.O. Schmitt, F.G. Worden and F. Dennis (Eds.), The Organization of the Cerebral Cortex, MIT Press, Cambridge, MA, pp. 199-235. Jones, E.G., Coulter, J.D., Burton, H. and Porter, R. (1977) Cells of origin and terminal distribution of corticostriatal fibers arising in the sensory-motor cortex of monkeys. J. comp. Neurol., 173: 53-80. Kalil, K. (1978) Patch-like termination of thalamic fibers in the putamen of the rhesus monkey: an autoradiographic study. Brain Res., 140: 333-339. Karten, H.J. (1969) The organization of the avian telencephalon and some speculations on the phylogeny of the amniotic telencephalon. Ann. N. Y. Acad. Sci., 167: 164-179. Karten, H.J. and Dubbledam, J.L. (1973)The organization and projections of the paleostriatal complex in the pigeon (Columbia livia). J. comp. Neurol., 148: 61-90. Kelly, A.E., Domesick, V.B. and Nauta, W.J.H. (1981) The amygdalostriatal projection in the rat. Anat. Rec., 199: 134A. Kiinzle, H. (1975) Bilateral projections from precentral motor cortex to the putamen and other parts of the basal ganglia. Brain Res., 88: 195-210. Lund, S.J. (1981) Intrinsic organization of the primate visual cortex, area 17, as seen in Golgi preparations. In F.O. Schmitt, F.G. Worden and F. Dennis @is.), The Organization ofrhe Cerebral Cortex,MIT Press, Cambridge, MA, pp. 105-124. Mensah, P.L. (1977) The internal organization of the mouse caudate nucleus: evidence for cell clustering and regional variation. Brain Res., 137: 53-66. Mesulam, M.-M. (1978) Tetramethyl benzidine for horseradish peroxidase neurohistochemistry: a non-carcinogenic blue reaction-product with superior sensitivity for visualizing neural afferents and efferents. J.oHistochem.Cytochem., 26: 106-117. Olson, L., Seiger, A. and Fuxe, K. (1972) Heterogeneity of striatal and limbic dopamine innervation: highly fluorescent islands in developing and adult rats. Brain Res., 44: 283-288. Papez, J.W. (1929) Comparative Neurology, Thomas Y. Crowell Co., New York, p. 319. Parent, A. and Olivier, A. (1970) Comparative histochemical study of the corpus striatum. J. Himforsch., 12: 73-81. Pert, C.B., Kuhar, M.J. and Snyder, S.H. (1976) Opiate receptor: autoradiographic localization in rat brain. Roc. nat. Acad. Sci. U.S.A.,73: 3729-3733. Ragsdale, C.W. and Graybiel, A.M. (1981) The fronto-striatal projection in the cat and monkey and its relationship to inhomogeneities established by acetylcholinesterase histochemistry . Brain Res., 208: 259-266. Romer, A S . (1%2) The Vertebrate Body, W.B. Saunders Co., Philadelphia. Royce, G.J. (1978) Autoradiographic evidence for a discontinuous projection to the caudate nucleus from the centromedian nucleus in the cat. Brain Res., 146: 145-150. Stemberger, L.A. (1979) Zmmunocytochemisfry,Wiley and Sons, New York. Tennyson, V.M., Barrett, R.E., Cohen, G., CBC, L., Heikkila, R.and Mytilineou, C. (1972) The developing neostriatum of the rabbit: correlation of fluorescence histochemistry, electron microscopy, endogenous dopamine levels, and [3qdopamine uptake. Brain Res., 46: 251-285. Young, W.S. and Kuhar, M.J. (1979) A new method for receptor autoradiography: [3H]opioid receptors in rat brain. Brain Res., 179: 255-270.