THE CANADIAN JOURNAL OF NEUROLOGICAL SCIENCES Neurotransmitters in the Mammalian Striatum: Neuronal Circuits and Heterogeneity

The major input and output pathways of the mammalian striatum have been well established. Recent studies have identified a number of neurotransmitters used by these pathways as well as by striatal interneurons, and have begun to unravel their synaptic connections. The major output neurons have been identified as medium spiny neurons which contain 7-aminobutyric acid (GABA), endogeneous opioids, and substance P. These neurons project to the pallidum and substantia nigra in a topographic and probably chemically organized manner. The major striatal afferents from the cerebral cortex, thalamus, and substantia nigra terminate, at least in part, on these striatal projection neurons. Striatal interneurons contain acetylcholine, GABA, and somatostatin plus neuropeptide Y, and appear to synapse on striatal projection neurons. In recent years, much activity has been directed to the neurochemical and hodological heterogeneities which occur at a macroscopic level in the striatum. This has led to the concept of a patch-matrix organization in the striatum. RESUME: Les neurotransmetteurs dans le striatum des mammiferes: circuits neuronaux et heterogeneite. Les principales voies afferentes et efTSrentes du striatum chez les mammiferes ont ete bien 6tablies. Des etudes recentes ont identifie certains neurotransmetteurs utilises par ces voies ainsi que par les interneurones du striatum et ont commence a preciser leurs connexions synaptiques. Les principaux neurones efferentes ont ete identifies comme etant les neurones epineux de taille moyenne qui contiennent de l'acide 7-aminobutyrique (GABA), des opioi'des endogenes et de la substance P. Ces neurones ont des projections, organisees topographiquement et probablement chimiquement, vers le pallidum et la substance noire. Les principaux neurones afferents depuis le cortex cerebral, le thalamus et la substance noire se terminent, du moins en partie, sur ces neurones de projection du corps strie. Les interneurones du corps strie contiennent de ^acetylcholine, du GABA et de la somatostatine et du neuropeptide Y, et semblent faire synapse avec les neurones de projection du corps strie. Ces dernieres annees, plusieurs etudes ont porte sur l'heterogeneite neurochimique et hodologique qui se rencontre au niveau macroscopique dans le striatum. Ces recherches ont mene a l'elaboration du concept de l'organisation du striatum en matrice parcellaire. Can. J. Neurol. Sci. 1987; 14:386-394 The striatum contains a variety of neurotransmitters, some of which have been associated with neurological disorders including Parkinson's and Huntington's diseases. The purpose of the present review is to provide an updated, brief summary of the recent advances in our knowledge of the biochemical anatomy of the striatum, with particular emphasis on: 1) the synaptic connections among striatal afferents, projection neurons, and interneurons, and 2) the neurochemical and hodological heterogeneities in the striatum. The reader is referred to the following reviews for more comprehensive treatment of the literature on the anatomy and neurochemistry of the striatum. '" 1. STRIATAL INPUTS The cortical afferents The major striatal input arises in the cerebral cortex which projects topographically to the striatum. At a gross level, the putamen receives primarily sensorimotor information, while the caudate nucleus receives major inputs from the limbic and associational cortical areas. The corticostriatal input has been suggested to arise from both supragranular and infragranular cortical layers, and some corticostriatal cells may also project to other subcortical regions. " Although most of the corticostriatal From the Division of Neurological Sciences. Department of Psychiatry. University of British Columbia. Vancouver Reprint requests to: K. Semba. Division of Neurological Sciences, Department of Psychiatry, University of British Columbia, Vancouver, B.C. V6T 2A1