THE LAMELLAR ORGANIZATION OF THE RAT SUBSTANTIA-NIGRA PARS RETICULATA- SEGREGATED PATTERNS OF STRIATAL AFFERENTS AND RELATIONSHIP TO THE TOPOGRAPHY OF CORTICOSTRIATAL PROJECTIONS

The striatonigral pathway provides one of the most direct routes for i nformation flow through the basal ganglia system. Via this pathway inf ormation from sensory, motor and associative areas of the cerebral cor tex are routed to a variety of thalamocortical and brainstem networks involved in the organization of motor behaviour. In a previous analysi s of the rat substantia nigra pars reticulata we have shown that the n igral cells which project to thalamus, tectum and tegmentum are topogr aphically ordered along a series of curved laminae. Extending these ob servations, the present study examined how striatal regions related to particular areas of the cerebral cortex innervate the lamellar keyboa rd of nigral output neurons. For this purpose, small microiontophoreti c injections of wheat germ agglutinin conjugated to horseradish peroxi dase were performed in the striatum and the distribution of retrograde ly-labelled cells in the cerebral cortex and anterogradely-labelled ax ons in the substantia nigra were conjointly examined. The results indi cate that with the exception of the striatal region related to the all ocortex, all the various components of the striatal functional mosaic art represented in the substantia nigra pars reticulata. This represen tation is organized under the form of longitudinal bands which compose a series of curved laminae enveloping a core located dorsolaterally i n the substantia nigra. The striatal mapping in substantia nigra pars reticulata is such that the projections of the auditory and visual com partments are confined to the most ventral lamina. More dorsally, an o rdered representation of the body is achieved by the nigral lamination . The oral and perioral body parts are centred on the dorsolateral cor e and the more distal parts of the face and limbs are progressively se t out in more peripheral laminae. In the region affiliated to the pref rontal cortex, the dorsal cingulate district innervate a ventromedial lamina, the prelimbic:insular district lie dorsal to it. Projections f rom lateral orbital and insular compartments extend laterally along th e dorsal margin of the pars reticulata. Since the ''onion-like'' distr ibution of striatal inputs is precisely the form observed in the distr ibution of nigral efferent neurons, the present observations favour th e view that the nigral lamination underlies formation of specific inpu t-output channels of processing. Evidence is considered that these cha nnels are specialized for particular classes of movements or behaviour s and integrate the various information relevant to the completion of these movements or behaviours. Copyright (C) 1996. Published by Elsevi er Science Ltd.