HETEROGENEOUS TOPOGRAPHICAL DISTRIBUTION OF THE STRIATONIGRAL AND STRIATOPALLIDAL NEURONS IN THE MATRIX COMPARTMENT OF THE CAT CAUDATE-NUCLEUS

The topographical organization of the striatonigral projection was inv estigated in the cat by comparing the localization and the intensity o f labelling of retrogradely labelled cells in the caudate nucleus foll owing one or multiple injections of horseradish peroxidase-wheat germ agglutinin into the center or along the rostrocaudal axis of the subst antia nigra pars reticulata. Second, the localizations of retrogradely labelled striatopallidal neurons and of clusters of aggregated striat onigral neurons (as outlined by the transport of C-14-material) were c ompared in cats that received four horseradish peroxidase-wheat germ a gglutinin injections into the internal segment of the globus pallidus and three nigral injections of C-14-amino acids into the substantia ni gra pars reticulata. Two types of striatonigral neurons located predom inantly within the matrix compartment were identified: poorly collater alized aggregated cells distributed in clusters and more numerous coll ateralized cells distributed outside the clusters. In addition, two ce ll types were distinguished within each cluster of aggregated neurons. Those innervating the center of the substantia nigra pars reticulata were observed after a single nigral injection of the tracer, whereas t hose projecting to distinct sites of the substantia nigra pars reticul ata along a rostrocaudal axis were observed only after multiple inject ions. Striatal neurons innervating the internal segment of the globus pallidus were heterogeneously distributed predominantly within the mat rix but outside the clusters of aggregated striatonigral neurons. Toge ther, these results provide further evidence for the heterogeneity of the matrix and for the complexity of matrix striatonigral connections that send both diverging and converging signals to the substantia nigr a pars reticulata. (C) 1995 Wiley-Liss, Inc.