CHOLINERGIC NEURONS ARE DISTRIBUTED PREFERENTIALLY IN AREAS RICH IN SUBSTANCE-P-LIKE IMMUNOREACTIVITY IN THE CAUDATE-NUCLEUS OF THE ADULT CAT

The distribution of cells stained immunocytochemically for the choline rgic marker choline acetyltransferase was compared to the pattern of s ubstance P immunoreactivity in the caudate nucleus of adult cats using a double-label immunocytochemical protocol and three-dimensional reco nstructions of adjacent sections single-labeled for either substance P or choline acetyltransferase. Substance P immunoreactivity was distri buted in a highly complex mosaic within the caudate nucleus of the cat . In the dorsal caudate nucleus, substance P-rich zones consisting of either clusters of substance P-positive cell bodies or fibers were see n against a lighter staining background. The density of cholinergic ne urons was found to be significantly greater within these substance P-r ich patches in comparison to surrounding regions. The pattern of subst ance P immunoreactivity within the ventral caudate nucleus differed fr om that in more dorsal regions. Clear substance P-rich patches were no t seen in this region, but a large substance P-rich area consisting of a dense plexus of substance P-containing fibers was visible. Embedded within this substance P-rich area were fairly discrete patches of lig ht substance P staining. As in the dorsal caudate nucleus, increased n umbers of cholinergic neurons and processes were associated with subst ance P-rich regions in the ventral caudate nucleus. Choline acetyltran sferase-positive perikarya also appeared to be concentrated in substan ce P-rich areas in the nucleus accumbens and olfactory tubercle. The r esults of this study suggest that a close relationship exists between the distribution of substance P fibers and cholinergic perikarya in th e striatum of the cat.