DISTRIBUTION AND NEUROCHEMICAL CHARACTER OF SUBSTANCE-P RECEPTOR (SPR)-IMMUNOREACTIVE STRIATAL NEURONS OF THE MACAQUE MONKEY - ACCUMULATIONOF SP FIBERS AND SPR NEURONS AND DENDRITES IN STRIOCAPSULES ENCIRCLING STRIOSOMES

The striatal distribution of the substance P receptor (SPR) protein wa s examined in relation to its ligand, the neuro-peptide SP, as well as to the neurochemical and compartmental composition of the neostriatum in rhesus monkeys (Macaca mulatta) in immunohistochemical experiments . About 2% of striatal neurons, displaying varicose, virtually spine-f ree dendrites characteristic of large and medium-sized aspiny interneu rons, expressed SPR immunoreactivity. SPR/choline acetyltransferase, S PR/somatostatin, SPR/GABA, SPR/calbindin D28k, and SPR/parvalbumin dou ble immunolabeling experiments demonstrated that SPR-positive cells ar e either cholinergic or somatostatinergic. Comparison of SP and SPR im munoreactivities in double-labeled and adjacent single-labeled section s revealed compartment-specific match and mismatch between the densiti es of the peptide and receptor. A matching high density of SP fibers a nd SPR cells and dendrites was only observed in the rim of the strioso me compartments. To our knowledge, this is the first evidence for an a natomical border comprised of dendritic processes that separate striat al compartments. We have termed these zones ''striocapsules,'' because they encircle and encapsulate striosomal cell islands. In the striata l matrix, an abundance of SPR-labeled profiles was complemented with l ight SP staining. By contrast, in the core of the striosomes, SPR labe ling was sparse and SP staining intense. SP-positive axon-like puncta frequently contacted SPR-positive dendrites in all striatal compartmen ts. The SP receptor/ligand match indicates a sharp increase in the eff icacy of SP action in the striocapsules, and suggests that the influen ce of SP might be heightened in this striatal subcompartment. (C) 1996 Wiley-Liss, Inc.