Immunohistochemical localization of substance P receptor in the central nervous system of the adult rat

Abstract

In an attempt to reveal the function sites of substance P (SP) in the central nervous system (CNS), the distribution of SP receptor (SPR) was immunocytochemically investigated in adult rat and compared with that of SP‐positive fibers. SPR‐like immunoreactivity (LI) was mostly localized to neuronal cell bodies and dendrites. Neurons with intense SPR‐LI were distributed densely in the cortical amygdaloid nucleus, hilus of the dentate gyrus, locus ceruleus, rostral half of the ambiguus nucleus, and intermediolateral nucleus of the thoracic cord; moderately in the caudatoputamen, nucleus accumbens, olfactory tubercle, median, pontine, and magnus raphe nuclei, laminae I and III of the caudal subnucleus of the spinal trigeminal nucleus, and lamina I of the spinal cord; and sparsely in the cerebral cortex, basal nucleus of Meynert, claustrum, gigantocellular reticular nucleus, and lobules IX and X of the cerebellar vermis. Neurons with weak to moderate SPR‐LI were distributed more widely throughout the CNS. The regional patterns of distribution of SPR‐LI were not necessarily the same as those of SP‐positive fibers. The entopeduncular nucleus, substantia nigra, and lateral part of the interpeduncular nucleus showed intense SP‐LI but displayed almost no SPR‐LI. Conversely, the hilus of the dentate gyrus, anterodorsal thalamic nucleus, central nucleus of the inferior colliculus, and dorsal tegmental nucleus showed intense to moderate SPR‐LI but contained few axons with SP‐LI. These findings confirmed the presence of the “ismatch” problem between SP and SPR localizations. However, the distribution of SPR‐LI was quite consistent with that of the SP‐binding activity, which has been studied via autoradiography. This indicates that the sites of SPR‐LI revealed in the present study represent most, if not all, sites of SP‐binding activity.