Patchy Distribution of Substance P Receptor Immunoreactivity in Developing Rat Striatum
It is the general view that substance P (SP) innervation of the striatum is provided primarily by local axon collaterals of SP-containing striatal neurons which send their axons preferentially to the internal pallidal segment and the substantia nigra pars reticulata (Gerfen, 1992; Graybiel, 1990; Wilson, 1990). Accumulated evidence indicates that the main targets of such intrinsic SP-containing fibers are composed of two subsets of striatal interneurons: large aspiny cholinergic neurons and medium-sized aspiny somatostatin-containing ones (Aubry et al., 1993; Kaneko et al., 1993; Martone et al., 1992; Gerfen, 1991; Elde et al., 1990; Bolam et al., 1986). In particular, our recent studies have clearly demonstrated that the postsynaptic expression of SP receptor (SPR) immunoreactivity in the adult striatum is localized to these interneurons, and that the dendritic network of the SPR-immunoreactive interneurons extends homogeneously over the striatum (Nakaya et al., 1994; Kaneko et al., 1993; Shigemoto et al., 1993). On the other hand, SP-binding sites in the developing striatum have previously been reported to be distributed transiently in a patchy fashion (Quirion and Dam, 1986). In this context, it is of interest to look into the developmental changeover of intrastriatal distribution of SPR immunoreactivity. Here, we asked three major questions as to (1) whether striatal SPR immunoreactivity is distributed in a patchy fashion during development; if so, (2) whether the SPR-immunoreactive patches are in register with the striatal patch or matrix compartment; and (3) whether SPR immunoreactivity within the SPR-immunoreactive patches is located in striatal interneurons.
KeywordsCholinergic Neuron Receptor Immunoreactivity Striatal Projection Neuron Matrix Compartment Striatal Interneuron
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