Neurokinin B‐producing projection neurons in the lateral stripe of the striatum and cell clusters of the accumbens nucleus in the rat

Neurons producing preprotachykinin B (PPTB), the precursor of neurokinin B, constitute 5% of neurons in the dorsal striatum and project to the substantia innominata (SI) selectively. In the ventral striatum, PPTB‐producing neurons are collected mainly in the lateral stripe of the striatum (LSS) and cell clusters of the accumbens nucleus (Acb). In the present study, we first examined the distribution of PPTB‐immunoreactive neurons in rat ventral striatum and found that a large part of the PPTB‐immunoreactive cell clusters was continuous to the LSS, but a smaller part was not. Thus, we divided the PPTB‐immunoreactive cell clusters into the LSS‐associated and non‐LSS‐associated ones. We next investigated the projection targets of the PPTB‐producing ventral striatal neurons by combining immunofluorescence labeling and retrograde tracing. After injection of Fluoro‐Gold into the basal component of the SI (SI b ) and medial part of the interstitial nucleus of posterior limb of the anterior commissure, many PPTB‐immunoreactive neurons were retrogradely labeled in the LSS‐associated cell clusters and LSS, respectively. When the injection site included the ventral part of the sublenticular component of the SI(SI sl ), retrogradely labeled neurons showed PPTB‐immunoreactivity frequently in non‐LSS‐associated cell clusters. Furthermore, these PPTB‐immunoreactive projections were confirmed by the double‐fluorescence method after anterograde tracer injection into the ventral striatum containing the cell clusters. Since the dorsalmost part of the SI sl is known to receive strong inputs from PPTB‐producing dorsal striatal neurons, the present results indicate that PPTB‐producing ventral striatal neurons project to basal forebrain target regions in parallel with dorsal striatal neurons without significant convergence. J. Comp. Neurol. 480:143–161, 2004. © 2004 Wiley‐Liss, Inc.