Anatomical location of a taste-related region in the thalamic reticular nucleus in rats

Abstract

To locate a taste-related region in the thalamic reticular nucleus (Rt), we explored a reticular region having connections with the thalamic taste relay and the cortical taste area (CTA), by neuronal tracing methods using HRP, WGA-HRP and biocytin. Tracer injections at the thalamic taste relay, i.e., the parvicellular part of the thalamic posteromedial ventral nucleus (VPMpc), labeled cell bodies and axon terminals in a confined portion of the ipsilateral Rt. This was located at the ventromedial-most portion of the nucleus at the level of approx. 1.2 mm rostral to the rostral end of the VPMpc. Tracer injections at the CTA ipsilaterally labeled axon terminals in the same region of the Rt, as did the thalamic injections. When WGA-HRP was injected at this taste-related region in the Rt, we observed labeled cell bodies in layer VI in the CTA; in the VPMpc we saw densely labeled axon terminals but few, if any, labeled cell bodies. The results indicated that the taste-related region in the Rt receives input from the VPMpc and CTA, and sends output to the VPMpc. They also showed that the reticulo-thalamic projections were much heavier than the thalamo-reticular ones in the taste system.