Abstract
The parabrachial nucleus (PB), the secondary taste relay, bilaterally projects to the parvicellular part of the posteromedial ventral thalamic nucleus (VPMpc), the thalamic relay, with ipsilateral dominance in rodents. However, the termination patterns in the VPMpc have not been consistent with distributions of electrophysiologically-identified taste neurons in the VPMpc. The present study examined precise termination patterns from the PB in the VPMpc using electrophysiologically-guided injections of wheat germ agglutinin-conjugated horseradish peroxidase in rats. Following tracer injections into the PB taste responsive regions, anterograde labels were bilaterally distributed in the VPMpc with ipsilateral dominance. Dense labels were seen rostrally in the central portion and caudally in the ventral portion of the VPMpc but labels were sparse or lacking in the caudodorsal area and peripheral portions of the nucleus. Dense labels were found in a slightly more lateral region on the contralateral side than on the ipsilateral side. The label distribution in the rostral VPMpc was similar to distributions of electrophysiologically recorded taste neurons in previous reports. The findings generally confirmed the previous anatomical reports, further revealed precise projection patterns from the PB taste area to the VPMpc subregions and explained well distributions of taste neurons in the VPMpc. [Jpn J Physiol 55 Suppl:S161 (2005)]
