Receptive field properties of thalamo-cortical taste relay neurons in the parvicellular part of the posteromedial ventral nucleus in rats.

Twenty-five taste and 35 mechanoreceptive neurons were recorded from the parvicellular part of the posteromedial ventral nucleus (VPMpc) in rats. Among them, 14 (56%) of the taste and 7 (18.4%) of the mechanoreceptive neurons were antidromically activated from the cortical taste area (CTA) with a latency of 1-4 ms and identified as thalamocortical (TC) relay neurons. No significant differences were evident in the receptive field properties or in the location in the VPMpc between the TC and non-TC neuron groups. Two classes of TC neurons were recognized: one class consisted of neurons which were most excited by NaCl among the four basic taste stimuli with receptive fields (RFs) confined to a part of the oral cavity, e.g. the anterior tongue, and the other class contained neurons which were most excited by sucrose or HCl, with RFs over a wide area of the oral cavity. Both the TC and non-TC neurons showed similar effects of CTA stimulation: post-stimulus time histograms revealed a long lasting inhibition followed by a rebound facilitation of spontaneous discharge.