The taste and mechanical response properties of neurons in the parvicellular part of the thalamic posteromedial ventral nucleus of the rat.

A total of 41 taste and 17 mechanoreceptive neurons were recorded in the parvicellular part of the posteromedial ventral nucleus of the thalamus (VPMpc) of amobarbital-anesthetized rats. Most of the taste neurons were located in the rostral part, while most of the mechanoreceptive neurons were located in the middle part of the VPMpc. Stimulation of the whole oral cavity with four basic taste stimuli produced smaller mean response magnitudes in these thalamic taste neurons than in the parabrachio-thalamic (P-T) taste relay neurons. Receptive fields (RFs) for most of the 21 taste neurons examined were located on the tongue or on the tongue and palate, as with P-T relay neurons. Some neurons had RFs ipsilaterally in the oral cavity, as do P-T relay neurons; but others had RFs contralaterally or bilaterally. Several neurons had large RFs in comparison with those of P-T relay neurons. A majority of the thalamic taste neurons were also mechanosensitive, and their RFs were larger for mechanical stimulation than for taste stimulation. Many (12/17) of the mechanoreceptive neurons had a low response threshold, activated by stroking the tissue with a glass rod; and others had a high response threshold, activated by a pinch with a pair of non-serrated forceps. Their RFs were contralaterally or bilaterally located on either the tongue, or palate or on both regions. One taste neuron and some mechanoreceptive neurons were also excited by mechanical stimulation on the cheek or lip. These observations may represent integrative processes for taste and mechanical oral information at the thalamic level.