Modulatory influences of red nucleus stimulation on the somatosensory responses of cat trigeminal subnucleus oralis neurons.

Little is known of the effect of red nucleus (RN) stimulation on somatosensory neurons despite its known anatomic projections to somatosensory relay nuclei. The effect of RN stimulation on the somatosensory responses of trigeminal subnucleus oralis (Vo) neurons was investigated in chloralose- or barbiturate-anesthetized cats. Arrays of bipolar stimulating electrodes were inserted into the contralateral and ipsilateral RN and the contralateral thalamus. Extracellular single-unit recordings were obtained in Vo with tungsten microelectrodes. Neurons in Vo were excited to just suprathreshold by electrical stimulation within their receptive fields. Red nucleus influences were studied by applying 100-ms, 500-Hz conditioning trains to the contralateral or ipsilateral RN 130 ms prior to the peripheral test stimulus. The effect of RN stimulation was also tested on mechanically evoked responses of Vo cells. The somatosensory responses of most cells (70/73) were inhibited after RN stimulation. Some of these cells (15/70) could be antidromically activated from the contralateral thalamus. Stimulation of the RN resulted in excitation followed by inhibition in nine Vo cells. The results suggest that the RN may modulate transmission of somatosensory information through Vo.