Effect of electrical stimulation of the medial thalamus on neuronal activity of the thalamic ventrobasal complex in the anesthetized cat / 全日本鍼灸学会雑誌

ABSTRACT

The preceding companion paper reported the influence of stimulation of the centre median nucleus (CM) of the thalamus on neuronal activity in the thalamic ventrobasal complex (VB). In the present study, a modification of the medial thalamus (MTh) except for the CM on activity in the somatosensory relay neurons of the thalamus was investigated in the cat. Extracellular multi-unitary discharges were recorded simultaneously from the VB using the multimicroelectrode system. The effects of MTh stimulation with a pulse train on VB neuronal activity were examined. The response of VB neuron to stimulation of other MTh nuclei were classified into the same four classes as that for CM stimulation : inhibited and then excited type; excited type; inhibited type; and non-responsive type. All four types of responses were observed in several nuclei of the MTh, such as the CM, central lateral nucleus (CL), mediodorsal nucleus (MD) and ventral posterior medial nucleus (VPM). MTh stimulation was more effective in nociceptive neurons than in non-nociceptive neurons. However, the effect of MTh stimulation differed among simultaneously recorded nociceptive neurons even when their receptive fields and recording sites were in close proximity. In some VB neurons, the response to stimulation applied to the center of the receptive field was also suppressed by MTh stimulation. Furthermore, an inhibitory effect on the response to stimulation applied to the periphery of the receptive field was observed even when the response to stimulation applied to the center of the receptive field was not inhibited by MTh stimulation. Thus, a large component of the MTh can modify VB neuronal activity and may be involved in the somatosensory system through complex mechanisms.