7 Effect of electrical stimulation of vagal afferents on trigeminal nociceptive neurons in the intralaminar nucleus of the thalamus

Abstract

Nociceptive neurons responding both to tooth pulp (TP) stimulation and to mesencephalic reticular formation (MRF) stimulation were recorded from the nucleus centralis lateralis (CL) of the thalamic intralaminar nuclei in cats anesthetized with urethane and chloralose. We investigated the effect of the cervical vagus nerve (CVN) stimulation on response of CL neurons to electrical stimulation of the TP and of the MRF. A total of 22 CL neurons responding both to MRF stimulation as well as to TP stimulation were obtained. In 9 of 22 neurons, electrical stimulation of the CVN inhibited responses of CL neurons to TP stimulation. However, the CVN stimulation had no effect on responses to electrical stimulation of the MRF. These results suggest that vagal afferents can activate the descending antinociceptive system that acts on the lower brainstem, and that there is no ascending pain suppression system acting on the CL that is controlled by vagal afferent input.