[Effect of stimulation of the central gray matter of the midbrain on responses of neurons of the ventroposteromedial nucleus of the thalamus in cats].

Effect of the midbrain central gray matter (CGM) stimulation on neuronal responses of the thalamic ventro-postero-medial (VPM) nucleus evoked by stimulation of the tooth pulp, A-alpha, A-delta fibres of the infraorbital nerve and caudal nucleus of the spinal trigeminal tract have been studied in cats under thiopental-chloralose anesthesia. It is shown that the CGM stimulation by a short train of stimuli evoked excitatory responses with a latency of 30 ms in part of investigated neurons. The conditioning CGM stimulation suppressed responses in neurons of "low-threshold", "convergent" and "high-threshold" groups. Responses induced by stimulation of the tooth pulp and A-delta fibres of the infraorbital nerve in 40% of neurons and by stimulation of the A-alpha fibres of the infraorbital nerve in about 26% of investigated thalamic neurons were completely suppressed. The inhibitory influence of the CGM stimulation on neuronal responses evoked by stimulation of peripheral nerves and caudal nucleus of the spinal trigeminal tract shows that the CGM influences directly the activity of thalamic neurons.