[Effect of stimulation of the central gray substance of the midbrain on neuronal responses of the thalamic medial nuclei in the cat].

Effect of the central gray matter (CGM) stimulation on neuronal responses in the thalamic nonspecific medial nuclei evoked by stimulation of the teeth pulp, A-alpha and A-sigma fibres of the infraorbital nerve and the caudal nucleus of the spinal trigeminal tract was studied in experiments on cats under thiopental-chloralose anesthesia. Stimulation of the CGM by a train of stimuli evoked excitatory responses with latency from 15 to 40 ms in a part of investigated neurons. Conditioning stimulation of the CGM led to the inhibition of responses evoked by afferent volleys in neurons of the "low-threshold", "high-threshold" and "convergent" groups. Responses evoked by stimulation of the teeth pulp and A-sigma fibres were inhibited in 100% and those evoked by stimulation of A-alpha fibres of the infraorbital nerve only in 86% of neurons. Presence of the inhibitory influence of the CGM on the thalamic neuron responses evoked both by stimulation of peripheral afferents and spinal trigeminal tract nucleus show that the CGM exerts a direct influence on the thalamic neuron activity.