Influences of central gray matter stimulation on thalamic neuron responses to high- and low-threshold stimulation of trigeminal nerve structures.

Responses of the thalamic non-specific medial nuclei and relay ventral posteromedial nucleus neurons evoked by stimulation of the teeth pulp of A alpha and A sigma fibers of infraorbital nerve and caudal nucleus of the spinal trigeminal tract were studied in cats under thiopental-chloralose anesthesia. Three groups of neurons were revealed: low-threshold, high-threshold and convergent. In medial nuclei, 29% of neurons formed the low-threshold group, 12% made up the high-threshold group and 59% were convergent.

[The suppression of the postsynaptic responses of the trigeminal nucleus motor neurons evoked by stimulation of the central gray substance of the midbrain].

Effects of the midbrain central gray matter (CGM) stimulation on responses of trigeminal motoneurons is investigated. It is shown that the conditioning CGM stimulation suppressed postsynaptic responses of motoneurons, evoked by stimulation of the tooth pulp and high-threshold fibres of the infraorbital nerve. The conditioning CGM stimulation exerts no influence on the antidromic responses of trigeminal motoneurons and jaw opening reflex, evoked by stimulation of the caudal nucleus of the spinal trigeminal tract.

[Role of the serotoninergic system in inhibiting the jaw-opening reflex induced by stimulation of the central gray matter of the midbrain].

Effect exerted by stimulation of the central grey matter (CGM) of the midbrain and nucleus raphe dorsalis (nRD) by a short train of stimuli (20) followed with the rate of 400/s on the high-threshold jaw-opening reflex (HJOR) evoked by electrical irritation of the tooth pulp was studied during serotonin synthesis blockade after parachlorphenylalanine (pCPA) administration (300 mg/kg intraperitoneally) in awake cats. It was found that the inhibitory effect of the CGM and nRD stimulation on HJOR decreased 24 hours after the pCPA injection. Inhibition of HJOR induced by CGM and nRD stimulation became minimal 96 hours after the pCPA administration: reflex magnitude decreased only by 33% and duration of inhibition was 200-250 ms.

[Effect of the stimulation of the central gray substance of the midbrain on the neuronal responses of the trigeminal caudal nucleus during peripheral excitations].

Experiment on cats under chloralose-nembutal anaesthesia has shown that 65% responses of caudal trigeminal nucleus neurons to the activation of the tooth pulp, A alpha and/or A delta infraorbital nerve afferents were completely suppressed by conditioning stimulation of the central grey matter (CGM) by a train of stimuli (10-20) that followed with the rate of 200-400/s, if the interval between conditioning and testing stimuli did not exceed 100 ms. Conditioning stimulation of the CGM inhibited responses of the "convergent" neurons to the activation of tooth pulp most efficiently (0.76) and those to the activation of A alpha afferents more weakly (0.