[Effect of partial transection of the medulla oblongata on inhibition of the mouth-opening reflex of the cat induced by stimulation of the mesencephalic central gray].

Effect of sections of the spinal trigeminal tract and caudal nucleus of the spinal trigeminal tract on the high-threshold jaw-opening reflex (HJR) evoked by tooth pulp stimulation and the low-threshold jaw-opening reflex (LJR) evoked by stimulation of the A-alpha infraorbital nerve fibres as well as on the suppression of these reflexes by the central grey matter was studied in cats under chloralose-nembutal anesthesia. After the trigeminal tract section HJR has increased by 8.52%. The LJR magnitude was either invariable either negligibly reduced or increased after the section. Stimulation of the central grey matter by a short train of stimuli evoked depression of HJR which reached 100% in intact animals, while after the section--only 40-60%. Inhibition of HJR after prolonged rhythmic stimulation of the central grey matter reached 80% in intact animals, while after the section--25-30%. There were no changes in the LJR depression when the central grey matter was stimulated by short trains of stimuli after section. The LJR suppression evoked by the prolonged central grey matter stimulation reached 25-50% in intact animals, while after the section the depression increased and reached 75% (three animals) or was reduced and reached 15-20% (four animals). It is concluded that the caudal nucleus of the spinal trigeminal tract exerts a considerable effect on the HJR inhibition (but less on the LJR inhibition) after the midbrain central grey matter stimulation.