Amygdaloid and cortical facilitation or inhibition of trigeminal motoneurons in the rat.

The effects of electrical stimulation of the rat's contralateral frontal cortex as well as bilateral central amygdaloid nuclei were examined on the masseteric and mylohyoid-anterior digastric motoneurons which innervate a jaw closing muscle and jaw opening ones, respectively. Thirty-six percent of masseteric motoneurons were inhibited and 14% were facilitated by stimulation of the cortex and the central amygdaloid nucleus. Fifteen percent were inhibited or facilitated by either stimulation, although 36% were unaffected. No masseteric motoneuron was facilitated by one, stimulation and inhibited by the other. A majority of mylohyoid-digastric motoneurons were facilitated by stimulation of the cortex and the central amygdaloid nucleus although 17% were facilitated by either stimulation and 17% were unaffected. No mylohyoid-digastric motoneuron was inhibited. Therefore, the frontal cortex and the central amygdaloid nucleus have convergent control of jaw movements primarily in the opening direction.