DESROCHERS, D.M.*; NISHIKAWA, K.C.: Hypoglossal sensory feedback control during feeding in the toad Bufo alvarius

This study explores the role of hypoglossal sensory feedback during feeding in the toad Bufo alvarius. Prior studies indicate that sensory feedback from the hypoglossal nerves can trigger inhibition of both tonic and phasic activity of the jaw levator muscles. Temporary inhibition of the jaw levators allows the jaw depressors to produce rapid mouth opening. Following bilateral hypoglossal transection, the levators and depressors fire simultaneously, preventing mouth opening during feeding attempts. Utilizing unilateral rather than bilateral hypoglossal transections, coupled with high-speed digital videography and EMG recordings from the jaw levators and depressors, I have further investigated hypoglossal feedback control of the anuran jaw musculature. Preliminary data show that while the mouth opens following unilateral transection, the velocity of mouth opening and the maximum gape angle are reduced. These results suggest that transection of the hypoglossal nerve on one side prevents the inhibition of tonic and phasic activity of the jaw levators only on that same side. Hence, on that side of the jaw, the levators and depressors may be firing simultaneously, resisting the efforts of the contralateral depressors to open the mouth and therefore reducing the speed and maximum gape angle of mouth opening. According to this scenario, each hypoglossal nerve carries information back to the central nervous system in a unilateral fashion. Nerve staining studies are currently being conducted to further test this hypothesis.