A hypoglossal reflex elicited by mechanical stimulation of the mandibular mucosa in the cat.

Electromyographic responses of extrinsic tongue muscle motor units to innocuous mechanical stimulation of the mandibular mucosa were studied in urethane-chloralose anesthetized cats. The mechanical stimulation either excited or inhibited spike discharges in some extrinsic tongue muscle motor units when applied to the alveolar gingival musosa on the lingual side. Excitatory receptive fields of styloglossal motor units were predominantly ipsilateral, and the molar and second premolar gingivae were the most effective. In contrast, excitatory receptive fields of hyoglossal motor units were predominantly contralateral, the molar gingiva being most effective. In genioglossal motor units, only the ipsilateral alveolar gingiva was excitatory, while ipsi- and/or contralateral alveolar gingivae were inhibitory. The inhibitory receptive field was located in the molar and/or second premolar alveolar gingivae. When an anesthetic spray was applied to the mucosal surface, the reflex response completely disappeared, indicating its origin to be located in the stimulated gingival mucosa. After cutting the lingual nerve, reflex responses to mechanical stimulation of the premolar and molar gingival mucosa was abolished. It was concluded that the premolar and molar gingival mucosa constitutes a part of the afferent source for the linguo-hypoglossal reflex.