Stimulation of the chewing area of the cerebral cortex induces inhibitory effects upon swallowing in sheep

Mastication and swallowing are two tightly integrated components of food in take behavior. We investigated the effects of stimulating the chewing area of the fronto-orbital cortex (CCx) on some muscles and medullary interneuro ns (Ins) or motoneurons (Mns) active during swallowing. For the purpose of comparison, the lingual nerve (LN) was also stimulated during the experimen ts. Electromyography (EMG) and extracellular neuronal recording were used, and swallowing was reflexly induced (RIS) by stimulation of the superior la ryngeal nerve (SLN). RIS was almost totally abolished during long-lasting r epetitive stimulation of CCx or LN, and was strongly facilitated after stim ulation cessation. Short-duration stimulation (one or a few pulses) of both the CCx and LN also inhibited triggering of deglutition when delivered jus t before the onset of RIS. This inhibition appeared as a delay or total sup pression of the EMG and neuronal swallowing activities. It was obvious at t he level of the muscles, the hypoglossal Mns and the premotoneurons (PMns; Ins of the ventral medulla near the nucleus ambiguus), as well as at the le vel of the Ins of the dorsal medulla (within or around the solitary tract n ucleus) which are assumed to be the core of the 'central pattern generator' (CPG) for swallowing. In addition to the 'chewing-related inhibition', man y ventral Ins exhibited a short latency synaptic activation after CCx and/o r LN stimulation Therefore, these Ins may play a pivotal role for reflex or cortical fast control of tongue (and jaw) muscles, and for coordinating th eir contractions in the context of mastication-deglutition interactions. (C ) 1999 Elsevier Science B.V. All rights reserved.