Effect of experimentally elicited rhythmic oral activity on the linguodigastric reflex in the lightly anesthetized...

The digastric reflex was elicited in lightly anesthetized juvenile rabbits by electrical stimulation of the tongue. The reflex was depressed by maintained intraoral mechanical stimuli and facilitated by transient intraoral mechanical stimuli applied using a vinyl tube in the buccal sulcus. Intraoral mechanical stimuli were also used to elicit rhythmic oral activities; these were of four types but only the two most easily distinguished types were studied further. One type, elicited by agitating a soft vinyl tube in the buccal sulcus (the tube was then taken further into the mouth by the animal and chewed), was categorized as "transport/chew"; another type, most easily elicited by fluid passed down the stationary tube (which was then removed), was categorized as "liquid." When initiated, the two rhythmic activities continued with no further external stimulation although the intraoral self-stimulation differed. When the digastric reflex was elicited during rhythmic movements, the response was phasically modulated. More than 80% of the digastric reflex responses elicited during jaw closure in "liquid" cycles were less than control values but less than 60% of responses elicited in the same phase of "transport/chew" cycles were less than control values; the difference was significant (P less than 0.001; chi 2). The findings were consistent with two hypotheses: that sensory input, generated by the animal during the rhythmic oral movements, modulates the reflex; and that stimuli initiating particular rhythmic oral movements select one of a number of potential modes of operation of the pattern generator, each with its characteristic pattern of modulation of the digastric reflex.