Analysis of rhythmical jaw movements produced by taste stimulation in rats

Taste stimulation of the mouth induces various oral movements, Sucrose or s alt solution induces rhythmical jaw movements (RJM) or tongue protrusion as an ingestive behavior. Bitter taste induces a gaping or tongue retraction as an aversive behavior. There is no report that describes the precise patt ern of jaw movements induced by taste stimulation The purpose of the presen t study is to clarify the pattern of the taste-induced RJM with electromyog raphic activities of the masticatory muscles in the anesthetized rat. When water was injected into the mouth of the rat, an RJM was induced. In this t ype of RJM, the lower jaw swung right and left side in each open-close cycl e alternately, The anterior digastric muscle was active in every opening ph ase, while activities of the jaw closing muscles were generally weak. The R JM induced by water was opening-dominant movements. Sucrose or salt solutio n induced a similar pattern of RTM to water-induced RJM. When acetic acid w as injected, amplitude of the alternate lateral jaw movement was significan tly larger than that in the water-induced RJM. The activity of the superfic ial temporalis muscle was large in those closing phases with ipsilateral si de movement, while it was small in the closing phases with contralateral mo vement. The pattern of quinine-induced RJM was characterized by small later al, large open-close and large antero-posterior movements, Tastes which are reported to induce ingestive behavior such as sweet or salty don't alter t he pattern of RJM; however, the tastes which induce aversive behavior make the pattern of RJM different from the water-induced RJM.