Glutamate activates neuronal discharges and rhythmical jaw movements in the rat

Rhythmical jaw movements (RJM) were induced by stimulation of the cerebral peduncle or the oral cavity in the anesthetized rat and iontophoretic application of glutamate was examined on each reticular neuron with phase-dependent rhythmical activity during RJM (RJM-phasic neuron). Glutamate activated six neurons rhythmically with simultaneous rhythmical jaw movements in five rats. However, glutamate activated fifty of the other 52 RJM-phasic neurons tonically without RJM. Therefore, a small number of RJM-phasic neurons (10.3%) was involved in the generation of RJM. The rhythmical activities of most RJM-phasic neurons should have been synaptically induced by activities of those RJM-generator neurons. Glutamate receptor blocking agents, cyano-nitroquinoxaline-dione and D-amino-phosphono-valerate were examined and the former was more effective on 17 neurons although the latter was more effective on three and both were equally effective on 13. Inhibitory synaptic mechanism is not necessary for RJM-generation since bicuculline or strychnine did not significantly alter the rhythmical pattern of activity in any neuron.