Using electrophysiological techniques in a decerebrate and arterially perfused in situ rat preparation (P9−24 days; n = 28), extracellular recording were recorded to investigate the interplay of neuronal discharge patterns involved in relationships between a respiratory state and lower jaw movements. The perfusate was an oxygenated (95% O2-5% CO2) Ringer’s solution containing an oncotic agent (Ficoll 70). Body temperature was set at room temperature. Respiratory discharge was recorded from the phrenic and/or the hypoglossal nerve, and neuronal discharge regarding lower jaw movements was obtained from the trigeminal nerve controlling the digastric muscle. The frequencies of neuronal burst discharges from all nerves increased with increases in the perfusion flow rates. When the flow rate was set at about 6× the total blood volume per minute, the phrenic discharge showed “eupneic pattern” and “regular rhythm”. As the flow rate further increased, the preparation was exposed to a hyperoxic/normocapnic state and all nerve discharges became clearly organized into episodes of greater frequency and duration, punctuated by periods of quiescence. All neouronal discharges involved in lower jaw movements were synchronous to the phrenic discharge at all flow rates tested. Although the frequencies of all burst discharges became faster when body temperature was set at above 25°C, the same results as mentioned above were obtained in all cases (n = 3). It was indicated that opening movements of mouth were generated in the inspiratory phase. When the preparation was perfused by Ringer’s solution infused with a 92% O2-8% CO2 gas mixture at room temperature, the same results mentioned above were obtained in all cases (n = 6) though the amplitude of all neuronal discharges increased. After the preparation was temporarily exposed to anoxia by applying 500 μM sodium cyanide (NaCN), the trigeminal discharge was produced in both the inspiratory and expiratory phases. After the preparation was exposed to an anoxic state by applying 500 μM NaCN for 1 to 2 minutes, the trigeminal discharge was completely produced in the expiratory phase (n = 5). Based on these results, it was indicated that the amount of inputs from the peripheral and central chemoreceptors changed the timing of opening and closing mouth. From the above, it was suggested that switching of lower jaw movements between the inspiratory and expiratory phases was generated by increasing and decreasing inputs from chemoreceptors.