Intracellular recording in trigeminal motoneurons of the anesthetized guinea pig during rhythmic jaw movements

Intracellular recordings were obtained from guinea pig trigeminal motoneurons during rhythmic jaw movements. The cells were identified by stimulation of the trigeminal mesencephalic nucleus which evokes excitatory postsynaptic potentials and spikes in jaw-closer motoneurons. The anesthetized guinea pig in the stereotaxic apparatus demonstrated spontaneous rhythmic jaw movements which were characterized by hyperpolarization of jaw-closer motoneurons, occurring concurrently with digastric muscle excitation during the jaw-opening phase of the cycle. The anesthetized guinea pig could also be induced to rhythmically clench and release a stick placed between the molar teeth. During this behavior intracellular recordings in jaw-closer motoneurons revealed a rapid depolarization leading to bursts of action potentials following the hyperpolarization which occurred during the jaw-opening phase of the cycle. The results demonstrate the feasibility of intracellular recording in guinea pig trigeminal motoneurons during rhythmic jaw movements. It was also shown that during the opening phase of the rhythmic jaw movement cycle there is a pronounced hyperpolarization present in the membrane potential of jaw-closer motoneurons. Resolution of the problem of central vs. peripheral origin of this hyperpolarization is significant for our understanding of the motor control of the jaw.