Food-induced firing patterns in motoneurons innervating the pharynx ofAplysia kurodai

Summary

• 1. InAplysia kurodai buccal ganglia, a pair of motoneurons (pharynx bursting or PB neurons), innervating the ipsilateral posterior pharynx muscles (Px) were identified by recording excitatory junction potentials (EJP) in the muscle fiber.

• 2. Seaweed extract applied to the lips in semi-intact preparations, induced rhythmic bursts of spikes in the PB neuron, out of phase with retractor muscle activity (response-I). Rhythmic bursts in the PB neuron were maintained even after cessation of retractor muscle activity (response-II). In both cases pharynx movements followed the bursts in the PB neuron.

• 3. During response-II, rhythmic changes of internal pressure in the pharynx followed the bursting activities of the PB neuron inducing sequential movements of the pharynx and esophagus.

• 4. The rhythmic change of membrane potential in the PB neuron and rhythmic pharynx movements during response-II were completely abolished by steady hyperpolarization of the PB neuron. In addition, rhythmic bursts of spikes were produced in the PB neuron by steady depolarization. Membrane properties of the PB neuron, in isolated preparations, were consistent with other endogenous bursting neurons, suggesting that rhythmic activity during response-II is an intrinsic property of the neuron.

• 5. Ipsilaterally, synchronous burst activities in the anterior and posterior Px were recorded during response-II. Rhythmic bursts generated in the PB neuron by steady depolarization, were synchronized with muscle potentials recorded in the ipsilateral anterior Px, suggesting that the PB neuron also induces the movement of the ipsilateral anterior Px.