Control of integration by extrinsic inputs in the crustacean pyloric circuit.

The pyloric circuit (14 neurones) in the stomatogastric ganglion of crustacea (Jasus, Homarus) is the central pattern generator of the motor output which governs the rhythmic movements of the pyloric chamber (Fig. 1). Although the intrinsic burstiness of these neurones plays a crucial role in the generation of the rhythmic output, it is demonstrated here that expression of this burstiness is completely dependent on extrinsic inputs (Fig. 2). Tonic firing of an identified interneurons (APM) projecting to the pyloric circuit is able to induce bursting in pyloric neurones. It also modifies the characteristics of the regenerative changes in membrane potential which underly bursting of these neurones (Fig. 3). Tonic firing of APM strongly modifies the phase at which each pyloric neurone fires in the cycle (Fig. 4 and 5). This phage control also appears to be achieved through control of the bursting properties of the pyloric neurones. Rhythmic firing of an identified pyloric oscillator neurone (CP) in the commissural ganglia (Fig. 6) that projects to the circuit in the stomatogastric ganglion, is able to entrain the pyloric rhythm (Fig. 7). Each pyloric neurone can be entrained by CP with different coupling ratios (Fig. 8). This higher order oscillator appears to act as a frequency controller of the bursting of each pyloric neurone.