Expression of the crustacean pyloric pattern generator in the intact animal

Summary

• 1. InJasus lalandii the activity of the central pattern generator of the pyloric motor output (the pyloric CPG) has been studied in intact free animals by electromyographic recording of the pyloric muscles (Fig. 2).

• 2. Two patterns of activity (pattern 1 and pattern 2) can be observed. Each pattern corresponds to a specific behavioural situation: pattern 1 is only observed in unfed lobsters and feeding invariably produces a switch from pattern 1 to pattern 2 (Fig. 3).

• 3. The two pyloric patterns differ in the period of the cycle (Fig. 4), the burst duration of the constrictors (Fig. 5), the latency of firing of the constrictors in the cycle (Fig. 6) and the phase of the constrictors in the cycle (Fig. 7). Correlation between period and constrictor latency is weak in pattern 1 and strong in pattern 2 (Fig. 8).

• 4. The two pyloric patterns can be recorded from in vitro preparations only when the stomatogastric ganglion (i.e. the CPG) is connected to the more rostral commissural ganglia (Fig. 9).

• 5. At least in pattern 1, cycling of the constrictors can occur when the dilators (known as pacemakers in the CPG) are silent (Fig. 10).

• 6. For these reasons, we concluded that a commissural oscillator could be participating in the organization of the pyloric output. However, the synaptic relationships which exist between the motor neurones (i.e. the CPG) cannot be neglected (Fig. 11) and this suggests that, in the intact animal, the motor output is organized by the cooperation of a premotor oscillator and a motor oscillator.