Interaction between abdominal ganglia during the performance of hormonally triggered behavioural programmes in moths

1. The isolated chain of four abdominal ganglia of Hyalophora cecropia has previously been shown to respond to the eclosion hormone by generating a pre-eclosion motor programme followed by the eclosion programme. 2. Abdominal nervous systems reduced at any two ganglia could still generate both programmes. 3. Selective addition of hormone to individual ganglia of the intact abdominal CNS resulted in the coordinated performance of both programmes by the entire CNS. 4. In the eclosion programme, burst frequency was little influenced by which ganglion was exposed to hormone but in many cases the eclosion waves were initiated by the neurones in the treated ganglion rather than at the normal site in the terminal ganglion. 5. When ganglia were removed from hormone-treated preparations during eclosion, the remainder of the chain showed a transient disruption in the bursting frequency but the frequency often eventually returned to pre-cut levels. Removal of anterior ganglia had no effect on the patterning of posterior bursts but removal of posterior ganglia resulted in a permanent reduction in the length of eclosion bursts in anterior ganglia. 6. It was concluded that the information for both the pre-eclosion and eclosion programmes is patterned into each ganglion of the abdominal chain. For the pre-eclosion behaviour, the endogenous programme becomes progressively longer in more posterior ganglia and each ganglion appears to have mutually exciting interactions with the other ganglia in the chain. In the intact animal the most anterior ganglion appears to drive the behaviour. By contrast, the eclosion behaviour also has segmental burst generators but they appear very similar in their properties. Each burst generator has an excitatory input on to the next anterior ganglion and inhibitory influences on posterior ganglia. Normally, the most posterior ganglion serves as driver for the eclosion behaviour.