Hormonal Release of Stereotyped Motor Programmes from the Isolated Nervous System of the Cecropia Silkmoth

Abstract

In the moth Hyalophora cecropia, injection of the eclosion hormone into pre-emergence (pharate) animals releases a stereotyped series of behaviours that assist the moth in escaping from the pupal cuticle and cocoon. The preeclosion behaviour begins 15 min after injection and lasts for 60 min. The first 30 min is an active period consisting of frequent abdominal rotations; a 30 min quiet period follows. This is followed by the eclosion behaviour which consists of rhythmic peristaltic waves which move up the abdomen at a frequency of 3-5 per min. The same behaviours can be elicited by injection of hormone into isolated pharate abdomens. The completely isolated abdominal CNS responded to the eclosion hormone by the generation of a programme of motor activity that mimicked that expected during the pre-eclosion and eclosion behaviours. The duration of the pre-eclosion behaviour programme in the isolated CNS was related to the general excitatory state of the preparation and varied from 57 to 325 min. In the latter instances, the behaviour lengthened as a unit with proportional increases occurring in the lengths of both the active and the quiet periods. But the structure of the individual rotational bursts appeared to be independent of these changes in the overall timing of the pre-eclosion programme. The frequency of bursts during the eclosion behaviour of the isolated CNS was always lower than that seen in intact animals. The frequency was not correlated with the length of the preceding pre-eclosion behaviour. It was concluded that the eclosion behaviour represented a behavioural programme that was distinct from the pre-eclosion behaviour. The structure of the eclosion bursts was independent of the frequency of bursting. Isolated pharate abdomens that had been aged for 2 days, often lost the ability to perform the pre-eclosion behaviour but still showed eclosion in response to hormone injection. In these cases the eclosion programme did not begin until 70-90 min after injection. Similar results were obtained with an isolated CNS preparation from an aged abdomen. Hormone was added to isolated CNS preparations and then washedout at various times thereafter. After an initial exposure of only a few minutes, the hormone could be removed without interference with the initiation or play-out of either the pre-eclosion or eclosion behaviours. It was concluded that the eclosion hormone acts directly on the CNS to trigger two distinct behavioural programmes. The sequential arrangement of these programmes is due primarily to their respective latencies. Each programme has a two-tier hierarchical arrangement which includes a burst timer and a burst pattern generator. Sensory feedback appears to affect different components of the two programmes. In the pre-eclosion programme, sensory input alters the pattern of the rotary bursts but apparently not the number of bursts generated during the behaviour. In the case of the eclosion programme, sensory feedback influences the frequency of bursting but not the pattern of the individual bursts.