Octopamine modulates a central pattern generator associated with egg-laying in the locust, Locusta migratoria

Abstract

Egg-laying in Locusta migratoria involves the control of a variety of complex behavioural patterns including those that regulate digging of the oviposition hole and retention of eggs during digging. These two behavioural patterns are under the control of central pattern generators (CPGs). The digging and egg-retention CPGs are coordinated and integrated with overlapping locations of neural substrate within the VIIth and VIIIth abdominal ganglia of the central nervous system (CNS). In fact, the egg-retention CPG of the VIIth abdominal ganglion is involved in both egg-retention and protraction of the abdomen during digging. The biogenic amine, octopamine, has peripheral effects on oviduct muscle, relaxing basal tension of the lateral and upper common oviduct and enabling egg passage. Here we show that octopamine also modulates the pattern of the egg-retention CPG by altering the motor pattern that controls the external ventral protractor of the VIIth abdominal segment. There is no change in the motor pattern that goes to the oviducts. Octopamine decreased the frequency of the largest amplitude action potential and decreased burst duration while leading to an increase in cycle duration and interburst interval. The effects of octopamine were greatly reduced in the presence of the α-adrenergic blocker, phentolamine, indicating that the action of octopamine was via a receptor. Thus, octopamine orchestrates events that can lead to oviposition, centrally inhibiting the digging behavior and peripherally relaxing the lateral and common oviducts to enable egg-laying.