Functional roles of neuropeptides in the insect central nervous system

With the completion of the Drosophila genome sequencing project we can begin to appreciate the extent of the complexity in the components involved in signal transfer and modulation in the nervous system of an animal with reasonably complex behavior. Of all the different classes of signaling substances utilized by the nervous system, the neuropeptides are the most diverse structurally and functionally. Thus peptidergic mechanisms of action in the central nervous system need to be analyzed in the context of the neuronal circuits in which they act and generalized traits cannot be established. By taking advantage of Drosophila molecular genetics and the presence of identifiable neurons, it has been possible to interfere with peptidergic signaling in small populations of central neurons and monitor the consequences on behavior. These studies and experiments on other insects with large identifiable neurons, permitting cellular analysis of signaling mechanisms, have outlined important principles for temporal and spatial action of neuropeptides in outputs of the circadian clock and in orchestrating molting behavior. Considering the large number of neuropeptides available in each insect species and their diverse distribution patterns, it is to be expected that different neuropeptides play roles in most aspects of insect physiology and behavior.