Insect Neuroanatomy and Neuroendocrinology

In insects the endocrine system is a part of the nervous system. Specialized neurons release neurohormones that regulate various processes such as development, homeostasis, excretion, heart activity, digestion, and reproduction. In addition, these neurohormones may be involved in the initiation of certain behaviors such as ecdysis, feeding, flight, and mating. The neurohormones are mostly peptides and many of them have been isolated and identified, providing a rich opportunity for the study of their functions. We have been studying the neuroendocrine system of insects, using Manduca sexta as a model. In these studies we use various methods, such as immunocytochemistry, neuronal tracing, microsurgery, bioassays, and organ transplantation and ablations. Our recent work on the neuroendocrine system includes studies of neurons that control photoperiodic induction of pupal diapause. We have found that these neurons express the clock protein PER and the neurohormone corazonin. These results suggest that photoperiodism relies on a clock-like mechanism and may be mediated by corazonin, and we plan to explore these possibilities.

The same neuropeptides that are released as hormones are also found in many interneurons and are released into the CNS as paracrine factors. Very little is known of their function, but evidence from other animal models indicate that they modulate neuronal excitability, and thus effect behavior. In some instances paracrine release of certain neuropeptides appears to be a broadly distributed, and we believe that this type of release may be involved a general up or down regulation of the responsiveness of the CNS, as in states of quiescence arousal. Recently we have identified a single pair of peptidergic interneurons that project to all parts of the CNS of the larvae larva of M. sexta, and we believe these neurons may be an ideal model for studying neuromodulation in insects. Using techniques of immunocytochemistry and targeted cell ablation, we hope to determine the function of these interneurons.