THE BIOLOGY OF THE PROTHORACICOTROPIC HORMONE PEPTIDERGIC NEURONS IN AN INSECT

The prothoracicotropic hormone and the cerebral peptidergic neurons th at produce it have traditionally been thought to have the singular fun ction of acting as a primary effector of insect postembryonic developm ent. Recent investigations of this neuroendocrine axis in the tobacco hornworm, Manduca sexta, are leading to a new view that these peptider gic neurons and their peptide phenotypes may be multifunctional. They may act in different ways depending upon the animal's developmental st age and site of phenotype release. The possibility for this functional diversity of the prothoracicotropic hormone is possibly even greater due to multiple neuronal sites of peptide expression within the centra l nervous system. Similarly, the L-NSC III may have more functions due to the expression of multiple peptide phenotypes. The data, thus far, have not enabled us to identify additional physiological roles for th e peptide, but they have provided insight into the experimental approa ches that might be effective in resolving these functions.