Pigment-dispersing factor in the locust abdominal ganglia may have roles as circulating neurohormone and central neuromodulator

Pigment-dispersing factor (PDF) is a neuropeptide that has been indicated a s a likely output signal from the circadian clock neurons in the brain of D rosophila. In addition to these brain neurons, there are PDF-immunoreactive (PDFI) neurons in the abdominal ganglia of Drosophila and other insects; t he function of these neurons is not known. We have analyzed PDFI neurons in the abdominal ganglia of the locust Locusta migratoria. These PDFI neurons can first be detected at about 45% embryonic development and have an adult appearance at about 80%. In each of the abdominal ganglia (A3-A7) there is one pair of lateral PDFI neurons and in each of the A5-A7 ganglia there is additionally a pair of median neurons. The lateral neurons supply varicose branches to neurohemal areas of the lateral heart nerves and perisympathet ic organs, whereas the median cells form processes in the terminal abdomina l ganglion and supply terminals on the hindgut. Because PDF does not influe nce hindgut contractility, it is possible that also these median neurons re lease PDF into the circulation. Release from one or both the PDFI neuron ty pes was confirmed by measurements of PDF-immunoreactivity in hemolymph by e nzyme immunoassay. PDF applied to the terminal abdominal ganglion triggers firing of action potentials in motoneurons with axons in the genital nerves of males and the 8th ventral nerve of females. Because this action is bloc ked in calcium-free saline, it is likely that PDF acts via interneurons. Th us, PDF seems to have a modulatory role in central neuronal circuits of the terminal abdominal ganglion that control muscles of genital organs. (C) 20 01 John Wiley & Sons, Inc.