FUNCTIONAL-CHARACTERIZATION OF THE NEURODEPRESSING HORMONE IN THE CRAYFISH

The effect of the neurodepressing hormone (NDH) was studied on different identified motoneurons in the abdominal ganglia of the crayfish Procambarus bouvieri (Ortmann). Although differences in sensitivity were apparent, all the neurons tested responded to NDH with a reduction in spontaneous firing rate, which lasted as long as NDH was present, and, depending on the concentration and time od action of the hormone, for even longer periods. NDH activity was determined in the various parts of the central nervous system of the crayfish, being highest in the eyestalk, gradually diminishing away from the eyestalk, with a cephalo‐caudal gradient, being lowest in the abdominal ganglia. High levels of NDH activity were detected in the blood. After eyestalk ablation, NDH concentrations steadily diminishes, in the blood and central nervous systems, until virtually disappearing after 4 days; from day 5 onwards, the activity is recovered up to its original levels. NDH synthesis takes place with a time constant of approximately 3 hr in cultured segments of central nervous system, being highest in the eyestalk. Copyright © 1979 John Wiley & Sons, Inc.