Functional characterization of the neurodepressing hormone in the crayfish

Abstract

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 of 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 concentration steadily diminishes in the blood and central nervous system, 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 isolated segments of central nervous system, being highest in the eyestalk.

Circadian clocks in crustaceans: identified neuronal and cellular systems

“…Surgical removal of crab X-organs causing continuous arrhythmic locomotory hyperactivity in crabs, and crayfish eyestalk ganglia extracts and in vitro release experiments from sinus glands eliciting inhibition of crayfish XOSG and motor neuron activities in electrophysiological assays suggested that NDH originates from the XOSG. NDH was, furthermore, found implicated in inhibitory effects on several circadian rhythms (6,126,(276)(277)(278). However, even the previously suggested and reasonably analysed small neuropeptide nature of NDH (279) was later totally questioned (280).…”