FUNCTIONAL-ASPECTS OF CENTRAL ELECTRICAL COUPLING IN MECHANORECEPTOR AFFERENTS OF CRAYFISH

Cuticular stress detector afferents (CSD1 and CSD2) in the walking leg s of crayfish have been studied in an in vitro preparation allowing in tracellular recordings of single neurones during mechanical stimulatio n of the organs. Lucifer yellow staining of single fibres showed them to be dye-coupled through junctions presumably located near their poin t of entry into the ganglion. In intracellular recordings from identif ied sensory fibres with 30-80-mV impulses, coupled afferent spikes wer e seen as depolarizing potentials of short duration but smaller amplit ude. Coupling sometimes involved fibres with quite different response characteristics to mechanical stimuli. Coupled spikes summated during strong mechanical stimuli. In silent CSD fibres, antidromic spikes cou ld occur which were triggered by the depolarization due to coupling. A ntidromic spikes were more frequent during strong stimuli and were in some cases shown to be triggered in a cooperative way when two afferen t spikes synchronously reached the ganglion. Our results suggest that central coupling of primary afferents may be a widespread phenomenon i n Crustacea and that it provides a threshold mechanism for selective a mplification of strong stimuli.