Dormant synapses in a crustacean neuromuscular system

Abstract

In adult spider crabs (Hyas araneas), kept captive for more than 5 months, excitatory junctional potentials recorded from the leg stretcher muscle preparation showed striking evidence of a loss of synaptic efficacy when compared to responses obtained from 'normal' synapses in earlier control animals. Two classes of aberrant synapses are described. One type gave rise to considerably depressed responses ([Formula: see text] at 10–20 Hz), while the other type (termed 'dormant') only became activated by a schedule of vigorous tetani followed by appropriate rest periods.Resting potentials and effective input resistance measurements in fibers displaying aberrant synaptic function showed no significant differences from controls. On the basis of their limited facilitation performance and marked tendency to exhibit depletion, it is proposed that presynaptic factors relating to a lower than normal store of releasable transmitter can account for such behaviour in aberrant synapses. The underlying trigger of such changes remains unknown.