Interactions of the Giant Fibres and Motor Giant Neurones of the Hermit Crab

A recent claim that the giant fibre of the hermit crab excites its contralateral motor giant neurone through a chemical rather than an electrical synapse (Stephens, 1986) was re-examined. We found that the reported increased latency (relative to the electrical ipsilateral synapse) was postsynaptic in origin, as was the increased spike ‘jitter’. There was no difference in synaptic latency between the electrical synapse and the supposed chemical one. We did not find a consistent resistance to N-ethylmaleimide (an uncoupler of electrical synapses) by the supposed chemical synapse, but the synapse was resistant to 2 mmol 1−1 cadmium, which blocks known chemical synapses in the system. Sub-threshold depolarizing current passed from the presynaptic giant fibre to the postsynaptic contralateral motor giant, and hyperpolarizing current passed antidromically. We conclude that the synapse is electrical and not chemical in nature.