Monosynaptic excitation of lateral giant fibres by proprioceptive afferents in the crayfish

Abstract

Giant interneurones mediate a characteristic `tail flip' escape response of the crayfish, Procambarus clarkii, which move it rapidly away from the source of stimulation. We have analysed the synaptic connections of proprioceptive sensory neurones with one type of giant interneurone, the lateral giant. Spikes in sensory neurones innervating an exopodite-endopodite chordotonal organ in the tailfan, which monitors the position and movements of the exopodite, are followed at a short and constant latency by excitatory postsynaptic potentials in a lateral giant interneurone (LG) recorded in the terminal abdominal ganglion. These potentials are unaffected by manipulation of the membrane potential of LG, by bath application of saline with a low calcium concentration, or by one containing the nicotinic antagonist, curare. The potentials evoked in LG by chordotonal organ stimulation are thus thought to be monosynaptic and electrically mediated. This is the first demonstration that LG receives input from sensory receptors other than exteroceptors in the terminal abdominal ganglion.