Summation of excitation and inhibition in the slowly adapting stretch receptor neuron of the crayfish

Abstract

The slowly adapting stretch receptor of the crayfish is inhibited via the large accessory neuron both by reflex activation of this inhibitory interneuron from the stretch receptor itself (autogenic inhibition) and by activation of the interneuron from stretch receptors in other abdominal segments (neighbourinhibition). Neighbour-inhibition increases proportionally with the increase in impulse frequency in the large accessory neuron produced by activity in neighbouring receptors and largely independently of the level of excitation in the stretch receptor itself. A simple model based on intracellular recordings from the receptor neuron predicts this behaviour fairly accurately. In this model each receptor impulse is followed by an IPSP after a delay proportional to the uninhibited interspike interval of the receptor (autogenic inhibition). The other IPSP's arrive randomly distributed in time (neighbour-inhibition). An alternative model in which all IPSP's arrive randomly produces similar results. This latter model can be modified to fit other neuronal systems.