Denervation reveals two components of neurotransmission in electroreceptor synapses

Denervation-induced changes in the synaptic efficacy of single electroreceptors in catfish (Ictalurus nebulosus, Teleostei) were studied in vivo under alfadolone anaesthesia. At 16 degrees C the following effects were found 48 h post-operatively: (1) the average amplitude of the extra-dermally recorded spikes decreased from 100 to less than 20 microV; (2) the average resting discharge decreased from 40 to less than 25 spikes/s; (3) neither the sensitivity nor the frequency characteristic changed. The results indicate that the resting discharge and the modulation mechanism of sensory synapses are controlled by different biochemical mechanisms. The resting discharge seems to be related to the trophic function of the afferent nerve and to its generator region, whereas the modulation mechanism is apparently associated with the receptor cell.