The emergence of electroreceptor organs in regenerating fish skin and concurrent changes in their transduction properties.

The process of regeneration of skin patch denervated empullary electroreceptor organs of the African catfish Clarias gariepinus has been investigated at an ambient temperature of 28 degrees C with both electrophysiological and histological methods. At day 1 after denervation none of the receptor organs on the skin patch showed afferent activity. At this stage none of the ampullary organs previously recorded showed a normal appearance. Degenerative changes consisted of a decreased number of receptor cells and an often invisible lumen. At day 7 regeneration seems to start with a high density of primordial ampullary organs, more than a seven-fold increase compared to controls. In these units, the level of spontaneous activity is very low: compared to controls, more than a two-fold increase in mean interspike interval. At this stage, the sensitivity to electrical stimuli is already at the level of untreated control organs. At day 15 there is a lower, i.e. approximately normal, density of ampullary organs with a normal morphology. In these units both spontaneous firing and sensitivity returned to normal. It can be concluded that the functional dichotomy between spontaneous firing and sensitivity that was found in degenerating ampullary electroreceptor organs is also found during the process of their regeneration, although the underlying cellular changes may be totally different. The speed of recovery suggests that only regeneration of the distal part of the sectioned nerve fibers takes place.