The regeneration of electroreceptors in Kryptopterus

The regeneration of ampullary electroreceptors was studied in the living catfish, Kryptopterus, by differential interference contrast optics. Electroreceptors in this transparent catfish are found, among other places, along the proximal portion of each anal fin ray, while the distal portion does not contain electroreceptors. Upon interruption of the sensory innervation, the electroreceptors disappear but regenerate when the skin is reinnervated. In this study, we tested the role of the skin and nerve in receptor regeneration with the following two experiments. First, a plug of fin containing electroreceptors was removed to determine whether electroreceptors could form in regenerated skin after the complete removal of all of the receptors within an interradial zone of the anal fin. Second, a portion of anal fin that contained electroreceptors was excised and a graft of electroreceptor-free (EF) fin was sutured in its place to determine whether epidermis that does not normally contain these receptors can be induced to form them. These grafts were compared to control grafts taken from proximal electroreceptor-containing (EC) fin. By 2 weeks following surgery, receptors were found in regenerated fin tissue and within the EC grafts. Electroreceptors also formed within most of the EF grafts. As electroreceptor regeneration does not require the presence of degenerated organs, and as electroreceptors can form in fin that normally does not contain receptors, we suggest that the formation of electroreceptors does not require old target sites and that epidermal cells can be induced to form receptors upon contact by regenerating axons. We discuss as well the factors that influence the pattern of receptor reappearance.