The relationship between nerve fiber regeneration and electroreceptor formation in the glass catfish, Kryptopterus

Michele Miller Bever, Purdue University

Abstract

The regeneration of ampullary electroreceptors was studied in the living catfish, Kryptopterus, using 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 will regenerate when the skin is reinnervated. In this study, we tested the role of the skin and nerve in receptor regeneration with the following 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 which 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 at various times after surgery. By two weeks following surgery, receptors were found in regenerated fin tissue and within the EC grafts. Electroreceptors also formed within most of the EF grafts. Since electroreceptor regeneration occurred after the removal of receptors and since electroreceptors formed in fin regions that normally do not contain receptors, we suggest that the formation of electroreceptors does not require old target sites and that ordinary epidermal cells can be induced to form receptors upon contact by a regenerating axon. Also in this study, we tested whether axons are more likely to induce electroreceptors in certain regions of fin epidermis than others. We rotated transplants so that the location of the electroreceptors was altered with respect to the regenerating axons in the host. When transplants were reversed rostrocaudally (RC grafts), new electroreceptors formed in the caudal half of the interradial zone, where degenerating electroreceptors were at the time of transplantation. When transplants were rotated so that the dorsoventral and rostrocaudal axes were reversed, some new receptors formed in the old target site regions that were located in the caudal interradial zone and in the distal half of the graft with respect to the host. We suggest that old target sites have a neurotropic influence on the regenerating electroreceptive axons.

Degree

Ph.D.

Advisors

Borgens, Purdue University.

Subject Area

Neurology|Aquaculture|Fish production

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