Regeneration of electroreceptors in weakly electric fish

Abstract

Weakly electric teleost fish possess two classes of electroreceptors: tuberous and ampullary organs. Ampullary organs are used for detecting prey, while tuberous organs detect the fish's own electric organ discharges (EODs) and those of conspecifics. EOD frequency varies among individuals within a species and a fish's tuberous receptors are sharply tuned to its own EOD frequency. In young, small fish both tuberous and ampullary afferents innervate only single organs. As fish grow new receptor cells are added to each organ and it divides into two daughter organs. This process continues resulting in numerous organs in a cluster; the afferent nerve innervates all the organs in a cluster. When a patch of skin is removed new skin grows back complete with new receptor organs of both classes. From our studies we have shown that: (1) new organs are found only in the presence of nerve fibres; (2) their morphological development during regeneration is similar to their normal development; (3) organs divide rapidly giving rise to daughter organs until each afferent fibre innervates the correct number of organs for a fish of its size; (4) receptor cells are broadly tuned below the EOD frequency of a given fish and they gradually increase their tuned frequency and sharpness of tuning until they become correctly tuned to that EOD frequency; (5) the correct matching of receptor tuning to EOD frequency occurs in fish in which the spinal cord has been severed or with lesions of the medullary pacemaker nucleus, thereby eliminating the EOD and any possible 'calibration' signal; and (6) basal and capsule cells of receptor organs in the intact skin around the wound divide after skin damage and are a possible source of precursor cells for new receptor organs.