Central Nervous System Changes Related to the Reduction of Visual Input in a Naturally Blind Fish (Astyanax hubbsi)

Tectal anatomy and physiology of the blind cave characin, Astyanaxhubbsi, have been compared with that of its sighted ancestorAstyanax mexicanus (the river fish) and with goldfish. Normaland experimental neuroanatomic methods have revealed that, withthe exception of a greatly reduced retinotectal projection,connectivity and structure of cave fish tecta are similar tothose described in sighted species. It appears that the rudimentaryretinotectal input is nonfunctional, since no tectal evokedresponses could be elicited with electrical or visual stimulationof the optic cyst, and all attempts to visually condition cavefish were unsuccessful. Attempts have also been made to record somatosensory, auditoryand lateral line activity in the tecta of the blind and sightedfish. A sparse somatic representation was found in the deeperportion of the sighted fish tecta which contrasts with a dense,well-organized one in the cave fish. No tectal responses werefound to auditory or lateral line stimuli. CNS plasticity is discussed in relation to studies of fish,amphibians, reptiles, birds and mammals, in which a reductionof sensory input by any one of a number of means has resultedin alterations of structure and function.