Central nervous system changes related to the reduction of visual input in a naturally blind fish (Astyanax hubbsi)

Abstract

Tectal anatomy and physiology of the blind cave characin, Astyanax hubbsi, have been compared with that of its sighted ancestor Astyanax mexicanus (the river fish) and with goldfish. Normal and experimental neuroanatomic methods have revealed that, with the exception of a greatly reduced retinotectal projection, connectivity and structure of cave fish tecta are similar to those described in sighted species. It appears that the rudimentary retinotectal input is nonfunctional, since no tectal evoked responses could be elicited with electrical or visual stimulation of the optic cyst, and all attempts to visually condition cave fish were unsuccessful.Attempts have also been made to record somatosensory, auditory and lateral line activity in the tecta of the blind and sighted fish. A sparse somatic representation was found in the deeper portion of the sighted fish tecta which contrasts with a dense, well-organized one in the cave fish. No tectal responses were found to auditory or lateral line stimuli.CNS plasticity is discussed in relation to studies of fish, amphibians, reptiles, birds and mammals, in which a reduction of sensory input by any one of a number of means has resulted in alterations of structure and function. © 1984 by the American Society of Zoologists.