Horizontal cells function normally in ethambutol-treated goldfish.
Ethambutol, a tuberculostatic drug, induces red-green colour vision defects in man and goldfish. The ethambutol-induced red-green colour vision defect in goldfish was argued to originate in the retina because after ethambutol application: (1) inhibitive interactions in red-green (double) opponent ganglion cells are lost [Van Dijk & Spekreijse, 1982 (Investigative Ophthalmology and Visual Science, 24, 128-133); Wietsma & Spekreijse, 1992 (Investigative Ophthalmology and Visual Science Suppl., 33, 1032)] and (2) the depolarizing responses to red light in the biphasic horizontal cells are reduced. To account for these findings Spekreijse, Wietsma and Neumeyer [(1991) Vision Research, 31, 551-562] suggested that ethambutol induced dark adaptation in the retina. In this paper the dark adaptation hypothesis is tested with the following results: (1) ethambutol changes only transiently the receptive field size and spectral sensitivity of horizontal cells; (2) the spectral characteristics of horizontal cells do not change in long-term ethambutol-treated goldfish; (3) formation of spinules on horizontal cell dendrites in cone terminals, a parameter for light adaptation, remains unaffected. Therefore we conclude that ethambutol does not induce functional dark adaptation of horizontal cells and that the ethambutol-induced red-green colour vision deficiency does not originate in the horizontal cell layers.
Wietsma
J J
JJ
Graduate School Neurosciences Amsterdam, Laboratory of Medical Physics and Informatics, University of Amsterdam, The Netherlands.
Kamermans
M
M
Spekreijse
H
H
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D003118:Color Perception / Q000187:drug effects; D003117:Color Vision Defects / Q000139:chemically induced; D003623:Dark Adaptation / Q000187:drug effects*; D004977:Ethambutol / Q000494:pharmacology* / Q000633:toxicity; D006054:Goldfish / Q000502:physiology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D008854:Microscopy, Electron; D010775:Photic Stimulation; D012160:Retina / Q000187:drug effects* / Q000648:ultrastructure; D013053:Spectrophotometry; D013997:Time Factors
D004977:Ethambutol