Ethambutol affects the spectral and polarisation sensitivity of on-responses in the optic nerve of rainbow trout

Juvenile rainbow trout (Oncorhynchus mykiss) were given ethambutol (900 mg kg(-1) body mass per day) for 4 weeks to examine its effects on vision. Usi ng multi-unit recording from the optic nerve, spectral sensitivity of the o n-responses were significantly affected in two regions, 340-440 nm and 600- 660 nm. Off-responses were statistically unaffected. Changes in sensitivity to polarised light were also observed with on-responses to vertically-pola rised light decreasing relative to horizontally-polarised light. In contras t, off-responses were less affected. The treatment effects were attributed to changes in the relative contribution of the photoreceptor channels as re corded at the level of the optic nerve. (C) 1999 Elsevier Science Ltd. All rights reserved.