MODULATING WAVELENGTH DISCRIMINATION IN GOLDFISH WITH ETHAMBUTOL AND STIMULUS-INTENSITY

Wavelength discrimination in goldfish was measured behaviourally. Both acute application of ethambutol injected into the eye and chronic app lication by feeding the animals daily 25 mg ethambutol for 1 month had the same effect on wavelength discrimination in the range of 560-640 nm. This means that: (1) electrophysiological experiments, in which dr ug application is primarily acute, reflect the same disturbance as beh avioural experiments in which application is chronic; and that (2) the origin of the color defect must be retinal. Furthermore reduction in stimulus intensity by 2 log units caused, in control fish, a similar d isturbance in wavelength discrimination as induced by ethambutol, wher eas an increase of stimulus intensity by 2 log units abolished in etha mbutol-fed fish the discrimination disturbance. These results indicate that ethambutol shifts the threshold for wavelength discrimination wi thout changing the absolute sensitivity of the cone systems. Copyright (C) 1996 Elsevier Science Ltd