Light-dependent suppression of the vestibulo-ocular reflex during development

IN the fish Oreochromis mossambicus, light conditions affect the developmen t of the roll-induced vestibuloocular reflex (rVOR). During development und er continous light-dark conditions the rVOR amplitude, which is the maximum eye movement during a complete 360 degrees lateral roll, shows a secondary drop after a first peak at stage 17 by 64% (36.3 degrees at stage 17; 13.0 degrees at stage 20). This drop was shifted by 2 stages to older postembry onal stages and was 33% (29.2 degrees at stage 20; 19.5 degrees at stage 22 ) less pronounced in animals which were exposed to complete darkness for se veral days. Because the period of rVOR diminution is sensitive to light con ditions, it is likely that outgrowing visual projection fibres reorganize t he neuronal network underlying visual-vestibular behavior thus transiently suppressing the rVOR. (C), 1999 Lippincott Williams & Wilkins.