Involvement of NMDA in a Plasticity Phenomenon Observed in the Adult Frog Monocular Optokinetic Nystagmus

The frog horizontal monocular optokinetic nystagmus (H-OKN) is asymmetrical, the reflex being evoked by a temporal-nasal (T-N) component, but not by a nasal-temporal (N-T) component. Coil recordings showed that, in adult animals, 8 days of monocular deprivation (by unilateral eyelid suture) provoked the appearance of a N-T component, the H-OKN becoming symmetrical, reacting for both directions of stimulation. This delay was shortened to 2 days following two successive unilateral pretectal administrations of NMDA or of LY 285 265, an NMDA agonist, the first 2 days of eyelid suture. The same results were obtained when chronic microinjections of NMDA or LY 285 265 were achieved, the frogs being maintained in total darkness during the week of eyelid suture. These data indicate that the plasticity phenomenon evidenced in the monocular frog H-OKN depends on the activation of the NMDA receptors of one pretectum. This activation was obtained either by a monocular light stimulation of 8 days duration, or by unilateral administration of drugs activating the NMDA glutamatergic pretectal system. In this last case, the light stimulation was no longer necessary. © 1997 Elsevier Science Ltd.