INVOLVEMENT OF NMDA IN A PLASTICITY PHENOMENON OBSERVED IN THE ADULT FROG MONOCULAR OPTOKINETIC NYSTAGMUS

The frog horizontal monocular optokinetic nystagmus (H-OKN) is asymmet rical, the reflex being evoked by a temporal-nasal (T-N) component, bu t not by a nasal-temporal (N-T) component. Coil recordings showed that , in adult animals, 8 days of monocular deprivation (by unilateral eye lid suture) provoked the appearance of a N-T component, the H-OKN beco ming symmetrical, reacting for both directions of stimulation. This de lay was shortened to 2 days following two successive unilateral pretec tal administrations of NMDA or of LY 285 265, an NMDA agonist, the fir st 2 days of eyelid suture. The same results were obtained when chroni c 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 monocula r frog H-OKN depends on the activation of the NMDA receptors of one pr etectum. This activation was obtained either by a monocular light stim ulation of 8 days duration, or by unilateral administration of drugs a ctivating the NMDA glutamatergic pretectal system. In this last case, the light stimulation was no longer necessary. (C) 1997 Elsevier Scien ce Ltd.