EXPERIENCE-DEPENDENT CHANGES IN THE IMPORTANCE OF N-METHYL-D-ASPARTATE (NMDA) RECEPTORS FOR VISUAL TRANSMISSION IN SUPERIOR COLLICULUS

The excitatory amino acid transmitter glutamate mediates visual activi ty in the superficial grey layer (SGS) of superior colliculus. At eye opening N-methyl-D-aspartate receptors (NMDA-rs) convey Little of the visual response, but with age their role in visual transmission increa ses to a peak at P21, then falls to the lower adult level. Visual depr ivation which begins before eye opening causes NMDA-rs to assume a gre ater importance for visual transmission in SGS. Here we explore the po ssibility that these experience-dependent changes in the role of NMDA- rs in the SGS are limited by age. We find that the effects of visual d eprivation on NMDA-r mediated visual activity are recoverable even aft er extensive dark rearing. Also, a short episode of visual experience is sufficient to allow the normal situation to be established and subs equent dark rearing is ineffective. Four-day periods of visual experie nce beginning at P14 or P25 have the same effect. Given that NMDA-rs t ake little part in visual transmission prior to P18, these data prompt a reconsideration of the role of NMDA-r mediated sensory transmission in the mechanisms by which early environmental experience influences the development of the visual system. (C) 1998 Elsevier Science B.V. A ll rights reserved.