EFFECT OF LONGER PERIODS OF DARK REARING ON NMDA RECEPTORS IN CAT VISUAL-CORTEX

1. Cats were reared in the dark to 3, 5, and 11 mo. We studied the N-m ethyl-D-aspartate (NMDA) receptor contribution to the visual response in the cortex, defined as the percentage reduction in visual response after application of 2-amino-5-phosphonovaleric acid (APV). We also st udied the firing rate in response to the optimal visual stimulus and t he spontaneous activity. We made comparisons of all these properties b etween light-reared and dark-reared animals. 2. The NMDA receptor cont ribution to the visual response in layers IV, V, and VI of dark-reared animals was substantially above that in light-reared animals at all a ges tested. 3. The specificity of receptive field properties in dark-r eared animals showed some degeneration between 6 wk and 3 mo of age. A t greater than or equal to 3 mo, almost no cells were specific for ori entation and direction of movement. 4. Firing rate was lower in dark-r eared animals at all ages, suggesting a decrease in excitatory drive t o the visual cortex. 5. Spontaneous activity was equal in dark- and li ght-reared animals, suggesting that the overall level of activity (inc luding visual responses as well as spontaneous activity) in light-rear ed animals is higher than in dark-reared animals. This should tend to upregulate glutamate receptors in general in dark-reared animals.