Changes in Glycoprotein Metabolism in the Cerebral Cortex Following First Exposure of Dark-reared Rats to Light

Abstract: The level of incorporation of [³H]fucose or [³H]lysine into subcel-lular fractions of the visual and motor cortices of 50-day-old dark-reared (D) and light-exposed (L) rats was determined. No differences were found between D and L rats in the incorporation of either precursor into subcellular fractions of the motor cortex, or in any fraction of the visual cortex except the synaptic-membrane fraction. After a 3-h light exposure the incorporation of [³H]fucose into the visual cortex synaptic-membrane fraction was elevated (L/D = 136%). Incorporation of [³H]lysine was elevated in the visual cortex synaptic-membrane fraction of L compared to D rats after a 1-h exposure (L/D = 118%). However, after a 3-h exposure the incorporation was depressed in this fraction (L/D = 79%). No differences could be found in the levels of activity of fucosyl transferase following first exposure to light but dark-rearing itself resulted in increased enzyme activity in the motor cortex compared to normal controls. First exposure of 20-day-old dark-reared rats to light led to an increase in the incorporation of [³H]fucose into soluble glycoproteins of both the visual and motor cortex and into particulate glycoproteins of the visual cortex only. These results are in contrast with those found with 50-day-old animals and suggest that the effects of light-exposure on [³H]fucose incorporation may be age-dependent.