Red-light-induced suppression of melatonin synthesis is mediated by N-methyl-D-aspartate receptor activation in retinally normal and retinally degenerate rats
Abstract
Pineal gland N-acetyltransferase (NAT) activity and pineal and serum levels of melatonin declined linearly in albino rats acutely exposed to different intensities of red light (600 nm or higher; low, 140 microW/cm2; moderate, 690 microW/cm2; high, 1200 microW/cm2) during the middle of the night. The high intensity red light was as effective as white light (780 microW/cm2) in suppressing NAT activity and pineal and circulating melatonin. Red-light-inhibited nighttime NAT activity and suppressed nocturnal melatonin levels in both retinally degenerate and normal rats. Pretreatment with the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 (10 mg/kg intraperitoneally) completely prevented the red-light-induced inhibition of nighttime melatonin synthesis. Magnesium chloride (300 mg/kg intraperitoneally) reduced the inhibitory effects of low and moderate intensities of red light but was ineffective when high red-light intensity was used. However, both agents failed to antagonize the suppression of nighttime melatonin synthesis elicted by the exposure to white light. Since retinally degenerate and retinally normal animals respond in the same way to both red-light and pharmacological intervention with the NMDA receptor blocker MK-...Continue Reading
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Effect of NMDA receptor blockade on melatonin and activity rhythm responses to a light pulse in rats
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