MELATONIN DECREASES THE AMPLITUDE OF THE B-WAVE OF THE HUMAN ELECTRORETINOGRAM

In a double-blind placebo crossover study of 13 healthy volunteers, th e pineal hormone melatonin (10 mg) was given at 4 pm, and the electror etinogram measured under conditions of dark and light adaptation. A si gnificant diminution of b-wave amplitude was found under both photopic (DELTA = 5.4 muV, p < 0.05) and scotopic conditions (DELTA = 7.4 muV, p < 0.01). These data indicate that melatonin may transduce the dark signal at the level of the retina as well as the pineal. Acute adminis tration of melatonin decreases sensitivity to light.