Intraventricular carbachol mimics the effects of light on the circadian rhythm in the rat pineal gland

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Science  26 Jan 1979:
Vol. 203, Issue 4378, pp. 358-361
DOI: 10.1126/science.32619


Environmental lighting regulates numerous circadian rhythms, including the cycle in pineal serotonin N-acetyltransferase activity. Brief exposure of rats to light can shift the phase of this enzyme's circadian rhythm. Light also rapidly reduces nocturnal enzyme activity. Intraventricular injections of carbachol, a cholinergic agonist, can mimic both of these effects. Light and carbachol presumably act on the suprachiasmatic nucleus of the hypothalamus. These experiments demonstrate the feasibility of using a neuropharmacologic approach to the mechanisms underlying mammalian circadian rhythms.