Effect of cocaine on rat pineal melatonin synthesis in vivo and in vitro.

Moderate concentrations (10 microM) of cocaine increased melatonin content and N-acetylserotonin and serotonin-N-acetyltransferase activity in rat pineal glands freshly placed in organ culture. Pineals cultured for 48 hours or taken from ganglionectomized animals did not respond to cocaine. Both procedures markedly reduced pineal noradrenalin (NA). Cocaine (5, 10, 20 mg/kg) given to adult intact rats stimulated pineal melatonin synthesis but only in animals exposed to constant light for 24 hours. Pineal denervation and/or adrenal demedullation neither completely eliminated NA from blood nor prevented cocaine-induced stimulation of melatonin synthesis in these light-primed animals.