PINEAL RESPONSE TO ISOPROTERENOL IN RATS CHRONICALLY TREATED WITH ELECTROCONVULSIVE SHOCK

Chronic electroconvulsive shock (ECS) has been shown to induce a downr egulation of beta1-adrenergic receptors in the rat cerebral cortex. Be cause the secretion of melatonin in the pineal gland is regulated prim arily by beta1-adrenoceptors, in the present study we investigated the effect of chronic administration of ECS on pineal beta-adrenergic res ponsiveness to isoproterenol. To this purpose, young adult male rats r eceived once daily for 8 days ECS (80 mA, 0.5 s) or sham ECS. On the d ay after the last ECS or sham treatment, they were injected with isopr oterenol hydrochloride (1 mg/kg SC) or volume-matched saline at 1600 h . Two hours later they were killed by decapitation. Results showed tha t the isoproterenol-induced increase in the pineal melatonin content w as blunted in rats treated with ECS as compared to sham-treated animal s (shock X drug interaction = p < 0.01). These data indicate that chro nic ECS treatment affects beta1 receptor-mediated melatonin production in the pineal gland. Further studies need to elucidate whether the bl unted melatonin response to isoproterenol in ECS-treated rats is due t o a downregulation of pinealocyte beta-adrenergic receptors.