EFFECTS OF METHYLPHENIDATE ON OXYTOCIN AND VASOPRESSIN LEVELS IN PINEALECTOMIZED RATS DURING LIGHT-DARK CYCLE

Although previous reports have shown that methylphenidate (MPH), in ad dition to its known behavioral effect, can influence the hypothalamo-p ituitary-adrenal axis by increasing the plasma ACTH, the pineal gland seems to be involved in neuroendocrinological processes too, e.g., in hypothalamic synthesis and release of oxytocin (OXY) and vasopressin ( AVP). Therefore, a study was performed to measure the OXY and AVP cont ent of the hypothalamus, neurohypophysis, and plasma after application of MPH in the morning and evening in pinealectomized (PE) as well as sham-operated control (SO) rats. Pinealectomy influenced both the dail y pattern (reversed in the neurohypophysis) and the levels of OXY and AVP. Starting from this different situation, application of MPH produc ed diverse effects. Hypothalamus: PE, increase in both hormones in the morning and evening; SO, decrease in morning OXY level. Neurohypophys is: PE, increase in morning OXY level; SO, decrease in both hormones e ven though in the morning only. Plasma: PE, decrease in morning OXY co ncentration; SO, increase in both hormones in the morning and decrease in the evening. The present results indicate that MPH application inf luences the hypothalamo-neurohypophysial system. Furthermore, the hypo thesis has been supported that this influence may be dependent on the circadian activity of the pineal gland as well. (C) 1997 Elsevier Scie nce Inc.