Central adrenergic system does not contribute to morphine stimulated pineal secretion of melatonin

The effect of long-term morphine treatment of rats subjected to central chemical sympathectomy (CCS) was studied. The experiment was performed on 7-week-old male Wistar rats. CCS was performed with 6-hydroxydopamine injected into the lateral ventricle of the brain. The serum concentration of melatonin was assayed by specific RIA. The study showed that morphine alone significantly increased melatonin concentrations in serum. CCS alone significantly decreased melatonin concentrations in serum at the time of highest secretory activity of the pineal gland. Long-term morphine treatment of rats subjected to CCS significantly increased the serum concentration of melatonin. Therefore, it may be concluded that the central adrenergic system does not take part in the morphine-stimulated secretion of melatonin.