Melatonin acts on the nucleus accumbens to increase acetylcholine release and modify the motor activity pattern of rats

Brain microdialysis coupled to high performance liquid chromatography with electrochemical detection (HPLC-ED) was used to evaluate the influence of m elatonin on extracellular concentration of acetylcholine (ACh) in the nucle us accumbens (NAc) of rats. Motor activity was simultaneously monitored dur ing the dialysis sessions with an activity meter. Melatonin and prazosin we re administered locally through the dialysis probe. It was found thar melat onin dose-dependently increased accumbens ACh. Melatonin (3 mu M) decreased horizontal activity and increased vertical activity, while another dose (1 00 mu M) enhanced both horizontal and vertical activity. Prazosin, a putati ve melatonin antagonist, blocked the effects of melatonin on both motor act ivity and ACh release when given 20 min before melatonin, Overall, these re sults suggest that melatonin modulates the release of ACh in the NAc and th e pattern of motor activity in the rat. (C) 1999 Elsevier Science B.V. All rights reserved.