Brain catecholaminergic neurotransmitters are involved in the regulation of food intake. Increased dopamin and noradrenaline release in the lateral hypothalamic area (LHA) results in inhibition of food intake whereas stimulative effects have been reported in the medial nucleus. Elevated noradrenaline levels have been shown in the hypothalamus and nucleus accumbens (NAC) of hyperphagic-hypermetabolic rats. Effects of melatonin on food intake in various species have been controversial. We have investigated the modulatory effects of melatonin on noradrenergic and dopaminergic neurotransmitters in brain areas which are involved in the regulation of food intake. Adult male Wistar rats were divided into two groups and fasted for 24 hours. The first group of animals were intraperitoneally injected with melatonin (2 mg/kg). Controls received ethanol + saline alone. All animals were decapitated 30 mins after injections and brains rapidly removed. LHA, NAC and ventromedial nucleus (VMN) were isolated from frozen brain clices by micropunch technique. Catecholamine content of these brain samples was determined by High Performance Liquid Chromotography-Electrochemical Detector. Administration of melatonin significantly elevated concentrations of noradrenaline and its metabolite, dihydroxyphenylglycol (DHPG) in LHA (p<0.01) and VMN (p<0.05; except DHPG). In the NAC, noradrenaline values were reduced (p<0.05), but DHPG was increased (p<0.005). No significant changes were seen in dopamin and 3,4-dihydroxyphenylacetic acid levels in NAC. In conclusion, we suggest that melatonin stimulates noradrenergic neurotransmission in the LHA and inhibits in the NAC that combination of these effects may in turn reduce food intake.
22 - 24 Mar 2004
British Endocrine Societies