Investigation of the effects of ghrelin, leptin and melatonin hormones on catecholaminergic neurotransmitter levels in the hippocampus of male rats

Hippocampus is an important region of limbic system plays important role for regulation of memory consolidation. It is known that noradrenalin (NA) and dopamine (DA) has significant roles on neuronal activity in hippocampus. Ghrelin, leptin and melatonin hormones have regulatory roles on hippocampal memory. This study was carried out to detect the effects of these hormones on catecholamine levels in the right and left hippocampus in adult male rats. After anesthesia by chloral hydrate, ghrelin, leptin and melatonin hormones were intracerebroventricularly injected to the animals. Twenty minutes later animals were decapitated and right and left hippocampus removed by incision from brain tissues. Hippocampus tissues were homogenisated and NA, DA and their metabolites (dihydroxyphenylglycol and dihydroxyphenylacetic acid, respectively) concentrations were detected by high performance liquid chromatography with electrochemical system. Data were statistically analysed by Mann Whitney-U Test.Leptin administration had not caused any difference in catecholamine concentrations compared to leptin vehicle group. Intracerebroventricularly administered ghrelin significantly decreased DA level in the right hippocampus while increased NA level in the left hippocampus compared to control values (p<0.05). Melatonin significantly decreased the NA level in the both hippocampus tissues, dihydroxyphenylglycol level in the right hippocampus and dihydroxyphenylacetic acid level in the left hippocampus compared to melatonin vehicle values (p<0.05).The results of this study have emphasized that ghrelin and melatonin hormones may have modulator effects on catecholaminergic neurotransmitter release in the rat hippocampus. This insight has revealed that these catecholaminergic modulations may be involved in known effects of ghrelin and melatonin hormones on the neuronal activity in hippocampus