Effects of melatonin on behavioral development and hippocampal glucocorticoid receptors in rats experienced neonatal maternal separation

Abstract

Objective To explore the effects of melatonin on behavioral development and hippocampal glucocorticoid receptors in rats with experienced neonatal maternal separation.Method Rat pups were randomly divided into maternal separation with melatonin group ( MT group),maternal separation with normal saline group ( MS group) and the control group.Rat pups were separated from their mothers and socially isolated from postnatal days one to 14.The rats in MT group were given melatonin[ 10 mg/(kg · d),i.p.] for 14 days from postnatal days 7 to 20.Water maze test was performed to assess learning and memory on days 28 to 29.The sections of hippocampus were obtained on days 30,then immunohistochemical staining and reverse transcriptase polymerase chain reaction (RT-PCR) was employed to detect the expression of glucocorticoid receptors (GR) gene in hippocampus.Results Compared with the control group [ (8.9 ±2.1 ) times],rats in the MS group [ ( 13.3 ±3.7) times] had significantly more times in leaning to get to the security area in the water maze test ( P ＜ 0.01 ),but the MT rats had less times than MS rats (P ＜0.01 ).The hippocampal GR expression in MS group showed significantly decreased as compared to the control group ( P ＜ 0.05 ),but no significant difference between MT group and control group.Conclusion Maternal separation could led to impaired behavior development and decreased hippocampal glucocorticoid receptors expression in rats, and exogenous melatonin could have protective effects on behavioral development through upregulating the glucocorticoid receptors expression in hippocampus. Key words: Melatonin; Behavior; Receptors, glucocorticoid; Maternal deprivation; Memory; Rats