Postnatal melatonin administration to stressed dams for ameliorating risk-taking behaviour in rat pups through maternal care improvement.

Abstract

Anxiety often occurs both concurrently and sequentially in childhood and adolescence in association with prenatal stress, which may reduce the quality of maternal care and then cause mood disorders among children in later life. Against this background, melatonin, as a powerful antioxidant, was used in the present study to ameliorate risk-taking behaviour induced by pure maternal care in rat pups. The Wistar rat dams recruited in this study were exposed to restraint stress from gestational day (GD) 11 until delivery. They further received melatonin (10mg/kg) during the postnatal days (PNDs) 0-7 by intraperitoneal (IP) injections at 4:00 PM. The pregnant rats were then divided into four groups, namely, control, stress, stress + melatonin and melatonin, and their maternal behaviour and corticosterone levels were measured. In the offspring, the outcomes of some behavioural tasks, including the elevated plus-maze (EPM) and open-field (OF) tests were ultimately assessed. The study results revealed that the quantity and quality of maternal care significantly declined and the plasma corticosterone levels compounded in the stressed dams. Melatonin treatment, however, improved their nursing behaviour and reduced their plasma corticosterone levels. The offspring performance in two tasks also showed an upward trend in risk-taking behaviour in the stress group, and melatonin administration ameliorated the effects of stress and lessened their anxiety-like behaviour. It was concluded that prenatal restraint stress could impair stress responses and quality of maternal care, whereas postnatal melatonin administration potentially contributed to the normalization of stress reaction and anxiolysis.