Behavioral effects of adult rats concurrently exposed to high doses of oral manganese and restraint stress

The behavioral effects Of concurrent exposure of high doses of manganese (Mn) and restraint stress were assessed in adult rats. Male Sprague-Dawley rats (250-300 g) received 0, 275 and 550 mg/kg/day of Mn in the drinking water for 19 weeks. Each group was divided into two subgroups. Animals in one subgroup were restrained for 2 h/day. During the treatment period, food and water intake, and body weight were weekly recorded. At the end of the treatment period, activity levels were monitored in an open-field. Learning was evaluated by a water-maze task during five consecutive days. A trial probe was also conducted to assess the time spent in the platform quadrant. Body weight and food consumption were significantly reduced in the group receiving 550 mg/kg/day of Mn. A two-way analysis of variance (ANOVA) revealed an overall effect of Mn on the total distance traveled. Differences on spatial learning were observed in the acquisition period, in which rats given 550 mg/kg/day of Mn (alone or restrained) were impaired in comparison with the control and the restrained only groups. In the probe trial, there was an impaired retention in the group treated with Mn at 550 mg/kg/day. The results of this investigation in the open-field and water maze suggest that it would be plausible that restraint stress and a high exposure to Mn interact at common neurotransmitter levels but inducing opposite effects. (c) 2005 Elsevier Ireland Ltd. All rights reserved.