Effects of different levels manganese exposure on learning and memory in neonate rats

Objective To observe the effects of different levels manganese(Mn) on spatial learning and memory in neonate rats. Methods Neonate rats were distributed to control (normal saline) and MnCl210, 20, 30mg/kg groups randomly. Each groups included 10 litters in a cage with a dam. Neonate rats were intraperitoneal injection exposed to MnCl2 over PND 1-21. All groups were evaluated behavioral performance using open field and Morris water maze. Blood and hippocampus Mn levels were determined using ICP-MS. Results 1)For each group, blood Mn were(35.58±13.77)μg/L, (80.00±12.98) μg/L, (238.51±31.43)μg/L, (348.47±34.07)μg/L and hippocampus Mn were (576.82±79.78)μg/g, (798.33±40.60) μg/g, (1017.23±117.23)μg/g, (1278.76±281.48)μg/g respectively. Blood and hippocampus Mn concentrations in Mn-exposed groups were significant increased compared to control(P <0.01), and there was a positive correlation in blood Mn and hippocampus Mn(OR=0.91, 95%CI=0.81-0.96, P<0.01). 2)There were no significant differences on travelled distance in open field among all groups, which meant that Mn exposure had no effect on their locomotion. 3)In the hidden platform trials of the Morris water maze test, only on 3rd day, Mn-expose groups spent more time to find the platform compared to the control(P<0.01). The average escape latency were(21.77±7.10)s, (33.78±9.95)s, (37.17±13.68)s, (41.92±16.74)s respectively .Though the latency were increased with the Mn exposure levels increasing among the Mn-expose groups, no statistically significant differences were observed. There were no statistically effects on latency to find the platform of all groups in other training days. The result in probe trails showed that there were no statistically effects on swimming velocity, the number of crossing over the former platform and the time spent in the targeted quadrant. Conclusion Mn exposure exerts effects on the learning, but no dose-effect relationship.There are no effects on memory of neonate rats of Mn exposure. Key words: Mn exposure; Neonate rats; Open field; Morris water maze; Learning and memory