ABSTRACT
Mercury is a widespread environmental and industrial pollutant which is used in food preservation, cosmetics, pharmaceutical companies and laboratories. The aim of the present study was to investigate the possible effects of mercury (Hg) exposure on the histomorphology of the hippocampus, cerebellar and cerebral cortices, and also to evaluate the effects of mercury on spatial learning and memory, and motor activity with the aid of Morris water maze and Montoya staircase tests respectively. Twenty four adult Wis-tar rats of both sexes, with average weight of 210gms were randomly divided into four groups I, II, III, and IV with six animals per group. The animals in groups II, III, and IV were administered mercury chloride orally at the concentration of 12.45, 24.9 and 49.8 mg/kg body weight respectively while group I served as control and was administered with normal saline. The administration lasted for a period of 21 days (3 weeks). Animals were trained for both spatial learning and memory, and motor function using Morris water maze and Montoya stair case tests respectively. The brain tissues was fixed in Bouin's fluid and processed for histopathological studies using H and E and Bielschowsky stains. Brain tissues were analyzed for trace element analysis using Neutron Activation Analysis (NAA-1). The results from spatial learning and memory test was statistically significant after the first week of administration of mercury chloride in group IV animals, by the second week, there was an increase in time to find the platform, also by third week of exposure to low dose of mercury, there was a statistical significant increased in latency time taken to find the platform as an escape route by the rats. The result from Montoya - 14 - staircase test showed reduced exploratory motor activity in rats exposed to high concentration of HgCl2 that was statistically significant in the third week. There was significant motor exploratory activity impairment due to mercury intoxication even at low doses. The trace element analysis with NAA-1 revealed a significant decrease in concentration of copper and zinc in the brain tissues of rats exposed to mercury The results also showed neurodegenerative changes in the hippocampus, cerebral and cerebellar cortices which range from cellular death and sparse distribution of cells and decreased in cell number which also contributed to the decreased in concentration of the copper and zinc concentrations in the hippocampus, cerebellar and cerebral cortices as well as loss in motor activity, and memory and learning deficit. The findings from this study showed that ingestion of mercury chloride has potential deleterious effects on brain as shown in the histopathology, decreased cell number, impairment of learning and memory, exploratory motor activity and reduction in essential trace element concentrations in the brain of Wis-tar rats.