Mercury Exposure and Post Exposure Recovery of the Cerebellar Cortex and Hippocampus of Adult Wistar Rats

Global environmental toxicants including Mercury (Hg) has potential health hazards to both human and animals. The studies investigate role of mercury exposure (ME) and mercury post exposure recovery (MPER) on grip strength and memory of adult Wistar rats. Eighteen adult Wistar rats were divided into three groups (I, II and III) with six rats per group. Group I as control, administered normal saline. Groups II and III were treated with doses of Hg at 12.45mg/kg and 24.9mg/kg respectively for twelve consecutive days. Motor balance test using grip strength test and novel objects recognition test for short term memory were conducted during ME and MPER phase. Animals were further divided into subgroups Ia&Ib, IIa&IIb, and IIIa&IIIb of three rats per subgroup. Rats in subgroup 'b' were allowed for 12 days MPER period while animals in subgroup a' were anesthetized. Brain tissues obtained were fixed in a Bouin's fluid for routine histological tissue processing. Motor balance coordination test indicates significant (p<0.01)decrease in time taken to release the string wire. The mean time in post exposure recovery period increased significantly (p<0.01). Short term memory test revealed a significant decrease and increase (p<0.001) for familial and novel objects during exposure and post exposure respectively. Histopathological observations reveal neurodegenerative changes in the cerebellar cortex and hippocampus that include pyknosis, karyorrhex is and karyolysis of the Purkinje cells and pyramidal cells in the hippocampus. Mean cell volume and number during ME and MPER showed decrease and increase (p<0.01) respectively. It was concluded from the study that mercury exposure impaired memory and motor activities, causes cellular death, loss of neuronal fibers and nuclei fragmentation. Cell size and number were depleted due to mercury toxicity. In MPER period, it restored some cellular morphology, improved behavioral activities, cell size and population.

Key Words: memory, motor, cell volume, cell number, cellular morphometry