ABSTRACT
Mercury is a ubiquitous and toxic heavy metal which has caused extensive environmental contamination and significant public health problems in many parts of the world and there is increasing evidence that the central nervous system is its main target. The present study evaluated the neurobehavioral, biochemical, and histo-architectural changes following oral administration of ethanolic extract of Psidium guajava leaves on the cerebrum, cerebellum and hippocampus of Mercuric chloride treated adult Wistar rats. Thirty-Five (35) adult Wistar rats were distributed randomly into seven groups with each group containing 5 rats. Group 1, served as the Control and was administered with distilled water, Group 2 was administered with 41.5 mg/kg bwt of mercuric chloride for 21days, Group 3 was administered with 1000 mg/kg bwt of ethanolic extract of Psidium guajava leaves for 21 days, Group 4 was administered with 41.5 mg/kg bwt of mercuric chloride for 21 days and distilled water for another 21days. Group 5was administered with 41.5 mg/kg bwt of mercuric chloride for 21 daysand 500mg/kg bwt of ethanolic extract of Psidium guajava leaves for another 21 days. Group 6 was administered with 41.5mg/kg bwt of mercuric chloride for 21 daysand 1000 mg/kg bwt of ethanolic extract of Psidium guajava leaves for another 21 days and Group 7 was administered with 41.5 mg/kg bwt of mercuric chloride for 21daysand1190mg/kg body weight of ascorbic acid for another 21 days. All the administrations were done orally via orogastric tube for a total of 42 days. Neurobehavioral tests such as Moris Water Maze to test for spatial learning and memory, beam walking for Motor coordination and Elevated Plus Maze test for anxiety related behaviours were done during and after the administration. The animals were sacrificed 12 hours after the last administration and the cerebrum, cerebellum and hippocampus were excised and some of the tissues were homogenized and was used for biochemical analyses of the oxidative stress markers such as Catalase (CAT), Superoxide Dismutase (SOD), Malondaldrehye (MDA) and Glutathione (GSH) concentration. While some of the brain tissues were fixed with Bouin?s fluid for histological studies. The result of Moris water maze test showed asignificant increase in the mean time taken by the animals exposed to mercuric chloride to locate the hidden platform (47.33�5.61 sec) when compared to the Control Group (3.33�0.33 sec), where as a decrease in the mean time taken to locate the hidden platform were observed in Groups treated with Psidium guajava (14.0�2.89 sec) and ascorbic acid (15.33�3.18 sec). The beam walking test showed the highest mean time taken to cross the beam to the safety hamster box was observed in groups exposed to mercuric chloride (25.55�6.52 sec) when compared to the Control group (3.15�0.54 sec). Treatment with Psidium guajava (7.08�1.03 sec) and ascorbic acid (9.84�0.70 sec) after mercury exposure showed significant decrease in the time taken by the experimental animals to cross the beam to the safety hamster box. The result of Oxidative stress study showed a significant increasein Malondialdehyde concentration and decrease in Catalase (CAT), Superoxide dismutase (SOD) and reduced glutathione (GSH) in groups exposed to Mercuric chloride, however, treatment with Psidium guajava and Ascorbic acid following mercury exposure did not show any significant difference when compared to the Control group. The result of the histological studies showed normal cytoarchtecture of cells in the Control group whereas alterations such as Vacuolation of cell bodies and degeneration of cells in groups exposed to mercuric chloride. Treatment with Psidium guajava and ascorbic acid ameliorated the changes observed in groups exposed to mercury only. It may be concluded that Psidium guajava leaves extract possess vital antioxidant properties that could ameliorate the toxic effect of mercury in the Cerebral Cortex, Cerebellum and Hippocampus of adult Wistar rats and as such could be used for treatment of mercury poisoning or heavy metal poisoning.