EFFECTS OF CHRONIC EXPOSURE TO CADMIUM, LEAD AND MERCURY ON BRAIN BIOGENIC-AMINES IN RAT

Abstract

Effects of chronic (45 days) treatment with different doses of cadmium chloride (0.25 and 1.0 mg/kg per day), methylmercury chloride (0.4 and 4.0 mg/kg per day) and lead acetate (0.2 and 1.0 mg/kg per day) and of 28 day withdrawal of treatment on the levels of acetylcholine (ACh) and activity of acetylcholinesterase (AChE) in cerebral cortex, and concentration of norepinephrine (NE) and 5-hydroxytryptamine (5-HT) in brain-stem were examined in rats. Exposure to both Cd and methylmercury produced significant decreases in cortical ACh and brain-stem 5-HT levels. In addition, brain-stem NE concentration was increased in methylmercury-treated rats. In contrast, chronic treatment with Pb resulted in enhanced cerebrocortical ACh levels but a decreased brain-stem NE concentration. Treatment with Cd also produced a transient enhancement of striatal dopamine levels. Cd-induced decreased in brain-stem 5-HT and Pb-induced accumulation of cortical ACh persisted even after 28 day withdrawal of treatment. Chronic exposure to low doses of heavy metals apparently produces differential changes in regional levels of various brain biogenic amines. These changes may represent the early signs of adverse effects on CNS function since they occur before any overt symptoms of neurotoxic effects of heavy metals become apparent.