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Ma T, Kramer RE, Baker RC, Fan LW, Ho IK: Effects of chronic dermal exposure to nonlethal doses of methyl parathion on brain regional acetylcholinesterase and muscarinic cholinergic receptors in female rats. J Neurosci Res. 2003 Jan 1;71(1):138-45.
The in vivo and in vitro effects of methyl parathion, a phosphorothionate insecticide, on cholinergic neurotransmitter systems in the brain of rats were investigated. Three groups of adult female rats received 0, 0.1, or 1.0 mg/kg methyl parathion via dermal exposure for 95 days. Exposure to 0.1 mg/kg methyl parathion produced inhibition of AChE in the caudate-putamen and thalamic nuclei, whereas 1.0 mg/kg resulted in inhibition of AChE in most brain regions. The same doses of methyl parathion had no effect on [(3) H] QNB binding to muscarinic receptors in the brain regions examined. The in vitro study demonstrated that methyl parathion causes preferential inhibition of AChE and [(3) H] QNB binding in specific brain regions. As an inhibitor of AChE, methyl paraoxon was 1,000-fold more potent than was methyl parathion. Similarly, methyl paraoxon showed brain region-specific inhibition of the enzyme. Generally, the brain stem was highly sensitive to organophosphate-induced inhibition of AChE activity and [(3) H] QNB binding. Because central respiratory neurons gather in the brain stem, preferential effects there and in other brain regions may underlie lethal toxicity of methyl parathion and other organophosphates. |
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