RESUMO
The effect of in vivo treatment with methylmercury [MeHg] and mercuric chloride [HgCl[2]] on the binding properties of muscarinic acetyicholine receptors in rat brain synaptosomes was investigated using the potent antagonist L-[[3]H] guinulidinyl benzilate [[3H] QNB] to study binding to the muscarinic receptors. Mercurial compounds were administered via gastric gavage in a single or multiple daily dose [8 mg/kg per dose]. In a single dose treatment the maximum inhibition [40-45%] of [3H] QNB binding was reached after 15 days of treatment with MeHg or HgCI[2]. When rats were treated with five successive doses, [3H] QNB binding decreased markedly with maximum inhibition of about 48% in 12 or 18 days after the last treatment with MeHg and HgCI[2], respectively. On the other hand, the ability of the muscarinic receptor agonist carbamoylcholine to displace [[3]H] QNB binding was not affected by treatment with these mercury compounds, suggesting that they do not have a differential effect on agonist or antagonist binding sites. MeHg caused a maximum inhibition of [3H]QNB binding faster than HgCI[2], and declined to control levels after 30 days