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Abstract
The effects of lead on muscarinic receptors in the brain of adult and juvenile mice
were studied in vivo. Lead was administered for periods of 10, 30, and 90 days to
adult mice. Perinatal exposure was achieved by treating gestating mice from the day
of conception. The exposure was continued after birth and during weaning until 30
days postnatal. Both groups, adult mice and pups or their mothers were given a solution
of 10, 100, and 1000 ppm inorganic lead in their drinking water, which was available
ad libitum. Radioligand binding studies were performed in vitro to determine receptor
densities (Bmax) and affinities (KD values) in brain membranes of the frontal cortex.
In addition, the binding of a selective muscarinic agonist and of an antagonist to
receptor subtypes was investigated. Inhibition curves of 3H-quinuclidinylbenzilate
(3H-QNB) labelled membranes were determined with the m1-antagonist pirenzepine and
the m2-agonist carbachol to distinguish between high- and low-affinity agonist and
antagonist states in the cortex. Few important changes in density or affinity to the
membrane receptors investigated were seen in animals treated with lead. Similarly
the properties of high- and low-affinity muscarinic receptor binding were unchanged
in the groups exposed to lead. In conclusion, the present results show that lead does
not affect the muscarinic receptors in mouse brain under the experimental conditions
used.