Developmental pattern of muscarinic receptors in normal and Down's syndrome fetal brain--an autoradiographic study.

The ontogeny of muscarinic cholinergic receptors in developing human brain was analyzed by in vitro receptor autoradiography with [3H]Quinuclidinyl Benzilate. It was found that muscarinic receptors develop relatively early; the levels at 24 weeks of gestation were comparable or even higher then the values in the adult brain, and that the levels of both M1 and M2 receptors increase with age. M1 receptors were concentrated mainly in forebrain regions while M2 receptors dominated in the thalamus. Scatchard analysis revealed Kd and Bmax values which are comparable to the adult values. Three brains of aborted Down's syndrome fetuses were examined in parallel and exhibited comparable levels and similar distribution to normal non-Down fetuses except for a modest increase of receptor levels which was observed in the striatum.