Muscarinic receptor sites in human foetal brain

The specific binding of the muscarinic cholinergic ligand N-methylscopolamine to human foetal brain has been measured. A level of binding of 64 pmol/g protein was found with a dissociation constant, K_d of 0.27 nM. Values of 0.17 nM min^?1 and 0.048 min^?1 for the association rate constant, K_on, and the dissociation rate constant K_off respectively, were obtained. The pharmacological properties of the binding site were found to be very similar to those reported for muscarinic receptors from adult mammalian brain except that the binding of pirenzepine and the nicotinic antagonists d-tubocurarine and decamethonium shows differences from that seen in adult brain.