Distribution and pharmacological characterization of muscarinic-cholinergic receptors in the cockroach brain.

The binding of [3H]quinuclidinyl benzilate to a cockroach brain preparation was investigated. Specific binding was saturable with a Kd of 0.25 nM and Scatchard analysis indicated a Bmax of 604 pmol/mg protein. Kinetic analysis indicated that the ligand is binding in a complex fashion while dissociation followed a simple kinetic process. The pharmacology of the site was typical of muscarinic receptors but the site cannot be characterized in terms of vertebrate muscarinic-receptor subtypes. Affinity of the receptor for agonists was modulated by Mg2+ and guanylylimidodiphosphate but not by pertussis toxin indicating the involvement of a pertussis-toxin insensitive G-protein. Carbamylcholine did not inhibit basal or forskolin-stimulated adenylate cyclase activity. The binding site was localized autoradiographically and was restricted to the median and lateral calyces of the brain.