Pharmacology of [ 3 H]mianserin binding in the nerve cord of the American cockroach, Periplaneta americana

The binding of [ 3 H]mianserin to homogenates of cockroach nerve cord was investigated, using a centrifugal binding assay. Nonspecific binding was defined as binding in the presence of 0.1 μM phentolamine. Specific binding was saturable and indicated a high affinity site (K D = 39.6 nM and B max = 0.8 fmol μGg −1 ) and a low affinity site (K D = 648.9 nM and B max = 5.9 fmol μg −1 ). The binding was reduced or abolished by heat, detergents, trypsin and HgCl 2 . Incorporation of CaCl 2 or NaCl into the medium reduced binding in a dose‐dependent fashion, whereas MgCl 2 and NaF inhibited binding in a biphasic manner. The stable GTP analog, 5′‐guanylylimidodiphosphate, reduced the high affinity binding at 10 μM. Phentolamine, D,L‐octopamine, demethylchlordimeform (DCDM), clonidine, and D,L‐synephrine are effective displacers of [ 3 H]mianserin‐binding, whereas dopamine, acetylcholine, serotonin (5‐HT), and histamine show poor or no displacement. The pharmacological properties of octopamine‐sensitive adenylate cyclase stimulation in cockroach nerve cord are similar to those of [ 3 H]mianserin‐binding.