~l-[~H]Lysergic Acid Diethylamide Binding to Serotonin Receptors in the Molluscan Nervous System RELATIONSHIP TO SEROTONIN-SENSITIVE ADENYLATE CYCLASE*

d-[3H]Lysergic acid diethylamide (LSD) bound to both dopamineand serotonin (5HT)-sensitive sites in a particulate fraction derived from the central nervous system of the snail Helix pomatia. Conditions were found which enabled the two sites to be studied independently. ['HILSD appeared to have a slightly higher affinity for dopamine-sensitive binding (Kd = 0.5 n ~ ) than for BHT-sensitive binding (Kd = 1.2 n ~ ) . A pharmacological analysis of the binding indicated that while dopamineand 5HT-related agonists clearly discriminated between the two sites, putative antagonists showed little specificity for dopamineor BHT-sensitive binding. The pharmacology of 5HT-sensitive r3H]LSD binding was studied in relation to a BHT-sensitive adenylate cyclase present in a particulate fraction derived from the same tissue. There was a very good correlation between the abilities of a range of agents to act as agonists or antagonists in the BHT-sensitive adenylate cyclase assay and their abilities to displace BHT-sensitive ['HILSD binding (r = 0.94; p < 0.001). In particular, d-LSD and a number of neuroleptic drugs were inhibitory in both assays in a stereoselective manner. These data suggest that in molluscan tissues, 5HT-sensitive I3HlLSD binding is related to the 5HT receptor which is coupled to adenylate cyclase.