Identification of planarian serotonin receptor by ligand binding and PCR studies.

Binding sites for [3H]lysergic acid diethylamide (LSD), a serotonin receptor agonist, were identified in planarian membranes by ligand binding studies. The Kd and Bmax values were approximately 4 microM and 0.2 pmol mg-1 protein, respectively. The serotonin (5-HT) receptor antagonists methiothepin and dihydroergocriptine were also efficient displacers of [3H]LSD binding. When planarians were decapitated in the presence of these antagonists, head regeneration was significantly retarded. These results suggest that planarians possess LSD binding sites which are involved in the process of regeneration. Furthermore, we found a putative (5-HT) receptor expressed in planarians by the degenerate primer polymerase chain reaction.