CHARACTERIZATION OF A DOPAMINE-SENSITIVE [H-3] LSD BINDING-SITE IN HONEYBEE (APIS-MELLIFERA) BRAIN

[H-3]Lysergic acid diethylamide ([H-3]LSD) binds on membrane homogenate of honeybee brain to both a dopamine-sensitive site (D-site) and a serotonin-sensitive site (S-Site). Under suitable conditions the properties of the two sites can be studied separately. Specific binding of [H-3]LSD to both the D-site and the S-site has high affinity and is saturable. The mean equilibrium dissociation constants (K-D) were 3.8 nM for the D- and 0.89 nM for the S-site. The densities (B-max values) of both binding sites were 1.7 pmol/mg protein for the D-site and O.79 pmol/mg protein for the S-site, [H-3]LSD binding to the D-site was reversible and reached equilibrium in about 30 min, Pharmacological displacement studies display a high binding affinity of the putative natural agonist dopamine to the D-site (K-i = 22 nM). The most potent displacers of D-site binding were lisuride, (+)-bromocriptine, chlorpromazine, S(+)-butaclamol, and 6,7-ADTN. The [H-3]LSD labelled D-site se;ems to be G-protein coupled, since addition of the stable GTP analogue GTP gamma S or NaCl to the incubation medium evoked a decrease of specific [H-3]LSD binding to the D-site.