CHARACTERIZATION OF SEROTONIN BINDING-SITES IN INSECT (LOCUSTA-MIGRATORIA) BRAIN

Radioligand binding studies using [H-3]serotonin, [H-3]ketanserin and [H-3]mianserin were used to characterize 5HT receptor sites in membrane preparations from the brain of the locust, Locusta migratoria migratorioides. The [H-3]serotonin binds reversibly to brain membrane preparations with high affinity and the receptor has 5HT1 characteristics. However, studies with specific antagonists suggest that the receptor differs pharmacologically from the 5HT1 receptor subtypes which have been identified in vertebrate brain. Scatchard analysis indicates that the binding sites have a single component with a dissociation constant of 2.98 +/- 0.19 nM and a B(max) value of 14.45 +/- 1.12 pmol/g tissue. Serotonin, bufotenin, NN-dimethyltryptamine, D-LSD, BOL are equipotent displacers of [H-3]serotonin binding. Several other potential agonists and antagonists were tested and shown to effect varying degrees of inhibition. Ca and Mg ions have no significant effect on the [H-3]serotonin binding; however, guanine nucleotides modulate the binding suggesting that G-protein is involved in the serotonin action. No specific, saturable ketanserin binding was found, thus indicating lack of a vertebrate-like 5HT2 receptor. [H-3]Mianserin binds to the brain membrane; however, the pharmacology of mianserin binding suggests that mianserin binds to an octapamine-rather than a serotonin-receptor.