Characterization of serotonin binding sites in insect ( Locusta migratoria) brain

Radioligand binding studies using [ 3H]serotonin, [ 3H]ketanserin and [ 3H]mianserin were used to characterize 5HT receptor sites in membrane preparations from the brain of the locust, Locusta migratoria migratorioides. The [ 3H]serotonin binds reversibly to brain membrane preparations with high affinity and the receptor has 5HT 1 characteristics. However, studies with specific antagonists suggest that the receptor differs pharmacologically from the 5HT 1 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±0.19nM and B max value of 14.45±1.12 pmol/g tissue. Serotonin, bufotenin, N, N-dimethyltryptamine, d-LSD, BOL are equipotent displacers of [ 3H]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 [ 3H]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 5HT 2 receptor. [ 3H]Mianserin binds to the brain membrane; however, the pharmacology of mianserin binding suggests that mianserin binds to an octapamine-rather than a serotonin-receptor.