Pharmacological characterization of the 5-HT1A receptor of Bombyx mori and its role in locomotion.

Serotonin is involved in the regulation of many physiological and behavioral processes in vertebrates and invertebrates. The effects of serotonin are mediated through interactions of several 5-HT receptor types. The expression and pharmacological properties of 5-HT1 have received more attention than other serotonin receptors, but its functions at the individual level are little studied in arthropods. Silkworm, a Lepidoptera model, almost has no reports about serotonin receptors. To analyze the function of Bm5-HT1A receptor in vitro, the ORF of Bm5-HT1A was cloned into the pcDNA3.1 vector and expressed in HEK 293 cells. Serotonin activation of Bm5-HT1A-expressing cells decreased forskolin-stimulated cAMP synthesis and had the most potent effect compared to other biogenic amines. Serotonin reduced cAMP synthesis in a dose-dependent manner, and half-maximal activation (EC50) occurred at a concentration of 1.17 × 10-7  M (117 nM). The pharmacological analysis demonstrated that the rank potency of agonists was pimozide >8-OH-DPAT >5-MeOT ~ αm-5-HT, and antagonists was WAY-100635 > prazosin > SB-269970 > methiothepin at the Bm5-HT1A receptor. Injecting the antagonist of Bm5-HT1A receptor into larvae caused slow or weak motility, and adults lowered courtship vitality or moving speed. Injecting dsRNA of Bm5-HT1A into adults also dropped locomotivity in courtship. These results show that the Bm5-HT1A receptor is related to locomotor activity. This study provides the first information of serotonin receptor on pharmacological in silkworm and on individual functions in arthropods.