Inverse agonist and neutral antagonist actions of synthetic compounds at an insect 5-HT 1 receptor: Research paper

Abstract

Background and purpose: 5-Hydroxytryptamine (5-HT) has been shown to control and modulate many physiological and behavioural functions in insects. In this study, we report the cloning and pharmacological properties of a 5-HT 1 receptor of an insect model for neurobiology, physiology and pharmacology. Experimental approach: A cDNA encoding for the Periplaneta americana 5-HT 1 receptor was amplified from brain cDNA. The receptor was stably expressed in HEK 293 cells, and the functional and pharmacological properties were determined in cAMP assays. Receptor distribution was investigated by RT-PCR and by immunocytochemistry using an affinity-purified polyclonal antiserum. Key results: The P. americana 5-HT 1 receptor (Pea5-HT 1) shares pronounced sequence and functional similarity with mammalian 5-HT 1 receptors. Activation with 5-HT reduced adenylyl cyclase activity in a dose-dependent manner. Pea5-HT 1 was expressed as a constitutively active receptor with methiothepin acting as a neutral antagonist, and WAY 100635 as an inverse agonist. Receptor mRNA was present in various tissues including brain, salivary glands and midgut. Receptor-specific antibodies showed that the native protein was expressed in a glycosylated form in membrane samples of brain and salivary glands. Conclusions and implications: This study marks the first pharmacological identification of an inverse agonist and a neutral antagonist at an insect 5-HT 1 receptor. The results presented here should facilitate further analyses of 5-HT 1 receptors in mediating central and peripheral effects of 5-HT in insects. © 2010 The British Pharmacological Society.