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The biogenic amine dopamine (DA) regulates various physiological and behavioral processes in insects through binding with specific receptors. Three types of typical receptors are known to date. Previously, we achieved functional and pharmacological characterization of the three DA receptors in the silkworm Bombyx mori (BmDopR1–3). BmDopR1 and BmDopR2 are functionally classified as D1-like DA receptors, and BmDopR3 as D2-like. The present pharmacological data and our previous studies suggested that bromocriptine (Bro), which acts as an agonist on the DA D2 receptors and also interacts with various serotonin and adrenergic receptors in vertebrates, is an agonist that also acts specifically on BmDopR3, with little effect on BmDopR1 and BmDopR2 in silkworms. Exploiting this subtype specificity of Bro, to offer clues on the involvement of DA and its receptors in silkworm feeding behavior, Bro was injected into fifth instar larvae and subsequent feeding and related behaviors (feeding amount, excretion amount, mandibular movement, and feeding behavior observation) were quantitatively evaluated. Bro injection increased feeding and excretion amounts but did not affect mandibular chewing speed. Visual observation of feeding behavior for 1 h revealed the prolongation of feeding and related moving time in Bro-injected larvae. Collectively, these results suggest that Bro directly acted on BmDopR3 as an agonist and promoted feeding and related behaviors in silkworm larvae. [Display omitted] • Bromocriptine acts specifically on a silkworm D2-like dopamine receptor BmDopR3 to reduce intracellular cAMP levels. • Bromocriptine injection promotes feeding and excretion of silkworms and affects no mandibular chewing speed. • Visual observation reveals the prolongation of feeding and related moving time in bromocriptine-injected larvae. [ABSTRACT FROM AUTHOR]

Octopamine (OA) is a biogenic amine that controls a variety of important physiological processes and behaviors of invertebrates. To identify the amino acid residues interacting with (R)-OA in a β-adrenergic-like OA receptor from the silkworm Bombyx mori (BmOAR2), the wild-type receptor and seven mutant receptors with an amino acid substitution at a potential orthosteric site were expressed in HEK-293 cells and examined for their ability to elevate intracellular cAMP levels ([cAMP]i) in response to (R)-OA. The S206A mutant receptor retained the ability to increase [cAMP]i after (R)-OA treatment. In contrast, the other six mutant receptors (D115A, S202A, Y300F, Y300N, Y300L, and Y300A) lacked the ability to elevate [cAMP]i. These results indicate that Asp115, Ser202, and Tyr300 participate in (R)-OA binding and the activation of BmOAR2. Homology modeling studies suggest that Ser202 and Tyr300 interact with the phenolic OH group of (R)-OA, whereas Asp115 interacts with the β-OH group and the NH2 group of (R)-OA. [ABSTRACT FROM AUTHOR]

Abstract: Dopamine (DA) is a physiologically important biogenic amine in insect peripheral and nervous tissues. We recently cloned two DA receptors (BmDopR1 and BmDopR2) from the silkworm Bombyx mori and identified them as D1-like receptors, which activate adenylate cyclase to increase intracellular cAMP levels. In this study, these two receptors were stably expressed in HEK-293 cells, and the dose-responsiveness to DA and their pharmacological properties were examined using cAMP assays. BmDopR1 showed a dose-dependent increase in cAMP levels at DA concentrations up to 10−7 M with EC50 of 3.30 nM, while BmDopR2 required 10−6 M DA for activation. In BmDopR1-expressing cells, DA at 10−6–10−4 M induced 30–50% lower cAMP production than 10−7 M DA. BmDopR2-expressing cells showed a standard sigmoidal dose–response, with maximum cAMP levels attained with 10−5–10−4 M DA and EC50 of 1.30 μM. Both receptors had similar agonist profiles, and the typical vertebrate D1-like receptor agonist SKF-38393 was ineffective. Experiments with antagonists revealed that BmDopR1 exhibits D1-like features. However, the pharmacology of BmDopR2 was distinct from D1-like receptors; the typical vertebrate D1-like receptor antagonist SCH-23390 was less potent than the nonselective antagonist flupenthixol and the D2-like receptor antagonist chlorpromazine. The rank order of activities of several antagonists for BmDopR1 and BmDopR2 was more similar to that of Drosophila melanogaster DA receptors than Apis mellifera DA receptors. These data suggest that DA receptors could be potential targets for specific insecticides or insectistatics. [Copyright &y& Elsevier]

The article presents findings of a research conducted on secreted placental alkaline phosphatase-based reporter assay system for screening of compounds acting at an octopamine receptor stably expressed in a mammalian cell line. It mentions that octoparnine receptors are attractive insecticide targets. It concludes that the system proved useful in high-throughput screening to develop octopamine receptor-specific insecticides.