Pharmacological analysis of dopamine modulation in theDrosophila melanogasterlarval heart

Abstract

Dopamine (DA) and other neurotransmitters affect nonneuronal tissues in insects by circulating in the hemolymph. In several organisms, DA has been shown to modulate distinct aspects of cardiac function but the signal transduction pathways that mediate dopaminergic effects on the heart are not well characterized. Here, we used a semiintact Drosophila melanogaster larva preparation and drugs targeting DA receptors and canonical second messenger pathways to identify signaling cascades that mediate the effect of DA on a myogenic heart. DA has a positive chronotropic effect that is mimicked by SKF38393 (type-1 DA receptor agonist) and quinpirole (type-2 DA receptor agonist). SCH23390 and spiperone (type-1 and type-2 DA receptor antagonists) are moderately effective at inhibiting DA's effect. An adenylate cyclase inhibitor (SQ,22536) is also effective at blocking the stimulatory effect of DA but the drug has its own dose-dependent effect. Activation of protein kinase C with a diacylglycerol analog has a stimulatory effect on heart rate (HR). These results suggest that (1) both DA receptor subtypes are expressed in third instar larva cardiac myocytes to increase HR in response to rising levels of DA in the hemolymph, and (2) canonical second messenger pathways modulate HR in D. melanogaster larvae. Having these disparate signaling cascades converge toward a common modulatory function appears redundant, but in the context of multiple cardioactive chemicals this redundancy is likely to increase the fidelity of signal transduction.

Dop1 enhances conspecific olfactory attraction by inhibiting miR-9a maturation in locusts

“…1b, c ). The blockade of Dop1 in gregarious locusts through RNAi knockdown and SCH23390 (a specific antagonist 34 , 35 ) injection significantly reduced their attraction to gregarious volatiles (RNAi knockdown, G 2 = 27.74, P < 0.001; SCH23390, G 2 = 66.63, P < 0.001) (Fig. 1d, e ; Supplementary Figure 3 ).…”

Two dopamine receptors play different roles in phase change of the migratory locust

“…We injected SKF38393, a specific agonist of D1-like dopamine receptor (Feng et al, 1996 ; Titlow et al, 2013 ), in the brains of solitary locusts to determine the role of Locusta Dop1 in modulating behavioral transition from solitary to gregarious phase. All injection procedures were performed under a stereo-dissection microscope using a NANOLITER injector 2000 (World Precision Instruments, Sarasota, FL, USA) with a glass micropipette tip (Guo et al, 2013 ).…”

“…We injected SCH23390 (5 mM × 69 nL; Sigma-Aldrich, USA), a specific antagonist of D1-like receptor (Kokay and Mercer, 1996 ; Titlow et al, 2013 ) in the brains of gregarious locusts before behavioral assay was performed to determine the role of Dop1 in gregarization of solitary locusts. After the antagonist was injected, fourth-stadium gregarious locusts were reared with other gregarious locusts for 1 h before behavioral assay was conducted.…”

Pharmacological identification of cholinergic receptor subtypes on Drosophila melanogaster larval heart

“…In insects, neuromodulators travel in the hemolymph and affect non-neuronal tissues in addition to acting as the primary mediator of communication between cells of the nervous system . A number of neuromodulators that are prominent in larvae, including dopamine (Neve et al 2004;Titlow et al 2013), serotonin (Dasari and Cooper 2006;Majeed et al 2013) and octopamine (Johnson et al 1997), have also shown to exhibit modulatory effects on the heart. It has previously been shown that ACh at concentrations between 1 mM and 1 M, decreases heart rate (HR) in Drosophila at the larval, pupal, and adult stages with no significant changes at concentrations lower than 1 mM (Zornik et al 1999); however, these studies were performed in the intact, whole animal with injections into the hemolymph.…”