Peptide-Induced Modulation of Synaptic Transmission and Escape Response inDrosophilaRequires Two G-Protein-Coupled Receptors

Abstract

Neuropeptides are found in both mammals and invertebrates and can modulate neural function through activation of G-protein-coupled receptors (GPCRS).The precise mechanisms by which many of these GPCRs modulate specific signaling cascades to regulate neural function are not well defined. We used Drosophila melanogaster as a model to examine both the cellular and behavioral effects of DPKQDFMRFamide, the most abundant peptide encoded by the dFMRF gene. We show that DPKQDFMRFamide enhanced synaptic transmission through activation of two G-protein-coupled receptors, Fmrf Receptor (FR) and Dromyosupressin Receptor-2 (DmsR-2). The peptide increased both the presynaptic Ca 2ϩ response and the quantal content of released transmitter. Peptide-induced modulation of synaptic function could be abrogated by depleting intracellular Ca 2ϩ stores or by interfering with Ca 2ϩ release from the endoplasmic reticulum through disruption of either the ryanodine receptor or the inositol 1,4,5-trisphosphate receptor. The peptide also altered behavior. Exogenous DPKQDFMRFamide enhanced fictive locomotion; this required both the FR and DmsR-2. Likewise, both receptors were required for an escape response to intense light exposure. Thus, coincident detection of a peptide by two GPCRs modulates synaptic function through effects of Ca 2ϩ -induced Ca 2ϩ release, and we hypothesize that these mechanisms are involved in behavioral responses to environmental stress.

Mode of Action of aDrosophilaFMRFamide in Inducing Muscle Contraction

“…Heterozygous IP 3 receptor mutant larvae (Itp-r83A 05616 ) exhibit 50% reduction in IP 3 receptor transcript levels (Klose et al, 2010). Fig.…”

“…Dromyosuppressin GPCRs DmsR-1 and DmsR-2 Presynaptic effects of DPKQDFMRFamide are mediated by both FR and one of the two dromyosuppressin receptors (Dms-R2 but not Dms-R1) (Klose et al, 2010). To investigate the potential involvement of the Drosophila myosuppressin receptors, homozygous transgenic flies carrying an inverted repeat for DmsR-1 and DmsR-2 under the control of UAS (UAS-DmsR-1 RNAi and UAS-DmsR-2 RNAi) were crossed with the same three drivers as FR (tubPGal4, 24B-Gal4 and elavGal4) as well as the appropriate outcross controls.…”

“…FR GPCRs in neurons (Klose et al, 2010) and requires CaMKII activity (Dunn and Mercier, 2005), we sought to determine whether peptide-induced contractions are also mediated by CaMKII. This question was addressed using pharmacological agents known to reduce CaMKII activity and a transgenic Drosophila line (ala1) that increases expression of the inhibitory peptide of CaMKII in response to heat shock (Griffith et al, 1993).…”

“…This peptide enhances nerve-evoked muscle contractions and synaptic transmission at neuromuscular junctions (Hewes et al, 1998;Dunn and Mercier, 2005). DPKQDFMRFamide increases the amount of transmitter released from nerve terminals (Hewes et al, 1998;Klose et al, 2010), and it also increases the amplitude of nerve-evoked calcium signals via release of calcium from intracellular stores (Klose et al, 2010). The enhancement of synaptic transmission requires calcium/calmodulin-dependent protein kinase (CaMKII) (Dunn and Mercier, 2005) and involves the FR GPCR (Klose et al, 2010).…”

“…DPKQDFMRFamide increases the amount of transmitter released from nerve terminals (Hewes et al, 1998;Klose et al, 2010), and it also increases the amplitude of nerve-evoked calcium signals via release of calcium from intracellular stores (Klose et al, 2010). The enhancement of synaptic transmission requires calcium/calmodulin-dependent protein kinase (CaMKII) (Dunn and Mercier, 2005) and involves the FR GPCR (Klose et al, 2010). The intracellular pathways mediating the peptide-induced contractions, however, have not been studied, and possible involvement of the FR GPCR has not been investigated.…”