Characterizing the physiological and behavioral roles of proctolin inDrosophila melanogaster

Abstract

The neuropeptide proctolin (RYLPT) plays important roles as both a neurohormone and a cotransmitter in arthropod neuromuscular systems. We used third-instar Drosophila larvae as a model system to differentiate synaptic effects of this peptide from its direct effects on muscle contractility and to determine whether proctolin can work in a cell-selective manner on muscle fibers. Proctolin did not appear to alter the amplitude of excitatory junctional potentials but did induce sustained muscle contractions in preparations where the CNS had been removed and no stimuli were applied to the remaining nerves. Proctolin-induced contractions were dose-dependent, were reduced by knocking down expression of the Drosophila proctolin receptor in muscle tissue, and were larger in some muscle cells than others (i.e., larger in fibers 4, 12, and 13 than in 6 and 7). Proctolin also increased the amplitude of nerve-evoked contractions in a dose-dependent manner, and the magnitude of this effect was also larger in some muscle cells than others (again, larger in fibers 4, 12, and 13 than in 6 and 7). Increasing the intraburst impulse frequency and number of impulses per burst increased the magnitude of proctolin's enhancement of nerve-evoked contractions and decreased the threshold and EC50 concentrations for proctolin to enhance nerve-evoked contractions. Reducing proctolin receptor expression decreased the velocity of larval crawling at higher temperatures, and thermal preference in these larvae. Our results suggest that proctolin acts directly on body-wall muscles to elicit slow, sustained contractions and to enhance nerve-evoked contractions, and that proctolin affects muscle fibers in a cell-selective manner.

Identification and expression analysis of the Spodoptera exigua neuropeptidome under different physiological conditions

“…Similarly, other neuropeptides previously described as gut-brain neuropeptides, such as CRF-DH44 (Cannell et al, 2016), diuretic hormone 31/calcitonin-like peptide, and diuretic hormone 45, also appear to be expressed in both the brain and gut of S. exigua. Additional gut-brain peptides identified in our transcriptomic approach are proctolin (Ormerod et al, 2016), myosuppressin (Vilaplana et al, 2008), neuropeptide F1, short neuropeptide F (Nässel and Wegener, 2011), tachykinin (Song et al, 2014) and orcokinin (OK; Sterkel et al, 2012).…”

Modulation of neuromuscular synapses and contraction inDrosophila3rd instar larvae

“…Physiological effects of proctolin on body wall muscles of 3rd instar larvae (Ormerod et al, 2016) suggest proctolin receptor expression. Proctolin increases the amplitude of nerve-evoked contractions at low concentrations (EC 50 2 nM) and induces contractions at much higher concentrations (EC 50 900 nM).…”

“…RNAi expression in neurons did not alter proctolin's effect, suggesting a postsynaptic action but no presynaptic action, and proctolin did not alter muscle EJPs. Proctolin-induced contractions involve extracellular Ca 2þ and intracellular Ca 2þ stores and are antagonized by the L-type channel blocker, nifedipine and an inhibitor of store-operated calcium channels (Ormerod et al, 2016). Muscle ablation indicated that proctolin induces contractions more strongly in muscles 4, 12 and 13 than in 6 and 7, and proctolin also enhances nerve-evoked contractions more strongly in 4, 12 and 13 than in 6 and 7 (Ormerod et al, 2016).…”

“…Proctolin-induced contractions involve extracellular Ca 2þ and intracellular Ca 2þ stores and are antagonized by the L-type channel blocker, nifedipine and an inhibitor of store-operated calcium channels (Ormerod et al, 2016). Muscle ablation indicated that proctolin induces contractions more strongly in muscles 4, 12 and 13 than in 6 and 7, and proctolin also enhances nerve-evoked contractions more strongly in 4, 12 and 13 than in 6 and 7 (Ormerod et al, 2016). These cell-selective effects of proctolin suggest that its receptor may be expressed more strongly in some muscle fibers than others, but this possibility remains to be examined.…”

Synaptic plasticity induced by differential manipulation of tonic and phasic motoneurons in Drosophila

“…To isolate contraction force mediated predominantly by the dorsal muscle 342 group (M1, M2, M3, M9, M10), 3 rd instar larvae were dissected along the ventral midline. Severed 343 abdominal nerves were placed in a suction electrode and the nerve bundle was stimulated at 344 increasing frequencies in HL3.1 saline containing 1.5 mM extracellular Ca 2+ as previously 345 described(Ormerod et al, 2016). Control MN1-Ib and MNIs GAL4 larval preparations showed 346 increasing contraction force when a 0.1 msec simulation was ramped from 1 Hz to 150 Hz for 600 347 ms (Figure 4E).…”