The peptide hormone pQDLDHVFLRFamide (crustacean myosuppressin) modulates theHomarus americanuscardiac neuromuscular system at multiple sites

Abstract

SUMMARY pQDLDHVFLRFamide is a highly conserved crustacean neuropeptide with a structure that places it within the myosuppressin subfamily of the FMRFamide-like peptides. Despite its apparent ubiquitous conservation in decapod crustaceans, the paracrine and/or endocrine roles played by pQDLDHVFLRFamide remain largely unknown. We have examined the actions of this peptide on the cardiac neuromuscular system of the American lobster Homarus americanus using four preparations: the intact animal, the heart in vitro, the isolated cardiac ganglion (CG), and a stimulated heart muscle preparation. In the intact animal, injection of myosuppressin caused a decrease in heartbeat frequency. Perfusion of the in vitro heart with pQDLDHVFLRFamide elicited a decrease in the frequency and an increase in the amplitude of heart contractions. In the isolated CG, myosuppressin induced a hyperpolarization of the resting membrane potential of cardiac motor neurons and a decrease in the cycle frequency of their bursting. In the stimulated heart muscle preparation, pQDLDHVFLRFamide increased the amplitude of the induced contractions, suggesting that myosuppressin modulates not only the CG, but also peripheral sites. For at least the in vitro heart and the isolated CG, the effects of myosuppressin were dose-dependent (10 -9 to 10 ) consistent with the peptide serving as a circulating hormone. Although cycle frequency, a parameter directly determined by the CG, consistently decreased when pQDLDHVFLRFamide was applied to all preparation types, the magnitudes of this decrease differed, suggesting the possibility that, because myosuppressin modulates the CG and the periphery, it also alters peripheral feedback to the CG.

Coordination of distinct but interacting rhythmic motor programs by a modulatory projection neuron using different co-transmitters in different ganglia

“…Given that at least some of the actions of the PS neurons within the STNS are inhibitory, specifically including a suppression of active pyloric cycling in H. gammarus (Cazalets et al, 1987;Cazalets et al, 1990a;Cazalets et al, 1990b;Meyrand et al, 1994), and that the insect peptide leucomyosuppressin also disrupts pyloric activity (Tierney et al, 1997), we hypothesized that the lobster myosuppressin pQDLDHVFLRFamide might be the FMRFamidelike peptide co-transmitter present in the lobster PS cells. Although we were unable to obtain a myosuppressin-specific antibody to assess the presence or absence of pQDLDHVFLRFamide in the PS neurons of H. americanus, a previously identified lobster cDNA encoding Crust-MS (Stevens et al, 2009) allowed for molecular screening of these cells for the peptide using RT-PCR. Specifically, mRNA isolated from the ivn (Fig.1A), in which the PS somata are located, was used as a template to synthesize nerve-specific cDNA; transcript-specific primers were subsequently used to amplify a portion of the Crust-MS-encoding sequence from the cDNA.…”

Distinct or shared actions of peptide family isoforms: I. Peptide-specific actions of pyrokinins in the lobster cardiac neuromuscular system

“…The methods used for the recording of whole heart physiology were identical to those described in Stevens et al (2009). Briefly, lobsters were packed in ice for 20-30 min before the heart, still attached to the dorsal carapace to maintain appropriate levels of stretch, was removed.…”

Forces generated during stretch in the heart of the lobsterHomarus americanusare anisotropic and are altered by neuromodulators

“…The signals from the force transducers were amplified by a Model 44 Brownlee Precision Instrumentation amplifier and recorded with a Cambridge Electronic Design (CED) Micro 1401 digitizer paired with Spike2 version 7.03 software (CED, Cambridge, UK). The output of the force transducer is reported in grams rather than Newtons for consistency with other studies that have studied single locations on the length-tension curve (Fort et al, 2004(Fort et al, , 2007aStevens et al, 2009;Christie et al, 2010b;Dickinson et al, 2015).…”

“…Using stimulation patterns generated in Spike2, the nerve was stimulated in bursts (235 ms, consisting of 15 pulses, each 0.5 ms duration, at 60 Hz) every 1.5 s over 80 s. After the first 15 bursts, a longitudinal uniaxial stretch was imposed on the heart. The group of 15 bursts before the initiation of stretch allowed sufficient time for facilitation (Anderson and Cooke, 1971) and burst-to-burst increases in contraction amplitude during stimulation to stabilize (Stevens et al, 2009). To prevent over-stimulation and nerve damage, the heart was only stimulated during the extension phase of stretch; following completion of the stretch, the heart rested for 5 min without stimulation before a transverse uniaxial stretch was initiated.…”

“…Although the effects of neuromodulators on crustacean CPGeffector systems are well documented, these studies have only examined the physiological effects at single locations on the lengthtension curve (Mercier and Russenes, 1992;Fort et al, 2004;Wilkens et al, 2005;Fort et al, 2007a,b;Stevens et al, 2009;Christie et al, 2010b;Dickinson et al, 2015). However, it is important to consider the functional space in which the neurotransmitters are working.…”