Regulation of pharyngeal motility by FMRFamide and related peptides in the medicinal leech, Hirudo medicinalis

Abstract

The medicinal leech possesses FMRFamide-like immunoreactivity in neural processes and somata associated with the pharynx and pharyngeal ganglia. The pharynx possessed about 25 immunoreactive somata; about half of the approximately 20 neurons of the pharyngeal ganglia were immunoreactive. We provide brief descriptions of several neurons located in the first neuromere of the subesophageal ganglion involved in controlling pharyngeal motility. Double-labeling experiments indicate that one of these cells, named Swallow neuron 1 (SW1), contains a FMRFamide-like peptide. Stimulation of SW1 caused the mouth to open and the pharynx to dilate. Upon termination of SW1 stimulation, the mouth closed, and a peristaltic wave progressed from the mouth down the length of the pharynx. Stimulation of SW1 did not produce 1:1 postsynaptic potentials in pharyngeal muscle cells. Thus, SW1 is apparently not a motor neuron. The pharynx responded to application of FMRFamide and related peptides by producing a series of 20- to 35-s phasic contractions superimposed upon an increase in basal tonus. The peptide-induced response was quantified by measuring increases in basal tonus, peak tension, and integrated area. Although there were some differences in the order of potency depending upon which parameter was considered, the approximate order of potency of RFamide peptides tested was: pQDPFLRFamide > or = FMRFamide approximately YGGFMRFamide > or = YMRFamide approximately FLRFamide approximately GGKYMRFamide approximately YLRFamide > leucomyosuppressin approximately perisulfakinin. Except for differences in potency, each of the RFamide peptides produced similar contractile waveforms. FMRFamide-induced responses were reduced by the protein kinase C inhibitor bisindolylmaleimide I (10 microM), the nonspecific protein kinase inhibitor H-7 (50 microM), and were increased by the protein phosphatase inhibitor okadaic acid (1 microM). However, the FMRFamide-induced response was unaffected by the protein kinase A inhibitor H-89 (1 microM), the phosphodiesterase inhibitor theophylline (1 mM), the phospholipase A(2) inhibitor OBAA (0.1 microM) or the cation channel blocker amiloride (100 microM).

Kinases, intracellular calcium, and apolipophorin‐III influence the adhesion of larval hemocytes of the lepidopterous insect, Galleria mellonella

“…Gö 6976, an autophosphorylation inhibitor of PKC a and b, known to inhibit invertebrate cell secretions (O'Gara et al, 1999), increased hemo- …”

Observations of serotonin and FMRFamide‐like immunoreactivity in palp sensory structures and the anterior nervous system of spionid polychaetes

“…This finding is interesting given that FMRFamide in the pharynx of the leech has been associated with a protein kinase C second messenger system that controls motility of the pharyngeal muscles (O'Gara et al, 1999). O'Gara et al (1999) also provide evidence of an RFamide-IP 3 (inositol phosphate) second messenger system. Mü ller and Westheide (2002) also observed complex FMRFamide-like immunoreactivity in the stomatogastric nervous system of four dinophilid polychaetes.…”

“…As a neurotransmitter in the polychaete Nereis virens, FMRFamide appears to act (perhaps with serotonin) on the muscles of the esophagus and gut to control intestinal motility (Krajniak and Greenberg, 1992). FMRFamide-like peptides also increase muscular contractions in the pharynx of the leech Hirudo medicinalis (O'Gara et al, 1999). Interestingly, immunoreactivity to FMRFamide antibodies revealed portions of the stomatogastric nervous system in dinophilid polychaetes that were not labeled by 5-HT antibodies (Mü ller and Westheide, 2002).…”

A review of FMRFamide- and RFamide-like peptides in metazoa

“…FMRFa also excites the longitudinal muscle of the leech Calabrese 1987, 1990). FMRFa-like immunoreactivity is present in neurones associated with the pharynx of H. medicinalis, including SW1 (swallow) neurone (O'Grady et al 1999). When SW1 is activated the pharynx dilates and the mouth opens.…”