fmrfamide and buccalin

The Drosophila FMRFamide gene encodes multiple FMRFamide-related peptides. These peptides are expressed by neurosecretory cells and may be released into the blood to act as neurohormones. We analyzed the effects of eight of these peptides on nerve-stimulated contraction (twitch tension) of Drosophila larval body-wall muscles. Seven of the peptides strongly enhanced twitch tension, and one of the peptides was inactive. Their targets were distributed widely throughout the somatic musculature. The effects of one peptide, DPKQDFMRFamide, were unchanged after the onset of metamorphosis. The seven active peptides showed similar dose-response curves. Each had a threshold concentration near 1 nM, and the EC50 for each peptide was approximately 40 nM. At concentrations <0.1 microM, the responses to each of the seven excitatory peptides followed a time course that matched the fluctuations of the peptide concentration in the bath. At higher concentrations, twitch tension remained elevated for 5-10 min or more after wash-out of the peptide. When the peptides were presented as mixtures predicted by their stoichiometric ratios in the dFMRFamide propeptide, the effects were additive, and there were no detectable higher-order interactions among them. One peptide was tested and found to enhance synaptic transmission. At 0.1 microM, DPKQDFMRFamide increased the amplitude of the excitatory junctional current to 151% of baseline within 3 min. Together, these results indicate that the products of the Drosophila FMRFamide gene function as neurohormones to modulate the strength of contraction at the larval neuromuscular junction. In this role these seven peptides appear to be functionally redundant.

Topics: Amino Acid Sequence; Animals; Drosophila melanogaster; Electrophysiology; Enkephalin, Methionine; FMRFamide; Kinetics; Larva; Metamorphosis, Biological; Muscle Contraction; Muscles; Neuromuscular Junction; Neuropeptides; Stimulation, Chemical; Synaptic Transmission

This paper investigates the distribution of four classes of neuropeptides, myomodulin, small cardioactive peptide (SCP), buccalin, and FMRFamide, in central neurons forming the network that underlies feeding behavior in the snail Lymnaea stagnalis. Intracellular dye-marking and immunocytochemical analysis, using antisera to the different classes of peptides, were applied to identified neurons of all three levels of the hierarchy of the circuitry: modulatory interneurons (cerebral giant cells, CGC; slow oscillator, SO), central pattern generator (CPG) interneurons (N1, N2, N3), motoneurons (B1-B10), and their peripheral target organs. Myomodulin immunoreactivity was detected in the CGC interneurons, in the SO, and in ventral N2-type CPG interneurons. Several large buccal motoneurons, the paired B1, B2, B3, B7, and neurons located in the dorsal posterior area (putative B4 cluster types) were also myomodulin immunoreactive. Target organs of buccal motoneurons, the buccal mass, salivary glands, and oesophagus contained myomodulin-immunopositive fibers. SCP appeared in N2-type interneurons and was found colocalized with myomodulin in the B1 and B2 motoneurons. SCP-containing neurons in the B4 cluster area were also detected. The buccal mass and salivary glands exhibited SCP-immunoreactive fibers. Buccalin immunoreactivity was scarce in the buccal ganglia and was identified only in N1-type interneurons and three pairs of dorsal posterior neurons. In the periphery, immunoreactive fibers were localized in the oesophagus only. None of the buccal neuronal types examined revealed immunoreactivity to SEQPDVDDYLRDVVLQSEEPLY ("SEEPLY"), a peptide encoded in the FMRFamide precursor protein of Lymnaea. SEEPLY immunoreactivity was confined to a pair of novel ventral neurons with projections to the laterobuccal nerve innervating the buccal mass. Immunoreactive fibers were also traced in this organ.

Topics: Amino Acid Sequence; Animals; Cheek; Feeding Behavior; FMRFamide; Immunohistochemistry; Interneurons; Invertebrate Hormones; Lymnaea; Molecular Sequence Data; Motor Neurons; Nerve Net; Neurons; Neuropeptides; Neurotransmitter Agents

At an identified neuro-neuronal synapse of the buccal ganglion of Aplysia, quantal release of acetylcholine (ACh) is increased by FMRFamide and decreased by histamine or buccalin. Activation of presynaptic receptors for these neuromodulators modifies a presynaptic Ca2+ current which is nifedipine-resistant and omega-conotoxin-sensitive. The voltage-sensitivity of these N-type Ca2+ channels is increased by FMRFamide and decreased by histamine through the intermediate of G proteins. Buccalin does not implicate G proteins and reduces the Ca2+ current without affecting the voltage-sensitivity of N-type Ca2+ channels. The possibility of relating the shifts in voltage-dependence of the Ca2+ current induced by FMRFamide and histamine to the phosphorylation state of the N-type Ca2+ channels is discussed. A scheme for the complex regulation of ACh release by presynaptic auto- and heteroreceptors is proposed.

Topics: Acetylcholine; Animals; Aplysia; Calcium Channels; FMRFamide; GTP-Binding Proteins; Histamine; Neurons; Neuropeptides; Receptors, Presynaptic; Synapses

An examination of the cellular properties and synaptic outputs of mechanoafferent neurons found on the ventrocaudal surface of the cerebral ganglion of Aplysia indicated that the cerebral mechanoafferent (CM) neurons are a heterogeneous population of cells. Based on changes in action potential duration in response to bath applications of 5-HT in the presence of TEA, CM neurons could be divided into 2 broad classes: mechanoafferents whose spikes broaden in response to 5-HT (CM-SB neurons) and mechanoafferents whose spikes narrow in response to 5-HT (CM-SN neurons). Morphological and electrophysiological studies of the CM-SN neurons indicated that they were comprised of previously identified interganglionic cerebral-buccal mechanoafferent (ICBM) neurons and a novel set of sensory neurons that send an axon into the LLAB cerebral nerve and have perioral zone receptive fields that are similar to those of ICBM neurons. Changes in spike width due to 5-HT were correlated with changes in synaptic output as indicated by the magnitudes of EPSPs evoked in postsynaptic neurons. Electrical stimulation of cerebral nerves and connectives also produced spike narrowing or broadening, and the sign of the effect was a function of the parameters of stimulation. Both heterosynaptic facilitation and heterosynaptic depression of EPSPs evoked in follower cells could be demonstrated. A variety of putative neuromodulators other than 5-HT were also found to affect the duration of action potentials in both classes of CM neurons. FMRFamide had effects opposite to that of 5-HT. SCPB and a recently characterized Aplysia neuropeptide, buccalin, broadened the spikes of both CM classes. Another neuropeptide, myomodulin, decreased the duration of CM-SB neuron spikes but had no effect on CM-SN spikes. Since the CM neurons appear to mediate a variety of competing behaviors, including feeding, locomotion, and defensive withdrawal, the various neuromodulator actions may contribute to the mechanisms whereby behaviors are selected and modified.

Topics: Action Potentials; Animals; Aplysia; Brain; FMRFamide; Ganglia; Mechanoreceptors; Neural Pathways; Neurons, Afferent; Neuropeptides; Neurotransmitter Agents; Reaction Time; Serotonin; Synapses