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PubMed1988

The nervus terminalis in amphibians: anatomy, chemistry and relationship with the hypothalamic gonadotropin-releasing hormone system.

The nervus terminalis (TN), a component of the olfactory system, is found in most vertebrates. The TN of some fishes and mammals contains neurons immunoreactive (ir) to gonadotropin-releasing hormone (LHRH), and to several other neuropeptides and neurotransmitter systems, but there is little information on TN chemistry in other vertebrate taxa. Using immunocytochemical techniques, we found LHRH-ir neurons in amphibian TNs. In anurans, but not in a urodele, the TN was also found to contain Phe-Met-Arg-Phe-NH2 (FMRFamide) immunoreactivity. LHRH-ir neurons of the TN and those of the septal-hypothalamic system are morphologically homogeneous and form a distinct anatomical continuum in amphibians. Based upon topographical and cytological criteria, we hypothesize that LHRH-ir systems in vertebrates might derive embryonically from the TN.

Animals↗
PubMed2005

Characterization of an RFamide-related peptide orphan GPCR in C. elegans.

We cloned and characterized an orphan FMRFamide-related peptide (FaRP) GPCR in Caenorhabditis elegans. We synthesized numerous structurally different FaRPs that were found in the C. elegans genome by bioinformatic analysis and used them to screen cells expressing the C26F1.6 receptor. Two peptides ending in M(orL)VRFamide elicited a calcium response in receptor-expressing mammalian Chinese hamster ovary cells. The response was dose-dependent and appeared to be very specific; that is, none of the other FaRPs were active, not even closely related peptides also ending in M(orL)VRFamide, which are encoded by the same peptide precursor. Pharmacological profiling with a truncated series of the most active peptide revealed that the full peptide sequence is necessary for receptor activation.

Animals↗
PubMed2003

Retrograde Gbb signaling through the Bmp type 2 receptor wishful thinking regulates systemic FMRFa expression in Drosophila.

Amidated neuropeptides of the FMRFamide class regulate numerous physiological processes including synaptic efficacy at the Drosophila neuromuscular junction (NMJ). We demonstrate here that mutations in wishful thinking (wit) a gene encoding a Drosophila Bmp type 2 receptor that is required for proper neurotransmitter release at the neuromuscular junction, also eliminates expression of FMRFa in that subset of neuroendocrine cells (Tv neurons) which provide the systemic supply of FMRFa peptides. We show that Gbb, a Bmp ligand expressed in the neurohemal organ provides a retrograde signal that helps specify the peptidergic phenotype of the Tv neurons. Finally, we show that supplying FMRFa in neurosecretory cells partially rescues the wit lethal phenotype without rescuing the primary morphological or electrophysiological defects of wit mutants. We propose that Wit and Gbb globally regulate NMJ function by controlling both the growth and transmitter release properties of the synapse as well as the expression of systemic modulators of NMJ synaptic activity.

Animals↗
PubMed2004

Independent roles of the dachshund and eyes absent genes in BMP signaling, axon pathfinding and neuronal specification.

In the Drosophila nerve cord, a subset of neurons expresses the neuropeptide FMRFamide related (Fmrf). Fmrf expression is controlled by a combinatorial code of intrinsic factors and an extrinsic BMP signal. However, this previously identified code does not fully explain the regulation of Fmrf. We have found that the Dachshund (Dac) and Eyes Absent (Eya) transcription co-factors participate in this combinatorial code. Previous studies have revealed an intimate link between Dac and Eya during eye development. Here, by analyzing their function in neurons with multiple phenotypic markers, we demonstrate that they play independent roles in neuronal specification, even within single cells. dac is required for high-level Fmrf expression, and acts potently together with apterous and BMP signaling to trigger Fmrf expression ectopically, even in motoneurons. By contrast, eya regulates Fmrf expression by controlling both axon pathfinding and BMP signaling, but cannot trigger Fmrf ectopically. Thus, we show that dac and eya perform entirely different functions in a single cell type to ultimately regulate a single phenotypic outcome.

Animals↗
PubMed2003

Central circuitry in the jellyfish Aglantha digitale IV. Pathways coordinating feeding behaviour.

The hydromedusan jellyfish Aglantha digitale feeds on small planktonic organisms carried to the margin by tentacle flexions. During feeding, the manubrium bends across ("points") and seizes the prey with flared lips. In immobilized preparations, pointing to a source of electrical stimulation was accurate, 70% of the time, to within 15 degrees. Cutting experiments showed that the conduction pathways concerned with pointing and lip flaring are located in eight radial strands consisting of a radial canal, a giant nerve axon and a bundle of small axons with FMRFamide-like immunoreactivity. Application of food juices to sites on the margin and tentacles evoked trains of impulses in the axon bundles (F events; conduction velocity 15.5+/-3.7 cm s(-1)) and in the epithelium lining the radial canals (E events; conduction velocity 28.5+/-3.5 cm s(-1)). Impulses were conducted circularly in the outer nerve ring (F events) or in the ring canal (E events). Unilateral flexions of the manubrium during pointing arise from preferential excitation of one or more of eight longitudinal "muscle bands" in the wall of the manubrium and peduncle. Lip flaring represents symmetrical contraction of all eight bands. Cutting experiments revealed that F events mediate pointing; E events mediate lip flaring. Thus the endodermal radial canals, which in other hydromedusae mediate protective 'crumpling', provide the conduction pathway for manubrial lip flaring. Aglantha's alternative protective response--escape swimming--makes crumpling unnecessary, releasing the pathway for use in feeding. Trains of E events, generated in the manubrium during ingestion, propagate to the margin and inhibit rhythmic (slow) swimming with a duration that depended on their number and frequency. Inhibition of swimming appeared to facilitate transfer of food from the margin to the mouth, but how it comes about is unclear.

Animals↗
PubMed2006

Near simultaneous release of classical and peptide cotransmitters from chromaffin cells.

Adrenal chromaffin cells are an important part of the neuroendocrine system and under stressful conditions release catecholamines into the blood, thus regulating many physiological processes. In addition to the catecholamines, chromaffin cells also synthesize a range of peptides, including neuropeptide Y. Although the catecholamines and peptides are both contained within dense core granules, whether they are copackaged is less clear. Here, I investigate whether a single dense core granule can be loaded with both types of transmitter molecules. Using amperometry and FMRFamide tagging, I simultaneously measure the secretion of the catecholamines and a neuropeptide from mouse chromaffin cells in vitro. I find that fusion of a single dense core granule releases both types of transmitters into the extracellular space. Significant amounts of peptide escape from a fusing granule in 1-2 ms: almost as rapidly as the catecholamines. This suggests that the kinetics of peptide secretion might not be as sluggish as sometimes thought.

Animals↗
PubMed1999

Roles of G-protein beta gamma, arachidonic acid, and phosphorylation inconvergent activation of an S-like potassium conductance by dopamine, Ala-Pro-Gly-Trp-NH2, and Phe-Met-Arg-Phe-NH2.

Dopamine and the neuropeptides Ala-Pro-Gly-Trp-NH2 (APGWamide or APGWa) and Phe-Met-Arg-Phe-NH2 (FMRFamide or FMRFa) all activate an S-like potassium channel in the light green cells of the mollusc Lymnaea stagnalis, neuroendocrine cells that release insulin-related peptides. We studied the signaling pathways underlying the responses, the role of the G-protein betagamma subunit, and the interference by phosphorylation pathways. All responses are blocked by an inhibitor of arachidonic acid (AA) release, 4-bromophenacylbromide, and by inhibitors of lipoxygenases (nordihydroguaiaretic acid and AA-861) but not by indomethacin, a cyclooxygenase inhibitor. AA and phospholipase A2 (PLA2) induced currents with similar I-V characteristics and potassium selectivity as dopamine, APGWa, and FMRFa. PLA2 occluded the response to FMRFa. We conclude that convergence of the actions of dopamine, APGWa, and FMRFa onto the S-like channel occurs at or upstream of the level of AA and that formation of lipoxygenase metabolites of AA is necessary to activate the channel. Injection of a synthetic peptide, which interferes with G-protein betagamma subunits, inhibited the agonist-induced potassium current. This suggests that betagamma subunits mediate the response, possibly by directly coupling to a phospholipase. Finally, the responses to dopamine, APGWa, and FMRFa were inhibited by activation of PKA and PKC, suggesting that the responses are counteracted by PKA- and PKC-dependent phosphorylation. The PLA2-activated potassium current was inhibited by 8-chlorophenylthio-cAMP but not by 12-O-tetradecanoylphorbol 13-acetate (TPA). However, TPA did inhibit the potassium current induced by irreversible activation of the G-protein using GTP-gamma-S. Thus, it appears that PKA targets a site downstream of AA formation, e.g., the potassium channel, whereas PKC acts at the active G-protein or the phospholipase.

Amino Acid Sequence↗
PubMed1999

Conformational ensembles: the role of neuropeptide structures in receptor binding.

Conformational properties of several similar FMRFamide-like neuropeptides from mollusks were investigated by nuclear magnetic resonance (NMR) spectroscopy. It was found that amino acid substitutions in the N-terminal variable regions of the peptides had dramatic effects on the populations of reverse turns in solution. The populations of turns, as measured by two independent NMR parameters, were found to be highly correlated (r(2) = 0.93 and 0. 82) with IC(50) values using receptor membrane preparations from Helix aspersa (Payza, 1987; Payza et al., 1989). These results suggest that the amount of turn in the free peptide can influence the receptor binding affinities of that peptide. On the basis of these observations, a model was developed in which only a single species from a conformational ensemble of an unbound peptide will bind to a particular receptor. Thus, the conformational ensemble reduces the effective concentration of a particular peptide with respect to a particular receptor.

Amino Acid Sequence↗
PubMed2002

The neuromuscular junctions of the slow and the fast excitatory axon in the closer of the crab Eriphia spinifrons are endowed with different Ca2+ channel types and allow neuron-specific modulation of transmitter release by two neuropeptides.

Most crustacean muscle fibers receive double excitatory innervation by functionally different motor neurons termed slow and fast. By using specific omega-toxins we show that the terminals of the slow closer excitor (SCE) and the fast closer excitor (FCE) at a crab muscle are endowed with different sets of presynaptic Ca(2+) channel types. omega-Agatoxin, a blocker of vertebrate P/Q-type channels, reduced the amplitude of EPSCs by decreasing the mean quantal content of transmitter release in both neurons by 70-85%, depending on the concentration. We provide the first evidence that omega-conotoxin-sensitive channels also participate in transmission at crustacean neuromuscular terminals and are colocalized with omega-agatoxin-sensitive channels in an axon-type-specific distribution. omega-Conotoxin, a blocker of vertebrate N-type channels, inhibited release by 20-25% only at FCE, not at SCE endings. Low concentrations of Ni(2+), which block vertebrate R-type channels, inhibited release in endings of the SCE by up to 35%, but had little effects in FCE endings. We found that two neuropeptides, the FMRFamide-like DF(2) and proctolin, which occur in many crustaceans, potentiated evoked transmitter release differentially. Proctolin increased release at SCE and FCE endings, and DF(2) increased release only at FCE endings. Selective blocking of Ca(2+) channels by different omega-toxins in the presence of peptides revealed that the target of proctolin-mediated modulation is the omega-agatoxin-sensitive channel (P/Q-like), that of DF(2) the omega-conotoxin-sensitive channel (N-like). The differential effects of these two peptides allows fine tuning of transmitter release at two functionally different motor neurons innervating the same muscle.

Animals↗
PubMed2003

The EGL-21 carboxypeptidase E facilitates acetylcholine release at Caenorhabditis elegans neuromuscular junctions.

Proneuropeptides are packaged into dense-core vesicles in which they are processed into active peptides by copackaged enzymes. Proprotein convertases (PCs) cleave precursors after dibasic residues, and carboxypeptidases remove basic residues from the C terminals. We show here that the Caenorhabditis elegans egl-21 gene encodes a protein that is very similar to carboxypeptidase E (CPE) and is broadly expressed in the nervous system. Mutants lacking either egl-21 CPE or egl-3, which encodes the C. elegans ortholog of PC type 2 (PC2), were defective for processing endogenously expressed FMRFamide (Phe-Met-Arg-Phe-NH2)-related peptides (FaRPs). Mutants lacking the unc-104 kinesin motor protein were defective for anterograde movement of dense-core vesicle components, including egl-3 PC2, egl-21 CPE, and FaRPs. We provide evidence that egl-3 PC2 and egl-21 CPE mutants have diminished acetylcholine release at neuromuscular junctions (NMJs). Taken together, these results suggest that egl-21 CPE and egl-3 PC2 process endogenous neuropeptides that facilitate acetylcholine release at C. elegans NMJs.

Acetylcholine↗
PubMedDate not supplied

[The facilitation of defensive reactions during food consumption in the snail helix: the participation of glucose and gastrin/cholecystokinin-like peptide].

Molecular and cellular mechanisms of the interrelations between the feeding and defense behaviour were studied in a snail Helix lucorum. The dynamics of defense reactions was investigated in snails with different levels of feeding motivation. Defense reactions were suppressed in hungry snails, while 15-20 min after the beginning of food intake they were facilitated. The facilitation depended on a duration of starvation. Injection of 0.5 ml of 5 mM glucose solution (up to the glucose level in the haemolymph of a food satiated snail, 1.6-2.0 mM) or injections of 20-30 ng of synthetic analogues of the gastrointestinal peptides (pentagastrin of octapeptide cholecystokinin, CCK-8) facilitated the defense reaction in a hungry snail. Parameters of the facilitation were similar to those in the period of food intake. Activity of the command neurons of defense behaviour (L-PPL1) after the carrot juice application to the lip of a semi-intact preparation from a hungry snail was glucose-dependent. Similar glucose-dependent changes of L-PPL1 activity were found after CCK-8, but not FMRFamide application during the perfusion with 0.5 mM glucose. L-PPL1, but not L-PPa2-3 neurons were most sensitive to glucose and CCK-8 level changes in the Ringer solution. Adaptive significance of the behavioural phenomena as well as glucose and gastrin/CCK-like peptide participation in these processes are discussed.

Animals↗
PubMed1992

Reconstruction of neural networks is organized by co-existence of various signal molecules or input activation in Helix pomatia L.

The overlapping neural networks consisting of multifunctional neurons were shown to take part alternatively in regulation of various visceral functions or behaviour. The reconstruction of the neural networks was shown to be a function of input activation or transmitter cocktail used at the vicinity of the neurons. In rearrangement of neural networks acetylcholine (Ach), serotonin (5HT) and molluscan neuropeptide, FMRFamide were found to be effective. The modulation occurs at the level of ion channels and at least three different types, namely the Ca-, delayed K- and the unspecific cation channels were shown to be responsible for it. The modulatory action of low molecular weight neurotransmitters and peptides was more often directed to the same species of ion channels, but the maximum of channel activation can appear at different voltage ranges. The modulation of afferent and efferent pathways by signal molecules can assure the mosaic-like functioning of the units of neural networks.

Acetylcholine↗
PubMedDate not supplied

[Structure and electrophysiological properties of bursting neurosecretory cells in a peripheral sensory ganglion of the pond snail Lymnaea stagnalis].

A group of peripheral neurosecretory oscillating neurons belonging to the type of parabolic bursters, were identified in the osphradium (peripheral putative chemosensory organ) of the pond snail Lymnaea stagnalis. The cells are unipolar, their process ramifies and terminates in the nerve. Applications of 5-HT caused long-lasting bursts with significantly increasing duration and frequency of spikes. GABA and FMRFamide inhibited the activity of these cells.

Action Potentials↗
PubMed1989

Altered branching of serotonin-containing neurons in Drosophila mutants unable to synthesize serotonin and dopamine.

The anatomy of peripheral serotonin-containing fibers (5-HT fibers) in the gut of wild-type Drosophila larvae was compared to mutants deficient in the gene that encodes the enzyme dopa decarboxylase (DfDdc mutants). The 5-HT fibers, located in the proventriculus and midgut, were visualized immunocytochemically by using a monoclonal antibody against 5-HT. Since DfDdc larvae are devoid of 5-HT and dopamine in the nervous system, the highly selective uptake capability of 5-HT neurons was used to visualize the 5-HT fibers. We found that the absence of 5-HT and dopamine in the nervous system of DfDdc animals does not prevent 5-HT fibers from reaching their appropriate targets. However, these fibers in the mutant show a 2-fold increase in the extent of branching. This effect is specific to 5-HT fibers, since glutamate-like and FMRFamide-like immunoreactive fibers of the proventriculus and midgut remain unaffected in the mutant. Low but detectable levels of dopamine and 5-HT in the CNS are sufficient to prevent the increase in arborization, as indicated by analyses of a temperature-sensitive Ddc allele (Ddcts2), which has very low dopa decarboxylase activity. The abnormally extensive branching of 5-HT fibers also can be partially rescued by feeding DfDdc larvae with dopamine. In contrast, feeding with a 5-HT-containing diet had no effect on the mutant phenotype. Hypotheses that could explain the mutant phenotype are proposed.

Animals↗
PubMed1989

Biological activities of ganglion extracts from a prosobranch mollusc, Fusinus ferrugineus.

Acetone extract of the ganglia of Fusinus ferrugineus was applied to C-18 cartridges, and the flowthrough and retained materials were bioassayed on the radula retractor muscle of the animal. The flowthrough was found to have a potent contractile action and the retained material a potent contraction-inhibiting action in addition to a weak contractile action. The retained material was then applied to a column (2.6 x 40 cm) of Sephadex G-15. Fractions of 4 ml each were collected, and their activities were assayed on twitch contractions of the radula retractor. Three peaks (E1, E2 and E3) of contraction-potentiating activity and one peak (I) of contraction-inhibiting activity were obtained. The maximum activities of peaks E1, E2 and E3 were found at fractions 22, 44 and 50, respectively. The maximum activity of peak I was found at fractions 28-30. All of the activities of these peaks were destroyed by incubating the fractions with the peptidase subtilisin, suggesting that the active substances in the peaks are peptides. Using some kinds of molluscan muscles, the actions of the substances were examined in greater detail. The results suggest that peak E1 may contain a novel excitatory peptide whose molecular weight is more than 1,000, and that peaks E2 and E3 may contain FMRFamide-related peptides. It is also suggested that peak I may contain two or more myomodulin-CARP-related inhibitory peptides.

Animals↗
PubMed1993

Peptidergic and aminergic centers in the Helix cerebral ganglia: somatotopy and immunocytochemistry.

In Helix cerebral ganglia the relationship between location of serotonin, dopamine, CARP, FMRFamide, Met-enkephalin, and substance P immunoreactive neurons and the different representation foci of the head areas was compared. The majority of immunoreactive neurons was located in representation foci, however, the extension of immunoreactive centers are larger than the representation foci. Therefore, the real extension of a representation focus with the additional non-efferent neurons might be larger than revealed by retrograde labelling.

Animals↗
PubMed1995

Further study on the effects of achatin-I, an Achatina endogenous neuroexcitatory tetrapeptide having a D-phenylalanine residue, on Achatina neurones.

Achatin-I (Gly-D-Phe-Ala-Asp), a tetrapeptide having a D-phenylalanine residue and isolated from Achatina ganglia, has been proposed as an excitatory neurotransmitter of Achatina neurones. In the present study, it was demonstrated using Achatina giant neurones that achetin-I, perfused at alow concentration, enhanced an inward current (Iin) caused by 5-hydroxytryptamine (fast component) and an outward current (Iout) caused by FMRFamide (Phe-Met-Arg-Phe-NH2), and that this peptide suppressed an Iin caused by oxytocin, and Iout caused by acetylcholine and APGW-amide (Ala-Pro-Gly-Trp-NH2). These findings indicate that achatin-I acts not only as a neurotransmitter but also as a neuromodulator for these neurones. In the preliminary experiments, it was shown that an Iin caused by achatin-I on an Achatina giant neurone type, PON (periodically oscillating neurone), was suppressed by H-89 (a PKA inhibitor) and W-7 (calmodulin inhibitor), and that an Iin caused by achatin-I on v-RCON (ventral-right cerebral distinct neurone) was suppressed by KT5823 (PKG inhibitor), suggesting that achatin-I acts on PON via the cyclic AMP-PKA system and on v-RCON via the cyclic GMP-PKG system. Moreover, calmodulin would play a role to produce the Iin for achatin-I on PON via the system mentioned.

Amino Acid Sequence↗
PubMed1997

Glutamine synthetase is a glial-specific marker in the olfactory regions of the lobster (Panulirus argus) nervous system.

Glutamine synthetase (GS) has been qualified as a very specific marker of astroglial-type neuroglia in vertebrate neural tissues. In this paper we have begun to examine the possibility that glial localization of GS could be a ubiquitous characteristic of complex nervous systems. To this end we have used immunohistochemistry to localize GS-like immunoreactivity in the olfactory regions of the complex nervous system of the arthropod, the spiny lobster Panulirus argus. We describe a novel method for affinity isolation of antibodies from crude serum. Using this approach we purified GS-specific antibodies to chick retina GS and used these to analyze the lobster brain and the primary olfactory organ. Western blots showed that the lobster brain contains an immunoreactive peptide with nearly the same molecular mass as that of chick retina GS. Northern blot analyses of mRNA and enzymatic activity assays also confirm that the lobster brain produces GS. Immunohistochemical staining of sectioned lobster olfactory lobes and sensory sensilla showed strong reactivity in specific cells. Comparison of the GS immunostaining pattern with that for FMRFamide, a well characterized marker of neurons in invertebrate neural tissues, it became clear that GS is indeed glial-specific in lobster neural tissues as it is in vertebrates. These results suggest that the compartmentalization of GS in non-neuronal cells is either an early step in neural evolution or is an obligate and fundamental characteristic of complex neural systems composed of both neurons and neuroglia.

Animals↗