A Possible Stimulatory Effect of FMRFamide on Neural Nitric Oxide Production in the Central Nervous System of Helix lucorum L

Inhibitory Effect of FMRFamide on NO Production During Immune Defense in Sepiella japonica

Neuropeptide Phe-Met-Arg-Phe-NH2 (FMRFamide), specifically existing in invertebrates, plays pivotal roles in various physiological processes. The involvement in neuroendocrine-immune regulation was explored in recent years, and it could modulate nitric oxide (NO) production under immune stress. However, detailed knowledge is still little known. In this study, we identified FMRFamide as an inhibitory factor on NO production in the immune reaction of Sepiella japonica. Firstly, Vibrio harveyi incubation caused significantly upregulated expression of FMRFamide precursor and NO synthase (NOS) in just hatched cuttlefish with quantitative Real-time PCR (qRT-PCR), which indicated that both were likely to be involved in the immune defense. The whole-mount in situ hybridization (ISH) detected FMRFamide precursor and NOS-positive signals appeared colocalization, suggesting that at histological and anatomical levels FMRFamide might interact with NOS. Next, NOS mRNA was highly significantly upregulated at 72 h when FMRFamide precursor mRNA was knocked down effectively with the RNA interference (RNAi) method; the results hinted that FMRFamide was likely to regulate NO production. Continuously, the inflammatory model was constructed in RAW 264.7 cells induced by lipopolysaccharide (LPS), FMRFamide administration resulted in a highly significant reduction of the NO level in dose- and time-response manners. Although the addition of the selected inducible NOS (iNOS) inhibitor had inhibited the NO production induced by LPS, the additional FMRFamide could still furtherly sharpen the process. Collectively, it was concluded that neuropeptide FMRFamide could indeed inhibit NO production to serve as feedback regulation at the late stage of immune response to protect hosts from excessive immune cytotoxicity. The inhibitory effect on NO production could not only be mediated by the NOS pathway but also be implemented through other pathways that needed to be furtherly explored. The results will provide data for comparing the structure and immune function of neuroendocrine-immune system (NEIS) between "advanced" cephalopods and other invertebrates and will provide new information for understanding the NEIS of cephalopods.

Neurotrophic factors and target-specific retrograde signaling interactions define the specificity of classical and neuropeptide cotransmitter release at identified Lymnaea synapses

Many neurons concurrently and/or differentially release multiple neurotransmitter substances to selectively modulate the activity of distinct postsynaptic targets within a network. However, the molecular mechanisms that produce synaptic heterogeneity by regulating the cotransmitter release characteristics of individual presynaptic terminals remain poorly defined. In particular, we know little about the regulation of neuropeptide corelease, despite the fact that they mediate synaptic transmission, plasticity and neuromodulation. Here, we report that an identified Lymnaea neuron selectively releases its classical small molecule and peptide neurotransmitters, acetylcholine and FMRFamide-derived neuropeptides, to differentially influence the activity of distinct postsynaptic targets that coordinate cardiorespiratory behaviour. Using a combination of electrophysiological, molecular, and pharmacological approaches, we found that neuropeptide cotransmitter release was regulated by cross-talk between extrinsic neurotrophic factor signaling and target-specific retrograde arachidonic acid signaling, which converged on modulation of glycogen synthase kinase 3. In this context, we identified a novel role for the Lymnaea synaptophysin homologue as a specific and synapse-delimited inhibitory regulator of peptide neurotransmitter release. This study is among the first to define the cellular and molecular mechanisms underlying the differential release of cotransmitter substances from individual presynaptic terminals, which allow for context-dependent tuning and plasticity of the synaptic networks underlying patterned motor behaviour.

Histamine and histidine decarboxylase in the olfactory system and brain of the common cuttlefish Sepia officinalis (Linnaeus, 1758)

Cephalopods are radically different from any other invertebrate. Their molluscan heritage, innovative nervous system, and specialized behaviors create a unique blend of characteristics that are sometimes reminiscent of vertebrate features. For example, despite differences in the organization and development of their nervous systems, both vertebrates and cephalopods use many of the same neurotransmitters. One neurotransmitter, histamine (HA), has been well studied in both vertebrates and invertebrates, including molluscs. While HA was previously suggested to be present in the cephalopod central nervous system (CNS), Scaros, Croll, and Baratte only recently described the localization of HA in the olfactory system of the cuttlefish Sepia officinalis. Here, we describe the location of HA using an anti-HA antibody and a probe for histidine decarboxylase (HDC), a synthetic enzyme for HA. We extended previous descriptions of HA in the olfactory organ, nerve, and lobe, and describe HDC staining in the same regions. We found HDC-positive cell populations throughout the CNS, including the optic gland and the peduncle, optic, dorso-lateral, basal, subvertical, frontal, magnocellular, and buccal lobes. The distribution of HA in the olfactory system of S. officinalis is similar to the presence of HA in the chemosensory organs of gastropods but is different than the sensory systems in vertebrates or arthropods. However, HA's widespread abundance throughout the rest of the CNS of Sepia is a similarity shared with gastropods, vertebrates, and arthropods. Its widespread use with differing functions across Animalia provokes questions regarding the evolutionary history and adaptability of HA as a transmitter.

A review of the actions of Nitric Oxide in development and neuronal function in major invertebrate model systems

Ever since the late-eighties when endothelium-derived relaxing factor was found to be the gas nitric oxide, endogenous nitric oxide production has been observed in virtually all animal groups tested and additionally in plants, diatoms, slime molds and bacteria. The fact that this new messenger was actually a gas and therefore didn't obey the established rules of neurotransmission made it even more intriguing. In just 30 years there is now too much information for useful comprehensive reviews even if limited to animals alone. Therefore this review attempts to survey the actions of nitric oxide on development and neuronal function in selected major invertebrate models only so allowing some detailed discussion but still covering most of the primary references. Invertebrate model systems have some very useful advantages over more expensive and demanding animal models such as large, easily identifiable neurons and simple circuits in tissues that are typically far easier to keep viable. A table summarizing this information along with the major relevant references has been included for convenience.

Immunohistochemical Approach to Understanding the Organization of the Olfactory System in the Cuttlefish, Sepia officinalis

Cephalopods are nontraditional but captivating models of invertebrate neurobiology, particularly in evolutionary comparisons. Cephalopod olfactory systems have striking similarities and fundamental differences with vertebrates, arthropods, and gastropods, raising questions about the ancestral origins of those systems. We describe here the organization and development of the olfactory system of the common cuttlefish, Sepia officinalis, using immunohistochemistry and in situ hybridization. FMRFamide and/or related peptides and histamine are putative neurotransmitters in olfactory sensory neurons. Other neurotransmitters, including serotonin and APGWamide within the olfactory and other brain lobes, suggest efferent control of olfactory input and/or roles in the processing of olfactory information. The distributions of neurotransmitters, along with staining patterns of phalloidin, anti-acetylated α-tubulin, and a synaptotagmin riboprobe, help to clarify the structure of the olfactory lobe. We discuss a key difference, the lack of identifiable olfactory glomeruli, in cuttlefish in comparison to other models, and suggest its implications for the evolution of olfaction.

FMRF-amide is a glucose-lowering hormone in the snail Helix aspersa

Although glucose is metabolically the most important carbohydrate in almost all living organisms, still little is known about the evolution of the hormonal control of cellular glucose uptake. In this study, we identify Phe-Met-Arg-Phe-amide (FMRFa), also known as molluscan cardioexcitatory tetrapeptide, as a glucose-lowering hormone in the snail Helix aspersa. FMRFa belongs to an evolutionarily conserved neuropeptide family and is involved in the neuron-to-muscle signal transmission in the snail digestive system. This study shows that, beyond this function, FMRFa also has glucose-lowering activity. We found neuronal transcription of genes encoding FMRFa and its receptor and moreover the hemolymph FMRFa levels were peaking at metabolically active periods of the snails. In turn, hypometabolism of the dormant periods was associated with abolished FMRFa production. In the absence of FMRFa, the midintestinal gland ("hepatopancreas") cells were deficient in their glucose uptake, contributing to the development of glucose intolerance. Exogenous FMRFa restored the absorption of hemolymph glucose by the midintestinal gland cells and improved glucose tolerance in dormant snails. We show that FMRFa was released to the hemolymph in response to glucose challenge. FMRFa-containing nerve terminals reach the interstitial sinusoids between the chondroid cells in the artery walls. We propose that, in addition to the known sites of possible FMRFa secretion, these perivascular sinusoids serve as neurohemal organs and allow FMRFa release. This study suggests that in evolution, not only the insulin-like peptides have adopted the ability to increase cellular glucose uptake and can act as hypoglycemic hormones.

FMRFamide-related peptides: anti-opiate transmitters acting in apoptosis

Members of the FMRFamide-related peptide (FaRP) family are neurotransmitters, hormone-like substances and tumor suppressor peptides. In mammals, FaRPs are considered as anti-opiate peptides due to their ability to inhibit opioid signaling. Some FaRPs are asserted to attenuate opiate tolerance. A recently developed chimeric FaRP (Met-enkephalin-FMRFa) mimics the analgesic effects of opiates without the development of opiate-dependence, displaying a future therapeutical potential in pain reduction. In this review we support the notion, that opiates and representative members of the FaRP family show overlapping effects on apoptosis. Binding of FaRPs to opioid receptors or to their own receptors (G-protein linked membrane receptors and acid-sensing ion channels) evokes or suppresses cell death, in a cell- and receptor-type manner. With the dramatically increasing incidence of opiate abuse and addiction, understanding of opioid-induced cell death, and in this context FaRPs will deserve growing attention.

Distribution of NADPH-diaphorase activity in the central nervous system of the young and adult land snail Megalobulimus abbreviatus

Nitric oxide (NO) is a gas produced through the action of nitric oxide synthase that acts as a neurotransmitter in the central nervous system (CNS) of adult gastropod mollusks. There are no known reports of the presence of NOS-containing neurons and glial cells in young and adult Megalobulimus abbreviatus. Therefore, NADPH-d histochemistry was employed to map the nitrergic distribution in the CNS of young and adult snails in an attempt to identify any transient enzymatic activity in the developing CNS. Reaction was observed in neurons and fibers in all CNS ganglia of both age groups, but in the pedal and cerebral ganglia, positive neurons were more intense than in other ganglia, forming clusters symmetrically located in both paired ganglia. However, neuronal NADPH-d activity in the mesocerebrum and pleural ganglia decreased from young to adult animals. In both age groups, positive glial cells were located beneath the ganglionic capsule, forming a network and surrounding the neuronal somata. The trophospongium of large and giant neurons was only visualized in young animals. Our results indicate the presence of a nitrergic signaling system in young and adult M. abbreviatus, and the probable involvement of glial cells in NO production.

The neuropeptide FMRFamide can protect cells against apoptosis in the snail digestive gland

FMRFamide-related peptides are widespread neurotransmitters or neurohormones regulating somatic or visceral motor activity. Some recent data indicate that these neuropeptides may be involved in the control of cell proliferation and apoptosis. In this work we investigated the possible effect of FMRFamide on cell viability in an invertebrate-type proliferating tissue. As a model, we used the midintestinal gland of the snail, Helix lucorum Linnaeus. Immunohistochemistry demonstrated the direct innervation of the gland cells by FMRFamide-containing nerve fibers. Midintestinal glands of snails were injected with 50 microM FMRFamide and the control with sterile deionised water or bovine serum albumin (BSA). Injections were administrated 4 times. Transmission electron microscopy, annexin V-labeling, thiazolyl blue (MTT) viability tests and ploidy analyses were carried out to define the viable/dead cell ratio in the tissue samples. FMRFamide increased the MTT-reduction of tissues, reduced the amount of apoptotic nuclei and annexin V-labeled cells. Deionised water or BSA injection induced cell death. Cell cycle analysis revealed that FMRFamide significantly elevated the amount of cells in G0/G1 phase, but did not induce mitosis. We conclude, that the FMRFamide can be a life-signal for cells, protect them from apoptosis without altering mitosis.

The action of RFamide neuropeptides on molluscs, with special reference to the gastropods Buccinum undatum and Busycon canaliculatum

The ever-growing RFamide neuropeptide superfamily has members in all animal phyla. Their effects in molluscs, on both smooth and cardiac muscle as well as on neurons, has been studied in detail. These neuropeptides exert a variety of functions: excitatory, inhibitory or even biphasic. Firstly, the literature on the excitatory effect of the RFamide neuropeptides on molluscan muscle and neurons has been reviewed, with greater emphasis and examples from the gastropods Buccinum undatum and Busycon canaliculatum. The peptides seem to be potent activators of contraction, sometimes generating slow tonic force and other times twitch activity. Secondly, the literature on the inhibitory effect of the superfamily has been reviewed. These peptides can exert an inhibitory effect, hyperpolarizing the cells rather than depolarizing them. Thirdly, the neuropeptides may play a variety of other roles, such as contributing to the regulation or maturation process of the animals. There have been cases recorded of RFamide neuropeptides acting as potent venoms in members of the Conus sp. The pathway of action of these multiple roles, their interaction with the parent neurotransmitters acetylcholine and serotonin, as well as the calcium dependency of the RFamide neuropeptides has been discussed, again with special reference to the above mentioned gastropods. A better understanding of the mode of action, the effects, and the importance of the RFamide neuropeptides on molluscan physiology and pharmacology has been attempted by reviewing the existing literature, recognizing the importance of the RFamide neuropeptide actions on molluscs.

Phe-met-arg-phe (FMRF)-amide is a substrate source of NO synthase in the gastropod nervous system

The possible involvement of the L-arginine-containing Phe-met-arg-phe (FMRF)-amide (FMRFa) in neuronal nitric oxide (NO) biosynthesis was studied in a gastropod species. We found NADPH-diaphorase-positive neurons and FMRFa-containing fibers in close proximity in the enteric nervous system. Administration of L-arginine and FMRFa induced quantitatively similar nitrite production in both intact intestinal tissues and tissue homogenates. These changes could be prevented by the presence of NOARG (an NO synthase inhibitor). Neither chemically modified FMRFa (D-arginine instead of L-arginine) nor amino acid constituents of FMRFa (methionine, phenylalanine) affected basal nitrite production. FMRFa-induced alterations were reduced in the presence of Na+ channel blockers (tetrodotoxin, amiloride, lidocaine), the Na+/K+ATPase inhibitor ouabain, or protease inhibitors (leupeptine, pepstatine-a). FMRFa and its amino acid constituents were analyzed by paper chromatography. When FMRFa was added to tissue homogenates, the peptide was eliminated within 1-2 min, whereas methionine, phenylalanine, arginine, and citrulline levels were elevated simultaneously. We tested the effects of FMRFa, L-arginine, and NOARG on intestinal contractile activity. FMRFa relaxed the intestine for 1-2 min and then induced contractions for 20-40 min. In the presence of NOARG, no relaxant effect of FMRFa was recorded. As administration of L-arginine strongly inhibits the mechanical activity of the intestinal muscle, NO production presumably plays a substantial role in the action of FMRFa, at least in the initial phase. Our biochemical data indicate a direct involvement of FMRFa in NO biosynthesis. FMRFa might be hydrolyzed by extracellular peptidases and then the locally released arginine might be transported into the cells and broken-down to produce NO. Depolarization-induced NO production attributable to the activation of amiloride-sensitive Na+ channels might also be involved.

Inhibition of the cdk5/p25 fragment formation may explain the antiapoptotic effects of melatonin in an experimental model of Parkinson's disease

In this study, the effects of melatonin on MPP+ -treated cerebellar granule neurons (CGNs) in culture were investigated. Results showed that MPP+ treatment significantly decreased cell viability and increased the apoptotic cell population at 24 and 48 hr. Calpain and caspase-3 activation was also determined, with results showing a strong increase in calpain (74%) and caspase 3 activity (70%), as measured by alpha-spectrin cleavage and fluorometric and colorimetric analysis, respectively. There are several studies suggesting that the activation of the cdk5/p35 pathway at its cleavage to cdk5/p25 may play a role in neuronal cell death in neurodegenerative diseases. Moreover, these studies indicate that this cleavage is mediated by calpains, and that MPP+ prompted an increase in cdk5 expression, as well as the cleavage of p35-p25, in a time-dependent manner. 1 mm Melatonin not only reduced the neurotoxic effects of MPP+ on cell viability, but also prevented apoptosis mediated by this Parkinsonian toxin in CGNs. 1 mm Melatonin reduced cdk5 expression, as well as the cleavage of p35-p25. These data indicate that melatonin possesses some neuro-protective properties against MPP+ -induced apoptosis. Moreover, these data suggest that the calpain/cdk5 signaling cascade has a potential role in the MPP+ -mediated apoptotic process in CGNs.

Neuroanatomical and immunocytochemical studies of the head retractor muscle innervation in the pond snail, Lymnaea stagnalis L

Axonal tracing and immunocytochemical techniques were used to study the innervation of the head retractor muscle (HRM) in the pond snail Lymnaea stagnalis L. Fibers of both the superior and inferior cervical nerves which innervate the HRM form endings that comply with the structure of chemical synapses. The somata of neurons with axons in these nerves are located in all except the buccal ganglia of the central nervous system, and this seems to be a special feature of the HRM motor system. By staining the filamentous actin with Oregon-green conjugated phalloidin, we demonstrated that the HRM has a multiterminal innervation and one muscle fiber can contain several synaptic endings which appear to be both morphologically and physiologically different. The morphological diversity of synaptic vesicles suggests a multiplicity of neurotransmitters acting on these nerve-muscle junctions. Immunocytochemical evidence was found for a strong serotonergic and FMRFamidergic innervation of muscle fibers through axons of the inferior cervical nerve. The thin fibers of the inferior cervical nerve possess immunoreactivity to glutamate, gamma-aminobutyric acid (GABA) and choline-acetyltransferase, and form sparser innervation patterns in the muscle. Our results indicate that several neurotransmitters are present in the nerves innervating the Lymnaea HRM and may therefore participate in the control of this muscle. The possible behavioral significance of such different neurotransmitter sets involved in the regulation of contractions is discussed.