FMRFamide-like immunoreactivity in the nervous system of Hydra

Regionalized nervous system in Hydra and the mechanism of its development

The last common ancestor of Bilateria and Cnidaria is considered to develop a nervous system over 500 million years ago. Despite the long course of evolution, many of the neuron-related genes, which are active in Bilateria, are also found in the cnidarian Hydra. Thus, Hydra is a good model to study the putative primitive nervous system in the last common ancestor that had the great potential to evolve to a more advanced one. Regionalization of the nervous system is one of the advanced features of bilaterian nervous system. Although a regionalized nervous system is already known to be present in Hydra, its developmental mechanisms are poorly understood. In this study we show how it is formed and maintained, focusing on the neuropeptide Hym-176 gene and its paralogs. First, we demonstrate that four axially localized neuron subsets that express different combination of the neuropeptide Hym-176 gene and its paralogs cover almost an entire body, forming a regionalized nervous system in Hydra. Second, we show that positional information governed by the Wnt signaling pathway plays a key role in determining the regional specificity of the neuron subsets as is the case in bilaterians. Finally, we demonstrated two basic mechanisms, regionally restricted new differentiation and phenotypic conversion, both of which are in part conserved in bilaterians, are involved in maintaining boundaries between the neuron subsets. Therefore, this study is the first comprehensive analysis of the anatomy and developmental regulation of the divergently evolved and axially regionalized peptidergic nervous system in Hydra, implicating an ancestral origin of neural regionalization.

Peptide-gated ion channels and the simple nervous system of Hydra

Neurons either use electrical or chemical synapses to communicate with each other. Transmitters at chemical synapses are either small molecules or neuropeptides. After binding to their receptors, transmitters elicit postsynaptic potentials, which can either be fast and transient or slow and longer lasting, depending on the type of receptor. Fast transient potentials are mediated by ionotropic receptors and slow long-lasting potentials by metabotropic receptors. Transmitters and receptors are well studied for animals with a complex nervous system such as vertebrates and insects, but much less is known for animals with a simple nervous system like Cnidaria. As cnidarians arose early in animal evolution, nervous systems might have first evolved within this group and the study of neurotransmission in cnidarians might reveal an ancient mechanism of neuronal communication. The simple nervous system of the cnidarian Hydra extensively uses neuropeptides and, recently, we cloned and functionally characterized an ion channel that is directly activated by neuropeptides of the Hydra nervous system. These results demonstrate the existence of peptide-gated ion channels in Hydra, suggesting they mediate fast transmission in its nervous system. As related channels are also present in the genomes of the cnidarian Nematostella, of placozoans and of ctenophores, it should be considered that the early nervous systems of cnidarians and ctenophores have co-opted neuropeptides for fast transmission at chemical synapses.

A novel neuropeptide (FRamide) family identified by a peptidomic approach in Hydra magnipapillata

In the course of systematic identification of peptide signaling molecules combined with the expressed sequence tag database from Hydra, we have identified a novel neuropeptide family that consists of two members with FRamide at the C-terminus; FRamide-1 (IPTGTLIFRamide) and FRamide-2 (APGSLLFRamide). The precursor sequence deduced from cDNA contained a single copy each of FRamide-1 and FRamide-2 precursor sequences. Expression analysis by whole-mount in situ hybridization showed that the gene was expressed in a subpopulation of neurons that were distributed throughout the body from tentacles to basal disk. Double in situ hybridization analysis showed that the expressing cell population was further subdivided into one population consisting of neurons expressing both the FRamide and Hym176 (neuropeptide) genes and the other consisting of neurons expressing only the FRamide gene. FRamide-1 evoked elongation of the body column of 'epithelial' Hydra that was composed of epithelial cells and gland cells but lacked all the cells in the interstitial stem cell lineage, including neurons. In contrast, FRamide-2 evoked body column contraction. These results suggest that both of the neuropeptides directly act on epithelial cells as neurotransmitters and regulate body movement in an axial direction.

Loss of DNA: a plausible molecular level explanation for crustacean neuropeptide gene evolution

Alignment of nucleotides of APGWamide, RPCH and AKH genes gives region stretches (common regions) present in all family member variants. Common regions were separated by gap sections in the larger variants of family members. Consensus sequences for single polynucleotides from virtual hybrid molecules of DNA were obtained by joining the common regions of DNA and deleting the extra DNA nucleotides. Conceptual translation of these virtual hybrids resulted in polypeptides similar to APGWamide, RPCH and the AKH pre-pro-peptide. Virtual polypeptides were also similar to LWamide and RFamide along hydras to mammals. DNA loss probably explains the origin of neuropeptides.

Symmetry breaking in stem cells of the basal metazoan Hydra

Among the earliest diverging animal phyla are the Cnidaria. Cnidaria were not only first in evolution having a tissue layer construction and a nervous system but also have cells of remarkable plasticity in their differentiation capacity. How a cell chooses to proliferate or to differentiate is an important issue in stem cell biology and as critical to human stem cells as it is to any other stem cell. Here I revise the key properties of stem cells in the freshwater polyp Hydra with special emphasis on the nature of signals that control the growth and differentiation of these cells.

Cnidarian chemical neurotransmission, an updated overview

The ultrastructural, histochemical, immunocytochemical, biochemical, molecular, behavioral and physiological evidence for non-peptidergic and peptidergic chemical neurotransmission in the Anthozoa, Hydrozoa, Scyphozoa and Cubozoa is surveyed. With the possible exception of data for the catecholamines and peptides in some animals, the set of cumulative data - the evidence from all methodologies - is incomplete. Taken together, the evidence from all experimental approaches suggests that both classical fast (acetylcholine, glutamate, GABA, glycine) and slow (catecholamines and serotonin) transmitters, as well as neuropeptides, are involved in cnidarian neurotransmission. Ultrastructural evidence for peptidergic, serotonergic, and catecholaminergic synaptic localization is available, but the presence of clear and dense-cored synaptic vesicles also suggests both fast and slow classical transmission. Immunocytochemical studies, in general, reveal a continuous, non-localized distribution of neuropeptides, suggesting a neuromodulatory role for them. Immunocytochemical and biochemical studies indicate the presence of glutamate, GABA, serotonin, catecholamines (and/or their receptors), RFamides, nitric oxide and eicosanoids in cnidarian neurons and tissues. Gene sequences for peptidergic preprohormones have been reported; putative gene homologies to receptor proteins for vertebrate transmitters have been found in Hydra. Behavioral and physiological studies implicate classical transmitters, neuropeptides, eicosanoids and nitric oxide in the coordination of the neuroeffector systems.

Pacemaker activity in hydra is modulated by glycine receptor ligands

In the mammalian central nervous system, the neurotransmitter, glycine, acts both on an inhibitory, strychnine-sensitive receptor (GlyR) and an excitatory, strychnine-insensitive site at the NMDA receptor. Here we present electrophysiological evidence that the strychnine-sensitive glycine agonists, glycine and taurine, and the antagonist, strychnine, affect the endodermal rhythmic potential (RP) system and that the ectodermal contraction burst (CB) pacemaker system is modulated by glycine and strychnine in hydra. The RP and CB pacemaker systems are responsible for the respective elongation and contraction of hydra's body column. Activity of the CB system, quantified by the rate of contraction bursts (CBs), the number of pulses per contraction burst (P/CB), and the duration of bursts, was decreased by glycine. Glycine, coadministered with the strychnine-insensitive glycine site blocker, indole-2-carboxylic acid (I2CA), decreased RPs but not CBs or P/CB. The effect was mimicked by taurine. Strychnine increased the duration of RP production, and decreased CB duration. The effect of glycine with I2CA was counteracted by strychnine. The results support the idea that a vertebrate-like GlyR may be involved in modulating activity of the endodermal RP system and suggest that a glycine site on an NMDA receptor may be involved in the CB system.

Involvement of Hydra achaete-scute gene CnASH in the differentiation pathway of sensory neurons in the tentacles

The proneural genes of achaete-scute (ac-sc) family that encodes the bHLH class transcription factors play a variety of roles in neurogenesis. In Hydra, the ac-sc homologue CnASH is involved in nematocyte differentiation. In the present study, we found that sensory neurons in the tentacles expressed CnASH, in addition to differentiating nematocytes in the body column of Hydra. Neuron precursors that migrated to the tentacle base did not express CnASH, and it took 1 day for them to become CnASH-expressing neurons. Thus, the CnASH-positive cells at the tentacle base appeared to be sensory cells at early stages of differentiation. Furthermore, the CnASH-positive neurons distributed from the base to the tip of tentacles suggest that the gene is also involved in maintenance of the differentiated state. In addition, we found that the sensory neurons in the tentacles consist of at least two subpopulations. The comparison of the CnASH expression with Nv1 expression in sensory cells that is detected by monoclonal antibody Nv1 showed that at least Nv1-positive/ CnASH-positive and Nv1-negative/ CnASH-positive sensory neurons existed in the tentacles.

Neuropeptides in cnidarians

Cnidarians are the lowest animal group having a nervous system. In the primitive nervous systems of cnidarians, peptides play important roles as neurotransmitters or neurohormones. So far, we have isolated and sequenced about 35 neuropeptides from different cnidarian classes (Hydrozoa, Scyphozoa, Anthozoa). All these neuropeptides have a C-terminal amide group, which protects against C-terminal degradation, but which also is important for receptor recognition. Also the N-termini of the cnidarian neuropeptides often contain different kinds of protecting groups (such as <Glu residues, L-3-phenyllactyl groups, and X-Pro or X-Pro-Pro sequences). Cnidarian neuropeptides are located in neuronal dense-core vesicles and are synthesized as preprohormones, which can contain up to 41 copies of a neuro peptide sequence. From Hydra, six different neuropeptide genes have been cloned so far. Each gene is expressed by a specific population of neurons, but in two instances coexpression of neuropeptide genes has been found. We have also cloned some of the cnidarian prohormone processing enzymes, among them the enzymes necessary for C-terminal amidation. These enzymes are closely related to their mammalian counterparts. All these data show that the primitive nervous systems of cnidarians have already acquired some of the sophisticated principles that we know from higher animals.

Distribution and development of FMRFamide-like immunoreactive neuronal systems in the brain of the brown trout, Salmo trutta fario

The distribution of Phe-Met-Arg-Phe-amide (FMRFamide) peptide-immunoreactive (FMRF-ir) cells and fibers in the terminal nerve and central nervous system was investigated in developing stages and adults of the brown trout, Salmo trutta fario. The first FMRF-ir neurons appeared in the terminal nerve system of 8-mm embryos in and below the olfactory placode. In the brain, FMRF-ir neurons were first observed in the rostral hypothalamus, primordial hypothalamic lobe, mesencephalic laminar nucleus, and locus coeruleus of 12- to 13 -m embryos. After hatching, FMRF-ir cells appeared in the lateral part of the ventral telencephalic area and the anterior tuberal nucleus. In adult trout, FMRF-ir cells were observed in all these areas. The number of FMRF-ir neurons increased markedly in some of these populations during development. Dense innervation by FMRF-ir fibers was observed in the dorsal and lateral parts of the dorsal telencephalic area, and in the ventral telencephalic area, the lateral preoptic area, the medial hypothalamic and posterior tubercle regions, midbrain tegmentum and rhombencephalic reticular areas, the central gray, the superior raphe nucleus, the secondary visceral nucleus, the vagal nuclei, and the area postrema. Fairly rich FMRF-ir innervation was also observed in the optic tectum and some parts of the torus semicircularis. The saccus vasculosus and hypophysis received a moderate amount of FMRF-ir fibers. Innervation of most of these regions appeared either in late alevins or fry, although FMRF-ir fibers in the preoptic area, hypothalamus, and reticular areas appeared in embryos. Comparative analysis of the complex innervation pattern observed in the brain of trout suggests that FMRF is involved in a variety of functions, like the FMRF family of peptides in mammals.

A novel neuropeptide, Hym-355, positively regulates neuron differentiation in Hydra

During the course of a systematic screening of peptide signaling molecules in Hydra a novel peptide, Hym-355 (FPQSFLPRG-NH(2)), was identified. A cDNA encoding the peptide was isolated and characterized. Using both in situ hybridization and immunohistochemistry, Hym-355 was shown to be expressed in neurons and hence is a neuropeptide. The peptide was shown to specifically enhance neuron differentiation throughout the animal by inducing interstitial cells to enter the neuron pathway. Further, co-treatment with a PW peptide, which inhibits neuron differentiation, nullified the effects of both peptides, suggesting that they act in an antagonistic manner. This effect is discussed in terms of a feedback mechanism for maintaining the steady state neuron population in Hydra.

Pattern of differentiated nerve cells in hydra is determined by precursor migration

The nervous system of the fresh water polyp hydra is built up as a nerve net spread over the whole body, with higher densities in the head and the foot. In adult hydra, as a result of continuous growth, new nerve cell differentiation takes place continuously. The pattern of nerve cell differentiation and the role of nerve cell precursor migration in establishing the pattern have been observed in vivo by vitally labelling precursor cells with DiI. The results indicate that nerve cell precursors arise directly from stem cells, complete a final cell cycle and divide, giving rise to two daughter cells, which differentiate into nerve cells. A subpopulation of the nerve cell precursors are migratory for a brief interval at the onset of the terminal cell cycle, then complete the cell cycle and divide at the site of differentiation. Labelling small patches of tissue in the head, body column and peduncle/foot with DiI indicated that formation of nerve cell precursors was nearly constant at all three positions. However, at least half of the labelled precursors in the body column migrated to the head or foot before differentiating; by contrast, precursors in head and foot differentiated in situ without significant migration. This redistribution leads to a net increase of nerve cell precursors in head and foot compared to body column and thus to the higher density of nerve cells in these regions.

Structure, development, and maintenance of the nerve net of the body column in Hydra

The anatomy and developmental dynamics of the nerve net in the body column of Hydra viridissima were examined immunocytochemically with a monoclonal antibody (CC04) that recognizes an antigen in nerve cells and with an antiserum against vasopressin. CC04+ neuron cell bodies, their neurites, and vasopressin-like-immunoreactive (VLI+) neurites could be clearly visualized on whole-mount preparations. All neurites of the CC04+ neurons in the body column were VLI+. However, only half of the VLI+ neurites in the body column were CC04+. Immunocytochemical analysis of macerated preparations showed that half of the neurons in the gastric region of the body column were CC04+. These results suggest that most of the neurons in the gastric region are VLI+. The density of the VLI+ neurites was uniform along the entire length of the body column. The CC04+ neuron density in the gastric region remained constant at all stages of asexual development and during foot regeneration. After pulse-labeling with 5-bromo-2'-deoxyuridine (BrdU), CC04+ neurons with labeled nuclei appeared in the body column. We conclude that neuron density in the gastric region is maintained at a constant value by insertion of new neurons in parallel with continuous epithelial cell division.

Peptides in the nervous systems of cnidarians: structure, function, and biosynthesis

Cnidarians are the lowest animal group having a nervous system and it was probably within this phylum or in a related ancestor group that nervous systems first evolved. The primitive nervous systems of cnidarians are strongly peptidergic. From a single sea anemone species, Anthopleura elegantissima, 17 different neuropeptides have been isolated so far, and we expect that many more neuropeptides (more than 30) must be present. All peptides are localized in neurons of cnidarians and we have demonstrated the presence of some of the peptides in neurosecretory dense-cored vesicles. Most neuropeptides have an excitatory or inhibitory action on whole cnidarians, muscle preparations, and isolated muscle cells, suggesting that these peptides are neurotransmitters or neuromodulators. One neuropeptide induces metamorphosis in planula larvae to become a polyp. This shows that cnidarian neuropeptides also are involved in developmental processes, such as cell differentiation and pattern formation. We have cloned the preprohormones for most of the cnidarian neuropeptides. These preprohormones have a high copy number of the immature neuropeptide sequence, which can be up to 37 neuropeptide copies per precursor molecule. In addition to well-known, "classical" processing enzymes, novel prohormone processing enzymes must be present in cnidarian neurons. These include a processing enzyme hydrolyzing at the C-terminal sides of acidic (Asp and Glu) residues and a dipeptidyl aminopeptidase digesting at the C-terminal sides of N-terminally located X-Pro and X-Ala sequences. All this shows that the primitive nervous systems of cnidarians are already quite complex, and that neuropeptides play a central role in the physiology of these animals.

The nervous systems of cnidarians

Cnidarians have simple nervous systems and it was probably within this group or a closely-related ancestor that nervous systems first evolved. The basic plan of the cnidarian nervous system is that of a nerve net which, at some locations, has condensed to form nerve plexuses, or circular or longitudinal nerve tracts which may be syncytia. At the ultrastructural level, many cnidarian neurons have the combined characteristics of sensory, motor, inter- and neurosecretory neurons and thus appear to be multifunctional. We propose that these multifunctional neurons resemble the ancestors of the more specialized neurons that we find in higher animals today. The primitive nervous system of cnidarians is strongly peptidergic: from a single sea anemone species Anthopleura elegantissima, we have now isolated 16 different novel neuropeptides. These peptides are biologically active and cause inhibitions or contractions in muscle preparations or isolated muscle cells from sea anemones. The various peptides are located in at least six distinct sets of neurons showing that sea anemone neurons have already specialized with respect to their peptide content. Using immuno-electronmicroscopy, we have found that the peptides are located in neuronal dense-cored vesicles associated with both synaptic and non-synaptic release sites. All these data indicate that evolutionarily "old" nervous systems use peptides as transmitters. We have also investigated the biosynthesis of the cnidarian neuropeptides. These neuropeptides are made as large precursor proteins which contain multiple (up to 36) copies of immature neuropeptides. Thus, the biosynthesis of neuropeptides in cnidarians is very efficient and comparable to that of higher invertebrates, such as molluscs and insects, and vertebrates.

Localization of FMRFamide-like peptides in Caenorhabditis elegans

The neuropeptide FMRFamide (Phe-Met-Arg-Phe-NH2) is a member of a large family of related peptides that have been found throughout the animal kingdom. By using an antiserum specific for the Arg-Phe-NH2 moiety, we have found that about 10% of the neurons in the nematode Caenorhabditis elegans are immunoreactive. Most of these neurons, which include sensory, motor, and interneurons, were identified on the basis of their number, position, and projection pattern and by analysis of characterized mutants. Neurons that were immunoreactive in hermaphrodite animals were generally also found in males, but each sex had, in addition, sex-specific immunoreactive cells. Staining of hermaphrodite animals from different larval stages suggests that the onset of FMRFamide-like expression is differentially regulated among the cells. We have found a possible neuromodulatory role for the related peptide FLRFamide (Phe-Leu-Arg-Phe-NH2). In an egg-laying assay, FLRFamide by itself was not active but could potentiate a serotonin effect. The FMRFamide-like immunoreactivity was also used as a marker to examine the differentiation of cells that normally undergo programmed cell death. Cells that are destined to die in the Pn.a lineages appear to differentiate and adopt the fate of lineally equivalent cells before cell death.

Immunocytochemical distribution of FMRFamide-like substance in the brain of the cloudy dogfish, Scyliorhinus torazame

The distribution of the molluscan cardioexcitatory tetrapeptide FMRFamide (Phe-Met-Arg-Phe-NH2) in the brain of the cloudy dogfish, Scyliorhinus torazame, was examined by immunocytochemistry. FMRFamide-like immunoreactivity was demonstrated to occur extensively in various regions of the dogfish brain, except for the corpus cerebelli. Immunoreactive neuronal perikarya were located in the ganglion of the nervus terminalis, the preoptic area, and the hypothalamic periventricular gray matter consisting of the nucleus medius hypothalamicus, the nucleus lateralis tuberis, and the nucleus lobi lateralis. Some of the immunoreactive cells in the hypothalamus were identified as cerebrospinal fluid-contacting neurons. The bulk of the immunostained fibers in the nervus terminalis penetrated into the midventral portion of the telencephalon and ran dorsocaudally toward the basal telencephalon and hypothalamus, showing radial projections or ramifications. The labeled fibers were abundant in the midbasal part of the telencephalon and in the hypothalamus, where some fibers were found in loose networks around the cell bodies of the nucleus septi and hypothalamic periventricular nuclei. The fibers demonstrated in the hypothalamus terminated around the vascular wall of the primary capillary plexus of the median eminence or penetrated deeply into the pars intermedia of the hypophysis. These results suggest that, in the dogfish, an FMRFamide-like substance participates in the regulation of adenohypophysial function. This molecule may have a role as a neurotransmitter and/or neuromodulator in the central nervous system.

The SALMFamides: a new family of neuropeptides isolated from an echinoderm

We have isolated two novel related neuropeptides from the radial nerve cords of the starfishes Asterias rubens and Asterias forbesi. One is an octapeptide with the amino acid sequence Gly-Phe-Asn-Ser-Ala-Leu-Met-Phe-NH2 and the other is a dodecapeptide with the amino acid sequence Ser-Gly-Pro-Tyr-Ser-Phe-Asn-Ser-Gly-Leu-Thr-Phe-NH2. The peptides were purified using high performance liquid chromatography (HPLC) and a radioimmunoassay for the molluscan FMRFamide-related neuropeptide, pQDPFLRFamide. Both peptides share minimal sequence identity with members of the family of FMRFamide-like peptides so we have designated them as founder members of a new family, the SALMFamides. We refer to the octapeptide as SALMFamide 1 (S1) and the dodecapeptide as SALMFamide 2 (S2). S1 and S2 are the first neuropeptides identified in species belonging to the phylum Echinodermata.

Serotonin-immunoreactive neurons in the cnidarian Renilla koellikeri

The cellular localization of 5-hydroxytryptamine (5-HT) was investigated in the pennatulid anthozoan Renilla koellikeri by means of peroxidase-antiperoxidase-immunohistochemistry with an antiserum against 5-HT-formaldehyde-protein conjugate. In many colonies, strong 5-HT-immunoreactivity was displayed by the cell bodies and beaded processes of relatively small neuronlike elements predominating in the outer ectoderm or scattered in the underlying mesoglea. The immunostained neurons of the mesoglea were generally bipolar and their relatively short processes extended toward myoepithelial cells. In the ectoderm, most immunostained neurons appeared pseudounipolar. These cell bodies were endowed with a small, superficially directed, conical appendage reaching the outer surface of the epithelium. Their neurites emerged from the inner pole of the perikarya and branched toward other immunopositive ectodermal and mesogleal nerve cells, or nematocytes in the tentacles. The networklike distribution of the presumed 5-HT ectodermal neurons varied between the different regions of colonies and along the autozooid column. In the context of earlier observations in cnidarians, these cytological features suggest a sensory as well as a modulatory function for 5-HT in Renilla koellikeri.

Distribution of FMRFamide-like immunoreactivity in the central nervous system of the Formosan monkey (Macaca cyclopsis)

The distribution of FMRFamide-like immunoreactivity in the central nervous system of the Formosan monkey (Macaca cyclopsis) was investigated employing immunohistochemical techniques. FMRFamide-containing cells were found to be widely distributed throughout the forebrain. Principal densities of FMRFamide neuronal perikarya were observed in the following areas: the amygdaloid complex, the olfactory tubercle, the cerebral cortex, the basal ganglia, the septum, the caudate-putamen and the arcuate nucleus. A large number of immunoreactive fibers were observed in areas ranging from the cerebral cortex to the spinal cord, and were noted in the following locations: the preoptic area, the tuberal and posterior hypothalamic areas, the bed nucleus of the stria terminalis, the nuclei of the spinal trigeminal nerve, the hypoglossal nucleus, the nucleus of the solitary tract, and the dorsal horn of the spinal cord. The results generally parallel those described in the rat and guinea pig.

Ultrastructural localization of RFamide-like peptides in neuronal dense-cored vesicles in the peduncle of Hydra

The presence of Arg-Phe-amide (RFamide)-like peptides in dense-cored vesicles in neurons of the peduncle of Hydra was demonstrated by immunogold electron microscopy. Thin sections of Lowicryl-embedded tissue labeled with antisera to RFamide and 5-nm gold-conjugated, secondary antibody and of Epon-Araldite-embedded tissue labeled with 15-nm gold particles revealed a concentration of RFamide-like immunoreactivity over the granular cores of vesicles in epidermal ganglion cells. Gold-labeled, dense-cored vesicles were present in the perikaryon, long thin neurites, and axon terminals of these neurons. The aggregation of labeled dense-cored vesicles in an axon terminal on the myoneme of an epitheliomuscular cell suggests a possible function of RFamide-like peptides in neuromuscular transmission. Gold staining of dense-cored vesicles completely disappeared when the RFamide antiserum was preabsorbed with 10 micrograms/ml RFamide. These results are the first demonstration that the dense-cored vesicles of Hydra neurons contain a neuropeptide.

Plasticity in the nervous system of adult hydra. II. Conversion of ganglion cells of the body column into epidermal sensory cells of the hypostome

Due to the tissue dynamics of hydra, every neuron is constantly changing its location within the animal. At the same time specific subsets of neurons defined by morphological or immunological criteria maintain their particular spatial distributions, suggesting that neurons switch their phenotype as they change their location. A position-dependent switch in neuropeptide expression has been demonstrated. The possibility that ganglion cells of the body column are converted into epidermal sensory cells of the head was examined using a monoclonal antibody, TS33, whose binding is restricted to a subset of epidermal sensory cells of the hypostome, the apical end of the head. When animals devoid of interstitial cells, which are the nerve cell precursors, were decapitated and allowed to regenerate, they formed TS33+ epidermal sensory cells. As this latter cell type is not found in the body column, and the interstitial cell-free animals contained only epithelial cells and ganglion cells in the part of the ectoderm that formed the head during regeneration, the TS33+ epidermal sensory cells most likely arose from the TS33- ganglion cells. The observation of epidermal sensory cells labeled with both TS33 and TS26, a monoclonal antibody that binds to ganglion cells, in regenerating and normal heads provides further support. The double-labeled cells are probably in transition from a ganglion cell to an epidermal sensory cell. These results provide a second example of position-dependent changes in neuron phenotype, and suggest that the differentiated state of a neuron in hydra is only metastable with regard to phenotype.

Coexistence of FMRFamide, met-enkephalin and serotonin in molluscan neurons

1. Coexistence of FMRFamide, met-enkephalin and serotonin immunoreactivities was examined in Achatina fulica and Aplysia kurodai. 2. Coexistence of FMRFamide and serotonin was found in some neurons of the visceral, right parietal and pedal ganglia of Achatina fulica, and in the pedal ganglion of Aplysia kurodai. 3. In Achatina fulica, coexistence of FMRFamide and met-enkephalin was found in a neuron of the left parietal ganglion and that of met-enkephalin and serotonin was found in a giant neuron of the right parietal ganglion. 4. Based on these results, the biological significance of coexistence was discussed.

Dynamics of FMRFamide immunoreactivity in response to physiologically active substances in the central nervous system of the snail, Achatina fulica

1. The changes in FMRFamide (Phe-Met-Arg-Phe-NH2) immunoreactivity in response to incubation in dopamine, serotonin, met-enkephalin, oxytocin, arg-vasopressin and FMRFamide were examined in the central nervous system of the snail, Achatina fulica. 2. When the central nervous system was cultured in medium which contained dopamine and in medium which contained serotonin, the number of immunoreactive neurons increased in the anterior part of the cerebral ganglion and decreased in the sub-esophageal ganglion. 3. When arg-vasopressin was added to the culture medium, the number of immunoreactive neurons increased in the pedal ganglion and decreased in the other sub-esophageal ganglion. 4. By contrast, when the central nervous system was cultured in medium which contained oxytocin, the number of immunoreactive neurons did not increase, but rather decreased, in each ganglion. 5. No changes in immunoreactivity were detected in the central nervous system when it was cultured in medium which contained FMRFamide. 6. It appears, from these results, that the production and release of FMRFamide from different neurons are differentially affected by the physiologically active substances tested.

Immunocytochemical localization of regulatory peptides in six species of trematode parasites

1. Frozen and paraffin sections of six species of trematodes: Schistosoma mansoni, S. mattheei, S. japonicum, Schistosomatium douthitti, Echinostoma paraensei and Fasciola hepatica have been incubated with antisera against leu-enkephalin, FMRF-amide, gastrin-17, luteinizing hormone releasing hormone, neurotensin, oxytocin, prolactin, substance P, thyroid stimulating hormone and cholecystokinin, using indirect immunofluorescence and biotin-avidin horseradish peroxidase detection systems. 2. Of the ten antisera tested, six (leu-enkephalin, FMRF-amide, gastrin-17, luteinizing hormone releasing hormone, substance P and cholecystokinin) showed significant immunoreactivity, primarily in the central and peripheral nervous system, and also perhaps in the osmoregulatory system of the three species of Schistosoma. 3. Immunopositive nerve fibers extended from ganglia to gut wall, uterus and vitelline follicles, and especially from subtegumental nerve plexi to sensory receptors on the surface or in dorsal nippled tubercles.

Purification and characterization of FMRFamidelike immunoreactive substances from the lobster nervous system: isolation and sequence analysis of two closely related peptides

In the preceding paper (Kobierski et al: J. Comp. Neurol. 266:1-15, '87) FMRFamidelike immunoreactivity (FLI) was localized to specific cells and processes in the nervous system of the lobster Homarus americanus. In an effort to establish a role for this material we have purified and characterized a variety of immunoreactive peptides that can be extracted from the secretory pericardial organs. By using gel-filtration chromatography and three different HPLC systems, it has been established that little or no authentic FMRFamide is present. Of the major immunoreactive components two peptides were purified in sufficient quantity for microsequence analysis and have been tentatively identified as the octapeptides Ser-Asp-Arg-Asn-Phe-Leu-Arg-Phe-amide (FLI 3) and Thr-Asn-Arg-Asn-Phe-Leu-Arg-Phe-amide (FLI 4). Both of these are novel neuropeptides with some sequence homology to the previously described FMRFamide family. The pericardial organs release FLI when depolarized with 100 mM K+ in the presence of calcium. Between 75 and 80% of this release is accounted for by FLI 3 and FLI 4. One of these peptides (FLI 4) has been synthesized and shown to cochromatograph with the endogenous immunoreactive material. Preliminary studies show that this peptide can act as a modulator of exoskeletal and cardiac neuromuscular junctions.

Distribution and partial characterization of FMRFamide-like peptides in the stomatogastric nervous systems of the rock crab, Cancer borealis, and the spiny lobster, Panulirus interruptus

The distribution of FMRFamide-like peptides was studied in the complete stomatogastric nervous system [the paired commissural ganglia, single oesophageal ganglion, and the single stomatogastric ganglion (STG)] of two decapod crustacean species, the spiny lobster Panulirus interruptus and the rock crab Cancer borealis, by using immunocytochemical techniques. Antiserum 231 from the O'Donohue laboratory and antiserum 671C (described here) gave essentially the same staining patterns. In the commissural ganglia of both species there were ten to 20 stained neurons and dense neuropilar staining. The oesophageal ganglion of the crab had four stained neurons. Lucifer Yellow backfills followed by immunostaining showed that the two larger stained neurons of the oesophageal ganglion sent processes into the inferior ventricular nerve. The two smaller neurons sent processes into the inferior oesophageal nerves. The oesophageal ganglion of the lobster had two stained neurons that sent processes into the inferior ventricular nerve as well. None of the somata of the STG stained in either species, but in both species stained fibers were seen in the stomatogastric nerve that entered the STGs and ramified profusely throughout the neuropil. In some preparations of the crab, a stained fiber was visible in the dorsal ventricular nerve. The amounts of the FMRFamide-like peptides found in all regions of the nervous system of P. interruptus and C. borealis were determined by radioimmune assay (RIA). Column chromatography and high-performance liquid chromatography suggest that, in both species, much if not all of the RIA-assayable material is accountable for by peptides that are larger and more hydrophobic than FMRFamide.

Phe-Met-Arg-Phe-amide (FMRFamide) stimulated growth hormone secretion in conscious OVX rats

The presence of FMRFamide (Phe-Met-Arg-Phe-amide)-like immunoreactivity in neuronal elements in the hypothalamus suggested a role for this in the hypothalamic control of the anterior pituitary function. We report here the action of FMRFamide on growth hormone release following intracerebroventricular administration to rats. The injection of 200 ng (313.8 picomoles) of FMRFamide (in 2 ul) produced a significantly increased plasma GH 15 min after injection. The GH-increasing effect of 400-800 ng (627-1255 picomoles) of FMRFamide was already developed after 5 min and lasted up to 30 min. No change was detected in the plasma FSH, LH and prolactin levels at any time during the experimental period. The intravenous administration of 10, 30 or 100 ug of FMRFamide had no effect on the plasma GH level. We conclude that FMRFamide can act at low doses to increase GH release through the inhibition of somatostatin release or the stimulation of GRF. We could not exclude a direct site of action in the pituitaries.

Isolation of pyroGlu-Gly-Arg-Phe-NH2 (Antho-RFamide), a neuropeptide from sea anemones

A radioimmunoassay has been developed for peptides containing the carboxyl-terminal sequence Arg-Phe-NH2 (RFamide). Using this radioimmunoassay and applying cation-exchange chromatography and HPLC, we have isolated an RFamide peptide from acetic acid extracts of the sea anemone Anthopleura elegantissima. Three different methods established that the structure of the Anthopleura RFamide peptide (Antho-RFamide) is pyroGlu-Gly-Arg-Phe-NH2. Comparison of synthetic and natural Antho-RFamide and their enzymatic breakdown products on six different HPLC columns confirmed the structure of the sea anemone peptide. Using synthetic Antho-RFamide as a standard in our radioimmunoassay, we measured high concentrations (3.2 nmol/g wet weight) of this peptide in extracts of Anthopleura. It is proposed that Antho-RFamide is a transmitter at neuromuscular synapses in sea anemones.

Plasticity in the nervous system of adult hydra. I. The position-dependent expression of FMRFamide-like immunoreactivity

The plasticity of nerve cells expressing the neuropeptide FMRFamide was examined in adult hydra. Using a whole-mount technique with indirect immunofluorescence, the spatial pattern of neurons showing FMRFamide-like immunoreactivity (FLI) was visualized. These neurons were located in the tentacles, hypostome, and peduncle, but not in the body column or basal disc. Since every neuron in the nerve net is continuously displaced toward an extremity and eventually sloughed, the constant pattern of FLI+ neurons could arise in one of two ways. When displaced into the appropriate region, FLI- neurons are converted to FLI+ neurons, or FLI+ neurons arise by differentiation from interstitial cells. To distinguish between these two possibilities, interstitial cells, the multipotent precursors of the nerve cells, were eliminated by treatment with hydroxyurea or nitrogen mustard. Following head, or foot and peduncle, removal from these animals, the missing structures regenerated. The spatial pattern of FLI+ neurons reappeared in the newly regenerated head or peduncle. This shows FLI- neurons in the body column were converted to FLI+ when their position was changed to the head or the peduncle. When the peduncle was grafted into the body column, it was converted to basal disc or body column tissue, and FLI disappeared. The appearance and loss of FLI was always position dependent. These results indicate that the neurons in the mature nerve net can change their neuropeptide phenotype in response to changes in their position.

Use of a monoclonal antibody to classify neurons isolated from the head region of Hydra

A mouse monoclonal antibody (JD1) to Hydra attenuata using the peroxidase-antiperoxidase (PAP) method revealed unipolar, bipolar, and multipolar sensory and ganglion cells in the head region of H. littoralis. Neurons isolated from macerated hypostomes and tentacles were classified according to the number of their cytoplasmic processes and the position of the cilium, when present, relative to the perikaryon. PAP-stained sensory cells had an apical ciliary cone, whereas ganglion cells did not. Neurons with cytoplasmic processes longer than 50 microns stained faintly, whereas those with processes shorter than 50 microns in length stained mainly dense brown. Unipolar neurons had an oval, crescent, round, or elliptic perikaryon with a single short axon. The perikaryal shape of bipolar neurons varied from round to tall triangular, short triangular, crescent, oval, or elliptic with two oppositely directed symmetric or asymmetric processes. Asymmetric processes were present in a bipolar sensory cell with a long apical cilium typical of gastrodermal sensory cells. One type of bipolar ganglion cell had a short perikaryal cilium. Another type had neurites longer than 50 microns. We found seven morphological variations of multipolar neurons, including one with an apical knob, two with a short perikaryal cilium, two with cytoplasmic loops near the perikaryon, one with perpendicular processes projecting from the major neurites, and one with a branched process longer than 50 microns opposite a tangled mass of neurites.

Nerve cells in hydra: monoclonal antibodies identify two lineages with distinct mechanisms for their incorporation into head tissue

The relationship between populations of nerve cells defined by two monoclonal antibodies was investigated in Hydra oligactis. A population of sensory nerve cells localized in the head (hypostome and tentacles) is identified by the binding of antibody JD1. A second antibody, RC9, binds ganglion cells throughout the animal. When the nerve cell precursors, the interstitial cells, are depleted by treatment with hydroxyurea or nitrogen mustard, the JD1+ nerve cells are lost as epithelial tissue is sloughed at the extremities. In contrast, RC9+ nerve cells remain present in all regions of the animal following treatment with either drug. When such hydra are decapitated to initiate head regeneration, the new head tissue formed is again free of JD1+ sensory cells but does contain RC9+ ganglion cells. Our studies indicate that (1) nerve cells are passively displaced with the epithelial tissue in hydra, (2) JD1+ sensory cells do not arise by the conversion of body column nerve cells that are displaced into the head, whereas RC9+ head nerve cells can originate in the body column, (3) formation of new JD1+ sensory cells requires interstitial cell differentiation. We conclude from these results that the two populations defined by these antibodies are incorporated into the h ad via different developmental pathways and, therefore, constitute distinct nerve cell lineages.

Identification of Aplysia neurons containing immunoreactive FMRFamide

Electrophysiological and immunocytochemical techniques were used in the abdominal ganglion of Aplysia to identify neurons containing immunoreactive FMRFamide. Large numbers of neurons were immunoreactive for FMRFamide, including R2, L2, L3, L4, L5, L6, 2 cells tentatively identified as L12 and L13, and a previously unidentified cluster on the ventral surface of the right lower quadrant. There was also heavy labelling of fibers, often with beaded varicosities, throughout the neuropil, the cell layers, and the sheath overlying the ganglion. This data provides further evidence that FMRFamide is an important neurotransmitter in Aplysia. The demonstration of immunoreactive FMRFamide in the giant cholinergic neurons R2 and LP1(1) suggests that these well-studied and experimentally convenient cells use acetylcholine and an FMRFamide-like peptide as cotransmitters.

Characterization of FMRF amide-like immunoreactivity in rat spinal cord by region-specific antibodies in radioimmunoassay and HPLC

Material in rat spinal cord extracts that reacts with antibodies to the molluscan tetrapeptide FMRF amide (Phe-Met-Arg-Phe-NH2) has been characterized by HPLC and radioimmunoassay using region specific antibodies. An antibody to the N-terminally extended analogue, Tyr-Gly-Gly-Phe-Met-Arg-Phe-NH2 (YGGFMRF amide), did not react with the rat material. Two antibodies to FMRF amide were characterized that differed markedly in their affinities for analogues with substitutions in the second and third positions from the C-terminus; both required the C-terminal amide, and neither showed appreciable sensitivity to substitutions in the fourth position from the C-terminus. With both antibodies the relative potency of the avian brain peptide, LPLRF amide, was about 0.1. Both antibodies revealed similar concentrations of immunoreactive material in rat spinal cord extracts. On reversed-phase HPLC using Techsil C18 and Spherisorb-phenyl columns, two peaks were separated that could be distinguished in retention times from FMRF amide, Leu-Pro-Leu-Arg-Phe-NH2 (LPLRF amide), and YGGFMRF amide. The results suggest that the rat spinal cord peptides are structurally related to the C-terminal tripeptide of FMRF amide and are probably extended at the N-terminus by sequences immunochemically distinct from other known peptides.