Parasites flicking the NPY gene on the host's switchboard: why NPY?

NPF activates a specific NPF receptor and regulates food intake in Pacific abalone Haliotis discus hannai

Neuropeptides function through G protein-coupled receptors (GPCRs) with high specificity, implying a significant degree of neuropeptide-GPCR coevolution. However, potential neuropeptide signaling systems in non-chordates are relatively elusive. We determined the specificity of the neuropeptide F (Hdh-NPF) signaling system with a cognate receptor (Hdh-NPFR) in the Pacific abalone, Haliotis discus hannai. Phylogenetic and exon–intron arrangement analyses of bilaterian NPF and the chordate ortholog NPY with their receptor sequences revealed a likely common ancestor, and Hdh-NPFR was similar to the NPYR2 subtype among the NPYR1, NPYR2, and NPYR5 subtypes. Among four Hdh-NPFR-related receptors, Hdh-NPFR specifically responded to Hdh-NPF peptide, supported by the dose–response luciferase reporter curve, intracellular Ca²⁺ mobilization, and phosphorylation of ERK1/2 and its inhibition with a protein kinase C inhibitor. Peptide fragmentations and shuffling of Hdh-NPF with human NPY could not activate the cellular response of Hdh-NPFR. Three-dimensional in silico modeling suggested that interaction of Hdh-NPF C-terminal amino acids with the extracellular loops of Hdh-NPFR is critical for Hdh-NPFR activation. In vivo injection of Hdh-NPF peptide increased food consumption, and knockdown of Hdh-NPF expression decreased food consumption in Pacific abalone. These findings provide evidence for co-evolution of the NPF/Y ligand-receptor system, enabling further research on mollusk orexigenic neuropeptides.

Comparative neuroanatomical distribution and expression levels of neuropeptide F in the central nervous system of the female freshwater prawn, Macrobrachium rosenbergii, during the ovarian cycle

Neuropeptide F (NPF) plays critical roles in controlling the feeding and reproduction of prawns. In the present study, we investigated changes in the expression levels of Macrobrachium rosenbergii neuropeptide F (MrNPF), and its neuroanatomical distribution in eyestalk (ES), brain (BR), subesophageal ganglion (SEG), thoracic ganglia (TG), and abdominal ganglia (AG), during the ovarian cycle of female prawn. By qRT-PCR, the amount of MrNPF transcripts exhibited a gradual increase in the ES, BR, and combined SEG and TG from stages I and II, to reach a maximum level at stage III, and slightly declined at stage IV, respectively. The highest to lowest expression levels were detected in combined SEG and TG, BR, ES, and AG, respectively. MrNPF immunolabeling was observed in several neuronal clusters, associated fibers, and neuropils of these central nervous system (CNS) tissues. MrNPF-ir was more intense in neurons and neuropils of SEG and TG than those found in other parts of the CNS. The number of MrNPF-ir neurons and intensity of MrNPF-ir were higher in the ES, BR, SEG, and TG at the late stages than those at the early stages of the ovarian cycle, while those in AG exhibited insignificant change. Taken together, there is a correlation between changes in the neuroanatomical distribution of MrNPF and stages of the ovarian cycle, implying that MrNPF may be an important neuropeptide that integrates sensory stimuli, including photo-, chemo-, and gustatory receptions, to control feeding and reproduction, particularly ovarian development, of this female prawn, M. rosenbergii.

Identification and localization of a gonadotropin-releasing hormone-related neuropeptide in Biomphalaria, an intermediate host for schistosomiasis

Freshwater snails of the genus Biomphalaria serve as obligatory hosts for the digenetic trematode Schistosoma mansoni, the causative agent for the most widespread form of intestinal schistosomiasis. Within Biomphalaria, S. mansoni larvae multiply and transform into the cercariae form that can infect humans. Trematode development and proliferation is thought to be facilitated by modifications of host behavior and physiological processes, including a reduction of reproduction known as "parasitic castration." As neuropeptides participate in the control of reproduction across phylogeny, a neural transcriptomics approach was undertaken to identify peptides that could regulate Biomphalaria reproductive physiology. The present study identified a transcript in Biomphalaria alexandrina that encodes a peptide belonging to the gonadotropin-releasing hormone (GnRH) superfamily. The precursor and the predicted mature peptide, pQIHFTPDWGNN-NH₂ (designated Biom-GnRH), share features with peptides identified in other molluscan species, including panpulmonates, opisthobranchs, and cephalopods. An antibody generated against Biom-GnRH labeled neurons in the cerebral, pedal, and visceral ganglia of Biomphalaria glabrata. GnRH-like immunoreactive fiber systems projected to all central ganglia. In the periphery, immunoreactive material was detected in the ovotestis, oviduct, albumen gland, and nidamental gland. As these structures serve crucial roles in the production, transport, nourishment, and encapsulation of eggs, disruption of the GnRH system of Biomphalaria could contribute to reduced reproductive activity in infected snails.

The unlimited potential of the great pond snail, Lymnaea stagnalis

Only a limited number of animal species lend themselves to becoming model organisms in multiple biological disciplines: one of these is the great pond snail, Lymnaea stagnalis. Extensively used since the 1970s to study fundamental mechanisms in neurobiology, the value of this freshwater snail has been also recognised in fields as diverse as host-parasite interactions, ecotoxicology, evolution, genome editing and 'omics', and human disease modelling. While there is knowledge about the natural history of this species, what is currently lacking is an integration of findings from the laboratory and the field. With this in mind, this article aims to summarise the applicability of L. stagnalis and points out that this multipurpose model organism is an excellent, contemporary choice for addressing a large range of different biological questions, problems and phenomena.

Corazonin signaling integrates energy homeostasis and lunar phase to regulate aspects of growth and sexual maturation in Platynereis

Gonadotropin Releasing Hormone (GnRH) acts as a key regulator of sexual maturation in vertebrates, and is required for the integration of environmental stimuli to orchestrate breeding cycles. Whether this integrative function is conserved across phyla remains unclear. We characterized GnRH-type signaling systems in the marine worm Platynereis dumerilii, in which both metabolic state and lunar cycle regulate reproduction. We find gnrh-like (gnrhl) genes upregulated in sexually mature animals, after feeding, and in specific lunar phases. Animals in which the corazonin1/gnrhl1 gene has been disabled exhibit delays in growth, regeneration, and maturation. Molecular analyses reveal glycoprotein turnover/energy homeostasis as targets of CRZ1/GnRHL1. These findings point at an ancestral role of GnRH superfamily signaling in coordinating energy demands dictated by environmental and developmental cues.

The molecular mechanisms by which animals integrate external stimuli with internal energy balance to regulate major developmental and reproductive events still remain enigmatic. We investigated this aspect in the marine bristleworm, Platynereis dumerilii, a species where sexual maturation is tightly regulated by both metabolic state and lunar cycle. Our specific focus was on ligands and receptors of the gonadotropin-releasing hormone (GnRH) superfamily. Members of this superfamily are key in triggering sexual maturation in vertebrates but also regulate reproductive processes and energy homeostasis in invertebrates. Here we show that 3 of the 4 gnrh-like (gnrhl) preprohormone genes are expressed in specific and distinct neuronal clusters in the Platynereis brain. Moreover, ligand–receptor interaction analyses reveal a single Platynereis corazonin receptor (CrzR) to be activated by CRZ1/GnRHL1, CRZ2/GnRHL2, and GnRHL3 (previously classified as AKH1), whereas 2 AKH-type hormone receptors (GnRHR1/AKHR1 and GnRHR2/AKHR2) respond only to a single ligand (GnRH2/GnRHL4). Crz1/gnrhl1 exhibits a particularly strong up-regulation in sexually mature animals, after feeding, and in specific lunar phases. Homozygous crz1/gnrhl1 knockout animals exhibit a significant delay in maturation, reduced growth, and attenuated regeneration. Through a combination of proteomics and gene expression analysis, we identify enzymes involved in carbohydrate metabolism as transcriptional targets of CRZ1/GnRHL1 signaling. Our data suggest that Platynereis CRZ1/GnRHL1 coordinates glycoprotein turnover and energy homeostasis with growth and sexual maturation, integrating both metabolic and developmental demands with the worm’s monthly cycle.

Neural Ganglia Transcriptome and Peptidome Associated with Sexual Maturation in Female Pacific Abalone (Haliotis discus hannai)

Genetic information of reproduction and growth is essential for sustainable molluscan fisheries and aquaculture management. However, there is limited knowledge regarding the reproductive activity of the commercially important Pacific abalone Haliotisdiscushannai. We performed de novo transcriptome sequencing of the ganglia in sexually immature and mature female Pacific abalone to better understand the sexual maturation process and the underlying molecular mechanisms. Of the ~305 million high-quality clean reads, 76,684 transcripts were de novo-assembled with an average length of 741 bp, 28.54% of which were annotated and classified according to Gene Ontology terms. There were 256 differentially expressed genes between the immature and mature abalone. Tandem mass spectrometry analysis, as compared to the predicted-peptide database of abalone ganglia transcriptome unigenes, identified 42 neuropeptide precursors, including 29 validated by peptidomic analyses. Label-free quantification revealed differential occurrences of 18 neuropeptide families between immature and mature abalone, including achatin, FMRFamide, crustacean cardioactive peptide, and pedal peptide A and B that were significantly more frequent at the mature stage. These results represent the first significant contribution to both maturation-related transcriptomic and peptidomic resources of the Pacific abalone ganglia and provide insight into the roles of various neuropeptides in reproductive regulation in marine gastropods.

Identification and Characterization of Neuropeptides by Transcriptome and Proteome Analyses in a Bivalve Mollusc Patinopecten yessoensis

Neuropeptides play essential roles in regulation of reproduction and growth in marine molluscs. But their function in marine bivalves – a group of animals of commercial importance – is largely unexplored due to the lack of systematic identification of these molecules. In this study, we sequenced and analyzed the transcriptome of nerve ganglia of Yesso scallop Patinopecten yessoensis, from which 63 neuropeptide genes were identified based on BLAST and de novo prediction approaches, and 31 were confirmed by proteomic analysis using the liquid chromatography-tandem mass spectrometry (LC-MS/MS). Fifty genes encode known neuropeptide precursors, of which 20 commonly exist in bilaterians and 30 are protostome specific. Three neuropeptides that have not yet been reported in bivalves were identified, including calcitonin/DH31, lymnokinin and pleurin. Characterization of glycoprotein hormones, insulin-like peptides, allatostatins, RFamides, and some reproduction, cardioactivity or feeding related neuropeptides reveals scallop neuropeptides have conserved molluscan neuropeptide domains, but some (e.g., GPB5, APGWamide and ELH) are characterized with bivalve-specific features. Thirteen potentially novel neuropeptides were identified, including 10 that may also exist in other protostomes, and 3 (GNamide, LRYamide, and Vamide) that may be scallop specific. In addition, we found neuropeptides potentially related to scallop shell growth and eye functioning. This study represents the first comprehensive identification of neuropeptides in scallop, and would contribute to a complete understanding on the roles of various neuropeptides in endocrine regulation in bivalve molluscs.

Role of neuropeptide F in regulating filter feeding of Manila clam, Ruditapes philippinarum

Endogenous signals which may be involved in the regulation of filter feeding in bivalves have never been examined. NPY/NPF homologue has been proved to play an important role in the regulation of food intake in vertebrate and several invertebrates. In this study, a NPF homologue was cloned from visceral ganglia of clam Ruditapes philippinarum. The full-length cDNA sequence was 892bp in length and encoded a precursor of 82 amino acid residues. We then examined the effects of fasting and refeeding on the filtration rates (FR), plasma glucose concentration (PGC), 5-HT, DA and the expression level of the rp-NPF and insulin transcript. The mRNA expression level of rp-NPF in visceral ganglion was increased during fasting, and rose to highest level on 72h after starvation and declined immediately after food had been supplied. Hemocoel injection of rp-NPF(5μg/g)significantly increased FR of clams within 2h. Compared to the controls, a significant increase in insulin mRNA levels was observed at 8h after injection. Contents of 5-HT and DA also increased in the 5μg/grp-NPF administrated clams at 8 and 24h after injection. These results suggest that, similar to vertebrates, NPF, insulin, 5-HT and DA may play a role in the regulation of feeding in R. philippinarum.

The red imported fire ant (Solenopsis invicta Buren) kept Y not F: predicted sNPY endogenous ligands deorphanize the short NPF (sNPF) receptor

Neuropeptides and their receptors play vital roles in controlling the physiology and behavior of animals. Short neuropeptide F (sNPF) signaling regulates several physiological processes in insects such as feeding, locomotion, circadian rhythm and reproduction, among others. Previously, the red imported fire ant (Solenopsis invicta) sNPF receptor (S. invicta sNPFR), a G protein-coupled receptor, was immunolocalized in queen and worker brain and queen ovaries. Differential distribution patterns of S. invicta sNPFR protein in fire ant worker brain were associated both with worker subcastes and with presence or absence of brood in the colony. However, the cognate ligand for this sNPFR has not been characterized and attempts to deorphanize the receptor with sNPF peptides from other insect species which ended in the canonical sequence LRLRFamide, failed. Receptor deorphanization is an important step to understand the neuropeptide receptor downstream signaling cascade. We cloned the full length cDNA of the putative S. invicta sNPF prepropeptide and identified the putative “sNPF” ligand within its sequence. The peptide ends with an amidated Tyr residue whereas in other insect species sNPFs have an amidated Phe or Trp residue at the C-terminus. We stably expressed the HA-tagged S. invicta sNPFR in CHO-K1 cells. Two S. invicta sNPFs differing at their N-terminus were synthesized that equally activated the sNPFR, SLRSALAAGHLRYa (EC₅₀ = 3.2 nM) and SALAAGHLRYa (EC₅₀ = 8.6 nM). Both peptides decreased the intracellular cAMP concentration, indicating signaling through the G_αi-subunit. The receptor was not activated by sNPF peptides from other insect species, honey bee long NPF (NPY) or mammalian PYY. Further, a synthesized peptide otherwise identical to the fire ant sequence but in which the C-terminal amidated amino acid residue ‘Y’ was switched to ‘F’, failed to activate the sNPFR. This discovery will now allow us to investigate the function of sNPY and its cognate receptor in fire ant biology.

Diversity of the RFamide Peptide Family in Mollusks

Since the initial characterization of the cardioexcitatory peptide FMRFamide in the bivalve mollusk Macrocallista nimbosa, a great number of FMRFamide-like peptides (FLPs) have been identified in mollusks. FLPs were initially isolated and molecularly characterized in model mollusks using biochemical methods. The development of recombinant technologies and, more recently, of genomics has boosted knowledge on their diversity in various mollusk classes. Today, mollusk FLPs represent approximately 75 distinct RFamide peptides that appear to result from the expression of only five genes: the FMRFamide-related peptide gene, the LFRFamide gene, the luqin gene, the neuropeptide F gene, and the cholecystokinin/sulfakinin gene. FLPs display a complex spatiotemporal pattern of expression in the central and peripheral nervous system. Working as neurotransmitters, neuromodulators, or neurohormones, FLPs are involved in the control of a great variety of biological and physiological processes including cardiovascular regulation, osmoregulation, reproduction, digestion, and feeding behavior. From an evolutionary viewpoint, the major challenge will then logically concern the elucidation of the FLP repertoire of orphan mollusk classes and the way they are functionally related. In this respect, deciphering FLP signaling pathways by characterizing the specific receptors these peptides bind remains another exciting objective.

Development of a Pacific oyster (Crassostrea gigas) 31,918-feature microarray: identification of reference genes and tissue-enriched expression patterns

BACKGROUND

Research using the Pacific oyster Crassostrea gigas as a model organism has experienced rapid growth in recent years due to the development of high-throughput molecular technologies. As many as 56,268 EST sequences have been sequenced to date, representing a genome-wide resource that can be used for transcriptomic investigations.

RESULTS

In this paper, we developed a Pacific oyster microarray containing oligonucleotides representing 31,918 transcribed sequences selected from the publicly accessible GigasDatabase. This newly designed microarray was used to study the transcriptome of male and female gonads, mantle, gills, posterior adductor muscle, visceral ganglia, hemocytes, labial palps and digestive gland. Statistical analyses identified genes differentially expressed among tissues and clusters of tissue-enriched genes. These genes reflect major tissue-specific functions at the molecular level, such as tissue formation in the mantle, filtering in the gills and labial palps, and reproduction in the gonads. Hierarchical clustering predicted the involvement of unannotated genes in specific functional pathways such as the insulin/NPY pathway, an important pathway under study in our model species. Microarray data also accurately identified reference genes whose mRNA level appeared stable across all the analyzed tissues. Adp-ribosylation factor 1 (arf1) appeared to be the most robust reference for normalizing gene expression data across different tissues and is therefore proposed as a relevant reference gene for further gene expression analysis in the Pacific oyster.

CONCLUSIONS

This study provides a new transcriptomic tool for studies of oyster biology, which will help in the annotation of its genome and which identifies candidate reference genes for gene expression analysis.

A comparative review of short and long neuropeptide F signaling in invertebrates: Any similarities to vertebrate neuropeptide Y signaling?

Neuropeptides referred to as neuropeptide F (NPF) and short neuropeptide F (sNPF) have been identified in numerous invertebrate species. Sequence information has expanded tremendously due to recent genome sequencing and EST projects. Analysis of sequences of the peptides and prepropeptides strongly suggest that NPFs and sNPFs are not closely related. However, the NPFs are likely to be ancestrally related to the vertebrate family of neuropeptide Y (NPY) peptides. Peptide diversification may have been accomplished by different mechanisms in NPFs and sNPFs; in the former by gene duplications followed by diversification and in the sNPFs by internal duplications resulting in paracopies of peptides. We discuss the distribution and functions of NPFs and their receptors in several model invertebrates. Signaling with sNPF, however, has been investigated mainly in insects, especially in Drosophila. Both in invertebrates and in mammals NPF/NPY play roles in feeding, metabolism, reproduction and stress responses. Several other NPF functions have been studied in Drosophila that may be shared with mammals. In Drosophila sNPFs are widely distributed in numerous neurons of the CNS and some gut endocrines and their functions may be truly pleiotropic. Peptide distribution and experiments suggest roles of sNPF in feeding and growth, stress responses, modulation of locomotion and olfactory inputs, hormone release, as well as learning and memory. Available data indicate that NPF and sNPF signaling systems are distinct and not likely to play redundant roles.

Neurohormones and neuropeptides encoded by the genome of Lottia gigantea, with reference to other mollusks and insects

The Lottia gigantea genome was prospected for the presence of genes coding neuropeptides and neurohormones. Four genes code insulin-related peptides: two genes code molluscan insulin-like growth hormones, one gene an insulin very similar to vertebrate insulin, and the fourth a peptide related to drosophila insulin-like peptide 7. Four other genes encode the cysteine-knot proteins GPA2/GPB5 and bursicon/parabursicon. Another 37 genes code for precursors of the following neuropeptides: achatin, APGWamide, allatostatin C, allatotropin, buccalin (perhaps an allatostatin A homolog), cerebrin, CCAP, conopressin, elevenin (the predicted neuropeptide made by abdominal neuron 11 in Aplysia), egg laying hormone (two genes), enterin, feeding circuit activating neuropeptide (FCAP), FFamide, FMRFamide, GGNG, a GnRH-like peptide, the newly discovered LASGLVamide, LFRFamide, LFRYamide, LRNFVamide, luqin, lymnokinin, myomodulin (two genes), the newly discovered NKY, NPY, pedal peptide (three genes), PKYMDT, pleurin, PXFVamide, small cardioactive peptides, tachykinins (two genes) and WWamide (an allatostatin B homolog). One gene was found to encode FWISamide, while about 20 closely related genes were found to encode WWFamide. These small neuropeptides appear homologous to the NdWFamide, which contains d-Trp; these genes are similar to the Aplysia gene encoding NWFamide. Some of these peptides had not been previously identified from mollusks, such as the predicted hormones similar to Drosophila and vertebrate insulins, bursicon, the putative proctolin homolog PKYMDT and allatostatin C. Together with neuropeptides which are likely homologs of other insect neuropeptides, such as cerebrin and WWamide, this shows that despite significant differences the molluscan and arthropod neuropeptidomes are more similar than generally recognized.

LFRFamides: a novel family of parasitation-induced -RFamide neuropeptides that inhibit the activity of neuroendocrine cells in Lymnaea stagnalis

We report the characterization of a cDNA encoding a novel -RFamide neuropeptide precursor that is up-regulated during parasitation in the snail Lymnaea stagnalis. Processing of this precursor yields five structurally related neuropeptides, all but one ending with the C-terminal sequence -LFRFamide, as was confirmed by direct mass spectrometry of brain tissue. The LFRFamide gene is expressed in a small cluster of neurons in each buccal ganglion, three small clusters in each cerebral ganglion, and one cluster in each lateral lobe of the cerebral ganglia. Application of two of the LFRFamide peptides to neuroendocrine cells that control either growth and metabolism or reproduction induced similar hyperpolarizing K+-currents, and inhibited electrical activity. We conclude that up-regulation of inhibitory LFRFamide neuropeptides during parasitation probably reflects an evolutionary adaptation that allows endoparasites to suppress host metabolism and reproduction in order to fully exploit host energy recourses.

Morphological basis for coordination of growth and reproduction processes in the CNS of two terrestrial snails

The morphology of cells immunoreactive to an antibody against molluscan insulin-related peptide (MIP-IR) was studied in two species of terrestrial snail: Helix lucorum L. and Eobania vermiculata L. Immunocytochemical staining with this antibody to MIP revealed 100-130 cells in the postcerebrum, located in two clusters with common pathways in the dorsal body nerve and the cerebral artery nerve. About 75% of the MIP-IR cells were labeled by backfilling of the dorsal body nerve in Helix and Eobania; the corresponding figures for labeling by backfilling of the cerebral artery nerve were about 60% in Helix and 30% in Eobania. Upon intracellular staining of neurons of the dorsomedial postcerebrum, where most of the MIP-IR cells were located, it was found that they projected either in the dorsal body nerve or in the cerebral artery nerve or in both. The obtained data suggest that growth and reproduction processes (both functions were attributed to the insulin-related peptide-containing neurons) are regulated by the two, partially coinciding subsets of postcerebral MIP-IR neurons with different types of branching.

Neuropeptide F and its expression in the yellow fever mosquito, Aedes aegypti

A neuropeptide F (NPF) was isolated from an extract of adult Aedes aegypti mosquitoes based on its immunoreactivity in a radioimmunoassay for Drosophila NPF. After sequencing the peptide, cDNAs encoding the NPF were identified from head and midgut. These cDNAs encode a prepropeptide containing a 36 amino acid peptide with an amidated carboxyl terminus, and its sequence shows it to be a member of the neuropeptide F/Y superfamily. Immunocytochemistry and Northern blots confirmed that both the brain and midgut of females are likely sources of NPF, found at its highest hemolymph titer before and 24 h after a blood meal.

NPY in invertebrates: molecular answers to altered functions during evolution

As in Lymnaea stagnalis NPY plays a key role in regulating energy flows but has no effect on food intake, two important questions arise: 1) How is the amount of food consumed related to energy storage? 2) Can we give a molecular explanation for this alteration in function of NPY during evolution? Recent data have shown that also in Lymnaea a leptin-like factor is produced by glycogen storing cells which inhibits food intake, a Lymnaea storage feedback factor (LySFF). So, food consumption seems in balance with the amount of energy stored in this animal. We suppose that NPY neurons in Lymnaea have receptors for LySFF so that their activity in regulating energy homeostasis reflects the amount of stored energy. By comparing the molecular structure of NPYs in invertebrates it became clear that only molluscan and arthropod NPY are synthesized from a prohormone similar to vertebrate NPYs and should be considered as real invertebrate homologs of NPY. Based on pharmacological data we suppose that the identified Lymnaea NPY receptor is a Y1 subtype. This might explain that LyNPY has no effect on food intake in Lymnaea as this function of NPY in mammals is regulated through the Y5 subtype receptor.

Regeneration as an application of gastropod neural plasticity

Gastropod research is providing many insights into mechanisms of neural regeneration. These observations were made possible by the pioneering work of individuals who described the nervous systems of gastropods, mapped prominent neurons and determined their roles and connections, and developed the techniques for culturing them. This information has allowed questions about injury responses, target selection, and pathway cues to be explored at the level of individually identified neurons. Because of gastropod studies, more is known about axon sealing, growth cone formation and behavior, signals that travel from the site of axotomy to the soma, and the second messengers that are activated there. The responses in neurons and non-neuronal cells during neural development and injury are coordinated by chemical messenger systems that are highly conserved, including neurotransmitters, cytokines, and neurotrophins. The nervous system is modified in learning paradigms by some of the same messenger systems activated by injury, because learning and injury both challenge neurons to change. The conservation of basic mechanisms that coordinate neuronal plasticity allows us to approach basic questions in relatively simple nervous systems with reasonable confidence that the findings will be relevant for other nervous systems, including possible applications to the mammalian nervous system.