GABA-, histamine-, and FMRFamide-immunoreactivity in the visual, vestibular and central nervous systems of Hermissenda crassicornis

Midbrain node for context-specific vocalisation in fish

Vocalizations communicate information indicative of behavioural state across divergent social contexts. Yet, how brain regions actively pattern the acoustic features of context-specific vocal signals remains largely unexplored. The midbrain periaqueductal gray (PAG) is a major site for initiating vocalization among mammals, including primates. We show that PAG neurons in a highly vocal fish species (Porichthys notatus) are activated in distinct patterns during agonistic versus courtship calling by males, with few co-activated during a non-vocal behaviour, foraging. Pharmacological manipulations within vocally active PAG, but not hindbrain, sites evoke vocal network output to sonic muscles matching the temporal features of courtship and agonistic calls, showing that a balance of inhibitory and excitatory dynamics is likely necessary for patterning different call types. Collectively, these findings support the hypothesis that vocal species of fish and mammals share functionally comparable PAG nodes that in some species can influence the acoustic structure of social context-specific vocal signals.

Histamine and gamma-aminobutyric acid in the nervous system of Pygospio elegans (Annelida: Spionidae): structure and recovery during reparative regeneration

Background

In recent two decades, studies of the annelid nervous systems were revolutionized by modern cell labeling techniques and state-of-the-art microscopy techniques. However, there are still huge gaps in our knowledge on the organization and functioning of their nervous system. Most of the recent studies have focused on the distribution of serotonin and FMRFamide, while the data about many other basic neurotransmitters such as histamine (HA) and gamma-aminobutyric acid (GABA) are scarce.

Results

Using immunohistochemistry and confocal microscopy we studied the distribution of histamine and gamma-aminobutyric acid in the nervous system of a spionid annelid Pygospio elegans and traced their redevelopment during reparative regeneration. Both neurotransmitters show specific patterns in central and peripheral nervous systems. HA-positive cells are concentrated mostly in the brain, while GABA-positive cell somata contribute equally to brain and segmental ganglia. Some immunoreactive elements were found in peripheral nerves. Both substances were revealed in high numbers in bipolar sensory cells in the palps. The first signs of regenerating HAergic and GABAergic systems were detected only by 3 days after the amputation. Further redevelopment of GABAergic system proceeds faster than that of HAergic one.

Conclusions

Comparisons with other annelids and mollusks examined in this respect revealed a number of general similarities in distribution patterns of HAergic and GABAergic cells in different species. Overall, the differences in the full redevelopment of various neurotransmitters correlate with neuronal development during embryogenesis. Our results highlight the importance of investigating the distribution of different neurotransmitters in comparative morphological and developmental studies.

Comparative Analysis of Neuropeptides in Homologous Interneurons and Prohormone Annotation in Nudipleuran Sea Slugs

Despite substantial research on neuronal circuits in nudipleuran gastropods, few peptides have been implicated in nudipleuran behavior. In this study, we expanded the understanding of peptides in this clade, using three species with well-studied nervous systems, Hermissenda crassicornis, Melibe leonina, and Pleurobranchaea californica. For each species, we performed sequence homology analysis of de novo transcriptome predictions to identify homologs to 34 of 36 prohormones previously characterized in the gastropods Aplysia californica and Lymnaea stagnalis. We then used single-cell mass spectrometry to characterize peptide profiles in homologous feeding interneurons: the multifunctional ventral white cell (VWC) in P. californica and the small cardioactive peptide B large buccal (SLB) cells in H. crassicornis and M. leonina. The neurons produced overlapping, but not identical, peptide profiles. The H. crassicornis SLB cells expressed peptides from homologs to the FMRFamide (FMRFa), small cardioactive peptide (SCP), LFRFamide (LFRFa), and feeding circuit activating peptides prohormones. The M. leonina SLB cells expressed peptides from homologs to the FMRFa, SCP, LFRFa, and MIP-related peptides prohormones. The VWC, previously shown to express peptides from the FMRFa and QNFLa (a homolog of A. californica pedal peptide 4) prohormones, was shown to also contain SCP peptides. Thus, each neuron expressed peptides from the FMRFa and SCP families, the H. crassicornis and M. leonina SLB cells expressed peptides from the LFRFa family, and each neuron contained peptides from a prohormone not found in the others. These data suggest each neuron performs complex co-transmission, which potentially facilitates a multifunctional role in feeding. Additionally, the unique feeding characteristics of each species may relate, in part, to differences in the peptide profiles of these neurons. These data add chemical insight to enhance our understanding of the neuronal basis of behavior in nudipleurans and other gastropods.

Regional expression of neuropeptides in the retina of the terrestrial slug Limax valentianus (Gastropoda, Stylommatophora, Limacidae)

Gastropods use lens-bearing eyes to detect ambient light. The retina contains photoreceptors that directly project to the brain. Here we identified the neurotransmitters that the retinal cells use for projection to the brain in the terrestrial slug Limax. We identified 12 genes encoding neuropeptides as well as a novel vesicular glutamate transporter, a marker of glutamatergic neuron, expressed in the retinal cells. Spatial expression profiles of the neuropeptide genes were determined by in situ hybridization. WWamide/MIP1/Pedal peptide2 were co-expressed in the neurons of the accessory retina. In the main retina, prohormone-4 was expressed in the ventro-lateral region. Clionin was expressed in the ventro-medial region. Pedal peptide was expressed in the anterior region of the main retina and in the accessory retina. Enterin was expressed in many neurons, including the accessory retina, but not in the dorsal region. FxRIamide1 and 2 were co-expressed in the posterior region. Prohormone-4 variant was uniformly expressed in many neurons but scarcely in the accessory retina. MIP2 was widely expressed throughout the dorso-ventral axis in the posterio-lateral region of the main retina. Myo1 was expressed in many neurons of the main retina but predominantly in the dorsal region. These expression patterns were confirmed by immunohistochemistry with specific antibodies against the neuropeptides. Projections of these peptidergic retinal neurons were confirmed by immunostaining of the optic nerve. Our present study revealed regional differentiation of the retina with respect to the neurotransmitters that the retinal cells use. neuropeptides, retina, neurotransmitter, gastropod, Lehmannia This article is protected by copyright. All rights reserved.

Immunohistochemical relationships of huntingtin-associated protein 1 with enteroendocrine cells in the pyloric mucosa of the rat stomach

Huntingtin-associated protein 1 (HAP1) is a neuronal cytoplasmic protein that is predominantly expressed in the brain and spinal cord. In addition to the central nervous system, HAP1 is also expressed in the peripheral organs including endocrine system. Different types of enteroendocrine cells (EEC) are present in the digestive organs. To date, the characterization of HAP1-immunoreactive (ir) cells remains unreported there. In the present study, the expression of HAP1 in pyloric stomach in adult male rats and its relationships with different chemical markers for EEC [gastrin, marker of gastrin (G) cells; somatostatin, marker of delta (D) cells; 5-HT, marker of enterochromaffin (EC) cells; histamine, marker of enterochromaffin-like (ECL) cells] were examined employing single- or double-labelled immunohistochemistry and with light-, fluorescence- or electron-microscopy. HAP1-ir cells were abundantly expressed in the glandular mucosa but were very few or none in the surface epithelium. Double-labelled immunofluorescence staining for HAP1 and markers for EECs showed that almost all the G-cells expressed HAP1. In contrast, HAP1 was completely lacking in D-cells, EC-cells or ECL-cells. Our current study is the first to clarify that HAP1 is selectively expressed in G-cells in rat pyloric stomach, which probably reflects HAP1's involvement in regulation of the secretion of gastrin.

Distribution of Molecules Related to Neurotransmission in the Nervous System of the Mussel Crenomytilus grayanus

In bivalves neurotransmitters are involved in a variety of behaviors, but their diversity and distribution in the nervous system of these organisms remains somewhat unclear. Here, we first examined immunohistochemically the distributions of neurons containing different neurotransmitters, neuropeptides, and related enzymes, as well as the proliferative status of neurons in the ganglia of the mussel Crenomytilus grayanus. H-Phe-Met-Arg-Phe-NH2 (FMRFamide), choline acetyltransferase (ChAT), γ-aminobutyric acid (GABA) and tyrosine hydroxylase (TH) were found to be expressed by neurons in all the ganglia, whereas serotonin (5-HT) neurons were found only in the cerebropleural and pedal, but not visceral ganglia. Moreover, incubation of living mussels in the presence of a 5-HT precursor (5-HTP) confirmed the absence of 5-HT-containing neurons from the visceral ganglia, indicating that the "serotonin center" of the visceral nervous system is located in the cerebral ganglia. Furthermore, immunostaining of molecules related to neurotransmission together with α-acetylated tubulin demonstrated that this cytoskeletal protein may be a potential pan-neuronal marker in bivalves. Adult mussel neurons do not proliferate, but a population of proliferating PCNA-LIP cells which do not express any of the neurotransmitters examined, perhaps glia cells, was detected in the ganglia. These novel findings suggest that the nervous system of bivalves contains a broad variety of signal molecules most likely involved in the regulation of different physiological and behavioral processes. In addition, proliferating cells may maintain and renew glial cells and neurons throughout the lives of bivalves.

Galanin immunoreactivity is sexually polymorphic in neuroendocrine and vocal-acoustic systems in a teleost fish

Galanin is a peptide that regulates pituitary hormone release, feeding, and reproductive and parental care behaviors. In teleost fish, increased galanin expression is associated with territorial, reproductively active males. Prior transcriptome studies of the plainfin midshipman (Porichthys notatus), a highly vocal teleost fish with two male morphs that follow alternative reproductive tactics, show that galanin is upregulated in the preoptic area-anterior hypothalamus (POA-AH) of nest-holding, courting type I males during spawning compared to cuckolding type II males. Here, we investigate possible differences in galanin immunoreactivity in the brain of both male morphs and females with a focus on vocal-acoustic and neuroendocrine networks. We find that females differ dramatically from both male morphs in the number of galanin-expressing somata and in the distribution of fibers, especially in brainstem vocal-acoustic nuclei and other sensory integration sites that also differ, though less extensively, between the male morphs. Double labeling shows that primarily separate populations of POA-AH neurons express galanin and the nonapeptides arginine-vasotocin or isotocin, homologues of mammalian arginine vasopressin and oxytocin that are broadly implicated in neural mechanisms of vertebrate social behavior including morph-specific actions on vocal neurophysiology in midshipman. Finally, we report a small population of POA-AH neurons that coexpress galanin and the neurotransmitter γ-aminobutyric acid. Together, the results indicate that galanin neurons in midshipman fish likely modulate brain activity at a broad scale, including targeted effects on vocal motor, sensory and neuroendocrine systems; are unique from nonapeptide-expressing populations; and play a role in male-specific behaviors.

The importance of identified neurons in gastropod molluscs to neuroscience

Gastropod molluscs have large neurons that are uniquely identifiable across individuals and across species based on neuroanatomical and neurochemical criteria, facilitating research into neural signaling and neural circuits. Novel neuropeptides have been identified through RNA sequencing and mass spectroscopic analysis of single neurons. The roles of peptides and other signaling molecules including second messengers have been placed in the context of small circuits that control simple behaviors. Despite the stereotypy, neurons vary over time in their activity in large ensembles. Furthermore, there is both intra-species and inter-species variation in synaptic properties and gene expression. Research on gastropod identified neurons highlights the features that might be expected to be stable in more complex systems when trying to identify cell types.

GABA as a Neurotransmitter in Gastropod Molluscs

The neurotransmitter gamma-aminobutyric acid (GABA) is widely distributed in the mammalian central nervous system, where it acts as a major mediator of synaptic inhibition. GABA also serves as a neurotransmitter in a range of invertebrate phyla, including arthropods, echinoderms, annelids, nematodes, and platyhelminthes. This article reviews evidence supporting the neurotransmitter role of GABA in gastropod molluscs, with an emphasis on its presence in identified neurons and well-characterized neural circuits. The collective findings indicate that GABAergic signaling participates in the selection and specification of motor programs, as well as the bilateral coordination of motor circuits. While relatively few in number, GABAergic neurons can influence neural circuits via inhibitory, excitatory, and modulatory synaptic actions. GABA's colocalization with peptidergic and classical neurotransmitters can broaden its integrative capacity. The functional properties of GABAergic neurons in simpler gastropod systems may provide insight into the role of this neurotransmitter phenotype in more complex brains.

Range extension for the region of sympatry between the nudibranchs Hermissenda opalescens and Hermissenda crassicornis in the northeastern Pacific

The mollusc nudibranch genus Hermissenda Bergh, 1879 was recently discovered to include three pseudocryptic species, dividing a single species H. crassicornis (sensu lato) into H. crassicornis Escholtz, 1831, H. opalescens J.G. Cooper, 1863, and H. emurai Baba, 1937. The species were distinguished by both genetic and morphological evidence, and the distribution of sampled animals suggested the three species had mostly distinct geographical ranges. Here, we report the presence of both H. crassicornis and H. opalescens in Barkley and Clayoquot Sounds, British Columbia, Canada, based on diagnostic characters and molecular data congruent with the differences described for these two species. This result extends the region of sympatry for the two species from northern California, USA, to, at least, Vancouver Island, British Columbia in 2016. Depending on how long this overlap has occurred, the possible northward expansion of H. opalescens would have implications for understanding the effects of short- or long-term environmental changes in ocean temperatures as well as complicating the interpretation of past neurobiological studies of H. crassicornis (sensu lato).