Dietary palmitic acid promotes a prometastatic memory via Schwann cells.

Fatty acid uptake and altered metabolism constitute hallmarks of metastasis1,2, yet evidence of the underlying biology, as well as whether all dietary fatty acids are prometastatic, is lacking. Here we show that dietary palmitic acid (PA), but not oleic acid or linoleic acid, promotes metastasis in oral carcinomas and melanoma in mice. Tumours from mice that were fed a short-term palm-oil-rich diet (PA), or tumour cells that were briefly exposed to PA in vitro, remained highly metastatic even after being serially transplanted (without further exposure to high levels of PA). This PA-induced prometastatic memory requires the fatty acid transporter CD36 and is associated with the stable deposition of histone H3 lysine 4 trimethylation by the methyltransferase Set1A (as part of the COMPASS complex (Set1A/COMPASS)). Bulk, single-cell and positional RNA-sequencing analyses indicate that genes with this prometastatic memory predominantly relate to a neural signature that stimulates intratumoural Schwann cells and innervation, two parameters that are strongly correlated with metastasis but are aetiologically poorly understood3,4. Mechanistically, tumour-associated Schwann cells secrete a specialized proregenerative extracellular matrix, the ablation of which inhibits metastasis initiation. Both the PA-induced memory of this proneural signature and its long-term boost in metastasis require the transcription factor EGR2 and the glial-cell-stimulating peptide galanin. In summary, we provide evidence that a dietary metabolite induces stable transcriptional and chromatin changes that lead to a long-term stimulation of metastasis, and that this is related to a proregenerative state of tumour-activated Schwann cells.

The parenting hub of the hypothalamus is a focus of imprinted gene action.

Imprinted genes are subject to germline epigenetic modification resulting in parental-specific allelic silencing. Although genomic imprinting is thought to be important for maternal behaviour, this idea is based on serendipitous findings from a small number of imprinted genes. Here, we undertook an unbiased systems biology approach, taking advantage of the recent delineation of specific neuronal populations responsible for controlling parental care, to test whether imprinted genes significantly converge to regulate parenting behaviour. Using single-cell RNA sequencing datasets, we identified a specific enrichment of imprinted gene expression in a recognised "parenting hub", the galanin-expressing neurons of the preoptic area. We tested the validity of linking enriched expression in these neurons to function by focusing on MAGE family member L2 (Magel2), an imprinted gene not previously linked to parenting behaviour. We confirmed expression of Magel2 in the preoptic area galanin expressing neurons. We then examined the parenting behaviour of Magel2-null(+/p) mice. Magel2-null mothers, fathers and virgin females demonstrated deficits in pup retrieval, nest building and pup-directed motivation, identifying a central role for this gene in parenting. Finally, we show that Magel2-null mothers and fathers have a significant reduction in POA galanin expressing cells, which in turn contributes to a reduced c-Fos response in the POA upon exposure to pups. Our findings identify a novel imprinted gene that impacts parenting behaviour and, moreover, demonstrates the utility of using single-cell RNA sequencing data to predict gene function from expression and in doing so here, have identified a purposeful role for genomic imprinting in mediating parental behaviour.

Long-term enhancements in antidepressant efficacy and neurogenesis: Effects of intranasal co-administration of neuropeptide Y 1 receptor (NPY1R) and galanin receptor 2 (GALR2) agonists in the ventral hippocampus.

This study evaluates the sustained antidepressant-like effects and neurogenic potential of a 3-day intranasal co-administration regimen of galanin receptor 2 (GALR2) agonist M1145 and neuropeptide Y Y1 receptor (NPY1R) agonist [Leu31, Pro34]NPY in the ventral hippocampus of adult rats, with outcomes analyzed 3 weeks post-treatment. Utilizing the forced swimming test (FST), we found that this co-administration significantly enhances antidepressant-like behaviors, an effect neutralized by the GALR2 antagonist M871, highlighting the synergistic potential of these neuropeptides in modulating mood-related behaviors. In situ proximity ligation assay (PLA) indicated a significant increase in GALR2/NPYY1R heteroreceptor complexes in the ventral hippocampal dentate gyrus, suggesting a molecular basis for the behavioral outcomes observed. Moreover, proliferating cell nuclear antigen (PCNA) immunolabeling revealed increased cell proliferation in the subgranular zone of the dentate gyrus, specifically in neuroblasts as evidenced by co-labeling with doublecortin (DCX), without affecting quiescent neural progenitors or astrocytes. The study also noted a significant uptick in the number of DCX-positive cells and alterations in dendritic morphology in the ventral hippocampus, indicative of enhanced neuronal differentiation and maturation. These morphological changes highlight the potential of these agonists to facilitate the functional integration of new neurons into existing neural circuits. By demonstrating the long-lasting effects of a brief, 3-day intranasal administration of GALR2 and NPY1R agonists, our findings contribute significantly to the understanding of neuropeptide-mediated neuroplasticity and herald novel therapeutic strategies for the treatment of depression and related mood disorders, emphasizing the therapeutic promise of targeting neurogenesis and neuronal maturation processes.

Structure of the human galanin receptor 2 bound to galanin and Gq reveals the basis of ligand specificity and how binding affects the G-protein interface.

Galanin is a neuropeptide expressed in the central and peripheral nervous systems, where it regulates various processes including neuroendocrine release, cognition, and nerve regeneration. Three G-protein coupled receptors (GPCRs) for galanin have been discovered, which is the focus of efforts to treat diseases including Alzheimer's disease, anxiety, and addiction. To understand the basis of the ligand preferences of the receptors and to assist structure-based drug design, we used cryo-electron microscopy (cryo-EM) to solve the molecular structure of GALR2 bound to galanin and a cognate heterotrimeric G-protein, providing a molecular view of the neuropeptide binding site. Mutant proteins were assayed to help reveal the basis of ligand specificity, and structural comparison between the activated GALR2 and inactive hß2AR was used to relate galanin binding to the movements of transmembrane (TM) helices and the G-protein interface.

Structural insights into galanin receptor signaling.

Galanin is a biologically active neuropeptide, and functions through three distinct G protein­coupled receptors (GPCRs), namely GALR1, GALR2, and GALR3. GALR signaling plays important roles in regulating various physiological processes such as energy metabolism, neuropathic pain, epileptic activity, and sleep homeostasis. GALR1 and GALR3 signal through the Gi/o pathway, whereas GALR2 signals mainly through the Gq/11 pathway. However, the molecular basis for galanin recognition and G protein selectivity of GALRs remains poorly understood. Here, we report the cryoelectron microscopy structures of the GALR1-Go and the GALR2-Gq complexes bound to the endogenous ligand galanin or spexin. The galanin peptide mainly adopts an alpha helical structure, which binds at the extracellular vestibule of the receptors, nearly parallel to the membrane plane without penetrating deeply into the receptor core. Structural analysis combined with functional studies reveals important structural determinants for the G protein selectivity of GALRs as well as other class A GPCRs. In addition, we show that the zinc ion is a negative allosteric regulator of GALR1 but not GALR2. Our studies provide insight into the mechanisms of G protein selectivity of GPCRs and highlight a potential function of the neuromodulator zinc ion as a modulator of GPCR signaling in the central nervous system.

Distinct neural networks derived from galanin-containing nociceptors and neurotensin-expressing pruriceptors.

Pain and itch are distinct sensations arousing evasion and compulsive desire for scratching, respectively. It's unclear whether they could invoke different neural networks in the brain. Here, we use the type 1 herpes simplex virus H129 strain to trace the neural networks derived from two types of dorsal root ganglia (DRG) neurons: one kind of polymodal nociceptors containing galanin (Gal) and one type of pruriceptors expressing neurotensin (Nts). The DRG microinjection and immunosuppression were performed in transgenic mice to achieve a successful tracing from specific types of DRG neurons to the primary sensory cortex. About one-third of nuclei in the brain were labeled. More than half of them were differentially labeled in two networks. For the ascending pathways, the spinothalamic tract was absent in the network derived from Nts-expressing pruriceptors, and the two networks shared the spinobulbar projections but occupied different subnuclei. As to the motor systems, more neurons in the primary motor cortex and red nucleus of the somatic motor system participated in the Gal-containing nociceptor-derived network, while more neurons in the nucleus of the solitary tract (NST) and the dorsal motor nucleus of vagus nerve (DMX) of the emotional motor system was found in the Nts-expressing pruriceptor-derived network. Functional validation of differentially labeled nuclei by c-Fos test and chemogenetic inhibition suggested the red nucleus in facilitating the response to noxious heat and the NST/DMX in regulating the histamine-induced scratching. Thus, we reveal the organization of neural networks in a DRG neuron type-dependent manner for processing pain and itch.

Structure and Function of Neuronal Circuits Linking Ventrolateral Preoptic Nucleus and Lateral Hypothalamic Area.

To understand how sleep-wakefulness cycles are regulated, it is essential to disentangle structural and functional relationships between the preoptic area (POA) and lateral hypothalamic area (LHA), since these regions play important yet opposing roles in the sleep-wakefulness regulation. GABA- and galanin (GAL)-producing neurons in the ventrolateral preoptic nucleus (VLPO) of the POA (VLPOGABA and VLPOGAL neurons) are responsible for the maintenance of sleep, while the LHA contains orexin-producing neurons (orexin neurons) that are crucial for maintenance of wakefulness. Through the use of rabies virus-mediated neural tracing combined with in situ hybridization (ISH) in male and female orexin-iCre mice, we revealed that the vesicular GABA transporter (Vgat, Slc32a1)- and galanin (Gal)-expressing neurons in the VLPO directly synapse with orexin neurons in the LHA. A majority (56.3 ± 8.1%) of all VLPO input neurons connecting to orexin neurons were double-positive for Vgat and Gal Using projection-specific rabies virus-mediated tracing in male and female Vgat-ires-Cre and Gal-Cre mice, we discovered that VLPOGABA and VLPOGAL neurons that send projections to the LHA received innervations from similarly distributed input neurons in many brain regions, with the POA and LHA being among the main upstream areas. Additionally, we found that acute optogenetic excitation of axons of VLPOGABA neurons, but not VLPOGAL neurons, in the LHA of male Vgat-ires-Cre mice induced wakefulness. This study deciphers the connectivity between the VLPO and LHA, provides a large-scale map of upstream neuronal populations of VLPO→LHA neurons, and reveals a previously uncovered function of the VLPOGABA→LHA pathway in the regulation of sleep and wakefulness.SIGNIFICANCE STATEMENT We identified neurons in the ventrolateral preoptic nucleus (VLPO) that are positive for vesicular GABA transporter (Vgat) and/or galanin (Gal) and serve as presynaptic partners of orexin-producing neurons in the lateral hypothalamic area (LHA). We depicted monosynaptic input neurons of GABA- and galanin-producing neurons in the VLPO that send projections to the LHA throughout the entire brain. Their input neurons largely overlap, suggesting that they comprise a common neuronal population. However, acute excitatory optogenetic manipulation of the VLPOGABA→LHA pathway, but not the VLPOGAL→LHA pathway, evoked wakefulness. This study shows the connectivity of major components of the sleep/wake circuitry in the hypothalamus and unveils a previously unrecognized function of the VLPOGABA→LHA pathway in sleep-wakefulness regulation. Furthermore, we suggest the existence of subpopulations of VLPOGABA neurons that innervate LHA.

Functional circuit architecture underlying parental behaviour.

Parenting is essential for the survival and wellbeing of mammalian offspring. However, we lack a circuit-level understanding of how distinct components of this behaviour are coordinated. Here we investigate how galanin-expressing neurons in the medial preoptic area (MPOAGal) of the hypothalamus coordinate motor, motivational, hormonal and social aspects of parenting in mice. These neurons integrate inputs from a large number of brain areas and the activation of these inputs depends on the animal's sex and reproductive state. Subsets of MPOAGal neurons form discrete pools that are defined by their projection sites. While the MPOAGal population is active during all episodes of parental behaviour, individual pools are tuned to characteristic aspects of parenting. Optogenetic manipulation of MPOAGal projections mirrors this specificity, affecting discrete parenting components. This functional organization, reminiscent of the control of motor sequences by pools of spinal cord neurons, provides a new model for how discrete elements of a social behaviour are generated at the circuit level.

Galanin Coordinates Macrophage-Associated Fibro-Inflammatory Response and Mitochondrial Integrity in Myocardial Infarction Reperfusion Injury.

Myocardial infarction activates an intense fibro-inflammatory reaction that is essential for cardiac remodeling and heart failure (HF). Bioactive peptide galanin plays a critical role in regulating cardiovascular homeostasis; however, its specific functional relevance in post-infarction fibro-inflammatory reprogramming remains obscure. Here, we show that galanin coordinates the fibro-inflammatory trajectory and mitochondrial integrity in post-infarction reperfusion injury. Aberrant deposition of collagen was associated with a marked increase in CD68-positive macrophage infiltration in cardiac tissue in mice subjected to myocardial ischemia/reperfusion (I/R) for 14 days compared to sham controls. Furthermore, we found that the myocardial expression level of a specific marker of M2 macrophages, CD206, was significantly down-regulated in I/R-challenged mice. In contrast, galanin treatment started during the reperfusion phase blunted the fibro-inflammatory responses and promoted the expression of CD206 in I/R-remodeled hearts. In addition, we found that the anti-apoptotic and anti-hypertrophic effects of galanin were associated with the preservation of mitochondrial integrity and promotion of mitochondrial biogenesis. These findings depict galanin as a key arbitrator of fibro-inflammatory responses to cardiac I/R injury and offer a promising therapeutic trajectory for the treatment of post-infarct cardiovascular complications.

Comparison of the Influence of Bisphenol A and Bisphenol S on the Enteric Nervous System of the Mouse Jejunum.

Bisphenols are dangerous endocrine disruptors that pollute the environment. Due to their chemical properties, they are globally used to produce plastics. Structural similarities to oestrogen allow bisphenols to bind to oestrogen receptors and affect internal body systems. Most commonly used in the plastic industry is bisphenol A (BPA), which also has negative effects on the nervous, immune, endocrine, and cardiovascular systems. A popular analogue of BPA-bisphenol S (BPS) also seems to have harmful effects similar to BPA on living organisms. Therefore, with the use of double immunofluorescence labelling, this study aimed to compare the effect of BPA and BPS on the enteric nervous system (ENS) in mouse jejunum. The study showed that both studied toxins impact the number of nerve cells immunoreactive to substance P (SP), galanin (GAL), vasoactive intestinal polypeptide (VIP), the neuronal isoform of nitric oxide synthase (nNOS), and vesicular acetylcholine transporter (VAChT). The observed changes were similar in the case of both tested bisphenols. However, the influence of BPA showed stronger changes in neurochemical coding. The results also showed that long-term exposure to BPS significantly affects the ENS.

Exogenous galanin alleviates hepatic steatosis by promoting autophagy via the AMPK-mTOR pathway.

Defective autophagy-induced intracellular lipid degradation is causally associated with non-alcoholic fatty liver disease (NAFLD) development. Therefore, agents that can restore autophagy may have potential clinical application prospects on this public health issue. Galanin (GAL) is a pleiotropic peptide that regulates autophagy and is a potential drug for the treatment of NAFLD. In this study, we used an MCD-induced NAFLD mouse model in vivo and an FFA-induced HepG2 hepatocyte model in vitro to evaluate the anti-NAFLD effect of GAL. Exogenous GAL supplementation significantly attenuated lipid droplet accumulation and suppressed hepatocyte TG levels in mice and cell models. Mechanistically, Galanin-mediated reduction of lipid accumulation was positively correlated with upregulated p-AMPK, as evidenced by upregulated protein expressions of fatty acid oxidation-related gene markers (PPAR-α and CPT1A), upregulated expressions of the autophagy-related marker (LC3B), and downregulated autophagic substrate p62 levels. In FFA-treated HepG2 cells, activation of fatty acid oxidation and autophagy-related proteins by galanin was reversed by autophagy inhibitors, chloroquine, and the AMPK inhibitor. Galanin ameliorates hepatic fat accumulation by inducing autophagy and fatty acid oxidation via the AMPK/mTOR pathway.

Spexin2 Is a Novel Food Regulator in Gallus gallus.

Spexin2 (SPX2), a paralog of SPX1, is a newly identified gene in non-mammalian vertebrates. Limited studies in fish have evidenced its important role in food intake and energy balance modulation. However, little is known about its biological functions in birds. Using the chicken (c-) as a model, we cloned the full-length cDNA of SPX2 by using RACE-PCR. It is 1189 base pair (bp) in length and predicted to generate a protein of 75 amino acids that contains a 14 amino acids mature peptide. Tissue distribution analysis showed that cSPX2 transcripts were detected in a wide array of tissues, with abundant expression in the pituitary, testis, and adrenal gland. cSPX2 was also observed to be ubiquitously expressed in chicken brain regions, with the highest expression in the hypothalamus. Its expression was significantly upregulated in the hypothalamus after 24 or 36 h of food deprivation, and the feeding behavior of chicks was obviously suppressed after peripheral injection with cSPX2. Mechanistically, further studies evidenced that cSPX2 acts as a satiety factor via upregulating cocaine and amphetamine regulated transcript (CART) and downregulating agouti-related neuropeptide (AGRP) in hypothalamus. Using a pGL4-SRE-luciferase reporter system, cSPX2 was demonstrated to effectively activate a chicken galanin II type receptor (cGALR2), a cGALR2-like receptor (cGALR2L), and a galanin III type receptor (cGALR3), with the highest binding affinity for cGALR2L. Collectively, we firstly identified that cSPX2 serves as a novel appetite monitor in chicken. Our findings will help clarify the physiological functions of SPX2 in birds as well as its functional evolution in vertebrates.

The Role of Galanin in Cerebellar Granule Cell Migration in the Early Postnatal Mouse during Normal Development and after Injury.

Galanin, one of the most inducible neuropeptides, is widely present in developing brains, and its expression is altered by pathologic events (e.g., epilepsy, ischemia, and axotomy). The roles of galanin in brain development under both normal and pathologic conditions have been hypothesized, but the question of how galanin is involved in fetal and early postnatal brain development remains largely unanswered. In this study, using granule cell migration in the cerebellum of early postnatal mice (both sexes) as a model system, we examined the role of galanin in neuronal cell migration during normal development and after brain injury. Here we show that, during normal development, endogenous galanin participates in accelerating granule cell migration via altering the Ca2+ and cAMP signaling pathways. Upon brain injury induced by the application of cold insults, galanin levels decrease at the lesion sites, but increase in the surroundings of lesion sites. Granule cells exhibit the following corresponding changes in migration: (1) slowing down migration at the lesion sites; and (2) accelerating migration in the surroundings of lesion sites. Experimental manipulations of galanin signaling reduce the lesion site-specific changes in granule cell migration, indicating that galanin plays a role in such deficits in neuronal cell migration. The present study suggests that manipulating galanin signaling may be a potential therapeutic target for acutely injured brains during development.SIGNIFICANCE STATEMENT Deficits in neuronal cell migration caused by brain injury result in abnormal development of cortical layers, but the underlying mechanisms remain to be determined. Here, we report that on brain injury, endogenous levels of galanin, a neuropeptide, are altered in a lesion site-specific manner, decreasing at the lesion sites but increasing in the surroundings of lesion sites. The changes in galanin levels positively correlate with the migration rate of immature neurons. Manipulations of galanin signaling ameliorate the effects of injury on neuronal migration and cortical layer development. These results shed a light on galanin as a potential therapeutic target for acutely injured brains during development.

Galanin expression varies with parental care and social status in a wild cooperatively breeding fish.

As many busy parents will attest, caring for young often comes at the expense of having time to feed and care for oneself. Galanin is a neuropeptide that regulates food intake and modulates parental care; however, the relative importance of galanin in the regulation of feeding versus caring by parents has never been evaluated before under naturalistic settings. Here, we assessed how expression of the galanin system varied in two brain regions, the hypothalamus (which regulates feeding) and the preoptic area (which modulates social behaviours including care) in a wild cichlid fish, Neolamprologus pulcher. Females with young had higher hypothalamic expression of galanin receptor 1a, and the highest expression of galanin and galanin receptor 1a was observed in females that foraged the least. However, expression of five other feeding-related neuropeptides did not change while females were caring for young suggesting that changes in the hypothalamic galanin system may not have been directly related to changes in food intake. The preoptic galanin system was unaffected by the presence of young, but preoptic galanin expression was higher in dominant females (which are aggressive, regularly reproduce and care for young) compared to subordinate females (which are submissive, rarely reproduce but often help care for young). Additionally, preoptic galanin expression was higher in fish that performed more territory defense. Overall, our results indicate that galanin has brain-region-specific roles in modulating both parental care and social status in wild animals.

Spexin modulates molecular thermogenic profile of adipose tissue and thermoregulatory behaviors in female C57BL/6 mice.

Thermoregulation is the physiological process by which an animal regulates body temperature in response to its environment. It is known that galanin, a neuropeptide widely distributed throughout the central nervous system and secreted by the gut, plays a role in thermoregulatory behaviors and metabolism. We tested the ability of the novel neuropeptide spexin, which shares sequence homology to galanin, to regulate these functions in female mice. Supraphysiological levels of spexin in C57BL/6 mice did not lead to weight loss after 50 days of treatment. Behavioral analysis of long-term spexin treatment showed it decreased anxiety and increased thermoregulatory nest building, which was not observed when mice were housed at thermoneutral temperatures. Treatment also disrupted the thermogenic profile of brown and white adipose tissue, decreasing mRNA expression of Ucp1 in BAT and immunodetection of ß3-adrenergic receptors in gWAT. Our results reveal novel functions for spexin as a modulator of thermoregulatory behaviors and adipose tissue metabolism.

Molecular Changes in the Dorsal Root Ganglion during the Late Phase of Peripheral Nerve Injury-induced Pain in Rodents: A Systematic Review.

The dorsal root ganglion is widely recognized as a potential target to treat chronic pain. A fundamental understanding of quantitative molecular and genomic changes during the late phase of pain is therefore indispensable. The authors performed a systematic literature review on injury-induced pain in rodent dorsal root ganglions at minimally 3 weeks after injury. So far, slightly more than 300 molecules were quantified on the protein or messenger RNA level, of which about 60 were in more than one study. Only nine individual sequencing studies were performed in which the most up- or downregulated genes varied due to heterogeneity in study design. Neuropeptide Y and galanin were found to be consistently upregulated on both the gene and protein levels. The current knowledge regarding molecular changes in the dorsal root ganglion during the late phase of pain is limited. General conclusions are difficult to draw, making it hard to select specific molecules as a focus for treatment.

Genomic and transcriptomic characterization of desmoplastic small round cell tumors.

Desmoplastic small round cell tumor (DSRCT) is a highly aggressive soft tissue tumor primarily affecting children and young adults. Most cases display a pathognomonic EWSR1-WT1 gene fusion, presumably constituting the primary driver event. Little is, however, known about secondary genetic changes that may affect tumor progression. We here studied 25 samples from 19 DSRCT patients using single nucleotide polymorphism arrays and found that all samples had copy number alterations. The most common imbalances were gain of chromosomes/chromosome arms 1/1q and 5/5p and loss of 6/6q and 16/16q, all occurring in at least eight of the patients. Five cases showed homozygous deletions, affecting a variety of known tumor suppressor genes, for example, CDKN2A and NF1. As almost all patients died of their disease, the impact of individual imbalances on survival could not be evaluated. Global gene expression analysis using mRNA sequencing on fresh-frozen samples from seven patients revealed a distinct transcriptomic profile, with enrichment of genes involved in neural differentiation. Two genes - GJB2 and GAL - that showed higher expression in DSRCT compared to control tumors could be further investigated for their potential as diagnostic markers at the protein level.

Time-restricted feeding prevents metabolic diseases through the regulation of galanin/GALR1 expression in the hypothalamus of mice.

PURPOSE: Time-restricted feeding (TRF) reverses obesity and insulin resistance, yet the central mechanisms underlying its beneficial effects are not fully understood. Recent studies suggest a critical role of hypothalamic galanin and its receptors in the regulation of energy balance. It is yet unclear whether TRF could regulate the expression of galanin and its receptors in the hypothalamus of mice fed a high-fat diet. METHODS: To test this effect, we subjected mice to either ad lib or TRF of a high-fat diet for 8 h per day. After 4 weeks, galanin and many neuropeptides associated with the function of metabolism were examined. RESULTS: The present findings showed that mice under TRF consume equivalent calories from a high-fat diet as those with ad lib access, yet are protected against obesity and have improved glucose metabolism. Plasma galanin, orexin A, irisin and adropin levels were significantly reversed by TRF regimen. Besides, TRF regimen reversed the progression of metabolic disorders in mice by increasing GLUT4 and PGC-1α expression in skeletal muscles. Moreover, the levels of galanin and GALR1 expression were severely diminished in the hypothalamus of the TRF mice, whereas GALR2 was highly expressed. CONCLUSIONS: TRF diminished galanin and GALR1 expression, and increased GALR2 expression in the hypothalamus of mice fed a high-fat diet. The current studies provide additional evidence that TRF is effective in improving HFD-induced hyperglycemia and insulin resistance in mice, and this effect could be associated with TRF-induced changes of the galanin systems in the hypothalamus. LEVEL OF EVIDENCE: No level of evidence, animal studies.

Involvement of galanin and galanin receptor 2 in a mouse model of allergic rhinitis.

BACKGROUND: Allergic rhinitis (AR) is caused by allergic reaction to allergens such as pollen. Galanin (GAL), a neuropeptide that regulates inflammatory processes, is widely expressed in the central and peripheral nervous systems. Although neuropeptides are implicated in arthritis and chemically induced ileitis, their roles in AR remain unclear. METHODS: We developed a murine model of AR and generated control, systemic sensitization, mild AR, and severe AR groups. We examined GAL and GAL receptor (GALR) mRNA and protein levels and localization patterns in each group using reverse transcription PCR, western blotting, and immunohistochemical analyses. Additionally, we evaluated the effects of M871, a GALR2 antagonist, on mice with severe AR. RESULTS: Gal and Galr2 are expressed in nasal mucosa and brain (control) samples from control and AR mice. GAL and GALR2 were expressed at similar levels and localized to ciliated epithelial and submucosal gland cells of the nasal mucosa in all four groups. Intranasal M871 administration significantly reduced the incidence of nose rubbing behaviors and sneezing (p < 0.001 in 30 min, respectively) in severe AR mice relative to that in controls. Mechanistically, we postulate that GALR2 is expressed in B cells, and M871 administration reduces IgE production, as well as the number of B cells in tissues. CONCLUSIONS: GAL signaling may not change progressively with increasing nasal sensitization, suggesting that this signaling process exacerbates, rather than directly trigger, AR. GAL-GALR2 signaling likely mediates AR development, suggesting that its inhibition represents a novel therapeutic strategy for AR.

Chronic Environmental or Genetic Elevation of Galanin in Noradrenergic Neurons Confers Stress Resilience in Mice.

The neuropeptide galanin has been implicated in stress-related neuropsychiatric disorders in humans and rodent models. While pharmacological treatments for these disorders are ineffective for many individuals, physical activity is beneficial for stress-related symptoms. Galanin is highly expressed in the noradrenergic system, particularly the locus coeruleus (LC), which is dysregulated in stress-related disorders and activated by exercise. Galanin expression is elevated in the LC by chronic exercise, and blockade of galanin transmission attenuates exercise-induced stress resilience. However, most research on this topic has been done in rats, so it is unclear whether the relationship between exercise and galanin is species specific. Moreover, use of intracerebroventricular (ICV) galanin receptor antagonists in prior studies precluded defining a causal role for LC-derived galanin specifically. Therefore, the goals of this study were twofold. First, we investigated whether physical activity (chronic wheel running) increases stress resilience and galanin expression in the LC of male and female mice. Next, we used transgenic mice that overexpress galanin in noradrenergic neurons (Gal OX) to determine how chronically elevated noradrenergic-derived galanin, alone, alters anxiogenic-like responses to stress. We found that three weeks of ad libitum access to a running wheel in their home cage increased galanin mRNA in the LC of mice, which was correlated with and conferred resilience to stress. The effects of exercise were phenocopied by galanin overexpression in noradrenergic neurons, and Gal OX mice were resistant to the anxiogenic effect of optogenetic LC activation. These findings support a role for chronically increased noradrenergic galanin in mediating resilience to stress.SIGNIFICANCE STATEMENT Understanding the neurobiological mechanisms underlying behavioral responses to stress is necessary to improve treatments for stress-related neuropsychiatric disorders. Increased physical activity is associated with stress resilience in humans, but the neurobiological mechanisms underlying this effect are not clear. Here, we investigate a potential causal mechanism of this effect driven by the neuropeptide galanin from the main noradrenergic nucleus, the locus coeruleus (LC). We show that chronic voluntary wheel running in mice increases stress resilience and increases galanin expression in the LC. Furthermore, we show that genetic overexpression of galanin in noradrenergic neurons causes resilience to a stressor and the anxiogenic effects of optogenetic LC activation. These findings support a role for chronically increased noradrenergic galanin in mediating resilience to stress.