Mice deficient for galanin receptor 2 have decreased neurite outgrowth from adult sensory neurons and impaired pain-like behaviour

Serum Spexin Level Is Negatively Associated With Peripheral Neuropathy and Sensory Pain in Type 2 Diabetes

Background: Spexin is a novel peptide hormone and has shown antinociceptive effects in experimental mice. This study is aimed at evaluating the association of serum spexin level with diabetic peripheral neuropathy (DPN) and related pain in a Chinese population. Methods: We enrolled 167 type 2 diabetes mellitus (T2DM) including 56 patients without DPN (non-DPN), 67 painless DPN, and 44 painful DPN. Serum spexin was measured using ELISA. Logistic regression models were performed to analyze the independent effects of spexin on prevalence of DPN and painful DPN. In streptozotocin (STZ)-induced diabetic mice, mechanical pain threshold was measured using electronic von Frey aesthesiometer. Human peripheral blood mononuclear cells (PBMCs) were isolated and further stimulated with lipopolysaccharide without or with spexin. The gene expression was assayed by qPCR. Results: Compared with non-DPN, serum spexin level decreased in painless DPN and further decreased in painful DPN. The odds of DPN was associated with low spexin level in T2DM, which was similar by age, sex, BMI, and diabetes duration, but attenuated in smokers. The odds of having pain was associated with decreased spexin level in DPN, which was similar by age, sex, smoking status, and diabetes duration, but attenuated in normal weight. Furthermore, we observed that mechanical pain threshold increased in spexin-treated diabetic mice. We also found that lipopolysaccharide treatment increased the mRNA level of TNF-α, IL-6, and MCP-1 in human PBMCs, while spexin treatment prevented this increase. Conclusions: These results suggested that spexin might serve as a protective factor for diabetes against neuropathology and pain-related pathogenesis.

Neuroendocrine and neuroimmune mechanisms underlying comorbidity of pain and obesity

Pain and obesity, as well as their associated impairments, are major health concerns. Understanding the relationship between the two is the focus of a growing body of research. However, early researches attribute increased mechanical stress from excessive weight as the main factor of obesity-related pain, which not only over-simplify the association, but also fail to explain some controversial outcomes arising from clinical investigations. This review focuses on neuroendocrine and neuroimmune modulators importantly involved in both pain and obesity, analyzing nociceptive and anti-nociceptive mechanisms based on neuroendocrine pathways including galanin, ghrelin, leptin and their interactions with other neuropeptides and hormone systems which have been reported to play roles in pain and obesity. Mechanisms of immune activities and metabolic alterations are also discussed, due to their intense interactions with neuroendocrine system and crucial roles in the development and maintenance of inflammatory and neuropathic pain. These findings have implications for health given rising rates of obesity and pain-related diagnoses, by providing novel weight-control and analgesic therapies targeted on specific pathways.

Diabetic Neuropathy: Review on Molecular Mechanisms

Diabetic mellitus is a worldwide endocrine and metabolic disorder with insulin insensitivity or deficiency or both whose prevalence could rise up to 592 million by 2035. Consistent hyperglycemia leads to one of the most common comorbidities like Diabetic Peripheral Neuropathy (DPN). DPN is underlined with unpleasant sensory experience, such as tingling and burning sensation, hyperalgesia, numbness, etc. Globally, 50-60% of the diabetic population is suffering from such symptoms as microvascular complications. Consistent hyperglycemia during DM causes activation/inhibition of various pathways playing important role in the homeostasis of neurons and other cells. Disruption of these pathways results into apoptosis and mitochondrial dysfunctions, causing neuropathy. Among these, pathways like Polyol and PARP are some of the most intensively studied ones whereas those like Wnt pathway, Mitogen activated protein kinase (MAPK), mTOR pathway are comparatively newly discovered. Understanding of these pathways and their role in pathophysiology of DN underlines a few molecules of immense therapeutic value. The inhibitors or activators of these molecules can be of therapeutic importance in the management of DPN. This review, hence, focuses on these underlying molecular mechanisms intending to provide therapeutically effective molecular targets for the treatment of DPN.

Galanin Regulates Myocardial Mitochondrial ROS Homeostasis and Hypertrophic Remodeling Through GalR2

The regulatory peptide galanin is broadly distributed in the central nervous systems and peripheral tissues where it modulates numerous physiological and pathological processes through binding to its three G-protein-coupled receptors, GalR1-3. However, the function and identity of the galaninergic system in the heart remain unclear. Therefore, we investigated the expression of the galanin receptors in cardiac cells and tissues and found that GalR2 is the dominant receptor subtype in adult mouse hearts, cardiomyocytes and H9C2 cardiomyoblasts. In vivo, genetic suppression of GalR2 promotes cardiac hypertrophy, fibrosis and mitochondrial oxidative stress in the heart. In vitro, GalR2 silencing by siRNA abolished the beneficial effects of galanin on cell hypertrophy and mitochondrial reactive oxygen species (ROS) production. These findings unravel new insights into the role of galaninergic system in the heart and suggest novel therapeutic strategies in heart disease.

A New Gal in Town: A Systematic Review of the Role of Galanin and Its Receptors in Experimental Pain

Galanin is a neuropeptide expressed in a small percentage of sensory neurons of the dorsal root ganglia and the superficial lamina of the dorsal horn of the spinal cord. In this work, we systematically reviewed the literature regarding the role of galanin and its receptors in nociception at the spinal and supraspinal levels, as well as in chronic pain conditions. The literature search was performed in PubMed, Web of Science, Scopus, ScienceDirect, OVID, TRIP, and EMBASE using "Galanin" AND "pain" as keywords. Of the 1379 papers that were retrieved in the initial search, we included a total of 141 papers in this review. Using the ARRIVE guidelines, we verified that 89.1% of the works were of good or moderate quality. Galanin shows a differential role in pain, depending on the pain state, site of action, and concentration. Under normal settings, galanin can modulate nociceptive processing through both a pro- and anti-nociceptive action, in a dose-dependent manner. This peptide also plays a key role in chronic pain conditions and its antinociceptive action at both a spinal and supraspinal level is enhanced, reducing animals' hypersensitivity to both mechanical and thermal stimulation. Our results highlight galanin and its receptors as potential therapeutic targets in pain conditions.

Involvement of Neuropeptide Galanin Receptors 2 and 3 in Learning, Memory and Anxiety in Aging Mice

The neuropeptide galanin (GAL), which is expressed in limbic brain structures, has a strong impact on the regulation of mood and behavior. GAL exerts its effects via three G protein-coupled receptors (GAL_1-3-R). Little is known about the effects of aging and loss of GAL-Rs on hippocampal-mediated processes connected to neurogenesis, such as learning, memory recall and anxiety, and cell proliferation and survival in the dorsal dentate gyrus (dDG) in mice. Our results demonstrate that loss of GAL₃-R, but not GAL₂-R, slowed learning and induced anxiety in older (12-14-month-old) mice. Lack of GAL₂-R increased cell survival (BrdU incorporation) in the dDG of young mice. However, normal neurogenesis was observed in vitro using neural stem and precursor cells obtained from GAL₂-R and GAL₃-R knockouts upon GAL treatment. Interestingly, we found sub-strain differences between C57BL/6J and C57BL/6N mice, the latter showing faster learning, less anxiety and lower cell survival in the dDG. We conclude that GAL-R signaling is involved in cognitive functions and can modulate the survival of cells in the neurogenic niche, which might lead to new therapeutic applications. Furthermore, we observed that the mouse sub-strain had a profound impact on the behavioral parameters analyzed and should therefore be carefully considered in future studies.

Beneficial effects of galanin system on diabetic peripheral neuropathic pain and its complications

Diabetic peripheral neuropathic pain (DPNP) is a distal spontaneous pain, caused by lesion of sensory neurons and accompanied by depression and anxiety frequently, which reduce life quality of patients and increase society expenditure. To date, antidepressants, serotonin-noradrenaline reuptake inhibitors and anticonvulsants are addressed as first-line therapy to DPNP, alone or jointly. It is urgently necessary to develop novel agents to treat DPNP and its complications. Evidences indicate that neuropeptide galanin can regulate multiple physiologic and pathophysiological processes. Pain, depression and anxiety may upregulate galanin expression. In return, galanin can modulate depression, anxiety, pain threshold and pain behaviors. This article provides a new insight into regulative effects of galanin and its subtype receptors on antidepressant, antianxiety and against DPNP. Through activating GALR1, galanin reinforces depression-like and anxiogenic-like behaviors, but exerts antinociceptive roles. While via activating GALR2, galanin is referred to as anti-depressive and anti-anxiotropic compounds, and at low and high concentration facilitates and inhibits nociceptor activity, respectively. The mechanism of the galanin roles is relative to increase in K⁺ currents and decrease in Ca²⁺ currents, as well as neurotrophic and neuroprotective roles. These data are helpful to develop novel drugs to treat DPNP and its complications.

Effects of trigeminal nerve injury on the expression of galanin and its receptors in the rat trigeminal ganglion

In the spinal nervous system, the expression of galanin (GAL) and galanin receptors (GALRs) that play important roles in the transmission and modulation of nociceptive information can be affected by nerve injury. However, in the trigeminal nervous system, the effects of trigeminal nerve injury on the expression of GAL are controversy in the previous studies. Besides, little is known about the effects of trigeminal nerve injury on the expression of GALRs. In the present study, the effects of trigeminal nerve injury on the expression of GAL and GALRs in the rat trigeminal ganglion (TG) were investigated by using quantitative real-time reverse transcription-polymerase chain reaction and immunohistochemistry. To identify the nerve-injured and nerve-uninjured TG neurons, activating transcription factor 3 (ATF3, the nerve-injured neuron marker) was stained by immunofluorescence. The levels of GAL mRNA in the rostral half and caudal half of the TG dramatically increased after transection of infraorbital nerve (ION) and inferior alveolar nerve (IAN), respectively. Immunohistochemical labeling of GAL and ATF3 revealed that GAL level was elevated in both injured and adjacent uninjured small and medium-sized TG neurons after ION/IAN transection. In addition, the levels of GAL₂R-like immunoreactivity were reduced in both injured and adjacent uninjured TG neurons after ION/IAN transection, while levels of GAL₁R and GAL₃R-like immunoreactivity remained unchanged. Furthermore, the number of small to medium-sized TG neurons co-expressing GAL- and GAL₁R/GAL₂R/GAL₃R-like immunoreactivity was significantly increased after ION/IAN transection. In line with previous studies in other spinal neuron systems, these results suggest that GAL and GALRs play functional roles in orofacial neuropathic pain and trigeminal nerve regeneration after trigeminal nerve injury.

A preliminary study on DRGs and spinal cord of a galanin receptor 2-EGFP transgenic mouse

The neuropeptide galanin functions via three G-protein coupled receptors, Gal_1-3-R. Both Gal₁-R and ₂-R are involved in pain signaling at the spinal level. Here a Gal₂-R-EGFP transgenic (TG) mouse was generated and studied in pain tests and by characterizing Gal₂-R expression in both sensory ganglia and spinal cord. After peripheral spared nerve injury, mechanical allodynia developed and was ipsilaterally similar between wild type (WT) and TG mice. A Gal₂-R-EGFP-positive signal was primarily observed in small and medium-sized dorsal root ganglion (DRG) neurons and in spinal interneurons and processes. No significant difference in size distribution of DRG neuronal profiles was found between TG and WT mice. Both percentage and fluorescence intensity of Gal₂-R-EGFP-positive neuronal profiles were overall significantly upregulated in ipsilateral DRGs as compared to contralateral DRGs. There was an ipsilateral reduction in substance P-positive and calcitonin gene-related peptide (CGRP)-positive neuronal profiles, and this reduction was more pronounced in TG as compared to WT mice. Moreover, Gal₂-R-EGFP partly co-localized with three pain-related neuropeptides, CGRP, neuropeptide Y and galanin, both in intact and injured DRGs, and with galanin also in local neurons in the superficial dorsal horn. Taken together, the present results provide novel information on the localization and phenotype of DRG and spinal neurons expressing the second galanin receptor, Gal₂-R, and on phenotypic changes following peripheral nerve injury. Gal2-R may also be involved in autoreceptor signaling.

Contributions of mTOR Activation-Mediated Upregulation of Synapsin II and Neurite Outgrowth to Hyperalgesia in STZ-Induced Diabetic Rats

Painful diabetic neuropathy (PDN) is among the common complications in diabetes mellitus (DM), with its underlying mechanisms largely unknown. Synapsin II is primarily expressed in the spinal dorsal horn, and its upregulation mediates a superfluous release of glutamate and a deficiency of GABAergic interneuron synaptic transmission, which is directly implicated in the facilitation of pain signals in the hyperalgesic nociceptive response. Recently, synapsin II has been revealed to be associated with the modulation of neurite outgrowth, whereas the process of this neuronal structural neuroplasticity following neuronal hyperexcitability still remains unclear. In this study, we found that under conditions of elevated glucose, TNF-α induced the activation of mTOR, mediating the upregulation of synapsin II and neurite outgrowth in dorsal horn neurons. In vivo, we demonstrated that mTOR and synapsin II were upregulated and coexpressed in the spinal dorsal horn neurons in rats with streptozotocin (STZ)-induced diabetes. Furthermore, the intrathecal administration of the mTOR inhibitor rapamycin or synapsin II shRNA significantly diminished the expression of synapsin II, effectively mitigating hyperalgesia in PDN rats. We are the first to discover that in STZ-induced diabetic rats the activation of mTOR mediates the upregulation of synapsin II and neurite outgrowth, both contributing to hyperalgesia. These findings may benefit the clinical therapy of PDN by provision of a novel target.

Conformational signatures in β-arrestin2 reveal natural biased agonism at a G-protein-coupled receptor

Discovery of biased ligands and receptor mutants allows characterization of G-protein- and β-arrestin-mediated signaling mechanisms of G-protein-coupled receptors (GPCRs). However, the structural mechanisms underlying biased agonism remain unclear for many GPCRs. We show that while Galanin induces the activation of the galanin receptor 2 (Galr2) that leads to a robust stimulation toward Gαq-protein and β-arrestin1/2, an alternative ligand Spexin and its analog have biased agonism toward G-protein signaling relative to Galanin. We used intramolecular fluorescein arsenical hairpin bioluminescence resonance energy transfer-based biosensors of β-arrestin2 combined with NanoBit technology to measure β-arrestin2–Galr2 interactions in real-time living systems. We found that Spexin and Galanin induce specific active conformations of Galr2, which may lead to different internalization rates of the receptor as well as different signaling outputs. This work represents an additional pharmacological evidence of endogenous G-protein-biased agonism at a GPCR.

Arfaxad Reyes-Alcaraz et al. report that galanin induces robust signaling mediated by β-arrestin1/2 and Gαq, whereas an alternative ligand spexin prefers the Gαq-protein signaling pathway. This study provides mechanistic insights into how endogenous ligands can generate biased signaling outputs.

A non-functional galanin receptor-2 in a multiple sclerosis patient

Multiple Sclerosis (MS) is an inflammatory neurodegenerative disease that affects approximately 2.5 million people globally. Even though the etiology of MS remains unknown, it is accepted that it involves a combination of genetic alterations and environmental factors. Here, after performing whole exome sequencing, we found a MS patient harboring a rare and homozygous single nucleotide variant (SNV; rs61745847) of the G-protein coupled receptor (GPCR) galanin-receptor 2 (GALR2) that alters an important amino acid in the TM6 molecular toggle switch region (W249L). Nuclear magnetic resonance imaging showed that the hypothalamus (an area rich in GALR2) of this patient exhibited an important volumetric reduction leading to an enlarged third ventricle. Ex vivo experiments with patient-derived blood cells (AKT phosphorylation), as well as studies in recombinant cell lines expressing the human GALR2 (calcium mobilization and NFAT mediated gene transcription), showed that galanin (GAL) was unable to stimulate cell signaling in cells expressing the variant GALR2 allele. Live cell confocal microscopy showed that the GALR2 mutant receptor was primarily localized to intracellular endosomes. We conclude that the W249L SNV is likely to abrogate GAL-mediated signaling through GALR2 due to the spontaneous internalization of this receptor in this patient. Although this homozygous SNV was rare in our MS cohort (1:262 cases), our findings raise the potential importance of impaired neuroregenerative pathways in the pathogenesis of MS, warrant future studies into the relevance of the GAL/GALR2 axis in MS and further suggest the activation of GALR2 as a potential therapeutic route for this disease.

Galanin Administration Partially Restores Erectile Function After Cavernous Nerve Injury and Mediates Endogenous Nitrergic Nerve Outgrowth In Vitro

BACKGROUND

Previously, we found that the neuropeptide galanin was strongly upregulated soon after bilateral cavernous nerve injury (BCNI) and that galanin and its receptors were expressed in nitrergic erectile innervation. Galanin has been observed to exert neuroregenerative effects in dorsal root ganglion neurons, but evidence for these effects in the major pelvic ganglion (MPG) after BCNI is lacking.

AIM

To evaluate the neurotropic effects of galanin receptor agonists and antagonists in vitro in nitrergic neurons and MPG and in vivo in rats after BCNI.

METHODS

Male Sprague-Dawley rats underwent BCNI and sham surgery. Organ culture and single-cell neuron culture of the MPG were performed. Osmotic pump treatment with the galanin agonist in vivo and measurement of erectile response to electrostimulation after BCNI, immunohistochemical localization of galanin and receptors in the human neurovascular bundle, and myographic analysis of rat corpus cavernosum smooth muscle relaxation to galanin receptor agonists were investigated.

OUTCOMES

Neurite outgrowth in vitro and erectile response to electrostimulation after BCNI in vivo, immunohistochemical localization of galanin and receptors, and penile muscle relaxation in vitro.

RESULTS

Galanin showed neurotrophic action in vitro and inhibition of endogenous galanin significantly impaired neurite outgrowth in nitrergic but not in sympathetic MPG neurons. In vivo administration of a selective galanin receptor-2 agonist, M1145, resulted in partial recovery of erectile function (EF) after BCNI. Galanin did not act as a direct vasodilator on corpus cavernosum muscle strips.

CLINICAL TRANSLATION

Endogenous neurotrophins such as galanin could be used as a strategy to improve EF for patients after BCNI from radical prostatectomy.

STRENGTHS AND LIMITATIONS

We evaluated the effect of galanin on nerve regeneration and EF recovery in vivo and in vitro. Limitations include the lack of washout period for the in vivo experiment and absence of differences in the expression of neuronal markers between treatment groups.

CONCLUSIONS

We identified galanin as a potential endogenous mechanism for nerve regeneration after BCNI, which could play a physiologic role in EF recovery after radical prostatectomy. In vivo treatment with exogenous galanin was beneficial in enhancing EF recovery after BCNI, but further research is necessary to understand the underlying mechanisms. Weyne E, Hannan JL, Gevaert T, et al. Galanin Administration Partially Restores Erectile Function After Cavernous Nerve Injury and Mediates Endogenous Nitrergic Nerve Outgrowth In Vitro. J Sex Med 2018;15:480-491.

Activiated galanin receptor 2 attenuates insulin resistance in skeletal muscle of obese mice

The results of our and other's studies showed that activation of galanin receptor 1 could mitigate insulin resistance via promoting glucose transporter 4 (GLUT4) expression and translocation in the skeletal muscle of rats. But no literature are available regarding the effect of galanin receptor 2 (GALR2) on insulin resistance in skeletal muscle of type 2 diabetes. Herein, in this study we intended to survey the effect of GALR2 and its signal mechanisms in the mice with high fat diet-induced obese. The mice were intraperitoneally injected with vehicle, GALR2 agonist M1145 and antagonist M871 respectively once a day for continuous 21 days. The skeletal muscles were processed for determination of glucose uptake, and GLUT4 mRNA and protein expression levels. The PGC-1α, AKT, p38MAPK, AS160, pAKT, pP38MAPK and pAS160 expression levels were quantitatively assessed too. We found that pharmacological activation of GALR2 enhanced energy expenditure, and increased GLUT4 expression and translocation in skeletal muscle of mice during high-fat diet regimens. Activation of GALR2 alleviated insulin resistance through P38MAPK/PGC-1α/GLUT4 and AKT/AS160/GLUT4 pathway in the skeletal muscle of mice. Overall, these results identify that GALR2 is a regulator of insulin resistance and activation of GALR2 represents a promising strategy against obesity-induced insulin resistance.

Injury-induced gp130 cytokine signaling in peripheral ganglia is reduced in diabetes mellitus

Neuropathy is a major diabetic complication. While the mechanism of this neuropathy is not well understood, it is believed to result in part from deficient nerve regeneration. Work from our laboratory established that gp130 family of cytokines are induced in animals after axonal injury and are involved in the induction of regeneration-associated genes (RAGs) and in the conditioning lesion response. Here, we examine whether a reduction of cytokine signaling occurs in diabetes. Streptozotocin (STZ) was used to destroy pancreatic β cells, leading to chronic hyperglycemia. Mice were injected with either low doses of STZ (5×60mg/kg) or a single high dose (1×200mg/kg) and examined after three or one month, respectively. Both low and high dose STZ treatment resulted in sustained hyperglycemia and functional deficits associated with the presence of both sensory and autonomic neuropathy. Diabetic mice displayed significantly reduced intraepidermal nerve fiber density and sudomotor function. Furthermore, low and high dose diabetic mice showed significantly reduced tactile touch sensation measured with Von Frey monofilaments. To look at the regenerative and injury-induced responses in diabetic mice, neurons in both superior cervical ganglia (SCG) and the 4th and 5th lumbar dorsal root ganglia (DRG) were unilaterally axotomized. Both high and low dose diabetic mice displayed significantly less axonal regeneration in the sciatic nerve, when measured in vivo, 48h after crush injury. Significantly reduced induction of two gp130 cytokines, leukemia inhibitory factor and interleukin-6, occurred in diabetic animals in SCG 6h after injury compared to controls. Injury-induced expression of interleukin-6 was also found to be significantly reduced in the DRG at 6h after injury in low and high dose diabetic mice. These effects were accompanied by reduced phosphorylation of signal transducer and activator of transcription 3 (STAT3), a downstream effector of the gp130 signaling pathway. We also found decreased induction of several gp130-dependent RAGs, including galanin and vasoactive intestinal peptide. Together, these data suggest a novel mechanism for the decreased response of diabetic sympathetic and sensory neurons to injury.

Involvement of galanin and galanin receptor 2 in nociceptive modulation in anterior cingulate cortex of normal rats and rats with mononeuropathy

The present study was performed to explore the role of galanin and galanin receptor 2 in nociceptive modulation in anterior cingulate cortex (ACC) of normal rats and rats with mononeuropathy. Intra-ACC injection of galanin induced significant increases in hindpaw withdrawal latencies (HWLs) to thermal and mechanical stimulations in both normal rats and rats with mononeuropathy, the increased HWLs were attenuated significantly by intra-ACC injection of galanin receptor 2 antagonist M871, indicating an involvement of galanin receptor 2 in nociceptive modulation in ACC. Interestingly, the galanin-induced HWL was significant higher in rats with mononeuropathy than that in normal rats tested by Randall Selitto test. Furthermore, both the galanin mRNA expression and galanin content increased significantly in ACC in rats with mononeuropathy than that in normal rats. Moreover, both the mRNA levels of galanin receptor 2 and the content of galanin receptor 2 in ACC increased significantly in rats with mononeuropathy than that in normal rats. These results found that galanin induced antinociception in ACC in both normal rats and rats with mononeuropathy. And there may be plastic changes in the expression of galanin and galanin receptor 2 in rats with mononeuropathy, as well as in the galanin-induced antinociception.

Targeted disruption of the orphan receptor Gpr151 does not alter pain-related behaviour despite a strong induction in dorsal root ganglion expression in a model of neuropathic pain

BACKGROUND

Gpr151 is an orphan GPCR whose function is unknown. The restricted pattern of neuronal expression in the habenula, dorsal horn of the spinal cord and dorsal root ganglion plus homology with the galanin family of receptors imply a role in nociception.

RESULTS

Real-time quantitative RT-PCR demonstrated a 49.9±2.9 fold highly significant (P<0.001) increase in Gpr151 mRNA expression in the dorsal root ganglion 7days after the spared nerve injury model of neuropathic pain. Measures of acute, inflammatory and neuropathic pain behaviours were not significantly different using separate groups of Gpr151 loss-of-function mutant mice and wild-type controls. Galanin at concentrations between 100nM and 10μM did not induce calcium signalling responses in ND7/23 cells transfected with Gpr151.

CONCLUSIONS

Our results indicate that despite the very large upregulation in the DRG after a nerve injury model of neuropathic pain, the Gpr151 orphan receptor does not appear to be involved in the modulation of pain-related behaviours. Further, galanin is unlikely to be an endogenous ligand for Gpr151.

A pharmacogenomic profile of human neural progenitors undergoing differentiation in the presence of the traditional Chinese medicine NeuroAiD

NeuroAiD, a traditional Chinese medicine widely used to treat stroke patients in China, was recently demonstrated in rodent models and in clinical trials to possess neuroregenerative and neuroprotective properties. In order to understand the mechanisms employed by NeuroAiD to bring about its neuroproliferative and neuroprotective effects, we investigated the impact of MLC901, a reformulated version of MLC601, on human neural progenitors undergoing neural differentiation at the molecular level by performing three independent microarray experiments. Functional annotations of the genes regulated by MLC901 that were associated with neurogenesis were found to be enriched. We also identified potential targets (FGF19, GALR2, MMP10, FGF3 and TDO2) of MLC901 that could promote neurogenesis and neuroprotection in the human brain. This work highlighted some interesting targets and offered some insights into the possible mechanism of action of MLC901. The discovery could also provide a platform to the development of future therapeutic targets.

The Role of Hypothalamic Neuropeptides in Neurogenesis and Neuritogenesis

The hypothalamus is a source of neural progenitor cells which give rise to different populations of specialized and differentiated cells during brain development. Newly formed neurons in the hypothalamus can synthesize and release various neuropeptides. Although term neuropeptide recently undergoes redefinition, small-size hypothalamic neuropeptides remain major signaling molecules mediating short- and long-term effects on brain development. They represent important factors in neurite growth and formation of neural circuits. There is evidence suggesting that the newly generated hypothalamic neurons may be involved in regulation of metabolism, energy balance, body weight, and social behavior as well. Here we review recent data on the role of hypothalamic neuropeptides in adult neurogenesis and neuritogenesis with special emphasis on the development of food intake and social behavior related brain circuits.

The generation of knock-in mice expressing fluorescently tagged galanin receptors 1 and 2

The neuropeptide galanin has diverse roles in the central and peripheral nervous systems, by activating the G protein-coupled receptors Gal1, Gal2 and the less studied Gal3 (GalR1-3 gene products). There is a wealth of data on expression of Gal1-3 at the mRNA level, but not at the protein level due to the lack of specificity of currently available antibodies. Here we report the generation of knock-in mice expressing Gal1 or Gal2 receptor fluorescently tagged at the C-terminus with, respectively, mCherry or hrGFP (humanized Renilla green fluorescent protein). In dorsal root ganglia (DRG) neurons expressing the highest levels of Gal1-mCherry, localization to the somatic cell membrane was detected by live-cell fluorescence and immunohistochemistry, and that fluorescence decreased upon addition of galanin. In spinal cord, abundant Gal1-mCherry immunoreactive processes were detected in the superficial layers of the dorsal horn, and highly expressing intrinsic neurons of the lamina III/IV border showed both somatic cell membrane localization and outward transport of receptor from the cell body, detected as puncta within cell processes. In brain, high levels of Gal1-mCherry immunofluorescence were detected within thalamus, hypothalamus and amygdala, with a high density of nerve endings in the external zone of the median eminence, and regions with lesser immunoreactivity included the dorsal raphe nucleus. Gal2-hrGFP mRNA was detected in DRG, but live-cell fluorescence was at the limits of detection, drawing attention to both the much lower mRNA expression than to Gal1 in mice and the previously unrecognized potential for translational control by upstream open reading frames (uORFs).

G-Protein-Coupled Receptors: Next Generation Therapeutic Targets in Head and Neck Cancer?

Therapeutic outcome in head and neck squamous cell carcinoma (HNSCC) is poor in most advanced cases. To improve therapeutic efficiency, novel therapeutic targets and prognostic factors must be discovered. Our studies have identified several G protein-coupled receptors (GPCRs) as promising candidates. Significant epigenetic silencing of GPCR expression occurs in HNSCC compared with normal tissue, and is significantly correlated with clinical behavior. Together with the finding that GPCR activity can suppress tumor cell growth, this indicates that GPCR expression has potential utility as a prognostic factor. In this review, we discuss the roles that galanin receptor type 1 (GALR1) and type 2 (GALR2), tachykinin receptor type 1 (TACR1), and somatostatin receptor type 1 (SST1) play in HNSCC. GALR1 inhibits proliferation of HNSCC cells though ERK1/2-mediated effects on cell cycle control proteins such as p27, p57, and cyclin D1, whereas GALR2 inhibits cell proliferation and induces apoptosis in HNSCC cells. Hypermethylation of GALR1, GALR2, TACR1, and SST1 is associated with significantly reduced disease-free survival and a higher recurrence rate. Although their overall activities varies, each of these GPCRs has value as both a prognostic factor and a therapeutic target. These data indicate that further study of GPCRs is a promising strategy that will enrich pharmacogenomics and prognostic research in HNSCC.

High butyric acid amounts induce oxidative stress, alter calcium homeostasis, and cause neurite retraction in nerve growth factor-treated PC12 cells

Butyric acid (BA) is a common secondary metabolite by-product produced by oral pathogenic bacteria and is detected in high amounts in the gingival tissue of patients with periodontal disease. Previous works have demonstrated that BA can cause oxidative stress in various cell types; however, this was never explored using neuronal cells. Here, we exposed nerve growth factor (NGF)-treated PC1(2) cells to varying BA concentrations (0.5, 1.0, 5.0 mM). We measured total heme, H(2)O(2), catalase, and calcium levels through biochemical assays and visualized the neurite outgrowth after BA treatment. Similarly, we determined the effects of other common periodontal short-chain fatty acids (SCFAs) on neurite outgrowth for comparison. We found that high (1.0 and 5.0 mM) BA concentrations induced oxidative stress and altered calcium homeostasis, whereas low (0.5 mM) BA concentration had no significant effect. Moreover, compared to other SCFAs, we established that only BA was able to induce neurite retraction.

Long non-coding RNA uc.217 regulates neurite outgrowth in dorsal root ganglion neurons following peripheral nerve injury

The intrinsic regeneration capacity of dorsal root ganglion (DRG) neurons can be activated after sciatic nerve injury, and peripheral nerve regeneration is a complex process regulated by multiple molecular responses and signaling pathways. Long non-coding RNAs (lncRNAs) are RNA transcripts > 200 nucleotides in length without protein-coding potential. They regulate gene expression at epigenetic, transcriptional and post-transcriptional levels, and are thus involved in many biological processes and human diseases. However, the role and mechanisms of lncRNAs in regulating the responses of DRG neurons to sciatic nerve injury are not fully investigated. We have previously analysed the expression profiles of lncRNAs and mRNAs in L4-6 DRGs, following rat sciatic nerve transection, by microarray analysis, and constructed a coexpression network of dysregulated lncRNAs and coding genes. In this study, one of these dysregulated lncRNAs, uc.217, was chosen for detailed examination of its expression changes and regulative functions in regenerative DRG neuronal outgrowth. Quantitative real-time PCR and in situ hybridisation confirmed that the expression of uc.217 was down-regulated in DRG neurons after sciatic nerve injury. Silencing of uc.217 expression by small interfering RNA could significantly promote neurite outgrowth in cultured DRG neurons. Moreover, bioinformatic analysis and experimental validation were performed to identify several potential targets of uc.217, which were involved in the regulation of DRG neuron outgrowth. Collectively, our results suggested that a new lncRNA, uc.217, played an important regulative role in peripheral nerve regeneration.

Physiology, signaling, and pharmacology of galanin peptides and receptors: three decades of emerging diversity

Galanin was first identified 30 years ago as a "classic neuropeptide," with actions primarily as a modulator of neurotransmission in the brain and peripheral nervous system. Other structurally-related peptides-galanin-like peptide and alarin-with diverse biologic actions in brain and other tissues have since been identified, although, unlike galanin, their cognate receptors are currently unknown. Over the last two decades, in addition to many neuronal actions, a number of nonneuronal actions of galanin and other galanin family peptides have been described. These include actions associated with neural stem cells, nonneuronal cells in the brain such as glia, endocrine functions, effects on metabolism, energy homeostasis, and paracrine effects in bone. Substantial new data also indicate an emerging role for galanin in innate immunity, inflammation, and cancer. Galanin has been shown to regulate its numerous physiologic and pathophysiological processes through interactions with three G protein-coupled receptors, GAL1, GAL2, and GAL3, and signaling via multiple transduction pathways, including inhibition of cAMP/PKA (GAL1, GAL3) and stimulation of phospholipase C (GAL2). In this review, we emphasize the importance of novel galanin receptor-specific agonists and antagonists. Also, other approaches, including new transgenic mouse lines (such as a recently characterized GAL3 knockout mouse) represent, in combination with viral-based techniques, critical tools required to better evaluate galanin system physiology. These in turn will help identify potential targets of the galanin/galanin-receptor systems in a diverse range of human diseases, including pain, mood disorders, epilepsy, neurodegenerative conditions, diabetes, and cancer.

Galanin modulates the neural niche to favour perineural invasion in head and neck cancer

Perineural invasion (PNI) is an indicator of poor survival in multiple cancers. Unfortunately, there is no targeted treatment for PNI since the molecular mechanisms are largely unknown. PNI is an active process, suggesting that cancer cells communicate with nerves. However, nerve-tumour crosstalk is understudied due to the lack of in vivo models to investigate the mechanisms. Here, we developed an in vivo model of PNI to characterise this interaction. We show that the neuropeptide galanin (GAL) initiates nerve-tumour crosstalk via activation of its G-protein-coupled receptor, GALR2. Our data reveal a novel mechanism by which GAL from nerves stimulates GALR2 on cancer cells to induce NFATC2-mediated transcription of cyclooxygenase-2 and GAL. Prostaglandin E2 promotes cancer invasion, and in a feedback mechanism, GAL released by cancer induces neuritogenesis, facilitating PNI. This study describes a novel in vivo model for PNI and reveals the dynamic interaction between nerve and cancer.

Galanin promotes neuronal differentiation from neural progenitor cells in vitro and contributes to the generation of new olfactory neurons in the adult mouse brain

Galanin is a pleiotropic neuropeptide widely expressed in the nervous system. It plays a role in many diverse physiological functions - including nociception, cognition and metabolism regulation - and acts as neurotrophic/neuroprotective factor for several neuronal populations. In this article we sought to determine the role of galanin on neural stem cell function and its contribution to the plasticity of the nervous system. Here we show that galanin and its receptors are expressed in neural progenitor cells (NPCs) isolated from the developing striatum. Stimulation with galanin results in upregulation of Bcl-Xl, Bcl-2, Mash-1 and Olig-2 that are part of well known pro-survival/pro-neuronal signalling pathways. Accordingly, treatment with galanin increases the number of neurons upon differentiation from these progenitors. We then show that these effects are recapitulated in NPCs isolated from the adult subventricular zone (SVZ), where galanin increases the total number of neurons and the number of newly-generated neurons upon differentiation in vitro. The significance of these findings is highlighted in the adult brain where loss of galanin leads to a marked decrease in the rate of adult SVZ neurogenesis and a reduction in the number of newly generated cells in the olfactory bulb. Interestingly, Gal-KO mice display normal performances in simple tasks of olfactory detection and discrimination, which points to the existence of a certain degree of redundancy in SVZ neurogenesis. Our findings establish the role of galanin as a modulator of neural stem cell function and support the importance of galanin for brain plasticity and repair.

Increased expression of the neuroregenerative peptide galanin in the major pelvic ganglion following cavernous nerve injury

INTRODUCTION

Erectile dysfunction (ED) remains a frequent complication of radical prostatectomy due to injury to the cavernous nerves (CNs). A recent microarray showed the neuropeptide galanin to be one of the most strikingly upregulated genes in the rat major pelvic ganglion (MPG) after bilateral CN crush injury (BCNI).

AIM

The aim of this study is to evaluate the temporal regulation of galanin in the MPG after BCNI and its relationship to functional nerve regeneration.

METHODS

Changes in galanin, galanin receptor (galR), and c-JUN mRNA expression were assessed in Sprague-Dawley rats after sham operation (n = 10) and at 48 hours (n = 10), 7 (n = 10), 14 (n = 5), 21 (n = 5), 30 (n = 5), and 60 (n = 5) days after BCNI using quantitative PCR. Erectile function was assessed by measuring intracavernous pressure (ICP) divided by mean arterial pressure (MAP) during CN electrostimulation. Immunohistochemistry was performed on the MPG in sham-operated animals and 5 days after BCNI.

MAIN OUTCOME MEASURES

ICP/MAP upon CN stimulation; galanin, galR1, -2, -3, and c-JUN mRNA expression at various time points after BCNI; and nNOS, galanin, and galR distribution in the MPG of sham-operated rats and after BCNI.

RESULTS

After BCNI, ICP/MAP values quickly deteriorate, while after 60 days, spontaneous restoration of erectile responses to CN stimulation is observed, reflecting CN regeneration. Galanin mRNA in the MPG is up to 186-fold upregulated compared with sham-operated rats at 48 hours and 7 days after BCNI and gradually declines with increasing time from injury, whereas galanin receptor expressions decrease and c-JUN gradually increases. Galanin expression shows a strong inverse correlation with erectile responses to CN stimulation with time from injury. Injured MPGs show a colocalization between galanin- and nNOS-positive neuronal cell population in the MPG.

CONCLUSIONS

Galanin is upregulated in the MPG in the early phase after CN injury after which it gradually decreases and is present in nNOS-positive neurons of the ganglion. We hypothesize that galanin upregulation is an important factor in the endogenous neuroregenerative response to CN injury.

Development of a high-throughput screening-compatible cell-based functional assay to identify small molecule probes of the galanin 3 receptor (GalR3)

The galanin 3 receptor (GalR3) belongs to the large G protein-coupled receptor (GPCR) family of proteins. GalR3 and two other closely related receptors, GalR1 and GalR2, together with their endogenous ligand galanin, are involved in a variety of physiological and pathophysiological processes. GalR3 in particular has been strongly implicated in addiction and mood-related disorders such as anxiety and depression. It has been the target of many drug discovery programs within the pharmaceutical industry, but despite the significant resources and effort devoted to discovery of galanin receptor subtype selective small molecule modulators, there have been very few reports for the discovery of such molecules. GalR3 has proven difficult to enable in cell-based functional assays due to its apparent poor cell surface expression in recombinant systems. Here, we describe the generation of a modified GalR3 that facilitates its cell surface expression while maintaining wild-type receptor pharmacology. The modified GalR3 has been used to develop a high-throughput screening-compatible, cell-based, cAMP biosensor assay to detect selective small molecule modulators of GalR3. The performance of the assay has been validated by challenging it against a test library of small molecules with known pharmacological activities (LOPAC; Sigma Aldrich). This approach will enable identification of GalR3 selective modulators (chemical probes) that will facilitate dissection of the biological role(s) that GalR3 plays in normal physiological processes as well as in disease states.

Galanin stimulates neurite outgrowth from sensory neurons by inhibition of Cdc42 and Rho GTPases and activation of cofilin

We and others have previously shown that the neuropeptide galanin modulates neurite outgrowth from adult sensory neurons via activation of the second galanin receptor; however, the intracellular signalling pathways that mediate this neuritogenic effect have yet to be elucidated. Here, we demonstrate that galanin decreases the activation state in adult sensory neurons and PC12 cells of Rho and Cdc42 GTPases, both known regulators of filopodial and growth cone motility. Consistent with this, activated levels of Rho and Cdc42 levels are increased in the dorsal root ganglion of adult galanin knockout animals compared with wildtype controls. Furthermore, galanin markedly increases the activation state of cofilin, a downstream effector of many of the small GTPases, in the cell bodies and growth cones of sensory neurons and in PC12 cells. We also demonstrate a reduction in the activation of cofilin, and alteration in growth cone motility, in cultured galanin knockout neurons compared with wildtype controls. These data provide the first evidence that galanin regulates the Rho family of GTPases and cofilin to stimulate growth cone dynamics and neurite outgrowth in sensory neurons. These findings have important therapeutic implications for the treatment of peripheral sensory neuropathies.

GABAergic terminals are a source of galanin to modulate cholinergic neuron development in the neonatal forebrain

The distribution and (patho-)physiological role of neuropeptides in the adult and aging brain have been extensively studied. Galanin is an inhibitory neuropeptide that can coexist with γ-aminobutyric acid (GABA) in the adult forebrain. However, galanin's expression sites, mode of signaling, impact on neuronal morphology, and colocalization with amino acid neurotransmitters during brain development are less well understood. Here, we show that galaninergic innervation of cholinergic projection neurons, which preferentially express galanin receptor 2 (GalR2) in the neonatal mouse basal forebrain, develops by birth. Nerve growth factor (NGF), known to modulate cholinergic morphogenesis, increases GalR2 expression. GalR2 antagonism (M871) in neonates reduces the in vivo expression and axonal targeting of the vesicular acetylcholine transporter (VAChT), indispensable for cholinergic neurotransmission. During cholinergic neuritogenesis in vitro, GalR2 can recruit Rho-family GTPases to induce the extension of a VAChT-containing primary neurite, the prospective axon. In doing so, GalR2 signaling dose-dependently modulates directional filopodial growth and antagonizes NGF-induced growth cone differentiation. Galanin accumulates in GABA-containing nerve terminals in the neonatal basal forebrain, suggesting its contribution to activity-driven cholinergic development during the perinatal period. Overall, our data define the cellular specificity and molecular complexity of galanin action in the developing basal forebrain.

Galanin receptors possibly modulate the obesity-induced change in pain threshold

Pain threshold may be up-regulated or down-regulated according to gender, age, race/ethnic and psychological state. Previous studies indicated that obesity may change pain threshold, both nociceptive and antinociceptive, which resulted from obesity-reduced variation of neuroendocrine. However there is a limited understanding of its molecular mechanism underlying this variation. A lot of evidence supports that galanin increases food intake and body weight to induce obesity in animals. This peptide may also modulate nociceptive susceptibility via central galanin receptor 1 and peripheral galanin receptor 2 in dorsal root ganglion. Whereas injury and obesity may up-regulate the galanin expression and stimulate its secretion to elevate the plasma levels of subjects. Pain may increase the risk of obesity through reduced physical activity. In this review, we highlighted the multiple bilateral interrelation between obesity and pain sensitivity, between galanin and obesity and between galanin and injure-induced pain. In view of the above, we reasoned that galanin receptors possibly participated in the modulation of the obesity-induced change in pain threshold, which need further direct evidence to support as yet. This review is helpful to explore the mechanism that galanin receptors regulate the obesity-induced change of pain sensitivity and to contribute to our understanding of the relation among galanin, obesity and pain threshold.

Galanin gene expression and effects of its knock-down on the development of the nervous system in larval zebrafish

Despite the known importance of galanin in the nervous system of vertebrates, the galanin gene structure and expression and the consequences of galanin deficiency in developing zebrafish are unknown. We cloned the galanin gene and analyzed its expression by using in situ hybridization, PCR, and immunocytochemistry throughout the early development of zebrafish until the end of the first week of life. The single zebrafish galanin gene encoded for a single amidated galanin peptide and a galanin message-associated peptide. Two forms resulting from alternative processing were identified. Galanin mRNA was maternally expressed and found in developing fish throughout early development. In situ hybridization showed the first positive neurons in three groups in the brain at 28 hours postfertilization. At 2 days postfertilization, three prosencephalic neuron groups were seen in the preoptic area and in rostral and caudal periventricular hypothalamus. In addition, two other groups of weakly stained neurons were visible, one in the midbrain and another in the hindbrain. Translation inhibition of galanin mRNA with morpholino oligonucleotides caused complete disappearance of galanin immunoreactivity in the brain until 7 dpf and did not induce known cascades of nonspecific pathways or morphological abnormalities. A minor disturbance of sensory ganglia was found. Galanin knockdown did not alter the expression of tyrosine hydroxylases 1 and 2, choline acetyltransferase, histidine decarboxylase, or orexin mRNA. The results suggest that galanin does not regulate the development of these key markers of specific neurons, although galanin-expressing fibers were in a close spatial proximity to several neurons of these neuronal populations.

Galanin-induced decreases in nucleus accumbens/striatum excitatory postsynaptic potentials and morphine conditioned place preference require both galanin receptor 1 and galanin receptor 2

The neuropeptide galanin has been shown to alter the rewarding properties of morphine. To identify potential cellular mechanisms that might be involved in the ability of galanin to modulate opiate reward, we measured excitatory postsynaptic potentials (EPSPs), using both field and whole-cell recordings from striatal brain slices extracted from wild-type mice and mice lacking specific galanin receptor (GalR) subtypes. We found that galanin decreased the amplitude of EPSPs in both the dorsal striatum and nucleus accumbens. We then performed recordings in slices from knockout mice lacking either the GalR1 or GalR2 gene, and found that the ability of galanin to decrease EPSP amplitude was absent from both mouse lines, suggesting that both receptor subtypes are required for this effect. In order to determine whether behavioral responses to opiates were dependent on the same receptor subtypes, we tested GalR1 and GalR2 knockout mice for morphine conditioned place preference (CPP). Morphine CPP was significantly attenuated in both GalR1 and GalR2 knockout mice. These data suggest that mesolimbic excitatory signaling is significantly modulated by galanin in a GalR1-dependent and GalR2-dependent manner, and that morphine CPP is dependent on the same receptor subtypes.

The pros and cons of growth factors and cytokines in peripheral axon regeneration

Injury to a peripheral nerve induces a complex cellular and molecular response required for successful axon regeneration. Proliferating Schwann cells organize into chains of cells bridging the lesion site, which is invaded by macrophages. Approximately half of the injured neuron population sends out axons that enter the glial guidance channels in response to secreted neurotrophic factors and neuropoietic cytokines. These lesion-associated polypeptides create an environment that is highly supportive for axon regrowth, particularly after acute injury, and ensure that the vast majority of regenerating axons are directed toward the distal nerve stump. Unfortunately, most neurotrophic factors and neuropoietic cytokines are also strong stimulators of axonal sprouting. Although some of the axonal branches will withdraw at later stages, the sprouting effect contributes to the misdirection of reinnervation that results in the lack of functional recovery observed in many patients with peripheral nerve injuries. Here, we critically review the role of neuronal growth factors and cytokines during axon regeneration in the peripheral nervous system. Their differential effects on axon elongation and sprouting were elucidated in various studies on intraneuronal signaling mechanisms following nerve lesion. The present data define a goal for future therapeutic strategies, namely, to selectively stimulate a Ras/Raf/ERK-mediated axon elongation program over an intrinsic PI3K-dependent axonal sprouting program in lesioned motor and sensory neurons. Instead of modulating growth factor or cytokine levels at the lesion site, targeting specific intraneuronal molecules, such as the negative feedback inhibitors of ERK signaling, has been shown to promote long-distance regeneration while avoiding sprouting of regenerating axons until they have reached their target areas.

The p21-activated kinase PAK 5 is involved in formalin-induced nociception through regulation of MAP-kinase signaling and formalin-specific receptors

p21-activated kinases (PAKs) are involved in signal cascades relevant for nociceptive processing and neuropathic pain. Particularly, the recently described group B PAKs 4, 5 and 6 regulate MAP-kinases and the rearrangement of the actin cytoskeleton, both of which have been linked to pain processing. However, a specific role of these PAKs in nociception has not yet been demonstrated. We found PAK 4, 5 and 6 expression in pain-relevant tissues in peripheral and CNS. Since viable knock-out mice only exist for the PAK isoform 5, we further assessed the impact of this PAK on acute and chronic pain using different behavioral models in mice. PAK 5 knock-out mice showed normal acute nociception and did not differ from wild type mice in their neuropathic pain behavior. However, the nociceptive response in formalin-induced paw inflammation was significantly reduced in knock-out mice associated with inhibition of MAP-kinase activation and a decreased number of formalin-induced c-Fos positive neurons in the spinal cord. Furthermore, in isolated neurons, we found a significantly reduced calcium response after stimulation of TRPA1-channels in PAK 5(-/-)- compared to PAK 5(+/+)-cells. Our results indicate that PAK 5 is involved in formalin-induced inflammatory nociception through regulation of MAPK-induced c-Fos-activation and formalin-specific TRP-channels.

Differential roles of galanin on mechanical and cooling responses at the primary afferent nociceptor

Background

Galanin is expressed in a small percentage of intact small diameter sensory neurons of the dorsal root ganglia and in the afferent terminals of the superficial lamina of the dorsal horn of the spinal cord. The neuropeptide modulates nociception demonstrating dose-dependent pro- and anti-nociceptive actions in the naïve animal. Galanin also plays an important role in chronic pain, with the anti-nociceptive actions enhanced in rodent neuropathic pain models. In this study we compared the role played by galanin and its receptors in mechanical and cold allodynia by identifying individual rat C-fibre nociceptors and characterising their responses to mechanical or acetone stimulation.

Results

Mechanically evoked responses in C-fibre nociceptors from naive rats were sensitised after close intra-arterial infusion of galanin or Gal2-11 (a galanin receptor-2/3 agonist) confirming previous data that galanin modulates nociception via activation of GalR2. In contrast, the same dose and route of administration of galanin, but not Gal2-11, inhibited acetone and menthol cooling evoked responses, demonstrating that this inhibitory mechanism is not mediated by activation of GalR2. We then used the partial saphenous nerve ligation injury model of neuropathic pain (PSNI) and the complete Freund’s adjuvant model of inflammation in the rat and demonstrated that close intra-arterial infusion of galanin, but not Gal2-11, reduced cooling evoked nociceptor activity and cooling allodynia in both paradigms, whilst galanin and Gal2-11 both decreased mechanical activation thresholds. A previously described transgenic mouse line which inducibly over-expresses galanin (Gal-OE) after nerve injury was then used to investigate whether manipulating the levels of endogenous galanin also modulates cooling evoked nociceptive behaviours after PSNI. Acetone withdrawal behaviours in naive mice showed no differences between Gal-OE and wildtype (WT) mice. 7-days after PSNI Gal-OE mice demonstrated a significant reduction in the duration of acetone-induced nociceptive behaviours compared to WT mice.

Conclusions

These data identify a novel galaninergic mechanism that inhibits cooling evoked neuronal activity and nociceptive behaviours via a putative GalR1 mode of action that would also be consistent with a TRP channel-dependent mechanism.

Galanin negatively modulates opiate withdrawal via galanin receptor 1

RATIONALE

The neuropeptide galanin has been shown to modulate opiate dependence and withdrawal. These effects could be mediated via activation of one or more of the three distinct G protein-coupled receptors, namely galanin receptors 1 (GalR1), 2 (GalR2), and 3 (GalR3).

OBJECTIVES

In this study, we used several transgenic mouse lines to further define the mechanisms underlying the role played by galanin and its receptors in the modulation of morphine dependence. First, transgenic mice expressing β-galactosidase under the control of the galanin promoter were used to assess the regulation of galanin expression in response to chronic morphine administration and withdrawal. Next, the behavioral responses to chronic morphine administration and withdrawal were tested in mice that over-express galanin, lack the GalR1 gene, or lack the GalR2 gene.

METHODS

Transgenic and matched wild-type mice were given increasing doses of morphine followed by precipitation of withdrawal by naloxone and behavioral responses to withdrawal were assessed.

RESULTS

Both morphine administration and withdrawal increased galanin gene transcription in the locus coeruleus (LC). Increasing galanin levels in the brain reduced signs of opiate withdrawal. Mice lacking GalR1 undergo more severe opiate withdrawal, whereas mice lacking GalR2 show no significant difference in withdrawal signs, compare with matched wild-type controls.

CONCLUSIONS

Opiate administration and withdrawal increase galanin expression in the LC. Galanin opposes the actions of morphine which leads to opiate dependence and withdrawal, an effect that is mediated via GalR1.

Peripheral galanin receptor 2 as a target for the modulation of pain

The neuropeptide galanin is widely expressed in the nervous system and has an important role in nociception. It has been shown that galanin can facilitate and inhibit nociception in a dose-dependent manner, principally through the central nervous system, with enhanced antinociceptive actions after nerve injury. However, following nerve injury, expression of galanin within the peripheral nervous system is dramatically increased up to 120-fold. Despite this striking increase in the peripheral nervous system, few studies have investigated the role that galanin plays in modulating nociception at the primary afferent nociceptor. Here, we summarise the recent work supporting the role of peripherally expressed galanin with particular reference to the dual actions of the galanin receptor 2 in neuropathic pain highlighting this as a potential target analgesic.

Differential activity by polymorphic variants of a remote enhancer that supports galanin expression in the hypothalamus and amygdala: implications for obesity, depression and alcoholism

The expression of the galanin gene (GAL) in the paraventricular nucleus (PVN) and in the amygdala of higher vertebrates suggests the requirement for highly conserved, but unidentified, regulatory sequences that are critical to allow the galanin gene to control alcohol and fat intake and modulate mood. We used comparative genomics to identify a highly conserved sequence that lay 42 kb 5' of the human GAL transcriptional start site that we called GAL5.1. GAL5.1 activated promoter activity in neurones of the PVN, arcuate nucleus and amygdala that also expressed the galanin peptide. Analysis in neuroblastoma cells demonstrated that GAL5.1 acted as an enhancer of promoter activity after PKC activation. GAL5.1 contained two polymorphisms; rs2513280(C/G) and rs2513281(A/G), that occurred in two allelic combinations (GG or CA) where the dominant GG alelle occurred in 70-83 % of the human population. Intriguingly, both SNPs were found to be in LD (R(2) of 0.687) with another SNP (rs2156464) previously associated with major depressive disorder (MDD). Recreation of these alleles in reporter constructs and subsequent magnetofection into primary rat hypothalamic neurones showed that the CA allele was 40 % less active than the GG allele. This is consistent with the hypothesis that the weaker allele may affect food and alcohol preference. The linkage of the SNPs analysed in this study with a SNP previously associated with MDD together with the functioning of GAL5.1 as a PVN and amygdala specific enhancer represent a significant advance in our ability to understand alcoholism, obesity and major depressive disorder.

Activation of the galanin receptor 2 in the periphery reverses nerve injury-induced allodynia

Background

Galanin is expressed at low levels in the intact sensory neurons of the dorsal root ganglia with a dramatic increase after peripheral nerve injury. The neuropeptide is also expressed in primary afferent terminals in the dorsal horn, spinal inter-neurons and in a number of brain regions known to modulate nociception. Intrathecal administration of galanin modulates sensory responses in a dose-dependent manner with inhibition at high doses. To date it is unclear which of the galanin receptors mediates the anti-nociceptive effects of the neuropeptide and whether their actions are peripherally and/or centrally mediated. In the present study we investigated the effects of direct administration into the receptive field of galanin and the galanin receptor-2/3-agonist Gal2-11 on nociceptive primary afferent mechanical responses in intact rats and mice and in the partial saphenous nerve injury (PSNI) model of neuropathic pain.

Results

Exogenous galanin altered the responses of mechano-nociceptive C-fibre afferents in a dose-dependent manner in both naive and nerve injured animals, with low concentrations facilitating and high concentrations markedly inhibiting mechano-nociceptor activity. Further, use of the galanin fragment Gal2-11 confirmed that the effects of galanin were mediated by activation of galanin receptor-2 (GalR2). The inhibitory effects of peripheral GalR2 activation were further supported by our demonstration that after PSNI, mechano-sensitive nociceptors in galanin over-expressing transgenic mice had significantly higher thresholds than in wild type animals, associated with a marked reduction in spontaneous neuronal firing and C-fibre barrage into the spinal cord.

Conclusions

These findings are consistent with the hypothesis that the high level of endogenous galanin in injured primary afferents activates peripheral GalR2, which leads to an increase in C-fibre mechanical activation thresholds and a marked reduction in evoked and ongoing nociceptive responses.

Messenger RNA and microRNA profiling during early mouse EB formation

Embryonic stem (ES) cells can be induced to differentiate into embryoid bodies (EBs) in a synchronised manner when plated at a fixed density in hanging drops. This differentiation procedure mimics post-implantation development in mouse embryos and also serves as the starting point of protocols used in differentiation of stem cells into various lineages. Currently, little is known about the potential influence of microRNAs (miRNAs) on mRNA expression patterns during EB formation. We have measured mRNA and miRNA expression in developing EBs plated in hanging drops until day 3, when discrete structural changes occur involving their differentiation into three germ layers. We observe significant alterations in mRNA and miRNA expression profiles during this early developmental time frame, in particular of genes involved in germ layer formation, stem cell pluripotency and nervous system development. Computational target prediction using Pictar, TargetScan and miRBase Targets reveals an enrichment of binding sites corresponding to differentially and highly expressed miRNAs in stem cell pluripotency genes and a neuroectodermal marker, Nes. We also find that members of let-7 family are significantly down-regulated at day 3 and the corresponding up-regulated genes are enriched in let-7 seed sequences. These results depict how miRNA expression changes may affect the expression of mRNAs involved in EB formation on a genome-wide scale. Understanding the regulatory effects of miRNAs during EB formation may enable more efficient derivation of different cell types in culture.