GAL1 Receptor Research Articles

Abstract 4465: Galectin-1 regulates CD147 and downstream pathways critical for glioma progression

Abstract Galectin-1 (Gal-1) is an important protein for glioma progression and glioma stem cell maintenance. Gal-1 may act through CD147, a potential Gal-1 receptor. CD147, also known as Basigin or extracellular matrix metalloproteinase inducer (EMMPRIN), is a transmembrane glycoprotein highly expressed in various cancer cells. An analysis utilizing the Gliovis database and encompassing 667 Glioblastoma Multiforme (GBM) patients segregated based on median CD147 expression levels delineated cohorts with above-median (n=339) and below-median (n=328) CD147 expression. Kaplan-Meier survival curves unveiled a significant association between heightened CD147 expression and reduced overall survival (OS) in this patient population. Experimental approaches employing immunoblotting and immunohistochemistry techniques on shGal-1 treated cell lysates and mouse brain samples exhibited decreased CD147 expression compared to respective controls. Additionally, immunocytochemical studies corroborated an augmented colocalization of Gal-1 and CD147, with a subsequent reduction in this association following shGal-1 treatment. Next, we used AC-73, a selective CD147 inhibitor, to determine the levels of CD147 and Gal-1. Treatment with 20μM AC-73 and siRNA for CD147 showed reduced CD147 levels in GSC33 and GSC20 cells while maintaining unaltered Gal-1 expression. Inhibiting CD147 did not affect Gal-1 levels, further suggesting Gal-1 acts upstream. CD147 activates matrix metalloproteinase-9 (MMP9), and CD147 knockdown reduced MMP9 levels, elucidating a Gal-1-CD147-MMP9 pathway. Overall, Gal-1 appears to act upstream of CD147 to regulate MMP9, integrins, and other factors important for glioma progression. Further elucidation of these pathways will provide insights into glioma biology and potential therapeutic targets. Citation Format: Maheedhara R. Guda, Andrew J. Tsung, Swapna Asuthkar, Kiran Velpula. Galectin-1 regulates CD147 and downstream pathways critical for glioma progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4465.

Unique pharmacodynamic properties and low abuse liability of the µ-opioid receptor ligand (S)-methadone.

(R,S)-methadone ((R,S)-MTD) is a µ-opioid receptor (MOR) agonist comprised of (R)-MTD and (S)-MTD enantiomers. (S)-MTD is being developed as an antidepressant and is considered an N-methyl-D-aspartate receptor (NMDAR) antagonist. We compared the pharmacology of (R)-MTD and (S)-MTD and found they bind to MORs, but not NMDARs, and induce full analgesia. Unlike (R)-MTD, (S)-MTD was a weak reinforcer that failed to affect extracellular dopamine or induce locomotor stimulation. Furthermore, (S)-MTD antagonized motor and dopamine releasing effects of (R)-MTD. (S)-MTD acted as a partial agonist at MOR, with complete loss of efficacy at the MOR-galanin Gal1 receptor(Gal1R) heteromer, a key mediator of the dopaminergic effects of opioids. In sum, we report novel and unique pharmacodynamic properties of (S)-MTD that are relevant to its potential mechanism of action and therapeutic use.One-sentence summary: (S)-MTD, like (R)-MTD, binds to and activates MORs in vitro, but (S)-MTD antagonizes the MOR-Gal1R heteromer, decreasing its abuse liability.

Galanin receptors modulate cutaneous vasodilation elicited by whole-body and local heating but not thermal sweating in young adults

Galanin receptor subtypes GAL1, GAL2, and GAL3 are involved in several biological functions. We hypothesized that 1) GAL3 receptor activation contributes to sweating but limits cutaneous vasodilation induced by whole-body and local heating without a contribution of GAL2; and 2) GAL1 receptor activation attenuates both sweating and cutaneous vasodilation during whole-body heating. Young adults underwent whole-body (n = 12, 6 females) and local (n = 10, 4 females) heating. Forearm sweat rate (ventilated capsule) and cutaneous vascular conductance (CVC; ratio of laser-Doppler blood flow to mean arterial pressure) were assessed during whole-body heating (water-perfusion suit circulated with warm (35 °C) water), while CVC was also assessed by local forearm heating (from 33 °C to 39 °C and elevated to 42 °C thereafter; each level of heating maintained for ∼30 min). Sweat rate and CVC were evaluated at four intradermal microdialysis forearm sites treated with either 1) 5% dimethyl sulfoxide (control), 2) M40, a non-selective GAL1 and GAL2 receptor antagonist, 3) M871 to selectively antagonize GAL2 receptor, or 4) SNAP398299 to selectively antagonize GAL3 receptor. Sweating was not modulated by any GAL receptor antagonist (P > 0.169), whereas only M40 reduced CVC (P ≤ 0.003) relative to control during whole-body heating. Relative to control, SNAP398299 augmented the initial and sustained increase in CVC during local heating to 39 °C, and the transient increase at 42 °C (P ≤ 0.028). We confirmed that while none of the galanin receptors modulate sweating during whole-body heating, GAL1 receptors mediate cutaneous vasodilation. Further, GAL3 receptors blunt cutaneous vasodilation during local heating.

QRFP receptor in GtoPdb v.2023.1

The human gene encoding the QRFP receptor (nomenclature as agreed by the NC-IUPHAR Subcommittee on the QRFP receptor [19]; QRFPR, formerly known as the Peptide P518 receptor), previously designated as an orphan GPCR receptor was identified in 2001 by Lee et al. from a hypothalamus cDNA library [17]. However, the reported cDNA (AF411117) is a chimera with bases 1-127 derived from chromosome 1 and bases 155-1368 derived from chromosome 4. When corrected, QRFPR (also referred to as SP9155 or AQ27) encodes a 431 amino acid protein that shares sequence similarities in the transmembrane spanning regions with other peptide receptors. These include neuropeptide FF2 (38%), neuropeptide Y2 (37%) and galanin Gal1 (35%) receptors. QRFP receptor was identified as a Gs-coupled GPCR [6, 14] that's activated by the endogenous peptides QRFP43 (43RFa) and QRFP26 (26RFa) [6, 14, 11]. However, Gq- and Gi/o-mediated signaling was also reported [11, 25]. Two naturally occurring mutations in the human QRFP receptor lead to distinct and opposite 26RFa-evoked signaling bias [20].

GALR2 and Y1R agonists intranasal infusion enhanced adult ventral hippocampal neurogenesis and antidepressant-like effects involving BDNF actions.

Dysregulation of adult hippocampal neurogenesis is linked to major depressive disorder (MDD), with more than 300 million people diagnosed and worsened by the COVID-19 pandemic. Accumulating evidence for neuropeptide Y (NPY) and galanin (GAL) interaction was shown in various limbic system regions at molecular-, cellular-,and behavioral-specific levels. The purpose of the current work was to evaluate the proliferating role of GAL2 receptor(GALR2) and Y1R agonists interaction upon intranasal infusion in the ventral hippocampus. We studied their hippocampal proliferating actions using the proliferating cell nuclear antigen (PCNA) on neuroblasts or stem cells and the expression of the brain-derived neurothrophic factor (BDNF). Moreover, we studied the formation of Y1R-GALR2 heteroreceptor complexes and analyzed morphological changes in hippocampal neuronal cells. Finally, the functional outcome of the NPY and GAL interaction on the ventral hippocampus was evaluated in the forced swimming test. We demonstrated that the intranasal infusion of GALR2 and the Y1R agonists promotes neuroblasts proliferation in the dentate gyrus of the ventral hippocampus and the induction of the neurotrophic factor BDNF. These effects were mediated by the increased formation of Y1R-GALR2 heteroreceptor complexes, which may mediate the neurites outgrowth observed on neuronal hippocampal cells. Importantly, BDNF action was found necessary for the antidepressant-like effects after GALR2 and the Y1R agonists intranasaladministration. Our data may suggest the translational development of new heterobivalent agonist pharmacophores acting on Y1R-GALR2 heterocomplexes in the ventral hippocampus for the novel therapy of MDD or depressive-affecting diseases.

Structure and functions of spexin as a new neuroendocrine signal

Spexin (SPX ) is a recently discovered endogenous peptide consisting of 14 amino acids. It was found that SPX, kisspeptin (KISS), and galanin (GAL) peptides belong to the same gene family and are also endogenous ligands of GAL2 and GAL3 receptors. The amino acid sequence of the SPX peptide is relatively conserved in vertebrates and invertebrates. The mRNA and protein of SPX are highly expressed both in peripheral organs and in the peripheral/central nervous system of mammals, birds, and fishes. Many biological roles of SPX has been found in non- mammal/mammals, including food intake, energy metabolism, reproduction, nociception, gastrointestinal motility, stress, and endocrine functions. This review collectively mentions the peptide structure of SPX, its receptors and distribution in tissues, and the biological activities of SPX on various organs.

Preferential Gs protein coupling of the galanin Gal1 receptor in the µ-opioid-Gal1 receptor heterotetramer

Recent studies have proposed that heteromers of µ-opioid receptors (MORs) and galanin Gal1 receptors (Gal1Rs) localized in the mesencephalon mediate the dopaminergic effects of opioids. The present study reports converging evidence, using a peptide-interfering approach combined with biophysical and biochemical techniques, including total internal reflection fluorescence microscopy, for a predominant homodimeric structure of MOR and Gal1R when expressed individually, and for their preference to form functional heterotetramers when co-expressed. Results show that a heteromerization-dependent change in the Gal1R homodimeric interface leads to a switch in G-protein coupling from inhibitory Gi to stimulatory Gs proteins. The MOR-Gal1R heterotetramer, which is thus bound to Gs via the Gal1R homodimer and Gi via the MOR homodimer, provides the framework for a canonical Gs-Gi antagonist interaction at the adenylyl cyclase level. These novel results shed light on the intense debate about the oligomeric quaternary structure of G protein-coupled receptors, their predilection for heteromer formation, and the resulting functional significance.

Galanin and Neuropeptide Y Interaction Enhances Proliferation of Granule Precursor Cells and Expression of Neuroprotective Factors in the Rat Hippocampus with Consequent Augmented Spatial Memory.

Dysregulation of hippocampal neurogenesis is linked to several neurodegenereative diseases, where boosting hippocampal neurogenesis in these patients emerges as a potential therapeutic approach. Accumulating evidence for a neuropeptide Y (NPY) and galanin (GAL) interaction was shown in various limbic system regions at molecular-, cellular-, and behavioral-specific levels. The purpose of the current work was to evaluate the role of the NPY and GAL interaction in the neurogenic actions on the dorsal hippocampus. We studied the Y1R agonist and GAL effects on: hippocampal cell proliferation through the proliferating cell nuclear antigen (PCNA), the expression of neuroprotective and anti-apoptotic factors, and the survival of neurons and neurite outgrowth on hippocampal neuronal cells. The functional outcome was evaluated in the object-in-place task. We demonstrated that the Y1R agonist and GAL promote cell proliferation and the induction of neuroprotective factors. These effects were mediated by the interaction of NPYY1 (Y1R) and GAL2 (GALR2) receptors, which mediate the increased survival and neurites’ outgrowth observed on neuronal hippocampal cells. These cellular effects are linked to the improved spatial-memory effects after the Y1R agonist and GAL co-injection at 24 h in the object-in-place task. Our results suggest the development of heterobivalent agonist pharmacophores, targeting Y1R–GALR2 heterocomplexes, therefore acting on the neuronal precursor cells of the DG in the dorsal hippocampus for the novel therapy of neurodegenerative cognitive-affecting diseases.

Dual electrochemical sensing of spiked virus and SARS-CoV-2 using natural bed-receptor (MV-gal1)

It has been necessary to use methods that can detect the specificity of a virus during virus screening. In this study, we use a dual platform to identify any spiked virus and specific SARS-CoV-2 antigen, sequentially. We introduce a natural bed-receptor surface as Microparticle Vesicle-Galactins1 (MV-gal1) with the ability of glycan binding to screen every spiked virus. MV are the native vesicles which may have the gal-1 receptor. Gal-1 is the one of lectin receptor which can bind to glycan. After dropping the MV-gal1 on the SCPE/GNP, the sensor is turned on due to the increased electrochemical exchange with [Fe(CN)6]−3/−4 probe. Dropping the viral particles of SARS-CoV-2 cause to turn off the sensor with covering the sugar bond (early screening). Then, with the addition of Au/Antibody-SARS-CoV-2 on the MV-gal1@SARS-CoV-2 Antigen, the sensor is turned on again due to the electrochemical amplifier of AuNP (specific detection).For the first time, our sensor has the capacity of screening of any spike virus, and the specific detection of COVID-19 (LOD: 4.57 × 102 copies/mL) by using the natural bed-receptor and a specific antibody in the point of care test.

Galanin receptors in GtoPdb v.2021.3

Galanin receptors (provisional nomenclature as recommended by NC-IUPHAR [57]) are activated by the endogenous peptides galanin and galanin-like peptide. Human galanin is a 30 amino-acid non-amidated peptide [52]; in other species, it is 29 amino acids long and C-terminally amidated. Amino acids 1-14 of galanin are highly conserved in mammals, birds, reptiles, amphibia and fish. Shorter peptide species (e.g. human galanin-1-19 [21] and porcine galanin-5-29 [170]) and N-terminally extended forms (e.g. N-terminally seven and nine residue elongated forms of porcine galanin [22, 170]) have been reported. More recently, the newly-identified peptide, spexin (SPX), has been reported to activate human GAL2 and GAL3 (but not GAL1) receptors in heterologous expression systems; and to alter GAL2/3 receptor-related behaviours in animals [89].

Galanin receptors in GtoPdb v.2021.2

Galanin receptors (provisional nomenclature as recommended by NC-IUPHAR [57]) are activated by the endogenous peptides galanin and galanin-like peptide. Human galanin is a 30 amino-acid non-amidated peptide [52]; in other species, it is 29 amino acids long and C-terminally amidated. Amino acids 1-14 of galanin are highly conserved in mammals, birds, reptiles, amphibia and fish. Shorter peptide species (e.g. human galanin-1-19 [21] and porcine galanin-5–29 [170]) and N-terminally extended forms (e.g. N-terminally seven and nine residue elongated forms of porcine galanin [22, 170]) have been reported. More recently, the newly-identified peptide, spexin (SPX), has been reported to activate human GAL2 and GAL3 (but not GAL1) receptors in heterologous expression systems; and to alter GAL2/3 receptor-related behaviours in animals [89].

QRFP receptor (version 2019.4) in the IUPHAR/BPS Guide to Pharmacology Database

The human gene encoding the QRFP receptor (nomenclature as agreed by the NC-IUPHAR Subcommittee on the QRFP receptor [16]; QRFPR, formerly known as the Peptide P518 receptor), previously designated as an orphan GPCR receptor was identified in 2001 by Lee et al. from a hypothalamus cDNA library [15]. However, the reported cDNA (AF411117) is a chimera with bases 1-127 derived from chromosome 1 and bases 155-1368 derived from chromosome 4. When corrected, QRFPR (also referred to as SP9155 or AQ27) encodes a 431 amino acid protein that shares sequence similarities in the transmembrane spanning regions with other peptide receptors. These include neuropeptide FF2 (38%), neuropeptide Y2 (37%) and galanin Gal1 (35%) receptors.

Opioid-galanin receptor heteromers mediate the dopaminergic effects of opioids.

Identifying non-addictive opioid medications is a high priority in medical sciences, but μ-opioid receptors mediate both the analgesic and addictive effects of opioids. We found a significant pharmacodynamic difference between morphine and methadone that is determined entirely by heteromerization of μ-opioid receptors with galanin Gal1 receptors, rendering a profound decrease in the potency of methadone. This was explained by methadone's weaker proficiency to activate the dopaminergic system as compared to morphine and predicted a dissociation of therapeutic versus euphoric effects of methadone, which was corroborated by a significantly lower incidence of self-report of "high" in methadone-maintained patients. These results suggest that μ-opioid-Gal1 receptor heteromers mediate the dopaminergic effects of opioids that may lead to a lower addictive liability of opioids with selective low potency for the μ-opioid-Gal1 receptor heteromer, exemplified by methadone.

Abstract 4860: A novel class of small-molecule inhibitors of galectin-1 for prostate cancer therapy

Abstract Galectin-1 (Gal-1) is a multifunctional carbohydrate-binding protein and plays a key role in cancer cell proliferation, apoptosis, cell cycle, tumor angiogenesis and evasion of immune responses. It is also directly involved in the process of angiogenesis and tumor immune escape. An elevated level of Gal-1 has been found in many cancers, including prostate cancer. We show by immunohistochemistry in human prostate tissue that Gal-1 expression level was very low in all non-tumor samples and highly expressed in prostate cancer tissues. In addition, Gal-1 was progressively upregulated from low- , intermediate- to high-grade prostate cancer. Taken together, Gal-1 is an excellent therapeutic target against cancer. Yet, no inhibitors against Gal-1 have been approved by the FDA for cancer treatment due to lack of potent, specific and in vivo effective molecules. We recently discovered a novel small-molecule inhibitor of Gal-1, named LLS2, through a high-throughput one-bead two-compound combinatorial library approach. LLS2 exhibits cytotoxic activity against prostate cancer and ovarian cancer cells. We synthesized a series of LLS2 analogs and performed structure-activity relationship studies, leading to a more potent inhibitor LLS30 that induced apoptosis in castration-resistant prostate cancer cells expressing high levels of Gal-1. Molecular modeling study showed LLS30 bound to the sugar-binding groove of Gal-1. In enzalutamide (ENZ)-resistant 22Rv1 prostate cancer cells expressing high levels of Gal-1 and androgen receptor (AR) splice variants, LLS30 could inhibit expression of AR splice variants and sensitize the cells to ENZ in a dose-dependent manner. Downregulation of Gal-1 by siRNA prevented the expression of alternatively spliced AR variants. More importantly, LLS30 showed potent in vivo antitumor efficacy and synergistic activities with docetaxel and ENZ against PC-3 and 22Rv1 prostate cancer models, respectively. Blood chemistry test from the treated animal showed minimum effect of LLS30 on the liver and kidney functions, implying low toxicity. LLS30 is an excellent drug candidate for preclinical development as a novel prostate cancer therapeutic. Citation Format: Ruiwu Liu, Tsung-Chieh Shih, Sophie Kiss, Xiaocen Li, Ting Wang, Jonathan S. Huynh, Chun-Te Wu, Yong Duan, Paramita M. Ghosh, Kit S. Lam. A novel class of small-molecule inhibitors of galectin-1 for prostate cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4860.

The antidepressant-like effect of galanin in the dorsal raphe nucleus of rats involves GAL2 receptors

Galanin is a neuropeptide distributed in human and rat brain regions that are involved with emotional regulation, such as the dorsal raphe nucleus (DRN). Galanin effects in the DRN are mediated by GAL1 and GAL2 receptors. Intracerebral infusion of a GAL2 (AR-M1896) or a GAL1 (M617) agonist induced either antidepressant or depressive-like effect, respectively, in rats exposed to the forced swimming test (FST). However, it is not clear if GAL1 and/or GAL2 receptors present in the DRN would be involved in such effects. Therefore, we investigated the effects induced by intra-DRN infusion of galanin (0.3 nmol), AR-M1896 (1 nmol, GAL2 agonist), or M617 (GAL1 agonist) in rats exposed to the FST. Galanin and AR-M1896 intra-DRN administration induced antidepressant-like effect in the FST. However, M617 did not induce any change in the FST. Neither M617 nor AR-M1896 changed the locomotor activity of rats in the open field test. Intra-DRN pre-treatment with M871 (1 nmol), a selective GAL2 antagonist, counteracted the antidepressant-like effect induced by galanin. These results suggest that galanin signaling through GAL2 receptors in the DRN produces triggers antidepressant-like effect.

Dorsal hippocampal galanin modulates anxiety-like behaviours in rats

Galanin, a peptide expressed in mammalian brain regions, has been implicated in anxiety and depression. Galanin signalling occurs through three G protein-linked receptors (GAL1, GAL2 and GAL3). Galanin regulates the release of neurotransmitters in some brain regions related to anxiety, including the hippocampus. GAL2 is the most abundant galanin receptor in the dorsal hippocampus. In this study, we evaluated whether galanin administered in the dorsal hippocampus affected anxiety-like behaviours of rats. We also investigated if GAL2 receptors are involved in the anxiogenic-like effect of galanin using a GAL2 antagonist, M871. To achieve these objectives, male adult Wistar rats received intra-dorsal hippocampal delivery of galanin (0.3 and 1.0 nmol/0.5 µl) or vehicle in experiment 1 and GAL2 antagonist M871 (1.0 and 3.0 nmol/0.5 µl) or vehicle in experiment 2. Twenty min after administration of drugs, the animals were tested in the elevated plus-maze (EPM). Galanin (1.0 nmol) induced anxiogenic-like behaviours, while the GAL2 receptor antagonist M871 (3.0 nmol) induced anxiolytic-like behaviours in rats exposed to the EPM, indicating a tonic effect of galanin. In experiment 3, we evaluated whether previous infusion of the GAL2 antagonist M871 (1 or 2 nmol) in the dorsal hippocampus would block the anxiogenic-like effect of galanin in rats tested in the EPM. We showed that M871 (2.0 nmol) counteracted the anxiogenic-like effect of galanin infused in the dorsal hippocampus of rats. Altogether, our results provide evidence that galanin promotes pharmacological and tonic anxiogenic-like effects in the dorsal hippocampus, possibly mediated by GAL2 receptors.

Galanin suppresses proliferation of human U251 and T98G glioma cells via its subtype 1 receptor.

Galanin is a neuropeptide with a widespread distribution throughout the nervous and endocrine systems, and recent studies have shown an anti-proliferative effect of galanin on several types of tumors. However, whether and how galanin and its receptors are involved in the regulation of cell proliferation in glioma cells remains unclear. In this study, the roles of galanin and its subtype 1 receptor (GAL1) in the proliferation of human U251 and T98G glioma cells were investigated. We found that galanin significantly suppressed the proliferation of U251 and T98G cells as well as tumor growth in nude mice. However, galanin did not exert apoptotic or cytotoxic effects on these two cell lines. In addition, we showed that galanin decreased the proliferation of U251 and T98G cells via its GAL1 receptor. Finally, we found that the GAL1 receptor was involved in the suppressive effects of galanin by activating ERK1/2.

Galanin subtype 1 and subtype 2 receptors mediate opposite anxiety-like effects in the rat dorsal raphe nucleus

About 40% of the dorsal raphe nucleus (DRN) neurons co-express serotonin (5-HT) and galanin. Serotonergic pathways from the DRN to the amygdala facilitate learned anxiety, while those from the DRN to the dorsal periaqueductal grey matter (DPAG) impair innate anxiety. Previously, we showed that galanin infusion in the DRN of rats induces anxiolytic effect by impairing inhibitory avoidance without changing escape behaviour in the elevated T-maze (ETM). Here, we evaluated: (1) which galanin receptors would be involved in the anxiolytic effect of galanin in the DRN of rats tested in the ETM; (2) the effects of galanin intra-DRN on panic-like behaviours evoked by electrical stimulation of the DPAG. The activation of DRN GAL1 receptors by M617 (1.0 and 3.0nmol) facilitated inhibitory avoidance, whereas the activation of GAL2 receptors by AR-M1896 (3.0nmol) impaired the inhibitory avoidance in the ETM, suggesting an anxiogenic and an anxiolytic-like effect respectively. Both agonists did not change escape behaviour in the ETM or locomotor activity in the open field. The anxiolytic effect of AR-M1896 was attenuated by the prior administration of WAY100635 (0.18nmol), a 5-HT1A antagonist. Galanin (0.3nmol) administered in the DRN increased discreetly flight behaviours induced by electrical stimulation of the DPAG, suggesting a panicolytic effect. Together, our results showed that galanin mediates opposite anxiety responses in the DRN by activation of GAL1 and GAL2 receptors. The anxiolytic effect induced by activation of Gal2 receptors may depend on serotonergic tone. Finally, the role of galanin in panic related behaviours remains uncertain.

Galanin inhibits GLP‐1 and GIP secretion via the GAL1 receptor in enteroendocrine L and K cells

Galanin is a widely expressed neuropeptide, which in the gut is thought to modulate gastrointestinal motility and secretion. We aimed to elucidate the poorly characterised mechanisms underlying the inhibitory effect of galanin and the potential involvement of G-protein coupled inwardly rectifying potassium, Kir 3, (GIRK) channels in glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) secretion. Purified murine L and K cells were analysed for expression of galanin receptors and GIRK subunits. Hormone secretion was measured from primary murine intestinal cultures. Intracellular cAMP was monitored in primary L cells derived from mice expressing the Epac2camps sensor under the control of the proglucagon promoter. Galanin receptor 1 (GAL1, Galr1) and GIRK channel 1 (Kir 3.1, Kcnj3) and 4 (Kir 3.4, Kcnj5) mRNA expression was highly enriched in K and L cells. Galanin and a selective GAL1 receptor agonist (M617) potently inhibited GLP-1 and GIP secretion from primary small intestinal cultures. In L cells, galanin significantly inhibited the forskolin-induced cAMP response. The GIRK1/4 activator ML297 significantly reduced glucose-stimulated and IBMX-stimulated GLP-1 secretion but had no effect on GIP. The GIRK blocker tertiapin-Q did not impair galanin-mediated GLP-1 inhibition. Galanin, acting via the GAL1 receptor and Gi -coupled signalling in L and K cells, is a potent inhibitor of GLP-1 and GIP secretion. Although GIRK1/4 channels are expressed in these cells, their activation does not appear to play a major role in galanin-mediated inhibition of incretin secretion.

Galanin microinjection into the dorsal periaqueductal gray matter produces paradigm-dependent anxiolytic effects.

Galanin is a peptide that is present in the central nervous system in mammals, including rodents and humans. The actions of galanin are mediated by three types of metabotropic receptors: GAL1, GAL2, and GAL3. GAL1 and GAL3 increase K(+) efflux, and GAL2 increases intracellular Ca(2+) levels. The distribution of galanin and its receptors suggests its involvement in fear and/or anxiety. The periaqueductal gray matter (PAG) is a key mediator of defensive behaviors that is both targeted by galaninergic projections and supplied with GAL1 receptors and, less markedly, GAL2 receptors. We examined the effects of galanin microinjections in the dorsal PAG (dPAG) on the performance of rats in different models of anxiety. Male Wistar rats (n=7-12) were implanted with guide cannulae in the dPAG. They received microinjections of either galanin (0.3, 1.0, and 3.0 nmol) or vehicle and were tested in the Vogel conflict test (VCT), elevated plus maze (EPM), and elevated T-maze (ETM). Rats that were tested in the ETM were further evaluated for exploratory activity in the open field test (OFT). Galanin microinjections had no effects on anxiety-like behavior in the EPM or VCT or exploratory activity in the EPM or OFT. In the ETM, however, microinjections of 3 nmol galanin impaired learned anxiety (i.e., avoidance of the open arms) without changing unconditioned fear (i.e., escape from the open arms). The present data suggest that galanin transmission in the dPAG inhibits the acquisition of anxiety-like responses in the ETM.