The galanin receptor-3 antagonist, SNAP 37889, inhibits cue-induced reinstatement of alcohol-seeking and increases c-Fos expression in the nucleus accumbens shell of alcohol-preferring rats.

INTRODUCTION: This study aimed to investigate the effects of the galanin-3 receptor antagonist, SNAP 37889, on c-Fos protein expression after cue-induced reinstatement of alcohol-seeking in the brains of alcohol-preferring rats. METHODS: Eighteen alcohol-preferring rats were trained to self-administer 10% v/v ethanol in the presence of response-contingent cues, which was followed by extinction. Rats were then treated with SNAP 37889 (30 mg/kg, i.p.) or vehicle, before being tested for cue-induced reinstatement. Administration of SNAP 37889 reduced cue-induced reinstatement of ethanol-seeking behaviour. To examine the effect of SNAP 37889 and cue-induced reinstatement on neuronal activation, c-Fos expression was measured in subregions of the medial prefrontal cortex and nucleus accumbens. RESULTS: SNAP 37889 administration increased c-Fos immunoreactivity in the nucleus accumbens shell, but was without effect in the nucleus accumbens core and the medial prefrontal cortex. Dual-label Fos/tyrosine hydroxylase immunohistochemistry was used to examine the effects of SNAP 37889 on dopamine neurons in the ventral tegmental area; however, no differences between SNAP 37889 and vehicle-treated rats were found. CONCLUSIONS: These data support previous findings of galanin-3 receptor involvement in cue-induced reinstatement of alcohol-seeking behaviour, and provide novel evidence that the ability of galanin-3 receptor antagonism to attenuate cue-induced reinstatement relates to activation of the nucleus accumbens shell.

GalR3 mediates galanin proliferative effects on postnatal hippocampal precursors.

Galanin, a neuropeptide co-released from noradrenergic and serotonergic projection neurons to the dentate gyrus, has recently emerged as an important mediator for signaling neuronal activity to the subgranular neurogenic stem cell niche supporting adult hippocampal neurogenesis. Galanin and its receptors appear to play key roles in depression-like behavior, and effects on hippocampal neurogenesis are relevant to pharmacological strategies for treating depression, which in part appear to rely on restoring altered neurogenesis. We previously demonstrated that the GalR2/3 receptor agonist Gal 2-11 is proliferative and proneurogenic for postnatal hippocampal progenitor cells; however, the specific receptor mediation remained to be identified. With the recent availability of M1145 (a specific GalR2 agonist), and SNAP 37889 (GalR3 specific antagonist), we extend our previous studies and show that while M1145 has no proliferative effect, the co-treatment of postnatal rat hippocampal progenitors with Gal 2-11 and SNAP 37889 completely abolished the Gal 2-11 proliferative effects. Taken together, these results clearly demonstrate that GalR3 and not GalR2 is the specific receptor subtype that mediates the proliferative effects of galanin on hippocampal progenitor cells. These results implicate GALR3 in the mediation of galanin neurogenic effects and, potentially, its neurogenic anti-depressant effects.

The galanin-3 receptor antagonist, SNAP 37889, suppresses alcohol drinking and morphine self-administration in mice.

The neuropeptide, galanin, is widely expressed in the central and peripheral nervous systems and is involved in a range of different functions including nociception, neurogenesis, hormone release, reproduction, cognitive function and appetite. Given the overlap between galanin expression and reward circuitry in the brain, galanin has been targeted for alcohol use disorder (AUD) and opioid dependency. Furthermore, the galanin-3 receptor (GAL3) specifically regulates emotional states and plays a role in motivation, reward and drug-seeking behaviour. We have previously shown that the GAL3 antagonist, SNAP 37889, reduces ethanol self-administration and cue-induced re-instatement in alcohol-preferring (iP) rats with no alterations in locomotor activity or anxiety-like behaviour. The aim of this study was to investigate whether SNAP 37889 reduces binge drinking and/or self-administration of morphine in mice. Using the Scheduled High Alcohol Consumption (SHAC) procedure, SNAP 37889 (30 mg/kg) treated mice drank significantly less ethanol, sucrose and saccharin than vehicle treated mice. Using an operant paradigm, SNAP 37889 reduced morphine self-administration but failed to impact cue-induced relapse-like behaviour. SNAP 37889 had no significant effect on locomotor activity, motor co-ordination, anxiety, nor was SNAP 37889 itself positively reinforcing. Liver assays showed that there was no alteration in the rate of hepatic ethanol metabolism between SNAP 37889 and vehicle treated mice suggesting that the reduction in ethanol intake via SNAP 37889 is due to a central effect of GAL3 signalling. This study implicates the GAL3 receptor in consummatory drive which may have wider implications for the treatment of different addictions.

In vitro toxicity of the galanin receptor 3 antagonist SNAP 37889.

Galanin and its receptors (GAL1, GAL2, GAL3) modulate a range of neuronal, immune and vascular activities. In vivo administration of SNAP 37889 (1-phenyl-3-[[3-(trifluoromethyl)phenyl]imino]-1H-indol-2-one), a potent small non-peptidergic antagonist of GAL3, was reported to reduce anxiety- and depression-related behavior, ethanol consumption, and antagonizes the effect of galanin on plasma extravasation in rodent models. Accordingly, SNAP 37889 has been proposed as a potential therapeutic agent to treat anxiety and depression disorders. Therefore, we evaluated the toxicity of SNAP 37889 to different cell types. Our experiments revealed that SNAP 37889 (≥10µM) induced apoptosis in epithelial (HMCB) and microglial (BV-2) cell lines expressing endogenous GAL3, in peripheral blood mononuclear cells and promyelocytic leukemia cells (HL-60) expressing GAL2, and in a neuronal cell line (SH-SY5Y) lacking galanin receptor expression altogether. In conclusion, SNAP 37889 is toxic to a variety of cell types independent of GAL3 expression. We caution that the clinical use of SNAP 37889 at doses that might be used to treat anxiety- or depression- related diseases could have unexpected non-galanin receptor-mediated toxicity, especially on immune cells.

Spexin Enhances Bowel Movement through Activating L-type Voltage-dependent Calcium Channel via Galanin Receptor 2 in Mice.

A novel neuropeptide spexin was found to be broadly expressed in various endocrine and nervous tissues while little is known about its functions. This study investigated the role of spexin in bowel movement and the underlying mechanisms. In functional constipation (FC) patients, serum spexin levels were significantly decreased. Consistently, in starved mice, the mRNA of spexin was significantly decreased in intestine and colon. Spexin injection increased the velocity of carbon powder propulsion in small intestine and decreased the glass beads expulsion time in distal colon in mice. Further, spexin dose-dependently stimulated the intestinal/colonic smooth muscle contraction. Galanin receptor 2 (GALR2) antagonist M871, but not Galanin receptor 3 (GALR3) antagonist SNAP37899, effectively suppressed the stimulatory effects of spexin on intestinal/colonic smooth muscle contraction, which could be eliminated by extracellular [Ca(2+)] removal and L-type voltage-dependent Ca(2+) channel (VDCC) inhibitor nifedipine. Besides, spexin dramatically increased the [Ca(2+)]i in isolated colonic smooth muscle cells. These data indicate that spexin can act on GALR2 receptor to regulate bowel motility by activating L-type VDCC. Our findings provide evidence for important physiological roles of spexin in GI functions. Selective action on spexin pathway might have therapeutic effects on GI diseases with motility disorders.

Galanin-3 receptor antagonism by SNAP 37889 reduces motivation to self-administer alcohol and attenuates cue-induced reinstatement of alcohol-seeking in iP rats.

The neuropeptide galanin has a role in promoting alcohol consumption and general feeding behavior. The galanin-3 receptor (GALR3) subtype is implicated in modulating the consumption of alcohol and has therefore been identified as a potential target for new pharmacotherapies to treat alcohol use disorders. We have previously shown that the selective GALR3 antagonist SNAP 37889 reduced voluntary alcohol consumption in iP (alcohol-preferring) rats. The present study firstly aimed to investigate the effect of GALR3 antagonism on the motivational properties of alcohol. Secondly, the potential of GALR3 as a therapeutic target in the prevention of relapse was investigated in response to alcohol-conditioned cues. Administration of SNAP 37889 (30 mg/kg, i.p.) significantly reduced the breakpoint for ethanol under a progressive-ratio operant responding schedule of reinforcement. SNAP 37889 also significantly reduced reinstatement of alcohol-seeking in response to re-exposure to conditioned cues that were previously associated with the availability of alcohol. Collectively, results from the current study provide new evidence of GALR3 involvement in cue-induced relapse and provide further evidence that GALR3 antagonism reduces the motivational drive to consume alcohol. These findings validate further research in to the potential use of SNAP 37889 and other GALR3 antagonists to treat alcohol abuse disorders in humans.

Theoretical characterization of galanin receptor type 3 (Gal3 ) and its interaction with agonist (GALANIN) and antagonists (SNAP 37889 and SNAP 398299): an in silico analysis.

In this study, we report on modeling of galanin receptor type 3 and its interaction with agonist and antagonists using in silico methodologies. Comparative structural modeling of galanin receptor type 3 was based on multiple templates. With the availability of reported selective galanin receptor type 3 antagonists, docking was carried out into the predicted binding site. Similarly, galanin, a reported agonist, was also modeled and then docked into the receptor's active site. CoMFA models were developed using ligand-based (q(2)  = 0.537, r(2)  = 0.961, noc = 5), and receptor-guided (docked mode 1: q(2)  = 0.574, r(2)  = 0.946, noc = 5), (docked mode 2: q(2)  = 0.499, r(2)  = 0.954, noc = 5) alignment schemes. CoMFA contour analysis revealed that bulky substitution around the meta position of the phenyl ring, as well as optimal substitution (para) of the phenyl ring, could produce molecules with improved activity. We also found that Gln79, Ile82, Asp86, Trp88, His99, Ile102, Tyr103, Glu170, Pro174, Ala175, Asp185, Arg273, His277, and Tyr281 are crucial, and mutational studies on these residues could be helpful. The results obtained from this study can further be exploited for structure-based drug design and also help the researchers to identify novel antagonists targeting galanin receptor type 3.

Galanin receptor 3--a potential target for acute pancreatitis therapy.

BACKGROUND: Galanin participates in the pathogenesis of acute pancreatitis (AP). The galanin receptor (GALR) sub-types involved, however, are unclear. We aimed to determine GALRs messenger RNA (mRNA) expression in mouse pancreas, describe their localization, and ascertain if GALR2 and GALR3 are involved in AP. METHODS: Galanin receptor expression in murine whole pancreas, acinar, and islet cells was quantified by polymerase chain reaction amplification of reverse-transcribed RNA for mRNA, Western blot analysis for protein and in situ hybridization for GALR localization. Isolated acinar cells were used to determine galanin's effect on amylase secretion. Acute pancreatitis was induced in mice by caerulein injections. Mice, with and without AP, were treated with the highly selective GALR2 antagonist M871, or the specific GALR3 antagonist SNAP-37889. Indices of AP were measured at 12 h. KEY RESULTS: Murine pancreas expresses mRNA for GALRs. In islets the expression of all GALR are comparable, whereas in acinar cells GALR3 is predominantly expressed. Western blot analysis confirmed that the GALR proteins are expressed by acinar cells. In situ hybridization analysis confirmed that GALR3 mRNA is present in islet and acinar cells, while mRNA for GALR1 and 2 is confined to islets. Galanin did not influence basal and caerulein-stimulated amylase release from acinar cells. M871 treatment reduced some, whereas SNAP-37889 treatment reduced all indices of AP (by 40-80%). CONCLUSIONS & INFERENCES: Galanin receptor mRNA and protein are expressed in mouse pancreas, with GALR3 mRNA predominating. GALR3 antagonism reduced the severity of AP whereas GALR2 antagonism was less effective. GALR3 is a potential target for treatment of AP.

The galanin-3 receptor antagonist, SNAP 37889, reduces operant responding for ethanol in alcohol-preferring rats.

BACKGROUND/OBJECTIVE: The galanin-3 receptor (GALR3) subtype has been identified as having a role in both feeding behaviour and the regulation of emotional states including anxiety. Despite the evidence for an association between galanin and alcohol, the current study is the first to explore the direct role of GALR3 in this context. The present study investigated the potential of the novel selective GALR3 antagonist, SNAP 37889, to reduce anxiety-like behaviour and voluntary ethanol consumption in the iP (alcohol-preferring) rat. This was achieved through a number of behavioural paradigms testing for anxiety, along with the operant self-administration model. RESULTS: Overall, male iP rats treated with SNAP 37889 at a dose of 30 mg/kg (i.p.) did not show altered locomotor activity or changes in anxiety-like behaviour in the elevated plus maze or light-dark paradigms. Treatment with SNAP 37889 (30 mg/kg, i.p.) reduced operant responding for solutions containing ethanol, sucrose and saccharin. Collectively, results from the current study showed that SNAP 37889 (30 mg/kg, i.p.) is effective in reducing operant responding for ethanol, independent of a sedative effect. CONCLUSIONS: These findings provide evidence that GALR3 antagonism reduces alcohol consumption and further suggest that GALR3 may be implicated in the rewarding effects of natural and drug reinforcers.

Evidence that the modulatory effect of galanin on inflammatory edema formation is mediated by the galanin receptor 3 in the murine microvasculature.

Neuropeptides released from cutaneous nerves are attracting interest as modulators of inflammation in the skin. Recently, we showed that the neuropeptides galanin and galanin-like peptide potently inhibit inflammatory edema by reduction of microvascular blood flow. Reverse transcription-polymerase chain reaction analysis of murine skin revealed the expression of galanin receptors 2 and 3. The aim of the present study was to elucidate which galanin receptor subtype mediates the galanin-evoked inhibition of inflammatory edema formation in the skin. In this study, we report that AR-M1896, a non-GalR1 agonist, inhibited plasma extravasation induced by substance P and calcitonin gene-related peptide in a manner similar to galanin, confirming a non-GalR1-mediated effect. SNAP 37889, a nonpeptidergic selective antagonist of galanin receptor 3 (GalR3), dose-dependently abolished the antiedema effect of galanin. Thus, we were able to show that SNAP 37889 selectively antagonized galanin in the periphery and suggest that GalR3 is the receptor subtype mediating galanin's effects on the dermal microvasculature.

Involvement of galanin receptors 1 and 2 in the modulation of mouse vagal afferent mechanosensitivity.

It is established that the gut peptide galanin reduces neuronal excitability via galanin receptor subtypes GALR1 and GALR3 and increases excitability via subtype GALR2. We have previously shown that galanin potently reduces mechanosensitivity in the majority of gastro-oesophageal vagal afferents, and potentiates sensitivity in a minority. These actions may have implications for therapeutic inhibition of gut afferent signalling. Here we investigated which galanin receptors are likely to mediate these effects. We performed quantitative RT-PCR on RNA from vagal (nodose) sensory ganglia, which indicated that all three GALR subtypes were expressed at similar levels. The responses of mouse gastro-oesophageal vagal afferents to graded mechanical stimuli were investigated before and during application of galanin receptor ligands to their peripheral endings. Two types of vagal afferents were tested: tension receptors, which respond to circumferential tension, and mucosal receptors which respond only to mucosal stroking. Galanin induced potent inhibition of mechanosensitivity in both types of afferents. This effect was totally lost in mice with targeted deletion of Galr1. The GALR1/2 agonist AR-M961 caused inhibition of mechanosensitivity in Galr1+/+ mice, but this was reversed to potentiation in Galr1-/- mice, indicating a minor role for GALR2 in potentiation of vagal afferents. We observed no functional evidence of GALR3 involvement, despite its expression in nodose ganglia. The current study highlights the complex actions of galanin at different receptor subtypes exhibiting parallels with the function of galanin in other systems.

A novel, systemically active, selective galanin receptor type-3 ligand exhibits antidepressant-like activity in preclinical tests.

The neuropeptide galanin is widely expressed in limbic nuclei in the brain, and plays an important role in the regulation of homeostatic and affective behaviors, in part through its modulation of central monoamine pathways. Recent evidence suggests that galanin and its receptors may be involved in the efficacy of various modalities of antidepressant treatments. We have previously demonstrated that systemically active, non-peptide galanin receptor type-1/2 agonists exhibit antidepressant-like effects in the rat forced swim test. Here we evaluate a novel galanin receptor type-3 (GalR3) antagonist in preclinical tests of anxiety and depression. At multiple doses, the compound displayed no effects in the elevated plus maze in mice. By contrast, the compound decreased time spent immobile in the tail suspension test by mice. Additionally, the GalR3 drug decreased time spent immobile in the forced swim test in rats, similarly to the effects of desipramine, yet did not increase locomotor activity in an open field test. These combined data from two species indicate that GalR3 receptor antagonists may exhibit antidepressant-like effects.

3-arylimino-2-indolones are potent and selective galanin GAL3 receptor antagonists.

A series of 3-imino-2-indolones are the first published, high-affinity antagonists of the galanin GAL3 receptor. One example, 1,3-dihydro-1-phenyl-3-[[3-(trifluoromethyl)phenyl]imino]-2H-indol-2-one (9), was shown to have high affinity for the human GAL3 receptor (Ki=17 nM) and to be highly selective for GAL3 over a broad panel of targets, including GAL1 and GAL2. Compound 9 was also shown to be an antagonist in a human GAL3 receptor functional assay (Kb=29 nM).

Anxiolytic- and antidepressant-like profiles of the galanin-3 receptor (Gal3) antagonists SNAP 37889 and SNAP 398299.

The neuropeptide galanin mediates its effects through the receptor subtypes Gal(1), Gal(2), and Gal(3) and has been implicated in anxiety- and depression-related behaviors. Nevertheless, the receptor subtypes relevant to these behaviors are not known because of the lack of available galanin-selective ligands. In this article, we use behavioral, neurochemical, and electrophysiological approaches to investigate the anxiolytic- and antidepressant-like effects of two potent small-molecule, Gal(3)-selective antagonists, SNAP 37889 and the more soluble analog SNAP 398299. Acute administration of SNAP 37889 or SNAP 398299 enhanced rat social interaction. Furthermore, acute SNAP 37889 was also shown to reduce guinea pig vocalizations after maternal separation, to attenuate stress-induced hyperthermia in mice, to increase punished drinking in rats, and to decrease immobility and increase swimming time during forced swim tests with rats. Moreover, SNAP 37889 increased the social interaction time after 14 days of treatment and maintained its antidepressant effects during forced swim tests with rats after 21 days of treatment. In microdialysis studies, SNAP 37889 partially antagonized the galanin-evoked reduction in hippocampal serotonin (5-hydroxytryptamine, 5-HT), as did the 5-HT(1A) receptor antagonist WAY100635. Their combination produced a complete reversal of the effect of galanin. SNAP 398299 partially reversed the galanin-evoked inhibition of dorsal raphe cell firing and galanin-evoked hyperpolarizing currents. These results indicate that Gal(3)-selective antagonists produce anxiolytic- and antidepressant-like effects, possibly by attenuating the inhibitory influence of galanin on 5-HT transmission at the level of the dorsal raphe nucleus.

[The expression of galanin and galanin receptors in olfactory ensheathing cells and effects of galanin on cells proliferation].

Olfactory ensheathing cells (OECs) were isolated from newborn rat olfactory bulb and cultured in vitro. RT-PCR was used to determine the expression of galanin and it's receptors in these cells. MTT analysis was used to detect the effects of galanin and agonist, antagonist of galanin receptors on the proliferation of OECs. Results show that OECs express mRNAs for galanin and GalR2 but not for two another receptors, GalR1 and GalR3. In addition, galanin and two receptor agonists, GAL1-11 and GAL2-11, can significantly inhibit the proliferation of OECs. But the influence can be blocked by M35, nonspecific antagonist of galanin receptors.