Galanin suppresses visceral afferent responses to noxious mechanical and inflammatory stimuli.

Galanin is a neuropeptide expressed by sensory neurones innervating the gastrointestinal (GI) tract. Galanin displays inhibitory effects on vagal afferent signaling within the upper GI tract, and the goal of this study was to determine the actions of galanin on colonic spinal afferent function. Specifically, we sought to evaluate the effect of galanin on lumbar splanchnic nerve (LSN) mechanosensitivity to noxious distending pressures and the development of hypersensitivity in the presence of inflammatory stimuli and colitis. Using ex vivo electrophysiological recordings we show that galanin produces a dose-dependent suppression of colonic LSN responses to mechanical stimuli and prevents the development of hypersensitivity to acutely administered inflammatory mediators. Using galanin receptor (GalR) agonists, we show that GalR1 activation, but not GalR2/3 activation, suppresses mechanosensitivity. The effect of galanin on colonic afferent activity was not observed in tissue from mice with dextran sodium sulfate-induced colitis. We conclude that galanin has a marked suppressive effect on colonic mechanosensitivity at noxious distending pressures and prevents the acute development of mechanical hypersensitivity to inflammatory mediators, an effect not seen in the inflamed colon. These actions highlight a potential role for galanin in the regulation of mechanical nociception in the bowel and the therapeutic potential of targeting galaninergic signaling to treat visceral hypersensitivity.

The Neuropeptide Galanin Is Required for Homeostatic Rebound Sleep following Increased Neuronal Activity.

Sleep pressure increases during wake and dissipates during sleep, but the molecules and neurons that measure homeostatic sleep pressure remain poorly understood. We present a pharmacological assay in larval zebrafish that generates short-term increases in wakefulness followed by sustained rebound sleep after washout. The intensity of global neuronal activity during drug-induced wakefulness predicted the amount of subsequent rebound sleep. Whole-brain mapping with the neuronal activity marker phosphorylated extracellular signal-regulated kinase (pERK) identified preoptic Galanin (Galn)-expressing neurons as selectively active during rebound sleep, and the relative induction of galn transcripts was predictive of total rebound sleep time. Galn is required for sleep homeostasis, as galn mutants almost completely lacked rebound sleep following both pharmacologically induced neuronal activity and physical sleep deprivation. These results suggest that Galn plays a key role in responding to sleep pressure signals derived from neuronal activity and functions as an output arm of the vertebrate sleep homeostat.

The potential antidepressant and antidiabetic effects of galanin system.

Epidemiological and clinical studies demonstrated that type 2 diabetes mellitus and depression are interconnected. Depression is an important risk factor for the development of type 2 diabetes mellitus, while patients with type 2 diabetes mellitus frequently have depressive symptoms. Despite many studies recently probed into the comorbid state of both diseases, so far the precise mechanism for this association is poorly understood. Experiments have demonstrated that neuropeptide galanin is involved in the pathogenesis of depression and type 2 diabetes mellitus. This review provides a new insight into the multivariate relationship among galanin, depression and type 2 diabetes mellitus, highlighting the effect of galanin system on the cross-talk between both diseases in human and rodent models. The current data support that activating central GalR2 attenuates insulin resistance and depressive feature in animal models. These may help us better understand the pathogenesis of both diseases and provide useful hints for the development of novel therapeutic approaches, i.e. to coadministrate GalR2 agonist with traditional antidepressive and antidiabetic medicines to treat depression and type 2 diabetes mellitus.

Influence of chronic administration of antidepressant drugs on mRNA for galanin, galanin receptors, and tyrosine hydroxylase in catecholaminergic and serotonergic cell-body regions in rat brain.

Activity of locus coeruleus (LC) neurons and release of the peptide galanin (GAL), which is colocalized with norepinephrine (NE) in LC neurons, has been implicated in depression and, conversely, in antidepressant action. The present study examined the influence of chronic administration (for 14days, via subcutaneously-implanted minipump) of antidepressant (AD) drugs representing three different classes (tricyclic [desipramine], selective serotonin reuptake inhibitor [SSRI] [paroxetine], and monoamine oxidase inhibitor [MAOI] [phenelzine]) on mRNA for GAL, GAL receptors (GalR1, GalR2, and GalR3), and tyrosine hydroxylase (TH), the rate-limiting enzyme for NE synthesis, in four brain regions--LC, A1/C1, dorsal raphe (DRN), and ventral tegmentum (VTA) of rats. Consistent with previous findings that chronic administration of AD drugs decreases activity of LC neurons, administration of AD drugs reduced mRNA for both GAL and TH in LC neurons. GAL and TH mRNA in LC neurons was highly correlated. AD drugs also reduced GAL and TH mRNA in A1/C1 and VTA but effects were smaller than in LC. The largest change in mRNA for GAL receptors produced by AD administration was to decrease mRNA for GalR2 receptors in the VTA region. Also, mRNA for GalR2 and GalR3 receptors was significantly (positively) correlated in all three predominantly catecholaminergic brain regions (LC, A1/C1, and VTA). Relative to these three brain regions, unique effects were seen in the DRN region, with the SSRI elevating GAL mRNA and with mRNA for GalR1 and GalR3 being highly correlated in this brain region. The findings show that chronic administration of AD drugs, which produces effective antidepressant action, results in changes in mRNA for GAL, GAL receptors, and TH in brain regions that likely participate in depression and antidepressant effects.

Fluoxetine reverts chronic restraint stress-induced depression-like behaviour and increases neuropeptide Y and galanin expression in mice.

Stressful life events and chronic stress are implicated in the development of depressive disorder in humans. Neuropeptide Y (NPY) and galanin have been shown to modulate the stress response, and exert antidepressant-like effects in rodents. To further investigate these neuropeptides in depression-like behaviour, NPY and galanin gene expression was studied in brains of mice subjected to chronic restraint stress (CRS) and concomitant treatment with the antidepressant fluoxetine (FLX). CRS caused a significant increase in depression-like behaviour that was associated with increased NPY mRNA levels in the medial amygdala. Concomitant FLX treatment reverted depression-like effects of CRS and led to significant increases in levels of NPY and galanin mRNA in the dentate gyrus, amygdala, and piriform cortex. These findings suggest that effects on NPY and galanin gene expression could play a role in the antidepressant effects of FLX.

Differences between orofacial inflammation and cancer pain.

Rat models of orofacial cancer exhibit both allodynia and hyperalgesia; however, it is unclear whether cancer-induced pain is secondary to cancer-induced inflammation. To address this question, we compared the effects of an anti-inflammatory drug, indomethacin, on pain and neurochemical changes in the medullary dorsal horn in orofacial inflammation and cancer models. Daily peripheral administration of indomethacin largely suppressed mechanical allodynia and thermal hyperalgesia in the inflammation model. The same procedure suppressed allodynia and hyperalgesia in the cancer model, but the suppression was weak when compared with that in the inflammation model. In the medullary dorsal horn, calcitonin gene-related peptide and substance P levels were significantly increased in the inflammation model, but did not change in the cancer model. These results suggest that pain in the orofacial cancer model is not significantly mediated by cancer-induced peripheral inflammation, although it may have some involvement.

A role for galanin in antidepressant actions with a focus on the dorsal raphe nucleus.

Selective serotonin reuptake inhibitors, such as fluoxetine (FLX), are the most commonly used drugs in the treatment of major depression. However, there is a limited understanding of their molecular mechanism of action. Although the acute effect of selective serotonin reuptake inhibitors in elevating synaptic serotonin concentrations is well known, the clinical amelioration of depressive symptoms requires 14-21 days of treatment, suggesting that numerous other rearrangements of function in the CNS must take place. In the present study, we demonstrated that 14 days of FLX treatment up-regulated galanin mRNA levels by 100% and GalR2-binding sites by 50%, in the rat dorsal raphe nucleus, where galanin coexists with serotonin. Furthermore, a galanin receptor antagonist, M40, attenuated the antidepressant-like effect of FLX in the forced swim test, a rodent preclinical screen commonly used to evaluate antidepressant-like efficacy. Direct activation of galanin receptors by a galanin receptor agonist, galnon, was found to produce an antidepressant-like effect in the same task. Two other antidepressant treatments also affected the galaninergic system in the monoaminergic nuclei: Electroconvulsive shock elevated galanin mRNA levels in dorsal raphe nucleus, whereas sleep deprivation increased galanin mRNA levels in the locus coeruleus, further underlining the connection between activation of the galaninergic system and antidepressant action of various clinically proven treatments.

Estimation of hormone replacement therapy influence on serum galanin level in postmenopausal women.

OBJECTIVE: The aim of this study was to evaluate the influence of exogenous hormones (estradiol and progestogen) used in hormone replacement therapy (HRT) on the serum galanin level in postmenopausal women with normal body weight. METHODS: We studied 20 postmenopausal patients (mean age 52.3 +/- 5.2 years) before and after 1 year of HRT. The mean duration of amenorrhea in these patients was 5.3 +/- 4.1 years. In all cases, body mass index was in the normal range (between 20 and 25 kg/m2). Serum galanin and estradiol concentrations were measured by radioimmunoassay before and after 1 year of treatment. Results were statistically analyzed with the use of specialist computer software. RESULTS: There was no statistically significant difference in serum galanin concentration before (8.24 +/- 3.63 pg/ml) and after (5.63 +/- 2.75 pg/ml) 1 year of HRT. Following HRT the serum estradiol level (0.09 +/- 0.015 ng/ml) was significantly higher than before starting therapy (0.021 +/- 0.018 ng/ml) (p < 0.001). Also, after HRT the mean serum follicle stimulating hormone (FSH) level (32.9 +/- 28.0 IU/l) was significantly lower than before starting therapy (91.7 +/- 38.5 IU/l) (p < 0.01). CONCLUSIONS: The study results suggest that HRT in postmenopausal women does not restore galanin levels to values typical of those in women of reproductive age.

Distribution of galanin immunoreactivity in the sheep diencephalon.

Although the physiological role of galanin has been demonstrated in several endocrine regulations in sheep, the anatomical characteristics of this neuronal system has never been studied. The distribution of galanin-containing neurones was described by immunohistochemistry using galanin antiserum in the diencephalon of adult ewes, both ovariectomized or treated with colchicine. Galanin-immunoreactivity was found throughout the diencephalon. In the ovariectomized ewes, galanin-immunoreactive neurones were mainly observed in the medial preoptic area and the infundibular nucleus. The highest density of immunoreactive fibres was found in the external layer of the median eminence. Numerous galanin-immunoreactive fibres were also observed in the preoptic area, the mediobasal hypothalamus, the periphery of the supraoptic and the paraventricular nuclei. With colchicine treatment, the number of labelled neurones increased, and additional galanin-immunoreactive perikarya were observed in the bed nucleus of the stria terminalis, the lateral septum, the supraoptic, the paraventricular and the periventricular nuclei and the paraventricular nucleus of the thalamus. In the caudal part of the diencephalon, the density of labelled neurones was lower in both groups of animals than in other species studied. Regardless of treatment, labelling was not seen in the suprachiasmatic nucleus and only rarely in the ventromedial nucleus. These results describe, for the first time, the distribution of galanin-immunoreactive neurones in the sheep diencephalon. Compared to other species studied, distribution in the sheep diencephalon has several distinct differences. In ovariectomized animals, the medial preoptic area presents more labelled neurones in sheep than in monkeys, whereas in the supraoptic nucleus the density of labelled neurones is lower in sheep than in humans or opossums. After colchicine treatment only very few differences were observed between sheep and rats, but in contrast to other species, the suprachiasmatic nucleus of the sheep does not contain labelled neurones.

Patterns of c-fos expression induced by fluvoxamine are different after acute vs. chronic oral administration.

Fluvoxamine is a selective serotonin (5-HT) reuptake inhibitor (SSRI) with a broad spectrum of behavioral and therapeutic effects, e.g. in depressive illness. We used the expression of c-fos, after both acute and chronic oral administration of fluvoxamine in the rat, to study its immediate and long-term effects, in relation to the distribution of Galanin (GAL) and Vasoactive Intestinal Polypeptide (VIP). After acute oral administration, most consistent increases were apparent in (parts of); the nucleus of the solitary tract, medial part; the lateral parabrachial nucleus, external part; the bed nucleus of the stria terminalis, dorsolateral part; and the central nucleus of the amygdala, lateral part. After chronic administration, distribution of Fos-IR was similar to acute administration, although numbers of Fos-IR neurons were no longer significantly different from control values. It is concluded that activation of 5-HT3-receptors in the caudal brainstem or gastro-intestinal afferents of the vagal nerve may play a role in the observed pattern of Fos-IR after fluvoxamine administration. The relationship with the antidepressant effects of fluvoxamine needs further investigations.

Effect of estrogen on the expression of galanin mRNA in pituitary tumor-sensitive and tumor-resistant rat strains.

The hypothesis that estrogen-induced pituitary tumors are mediated by the neuropeptide galanin was tested using tumor-resistant (Sprague-Dawley; SD) and tumor-sensitive (Fischer 344; F344) rat strains. Diethylstilbestrol (DES) increased expression of galamin mRNA in both strains after 1, 2, and 4 weeks of treatment and doubled pituitary weights in F344 rats while pituitary weights in SD rats were unchanged by DES treatment. In F344 rats, both the expression of galanin mRNA and pituitary weights increased linearly with the length of DES treatment. In SD rats however, despite increasing levels of galanin mRNA, pituitary weights did not increase. These data indicate that galanin gene expression, by itself, is not sufficient to account for increased pituitary growth. However, our data do not rule out the possibility that galanin has an indirect role in promoting pituitary growth.

Regulation of galanin by dexamethasone in the rat anterior pituitary and the uterus.

Galanin is a 29 amino acid neuropeptide widely distributed throughout the mammalian nervous and endocrine system. We have previously reported that estrogen dramatically increases galanin gene expression and protein synthesis in the anterior pituitary (AP), while the expression in the uterus (UT) of the same animals is transient and similar to the induction of protooncogenes (c-fos, c-jun, c-myc). In order to examine if this pattern of induction is specific to estrogen administration, we investigated the effect of glucocorticoids, another steroid, on the gene expression of galanin in the AP and in the UT of ovariectomized female rats and in the AP of male rats. Using Northern blot analysis, the AP and the UT showed almost undetectable levels of galanin mRNA, but in vivo treatment of female rats with 1 mg/kg body weight of dexamethasone (DEX) led to a significant increase of galanin mRNA levels in both AP and UT. Similarly, DEX (0.1-5 mg/kg i.p.) significantly stimulated galanin mRNA levels in the AP of the male rats. In both males and females the peak of induction was at 9 h after injection that is different from the 3-hour peak after estrogen administration. Daily injection of DEX for up to 7 days sustained the levels of galanin mRNA in both the AP and the UT, in contrast to the transient induction of galanin in the UT after estrogen administration. No change was noted in the galanin protein content of AP (control = 30 +/- 3.5 ng/mg protein; DEX treated = 38 +/- 4.2 ng/mg protein). Interestingly, in the UT of ovariectomized rats the combination of DEX and DES (diethylstilbestrol) treatment for 2 days resulted in a synergistic stimulation of galanin mRNA. In summary, these data demonstrate a tissue- and steroid-specific regulation of the galanin gene in AP and UT and suggest that DEX regulates the galanin gene possibly through a pathway different from estrogen.