Glyphosate-induced changes in the expression of galanin and GALR1, GALR2 and GALR3 receptors in the porcine small intestine wall

Glyphosate is the active ingredient of glyphosate-based herbicides and the most commonly used pesticide in the world. The goal of the present study was to verify whether low doses of glyphosate (equivalent to the environmental exposure) evoke changes in galanin expression in intramural neurons in the small intestine in pigs and to quantitatively determine changes in the level of galanin receptor encoding mRNA (GALR1, GALR2, GALR3) in the small intestine wall. The experiment was conducted on 15 sexually immature gilts divided into three study groups: control (C)-animals receiving empty gelatin capsules; experimental 1 (G1)-animals receiving a low dose of glyphosate (0.05 mg/kg b.w./day); experimental 2 (G2)-animals receiving a higher dose of glyphosate (0.5 mg/kg b.w./day) orally in gelatine capsules for 28 days. Glyphosate ingestion led to an increase in the number of GAL-like immunoreactive intramural neurons in the porcine small intestine. The results of RT-PCR showed a significant increase in the expression of mRNA, which encodes the GAL-receptors in the ileum, a decreased expression in the duodenum and no significant changes in the jejunum. Additionally, intoxication with glyphosate increased the expression of SOD2-encoding mRNA in the duodenum and decreased it in the jejunum and ileum, but it did not affect SOD1 expression. The results suggest that it may be a consequence of the cytotoxic and/or neurotoxic properties of glyphosate and/or its ability to induce oxidative stress.

Galanin Receptors (GALR1, GALR2, and GALR3) Immunoexpression in Enteric Plexuses of Colorectal Cancer Patients: Correlation with the Clinico-Pathological Parameters

Galanin (GAL) is an important neurotransmitter released by the enteric nervous system (ENS) neurons located in the muscularis externa and submucosa enteric plexuses that acts by binding to GAL receptors 1, 2 and 3 (GALR1, 2 and 3). In our previous studies, the GAL immunoexpression was compared in colorectal cancer (CRC) tissue and the adjacent parts of the large intestine wall including myenteric and submucosal plexuses. Recently we have also found that expression levels of GALR1 and GALR3 proteins are elevated in CRC tissue as compared with their expression in epithelial cells of unchanged mucosa. Moreover, higher GALR3 immunoreactivity in CRC cells correlated with better prognosis of CRC patients. To understand the distribution of GALRs in enteric plexuses distal and close to CRC invasion, in the present study we decided to evaluate GALRs expression within the myenteric and submucosal plexuses located proximally and distally to the cancer invasion and correlated the GALRs expression levels with the clinico-pathological data of CRC patients. The immunohistochemical and immunofluorescent methods showed only slightly decreased immunoexpression of GALR1 and GALR3 in myenteric plexuses close to cancer but did not reveal any correlation in the immunoexpression of all three GAL receptors in myenteric plexuses and tumour progression. No significant changes were found between the expression levels of GALRs in submucosal plexuses distal and close to the tumour. However, elevated GALR1 expression in submucosal plexuses in vicinity of CRC correlated with poor prognosis, higher tumour grading and shorter overall survival. When myenteric plexuses undergo morphological and functional alterations characteristic for atrophy, GALRs maintain or only slightly decrease their expression status. In contrast, the correlation between high expression of GALR1 in the submucosal plexuses and overall survival of CRC patients suggest that GAL and GALRs can act as a components of local neuro-paracrine pro-proliferative pathways accelerating the invasion and metastasis of cancer cell. The obtained results suggest an important role of GALR1 in submucosal plexuses function during the progression of CRC and imply that GALR1 expression in submucosal plexuses of ENS could be an important predictive factor for CRC progression.

Galanin Receptors (GalR1, GalR2, and GalR3) Expression in Colorectal Cancer Tissue and Correlations to the Overall Survival and Poor Prognosis of CRC Patients

Colorectal cancer (CRC) is the second most common cause of cancer in women and the third in men. The postoperative pathomorphological evaluation of patients with CRC is extremely important for future therapeutic decisions. Although our previous studies demonstrated high galanin (GAL) presence within tumor tissue and an elevated concentration of GAL in the serum of CRC patients, to date, there is a lack of data regarding GAL receptor (GalR) protein expression in CRC cells. Therefore, the aim of this study was to evaluate the presence of all three types of GalRs (GalR1, GalR2 and GalR3) within epithelial cells of the human colon and CRC tissue with the use of the immunohistochemical method and to correlate the results with the clinical-pathological data. We found stronger immunoreactivity of GalR1 and GalR3 in CRC cells compared to epithelial cells of the unchanged mucosa of the large intestine. No differences in the GalR2 protein immunoreactivity between the studied tissues were noted. We also found that the increased immunoexpression of the GalR3 in CRC tissue correlated with the better prognosis and longer survival (p < 0.0079) of CRC patients (n = 55). The obtained results suggest that GalR3 may play the role of a prognostic factor for CRC patients. Based on data from the TCGA-COAD project deposited in the GDC Data Portal, we also found that GalR mRNA in cancer samples and the adjacent normal tissue did not correlate with immunoexpression of the GalR proteins in CRC cells and epithelial cells of the unchanged mucosa.

Activation of Galanin Receptor 1 with M617 Attenuates Neuronal Apoptosis via ERK/GSK-3β/TIP60 Pathway After Subarachnoid Hemorrhage in Rats

Subarachnoid hemorrhage (SAH) is a devastating cerebrovascular disease. Neuronal apoptosis plays an important pathological role in early brain injury after SAH. Galanin receptor 1 (GalR1) activation was recently shown to be anti-apoptotic in the setting of ischemic stroke. This study aimed to explore the anti-neuronal apoptosis effect of GalR1 activation after SAH, as well as the underlying mechanisms. GalR1 CRISPR and GalR1 selective agonist, M617, was administered, respectively. Extracellular-signal-regulated kinase (ERK) inhibitor (U0126) and glycogen synthase kinase 3-beta (GSK3-β) CRISPR were administered to investigate the involvement of the ERK/GSK3-β pathway in GalR1-mediated neuroprotection after SAH. Outcome assessments included neurobehavioral tests, western blot, and immunohistochemistry. The results showed that endogenous ligand galanin (Gal) and GalR1 were markedly increased in the ipsilateral brain hemisphere at 12 h and 24 h after SAH. GalR1 were expressed mainly in neurons, but expression was also observed in some astrocytes and microglia. GalR1 CRISPR knockdown exacerbated neurological deficits and neuronal apoptosis 24 h after SAH. Moreover, activation of GalR1 with M617 significantly improved short- and long-term neurological deficits but decreased neuronal apoptosis after SAH. Furthermore, GalR1 activation dysregulated the protein levels of phosphorylated ERK and GSK-3β, but downregulated the phosphorylated Tat-interactive protein 60 (TIP60) and cleaved caspase-3 at 24 h after SAH. GalR1 CRISPR, U0126, and GSK-3β CRISPR abolished the beneficial effects of GalR1 activation at 24 h after SAH in rats. Collectively, the present study demonstrated that activation of GalR1 using M617 attenuated neuronal apoptosis through the ERK/GSK-3β/TIP60 pathway after SAH in rats. GalR1 may serve as a promising therapeutic target for SAH patients.

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.

Coordinated Targeting of Galanin Receptors on Cholangiocytes and Hepatic Stellate Cells Ameliorates Liver Fibrosis in Multidrug Resistance Protein 2 Knockout Mice

Galanin (Gal) is a peptide with a role in neuroendocrine regulation of the liver. In this study, we assessed the role of Gal and its receptors, Gal receptor 1 (GalR1) and Gal receptor 2 (GalR2), in cholangiocyte proliferation and liver fibrosis in multidrug resistance protein 2 knockout (Mdr2KO) mice as a model of chronic hepatic cholestasis. The distribution of Gal, GalR1, and GalR2 in specific liver cell types was assessed by laser-capture microdissection and confocal microscopy. Galanin immunoreactivity was detected in cholangiocytes, hepatic stellate cells (HSCs), and hepatocytes. Cholangiocytes expressed GalR1, whereas HSCs and hepatocytes expressed GalR2. Strategies were used to either stimulate or block GalR1 and GalR2 in FVB/N (wild-type) and Mdr2KO mice and measure biliary hyperplasia and hepatic fibrosis by quantitative PCR and immunostaining of specific markers. Galanin treatment increased cholangiocyte proliferation and fibrogenesis in both FVB/N and Mdr2KO mice. Suppression of GalR1, GalR2, or both receptors in Mdr2KO mice resulted in reduced bile duct mass and hepatic fibrosis. In vitro knockdown of GalR1 in cholangiocytes reduced α-smooth muscle actin expression in LX-2 cells treated with cholangiocyte-conditioned media. A GalR2 antagonist inhibited HSC activation when Gal was administered directly to LX-2 cells, but not via cholangiocyte-conditioned media. These data demonstrate that Gal contributes not only to cholangiocyte proliferation but also to liver fibrogenesis via the coordinate activation of GalR1 in cholangiocytes and GalR2 in HSCs.

Galanin System in Human Glioma and Pituitary Adenoma

Expression of neuropeptides and their corresponding receptors has been demonstrated in different cancer types, where they can play a role in tumor cell growth, invasion, and migration. Human galanin (GAL) is a 30-amino-acid regulatory neuropeptide which acts through three G protein-coupled receptors, GAL₁-R, GAL₂-R, and GAL₃-R that differ in their signal transduction pathways. GAL and galanin receptors (GALRs) are expressed by different tumors, and direct involvement of GAL in tumorigenesis has been shown. Despite its strong expression in the central nervous system (CNS), the role of GAL in CNS tumors has not been extensively studied. To date, GAL peptide expression, GAL receptor binding and mRNA expression have been reported in glioma, meningioma, and pituitary adenoma. However, data on the cellular distribution of GALRs are sparse. The aim of the present study was to examine the expression of GAL and GALRs in different brain tumors by immunohistochemistry. Anterior pituitary gland (n = 7), pituitary adenoma (n = 9) and glioma of different WHO grades I-IV (n = 55) were analyzed for the expression of GAL and the three GALRs with antibodies recently extensively validated for specificity. While high focal GAL immunoreactivity was detected in up to 40% of cells in the anterior pituitary gland samples, only one pituitary adenoma showed focal GAL expression, at a low level. In the anterior pituitary, GAL₁-R and GAL₃-R protein expression was observed in up to 15% of cells, whereas receptor expression was not detected in pituitary adenoma. In glioma, diffuse and focal GAL staining was noticed in the majority of cases. GAL₁-R was observed in eight out of nine glioma subtypes. GAL₂-R immunoreactivity was not detected in glioma and pituitary adenoma, while GAL₃-R expression was significantly associated to high-grade glioma (WHO grade IV). Most interestingly, expression of GAL and GALRs was observed in tumor-infiltrating immune cells, including neutrophils and glioma-associated macrophages/microglia. The presence of GALRs on tumor-associated immune cells, especially macrophages, indicates that GAL signaling contributes to homeostasis of the tumor microenvironment. Thus, our data indicate that GAL signaling in tumor-supportive myeloid cells could be a novel therapeutic target.

Involvement of galanin and galanin receptor 1 in nociceptive modulation in the central nucleus of amygdala in normal and neuropathic rats

The present study was performed to explore the role of galanin and galanin receptor 1 (GalR 1) in nociceptive modulation in the central nucleus of amygdala (CeA) in normal rats and rats with neuropathy, and the involvement of GalR 1 and PKC was also investigated. The hindpaw withdrawal latencies (HWLs) to thermal and mechanical stimulations were increased in a dose-dependent manner after intra-CeA injection of galanin in both normal rats and rats with neuropathy. The increased HWLs were significantly attenuated by intra-CeA injection of galanin receptor antagonist M40, indicating an involvement of galanin receptor in nociceptive modulation in CeA. Furthermore, intra-CeA administration of the GalR 1 agonist M 617 induced increases in HWLs in normal rats, suggesting that GalR 1 may be involved in galanin-induce antinociception in CeA. Additionally, intra-CeA injection of the PKC inhibitor inhibited galanin-induced antinociception, showing an involvement of PKC in galanin-induced antinociception in CeA of normal rats. Moreover, there was a significant increase in GalR1 content in CeA in rats with neuropathy than that in normal rats. These results illustrated that galanin induced antinociception in CeA in normal rats and rats with neuropathy, and there is an up-regulation of GalR1 expression in rats with neuropathy.

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.

The Effect of Stress on the Galaninergic System in the Rat Adenohypophysis: mRNA Expression and Immunohistochemistry of Galanin Receptors

The neuropeptide galanin is a widely distributed neurotransmitter/neuromodulator that regulates a variety of physiological processes and also participates in the regulation of stress responses. The effect of stress is dependent on the activity of the hypothalamic-adenohypophyseal-adrenal axis. Although the adenohypophysis is a crucial part of this axis, galanin peptides and their receptors have not yet been identified in this part of the pituitary after activation of the stress response. Since there are many controversies about the occurrence of individual galanin receptor subtypes in the adenohypophysis under basal conditions, we decided to verify their presence immunohistochemically, and we clearly demonstrated that the adenohypophysis expresses neuropeptides galanin, galanin-like peptide, and subtypes of galanin receptors GalR1, GalR2 and GalR3. The specificity of the reactions was confirmed by Western blots for galanin receptors. Using real-time qPCR we also demonstrated the presence of three GalR subtypes, with the highest expression of GalR2. In addition, we tested the effect of stress. We found that acute stress did not induce any changes in the GalR2 expression, but increased expression of GalR1 and decreased that of GalR3. We confirmed the involvement of the galanin system in the stress regulation in the adenohypophysis.

Pharmacological stimulation of GAL1R but not GAL2R attenuates kainic acid-induced neuronal cell death in the rat hippocampus

The neuropeptide galanin is widely distributed in the central and peripheral nervous systems and part of a bigger family of bioactive peptides. Galanin exerts its biological activity through three G-protein coupled receptor subtypes, GAL1-3R. Throughout the last 20years, data has accumulated that galanin can have a neuroprotective effect presumably mediated through the activation of GAL1R and GAL2R. In order to test the pharmaceutical potential of galanin receptor subtype selective ligands to inhibit excitotoxic cell death, the GAL1R selective ligand M617 and the GAL2R selective ligand M1145 were compared to the novel GAL1/2R ligand M1154, in their ability to reduce the excitotoxic effects of intracerebroventricular injected kainate acid in rats. The peptide ligands were evaluated in vitro for their binding preference in a competitive (125)I-galanin receptor subtype binding assay, and G-protein signaling was evaluated using both classical signaling and a label-free real-time technique. Even though there was no significant difference in the time course or severity of the kainic acid induced epileptic behavior in vivo, administration of either M617 or M1154 before kainic acid administration significantly attenuated the neuronal cell death in the hippocampus. Our results indicate the potential therapeutic value of agonists selective for GAL1R in the prevention of neuronal cell death.

Central Administration of Galanin Receptor 1 Agonist Boosted Insulin Sensitivity in Adipose Cells of Diabetic Rats

Our previous studies testified the beneficial effect of central galanin on insulin sensitivity of type 2 diabetic rats. The aim of the study was further to investigate whether central M617, a galanin receptor 1 agonist, can benefit insulin sensitivity. The effects of intracerebroventricular administration of M617 on insulin sensitivity and insulin signaling were evaluated in adipose tissues of type 2 diabetic rats. The results showed that central injection of M617 significantly increased plasma adiponectin contents, glucose infusion rates in hyperinsulinemic-euglycemic clamp tests, GLUT4 mRNA expression levels, GLUT4 contents in plasma membranes, and total cell membranes of the adipose cells but reduced the plasma C-reactive protein concentration in nondiabetic and diabetic rats. The ratios of GLUT4 contents were higher in plasma membranes to total cell membranes in both nondiabetic and diabetic M617 groups than each control. In addition, the central administration of M617 enhanced the ratios of pAkt/Akt and pAS160/AS160, but not phosphorylative cAMP response element-binding protein (pCREB)/CREB in the adipose cells of nondiabetic and diabetic rats. These results suggest that excitation of central galanin receptor 1 facilitates insulin sensitivity via activation of the Akt/AS160 signaling pathway in the fat cells of type 2 diabetic rats.

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).

Coevolution of the spexin/galanin/kisspeptin family: Spexin activates galanin receptor type II and III

The novel neuropeptide spexin (SPX) was discovered using bioinformatics. The function of this peptide is currently under investigation. Here, we identified SPX along with a second SPX gene (SPX2) in vertebrate genomes. Syntenic analysis and relocating SPXs and their neighbor genes on reconstructed vertebrate ancestral chromosomes revealed that SPXs reside in the near vicinity of the kisspeptin (KISS) and galanin (GAL) family genes on the chromosomes. Alignment of mature peptide sequences showed some extent of sequence similarity among the 3 peptide groups. Gene structure analysis indicated that SPX is more closely related to GAL than KISS. These results suggest that the SPX, GAL, and KISS genes arose through local duplications before 2 rounds (2R) of whole-genome duplication. Receptors of KISS and GAL (GAL receptor [GALR]) are phylogenetically closest among rhodopsin-like G protein-coupled receptors, and synteny revealed the presence of 3 distinct receptor families KISS receptor, GALR1, and GALR2/3 before 2R. A ligand-receptor interaction study showed that SPXs activate human, Xenopus, and zebrafish GALR2/3 family receptors but not GALR1, suggesting that SPXs are natural ligands for GALR2/3. Particularly, SPXs exhibited much higher potency toward GALR3 than GAL. Together, these results identify the coevolution of SPX/GAL/KISS ligand genes with their receptor genes. This study demonstrates the advantage of evolutionary genomics to explore the evolutionary relationship of a peptide gene family that arose before 2R by local duplications.

Identification of galanin and its receptor GalR1 as novel determinants of resistance to chemotherapy and potential biomarkers in colorectal cancer

PURPOSE

A major factor limiting the effective clinical management of colorectal cancer (CRC) is resistance to chemotherapy. Therefore, the identification of novel, therapeutically targetable mediators of resistance is vital.

EXPERIMENTAL DESIGN

We used a CRC disease-focused microarray platform to transcriptionally profile chemotherapy-responsive and nonresponsive pretreatment metastatic CRC liver biopsies and in vitro samples, both sensitive and resistant to clinically relevant chemotherapeutic drugs (5-FU and oxaliplatin). Pathway and gene set enrichment analyses identified candidate genes within key pathways mediating drug resistance. Functional RNAi screening identified regulators of drug resistance.

RESULTS

Mitogen-activated protein kinase signaling, focal adhesion, cell cycle, insulin signaling, and apoptosis were identified as key pathways involved in mediating drug resistance. The G-protein-coupled receptor galanin receptor 1 (GalR1) was identified as a novel regulator of drug resistance. Notably, silencing either GalR1 or its ligand galanin induced apoptosis in drug-sensitive and resistant cell lines and synergistically enhanced the effects of chemotherapy. Mechanistically, GalR1/galanin silencing resulted in downregulation of the endogenous caspase-8 inhibitor FLIP(L), resulting in induction of caspase-8-dependent apoptosis. Galanin mRNA was found to be overexpressed in colorectal tumors, and importantly, high galanin expression correlated with poor disease-free survival of patients with early-stage CRC.

CONCLUSION

This study shows the power of systems biology approaches to identify key pathways and genes that are functionally involved in mediating chemotherapy resistance. Moreover, we have identified a novel role for the GalR1/galanin receptor-ligand axis in chemoresistance, providing evidence to support its further evaluation as a potential therapeutic target and biomarker in CRC.

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.

Changes in galanin and GalR1 gene expression in discrete brain regions after transient occlusion of the middle cerebral artery in female rats

Injury to neurons results in up-regulation of galanin in some central and peripheral systems, and it has been suggested that this neuropeptide may play a protective and trophic role, primarily mediated by galanin receptor 2 (GalR2). The objective of the present study was to investigate galanin, GalR1, GalR2 and GalR3 gene expression in the female rat brain 7 days after a 60-min unilateral occlusion of the middle cerebral artery followed by reperfusion. Quantitative real-time PCR was employed in punch-biopsies from the locus coeruleus, somatosensory cortex and dorsal hippocampal formation, including sham-operated rats as controls. Galanin gene expression showed a ∼2.5-fold increase and GalR1 a ∼1.5-fold increase in the locus coeruleus of the ischemic hemisphere compared to the control side. Furthermore, the GalR1 mRNA levels decreased by 35% in somatosensory cortex of the ischemic hemisphere. Immunohistochemical analysis indicated a depletion of galanin from cell bodies and dendrites in the locus coeruleus after middle cerebral artery occlusion. The present results suggest that a stroke-induced forebrain lesion up-regulates synthesis of galanin and GalR1 in the locus coeruleus, a noradrenergic cell group projecting to many forebrain areas, including cortex and the hippocampal formation. These results support the notion that galanin may play a role in the response of the central nervous system to injury.

Galanin receptor-expressing dorsal horn neurons: role in nociception

Galanin, along with enkephalins and neuropeptide Y, has been hypothesized to negatively modulate nociception in the superficial dorsal horn of the spinal cord. In the present study, we sought to determine the role of presumably excitatory dorsal horn galanin receptor-expressing neurons in nociception by selectively destroying GalR1-expressing superficial dorsal horn interneurons using lumbar intrathecal injections of the targeted cytotoxin, galanin-saporin (Gal-sap). Lumbar intrathecal injection of Gal-sap (500 ng) reduced immunoperoxidase staining for GalR1 in the superficial dorsal horn without affecting primary afferent neurons in lumbar dorsal root ganglia. Lumbar intrathecal Gal-sap also: 1--reduced nocifensive reflex responding on the thermal plate at 0.3 °C, 44 °C, and 47 °C; 2--increased hot side occupancy in a thermal preference task (15 °C vs 45 °C); and, 3--decreased escape from 44 °C and 47 °C, but not 20 °C. Thus, similar to lesions of mu opiate receptor-expressing dorsal horn interneurons, selective destruction of GalR1-expressing superficial dorsal horn neurons produces heat hypo-algesia, likely due to loss of GalR1-expressing excitatory interneurons leading to reduced activation of nociceptive projection neurons in response to aversive heat. These results are different than those seen with intrathecal neuropeptide Y-saporin and suggest the potential value of selectively targeting GalR1-expressing dorsal horn neurons to control pain.

Regulation of the galanin system in the brainstem and hypothalamus by electroconvulsive stimulation in mice

Induction of seizures by electroconvulsive stimulation (ECS) is amongst the most efficacious treatments for major depression. However, the working mechanism by which ECS exerts its antidepressant effects remains elusive. The galanin system is regulated by ECS in seizure-prone brain regions and has been shown to modulate depression-like behaviour. To further explore its potential role in the antidepressant effects of ECS the galanin system was investigated by in situ hybridisation and [(125)I]-galanin receptor binding during repeated ECS in the locus coeruleus, dorsal raphe and discrete nuclei of the hypothalamus. Adult mice were treated with ECS once daily for 14 consecutive days, a paradigm previously shown to exert antidepressant-like effects. Significant increases in galanin transcription were found in the locus coeruleus and dorsomedial nuclei of the hypothalamus. In addition, GalR2 mRNA levels in the ventro- and dorsomedial nuclei of the hypothalamus were upregulated whereas no GalR1 mRNA upregulation was observed. [(125)I]-galanin receptor binding was downregulated in the ventromedial nuclei of the hypothalamus and dorsal raphe. These data show that the galanin system is regulated by repeated ECS in brain regions involved in monoaminergic neurotransmission and stress modulation thus indicating a possible role of the galanin system in the therapeutic effects of ECS.

Galanin stimulates cortisol secretion from human adrenocortical cells through the activation of galanin receptor subtype 1 coupled to the adenylate cyclase-dependent signaling cascade

Previous studies showed that galanin receptors are expressed in the rat adrenal, and galanin modulates glucocorticoid secretion in this species. Hence, we investigated the expression of the various galanin receptor subtypes (GAL-R1, GAL-R2 and GAL-R3) in the human adrenocortical cells, and the possible involvement of galanin in the control of cortisol secretion. Reverse transcription-polymerase chain reaction detected the expression of GAL-R1 (but not GAL-R2 and GAL-R3) in the inner zones of the human adrenal cortex. The galanin concentration dependently enhanced basal, but not ACTH-stimulated secretion of cortisol from dispersed inner adrenocortical cells (maximal effective concentration, 10(-8) M). The cortisol response to 10(-8) M galanin was abrogated by GAL-R1 immunoneutralization, and unaffected by GAL-R2 or GAL-R3 immunoneutralization. Galanin (10(-8) M) and ACTH (10(-9) M) enhanced cyclic-AMP production from dispersed cells, and the response was suppressed by the adenylate cyclase inhibitor SQ-22536 (10(-4) M). Galanin did not affect inositol triphosphate release, which, in contrast, was raised by angiotensin-II (10(-8) M). SQ-22536 and the protein kinase (PK)A inhibitor H-89 (10(-5) M) abolished the cortisol response to 10(-8) M galanin, while the phospholipase C inhibitor U-73122 and the PKC inhibitor calphostin-C were ineffective. Preincubation with pertussis toxin (Ptx) (0.5 microg/ml) partially inhibited the cortisol response to galanin. We conclude that galanin stimulates cortisol secretion from human inner adrenocortical cells, acting through GAL-R1 coupled to the adenylate cyclase/PKA-dependent signaling cascade via a Ptx-sensitive Galpha protein.

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.

Galanin enhances corticosterone secretion from dispersed rat adrenocortical cells through the activation of GAL-R1 and GAL-R2 receptors coupled to the adenylate cyclase-dependent signaling cascade

Galanin is a regulatory peptide, which acts via three subtypes of receptors, named GAL-R1, GAL-R2 and GAL-R3. Reverse transcription-polymerase chain reaction demonstrated the expression of GAL-R1 and GAL-R2, but not GAL-R3 mRNAs in dispersed rat adrenal zona fasciculata-reticularis (inner) cells. The immuno-blockade of GAL-R1 and GAL-R2, but not GAL-R3, decreased the binding of [3H]galanin to dispersed cells, a complete inhibition being obtained only by the simultaneous blockade of both receptor subtypes. Galanin stimulated corticosterone and cyclic-AMP release from dispersed inner rat adrenocortical cells, while inositol triphosphate production was not affected. Again these responses to galanin were reversed by both the GAL-R1 and GAL-R2, but not the GAL-R3 immuno-blockade. The adenylate cyclase inhibitor SQ-22536 and the protein kinase (PK) A inhibitor H-89 abolished the corticosterone response of dispersed cells to galanin, while the phospholipase C inhibitor U-73122 and the PKC inhibitor calphostin-C were ineffective. We conclude that rat inner adrenocortical cells express GAL-R1 and GAL-R2 as mRNA and protein, and galanin stimulates corticosterone secretion acting via these receptor subtypes which are both coupled to the adenylate cyclase/PKA-dependent signaling pathway.

Galanin receptor 1 is expressed in a subpopulation of glutamatergic interneurons in the dorsal horn of the rat spinal cord

The 29/30 amino acid neuropeptide galanin has been implicated in pain processing at the spinal level and local dorsal horn neurons expressing the Gal(1) receptor may play a critical role. In order to determine the transmitter identity of these neurons, we used immunohistochemistry and antibodies against the Gal(1) receptor and the three vesicular glutamate transporters (VGLUTs), as well as in situ hybridization, to explore a possible glutamatergic phenotype. Gal(1) protein, which could not be demonstrated in Gal(1) knockout mice, colocalized with VGLUT2 protein, but not with glutamate decarboxylase, in many nerve endings in lamina II. Moreover, Gal(1) and VGLUT2 transcripts were often found in the same cell bodies in laminae I-IV. Gal(1)-protein and galanin-peptide showed an overlapping distribution but were not colocalized. Gal(1) staining did not appear to be affected by dorsal rhizotomy. Taken together, these findings provide strong evidence that Gal(1) is a heteroreceptor expressed on excitatory glutamatergic dorsal horn interneurons. Activation of such Gal(1) receptors may thus decrease the inhibitory tone in the superficial dorsal horn, and possibly cause antinociception.

Differential distribution and regulation of galanin receptors- 1 and -2 in the rat lumbar spinal cord

The expression of the galanin receptor-1 and -2 (Gal(1) and Gal(2)) messenger ribonucleic acids (mRNAs) was studied in the lower spinal cord of rat by means of in situ hybridization, using ribonucleic acid probes (riboprobes). Naïve rats as well as rats with unilateral axotomy of the sciatic nerve or unilateral inflammation of the hindpaw were analyzed. In naïve rats, numerous Gal(1) mRNA-positive (+) neurons were detected in lamina (L) I-III. In addition, several Gal(1) mRNA(+) neurons were seen in deeper layers, including the ventral horns, area X, and the lateral spinal nucleus. In contrast, few and comparatively weakly labeled Gal(2) mRNA(+) neurons were observed, mostly in the ventral horns and in area X, with fewer in the dorsal horn and in the sympathetic and parasympathetic intermediate lateral cell columns. Axotomy induced a strong increase in intensity and number of Gal(2) mRNA(+) motoneurons ipsilateral to the lesion. In contrast, nerve cut or hindpaw inflammation did not alter the expression of Gal(1) or Gal(2) in the dorsal horn. The present (and previous) results suggest that galanin, acting through Gal(1) and Gal(2) receptors, has a modulatory role on spinal excitability, not only via interneurons in superficial dorsal horn, but also on neurons in deep layers and area X, as well as on the sympathetic and parasympathetic outflow. Furthermore, the nerve injury-induced Gal(2) upregulation in motor neurons suggests a role for galanin in survival/regeneration mechanisms.

In vivo interaction between serotonin and galanin receptors types 1 and 2 in the dorsal raphe: implication for limbic seizures

The neuropeptide galanin suppresses seizure activity in the hippocampus by inhibiting glutamatergic neurotransmission. Galanin may also modulate limbic seizures through interaction with other neurotransmitters in neuronal populations that project to the hippocampus. We examined the role of galanin receptors types 1 and 2 in the dorsal raphe (DR) in the regulation of serotonergic transmission and limbic seizures. Infusion of a mixed agonist of galanin receptors types 1 and 2 [galanin (1-29)] into the DR augmented the severity of limbic seizures in both rats and wild-type mice and concurrently reduced serotonin concentration in the DR and hippocampus as measured by immunofluorescence or HPLC. In contrast, injection of the galanin receptor type 2 agonist galanin (2-11) mitigated the severity of seizures in both species and increased serotonin concentration in both areas. Injection of both galanin fragments into the DR of galanin receptor type 1 knockout mice exerted anticonvulsant effects. Both the proconvulsant activity of galanin (1-29) and seizure suppression by galanin (2-11) were abolished in serotonin-depleted animals. Our data indicate that, in the DR, galanin receptors types 1 and 2 modulate serotonergic transmission in a negative and a positive fashion, respectively, and that these effects translate into either facilitation or inhibition of limbic seizures.

Homodimerization and internalization of galanin type 1 receptor in living CHO cells

Galanin is a 29- to 30-aa-long neuropeptide affecting feeding, cognitive, and sexual behavior. It exerts its effects through galanin receptors 1, 2 and 3, which are all seven transmembrane domain G-protein coupled receptors (GPCRs). The GPCRs have been shown to function as monomers, homodimers, heterodimers and oligomers. In this study, we examined the extent of galanin receptor 1 (GalR1) dimerization and internalization in living CHO cells using fluorescence resonance energy transfer (FRET) and time lapse confocal imaging. Ratio imaging analysis and emission spectral analysis revealed substantial homodimerization of GalR1. In addition, internalization of GalR1 after 1h of agonist stimulation with the GalR1 agonist galanin (1-29) was observed with time lapse fluorescence imaging, whereas stimulation with the GalR2 specific agonist galanin (2-11) did not lead to internalization. Treatment of GalR1 transfected cells with the non-selective adenylyl cyclase activator forskolin influenced the rate of internalization when administered together with galanin (1-29). These results indicate that GalR1 can act as a dimer on the cell surface and that receptor desensitization and internalization was observed after stimulation with the agonist galanin (1-29). Western blots further confirm the FRET data that GalR1-XFP dimerizes and can be detected in the cell as a monomer or dimer using antibodies to XFP. Internalization and dimerization of GalR1 is shown, contributing to the regulation of galanergic signaling.

Distribution of galanin receptor 1-immunoreactive neurons in the ovine hypothalamus: colocalization with GnRH

Galanin is implicated in numerous physiological functions, including reproduction. Where and how galanin acts in the brain is poorly understood, but recent evidence suggests that it is predominantly through the GAL-R1 receptor. Using an antibody raised against the third intracellular loop of rat GAL-R1, a region that is highly conserved among species, our first objective was to determine the distribution of cells expressing immunoreactive GAL-R1 in the hypothalamus of the sheep. GAL-R1-immunoreactive cells were spread widely in the ovine diencephalon and overlapped with the known distribution of GnRH neurons. Galanin has been shown to enhance GnRH secretion, but it is not known whether this effect is transduced at the level of the GnRH neuron or is indirect. Thus, our second objective was to establish if GnRH neurons throughout the hypothalamus expressed GAL-R1 receptors and, if so, whether GAL-R1 expression in GnRH neurons was influenced by season, gender and/or stage of the estrous cycle. In rams and ewes during the non-breeding season, only a tenth of the GnRH neurons expressed immunocytochemically detectable GAL-R1 receptors. In contrast, a fifth of the GnRH neurons expressed immunocytochemically detectable GAL-R1 in the luteal phase, whereas only a twentieth expressed GAL-R1 in the follicular phase. These data suggest that galanin may affect a subpopulation of GnRH neurons through the GAL-R1 receptor and that this affect may be modulated by steroids.

GalR1, but not GalR2 or GalR3, levels are regulated by galanin signaling in the locus coeruleus through a cyclic AMP-dependent mechanism

The galanin receptors GalR1, GalR2 and GalR3 are widely expressed throughout the mouse brain and are enriched in catecholaminergic nuclei. Here, we show that GalR1 protein levels are regulated by neuronal activity and changes in cAMP levels. GalR1, but not GalR2 or GalR3, is specifically up-regulated in the LC-like Cath.a cell line in a cAMP-dependent manner. GalR1 protein and mRNA levels are also up-regulated in the LC of galanin knockout mice, whereas GalR2 and GalR3 are not. Lack of galanin-maintained cAMP tone in the galanin knockout mouse appears to result in a loss of negative feedback resulting in increased levels of CREB phosphorylation and increased GalR1 expression. These findings suggest that changes in levels of GalR1 may play an important role in modulating signaling events and neuroplasticity underlying physiological functions of the LC.

G protein-coupled galanin receptor distribution in the rat central nervous system

The action of galanin in the central nervous system is mediated by at least three galanin receptor subtypes (GalR1, GalR2 and GalR3) which belong to the family of G protein-coupled receptors. GalR1 and GalR2 are coupled to G(i/o) proteins, although the latter may also be coupled to G(q/11) proteins. The aim of the present study was to identify the anatomical distribution and quantify the density of GalRs coupled to G proteins. The galanin (10(-6) M) stimulated guanosine 5'-(gamma-[35S] thio)triphosphate binding assay was used in tissue sections from the rat brain. Maximal percentages of stimulation over basal levels were found in the anterior olfactory nucleus and in the lateral olfactory tract nucleus ( approximately 54%). High levels of stimulation were recorded in diverse hypothalamic nuclei (16-28%), in the amygdala (central amygdaloid nucleus, 40%), in the spinal trigeminal tract (23%) and in layers 1-2 of the spinal cord (26%). Moderate binding stimulation (5-13%) was observed in thalamus, substantia nigra pars compacta, parabrachial nucleus, locus coeruleus and dorsal raphe nucleus. The lowest stimulation induced by galanin was recorded in diverse areas of the cortex, striatum, hippocampus and substantia nigra pars reticulata. The results show an anatomical distribution similar to that described for GalR1. However, in diverse brain areas, in which a high density of these receptors has previously been reported, only a moderate coupling to G proteins was found. These findings would suggest that the efficacy of galanin to induce an effective coupling of its receptors to G proteins could be different depending on the brain area.

Distribution and differential regulation of galanin receptor subtypes in rat brain: effects of seizure activity

Galanin, acting at the GalR1-3 subtypes of galanin receptors, is involved in the regulation of cognition, mood, feeding, seizure activity and pain. The understanding of galanin's effects in molecular and cellular terms has been hampered by the lack of receptor subtype selective ligands and antibodies. Previous in situ hybridization data showed that GalR1 and GalR2 receptors are abundant in the rat brain, while the distribution of GalR3 is contradictory and most studies demonstrated a low expression levels in the rat brain. The distribution of galanin receptor subtypes at protein level is unknown. In the present study, we report the regional distribution of the galanin receptors: GalR1 and non-GalR1 receptors, using a recently synthesized high affinity GalR2/3 selective ligand, galanin (2-11), and galanin (1-29), as competitors, in saturating (125)I-galanin membrane binding assay. We show that paraventricular nucleus (PVN) express predominantly GalR1, whereas areas like the dorsal raphe nucleus (DRN), hippocampus and amygdala express both the GalR1 and non-GalR1 receptors. We speculate that the GalR2/3 binding sites detected by galanin (2-11) binding in our study probably represent mostly GalR2 receptors. In addition, we show regionally specific and subtype specific regulation of galanin receptors. Status epilepticus (SE), known to deplete galanin from axonal projections of locus coeruleus and septum/diagonal band neurons in the hippocampus and to induce galanin expression in a subset of hippocampal cells, down regulates GalR2 receptor mRNA and proteins by 30% without altering the GalR1 receptors.

Galanin impairs performance on learning and memory tasks: findings from galanin transgenic and GAL-R1 knockout mice

Galanin (GAL) impairs performance on cognitive tasks when administered centrally to rats. GAL transgenic (GAL-tg) mice overexpressing endogenous GAL show deficits on the probe trial of the Morris water maze spatial learning task, on the social transmission of food preference olfactory memory task, and on the trace cued fear conditioning emotional learning and memory task. Knockout mice deficient in the GAL-R1 receptor subtype were normal on most memory tasks, while showing a small deficit in trace cued fear conditioning, suggesting a selective role for the GAL-R1 in aversive memories, and implicating other GAL receptor subtypes in spatial learning and olfactory social memory. The growing body of rodent literature implicating excess GAL in cognitive impairment is relevant to the overexpression of GAL in the basal forebrain during the progression of Alzheimer's disease.

Galanin and spinal nociceptive mechanisms: recent results from transgenic and knock-out models

Genetically modified mice with transgenic overexpression of galanin or depletion of genes for galanin or galanin receptors have become available, providing a new approach for analyzing the role of galanin in nociception. Mice overexpressing galanin had a moderate heat hypoalgesia, reduced spinal sensitization after repetitive C-fiber stimulation and reduced development of neuropathic pain-like behavior after sciatic nerve injury. On the other hand, mice lacking the GALR1 receptor (Galr1-/-) exhibited only slight increase in heat nociception in the hot plate, but not tail flick, test and showed no increase in spinal sensitization. The duration, but not magnitude, of neuropathic pain-like behaviors, was increased in Galr1-/- mice after nerve injury. These results support an inhibitory effect of galanin on nociception, but the physiological role played by galanin via GALR1 receptors needs to be further studied.

Constitutive and ligand-induced internalization of EGFP-tagged galanin R2 and Rl receptors in PC12 cells

In the present experiments trafficking of the galanin R1-(GALR1) and, in particular, the galanin R2 receptor (GALR2) was studied after fusion with enhanced green fluorescent protein (GALR1-EGFP and GALR2-EGFP) and transfection into PC12 cells. Both fusion proteins were predominantly localized on the plasma membrane and internalized in a dose dependent manner after incubation with galanin. Preincubation with M35 or M40 did not prevent galanin-induced internalization of GALR1-EGFP or GALR2-EGFP. However, AR-M1896, a selective GALR2 agonist, caused GALR2, but not GALR1 internalization. Hyperosmotic sucrose inhibited internalization of GALR2-EGFP. After co-incubation with galanin, GALR2-EGFP was co-localized with internalized Texas Red transferrin, a marker of the clathrin endocytic pathway. Experiments with protein synthesis inhibition and Texas Red transferrin suggest that GALR2 is constitutively internalized. Studies in progress will show if this is the case also for GALR1.

Characterization of GalR1, GalR2, and GalR3 immunoreactivity in catecholaminergic nuclei of the mouse brain

The distribution of immunoreactivity for the three identified neuropeptide galanin receptors, GalR1, GalR2, and GalR3, was determined in areas of the mouse brain involved in drug addiction, including the ventral tegmental area (VTA), substantia nigra (SN), nucleus accumbens (NA), and locus coeruleus (LC). All three galanin receptors are found in the VTA, SN, NA, and LC; however, GalR1 protein is most highly represented in the VTA, NA, and SN, suggesting that GalR1 may play a predominant role in galanin-mediated regulation of dopamine neurotransmission. GalR1 and GalR3 protein levels are high in the LC, suggesting that these isoforms may be important for galanin-mediated regulation of noradrenergic transmission during opiate withdrawal. Although the distribution of GalR1, GalR2, and GalR3 largely recapitulates the pattern of galanin binding throughout the brain, some discrepancies exist, suggesting that another galanin receptor(s) may be present in some brain areas. Overall, GalR1, GalR2, and GalR3 are distributed widely throughout the brain, correlate with widespread galanin binding, and colocalize with tyrosine hydroxylase in catecholaminergic brain areas.

Identification of galanin receptor 1 on excitatory motor neurons in the guinea pig ileum

Exogenously administered galanin inhibits cholinergic transmission to the longitudinal muscle and reduces peristaltic efficiency in the guinea pig ileum with a mechanism partially mediated by galanin receptor 1 (GAL-R1). We investigated the effect of exogenous galanin 1-16, which has high affinity for GAL-R1, on the ascending excitatory reflex of the circular muscle elicited by radial distension in isolated segments of guinea pig ileum. We used a three-compartment bath that allows dissecting the ascending pathway into the oral (site of excitatory motor neurons), intermediate (site of ascending interneurons) and caudal compartment (site of intrinsic primary afferent neurons). Galanin 1-16 (0.3-3 micromol L(-1)) applied to the oral compartment inhibited in a concentration-dependent manner the ascending excitatory reflex elicited by the wall distension in the caudal compartment. This effect was antagonized by the GAL-R1 antagonist, RWJ-57408 (1 and 10 micromol L(-1)). By contrast, galanin 1-16 was ineffective when added to the intermediate or caudal compartment up to 3 micromol L(-1). GAL-R1 immunoreactive neurons did not contain neuron-specific nuclear protein, a marker for intrinsic primary afferent neurons. These findings indicate that GAL-R1s are present on motor neurons responsible for the ascending excitatory reflex, but not on ascending interneurons and intrinsic primary afferent neurons.

Galanin receptor 1 has anti-proliferative effects in oral squamous cell carcinoma

In the United States, oral cancer accounts for more deaths annually than cervical cancer, leukemias, or Hodgkin's lymphoma. Studies have shown that aberrations of chromosome 18q develop with tumor progression and are associated with significantly decreased survival in head and neck cancer patients. The G-protein-coupled receptor, galanin receptor 1 (GALR1), maps to this region of chromosome 18q. Although the role of GALR1 has been well characterized in neuronal cells, little is known regarding this receptor in non-neuronal cells. In this study, the expression, mitogenic function, and signaling mechanism of GALR1 are investigated in normal and malignant oral epithelial cells. mRNA expression was determined via reverse transcriptase-PCR. Protein quantification was done via immunoblot analysis and enzyme-linked immunosorbent assay. For functional and signaling studies, an inhibitory antibody was generated to the N-terminal ligand binding domain of GALR1. GALR1 protein and mRNA expression and GAL secretion were detected at variable levels in immortalized human oral keratinocytes and human oropharyngeal squamous cell carcinoma cell lines. Upon competitive inhibition of GALR1, proliferation was up-regulated in immortalized and malignant keratinocytes. Furthermore, studies with the inhibitory antibody and U0126, the MAPK inhibitor, show that GALR1 inhibits proliferation in immortalized and malignant keratinocytes by inactivating the MAPK pathway. GALR1s inhibitory effects on proliferation in epithelial cells raises the possibility that inactivation or disregulation of this receptor can lead to uncontrolled proliferation and neoplastic transformation.

[125I]-Galanin binding in brain of wildtype, and galanin- and GalR1-knockout mice: Strain and species differences in GalR1 density and distribution

Widespread production of knockout and transgenic mice has led to an increased use of mice as animal models for studies of normal- and patho-physiology. Hence, the precise mapping of central transmitter/peptide systems in the mouse has become essential for the interpretation of functional studies and for the correct correlation with findings obtained in the rat, primates and/or human. In this regard, the current study reports the autoradiographic localization of [(125)I]-galanin (GAL) binding sites in brain of the common C57BL/6J and 129OlaHsd mouse strains, as well as in GAL and galanin receptor-1 (GalR1) knockout (KO) mice. In C57BL/6J and 129OlaHsd mice, [(125)I]-GAL binding sites were detected throughout the brain, including moderate-high relative densities in the basal ganglia (caudate putamen, nucleus [n.] accumbens, olfactory tubercle, substantia nigra), limbic regions (septum, bed n. stria terminalis, ventral hippocampus, amygdala), cingulate, retrosplenial, entorhinal cortex, centro-lateral/medial thalamic n., preoptic/lateral hypothalamus, midbrain (superior colliculus, periaqueductal gray), pons/medulla oblongata (parabrachial, pontine reticular and solitary tract n.) and cerebellar cortex. [(125)I]-GAL binding levels were low or absent in main olfactory bulb, neocortex, ventrolateral/geniculate thalamic n., dorsal hippocampus, inferior colliculus and cranial motor n. In simultaneous determinations, relative [(125)I]-GAL binding site densities in brain were generally lower in C57BL/6J than in 129OlaHsd mice, while the density and distribution of central binding in the GAL-KO mouse was essentially identical to that in its background-129OlaHsd strain. In contrast, no specific [(125)I]-GAL binding was detected in any region of GalR1-KO mouse brain, revealing that under the experimental conditions used, the peptide ligand binding is predominantly (exclusively) to the GalR1 subtype. This evaluation of GAL receptor site distribution in mouse brain has revealed similarities and some differences with the equivalent system in rat and provides a valuable reference for future comparative studies of central GAL transmission.

Targeting of antisense PNA oligomers to human galanin receptor type 1 mRNA

In this work, we have targeted positions 18-38 of the human galanin receptor type 1 (GalR1) mRNA coding sequence with different peptide nucleic acid (PNA) oligomers. This region has previously been shown to be a good antisense region and therefore we aimed to identify the subregions and/or thermodynamic parameters determining the antisense efficacy. Nine different PNA oligomers were conjugated to a cell-penetrating peptide, transportan, to enhance their cellular uptake. Concentration-dependent down-regulation of GalR1 protein expression in human melanoma cell line Bowes was measured by radioligand binding assay. No reduction of GalR1 mRNA level was observed upon PNA treatment, thus, the effect was concluded to be translational arrest. Judging from the EC50 values, antisense PNA oligomers targeting regions 24-38 (EC50=70 nM) or 27-38 (EC50=80 nM) were the most potent suppressors of protein expression. No parameter predicted by M-fold algorithm was found to correlate with the measured antisense activities. Presence of some subregions was found not to increase antisense efficiency of PNA. Presence of a short unpaired triplet between nucleotides 33 and 35 in the target region was, on the other hand, found to be the most critical for efficient GalR1 down-regulation. Thus, the results are of high impact in designing antisense oligomers. Specific results of this study demonstrate 20-fold more efficient antisense down-regulation of GalR1 as achieved before.

Role of galanin receptor 1 in peristaltic activity in the guinea pig ileum

Galanin effects are mediated by distinct receptors, galanin receptor 1 (GAL-R1), GAL-R2 and GAL-R3. Here, we analyzed 1) the role of GAL-R1 in cholinergic transmission and peristalsis in the guinea-pig ileum using longitudinal muscle-myenteric plexus preparations and intact segments of the ileum in organ bath, and 2) the distribution of GAL-R1 immunoreactivity in the myenteric plexus with immunohistochemistry and confocal microscopy. Galanin inhibited electrically stimulated contractions of longitudinal muscle-myenteric plexus preparations with a biphasic curve. Desensitization with 1 microM galanin suppressed the high potency phase of the curve, whereas the GAL-R1 antagonist, RWJ-57408 (1 microM), inhibited the low potency phase. Galanin (3 microM) reduced the longitudinal muscle contraction and the peak pressure, and decreased the compliance of the circular muscle. All these effects were antagonized by RWJ-57408 (1 or 10 microM). RWJ-57408 (10 microM) per se did not affect peristalsis parameters in normal conditions, nor when peristalsis efficiency was reduced by partial nicotinic transmission blockade with hexamethonium. In the myenteric plexus, GAL-R1 immunoreactivity was localized to neurons and to fibers projecting within the plexus and to the muscle. GAL-R1 was expressed mostly by cholinergic neurons and by some neurons containing vasoactive intestinal polypeptide or nitric oxide synthase. This study indicates that galanin inhibits cholinergic transmission to the longitudinal muscle via two separate receptors; GAL-R1 mediates the low potency phase. The reduced peristalsis efficiency could be explained by inhibition of the cholinergic drive, whereas the decreased compliance is probably due to inhibition of descending neurons and/or to the activation of an excitatory muscular receptor. Endogenous galanin does not appear to affect neuronal pathways subserving peristalsis in physiologic conditions via GAL-R1.

Regulation of galanin receptor GalR1 mRNA expression by ovarian steroids in oestrogen receptor alpha-immunoreactive neurones: identification of distinct populations of neurones in the preoptic area

This study examined whether gonadal steroids are involved in regulating galanin receptor 1 (GalR1) mRNA expression in neurones that contain oestrogen receptor alpha (ERalpha), in three regions of the preoptic area (POA) known to be involved in the control of gonadotropin secretion. Double-labelling immunohistochemistry using an antibody against the ERalpha and in situ hybridization experiments using a 35S-labelled riboprobe specific for GalR1 mRNAs revealed that ERalpha is expressed in a large proportion of GalR1 mRNA-expressing neurones of the POA in the ovariectomized (OVX) female rat. Oestradiol (E2) and oestradiol plus progesterone (E2 + P) treatments of OVX rats significantly decreased the proportion of GalR1 mRNA/ERalpha immunoreactive (ERalpha-IR) neurones in the anteroventral periventricular nucleus (AVPV), medial preoptic nucleus (MPN) and medial preoptic area (MPO). The expression of GalR1 mRNA in ERalpha-IR neurones varied according the hormonal status of the female animals. In the AVPV, during the oestrous cycle, the hybridization signal significantly increased at oestrus. E2 and E2 + P treatments of OVX rats did not induced significant variation of levels of GalR1 mRNAs in ERalpha-IR neurones. In the MPN, E2 treatment of OVX rats resulted in significant increase in GalR1 mRNA expression in ERalpha-IR neurones. Similarly, levels of the GalR1 hybridization signal increased during afternoon of proestrus and oestrus. In the MPO, treatment of OVX rats with E2 + P significantly decreased GalR1 mRNA expression in ERalpha-IR neurones. The expression of GalR1 mRNA did not change during the oestrous cycle in this area. These findings suggest that the hypothalamic action of galanin on gonadotopin-releasing hormone (GnRH) secretion may pass through the specific population of GalR1/ERalpha-IR neurones of the MPN in mediating the oestrogen action on the GnRH system at the moment of the luteinizing hormone surge.

Galanin increases membrane excitability and enhances Ca(2+) currents in adult, acutely dissociated dorsal root ganglion neurons

We examined the effect of galanin (10(-15) - 10(-7) M) on dispersed, mainly small-sized dorsal root ganglion (DRG) neurons in adult rats using whole-cell patch-clamp. Galanin and AR-M1896, a selective galanin type 2 receptor (GalR2) agonist, both significantly increased the number of action potentials in response to current pulses in 77% of the neurons, indicating an increase in excitability. Galanin also caused a rise in input resistance, decreased the holding current for -60 mV and depolarized the resting potential. In addition, Ca(2+) currents elicited by voltage steps were significantly increased by both galanin and AR-M1896 in nearly 70% of the cells. This enhancement was observed in 30% of the neurons in the presence of nimodipine or omega-conotoxin, but in each case approximately 60% less than without blocking either N- or L-type Ca(2+) channels, indicating modulation of both types of Ca(2+) channels. The percentage of small- and medium-sized neurons expressing GalR2 mRNA in DRGs in situ was similar to that showing increased excitability and Ca(2+) current after galanin application, i.e. approximately 70-80% of the neurons. The findings suggest that GalR2 has a role in controlling both the excitability, probably by inhibition of GIRK or leak K(+) channels, and Ca(2+) entry in a large population of presumably nociceptive neurons. The combination of the two effects, which possibly arise from separate biochemical pathways, would increase excitability and enhance intracellular Ca(2+) signalling which would enhance sensory transmission. These mechanisms involving GalR2 receptors may underlie the pronociceptive effects of galanin described in the literature.

Analysis of the contribution of galanin receptors 1 and 2 to the central actions of galanin-like peptide

Galanin-like peptide (GALP) shares partial sequence identity with galanin and exhibits agonistic activity at two of the galanin receptor subtypes (GALR1 and GALR2) in vitro. The goal of these experiments was to determine whether galanin receptors mediate the effects of central GALP administration on food intake, body weight, and luteinizing hormone (LH) secretion in the mouse. We first evaluated the effects of intracerebroventricular injections of GALP or its vehicle alone in GALR1 knockout mice, GALR2 knockout mice, and their respective wild-type controls. GALP reduced food intake and body weight after 24 h to a similar degree in wild-type, GALR1 knockout, and GALR2 knockout mice. The wild-type, GALR1 knockout, and GALR2 knockout mice also exhibited significant increases in serum levels of LH following the GALP injections. To help delineate the biologically active moiety of the GALP molecule, we injected wild-type mice with shorter fragments of the full-length GALP peptide. Neither GALP((1-21)) (the fragment containing the galanin-homologous sequence) nor GALP((22-60)) (the C-terminal portion of the GALP molecule lacking sequence identity with galanin) had any discernable effect on food intake, body weight or circulating LH. These observations demonstrate that neither GALR1 nor GALR2 are essential for mediating the effects of GALP on feeding, body weight or LH secretion. Furthermore, the galanin-homologous region of the GALP molecule is not sufficient to mimic the effects of full-length GALP. Together, these findings argue against the hypothesis that GALP signals solely through galanin receptors in vivoand suggest the existence of a yet-to-be-identified GALP-specific receptor.

Galanin acts at GalR1 receptors in spinal antinociception: synergy with morphine and AP-5

The neuropeptide galanin (Gal) and its receptors (GalR1, GalR2, and GalR3) are expressed in spinal cord. We have characterized the pharmacology of the antinociceptive effects of intrathecally (i.t.) administered galanin and its analogs in the formalin test in rats, using an automated flinch detection system. Intrathecal injection of rat galanin (Gal(1-29)) or human galanin (Gal(1-30)) produced a dose-dependent inhibition of formalin-evoked flinching in phase 2, but not in phase 1. Relative potency of galanin homologs is Gal(1-29) >or= Gal(1-30) > galanin-like peptide(1-24) >or= Gal(2-11) = Gal (3-29) (an inactive analog). Galanin(1-29) and Gal(1-30) are both high-affinity agonists to GalR1/R2, whereas Gal(2-11) is a GalR2 receptor agonist. Our data suggest that i.t. galanin-produced antinociception is mediated by activation of GalR1 receptors. When comparing antinociceptive effects of i.t. Gal(1-29) to morphine and to 2-amino-5-phosphonopentanoic acid (AP-5, an N-methyl-d-aspartate antagonist), Gal(1-29) is of intermediate potency between these two analgesic agents based on the ED(50) values. An isobolographic analysis showed synergy between Gal(1-29) and morphine and between Gal(1-29) and AP-5 on the second phase. Fixed ratio dose combinations of morphine and Gal(1-29), or AP-5 and Gal(1-29) produced significantly greater antinociception than predicted from simple additivity. In summary, the present findings reveal that 1) spinal galanin produces a reliable inhibition of formalin-induced facilitated nociceptive processing, an effect possibly mediated by GalR1 receptors; and 2) galanin potentiates i.t. morphine and AP-5-induced antinociception.