Specific expression of galanin in the peri-infarct zone after permanent focal cerebral ischemia in the rat

Single-nucleotide polymorphism rs948854 in human galanin gene and multiple sclerosis: a gender-specific risk factor

We performed comparative analyses of the genotype distribution and allelic frequencies of the rs948854 polymorphism (G/A) in the galanin gene's promoter in patients with multiple sclerosis (MS) and in healthy matched controls. In total 111 patients and 115 control subjects were included. The analyses revealed that the presence of the minor allele (G) increased susceptibility to MS in men (OR = 2.49, P = 0.008) but not in women. The presence of the G allele in men was also significantly associated with the late onset of MS. Furthermore, rs948854 polymorphism affected the rate of MS progression depending on the sex of the patients. In woman (typically slowly progressing), the percentage of patients with the slow (<0.5 EDSS score per year) progression rate was significantly reduced (χ²  = 5.7, P = 0.017) in the minor allele carriers group (52.6%), in comparison with the wild-type carriers (83.9%). In men (typically quickly progressing), the number of patients with fast progression rate (≥0.75 EDSS score per year) tended to increase in the minor allele carriers group (50%) compared with number of patients with the wild-type carriers (31.3%). These data demonstrate for the first time an association between rs948854 polymorphism and multiple sclerosis and, further, that this association is sex specific. They also point to diagnostic and prognostic benefits of genetic screening of patients with multiple sclerosis. © 2016 Wiley Periodicals, Inc.

Galanin's implications for post-stroke improvement

Stroke leads to a variety of pathophysiological conditions such as ischemic infarct, cerebral inflammation, neuronal damage, cognitive decline, and depression. Many endeavors have been tried to find the therapeutic solutions to attenuate severe neuropathogenesis after stroke. Several studies have reported that a decrease in the neuropeptide regulator ‘galanin’ is associated with neuronal loss, learning and memory dysfunctions, and depression following a stroke. The present review summarized recent evidences on the function and the therapeutic potential of galanin in post-ischemic stroke to provide a further understanding of galanin's role. Hence, we suggest that galanin needs to be considered as a therapeutic factor in the alleviation of post-stroke pathologies.

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

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

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 systems and ischemia: peptide and receptor plasticity in neurons and oligodendroglial precursors

Cerebral cortex contains few if any galanin neurons, but receives galanin-ergic inputs from subcortical areas. Apart from our earlier study on the response to cortical spreading depression, little is known about the presence and function of galanin in normal or injured cortex and to gain more insight into its possible roles, we investigated the temporal effects of focal ischemia on the expression of galanin and galanin receptors (GalRs). Focal ischemia induced in the rat by unilateral middle cerebral artery occlusion increased galanin and GalR1 mRNAs in penumbral/undamaged areas on the first and second day post-ischemia, while increased GalR2 mRNA was observed in the same regions only on the second day. Immunohistochemical studies revealed galanin immunoreactive neurons in the frontal/ cingulate cortex and abundant galanin-immunoreactivity in nerve axons/fibres within the penumbral areas, between the third and the seventh day after ischemia. Galanin mRNA and immunoreactivity was also increased in a population of small cells thought to be NG2-positive oligodendrocyte precursors. Up-regulation of galanin and GalRs in various cell populations following severe ischemic injury further demonstrates the marked plasticity of galanin and GalR1/2 expression after brain injury, and together with data reported elsewhere in this volume, suggests a functional role for galanin signalling in such pathophysiological conditions.

Effects of intracerebroventricular galanin or a galanin receptor 2/3 agonist on the lesion induced by transient occlusion of the middle cerebral artery in female rats

Several studies have shown that injury to the central and peripheral nervous system can increase expression of galanin, a 29 amino acid neuropeptide. Moreover, there is evidence that galanin, especially through its galanin receptor 2 (GalR2) receptor, plays a neuroprotective role in different injury models. However, direct studies of a possible neuroprotective effect of galanin in experimental stroke models are lacking. Galanin, a GalR2/3 agonist or artificial CSF was continuously infused intracerebroventricularly (i.c.v.) in naïve female rats after a 60min transient and focal occlusion of the middle cerebral artery. The animals were sacrificed, and the ischemic lesion was visualized using 2,3,5-triphenyltetrazolium hydrochloride (TTC) staining. The lesion was 98% larger after i.c.v. administration of the GalR2/3 agonist (2.4nmol/day) seven days after occlusion compared to artificial CSF (p=0.023). No statistically significant differences were found after seven days in the groups treated with galanin in three different concentrations (0.24, 2.4 and 24nmol/day; p=0.939, 0.715 and 0.977, respectively). There was no difference in the size of the ischemic lesions measured after three days in the galanin-treated group (2.4nmol/d) compared to artificial CSF (p=0.925). The present results show, surprisingly, that a GalR2/3 agonist doubled the size of the ischemic lesion. Whether this effect primarily reflects the properties of the current model, species, gender and/or the mode of galanin administration, e.g. causing desensitization, or whether galanin indeed lacks neuroprotective effect of its own, remains to be corroborated.

Hypothermia-induced increase in galanin concentrations and ischemic neuroprotection in the rat brain

The effects of hypothermia on galanin concentrations and the relation between ischemic brain lesions, hypothermia and galanin concentrations in a transient and focal rat stroke model were investigated in order to elucidate whether hypothermia-induced alterations in galanin concentrations could constitute a part of the established neuroprotective effect of hypothermia. Female rats were allocated to normothermia (37 degrees C) or hypothermia (33 degrees C) treatments during a 60 min microclip middle cerebral artery occlusion. The ischemic lesions were visualized after observation periods of 2 or 7 days and the concentration of galanin measured by radioimmunoassay in extracts of punch biopsies from both the lesioned and the contralateral control hemisphere. Hypothermia-induced an overall increase in the concentrations of immunoreactive galanin (p<0.001). The elevated galanin levels were predominantly found in the non-ischemic control hemisphere, in the hippocampus, thalamus and the posterior part of parietal cortex. The galanin concentrations were lower in the ischemic hemisphere in both the normo- and hypothermic animals compared to the corresponding contra lateral intact hemisphere (p=0.049). The factor of time, 2 respectively 7 days, did not show any significant difference regarding the galanin concentrations (p=0.844). Multivariate analyses of variance revealed significant effect of ischemia on the size of the ischemic brain lesions (p=0.001) but no overall effect of temperature when data from both 2 and 7 days observation periods were analyzed together. The ischemic lesions were generally larger at 33 degrees after 2 days (p=0.230). Prolonged observation time of 7 days resulted in a significant reduction of the ischemic brain lesion (p=0.011) with smaller ischemic lesions in the hypothermic group. Our data support the notion that hypothermia-induced increase in the tissue concentrations of galanin in the brain are the result of changes from optimal homeostatic conditions - the hypothermia-induced stress - rather than the ischemia/re-perfusion lesion induced changes in galanin concentrations. Hypothermia-induced elevation in galanin concentration is therefore not likely to be amongst the major protective mechanisms of hypothermia.