Galanin receptor 1 plays an antinociceptive effect via inhibiting PKA activation in the nucleus accumbens of rats with neuropathic pain.

Galanin and galanin receptors (GalRs) have been reported to be involved in the transmission and modulation of nociceptive information in the central nervous system (CNS). However, the underlying mechanism of the antinociception of GalRs in neuropathic pain remains unclear. This study investigated the antinociception induced by galanin receptor 1 (GalR1) via protein kinase A (PKA) signaling pathway in the nucleus accumbens (NAc) of rats with neuropathic pain. A mononeuropathy model was replicated by ligation of the left sciatic nerve, following which the expression of phospho-PKA (p-PKA) in the NAc were markedly up-regulated at 14(th) and 28(th) day after ligation of sciatic nerve, and p-PKA expression was down-regulated by intra-NAc injection of GalR1 agonist M617, but the GalR1 antagonist M35 did not have an effect. We also found that M35 in the NAc blocked the M617-induced increase in the hind paw withdrawal latencies (HWLs) of rats with mononeuropathy, but M35 alone had no effect on HWLs, and PKA inhibitor H-89 attenuated the M617-induced an increase in the HWLs. These results suggested that GalR1 induced an antinociception via inhibiting PKA activation, implying that GalR agonists may be potential and potent therapeutic options to treat chronic neuropathic pain.

Expression of galanin and its receptors are perturbed in a rodent model of mild, blast-induced traumatic brain injury.

The symptomatology, mood and cognitive disturbances seen in post-traumatic stress disorder (PTSD) and mild blast-induced traumatic brain injury (mbTBI) overlap considerably. However the pathological mechanisms underlying the two conditions are currently unknown. The neuropeptide galanin has been suggested to play a role in the development of stress and mood disorders. Here we applied bio- and histochemical methods with the aim to elucidate the nature of any changes in the expression of galanin and its receptors in a rodent model of mbTBI. In situ hybridization and quantitative polymerase chain reaction studies revealed significant, injury-induced changes, in some cases lasting at least for one week, in the mRNA levels of galanin and/or its three receptors, galanin receptor 1-3 (GalR1-3). Such changes were seen in several forebrain regions, and the locus coeruleus. In the ventral periaqueductal gray GalR1 mRNA levels were increased, while GalR2 were decreased. Analysis of galanin peptide levels using radioimmunoassay demonstrated an increase in several brain regions including the locus coeruleus, dorsal hippocampal formation and amygdala. These findings suggest a role for the galanin system in the endogenous response to mbTBI, and that pharmacological studies of the effects of activation or inhibition of different galanin receptors in combination with functional assays of behavioral recovery may reveal promising targets for new therapeutic strategies in mbTBI.

Galanin expression in the mouse major pelvic ganglia during explant culture and following cavernous nerve transection.

Autonomic neurons commonly respond to injury/axotomy with an increased expression of neuropeptides including galanin and pituitary adenylyl cyclase-activating polypeptide (PACAP). The increased peptide expression may enhance neuronal survival and axonal regeneration. Using quantitative (Q) PCR and immunocytochemistry, the present study tested whether galanin expression increased in male mouse major pelvic ganglia (MPG) neurons in response to injury. Galanin transcript expression increased significantly in MPG neurons following 72 h in explant culture and 72 h after unilateral transection of the cavernous nerve. Under both conditions, the increase in galanin transcript levels was greater than the increase in PACAP transcript levels. In control MPG, galanin-IR nerve fibers formed pericellular arrangements around MPG neurons although few galanin-IR cells were evident and many of the galanin-IR cells may be small intensely fluorescent (SIF) cells. In 3-day-cultured MPGs, many more galanin-IR cells and nerve fibers were noted. The increased galanin expression was most apparent in neurons that were also immunoreactive for neuronal nitric oxide synthase, rather than tyrosine hydroxylase. Some explant-cultured MPG neurons exhibited immunoreactivity to galanin and PACAP. As reported previously for PACAP, there is an injury-induced increase in MPG galanin expression, which occurs preferentially in the parasympathetic postganglionic neurons.

The neuropeptide galanin and variants in the GalR1 gene are associated with nicotine dependence.

The neuropeptide galanin and its receptors are expressed in brain regions implicated in drug dependence. Indeed, several lines of evidence support a role for galanin in modulating the effects of drugs of abuse, including morphine, cocaine, amphetamine, and alcohol. Despite these findings, the role of galanin and its receptors in the effects of nicotine is largely underexplored. Here, using mouse models of nicotine reward and withdrawal, we show that there is a significant correlation between mecamylamine-precipitated nicotine withdrawal somatic signs and basal galanin or galanin receptor 1 (GALR1) expression in mesolimbocortical dopamine regions across the BXD battery of recombinant inbred mouse lines. The non-peptide galanin receptor agonist, galnon, also blocks nicotine rewarding effects and reverses mecamylamine-precipitated nicotine withdrawal signs in ICR mice. Additionally, we conducted a meta-analysis using smoking information from six European-American and African-American data sets. In support of our animal data, results from the association study show that variants in the GALR1 gene are associated with a protective effect in nicotine dependence (ND). Taken together, our data suggest that galanin has a protective role against progression to ND, and these effects may be mediated through GALR1.

Expression of galanin and galanin receptor-1 in normal bone and during fracture repair in the rat.

The neuropeptide galanin (GAL) has recognized physiological actions in the nervous system and other tissues, but there is no documented evidence of GAL influencing normal or pathological bone metabolism. GAL expression, however, is upregulated in central and peripheral nerves following axotomy and is known to influence neural regeneration. Thus, severance of skeletal-associated nerves during fracture could similarly increase local GAL concentrations and thereby influence fracture healing. The initial aim of this study was therefore to identify the presence of GAL in normal bone and/or fracture callus by assessing the concentration and cellular localization of GAL in intact and/or fractured rat rib, using radioimmunoassay and immunohistochemistry, respectively. Groups of Sprague-Dawley rats (13 weeks old) had their left sixth ribs surgically fractured or underwent sham surgery and then calluses and nonfractured rib samples were analyzed at 1 and 2 weeks postsurgery (n = 5-6 per group). Low (basal) concentrations of GAL were detected in control ribs, whereas at 1 and 2 weeks postfracture, callus samples contained markedly increased levels of peptide ( approximately 32- and 18-fold increase, respectively, relative to controls; P < 0.01), revealing a strong upregulation during bone healing. Plasma GAL concentrations were also increased at 2 weeks postfracture (P < 0.005). In normal (nonfractured) rib, minimal levels of GAL-like immunoreactivity (LI) were present in cortical bone, periosteum, endosteum, and surrounding skeletal muscle. In costal cartilage plates, intense GAL-LI was present in all chondrocytes of the hypertrophic zone and in a population of chondrocytes in the reserve zone. GAL-LI was not present, however, in chondrocytes in the proliferative zone of costal cartilage or skeletal muscle fibers. In fracture callus, levels of GAL-LI were moderate to intense in osteoprogenitor cells and osteoblasts, in some chondrocytes, and in cartilaginous, osseous, and periosteal matrices. Subsequent studies revealed the presence of galanin receptor-1-like immunoreactivity (GALR1-LI) in most cell types shown to contain GAL-LI, although the distribution of GALR1-LI was more extensive in reserve zone chondrocytes than that of GAL-LI; and GALR1-LI also appeared in late proliferative zone chondrocytes of costal cartilage. In summary, GAL concentrations were significantly increased in fracture callus and plasma of rats that underwent rib fracture. In addition, GAL- and GALR1-LI was also detected in specific cells and structures within costal cartilage, bone, and fracture callus. These results strongly implicate GAL in aspects of cartilage growth plate physiology and fracture repair, possibly acting in an autocrine/paracrine fashion via GALR1.