Use of genetically engineered transgenic mice to investigate the role of galanin in the peripheral nervous system after injury

Adaptative responses of myenteric neurons of Sphoeroides testudineus to environmental pollution

Contamination in estuarine regions affects the local biota damaging the ecosystems and reaching humans. The gastrointestinal tract is a dynamic environment capable of obtaining nutrients and energy from food while it protects the host against harmful toxins and pathogens from the external environment. These functions are modulated by the enteric nervous system and changes in its structure can result in gastrointestinal disorders. The objective of this study was to evaluate if the environmental contaminants have effects on the myenteric neuronal plasticity of pufferfish Sphoeroides testudineus. Animals were collected in Barra do Una River, located at Jureia-Itatins Mosaic of Protected Areas (reference area - RA) and in the Santos Estuarine System (impacted area - IA). Morpho-quantitative analyses of the general and metabolically active myenteric neuronal populations of the proximal and distal intestine were made. Disarrangement was observed in the general organization of the myenteric plexus, with an expressive reduction of the neuronal groups (nodes) in the animals of IA. The vulnerability of the myenteric plexus was evidenced by a decrease in density and cellular profile of the general neuronal population, followed by an increase of the metabolism of the remaining neurons, which in turn was verified by a growth of the area of the cellular and nuclear profiles of the metabolically active neuronal population. Through these analyses, we concluded that animals inhabiting polluted regions present alterations in the myenteric neuronal plasticity, as a way of maintaining the functions of the gastrointestinal tract.

The Influence of High and Low Doses of Bisphenol A (BPA) on the Enteric Nervous System of the Porcine Ileum

Bisphenol A, used in the production of plastic, is able to leach from containers into food and cause multidirectional adverse effects in living organisms, including neurodegeneration and metabolic disorders. Knowledge of the impact of BPA on enteric neurons is practically non-existent. The destination of this study was to investigate the influence of BPA at a specific dose (0.05 mg/kg body weight/day) and at a dose ten times higher (0.5 mg/kg body weight/day), given for 28 days, on the porcine ileum. The influence of BPA on enteric neuron immunoreactive to selected neuronal active substances, including substance P (SP), vasoactive intestinal polypeptide (VIP), galanin (GAL), vesicular acetylcholine transporter (VAChT—used here as a marker of cholinergic neurons), and cocaine- and amphetamine-regulated transcript peptide (CART), was studied by the double immunofluorescence method. Both doses of BPA affected the neurochemical characterization of the enteric neurons. The observed changes depended on the type of enteric plexus but were generally characterized by an increase in the number of cells immunoreactive to the particular substances. More visible fluctuations were observed after treatment with higher doses of BPA. The results confirm that even low doses of BPA may influence the neurochemical characterization of the enteric neurons and are not neutral for living organisms.

Zinc Transporter 3 (ZnT3) in the Enteric Nervous System of the Porcine Ileum in Physiological Conditions and during Experimental Inflammation

Zinc transporter 3 (ZnT3) is a member of the solute-linked carrier 30 (SLC 30) zinc transporter family. It is closely linked to the nervous system, where it takes part in the transport of zinc ions from the cytoplasm to the synaptic vesicles. ZnT3 has also been observed in the enteric nervous system (ENS), but its reactions in response to pathological factors remain unknown. This study, based on the triple immunofluorescence technique, describes changes in ZnT3-like immunoreactive (ZnT3-LI) enteric neurons in the porcine ileum, caused by chemically-induced inflammation. The inflammatory process led to a clear increase in the percentage of neurons immunoreactive to ZnT3 in all "kinds" of intramural enteric plexuses, i.e., myenteric (MP), outer submucous (OSP) and inner submucous (ISP) plexuses. Moreover, a wide range of other active substances was noted in ZnT3-LI neurons under physiological and pathological conditions, and changes in neurochemical characterisation of ZnT3⁺ cells in response to inflammation depended on the "kind" of enteric plexus. The obtained results show that ZnT3 is present in the ENS in a relatively numerous and diversified neuronal population, not only in physiological conditions, but also during inflammation. The reasons for the observed changes are not clear; they may be connected with the functions of zinc ions and their homeostasis disturbances in pathological processes. On the other hand, they may be due to adaptive and/or neuroprotective processes within the pathologically altered gastrointestinal tract.

Neuropeptide profile changes in sensory neurones after partial prepyloric resection in pigs

This report details the first identification of the sources of sensory innervation of the porcine stomach prepyloric region. The Fast Blue (FB) retrograde tracing technique detected the sensory prepyloric neurons in the bilateral nodose ganglia (NGs) as well as thoracic dorsal root ganglia (DRGs). Double-labelling immunofluorescence demonstrated expression of substance P (SP), calcitonin gene-related peptide (CGRP), neuronal isoform of nitric oxide synthase (nNOS), vasoactive intestinal polypeptide (VIP) and galanin (GAL) in both NGs and DRGs. Additionally, we found that partial resection of the stomach prepyloric area increased expression of the SP, CGRP, NOS, VIP and GAL in the prepyloric sensory neurons. In the control left NGs, both a higher total number of FB-positive perikarya as well as a higher percentage of the peptides expressing prepyloric neurons were visualized than in the right NGs. However, compared to the control group, prepyloric resection evoked greater increases in peptide expression in the right-side NGs sensory neurons. In the ganglia of this side, the proportion of the SP-IR perikarya increased by approximately 15%, while CGRP-IR increased by 28%, NOS-IR 14%, VIP-IR 43% and GAL-IR 13%. On the opposite left side, the ganglia proportion of the CGRP-IR perikarya increased by approximately 10%, while NOS-IR increased by 3%, VIP-IR 36% and GAL-IR by 2%. The only decrease (by 5%) was observed in the case of SP expression. We also found that 92% of the sensory neurons originated from NGs and 8% from DRGs. Our results indicate that, in the pig, SP, CGRP, NOS, VIP and GAL participate in the vagal sensory transduction from the stomach prepyloric area. Moreover, increased expression of the peptides and neuronal isoform of nitric oxide synthase in the sensory neurons following transection of their peripheral dendrites suggests their possible participation in the neuronal recovery and/or reinnervation process.

Alterations of neurochemical expression of the coeliac-superior mesenteric ganglion complex (CSMG) neurons supplying the prepyloric region of the porcine stomach following partial stomach resection

The purpose of the present study was to determine the response of the porcine coeliac-superior mesenteric ganglion complex (CSMG) neurons projecting to the prepyloric area of the porcine stomach to peripheral neuronal damage following partial stomach resection. To identify the sympathetic neurons innervating the studied area of stomach, the neuronal retrograde tracer Fast Blue (FB) was applied to control and partial stomach resection (RES) groups. On the 22nd day after FB injection, following laparotomy, the partial resection of the previously FB-injected stomach prepyloric area was performed in animals of RES group. On the 28th day, all animals were re-anaesthetized and euthanized. The CSMG complex was then collected and processed for double-labeling immunofluorescence. In control animals, retrograde-labelled perikarya were immunoreactive to tyrosine hydroxylase (TH), dopamine β-hydroxylase (DβH), neuropeptide Y (NPY) and galanin (GAL). Partial stomach resection decreased the numbers of FB-positive neurons immunopositive for TH and DβH. However, the strong increase of NPY and GAL expression, as well as de novo-synthesis of neuronal nitric oxide synthase (nNOS) and leu5-Enkephalin (LENK) was noted in studied neurons. Furthermore, FB-positive neurons in all pigs were surrounded by a network of cocaine- and amphetamine-regulated transcript peptide (CART)-, calcitonin gene-related peptide (CGRP)-, and substance P (SP)-, vasoactive intestinal peptide (VIP)-, LENK- and nNOS- immunoreactive nerve fibers. This may suggest neuroprotective contribution of these neurotransmitters in traumatic responses of sympathetic neurons to peripheral axonal damage.

Effect of carnosine, methylprednisolone and their combined application on irisin levels in the plasma and brain of rats with acute spinal cord injury

Spinal cord injury (SCI) might occur to anybody at any time and any age. In its treatment, methylprednisolone (MP) is a first choice worldwide, but there is still no significant breakthrough in truly beneficial treatment due to SCI's complex pathophysiology. We investigated the effect of carnosine, methylprednisolone (MP) and its combination on irisin levels in the plasma, brain and medulla spinalis tissues in SCI using a rat model. The rats were divided into 6 groups: I (Control, saline); II (sham animals with laminectomy without cross-clamping); III (SCI); IV (SCI treated with 150mg/kg carnosine); V (SCI treated with 30mg/kg methylprednisolone); and VI (SCI treated with a combination of carnosine and MP). The animals were given traumatic SCI after laminectomy, using 70-g closing force aneurysm clips (Yasargil FE 721). Irisin concentration was measured by ELISA. The distribution of irisin in brain and spinal cord tissues was examined by immunochemistry. Irisin was mainly expressed in the astrocytes and microglia of brain tissues, and multipolar neurones of the anterior horn of spinal cord tissue in rats of all groups, indicating that irisin is physiologically indispensable. MP and carnosine and the combination of the two, significantly increased irisin in plasma and were accompanied by a significant rise in irisin immunoreactivity of brain and spinal cord tissues of the injured rats compared with control and sham. This finding raises the possibility that methylprednisolone and carnosine regulate the brain and spinal cord tissues in SCI by inducing irisin expression, and may therefore offer a better neurological prognosis.

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.

Role of neuropeptides, neurotrophins, and neurohormones in skin wound healing

Due to the close interactions between the skin and peripheral nervous system, there is increasing evidence that the cutaneous innervation is an important modulator of the normal wound healing process. The communication between sensory neurons and skin cells involves a variety of molecules (neuropeptides, neurohormones, and neurotrophins) and their specific receptors expressed by both neuronal and nonneuronal skin cells. It is well established that neurotransmitters and nerve growth factors released in skin have immunoregulatory roles and can exert mitogenic actions; they could also influence the functions of the different skin cell types during the wound healing process.

Galanin gene expression and effects of its knock-down on the development of the nervous system in larval zebrafish

Despite the known importance of galanin in the nervous system of vertebrates, the galanin gene structure and expression and the consequences of galanin deficiency in developing zebrafish are unknown. We cloned the galanin gene and analyzed its expression by using in situ hybridization, PCR, and immunocytochemistry throughout the early development of zebrafish until the end of the first week of life. The single zebrafish galanin gene encoded for a single amidated galanin peptide and a galanin message-associated peptide. Two forms resulting from alternative processing were identified. Galanin mRNA was maternally expressed and found in developing fish throughout early development. In situ hybridization showed the first positive neurons in three groups in the brain at 28 hours postfertilization. At 2 days postfertilization, three prosencephalic neuron groups were seen in the preoptic area and in rostral and caudal periventricular hypothalamus. In addition, two other groups of weakly stained neurons were visible, one in the midbrain and another in the hindbrain. Translation inhibition of galanin mRNA with morpholino oligonucleotides caused complete disappearance of galanin immunoreactivity in the brain until 7 dpf and did not induce known cascades of nonspecific pathways or morphological abnormalities. A minor disturbance of sensory ganglia was found. Galanin knockdown did not alter the expression of tyrosine hydroxylases 1 and 2, choline acetyltransferase, histidine decarboxylase, or orexin mRNA. The results suggest that galanin does not regulate the development of these key markers of specific neurons, although galanin-expressing fibers were in a close spatial proximity to several neurons of these neuronal populations.

Galanin-expression and galanin-dependent sensory neurons are not required for itch

Background

Galanin is a key modulator of nociception, and it is also required for the developmental survival of a subset of C-fibre sensory neurons which are critical to the mediation of neuropathic and inflammatory pain. However, the potential modulatory roles played by galanin, or the galanin-dependent neurons, in pruritoceptive mechanisms underlying the sensation of itch have not been investigated.

Findings

Here we report that mice carrying a loss-of-function mutation in the galanin gene (Gal-KO) show no differences in spontaneous behavioural itch responses compared to wild-type (WT) controls. Similarly, the responses to a range of pruritogens are not significantly different between the two genotypes.

Conclusions

These results suggest that neither galanin expression, nor the galanin-dependent subpopulation of sensory neurons is required for itch-related behaviours.

Downstream effector molecules in successful peripheral nerve regeneration

The robust axon regeneration that occurs following peripheral nerve injury is driven by transcriptional activation of the regeneration program and by the expression of a wide range of downstream effector molecules from neuropeptides and neurotrophic factors to adhesion molecules and cytoskeletal adaptor proteins. These regeneration-associated effector molecules regulate the actin-tubulin machinery of growth-cones, integrate intracellular signalling and stimulatory and inhibitory signals from the local environment and translate them into axon elongation. In addition to the neuronally derived molecules, an important transcriptional component is found in locally activated Schwann cells and macrophages, which release a number of cytokines, growth factors and neurotrophins that support neuronal survival and axonal regeneration and that might provide directional guidance cues towards appropriate peripheral targets. This review aims to provide a comprehensive up-to-date account of the transcriptional regulation and functional role of these effector molecules and of the information that they can give us with regard to the organisation of the regeneration program.

Expression of galanin and galanin receptor mRNA in skin during the formation of granulation tissue

Galanin is a neuropeptide widely distributed in the central and peripheral nervous systems. Although its role in non-neural cells is poorly understood, it is known that during inflammation, the dermis layer of the skin produces and releases galanin. The aim of this report is to study the expression of galanin in granulation tissue. After inducing inflammation by cotton thread implantation, galanin-like immunoreactivity (galanin-LI) in plasma reached a maximum on the third day. Galanin-LI was observed in fibroblast-like cells occurring close to collagen fibers in developing granulation tissue. Furthermore, galanin receptor subtypes 1 and 2 (GALR1 and GALR2)-expressing cells were observed around microvessels and were found to produce desmin. Galanin was injected along the cotton threads immediately after implantation, resulting in rapid formation of granulation tissue, and an increase in the contents of microvessels, indicating a stimulatory effect of galanin on the process of angiogenesis in granulation tissue. The results demonstrate that some galanin was released from fibroblast-like cells during the formation of granulation tissue, and that it stimulated angiogenesis.

Intact attentional processing but abnormal responding in M1 muscarinic receptor-deficient mice using an automated touchscreen method

Cholinergic receptors have been implicated in schizophrenia, Alzheimer's disease, Parkinson's disease, and Huntington's disease. However, to better target therapeutically the appropriate receptor subsystems, we need to understand more about the functions of those subsystems. In the current series of experiments, we assessed the functional role of M(1) receptors in cognition by testing M(1) receptor-deficient mice (M1R(-/-)) on the five-choice serial reaction time test of attentional and response functions, carried out using a computer-automated touchscreen test system. In addition, we tested these mice on several tasks featuring learning, memory and perceptual challenges. An advantage of the touchscreen method is that each test in the battery is carried out in the same task setting, using the same types of stimuli, responses and feedback, thus providing a high level of control and task comparability. The surprising finding, given the predominance of the M(1) receptor in cortex, was the complete lack of effect of M(1) deletion on measures of attentional function per se. Moreover, M1R(-/-) mice performed relatively normally on tests of learning, memory and perception, although they were impaired in object recognition memory with, but not without an interposed delay interval. They did, however, show clear abnormalities on a variety of response measures: M1R(-/-) mice displayed fewer omissions, more premature responses, and increased perseverative responding compared to wild-types. These data suggest that M1R(-/-) mice display abnormal responding in the face of relatively preserved attention, learning and perception.

Skin incision induces expression of axonal regeneration-related genes in adult rat spinal sensory neurons

Skin incision and nerve injury both induce painful conditions. Incisional and postsurgical pain is believed to arise primarily from inflammation of tissue and the subsequent sensitization of peripheral and central neurons. The role of axonal regeneration-related processes in development of pain has only been considered when there has been injury to the peripheral nerve itself, even though tissue damage likely induces injury of resident axons. We sought to determine if skin incision would affect expression of regeneration-related genes such as activating transcription factor 3 (ATF3) in dorsal root ganglion (DRG) neurons. ATF3 is absent from DRG neurons of the normal adult rodent, but is induced by injury of peripheral nerves and modulates the regenerative capacity of axons. Image analysis of immunolabeled DRG sections revealed that skin incision led to an increase in the number of DRG neurons expressing ATF3. RT-PCR indicated that other regeneration-associated genes (galanin, GAP-43, Gadd45a) were also increased, further suggesting an injury-like response in DRG neurons. Our finding that injury of skin can induce expression of neuronal injury/regeneration-associated genes may impact how clinical postsurgical pain is investigated and treated.

PERSPECTIVE

Tissue injury, even without direct nerve injury, may induce a state of enhanced growth capacity in sensory neurons. Axonal regeneration-associated processes should be considered alongside nerve signal conduction and inflammatory/sensitization processes as possible mechanisms contributing to pain, particularly the transition from acute to chronic pain.

Galanin receptor subtypes 1 and 2 as therapeutic targets in head and neck squamous cell carcinoma

IMPORTANCE OF THE FIELD

Despite advances in the therapeutic approaches for head and neck squamous cell carcinoma (HNSCC) at some sites, no substantial improvement in treatment efficacy and survival has occurred over the past several decades. Recent application of molecular biology has focused on the importance of galanin and its receptors as potential therapeutic targets for HNSCC.

AREAS COVERED IN THIS REVIEW

Our aim is to examine galanin receptor 1 (GALR1) and galanin receptor 2 (GALR2) as HNSCC therapeutic targets and explore opportunities and strategies for making use of GALR1 and GALR2 signaling.

WHAT THE READER WILL GAIN

This review provides recent data about galanin receptor signaling and function in various cell types, especially HNSCC. Signaling through GALR1 induces cell cycle arrest and suppresses proliferation in HNSCC. Similar to GALR1, GALR2 not only induces cell cycle arrest but also apoptosis, which was not observed with GALR1.

TAKE HOME MESSAGES

GALR1 and GALR2 act as tumor suppressors in HNSCC, in a p53-independent manner. The current data suggest that GALR1 and GALR2 are potentially significant therapeutic targets and prognostic factors in HNSCC.

Inflammation- and axotomy-induced changes in galanin-like immunoreactive (GAL-LI) nerve structures in the porcine descending colon

This study reports on changes caused by chemically driven inflammation and axotomy in galanin-like immunoreactive (GAL-LI) nerve structures in the porcine descending colon. The distribution pattern of GAL-LI structures was studied using the immunofluorescence technique in the circular muscle layer, the myenteric (MP), outer submucous (OSP) and inner submucous plexuses (ISP), and also in the mucosal layer. Under physiological conditions GAL-LI perikarya were shown to constitute 3.68 +/- 0.32%, 7.02 +/- 0.93% and 10.99 +/- 0.71% in MP, OSP and ISP, respectively. Both colitis and axotomy caused an increase in GAL-like immunoreactivity, which was different in particular parts of the bowel segment studied. The numbers of GAL-LI perikarya increased to 14.16 +/- 0.49%, 16.78 +/- 1.09% and 37.46 +/- 1.18% during colitis and 7.92 +/- 0.72%, 10.44 +/- 0.71% and 16.20 +/- 0.96% after axotomy in MP, OSP and ISP, respectively. Both these processes caused an increase in the number of GAL-LI nerve fibres in the circular muscle and mucosal layers as well as the appearance of a population of GAL-LI cells in the mucosa.

Galanin family of peptides in skin function

The skin, the largest organ of the body, functions as a barrier between the body proper and the external environment, as it is constantly exposed to noxious stressors. During the last few years, the concept of an interactive network involving cutaneous nerves, the neuroendocrine axis, and the immune system has emerged. The neuroendocrine system of the skin is composed of locally produced neuroendocrine mediators that interact with specific receptors. Among these mediators are neuropeptides, including members of the galanin peptide family--galanin, galanin-message associated peptide, galanin-like peptide, and alarin--which are produced in neuronal as well as nonneuronal cells in the skin. Here, we review the expression of the galanin peptides and their receptors in the skin, and the known functions of galanin peptides in different compartments of the skin. We discuss these data in light of the role of the galanin peptide family in inflammation and cell proliferation.

Bone marrow stromal cells attenuate injury-induced changes in galanin, NPY and NPY Y1-receptor expression after a sciatic nerve constriction

Single ligature nerve constriction (SLNC) of the rat sciatic nerve triggers neuropathic pain-related behaviors and induces changes in neuropeptide expression in primary afferent neurons. Bone marrow stromal cells (MSCs) injected into the lumbar 4 (L4) dorsal root ganglia (DRGs) of animals subjected to a sciatic nerve SLNC selectively migrate to the other ipsilateral lumbar DRGs (L3, L5 and L6) and prevent mechanical and thermal allodynia. In this study, we have evaluated the effect of MSC administration on the expression of the neuropeptides galanin and NPY, as well as the NPY Y(1)-receptor (Y(1)R) in DRG neurons. Animals were subjected to a sciatic nerve SLNC either alone or followed by the administration of MSCs, phosphate-buffered saline (PBS) or bone marrow non-adherent mononuclear cells (BNMCs), directly into the ipsilateral L4 DRG. Seven days after injury, the ipsilateral and contralateral L4-5 DRGs were dissected out and processed for standard immunohistochemistry, using specific antibodies. As previously reported, SLNC induced an ipsilateral increase in the number of galanin and NPY immunoreactive neurons and a decrease in Y(1)R-positive DRG neurons. The intraganglionic injection of PBS or BNMCs did not modify this pattern of expression. In contrast, MSC administration partially prevented the injury-induced changes in galanin, NPY and Y(1)R expression. The large number of Y(1)R-immunoreactive neurons together with high levels of NPY expression in animals injected with MSCs could explain, at least in part, the analgesic effects exerted by these cells. Our results support MSC participation in the modulation of neuropathic pain and give insight into one of the possible mechanisms involved.

Effects of norepinephrine on galanin expression in dorsal root ganglion neurons in vitro

BACKGROUND

Norepinephrine (NE) is a key neurotransmitter that functionally activates adrenoreceptors expressed in sympathetic neurons. Functional α1-adrenoreceptors are also expressed in dorsal root ganglion (DRG) primary sensory neurons and regulate neurogenic inflammation and nociceptive responses. Galanin is involved in inflammation and nociception. It has been suggested that galanin receptor (GalR) 1 and GalR3 activation induces analgesia at the level of the spinal cord, while activation of GalR2 has a pronociceptive role in the periphery. Whether activation or inhibition of α-adrenoreceptors influences galanin expression remains unknown.

OBJECTIVE

The aim of the present study was to investigate whether the α-adrenoreceptor agonist NE, the α1-adrenoreceptor antagonist prazosin, and the α2-adrenoreceptor antagonist yohimbine affect galanin expression in primary cultured DRG neurons.

METHODS

DRG was dissected from 240 embryonic 15-day-old Wistar rats, cultured as dissociated cells for 2 days, and then exposed to NE (10(-4) mol/L) for another 4 days. In the NE + prazosin group and the NE + yohimbine group, DRG neurons were pretreated with prazosin (10(-6) mol/L) and yohimbine (10(-5) mol/L), respectively, 10 minutes prior to the NE challenge. The neurons cultured continuously in media served as the controls. All of the cultured samples were processed to detect galanin mRNA and galanin peptide expression by reverse transcriptase-polymerase chain reaction and Western blot, respectively. Five samples were tested for each procedure.

RESULTS

Forty samples were prepared for this study and included in the analysis. After 4 days of incubation, mean (SD) galanin mRNA/β-actin mRNA concentration ratio was significantly increased with NE compared with controls (0.3349 [0.0413] vs 0.2411 [0.0519]; P < 0.05). Pretreatment with prazosin seemed to block the effects of NE (0.2522 [0.0496]; P < 0.05 vs NE), while yohimbine did not appear to significantly alter the effects of NE on elevation of galanin mRNA/β-actin mRNA concentration (0.3154 [0.0239]; P < 0.05 vs controls). After 4 days of incubation, galanin/β-actin concentration ratio was significantly higher with NE compared with controls (0.4406 [0.0655] vs 0.2295 [0.0794]; P < 0.01). Pretreatment with prazosin appeared to inhibit NE-induced galanin peptide expression (0.3156 [0.0942]; P < 0.05 vs NE), while yohimbine did not appear to alter the effects of NE on elevation of galanin peptide concentration (0.3700 [0.0533]; P < 0.05 vs controls). Coclusions: In this small in vitro study, NE, likely due to action on α1-adrenoreceptors but not α2-adrenoreceptors, was associated with an increase in galanin mRNA concentration and galanin peptide expression in these DRG neurons. These findings might be relevant to noradrenergic pain modulation.

Sensory-nerve-derived neuropeptides: possible therapeutic targets

This review examines our developing understanding of the families and activities of some of the best known sensory-nerve-derived inflammatory neuropeptides, namely substance P, calcitonin gene-related peptide and galanin. Evidence to date shows involvement of these transmitters in a wide range of systems that includes roles as inflammatory modulators. There is an increasing understanding of the mechanisms involved in the release of the peptides from sensory nerves and these are key in understanding the potential of neuropeptides in modulating inflammatory responses and may also provide novel targets for anti-inflammatory therapy. The neuropeptides released act via specific G protein coupled receptors, most of which have now been cloned. There is knowledge of selective agonists and antagonists for many subtypes within these families. The study of neuropeptides in animal models has additionally revealed pathophysiological roles that in turn have led to the development of new drugs, based on selective receptor antagonism.

Regulation of galanin and galanin receptor 2 expression by capsaicin in primary cultured dorsal root ganglion neurons

Galanin is a 29-amino-acid neuropeptide expressed in dorsal root ganglion (DRG) neurons which is thought to play a role in modulation of nociception in neuropathic states. Activation of galanin receptor 2 (GalR2) plays a pronociceptive role and enhances capsaicin-induced nociception in the periphery. GalR2 and vanilloid receptor 1 (VR1) are co-expressed in DRG neurons. Capsaicin evokes acute pain via activation of VR1 expressed in primary sensory neurons. It is not known to what extent galanin and its receptor GalR2 expression is regulated by capsaicin in DRG neurons. Effects of acute (4 h) or chronic (4 d) treatment with capsaicin at different concentrations (0.01, 0.1, 1 micromol/L) on galanin and GalR2 expression in primary cultured DRG neurons were investigated in the present study. Our results showed that acute exposure of high concentration capsaicin (1 micromol/L) increased galanin expression, whereas chronic exposure of low concentration capsaicin (0.01, 0.1 micromol/L) promoted galanin expression. Only chronic exposure of 0.1 micromol/L concentration capsaicin could elevate GalR2 expression, whereas capsaicin did not have this effect at any other conditions in this experiment. These results indicated that certain concentrations or exposure time of capsaicin stimulation may be relevant to upregulation of galanin and its receptor GalR2 expression in DRG cultures suggesting a response to peripheral neuronal stimulation. And also, capsaicin-induced GalR2 expression may be also modulated by capsaicin-induced galanin expression. The possible significance of the neurotransmission of nociceptive information involved in galanin or GalR2 expression caused by capsaicin is still to be clarified.

Galanin: a potential role in mesolimbic dopamine-mediated instrumental behavior

The involvement of the neuropeptide galanin in the consumption of the primary "commodities" of food and water is well established. However, the present review describes anatomical and behavioral evidence that suggests that galanin may also modulate ascending mesolimbic dopamine function and thereby play an inhibitory role in the systems by which instrumental behavior is energized toward acquiring primary commodities. General anatomical frameworks for this interaction are presented and future studies that could evaluate it are discussed.

Postendocytotic traffic of the galanin R1 receptor: a lysosomal signal motif on the cytoplasmic terminus

The neuropeptide galanin R1 receptor (GalR1) was tagged at its C terminus with EGFP (GalR1-EGFP) to study receptor localization and trafficking. In PC12 and HEK293 cells, functional GalR1-EGFP was expressed on the plasma membrane and internalized into cytoplasmic vesicles after galanin stimulation. The internalization was blocked by 0.4 M sucrose and by silencing of clathrin with siRNA methodology. Internalized GalR1-EGFP and LysoTracker, a lysosomal marker, overlapped in intracellular vesicles after prolonged galanin stimulation. This colocalization was strongly reduced after site-directed mutagenesis of the motif YXXØ on the C terminus of GalR1 (where Ø is a bulky hydrophobic residue and X any amino acid). Taken together, these data suggest that GalR1 is internalized via the clathrin-dependent, endocytic pathway and then, to a large extent, delivered to lysosomes for degradation through the lysosome-targeting signal YXXØ.

The myelin-associated glycoprotein inhibitor BENZ induces outgrowth and survival of rat dorsal root ganglion cell cultures

The novel myelin-associated glycoprotein (MAG) inhibitor BENZ binds to the N-acetylneuraminic acid (Neu5Ac) portion of the N-terminal Ig-like domain of MAG. Treatment of rat dorsal root ganglion (DRG) cell cultures with BENZ-induced outgrowth of neurofilament 200-positive neurites improved survival of neurons and increased the number of GFAP-positive cells, as determined by fluorescence and confocal laser microscopy and by Western immunoblotting. Furthermore, treatment of DRG cell cultures with BENZ repressed gene and protein expression of the small GTPase RhoA but induced expression of Rho GTP-activating proteins 5 and 24, likely to counteract protein kinase A activity. Specifically, expression of inhibitors of neurite outgrowth, for example, Rock2 and PAK4, was repressed, but cofilin 1, a promoter of axonal growth, was induced. We propose that the MAG inhibitor BENZ abrogates the RhoA-ROCK-cofilin pathway to promote neurite outgrowth. Our findings require confirmation by in vivo animal studies.

Galanin decreases proliferation of PC12 cells and induces apoptosis via its subtype 2 receptor (GalR2)

Galanin is a neuropeptide with a wide range of effects in the nervous and endocrine systems, mediated through three G protein-coupled receptor subtypes (GalR1-3). Interestingly, galanin and its receptors are also expressed in certain tumors. Here we studied the effects of galanin in rat pheochromocytoma (PC12) cells stably transfected with GFP-tagged GalR2. Galanin at 100 nM inhibited cell proliferation in both nontransfected and transfected cells. Conversly, both galanin and the GalR2(R3)-agonist AR-M1896 induced caspase-dependent apoptotic cell death only in GalR2-transfected cells. Western-blot analyses of downstream mediators of the G(q/11)-type G protein showed down-regulation of pAkt and pBad in galanin-exposed transfected cells. Also, the specific PI3 kinase inhibitor LY-294002 increased the level of pBad and decreased activation of caspases. In addition, p21(cip1) levels were up-regulated in galanin-exposed PC12 cells and down-regulated in galanin-exposed GalR2-transfected cells. In agreement, FACS analyses of galanin exposed cells showed occurrence of cell cycle arrest in PC12 cells and cell death in transfected cells. Finally, as shown with real-time PCR, galanin and its receptors were expressed at very high levels in human pheochromocytoma tissues as compared with normal adrenal medulla. These findings point to GalR2 as a possible target for therapeuthic interventions in pheochromocytoma.

Differential galanin upregulation in dorsal root ganglia and spinal cord after graded single ligature nerve constriction of the rat sciatic nerve

Single ligature nerve constriction (SLNC) is a newly developed animal model for the study of neuropathic pain. SLNC of the rat sciatic nerve induces pain-related behaviors, as well as changes in the expression of neuropeptide tyrosine and the Y(1) receptor in lumbar dorsal root ganglia (DRGs) and spinal cord. In the present study, we have analyzed the expression of another neuropeptide, galanin, in lumbar DRGs and spinal cord after different degrees of constriction of the rat sciatic nerve. The nerve was ligated and reduced to 10-30, 40-80 or 90% of its original diameter (light, medium or strong SLNCs). At different times after injury (7, 14, 30, 60 days), lumbar 4 and 5 DRGs and the corresponding levels of the spinal cord were dissected out and processed for galanin-immunohistochemistry. In DRGs, SLNC induced a gradual increase in the number of galanin-immunoreactive (IR) neurons, in direct correlation with the degree of constriction. Thus, after light SLNC, a modest upregulation of galanin was observed, mainly in small-sized neurons. However, following medium or strong SLNCs, there was a more drastic increase in the number of galanin-IR neurons, involving also medium and large-sized cells. The highest numbers of galanin-IR neurons were detected 14 days after injury. In the dorsal horn of the spinal cord, medium and strong SLNCs induced a marked ipsilateral increase in galanin-like immunoreactivity in laminae I-II. These results show that galanin expression in DRGs and spinal cord is differentially regulated by different degrees of nerve constriction and further support its modulatory role on neuropathic pain.

Expression of the vesicular glutamate transporters-1 and -2 in adult mouse dorsal root ganglia and spinal cord and their regulation by nerve injury

The expression of two vesicular glutamate transporters (VGLUTs), VGLUT1 and VGLUT2, was studied with immunohistochemistry in lumbar dorsal root ganglia (DRGs), the lumbar spinal cord and the skin of the adult mouse. About 12% and 65% of the total number of DRG neuron profiles (NPs) expressed VGLUT1 and VGLUT2, respectively. VGLUT1-immunoreactive (IR) NPs were usually medium- to large-sized, in contrast to a majority of small- or medium-sized VGLUT2-IR NPs. Most VGLUT1-IR NPs did not coexpress calcitonin gene-related peptide (CGRP) or bound isolectin B4 (IB4). In contrast, approximately 31% and approximately 42% of the VGLUT2-IR DRG NPs were also CGRP-IR or bound IB4, respectively. Conversely, virtually all CGRP-IR and IB4-binding NPs coexpressed VGLUT2. Moderate colocalization between VGLUT1 and VGLUT2 was also observed. Sciatic nerve transection induced a decrease in the overall number of VGLUT1- and VGLUT2-IR NPs (both ipsi- and contralaterally) and, in addition, a parallel, unilateral increase of VGLUT2-like immunoreactivity (LI) in a subpopulation of mostly small NPs. In the dorsal horn of the spinal cord, strong VGLUT1-LI was detected, particularly in deep dorsal horn layers and in the ventral horns. VGLUT2-LI was abundant throughout the gray spinal matter, 'radiating' into/from the white matter. A unilateral dorsal rhizotomy reduced VGLUT1-LI, while apparently leaving unaffected the VGLUT2-LI. Transport through axons for both VGLUTs was confirmed by their accumulation after compression of the sciatic nerve or dorsal roots. In the hind paw skin, abundant VGLUT2-IR nerve fibers were observed, sometimes associated with Merkel cells. Lower numbers of VGLUT1-IR fibers were also detected in the skin. Some VGLUT1-IR and VGLUT2-IR fibers were associated with hair follicles. Based on these data and those by Morris et al. [Morris JL, Konig P, Shimizu T, Jobling P, Gibbins IL (2005) Most peptide-containing sensory neurons lack proteins for exocytotic release and vesicular transport of glutamate. J Comp Neurol 483:1-16], we speculate that virtually all DRG neurons in adult mouse express VGLUTs and use glutamate as transmitter.

Involvement of galanin in nociceptive regulation in the arcuate nucleus of hypothalamus in rats with mononeuropathy

The hindpaw withdrawal latencies (HWLs) to noxious thermal and mechanical stimulation increased significantly after intra-hypothalamic arcuate nucleus (ARC) injection of galanin in mononeuropathic rats, while intra-ARC injection of the putative antagonist of galanin receptors markedly reduced the HWLs. The number of galaninergic neurons in the ARC increased in rats with mononeuropathy than that in normal rats. The results demonstrated that both endogenous and exogenous galanin were involved in the regulation of nociception in the ARC of rats with peripheral nerve injury.

Plasma neuropeptides in patients undergoing lumbar discectomy

STUDY DESIGN

A prospective analysis of patients with lumbar disc herniation (LDH).

OBJECTIVES

To determine the role of neuropeptides as a biochemical signature of pain states in patients with LDH.

SUMMARY OF BACKGROUND DATA

Increases in the plasma level of neuropeptides have been reported in patients suffering from a variety of painful conditions. However, there is no such report on patients with LDH.

METHODS

From a total of 27 patients with a single-level LDH, blood samples were collected before and 3 weeks after lumbar discectomy. Plasma levels of alpha calcitonin gene-related peptide (CGRP), galanin, neuropeptide Y, and substance P were determined by using enzyme-linked immunosorbent assay. The association or correlation between preoperative concentration of plasma neuropeptides and gender, patients' age, and VAS were analyzed statistically. Also, the concentration of plasma neuropeptides was compared before and after lumbar discectomy.

RESULTS

Preoperative plasma levels of CGRP were correlated significantly with the extent of sciatica as determined by VAS. In addition, plasma levels of CGRP and galanin significantly decreased after lumbar discectomy in line with the disappearance of pain symptoms.

CONCLUSIONS

These findings indicate the role of plasma CGRP and possibly galanin as a systemic neurochemical signature of pain states in patients with LDH.

Galanin receptor subtype 2 (GalR2) null mutant mice display an anxiogenic-like phenotype specific to the elevated plus-maze

The neuropeptide galanin has been implicated in anxiety-related behaviors, cognition, analgesia, and feeding in rodents. Neuromodulatory actions of galanin are mediated by three G-protein coupled receptors, GalR1, GalR2, and GalR3. The present study investigates the role of the GalR2 receptor by evaluating behavioral phenotypes of mice with a targeted mutation in the GalR2 gene. A three-tiered behavioral phenotyping approach first examined control measures of general health, body weight, neurological reflexes, sensory abilities and motor function. Mice were then assessed on several tests for cognitive and anxiety-like behaviors. GalR2 null mutants and heterozygotes were not significantly different from wildtype littermates on two cognitive tests previously shown to be sensitive to galanin manipulation: acquisition of the Morris water maze spatial task, and trace cued and contextual fear conditioning, an emotional learning and memory task. Two independent cohorts of GalR2 null mutant mice demonstrated an anxiogenic-like phenotype in the elevated plus-maze. No genotype differences were detected on several other measures of anxiety-like behavior. The discovery of an anxiogenic phenotype specific to the elevated plus-maze, similar to findings in GalR1 null mutants, highlights the potential therapeutic efficacy of targeting GalR1 and GalR2 receptors in treating anxiety disorders.

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.

Neurotrophins: mediators and modulators of pain

The neurotrophin family of neurotrophic factors are well-known for their effects on neuronal survival and growth. Over the past decade, considerable evidence has accumulated from both humans and animals that one neurotrophin, nerve growth factor (NGF), is a peripheral pain mediator, particularly in inflammatory pain states. NGF is upregulated in a wide variety of inflammatory conditions, and NGF-neutralizing molecules are effective analgesic agents in many models of persistent pain. Such molecules are now being evaluated in clinical trials. NGF regulates the expression of a second neurotrophin, brain-derived neurotrophic factor (BDNF), in nociceptors. BDNF is released when nociceptors are activated, and it acts as a central modulator of pain. The chapter reviews the evidence for these roles (and briefly the effects of other neurotrophins), the range of conditions under which they act, and their mechanism of action.

Galanin receptor expression in cultured human keratinocytes and in normal human skin

Galanin (GAL) is a biologically active neuropeptide that is widely distributed in the nervous system. GAL exerts diverse action via the GAL receptors (GALR1, GALR2, and GALR3), which belong in the superfamily of G-protein-coupled transmembrane receptors. In human skin, GAL-like immunoreactivity has been reported in free nerve endings and fibers of the dermis. The extraneuronal expression of GAL has also been demonstrated. Although the GALRs are essential for biological functions, the expressions of different GALR subtypes in cultured human keratinocytes have not yet been investigated. The aim of our study was to investigate the mRNA and protein expressions of the different GALRs in the HaCaT immortalized keratinocyte cell line and in cultured human keratinocytes. When reverse transcription (RT)-polymerase chain reaction (PCR) was used with different GALR-specific primers, only GALR2 mRNA was identified in cultured HaCaT cells and keratinocytes. Sequencing of the PCR products proved the presence of GALR2 mRNA in the keratinocytes. The presence of GALR2 protein was next investigated, using a polyclonal antibody against human GALR2. Both the HaCaT cells and the cultured keratinocytes displayed specific immunohistochemical staining, with higher intensity on the surface of the keratinocytes. Immunohistochemical investigations of normal human skin specimens revealed that GALR2 was expressed with high intensity in the basal layer of the epidermis and also around the hair follicles in the dermis. GAL treatment of the keratinocytes resulted in an increase in cytosolic Ca2+ concentration, suggesting that GALR2 is a functional receptor. Further studies are necessary to clarify the biological effects of GAL in the skin.

Phenotyping of sensory and sympathetic ganglion neurons of a galanin-overexpressing mouse--possible implications for pain processing

The distribution of galanin was studied in the lumbar 5 dorsal root ganglia (DRGs) and spinal cord, superior cervical ganglia (SCGs), and skin of transgenic mice overexpressing galanin under the dopamine beta-hydroxylase (DBH) promoter (GalOE-DBH mice) and in wild type (WT) mice. The DRGs and spinal cord were analysed before and after a unilateral, complete transection (axotomy) of the sciatic nerve and after dorsal rhizotomy. Both galanin protein and transcript were studied by, respectively, immunohistochemistry and in situ hybridization. Increased galanin expression was observed in several small, medium-sized and large DRG neuron profiles (NPs) in the naïve transgenic mouse, frequently in neurons lacking calcitonin gene-related peptide (CGRP) and isolectin B4-binding. This lack of coexistence was particularly evident in the medium-sized/large NPs. In the dorsal horn of the spinal cord, no differences were detected between GalOE-DBH and WT mice, both displaying a strong galanin-positive neuropil in the superficial laminae of the dorsal horn, but the transgenic mice showed a more abundant galanin-positive innervation of the ventral horn. A 12-day dorsal rhizotomy, surprisingly, failed to alter the galanin staining patterns in the dorsal (and ventral) dorsal horn. Unilateral axotomy induced upregulation of galanin in DRG NPs of all sizes in both types of mouse. In the hindpaw skin, a profuse galanin-positive fiber plexus was observed in sweat glands and around blood vessels of the transgenic mice, being much more restricted in WT mice. Finally, GalOE mice exhibited a strong galanin-like immunoreactivity in most SCG NPs. The overexpression of the peptide in DRGs and SCGs was paralleled by increased mRNA levels. The present results show that overexpression of galanin under the control of the DBH promoter does not only occur, as expected in these mice, in noradrenline/adrenaline neurons but also in DRG neurons, particularly in large and medium-sized NPs. To what extent and how this overexpression pattern is related to the previously shown elevated pain threshold under normal and lesion conditions is discussed [Grass, S., Crawley, J.N., Xu, X.J., Wiesenfeld-Hallin, Z., 2003a. Reduced spinal cord sensitization to C-fibre stimulation in mice over-expressing galanin. Eur. J. Neurosci. 17, 1829-1832; Hygge-Blakeman, K., Brumovsky, P., Hao, J.X., Xu, X.J., Hökfelt, T., Crawley, J.N., Wiesenfeld-Hallin, Z., 2004. Galanin over-expression decreases the development of neuropathic pain-like behaviour in mice after partial sciatic nerve injury. Brain Res. 1025, 152-158].

Sensory neuronal phenotype in galanin receptor 2 knockout mice: focus on dorsal root ganglion neurone development and pain behaviour

Galanin is a 29-amino-acid peptide expressed in dorsal root ganglion (DRG) neurones and spinal dorsal horn neurones. It affects pain threshold and has developmental and trophic effects. Galanin acts at three G-protein-coupled receptors, galanin receptors (GalR1-3), each expressed in the DRGs as suggested by in situ hybridization and/or reverse transcriptase-polymerase chain reaction. The GalR2 knockout (-/-) mice permit studies on the contributions of this receptor subtype to the role of galanin at the spinal level. At 1 week after sciatic nerve transection (axotomy), there were 16-20% fewer neurones in intact and contralateral DRGs of -/- mice as compared with wild-type (WT) mice. In addition, a significant neurone loss (26% reduction) was found in the ipsilateral DRGs of WT mice, whereas no further neurone loss was seen in -/- mice. Expression of several peptides has been examined after axotomy, including galanin, neuropeptide Y and two of its receptors as well as substance P, and no significant differences were found between -/- and WT mice in either ipsi- or contralateral DRGs, respectively. After thermal injury and spinal nerve ligation, onset and duration of hyperalgesia in the injured paw were similar in GalR2-/- and WT animals. Recovery from spinal nerve ligation-caused allodynia had the same kinetics in -/- and WT animals. These data are in line with earlier observations from the peripheral and central nervous system, suggesting that galanin actions mediated by GalR2 subtype are of importance in neurodevelopment and neuroprotection.

Galanin and its receptors: introduction to the Third International Symposium, San Diego, California, USA, 21-22 October 2004

The Third Galanin Symposium presented many different and exciting results on galanin research reflecting a major progress since the previous symposium in 1998. A major impression was the many possible relationships of galaninergic mechanisms to important brain functions such as development, cognition and ageing as well as many aspects related to a wide spectrum of diseases, including Alzheimer's disease, anxiety/depression, addiction, obesity, pain and tumour growth. These studies were based on an extensive armament of methodologies including various strains of transgenic mice. Unfortunately, the pharmaceutical industry had only a minor participation. Nevertheless, exciting developments in the generation of agonists and antagonists are emerging, providing hope that we at the next symposium will be able to validitate many of the challenging hypotheses concerning galanin and disease with the help of pharmacological tools.