Peripheral Galanin Receptor 2 as a Target for the Modulation of Pain

The neuropeptide galanin is widely expressed in the nervous system and has an important role in nociception. It has been shown that galanin can facilitate and inhibit nociception in a dose-dependent manner, principally through the central nervous system, with enhanced antinociceptive actions after nerve injury. However, following nerve injury, expression of galanin within the peripheral nervous system is dramatically increased up to 120-fold. Despite this striking increase in the peripheral nervous system, few studies have investigated the role that galanin plays in modulating nociception at the primary afferent nociceptor. Here, we summarise the recent work supporting the role of peripherally expressed galanin with particular reference to the dual actions of the galanin receptor 2 in neuropathic pain highlighting this as a potential target analgesic

Inhibition of kynureninase (L-kynurenine hydrolase, EC 3 . 7. 1 . 3) by oestrone sulphate: an alternative explanation for abnormal results of tryptophan load tests in women receiving oestrogenic steroids

1. A partial purification of kynureninase (L-kynurenine hydrolase, EC 3 . 7. 1 . 3) from rat liver and a total resolution of the apoenzyme have been achieved. The hypothesis that conjugates of oestrogenic steroids compete with pyridoxal phosphate for the cofactor binding site of the enzyme, and so disturb tryptophan metabolism, leading to apparent vitamin B6 deficiency, has been tested. 2. Kynureninase from rat liver was partially purified, and the cofactor-free apoenzyme was prepared. Oestrone sulphate inhibited the enzyme uncompetitively with respect to pyridoxal phosphate, and competitively with respect to kynurenine, with a mean (+/- SE) inhibitor constant (Ki) of 82 +/- 6 microM. 3. The addition of a saturating concentration of pyridoxal phosphate to unfractionated liver homogenates led to an approximately fivefold increase in kynureninase activity, indicating the presence of a relatively large amount of apo-kynureninase in the tissue. 4. It is suggested that the abnormal results of tryptophan load tests in women receiving oestrogens are the result of inhibition of kynureninase by oestrogen conjugates, and that there is no evidence for oestrogen-induced vitamin B deficiency in such cases

Characterisation of the nociceptive phenotype of suppressible galanin overexpressing transgenic mice

The neuropeptide galanin is widely expressed in both the central and peripheral nervous systems and is involved in many diverse biological functions. There is a substantial data set that demonstrates galanin is upregulated after injury in the DRG, spinal cord and in many brain regions where it plays a predominantly antinociceptive role in addition to being neuroprotective and pro-regenerative. To further characterise the role of galanin following nerve injury, a novel transgenic line was created using the binary transgenic tet-off system, to overexpress galanin in galaninergic tissue in a suppressible manner. The double transgenic mice express significantly more galanin in the DRG one week after sciatic nerve section (axotomy) compared to WT mice and this overexpression is suppressible upon administration of doxycycline. Phenotypic analysis revealed markedly attenuated allodynia when galanin is overexpressed and an increase in allodynia following galanin suppression. This novel transgenic line demonstrates that whether galanin expression is increased at the time of nerve injury or only after allodynia is established, the neuropeptide is able to reduce neuropathic pain behaviour. These new findings imply that administration of a galanin agonist to patients with established allodynia would be an effective treatment for neuropathic pain

Measuring vascular reactivity with breath-holds after stroke: a method to aid interpretation of group-level BOLD signal changes in longitudinal fMRI studies

Blood oxygenation level dependent (BOLD) contrast fMRI is a widely used technique to map brain function, and to monitor its recovery after stroke. Since stroke has a vascular etiology, the neurovascular coupling between cerebral blood flow and neural activity may be altered, resulting in uncertainties when interpreting longitudinal BOLD signal changes. The purpose of this study was to demonstrate the feasibility of using a recently validated breath-hold task in patients with stroke, both to assess group level changes in cerebrovascular reactivity (CVR) and to determine if alterations in regional CVR over time will adversely affect interpretation of task-related BOLD signal changes. Three methods of analyzing the breathhold data were evaluated. The CVR measures were compared over healthy tissue, infarcted tissue, and the peri-infarct tissue, both sub-acutely (~two weeks) and chronically (~four months). In this cohort, a lack of CVR differences in healthy tissue between the patients and controls indicates that any group level BOLD signal change observed in these regions over time is unlikely to be related to vascular alterations. CVR was reduced in the peri-infarct tissue but remained unchanged over time. Therefore, although a lack of activation in this region compared to the controls may be confounded by a reduced CVR, longitudinal grouplevel BOLD changes may be more confidently attributed to neural activity changes in this cohort. By including this breath-hold based CVR assessment protocol in future studies of stroke recovery, researchers can be more assured that longitudinal changes in BOLD signal reflect true alterations in neural activity

Probable mechanisms of regulation of the utilization of dietary tryptophan, nicotinamide and nicotinic acid as precursors of nicotinamide nucleotides in the rat

1. The regulation of the utilization of dietary tryptophan, nicotinamide and nicotinic acid as precursors of the nicotinamide nucleotides has been studied in groups of rats fed on diets providing only one of these precursors at a time, in amounts adequate to meet their requirements for nucleotide synthesis. 2. The concentration of nicotinamide nucleotides in the liver of rats receiving a high-tryptophan diet was 56% higher than in animals fed on a diet providing a minimum amount of tryptophan, together with nicotinic acid or nicotinamide. The excretion of N1-methyl nicotinamidc was three times higher in the tryptophan-fed animals than in the other two groups. 3. The concentration of quinolinic acid in the liver was significantly higher in animals receiving the high-tryptophan diet than in the other two groups; that of nicotinic acid was highest in those animals receiving the nicotinic-acid-containing diet. The concentration of nicotinamide was highest in the livers of those animals receiving the high-tryptophan diet, and lowest in those receiving the nicotinic-acid-contaning diet. 4. The values of the Michaelis constant Km of nicotinamide deamidase (nicotinamide amidohydrolase. EC 3.5,1,19) and nicotinamide phosphoribosylltransferase (nicotinamide nucleotide: pyrophosphate phosphoribosyltransferase, EC 2.4.2.12) were approximately equal, and approximately one-tenth of the concentration of nicotinamide was in the liver. This suggests that both these enzymes normally function at their maximum rate, and a change in the availability of nicotinamide would not affect the rate of its incorporation into nucleotides. 5. The maximum rate of reaction (Vmax) of nicotinamide deamidase was twice that of nicotinamide phosphoribosyltransferase; this suggests that unless compartmental or other factors are involved, the major route of nicotinamide utilization will be by way of deamidation. 6. The Km of nicotinate phosphoribosyltransferase (nicotinate nucleotide: pyrophosphate phosphoribosyltransferase, EC 2.4.2.11) was less than twice the concentration of nicotinic acid in the liver, so that a change in the availability of nicotinic acid might be expected to lead to a small change in the rate of its utilization. 7. The Km of quinolinate phosphoribosyltransferase (nicotinate nucleotide: pyrophosphate phosphoribosyltransferase (carboxylating) EC 2.4.2.19) was approximately 100 times greater than the concentration of quinolinic acid in the liver, so that any change in the availability of quinolinic acid would be expected to lead to a considerable change in the rate of its utilization. The Vmax of quinolinate phosphoribosyltransferase was relatively low, so that under conditions of high tryptophan flux, some accumulation of quinolinic acid might be expected. This was observed in animals receiving the high-tryptophan diet. 8. It is concluded that it is unlikely that the utilization of quinolinic acid, arising from tryptophan. for the synthesis of nicotinamide nucleotides is regulated, but that control over tissue concentrations of nucleotides is achieved by hydrolysis of NAD to nicotinamide. Incorporation of nicotinamide into nucleotides seems to be strictly limited by the activity of the enzymes involved

Evaluating the role of a galanin enhancer genotype on a range of metabolic, depressive and addictive phenotypes

Funded by •ERC. Grant Number: 284167 •NIH. Grant Number: 1RO1DK0921127-01 •NWO. Grant Numbers: 463-06-001, 451-04-034Peer reviewedPublisher PD

Targeted disruption of the orphan receptor Gpr151 does not alter pain-related behaviour despite a strong induction in dorsal root ganglion expression in a model of neuropathic pain

BACKGROUND: Gpr151 is an orphan GPCR whose function is unknown. The restricted pattern of neuronal expression in the habenula, dorsal horn of the spinal cord and dorsal root ganglion plus homology with the galanin family of receptors imply a role in nociception. RESULTS: Real-time quantitative RT-PCR demonstrated a 49.9 ± 2.9 fold highly significant (P < 0.001) increase in Gpr151 mRNA expression in the dorsal root ganglion 7 days after the spared nerve injury model of neuropathic pain. Measures of acute, inflammatory and neuropathic pain behaviours were not significantly different using separate groups of Gpr151 loss-of-function mutant mice and wild-type controls. Galanin at concentrations between 100 nM and 10 μM did not induce calcium signalling responses in ND7/23 cells transfected with Gpr151. CONCLUSIONS: Our results indicate that despite the very large upregulation in the DRG after a nerve injury model of neuropathic pain, the Gpr151 orphan receptor does not appear to be involved in the modulation of pain-related behaviours. Further, galanin is unlikely to be an endogenous ligand for Gpr151

Activation of the galanin receptor 2 in the periphery reverses nerve injury-induced allodynia

<p>Abstract</p> <p>Background</p> <p>Galanin is expressed at low levels in the intact sensory neurons of the dorsal root ganglia with a dramatic increase after peripheral nerve injury. The neuropeptide is also expressed in primary afferent terminals in the dorsal horn, spinal inter-neurons and in a number of brain regions known to modulate nociception. Intrathecal administration of galanin modulates sensory responses in a dose-dependent manner with inhibition at high doses. To date it is unclear which of the galanin receptors mediates the anti-nociceptive effects of the neuropeptide and whether their actions are peripherally and/or centrally mediated. In the present study we investigated the effects of direct administration into the receptive field of galanin and the galanin receptor-2/3-agonist Gal2-11 on nociceptive primary afferent mechanical responses in intact rats and mice and in the partial saphenous nerve injury (PSNI) model of neuropathic pain.</p> <p>Results</p> <p>Exogenous galanin altered the responses of mechano-nociceptive C-fibre afferents in a dose-dependent manner in both naive and nerve injured animals, with low concentrations facilitating and high concentrations markedly inhibiting mechano-nociceptor activity. Further, use of the galanin fragment Gal2-11 confirmed that the effects of galanin were mediated by activation of galanin receptor-2 (GalR2). The inhibitory effects of peripheral GalR2 activation were further supported by our demonstration that after PSNI, mechano-sensitive nociceptors in galanin over-expressing transgenic mice had significantly higher thresholds than in wild type animals, associated with a marked reduction in spontaneous neuronal firing and C-fibre barrage into the spinal cord.</p> <p>Conclusions</p> <p>These findings are consistent with the hypothesis that the high level of endogenous galanin in injured primary afferents activates peripheral GalR2, which leads to an increase in C-fibre mechanical activation thresholds and a marked reduction in evoked and ongoing nociceptive responses.</p