Inflammatory mediator-induced modulation of GABAA currents in human sensory neurons.

The purpose of the present study was to characterize the properties of A-type GABA receptor (GABAA receptor) currents in human sensory neurons. Neurons were obtained from adult organ donors. GABAA currents were recorded in isolated neurons. Both large inactivating low-affinity currents and smaller persistent high-affinity currents were present in all of the 129 neurons studied from 15 donors. The kinetics of human GABAA currents were slower than those in rat sensory neurons. GABA currents were completely blocked by bicuculline (10 µM), and persistent currents were activated by the δ-subunit-preferring agonist, 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-3-ol (THIP). The GABA current equilibrium potential was ∼ 20 mV more hyperpolarized than in rat neurons. Both low- and high-affinity currents were increased by inflammatory mediators but via different second messenger pathways. These results highlight potentially important species differences in the properties of ion channels present in their native environment and suggest the use of human sensory neurons may be a valuable tool to test compounds prior to use in humans.

OPRM1 receptor as new biomarker to help the prediction of post mastectomy pain and recurrence in breast cancer.

Breast cancer is the most common type of cancer among women worldwide. Short-term postsurgical recovery is complicated by many factors, including imbalanced inflammatory and immune response, acute pain associated with functional impairment, and chronic postmastectomy pain (CPMP), developed by about 25-60% of patients. Opioids, most common drugs used for treatment of cancer pain, are immunosuppressive, and therefore, they might directly and/or indirectly influence long-term cancer recurrence. Moreover, they also produce endocrinopathy, which consists primarily of hypothalamic-pituitary-gonadal axis or hypothalamic-pituitary-adrenal axis dysfunction. The interindividual variability in both CPMP and opioid response is believed to be largely underlined by genetic variability in the gene locus for µ-opioid receptor (OPRM1) that modulates opioid pharmacodynamics. For this reason, OPRM1 genotype may play a key role both in short-term postmastectomy outcome and in long-term follow-up, becoming a new biomarker for breast cancer recurrence in patients suffering from chronic postmastectomy pain managed by opioid therapy. Hence OPRM1 might be used in near future to customize the opioid therapy, avoiding not only opioid side effects but also the disease progression. In this review we evaluate the literature state of the art on this topic and possible steps towards obtaining the safest individualized postmastectomy analgesic therapy. Therefore, a personalized pain treatment strategy might be useful to both manage pain and control cancer disease progression.

Janus molecule I: dichotomous effects of COMT in neuropathic vs nociceptive pain modalities.

The enzyme catechol-O-methyltransferase (COMT) has been shown to play a critical role in pain perception by regulating levels of epinephrine (Epi) and norepinephrine (NE). Although the key contribution of catecholamines to the perception of pain has been recognized for a long time, there is a clear dichotomy of observations. More than a century of research has demonstrated that increasing adrenergic transmission in the spinal cord decreases pain sensitivity in animals. Equally abundant evidence demonstrates the opposite effect of adrenergic signaling in the peripheral nervous system, where adrenergic signaling increases pain sensitivity. Viewing pain processing within spinal and peripheral compartments and determining the directionality of adrenergic signaling helps clarify the seemingly contradictory findings of the pain modulatory properties of adrenergic receptor agonists and antagonists presented in other reviews. Available evidence suggests that adrenergic signaling contributes to pain phenotypes through α(1/2) and ß(2/3) receptors. While stimulation of α(2) adrenergic receptors seems to uniformly produce analgesia, stimulation of α(1) or ß receptors produces either analgesic or hyperalgesic effects. Establishing the directionality of adrenergic receptor modulation of pain processing, and related COMT activity in different pain models are needed to bring meaning to recent human molecular genetic findings. This will enable the translation of current findings into meaningful clinical applications such as diagnostic markers and novel therapeutic targets for complex human pain conditions.

Influence of psychological factors on risk of temporomandibular disorders.

Psychological characteristics potentially may be a cause or consequence of temporomandibular disorder (TMD). We hypothesized that psychological characteristics associated with pain sensitivity would influence risk of first-onset TMD, but the effect could be attributed to variation in the gene encoding catechol-O-methyltransferase (COMT). We undertook a prospective cohort study of healthy female volunteers aged 18-34 yrs. At baseline, participants were genotyped, they completed psychological questionnaires, and underwent quantitative sensory testing to determine pain sensitivity. We followed 171 participants for up to three years, and 8.8% of them were diagnosed with first-onset TMD. Depression, perceived stress, and mood were associated with pain sensitivity and were predictive of 2- to 3-fold increases in risk of TMD (P < 0.05). However, the magnitude of increased TMD risk due to psychological factors remained unchanged after adjustment for the COMT haplotype. Psychological factors linked to pain sensitivity influenced TMD risk independently of the effects of the COMT haplotype on TMD risk.

Alcoholism is associated with GALR3 but not two other galanin receptor genes.

The neuropeptide galanin is widely expressed in the periphery and the central nervous system and mediates diverse physiological processes and behaviors including alcohol abuse, depression and anxiety. Four genes encoding galanin and its receptors have been identified (GAL, GALR1, GALR2 and GALR3). Recently we found that GAL haplotypes were associated with alcoholism, raising the possibility that genetic variation in GALR1, GALR2 and GALR3 might also alter alcoholism risk. Tag single nucleotide polymorphisms (SNPs) were identified by genotyping SNP panels in controls from five populations. For the association study with alcoholism, six GALR1, four GALR2 and four GALR3 SNPs were genotyped in a large cohort of Finnish alcoholics and non-alcoholics. GALR3 showed a significant association with alcoholism that was driven by one SNP (rs3,091,367). Moreover, the combination of the GALR3 rs3,091,367 risk allele and GAL risk haplotypes led to a modestly increased odds ratio (OR) for alcoholism (2.4) as compared with the effect of either GAL (1.9) or GALR3 alone (1.4). Likewise, the combination of the GALR3 and GAL risk diplotypes led to an increased OR for alcoholism (4.6) as compared with the effect of either GAL (2.0) or GALR3 alone (1.6). There was no effect of GALR1 or GALR2 on alcoholism risk. This evidence suggests that GALR3 mediates the alcoholism-related actions of galanin.

Association of galanin haplotypes with alcoholism and anxiety in two ethnically distinct populations.

The neuropeptide galanin (GAL) is widely expressed in the central nervous system. Animal studies have implicated GAL in alcohol abuse and anxiety: chronic ethanol intake increases hypothalamic GAL mRNA; high levels of stress increase GAL release in the central amygdala. The coding sequence of the galanin gene, GAL, is highly conserved and a functional polymorphism has not yet been found. The aim of our study was, for the first time, to identify GAL haplotypes and investigate associations with alcoholism and anxiety. Seven single-nucleotide polymorphisms (SNPs) spanning GAL were genotyped in 65 controls from five populations: US and Finnish Caucasians, African Americans, Plains and Southwestern Indians. A single haplotype block with little evidence of historical recombination was observed for each population. Four tag SNPs were then genotyped in DSM-III-R lifetime alcoholics and nonalcoholics from two population isolates: 514 Finnish Caucasian men and 331 Plains Indian men and women. Tridimensional Personality Questionnaire harm avoidance (HA) scores, a dimensional measure of anxiety, were obtained. There was a haplotype association with alcoholism in both the Finnish (P=0.001) and Plains Indian (P=0.004) men. The SNPs were also significantly associated. Alcoholics were divided into high and low HA groups (>or= and

Haplotype block and superblock structures of the alpha1-adrenergic receptor genes reveal echoes from the chromosomal past.

A significant proportion of the human genome is contained within haplotype blocks across which pairwise linkage disequilibrium (LD) is very high. However, LD is also often high between markers at more remote distances, and within different haplotype blocks. Here, we evaluate the origins of haplotype block structure in the three genes for alpha1 adrenergic receptors (alpha1-AR) in the human genome ( ADRA1A, ADRA1B and ADRA1D) by genotyping dense single-nucleotide polymorphism (SNP) marker maps, and show that LD signals between distant markers are due to the presence of extended haplotype superblocks in individuals with ancient chromosomes which have escaped historic recombination. ARs mediate the physiological effects of epinephrine and norepinephrine, and are targets of many therapeutic drugs. This work has identified haplotype backgrounds of alpha1-AR missense variants, haplotype block structures in US Caucasians and African Americans, and haplotype tag SNPs for each block, and we present strong evidence for ancient haplotype block superstructure at these genes which has been partially disrupted by recombination, and evidence for reinstatement of linkage disequilibrium by subsequent recombination events. ADRA1A is comprised of four haplotype blocks in US Caucasians, while in African Americans Block 1 is split. ADRA1B has four blocks in US Caucasians, but in African Americans only the first two blocks are present. ADRA1D has two blocks in US Caucasians, and the first block is replaced by two smaller blocks in African Americans. For both ADRA1A and ADRA1B, haplotype superstructures may represent a novel, higher-level hierarchy in the human genome, which may reduce redundancy of testing by further aggregation of genotype data.

Haplotype structure of inflammatory cytokines genes (IL1B, IL6 and TNF/LTA) in US Caucasians and African Americans.

The major inflammatory cytokines interleukin(IL)1beta, IL6 and tumor necrosis factor alpha (TNFalpha) play a crucial role in infection, inflammation and stress responses. Previously, three coding genes were resequenced, identifying promoter polymorphisms that were used in association studies of neurodegenerative diseases, metabolic disorders and cancer. These studies have produced intriguing but inconsistent results, potentially because the known functional variants: IL1B-511 C>T, IL6-174 G>C and TNF-308 G>A provided an incomplete picture of the total functional diversity at these genes. Therefore, we created marker panels for IL1B, IL6 and TNF/LTA that included the known functional marker but also other markers evenly spaced and with sufficient density to identify haplotype block structure and to maximize haplotype diversity. A total of 26 markers were genotyped in 96 US Caucasians and 96 African Americans. In both populations, a single block with little evidence of historical recombination was observed in IL1B, IL6 and TNF/LTA. For each gene, haplotypes captured the information content of each functional locus, even if that locus was not genotyped, and presumably haplotypes would capture the signal from unknown functional loci whose alleles are of moderate abundance. This study demonstrates the utility of using gene haplotype maps and marker panels as tools for linkage studies on related phenotypes.

Correlation of intact sensibility and neuropathic pain-related behaviors in eight inbred and outbred rat strains and selection lines.

In some rat strains, total hindpaw denervation triggers autotomy, a behavior of self mutilation presumably related to neuropathic pain. Partial sciatic ligation (PSL) in rats produces tactile allodynia and heat hyperalgesia but not autotomy. Our aims in this study were to examine: (1) whether sensibility of intact rats to noxious and non-noxious stimuli is strain-dependent; (2) whether sensibility of intact rats could predict levels of autotomy, or of allodynia and hyperalgesia in the PSL model; and (3) whether autotomy levels are correlated with levels of allodynia or hyperalgesia. Here we report that in two inbred rat strains (Lewis and Fisher 344), two outbred rat strains (Sabra and Sprague-Dawley) and four selection lines of rats (Genetically Epilepsy-Prone Rats, High Autotomy, Low Autotomy and Flinders Sensitive Line), tactile sensitivity and response duration to noxious heat of intact animals were strain-dependent. Levels of autotomy following hindpaw denervation and of allodynia and hyperalgesia in the PSL model were also strain-dependent. Thus, these traits are determined in part by genetic factors. Sensory sensibility of intact rats was not correlated with levels of autotomy following total denervation, or allodynia and hyperalgesia following partial denervation. We suggest that preoperative sensibility of intact rats is not a predictor of levels of neuropathic disorders following nerve injury. Likewise, no correlation was found between autotomy, allodynia and hyperalgesia, suggesting that neuropathic pain behaviors triggered by nerve injury of different etiologies are mediated by differing mechanisms.

Preoperative open field behavior predicts levels of neuropathic pain-related behavior in mice.

Exploratory open field (OF) activity was assessed in seven different mouse strains and selection lines. We counted the number of beam interruptions made by three cagemate mice at a time. This assay tests reactivity to aversive stimuli, anxiety and emotionality. One hindlimb was then totally denervated by transecting the sciatic and saphenous nerves on one side, and autotomy, a behavior thought to be related to neuropathic pain, was quantified over 35 days. We report that OF activity and autotomy are highly variable across different strains/lines. These results reaffirm the genetic control of these behaviors. We also found that these behaviors are inversely and significantly correlated. We suggest that common genetically-determined neural mechanisms may underlie anxiety, emotionality and neuropathic pain in mice.

Dietary supplementation with the inhibitory amino acid taurine suppresses autotomy in HA rats.

Taurine is an inhibitory amino acid in the CNS. When supplied to rats it produces analgesia in some acute pain tests. Here we examined the effect of taurine supplementation on sensitivity to pain in intact rats, and whether perioperative dietary supplementation with taurine in rats would suppress autotomy, a behavior produced by peripheral neurectomy and related to neuropathic pain. Thermal pain sensitivity of intact rats consuming 1% taurine in the drinking solution for 2 weeks was not significantly different from that of control rats. Autotomy levels, determined in rats consuming taurine pre-, post- or perioperatively were significantly lower than in matching control groups. We conclude that taurine plays an important role in the autotomy model, presumably by protecting inhibitory neurons in the CNS against an excitotoxic damage triggered by injury discharge and ectopic input from the severed nerves.