Mediators of synaptic activity in anxiety- and depression-related behaviors

Depression and anxiety are leading causes of years lost to disability, despite antidepressants being among the most commonly prescribed medications. Most currently prescribed antidepressants were found serendipitously rather than from an understanding of the biological mechanisms underlying depression. Recent evidence supports instead the antidepressant efficacy of glutamate-targeting drugs, such as ketamine, which promote plastic changes in synaptic structure and function. Here we employed pharmacological and genetic approaches to study the role of various molecules known to mediate synaptic activity and plasticity in baseline depression- and anxiety-related behaviors and antidepressant-like effects in mice. Specifically, we examined voltage-gated potassium channels (Kv4.2) known to regulate dendritic excitability, a molecule of the postsynaptic density (PSD-95), and glutamatergic receptors, including the GluA1 subunit of alpha-amino-3-hydroxy-5- methyl-4-isoxazolepropionic acid (AMPA) receptors and its phosphorylation sites, and the GluN1, GluN2B, and GluN2A subunits of N-methyl-D-aspartate (NMDA) receptor. We employed traditional assays for murine depression-related behavior, including the forced swim test (FST), and a novel test for responses to repeated swim stress. We found that mice with constitutive deletions to GluA1, GluN2A and PSD-95 showed reduced depression-related behaviors in the FST, but similar behavioural effects were not observed in mice with a conditional cell-type specific knockout of NMDAR subunits. However, pharmacological blockade of GluN2B, via administration of Ro 25-6981, reduced depression-like behavior in the FST. This antidepressant-like effect was replicated by microinfusion of Ro 25-6981 into the medial prefrontal cortex (mPFC). By contrast, neither lentiviral-mediated knockdown of GluN2B nor conditional GluN2B deletion in forebrain pyramidal neurons or interneurons was sufficient to reduce depression-like behavior in the FST. Pharmacological GluN2B antagonism via Ro 25-6981 similarly reduced despair-like behavior during a repeated swim stress, and, unlike spontaneous swim measures, this effect was replicated by genetic deletion of GluN2B on pyramidal cells, but not interneurons. Collectively, these results suggest that multiple synaptically expressed molecules mediate depressionrelated behavior. GluN2B-containing NMDARs play a role in mediating depressionrelated behaviors during acute and repeated stressors, depending upon the pharmacological or genetic manipulations used, cell-type and brain region localization. Together this suggests that multiple synaptic proteins are important in depression-related behavior. However, reduction of GluN2B receptors does not per se lead to changes in depression-related behaviors. Here we suggest that it is the NMDAR-antagonist induced rise in extracellular glutamate and subsequent increase in synaptic transmission, such as through AMPARs, that is necessary for an antidepressant-like response and is lacking in the genetic deletions of GluN2B. In the repeated stress procedure our data supports a role of GluN2B transmission selective to pyramidal cells in mediating the behavioural alterations that lead to despair-like behavior. This would fit with previous data showing systemic NMDAR antagonism reduced atrophy in these same cell types, and suggests that it is the pyramidal cell NMDARs that mediate the morphological and behavioural effects of repeated stress

Do motor control genes contribute to interindividual variability in decreased movement in patients with pain?

<p>Abstract</p> <p>Background</p> <p>Because excessive reduction in activities after back injury may impair recovery, it is important to understand and address the factors contributing to the variability in motor responses to pain. The current dominant theory is the "fear-avoidance model", in which the some patients' heightened fears of further injury cause them to avoid movement. We propose that in addition to psychological factors, neurochemical variants in the circuits controlling movement and their modification by pain may contribute to this variability. A systematic search of the motor research literature and genetic databases yielded a prioritized list of polymorphic motor control candidate genes. We demonstrate an analytic method that we applied to 14 of these genes in 290 patients with acute sciatica, whose reduction in movement was estimated by items from the Roland-Morris Disability Questionnaire.</p> <p>Results</p> <p>We genotyped a total of 121 single nucleotide polymorphisms (SNPs) in 14 of these genes, which code for the dopamine D2 receptor, GTP cyclohydrolase I, glycine receptor α1 subunit, GABA-A receptor α2 subunit, GABA-A receptor β1 subunit, α-adrenergic 1C, 2A, and 2C receptors, serotonin 1A and 2A receptors, cannabinoid CB-1 receptor, M1 muscarinic receptor, and the tyrosine hydroxylase, and tachykinin precursor-1 molecules. No SNP showed a significant association with the movement score after a Bonferroni correction for the 14 genes tested. Haplotype analysis of one of the blocks in the GABA-A receptor β1 subunit showed that a haplotype of 11% frequency was associated with less limitation of movement at a nominal significance level value (p = 0.0025) almost strong enough to correct for testing 22 haplotype blocks.</p> <p>Conclusion</p> <p>If confirmed, the current results may suggest that a common haplotype in the GABA-A β1 subunit acts like an "endogenous muscle relaxant" in an individual with subacute sciatica. Similar methods might be applied a larger set of genes in animal models and human laboratory and clinical studies to understand the causes and prevention of pain-related reduction in movement.</p

Expansion of the human μ-opioid receptor gene architecture: novel functional variants

The μ-opioid receptor (OPRM1) is the principal receptor target for both endogenous and exogenous opioid analgesics. There are substantial individual differences in human responses to painful stimuli and to opiate drugs that are attributed to genetic variations in OPRM1. In searching for new functional variants, we employed comparative genome analysis and obtained evidence for the existence of an expanded human OPRM1 gene locus with new promoters, alternative exons and regulatory elements. Examination of polymorphisms within the human OPRM1 gene locus identified strong association between single nucleotide polymorphism (SNP) rs563649 and individual variations in pain perception. SNP rs563649 is located within a structurally conserved internal ribosome entry site (IRES) in the 5′-UTR of a novel exon 13-containing OPRM1 isoforms (MOR-1K) and affects both mRNA levels and translation efficiency of these variants. Furthermore, rs563649 exhibits very strong linkage disequilibrium throughout the entire OPRM1 gene locus and thus affects the functional contribution of the corresponding haplotype that includes other functional OPRM1 SNPs. Our results provide evidence for an essential role for MOR-1K isoforms in nociceptive signaling and suggest that genetic variations in alternative OPRM1 isoforms may contribute to individual differences in opiate responses

Quantitative trait loci for sensitivity to ethanol intoxication in a C57BL/6J × 129S1/SvImJ inbred mouse cross

Individual variation in sensitivity to acute ethanol (EtOH) challenge is associated with alcohol drinking and is a predictor of alcohol abuse. Previous studies have shown that the C57BL/6J (B6) and 129S1/SvImJ (S1) inbred mouse strains differ in responses on certain measures of acute EtOH intoxication. To gain insight into genetic factors contributing to these differences, we performed quantitative trait locus (QTL) analysis of measures of EtOH-induced ataxia (accelerating rotarod), hypothermia, and loss of righting reflex (LORR) duration in a B6 × S1 F2 population. We confirmed that S1 showed greater EtOH-induced hypothermia (specifically at a high dose) and longer LORR compared to B6. QTL analysis revealed several additive and interacting loci for various phenotypes, as well as examples of genotype interactions with sex. QTLs for different EtOH phenotypes were largely non-overlapping, suggesting separable genetic influences on these behaviors. The most compelling main-effect QTLs were for hypothermia on chromosome 16 and for LORR on chromosomes 4 and 6. Several QTLs overlapped with loci repeatedly linked to EtOH drinking in previous mouse studies. The architecture of the traits we examined was complex but clearly amenable to dissection in future studies. Using integrative genomics strategies, plausible functional and positional candidates may be found. Uncovering candidate genes associated with variation in these phenotypes in this population could ultimately shed light on genetic factors underlying sensitivity to EtOH intoxication and risk for alcoholism in humans

Multiple chronic pain states are associated with a common amino acid–changing allele in KCNS1

Not all patients with nerve injury develop neuropathic pain. The extent of nerve damage and age at the time of injury are two of the few risk factors identified to date. In addition, preclinical studies show that neuropathic pain variance is heritable. To define such factors further, we performed a large-scale gene profiling experiment which plotted global expression changes in the rat dorsal root ganglion in three peripheral neuropathic pain models. This resulted in the discovery that the potassium channel alpha subunit KCNS1, involved in neuronal excitability, is constitutively expressed in sensory neurons and markedly downregulated following nerve injury. KCNS1 was then characterized by an unbiased network analysis as a putative pain gene, a result confirmed by single nucleotide polymorphism association studies in humans. A common amino acid changing allele, the ‘valine risk allele’, was significantly associated with higher pain scores in five of six independent patient cohorts assayed (total of 1359 subjects). Risk allele prevalence is high, with 18–22% of the population homozygous, and an additional 50% heterozygous. At lower levels of nerve damage (lumbar back pain with disc herniation) association with greater pain outcome in homozygote patients is P = 0.003, increasing to P = 0.0001 for higher levels of nerve injury (limb amputation). The combined P-value for pain association in all six cohorts tested is 1.14 E−08. The risk profile of this marker is additive: two copies confer the most, one intermediate and none the least risk. Relative degrees of enhanced risk vary between cohorts, but for patients with lumbar back pain, they range between 2- and 3-fold. Although work still remains to define the potential role of this protein in the pathogenic process, here we present the KCNS1 allele rs734784 as one of the first prognostic indicators of chronic pain risk. Screening for this allele could help define those individuals prone to a transition to persistent pain, and thus requiring therapeutic strategies or lifestyle changes that minimize nerve injury