Α2 Receptor Subunits Research Articles

Selective knockdown of GABAA-α2 subunit in the dorsal dentate gyrus in adulthood induces anxiety, learning and memory deficits and impairs synaptic plasticity.

Animal studies and clinical trials suggest that maintenance of gamma-aminobutyric acid (GABA)-ergic activity may be crucial in coping with stressful conditions, anxiety and mood disorders. Drugs highly efficient in promoting anxiolysis were shown to activate this system, particularly via the α2-subunit of type A receptors (GABAA α2). Given the high expression of GABAA α2 in the dentate gyrus (DG) sub-field of the hippocampus, we sought to examine whether manipulation of the α2 subunit in this area will evoke changes in emotional behaviour, memory and learning as well as in synaptic plasticity. We found that knockdown of GABAAα2 receptor specifically in the dorsal DG of rats caused increased anxiety without affecting locomotor activity. Spatial memory and learning in the Morris water maze were also impaired in GABAAα2 receptor knocked down rats, an effect accompanied by alterations in synaptic plasticity, as assessed by long-term potentiation in the DG. Our findings provide further support to the notion that emotional information processing in the hippocampus may be controlled, at least in part, via the inhibitory GABAA α2 receptor subunit, opening a potential avenue for early interventions from pre- puberty into adulthood, as a strategy for controlling anxiety-related psychopathology.

GABAergic interneurons expressing the α2 nicotinic receptor subunit are functionally integrated in the striatal microcircuit.

The interactions between the striatal cholinergic and GABAergic systems are crucial in shaping reward-related behavior and reinforcement learning; however, the synaptic pathways mediating them are largely unknown. Here, we use Chrna2-Cre mice to characterize striatal interneurons (INs) expressing the nicotinic α2 receptor subunit. Using triple patch-clamp recordings combined with optogenetic stimulations, we characterize the electrophysiological, morphological, and synaptic properties of striatal Chrna2-INs. Striatal Chrna2-INs have diverse electrophysiological properties, distinct from their counterparts in other brain regions, including the hippocampus and neocortex. Unlike in other regions, most striatal Chrna2-INs are fast-spiking INs expressing parvalbumin. Striatal Chrna2-INs are intricately integrated in the striatal microcircuit, forming inhibitory synaptic connections with striatal projection neurons and INs, including other Chrna2-INs. They receive excitatory inputs from primary motor cortex mediated by both AMPA and NMDA receptors. A subpopulation of Chrna2-INs responds to nicotinic input, suggesting reciprocal interactions between this GABAergic interneuron population and striatal cholinergic synapses.

Induced pluripotent stem cell reprogramming-associated methylation at the GABRA2 promoter and chr4p12 GABAA subunit gene expression in the context of alcohol use disorder.

Twin studies indicate that there is a significant genetic contribution to the risk of developing alcohol use disorder (AUD). With the exception of coding variants in ADH1B and ALDH2, little is known about the molecular effects of AUD-associated loci. We previously reported that the AUD-associated synonymous polymorphism rs279858 within the GABAA α2 receptor subunit gene, GABRA2, was associated with gene expression of the chr4p12 GABAA subunit gene cluster in induced pluripotent stem cell (iPSC)-derived neural cultures. Based on this and other studies that showed changes in GABRA2 DNA methylation associated with schizophrenia and aging, we examined methylation in GABRA2. Specifically, using 69 iPSC lines and neural cultures derived from 47 of them, we examined whether GABRA2 rs279858 genotype predicted methylation levels and whether methylation was related to GABAA receptor subunit gene expression. We found that the GABRA2 CpG island undergoes random stochastic methylation during reprogramming and that methylation is associated with decreased GABRA2 gene expression, an effect that extends to the GABRB1 gene over 600 kb distal to GABRA2. Further, we identified additive effects of GABRA2 CpG methylation and GABRA2 rs279858 genotype on expression of the GABRB1 subunit gene in iPSC-derived neural cultures.

Pathways to Youth Behavior: The Role of Genetic, Neural, and Behavioral Markers

Neural and temperamental mechanisms through which a genetic risk marker in the γ-amino butyric acid α2 receptor subunit (GABRA2) impacts adolescent functioning were investigated. Participants (N=80; 29 female) completed an emotional word task during functional magnetic resonance imaging. Behavioral control, negative emotionality, and resiliency temperament constructs were assessed. Externalizing and internalizing problems were the outcomes. Those with the GABRA2 minor allele had reduced activation to positive words in the angular gyrus, middle temporal gyrus, and cerebellum, and to negative words in frontal, parietal, and occipital cortices. Reduced activation in the angular gyrus predicted greater negative emotionality and, in turn, elevated externalizing problems. Reduced activation in the inferior parietal cortex predicted greater resiliency and, in turn, low externalizing problems.

Association study of GABAA α2 receptor subunit gene variants in antipsychotic-associated weight gain.

Schizophrenia treatment has been hampered by undesirable adverse effects, including weight gain and associated complications. Recent candidate gene studies have been exploring the appetite regulation pathways in antipsychotic-associated weight gain (AAWG) with some promising leads. Genome-wide association studies of obesity have pointed to a number of potential candidate genes, such as MC4R, that were later found to be shared with AAWG. GABAA α2 receptor subunit (GABRA2) was another potential candidate gene for obesity from genome-wide association studies; however, it has not been explored in AAWG. We examined 9 single nucleotide polymorphisms across the GABRA2 gene. Prospective weight change was assessed for a total of 160 schizophrenia patients of European ancestry. The rs279858 marker was associated with percent weight change, with the patients homozygous for the TT genotype experiencing higher percentage weight gain on average than the C allele carriers (P = 0.009). When we performed the analysis considering each clinical site using a meta-analytic method, the results remained statistically significant (P = 1.4e-4). These findings became even more significant when we considered only patients taking clozapine or olanzapine, the 2 medications with higher risk for weight gain (P < 1e-10). GABRA2 genetic variants may play a role in predicting AAWG. However, replication in larger and independent samples is required.

Altered GABAergic and glutamatergic activity within the rat hippocampus and amygdala in rats subjected to repeated corticosterone administration but not restraint stress

We investigated the effect of two well characterized preclinical animal models of depression – repeated injections of corticosterone (CORT) and repeated restraint stress – on markers of GABAergic and glutamatergic activity in the hippocampus and amygdala. Stress is an identified risk factor for the onset of major depression, but the neurobiological mechanisms by which stress may produce depressogenic effects are not clear. Rats received one of the following four treatments for 21 consecutive days: daily single CORT injections (40mg/kg), daily single vehicle injections, daily 6h of restraint stress, or daily handling. After the 21-day stress period, all rats were sacrificed and hippocampal and amygdalar tissue was collected and prepared for Western blot analyses. We examined the effect of CORT and restraint stress on glutamate decarboxylase (GAD)-65 and GAD67, as well as the α1, α2, α3, and β2–3 GABAA receptor subunits, and the vesicular glutamate transporter (VGLUT)-2. We found that CORT significantly decreased GAD65 and the α2 receptor subunit and increased VGLUT2 within the hippocampus. We also found that CORT decreased GAD67 and the α2 receptor subunit in the amygdala. However, restraint stress had no significant effect on protein expression in either the hippocampus or the amygdala. These findings parallel our previous results showing that repeated CORT injections, but not restraint stress, increase depression-like behavior in rats, and suggest that the depressogenic effects of CORT may be related to alterations in GABAergic and glutamatergic neurotransmission in stress-sensitive regions of the brain.

GABRA2 markers moderate the subjective effects of alcohol

Individual differences in subjective responses (SRs) to alcohol are moderated by genetic variants and may be risk factors for the development of alcohol use disorders. Variation in the GABA(A) α2 receptor subunit gene (GABRA2) has been associated with alcohol dependence (AD). Therefore, we examined whether individual differences in SRs, which reflect sensitivity to the effects of alcohol, are associated with variation in GABRA2. Sixty-nine healthy subjects (21-30 years) underwent a laboratory-based within-session cumulative oral alcohol dosing procedure, achieving a mean peak blood alcohol level of 100.4 mg/dl (standard error = 2.5). Subjective assessments were obtained throughout the session, including ascending and descending limbs of the alcohol curve. We genotyped single nucleotide polymorphisms (SNPs) across the chromosome 4 region spanning GABRA2 and analyzed the effect of genotype and haplotypes on subjective responses to alcohol. Population substructure was characterized through the use of ancestry informative markers. Individual SNP analysis demonstrated that carriers of the minor alleles for SNPs rs279858, rs279844, rs279845, rs279826, rs279828 and rs279836 had lower 'Negative' alcohol effects scores than individuals homozygous for the common allele at each SNP (P = 0.0060, P = 0.0035, P = 0.0045, P = 0.0043, P = 0.0037 and P = 0.0061, respectively). Haplotype effects of block 1 showed concordant results with SNPs in this block (P = 0.0492 and P = 0.0150 for haplotypes 1 and 4, respectively). The minor alleles for several of these SNPs have previously been associated with AD. Our findings provide further evidence that variation within GABRA2 is associated with attenuated negative responses to alcohol, a known risk factor for vulnerability to alcohol use disorders.

Impulsiveness and insula activation during reward anticipation are associated with genetic variants in GABRA2 in a family sample enriched for alcoholism

Genetic factors, externalizing personality traits such as impulsivity, and brain processing of salient stimuli all can affect individual risk for alcoholism. One of very few confirmed genetic association findings differentiating alcoholics from non-alcoholics is with variants in the inhibitory γ-amino butyric acid α2 receptor subunit (GABRA2) gene. Here we report the association of two of these GABRA2 variants with measures of alcohol symptoms, impulsivity and with insula cortex activation during anticipation of reward or loss using functional magnetic resonance imaging (fMRI). In a sample of 173 families (449 subjects), 129 of whom had at least one member diagnosed with alcohol dependence or abuse, carriers for the G allele in two single-nucleotide polymorphisms (SNPs) and haplotypes were more likely to have alcohol dependence symptoms (rs279858, P=0.01; rs279826, P=0.05; haplotype, P=0.02) and higher NEO Personality Inventory-Revised (NEO-PI-R) Impulsiveness scores (rs279858, P=0.016; rs279826, P=0.012; haplotype, P=0.032) with a stronger effect in women (rs279858, P=0.011; rs279826, P=0.002; haplotype, P=0.006), all P-values are corrected for family history and age. A subset of offspring from these families (n=44, 20 females), genotyped for GABRA2, participated in an fMRI study using a monetary incentive delay task. Increased insula activation during reward (r(2)=0.4; P=0.026) and loss (r(2)=0.38; P=0.039) anticipation was correlated with NEO-PI-R Impulsiveness and further associated with the GG genotype for both SNPs (P's<0.04). Our results suggest that GABRA2 genetic variation is associated with Impulsiveness through variation of insula activity responses, here evidenced during anticipatory responses.