Cross-talk between GABAergic postsynapse and microglia regulate synapse loss after brain ischemia.

Microglia interact with neurons to facilitate synapse plasticity; however, signal(s) contributing to microglia activation for synapse elimination in pathology are not fully understood. Here, using in vitro organotypic hippocampal slice cultures and transient middle cerebral artery occlusion (MCAO) in genetically engineered mice in vivo, we report that at 24 hours after ischemia, microglia release brain-derived neurotrophic factor (BDNF) to downregulate glutamatergic and GABAergic synapses within the peri-infarct area. Analysis of the cornu ammonis 1 (CA1) in vitro shows that proBDNF and mBDNF downregulate glutamatergic dendritic spines and gephyrin scaffold stability through p75 neurotrophin receptor (p75NTR) and tropomyosin receptor kinase B (TrkB) receptors, respectively. After MCAO, we report that in the peri-infarct area and in the corresponding contralateral hemisphere, similar neuroplasticity occurs through microglia activation and gephyrin phosphorylation at serine-268 and serine-270 in vivo. Targeted deletion of the Bdnf gene in microglia or GphnS268A/S270A (phospho-null) point mutations protects against ischemic brain damage, neuroinflammation, and synapse downregulation after MCAO.

Docosahexaenoic acid (DHA): a modulator of microglia activity and dendritic spine morphology.

BACKGROUND: Recent studies have revealed that excessive activation of microglia and inflammation-mediated neurotoxicity are implicated in the progression of several neurological disorders. In particular, chronic inflammation in vivo and exposure of cultured brain cells to lipopolysaccharide (LPS) in vitro can adversely change microglial morphology and function. This can have both direct and indirect effects on synaptic structures and functions. The integrity of dendritic spines, the postsynaptic component of excitatory synapses, dictates synaptic efficacy. Interestingly, dysgenesis of dendritic spines has been found in many neurological diseases associated with ω-3 polyunsaturated fatty acid (PUFA) deficiency and cognitive decline. In contrast, supplemented ω-3 PUFAs, such as docosahexaenoic acid (DHA), can partly correct spine defects. Hence, we hypothesize that DHA directly affects synaptic integrity and indirectly through neuron-glia interaction. Strong activation of microglia by LPS is accompanied by marked release of nitric oxide and formation of lipid bodies (LBs), both dynamic biomarkers of inflammation. Here we investigated direct effects of DHA on synaptic integrity and its indirect effects via microglia in the hippocampal CA1 region. METHODS: Microglia (N9) and organotypic hippocampal slice cultures were exposed to the proinflammagen LPS (100 ng/ml) for 24 h. Biochemical and morphological markers of inflammation were investigated in microglia and CA1 regions of hippocampal slices. As biomarkers of hyperactive microglia, mitochondrial function, nitric oxide release and LBs (number, size, LB surface-associated proteins) were assessed. Changes in synaptic transmission of CA1 pyramidal cells were determined following LPS and DHA (25-50 µM) treatments by recording spontaneous AMPA-mediated miniature excitatory postsynaptic currents (mEPSCs). RESULTS: Microglia responded to LPS stimulation with a significant decrease of mitochondrial function, increased nitric oxide production and an increase in the formation of large LBs. LPS treatment led to a significant reduction of dendritic spine densities and an increase in the AMPA-mediated mEPSC inter-event interval (IEI). DHA normalized the LPS-induced abnormalities in both neurons and microglia, as revealed by the restoration of synaptic structures and functions in hippocampal CA1 pyramidal neurons. CONCLUSION: Our findings indicate that DHA can prevent LPS-induced abnormalities (neuroinflammation) by reducing inflammatory biomarkers, thereby normalizing microglia activity and their effect on synaptic function.

Intranasal oxytocin administration prior to exposure therapy for arachnophobia impedes treatment response.

BACKGROUND: Recent years have seen the emergence of a new paradigm for treatment of anxiety disorders focusing on development of drugs that facilitate psychotherapies via targeted effects on neuroplasticity. One compound that has generated interest in this regard is oxytocin (OT), a mammalian neuropeptide that modulates activity of the neurocircuit mediating fear extinction and memory processes. Recent research in healthy humans has suggested that intranasal OT administered prior to fear extinction training enhances fear extinction performance, supporting its potential to augment exposure-based psychotherapy. Here, we tested the hypothesis that OT treatment would facilitate response to exposure therapy in patients with specific phobia. METHODS: We conducted a small proof-of-concept trial investigating the effect of pretreatment intranasal OT administration on a brief, single-session exposure treatment for arachnophobia (fear of spiders). The study was randomized, double-blind, and placebo controlled (n = 13 placebo, 11 females; n = 10 OT, 8 females) with 1-week and 1-month follow-up assessments. Dependent measures attended to arachnophobia symptoms (self-report), phobic behavior (behavioral avoidance of spider task), and treatment credibility/therapeutic alliance. RESULTS: Administration of OT prior to exposure therapy tended to impede treatment response as measured by self-report of symptoms at both follow-up periods. OT treatment did not significantly affect behavioral measures of fear. Immediately after OT administration but before therapy, the OT group trended toward less confidence in the treatment. The OT group also trended toward lower ratings of therapeutic alliance than placebo. CONCLUSIONS: These results suggest that OT administration effects on extinction may vary depending on conditions and population.

Blocking brain-derived neurotrophic factor inhibits injury-induced hyperexcitability of hippocampal CA3 neurons.

Brain trauma can disrupt synaptic connections, and this in turn can prompt axons to sprout and form new connections. If these new axonal connections are aberrant, hyperexcitability can result. It has been shown that ablating tropomyosin-related kinase B (TrkB), a receptor for brain-derived neurotrophic factor (BDNF), can reduce axonal sprouting after hippocampal injury. However, it is unknown whether inhibiting BDNF-mediated axonal sprouting will reduce hyperexcitability. Given this, our purpose here was to determine whether pharmacologically blocking BDNF inhibits hyperexcitability after injury-induced axonal sprouting in the hippocampus. To induce injury, we made Schaffer collateral lesions in organotypic hippocampal slice cultures. As reported by others, we observed a 50% reduction in axonal sprouting in cultures treated with a BDNF blocker (TrkB-Fc) 14 days after injury. Furthermore, lesioned cultures treated with TrkB-Fc were less hyperexcitable than lesioned untreated cultures. Using electrophysiology, we observed a two-fold decrease in the number of CA3 neurons that showed bursting responses after lesion with TrkB-Fc treatment, whereas we found no change in intrinsic neuronal firing properties. Finally, evoked field excitatory postsynaptic potential recordings indicated an increase in network activity within area CA3 after lesion, which was prevented with chronic TrkB-Fc treatment. Taken together, our results demonstrate that blocking BDNF attenuates injury-induced hyperexcitability of hippocampal CA3 neurons. Axonal sprouting has been found in patients with post-traumatic epilepsy. Therefore, our data suggest that blocking the BDNF-TrkB signaling cascade shortly after injury may be a potential therapeutic target for the treatment of post-traumatic epilepsy.

The effect of intranasal oxytocin treatment on conditioned fear extinction and recall in a healthy human sample.

RATIONALE: To improve outcomes for patients undergoing extinction-based therapies (e.g., exposure therapy) for anxiety disorders such as post-traumatic stress disorder (PTSD), there has been interest in identifying pharmaceutical compounds that might facilitate fear extinction learning and recall. Oxytocin (OT) is a mammalian neuropeptide that modulates activation of fear extinction-based neural circuits and fear responses. Little is known, however, about the effects of OT treatment on conditioned fear responding and extinction in humans. OBJECTIVES: The purpose of the present study was to assess the effects of OT in a fear-potentiated startle task of fear conditioning and extinction. METHODS: A double-blind, placebo-controlled study of 44 healthy human participants was conducted. Participants underwent a conditioned fear acquisition procedure, after which they were randomized to treatment group and delivered OT (24 IU) or placebo via intranasal (IN) spray. Forty-five minutes after treatment, participants underwent extinction training. Twenty-four hours later, subjects were tested for extinction recall. RESULTS: Relative to placebo, the OT group showed increased fear-potentiated startle responding during the earliest stage of extinction training relative to placebo; however, all treatment groups showed the same level of reduced responding by the end of extinction training. Twenty-four hours later, the OT group showed significantly higher recall of extinction relative to placebo. CONCLUSIONS: The current study provides preliminary evidence that OT may facilitate fear extinction recall in humans. These results support further study of OT as a potential adjunctive treatment for extinction-based therapies in fear-related disorders.

Evidence for association of bipolar disorder to haplotypes in the 22q12.3 region near the genes stargazin, IFT27 and parvalbumin.

We have previously reported genome-wide significant linkage of bipolar disorder to a region on 22q12.3 near the marker D22S278. Towards identifying the susceptibility gene, we have conducted a fine-mapping association study of the region in two independent family samples, an independent case-control sample and a genome-wide association dataset. Two hundred SNPs were first examined in a 5 Mb region surrounding the D22S278 marker in a sample of 169 families and analyzed using PLINK. The peak of association was a haplotype near the genes stargazin (CACNG2), intraflagellar transport protein homolog 27 (IFT27) and parvalbumin (PVALB; P = 4.69 × 10(-4)). This peak overlapped a significant haplotype in a family based association study of a second independent sample of 294 families (P = 1.42 × 10(-5)). Analysis of the combined family sample yielded statistically significant evidence of association to a rare three SNP haplotype in the gene IFT27 (P = 8.89 × 10(-6)). Twelve SNPs comprising these haplotypes were genotyped in an independent sample of 574 bipolar I cases and 550 controls. Statistically significant association was found for a haplotype window that overlapped the region from the first two family samples (P = 3.43 × 10(-4)). However, analyses of the two family samples using the program LAMP, found no evidence for association in this region, but did yield significant evidence for association to a haplotype 3' of CACNG2 (P = 1.76 × 10(-6)). Furthermore, no evidence for association was found in a large genome-wide association dataset. The replication of association to overlapping haplotypes in three independent datasets suggests the presence of a bipolar disorder susceptibility gene in this region.

Genome-wide significant association between a 'negative mood delusions' dimension in bipolar disorder and genetic variation on chromosome 3q26.1.

Research suggests that clinical symptom dimensions may be more useful in delineating the genetics of bipolar disorder (BD) than standard diagnostic models. To date, no study has applied this concept to data from genome-wide association studies (GWAS). We performed a GWAS of factor dimensions in 927 clinically well-characterized BD patients of German ancestry. Rs9875793, which is located in an intergenic region of 3q26.1 and in the vicinity of the solute carrier family 2 (facilitated glucose transporter), member 2 gene (SLC2A2), was significantly associated with the factor analysis-derived dimension 'negative mood delusions' (n=927; P=4.65 × 10(-8), odds ratio (OR)=2.66). This dimension was comprised of the symptoms delusions of poverty, delusions of guilt and nihilistic delusions. In case-control analyses, significant association with the G allele of rs9875793 was only observed in the subgroup of BD patients who displayed symptoms of 'negative mood delusions' (allelic χ(2) model: P(G)=0.0001, OR=1.92; item present, n=89). Further support for the hypothesis that rs9875793 is associated with BD in patients displaying 'negative mood delusions' symptom, such as delusions of guilt, was obtained from an European American sample (GAIN/TGEN), which included 1247 BD patients and 1434 controls (P(EA)=0.028, OR=1.27).

Further evidence for linkage of bipolar disorder to chromosomes 6 and 17 in a new independent pedigree series.

OBJECTIVES: We have previously reported the results of a linkage analysis of bipolar disorder in an initial set of 20 pedigrees ascertained through collaboration among three sites. We now report the results of our genome-wide linkage analysis in an independent sample of 34 pedigrees segregating bipolar disorder. METHODS: Families were ascertained through a bipolar I or II disorder proband for the presence of bipolar I disorder, bipolar II disorder, or recurrent major depression in at least two other family members. A total of 440 markers at an average spacing of 8 cM were genotyped in 229 family members using fluorescent methods. RESULTS: Initial nonparametric analyses of chromosomes 6 and 17 provided evidence for a modest replication of linkage to these chromosomes previously reported in other studies. Additional analyses using multipoint parametric methods provided further evidence to support the 6q25 region with a heterogeneity logarithm of odds score of 3.28. Evidence from two-point parametric analyses also provides a modest replication of our previous findings of linkage to the 23 cM region of chromosome 22q13 in our original University of California, San Diego sample of 20 families and 57 families from the National Institute of Mental Health bipolar disorder sample. CONCLUSIONS: Our results suggest replication of some reported linkage peaks, such as 6q25 and 17p12; however, other peaks from our own previous study, such as 5p15, 13q32, and 22q13, were either not replicated or were only modestly replicated in these analyses.

Genome-wide association of bipolar disorder suggests an enrichment of replicable associations in regions near genes.

Although a highly heritable and disabling disease, bipolar disorder's (BD) genetic variants have been challenging to identify. We present new genotype data for 1,190 cases and 401 controls and perform a genome-wide association study including additional samples for a total of 2,191 cases and 1,434 controls. We do not detect genome-wide significant associations for individual loci; however, across all SNPs, we show an association between the power to detect effects calculated from a previous genome-wide association study and evidence for replication (P = 1.5×10(-7)). To demonstrate that this result is not likely to be a false positive, we analyze replication rates in a large meta-analysis of height and show that, in a large enough study, associations replicate as a function of power, approaching a linear relationship. Within BD, SNPs near exons exhibit a greater probability of replication, supporting an enrichment of reproducible associations near functional regions of genes. These results indicate that there is likely common genetic variation associated with BD near exons (±10 kb) that could be identified in larger studies and, further, provide a framework for assessing the potential for replication when combining results from multiple studies.

Suggestive evidence for linkage of ADHD features in bipolar disorder to chromosome 10p14.

Higher rates of bipolar disorder amongst the first-degree relatives of probands with ADHD, and increased rates of ADHD in the relatives of bipolar probands have been reported in many studies. This suggests some commonality in the genetic basis for bipolar disorder and ADHD. We hypothesized that ADHD symptoms in bipolar disorder may access a quantitative subphenotype that is genetically less complex and therefore advantageous for mapping studies. The Wender Utah Rating Scale (WURS) was used to quantify ADHD features in 57 bipolar families collected for linkage studies. The factor structure of the WURS was first examined, and heritability was estimated. Linkage analysis was then conducted using the WURS total score and factor scores as quantitative traits. Three factors were identified: impulsivity and defiant behavior, mood instability and anxiety, and inattention. The total WURS and factor scores were each significantly heritable (0.34

The pharmacogenetics of lithium response depends upon clinical co-morbidity.

BACKGROUND: Based on results from randomized, controlled clinical trials, lithium monotherapy or lithium with the addition of an antipsychotic remains a first-line treatment option for both acute and long-term mood stabilization in bipolar mania. However, response to lithium is poor in bipolar patients who exhibit clinical characteristics such as rapid cycling and mixed manic states, suggesting that they may have a biologically and genetically distinct form of bipolar disorder. A test that could predict response to lithium based upon genetic factors would have significant clinical value. METHODS: Eight clinical characteristics were assessed in 92 lithium responders and 92 nonresponders; all probands were from families recruited for linkage studies. Lithium response was rated retrospectively from a standardized interviews and medical records. Eight candidate genes were selected from those reported to be associated with susceptibility to illness, lithium response, or lithium mechanism of action. Sixty-seven single nucleotide polymorphisms (SNPs) were genotyped in these subjects and analyzed for association with the defined clinical characteristics. RESULTS: Using q-value analysis for multiplicity correction, we found significant interactions between lithium response and SNPs (rs1387923 and rs1565445) in the gene encoding neurotrophic tyrosine kinase receptor type 2 (NTRK2) and suicidal ideation, and between SNP rs2064721 in the gene encoding inositol polyphosphate-1-phosphatase (INPP1) and post-traumatic stress disorder. CONCLUSION: These data support the idea that response to lithium has a multi-genetic etiology dependent upon manifestations of other clinical co-diagnoses.

Genomewide linkage analyses of bipolar disorder: a new sample of 250 pedigrees from the National Institute of Mental Health Genetics Initiative.

We conducted genomewide linkage analyses on 1,152 individuals from 250 families segregating for bipolar disorder and related affective illnesses. These pedigrees were ascertained at 10 sites in the United States, through a proband with bipolar I affective disorder and a sibling with bipolar I or schizoaffective disorder, bipolar type. Uniform methods of ascertainment and assessment were used at all sites. A 9-cM screen was performed by use of 391 markers, with an average heterozygosity of 0.76. Multipoint, nonparametric linkage analyses were conducted in affected relative pairs. Additionally, simulation analyses were performed to determine genomewide significance levels for this study. Three hierarchical models of affection were analyzed. Significant evidence for linkage (genomewide P<.05) was found on chromosome 17q, with a peak maximum LOD score of 3.63, at the marker D17S928, and on chromosome 6q, with a peak maximum LOD score of 3.61, near the marker D6S1021. These loci met both standard and simulation-based criteria for genomewide significance. Suggestive evidence of linkage was observed in three other regions (genomewide P<.10), on chromosomes 2p, 3q, and 8q. This study, which is based on the largest linkage sample for bipolar disorder analyzed to date, indicates that several genes contribute to bipolar disorder.