Left DLPFC activity is associated with plasma kynurenine levels and can predict treatment response to escitalopram in major depressive disorder.

AIM: To establish treatment response biomarkers that reflect the pathophysiology of depression, it is important to use an integrated set of features. This study aimed to determine the relationship between regional brain activity at rest and blood metabolites related to treatment response to escitalopram to identify the characteristics of depression that respond to treatment. METHODS: Blood metabolite levels and resting-state brain activity were measured in patients with moderate to severe depression (n = 65) before and after 6-8 weeks of treatment with escitalopram, and these were compared between Responders and Nonresponders to treatment. We then examined the relationship between blood metabolites and brain activity related to treatment responsiveness in patients and healthy controls (n = 36). RESULTS: Thirty-two patients (49.2%) showed a clinical response (>50% reduction in the Hamilton Rating Scale for Depression score) and were classified as Responders, and the remaining 33 patients were classified as Nonresponders. The pretreatment fractional amplitude of low-frequency fluctuation (fALFF) value of the left dorsolateral prefrontal cortex (DLPFC) and plasma kynurenine levels were lower in Responders, and the rate of increase of both after treatment was correlated with an improvement in symptoms. Moreover, the fALFF value of the left DLPFC was significantly correlated with plasma kynurenine levels in pretreatment patients with depression and healthy controls. CONCLUSION: Decreased resting-state regional activity of the left DLPFC and decreased plasma kynurenine levels may predict treatment response to escitalopram, suggesting that it may be involved in the pathophysiology of major depressive disorder in response to escitalopram treatment.

The influence of aging on the methylation status of brain-derived neurotrophic factor gene in blood.

OBJECTIVE: Brain-derived neurotrophic factor (BDNF) is involved in the pathophysiology of psychiatric disorders in adults and elderly individuals, and as a result, the DNA methylation (DNAm) of the BDNF gene in peripheral tissues including blood has been extensively examined to develop a useful biomarker for psychiatric disorders. However, studies to date have not previously investigated the effect of age on DNAm of the BDNF gene in blood. In this context, we measured DNAm of 39 CpG units in the CpG island at the promoter of exon I of the BDNF gene. METHODS: We analyzed genomic DNA from peripheral blood of 105 health Japanese women 20 to 80 years of age to identify aging-associated change in DNAm of the BDNF gene. In addition, we examined the relationship between total MMSE scores, numbers of stressful life events, and serum BDNF levels on DNAm of the BDNF gene. The DNAm rate at each CpG unit was measured using a MassArray® system (Agena Bioscience), and serum BDNF levels were measured by ELISA. RESULTS: There was a significant correlation between DNAm and age in 13 CpGs. However, there was no significant correlation between DNAm and total MMSE scores, numbers of life events, or serum BDNF levels. CONCLUSION: Despite the small number of subjects and the inclusion of only female subjects, our results suggest that DNAm of 13 CpGs of the BDNF gene may be an appropriate biomarker for aging and useful for predicting increased susceptibility to age-related psychiatric disorders.

Optogenetic stimulation of infralimbic PFC reproduces ketamine's rapid and sustained antidepressant actions.

Ketamine produces rapid and sustained antidepressant actions in depressed patients, but the precise cellular mechanisms underlying these effects have not been identified. Here we determined if modulation of neuronal activity in the infralimbic prefrontal cortex (IL-PFC) underlies the antidepressant and anxiolytic actions of ketamine. We found that neuronal inactivation of the IL-PFC completely blocked the antidepressant and anxiolytic effects of systemic ketamine in rodent models and that ketamine microinfusion into IL-PFC reproduced these behavioral actions of systemic ketamine. We also found that optogenetic stimulation of the IL-PFC produced rapid and long-lasting antidepressant and anxiolytic effects and that these effects are associated with increased number and function of spine synapses of layer V pyramidal neurons. The results demonstrate that ketamine infusions or optogenetic stimulation of IL-PFC are sufficient to produce long-lasting antidepressant behavioral and synaptic responses similar to the effects of systemic ketamine administration.

Rapid antidepressant actions of scopolamine: Role of medial prefrontal cortex and M1-subtype muscarinic acetylcholine receptors.

Clinical studies demonstrate that scopolamine, a non-selective muscarinic acetylcholine receptor (mAchR) antagonist, produces rapid therapeutic effects in depressed patients, and preclinical studies report that the actions of scopolamine require glutamate receptor activation and the mechanistic target of rapamycin complex 1 (mTORC1). The present study extends these findings to determine the role of the medial prefrontal cortex (mPFC) and specific muscarinic acetylcholine receptor (M-AchR) subtypes in the actions of scopolamine. The administration of scopolamine increases the activity marker Fos in the mPFC, including the infralimbic (IL) and prelimbic (PrL) subregions. Microinfusions of scopolamine into either the IL or the PrL produced significant antidepressant responses in the forced swim test, and neuronal silencing of IL or PrL blocked the antidepressant effects of systemic scopolamine. The results also demonstrate that the systemic administration of a selective M1-AChR antagonist, VU0255035, produced an antidepressant response and stimulated mTORC1 signaling in the PFC, similar to the actions of scopolamine. Finally, we used a chronic unpredictable stress model as a more rigorous test of rapid antidepressant actions and found that a single dose of scopolamine or VU0255035 blocked the anhedonic response caused by CUS, an effect that requires the chronic administration of typical antidepressants. Taken together, these findings indicate that mPFC is a critical mediator of the behavioral actions of scopolamine and identify the M1-AChR as a therapeutic target for the development of novel and selective rapid-acting antidepressants.

BDNF release is required for the behavioral actions of ketamine.

BACKGROUND: Recent studies demonstrate that the rapid antidepressant ketamine increases spine number and function in the medial prefrontal cortex (mPFC), and that these effects are dependent on activation of glutamate α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors and brain-derived neurotrophic factor (BDNF). In vitro studies also show that activation of AMPA receptors stimulates BNDF release via activation of L-type voltage-dependent calcium channels (VDCC). METHODS: Based on this evidence, we examined the role of BDNF release and the impact of L-type VDCCs on the behavioral actions of ketamine. RESULTS: The results demonstrate that infusion of a neutralizing BDNF antibody into the mPFC blocks the behavioral effects of ketamine in the forced swim test (FST). In addition, we show that pretreatment with nifedipine or verapamil, two structurally-different L-type calcium channel antagonists, blocks the behavioral effects of ketamine in the FST. Finally, we show that ketamine treatment stimulates BDNF release in primary cortical neurons and that this effect is blocked by inhibition of AMPA receptors or L-type VDCCs. CONCLUSIONS: Taken together, these results indicate that the antidepressant effects of ketamine are mediated by activation of L-type VDCCs and the release of BDNF. They further elucidate the cellular mechanisms underlying this novel rapid-acting antidepressant.

Long-term mental health and resilience of the first responders in Japanese ground self-defense forces engaging body recovery after the great east Japan earthquake.

Handling human remains is extremely difficult and stressful task, and it can contribute to the development of stress-related mental health problems. To prevent disaster from the development of mental disorders in first responders, it will be important to elucidate factors sustaining psychological well-being following the events requiring handling of human remains. Japanese Ground Self-Defense Forces (JGSDF) first responders (n = 146), involved in human remains recovery after the Great East Japan Earthquake (GEJE) participated. We examined the psychological resilience (S-H Resilience Test), depressive symptoms (SDS), and psychological distress (GHQ-28) 6 years after GEJE, in three groups; Group A: no contact no view of human remains, B: view only of human remains, and C: direct handling of human remains. S-H Resilience test evaluated the 3 subclasses of resilience; Social Support, Self Efficacy, Sociality. One-way ANOVA revealed the significant difference in resilience scores between Group B and C without any differences in depressive symptoms or psychological distress among the 3 groups. Multiple regression analyses revealed that depressive symptoms and resilience were associated with psychological distress in all participants. Path analyses showed that whereas one subtype of resilience indirectly reduced psychological distress through lower depressive symptoms in Group A (Social Support) and Group B (Sociality), both subtypes of resilience indirectly reduced psychological distress by lowering depressive symptoms in Group C. These findings suggest that exposure to higher stressful situation may decrease the psychological resilience based on the S-H Resilience test, and two subtypes of resilience may be necessary to sustain the psychological well-being.

Involvement of dysregulated hippocampal histone H3K9 methylation at the promoter of the BDNF gene in impaired memory extinction.

RATIONALE: Since the precise mechanisms of posttraumatic stress disorder (PTSD) remain unknown, effective treatment interventions have not yet been established. Impaired extinction of fear memory (EFM) is one of the core symptoms of PTSD and is associated with stress-induced epigenetic change in gene expression. OBJECTIVES: In this study, we examined whether the involvement of histone H3 lysine 9 dimethylation (H3K9me2) in EFM is mediated through brain-derived neurotrophic factor (BDNF) expression in the hippocampus, and whether BIX01294, a selective G9a and GLP histone methyltransferase inhibitor, could be treatment for impaired EFM in an animal model of PTSD. METHODS: The single prolonged stress (SPS) paradigm was used to model PTSD. We measured BDNF mRNA levels by RT-PCR, and H3K9me2 levels in the BDNF gene promoters by chromatin immunoprecipitation-qPCR. After undergoing contextual fear conditioning and hippocampal injection of BIX01294, male rats were subjected to extinction training and extinction testing and their freezing times and BDNF mRNA levels were measured. RESULTS: Compared to sham rats, SPS rats showed decreased BDNF mRNA levels 2 h after extinction training, no significant changes in levels of global H3K9me2 prior to extinction training, and increased levels of H3K9me2 in BDNF gene promoter IV, but not in BDNF gene promoter I. Administration of BIX01294 ameliorated the decrease in BDNF mRNA levels 2 h after extinction training and subsequently alleviated impaired EFM in extinction tests in SPS rats. CONCLUSION: We conclude that reduced hippocampal levels of BDNF mRNA due to increase in H3K9me2 levels may play a role in PTSD-associated EFM impairment, and BIX01294 could be a PTSD treatment option.

Neonatal Isolation Increases the Susceptibility to Learned Helplessness through the Aberrant Neuronal Activity in the Ventral Pallidum of Rats.

Objective: : Environmental deprivation, a type of childhood maltreatment, has been reported to constrain the cognitive developmental processes such as associative learning and implicit learning, which may lead to functional and morphological changes in the ventral pallidum (VP) and pessimism, a well-known cognitive feature of major depression. We examined whether neonatal isolation (NI) could influence the incidence of learned helplessness (LH) in a rat model mimicking the pessimism, and the number of vesicular glutamate transporter 2 (VGLUT2)-expressing VP cells and Penk-expressing VP cells. Methods: : The number of escape failures from foot-shocks in the LH test was measured to examine stress-induced depression-like behavior in rats. The number of VGLUT2-expressing VP cells and Penk-expressing VP cells was measured by immunohistochemistry. Results: : In NI rats compared with Sham rats, the incidence of LH in adulthood was increased and VGLUT2-expressing VP cells but not Penk-expressing VP cells in adulthood were decreased. VGLUT2-expressing VP cells were decreased only in the LH group of NI rats and significantly correlated with the escape latency in the LH test. Conclusion: : These findings suggest that the aberrant VP neuronal activity due to environmental deprivation early in life leads to pessimistic associative and implicit learning. Modulating VP neuronal activity could be a novel therapeutic and preventive strategy for the patients with this specific pathophysiology.

Electroconvulsive seizure, but not imipramine, rapidly up-regulates pro-BDNF and t-PA, leading to mature BDNF production, in the rat hippocampus.

Electroconvulsive therapy is the most effective treatment for antidepressant-resistant depression, although its mechanism has not been fully elucidated. Previous studies have demonstrated that electroconvulsive seizures (ECS) induce expression of brain-derived neurotrophic factor (BDNF) in the rat hippocampus. However, in contrast with mature BDNF (mBDNF) known to have antidepressant effects, its precursor (pro-BDNF) has harmful effects on neurons. We therefore hypothesized that efficient processing of pro-BDNF is a critical requirement for the antidepressant effects of ECS. We found that single administration of ECS rapidly increased not only hippocampal levels of pro-BDNF but also those of prohormone convertase 1 (PC1) and tissue-plasminogen activator (t-PA), which are proteases involved in intra- and extracellular pro-BDNF processing, respectively. Interestingly, pro-BDNF and t-PA levels were increased in hippocampal synaptosomes after single ECS, suggesting their transport to secretory sites. In rats receiving 10-d repeated ECS, accumulation of pro-BDNF and a resultant increase in mBDNF levels were observed. While t-PA levels increased and accumulated following repeated ECS, PC1 levels did not, suggesting that intracellular processing capacity is limited. Finally, chronic administration of imipramine significantly increased mBDNF levels, but not pro-BDNF and protease levels, indicating that the therapeutic mechanism of imipramine differs from that of ECS. Taken together, these results suggest that, while intra- and extracellular proteases are involved in pro-BDNF processing in single ECS, t-PA plays a dominant role following repeated ECS. Such efficient pro-BDNF processing as well as strong induction of BDNF expression may contribute to the antidepressant effects of ECS.

Interferon signaling and hypercytokinemia-related gene expression in the blood of antidepressant non-responders.

Only 50% of patients with depression respond to the first antidepressant drug administered. Thus, biomarkers for prediction of antidepressant responses are needed, as predicting which patients will not respond to antidepressants can optimize selection of alternative therapies. We aimed to identify biomarkers that could predict antidepressant responsiveness using a novel data-driven approach based on statistical pattern recognition. We retrospectively divided patients with major depressive disorder into antidepressant responder and non-responder groups. Comprehensive gene expression analysis was performed using peripheral blood without narrowing the genes. We designed a classifier according to our own discrete Bayes decision rule that can handle categorical data. Nineteen genes showed differential expression in the antidepressant non-responder group (n = 15) compared to the antidepressant responder group (n = 15). In the training sample of 30 individuals, eight candidate genes had significantly altered expression according to quantitative real-time polymerase chain reaction. The expression of these genes was examined in an independent test sample of antidepressant responders (n = 22) and non-responders (n = 12). Using the discrete Bayes classifier with the HERC5, IFI6, and IFI44 genes identified in the training set yielded 85% discrimination accuracy for antidepressant responsiveness in the 34 test samples. Pathway analysis of the RNA sequencing data for antidepressant responsiveness identified that hypercytokinemia- and interferon-related genes were increased in non-responders. Disease and biofunction analysis identified changes in genes related to inflammatory and infectious diseases, including coronavirus disease. These results strongly suggest an association between antidepressant responsiveness and inflammation, which may be useful for future treatment strategies for depression.

Chemogenetic activation of the mPFC alleviates impaired fear memory extinction in an animal model of PTSD.

BACKGROUND AND AIM: Although impaired extinction of fear memory (EFM) is a hallmark symptom of posttraumatic stress disorder (PTSD), the mechanisms underlying the impairment are unknown. Activation of the infralimbic cortex (IL) in the medial prefrontal cortex (mPFC) has been reported to predict successful fear extinction, whereas functionally disrupting this region impairs extinction. We examined whether chemogenetic activation of the IL could alleviate impaired EFM in a single prolonged stress (SPS) rat model of PTSD. METHODS: Chemogenetic activation of IL and prelimbic (PL) excitatory neurons was undertaken to evaluate EFM using a contextual fear conditioning paradigm. Neuronal activity in the IL was recorded using a 32-multichannel silicon electrode. To examine histological changes in the mPFC, apoptosis was measured by TUNEL staining. RESULTS: Chemogenetic activation of excitatory neurons in the IL, but not the PL, enhanced EFM in sham rats and resulted in alleviation of EFM impairment in SPS rats. The alleviation of impaired EFM in SPS rats was observed during the extinction test session. Neuronal activity in the IL of SPS rats was lower than that of sham rats after clozapine-n-oxide administration. Increased apoptosis was found in the IL of SPS rats. CONCLUSIONS: These findings suggest that a decreased excitatory response in the IL due, at least in part, to an increase in apoptosis in SPS rats leads to impaired EFM, and that neuronal activation during extinction training could be useful for the treatment of impaired EFM in PTSD patients.

Optimized protocol for the extraction of RNA and DNA from frozen whole blood sample stored in a single EDTA tube.

Cryopreservation of whole blood is useful for DNA collection, and clinical and basic research. Blood samples in ethylenediaminetetraacetic acid disodium salt (EDTA) tubes stored at - 80 °C are suitable for DNA extraction, but not for high-quality RNA extraction. Herein, a new methodology for high-quality RNA extraction from human blood samples is described. Quickly thawing frozen whole blood on aluminum blocks at room temperature could minimize RNA degradation, and improve RNA yield and quality compared with thawing the samples in a 37 °C water bath. Furthermore, the use of the NucleoSpin RNA kit increased RNA yield by fivefold compared with the PAXgene Blood RNA Kit. Thawing blood samples on aluminum blocks significantly increased the DNA yield by ~ 20% compared with thawing in a 37 °C water bath or on ice. Moreover, by thawing on aluminum blocks and using the NucleoSpin RNA and QIAamp DNA Blood kits, the extraction of RNA and DNA of sufficient quality and quantity was achieved from frozen EDTA whole blood samples that were stored for up to 8.5 years. Thus, extracting RNA from frozen whole blood in EDTA tubes after long-term storage is feasible. These findings may help advance gene expression analysis, as well as biomarker research for various diseases.

[Epigenetic mechanism of depression].

Numerous epigenetic studies have revealed that the acetylated status of histone as well as methylated status of cytosine is closely involved in gene transcription. Preclinical and clinical studies demonstrate that changes in levels of various genes in the brain including BDNF, play a role in the pathophysiology of depression. It is well known that the levels of BDNF mRNA and protein in the rat brain, such as frontal cortex and hippocampus, was decreased in response to stress, but the precise mechanism of stress-induced downregulation of BDNF has yet to be characterized. In this context, we examined the influence of a single immobilization stress (SIS) on the levels of total BDNF mRNA with each exon mRNA by real-time PCR and acetylated histone at the promoters of the BDNF gene by chromatin immunoprecipitaion assay in the rat hippocampus. SIS significantly decreased the levels of total BDNF mRNA with significant reduced levels of exon I and IV mRNA. Significant decreases in acetylated histone H3, but not H4, were found at the promoters of exons I, IV, and VI. On the other hand, antidepressant-like effects has been reported with sodium butylate (SB), a histone deacetylase (HDAC) inhibitor, promoting gene transcription. We also found antidepressant-like effect of repeated administration of SB in the forced swim test using rats. In addition, we found that upregulation in transthyretin mRNA in the rat hippocampus is, at least in part, associated with this effect using DNA microarray and real-time PCR. Based on these findings, it is postulated that epigenetic regulation of the BDNF gene by stress and antidepressants may be involved in the pathophysiology of depression.

The role of glucocorticoid receptors in the induction and prevention of hippocampal abnormalities in an animal model of posttraumatic stress disorder.

RATIONALE: Since the precise mechanisms of posttraumatic stress disorder (PTSD) remain unknown, effective treatment interventions have not yet been established. Numerous clinical studies have led to the hypothesis that elevated glucocorticoid levels in response to extreme stress might trigger a pathophysiological cascade which consequently leads to functional and morphological changes in the hippocampus. OBJECTIVES: To elucidate the pathophysiology of PTSD, we examined the alteration of hippocampal gene expression through the glucocorticoid receptor (GR) in the single prolonged stress (SPS) paradigm, a rat model of PTSD. METHODS: We measured nuclear GRs by western blot, and the binding of GR to the promoter of Bcl-2 and Bax genes by chromatin immunoprecipitation-qPCR as well as the expression of these 2 genes by RT-PCR in the hippocampus of SPS rats. In addition, we examined the preventive effects of a GR antagonist on SPS-induced molecular, morphological, and behavioral alterations (hippocampal gene expression of Bcl-2 and Bax, hippocampal apoptosis using TUNEL staining, impaired fear memory extinction (FME) using the contextual fear conditioning paradigm). RESULTS: Exposure to SPS increased nuclear GR expression and GR binding to Bcl-2 gene, and decreased Bcl-2 mRNA expression. Administration of GR antagonist immediately after SPS prevented activation of the glucocorticoid cascade, hippocampal apoptosis, and impairment FME in SPS rats. CONCLUSION: The activation of GRs in response to severe stress may trigger the pathophysiological cascade leading to impaired FME and hippocampal apoptosis. In contrast, administration of GR antagonist could be useful for preventing the development of PTSD.

Kynurenic acid is a potential overlapped biomarker between diagnosis and treatment response for depression from metabolome analysis.

Since optimal treatment at an early stage leads to remission of symptoms and recovery of function, putative biomarkers leading to early diagnosis and prediction of therapeutic responses are desired. The current study aimed to use a metabolomic approach to extract metabolites involved in both the diagnosis of major depressive disorder (MDD) and the prediction of therapeutic response for escitalopram. We compared plasma metabolites of MDD patients (n = 88) with those in healthy participants (n = 88) and found significant differences in the concentrations of 20 metabolites. We measured the Hamilton Rating Scale for Depression (HRSD) on 62 patients who completed approximately six-week treatment with escitalopram before and after treatment and found that kynurenic acid and kynurenine were significantly and negatively associated with HRSD reduction. Only one metabolite, kynurenic acid, was detected among 73 metabolites for overlapped biomarkers. Kynurenic acid was lower in MDD, and lower levels showed a better therapeutic response to escitalopram. Kynurenic acid is a metabolite in the kynurenine pathway that has been widely accepted as being a major mechanism in MDD. Overlapping biomarkers that facilitate diagnosis and prediction of the treatment response may help to improve disease classification and reduce the exposure of patients to less effective treatments in MDD.

Maternal postpartum learned helplessness (LH) affects maternal care by dams and responses to the LH test in adolescent offspring.

It is known that the early environment affects the mental development of rodent and human offspring. However, it is not known specifically whether a postpartum depressive state influences the depressive state in offspring. Using learned helplessness (LH) in rats as an animal model of depression, we examined the influence of maternal postpartum LH on responses to the LH test of offspring. Dam rats were judged as LH or non-helpless (nLH) on postnatal days (PN) 2-3, and maternal behavior was recorded during PN2-14. On PN 45-46, offspring were subjected to the LH test. Plasma corticosterone (CORT) levels, hippocampal levels of glucocorticoid receptor (GR) and brain-derived neurotrophic factor (BDNF) mRNA were measured before and after the LH test in offspring. Active nursing in LH dams was significantly lower than that in nLH dams. Susceptibility to LH in the offspring of LH dams was significantly higher than in those of nLH dams, and was negatively correlated with active nursing by LH dams. The GR mRNA levels before and after the LH test were lower in the offspring of LH dams than in those of nLH dams, and the reduced basal GR mRNA and protein might have resulted in the higher CORT response after the LH test. There was no significant difference in BDNF mRNA in the offspring of LH and nLH dams. These findings suggest that early postpartum LH decreased active nursing and increased depression-like behavior in the adolescent offspring via dysfunction of the hypothalamic-pituitary-adrenal axis.

Single prolonged stress: toward an animal model of posttraumatic stress disorder.

Although selective serotonin reuptake inhibitors (SSRIs) are reported to be effective in decreasing posttraumatic stress disorder (PTSD) symptoms, a subgroup of PTSD patients remain chronically symptomatic and maintain conditioned fear responses to traumatic stimuli. In this context, the establishment of an appropriate animal model of PTSD is necessary to promote better understanding of the mechanisms of the disorder and to facilitate the development of more effective therapeutic alternatives to SSRIs. Although no single widely accepted animal model of PTSD has been established to date, the single prolonged stress (SPS) animal model has been partially validated as a model for PTSD. SPS rats mimic the pathophysiological abnormalities and behavioral characteristics of PTSD, such as enhanced anxiety-like behavior and glucocorticoid negative feedback, and they exhibit the expected therapeutic response to paroxetine on enhanced fear memory. In addition, SPS rats exhibit enhanced freezing in response to contextual fear conditioning, and impaired extinction of fear memory, which is alleviated by D-cycloserine. The enhanced consolidation and impaired extinction of fear memory found in SPS rats suggests that this model has additional value because recent studies of PTSD indicate that memory abnormalities are a central feature. In this study, we summarize the behavioral and pathophysiological PTSD-like symptoms in SPS, focusing on memory abnormalities, and evaluate the validity of SPS as an animal model of PTSD.

Combined brain-derived neurotrophic factor with extinction training alleviate impaired fear extinction in an animal model of post-traumatic stress disorder.

Impaired fear memory extinction (Ext) is one of the hallmark symptoms of post-traumatic stress disorder (PTSD). However, since the precise mechanism of impaired Ext remains unknown, effective interventions have not yet been established. Recently, hippocampal-prefrontal brain-derived neurotrophic factor (BDNF) activity was shown to be crucial for Ext in naïve rats. We therefore examined whether decreased hippocampal-prefrontal BDNF activity is also involved in the Ext of rats subjected to a single prolonged stress (SPS) as a model of PTSD. BDNF levels were measured by enzyme-linked immunosorbent assay (ELISA), and phosphorylation of TrkB was measured by immunohistochemistry in the hippocampus and medial prefrontal cortex (mPFC) of SPS rats. We also examined whether BDNF infusion into the ventral mPFC or hippocampus alleviated the impaired Ext of SPS rats in the contextual fear conditioning paradigm. SPS significantly decreased the levels of BDNF in both the hippocampus and mPFC and TrkB phosphorylation in the ventral mPFC. Infusion of BDNF 24 hours after conditioning in the infralimbic cortex (ILC), but not the prelimbic cortex (PLC) nor hippocampus, alleviated the impairment of Ext. Since amelioration of impaired Ext by BDNF infusion did not occur without extinction training, it seems the two interventions must occur consecutively to alleviate impaired Ext. Additionally, BDNF infusion markedly increased TrkB phosphorylation in the ILC of SPS rats. These findings suggest that decreased BDNF signal transduction might be involved in the impaired Ext of SPS rats, and that activation of the BDNF-TrkB signal might be a novel therapeutic strategy for the impaired Ext by stress.

Effects of single prolonged stress and D-cycloserine on contextual fear extinction and hippocampal NMDA receptor expression in a rat model of PTSD.

Although the impaired extinction of traumatic memory is one of the hallmark symptoms of posttraumatic stress disorder (PTSD), the underlying mechanisms of impaired extinction are unclear and effective pharmacological interventions have not yet been developed. Single prolonged stress (SPS) has been proposed as an animal model of PTSD, since rats subjected to SPS (SPS rats) show enhanced negative feedback of the HPA axis and increased contextual fear, which are characteristics similar to those observed in patients with PTSD. In this study, using SPS rats, we examined (a) the ability of SPS to impair fear extinction, (b) whether D-cycloserine (DCS) can alleviate impaired fear extinction in SPS rats, and (c) the effect of SPS and/or DCS on the levels of N-methyl-D-aspartate (NMDA) receptor subunit mRNAs in the rat hippocampus during extinction training. SPS rats exhibited impaired fear extinction in the contextual fear test, which was alleviated by the repeated administration of DCS. The effect of enhanced extinction, induced by the administration of DCS to SPS rats, was maintained for one week following extinction training. SPS induced significant upregulation of the levels of NMDA receptor subunit mRNAs before and during the period of extinction training, while repeated administration of DCS eliminated the enhanced mRNA levels of NMDARs. Behavioral analyses indicated that SPS is an appropriate animal model of PTSD and that DCS may be effective in the treatment of PTSD. These findings suggest that DCS, irrespective of its mechanistic involvement in the enhancement of fear extinction, may help to reverse hippocampal plasticity, and thus reverse the NMDA compensatory alterations.