Repeated unpredictable stress and antidepressants differentially regulate expression of the bcl-2 family of apoptotic genes in rat cortical, hippocampal, and limbic brain structures

Stress-induced activation of the brainstem Bcl-xL gene expression in rats treated with fluoxetine: correlations with serotonin metabolism and depressive-like behavior

Mechanisms underlying stress-induced depression and antidepressant drug action were shown to involve alterations in serotonergic (5-HT) neurotransmission and expression of genes coding for proteins associated with neurotrophic signaling pathways and cell-survival in the hippocampus and cortex. Expression of these genes in the brainstem containing 5-HT neurons may also be related to vulnerability or resilience to stress-related psychopathology. Here we investigated 5-HT markers and expression of genes for Brain-Derived Neurotrophic Factor (BDNF) and apoptotic proteins in the brainstem in relation to swim stress-induced behavioral despair. We found that anti-apoptotic Bcl-xL gene is sensitive to stress during the course of fluoxetine administration. Responsiveness of this gene to stress appeared concomitantly with an antidepressant-like effect of fluoxetine in the forced swim test. Bcl-xL transcript levels showed negative correlations with duration of immobility in the test and 5-HT turnover in the brainstem. In contrast, BDNF and pro-apoptotic protein Bax mRNA levels were unchanged by either fluoxetine or stress, suggesting specificity of Bcl-xL gene responses to these treatments. We also found that the levels of mRNAs for tryptophan hydroxylase-2 (TPH2) and 5-HT transporter (5-HTT) were significantly down-regulated following prolonged treatment with fluoxetine, but were not affected by stress. Unlike TPH2 and 5-HTT, 5-HT1A receptor mRNA levels were not altered by fluoxetine but significantly increased in response to swim stress. These data show that long-term fluoxetine treatment leads to changes in 5-HT and Bcl-xL responses to stress associated with antidepressant-like effects of the drug. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Fluoxetine Up-Regulates Bcl-xL Expression in Rat C6 Glioma Cells

OBJECTIVE

To analyze both differentially expressed genes and the Bcl-xL protein expression after acute and chronic treatment with fluoxetine in rat C6 glioma cells.

METHODS

C6 glioma cells were cultured for 24 h or 72 h after treatment with 10 µM fluoxetine, and gene expression patterns were observed using microarray and qRT-PCR. Then, cells were cultured for 6 h, 24 h, 72 h or 96 h after treatment with 10 µM fluoxetine, and the expression of Bcl-xL protein was measured using western blot.

RESULTS

As determined by microarray, treatment with fluoxetine for 24 h up-regulated 33 genes (including Bcl-xL and NCAM140) and down-regulated 7 genes (including cyclin G-associated kinase). Treatment with fluoxetine for 72 h up-regulated 53 genes (including Gsα and Bcl-xL) and down-regulated 77 genes (including Gαi2 and annexin V). Based on the qRT-PCR results, there was an increase in Gsα mRNA and a decrease in Gαi2 mRNA at 72 h in fluoxetine-treated cells as compared to control, a result that was consistent with microarray. We also observed an increase in Bcl-xL mRNA (both at 24 h and at 72 h) in fluoxetine-treated cells as compared to control, demonstrating a tendency to increase gradually. Bcl-xL protein expression increased as the duration of fluoxetine treatment increased.

CONCLUSION

These results suggest that chronic treatment with fluoxetine not only initiates the cAMP pathway through inducing Gsα expression but also induces Bcl-xL expression, thus inhibiting apoptosis.

In animal models, psychosocial stress-induced (neuro)inflammation, apoptosis and reduced neurogenesis are associated to the onset of depression

Recently, the inflammatory and neurodegenerative (I&ND) hypothesis of depression was formulated (Maes et al., 2009), i.e. the neurodegeneration and reduced neurogenesis that characterize depression are caused by inflammation, cell-mediated immune activation and their long-term sequels. The aim of this paper is to review the body of evidence that external stressors may induce (neuro)inflammation, neurodegeneration and reduced neurogenesis; and that antidepressive treatments may impact on these pathways. The chronic mild stress (CMS) and learned helplessness (LH) models show that depression-like behaviors are accompanied by peripheral and central inflammation, neuronal cell damage, decreased neurogenesis and apoptosis in the hippocampus. External stress-induced depression-like behaviors are associated with a) increased interleukin-(IL)1β, tumor necrosis factor-α, IL-6, nuclear factor κB, cyclooxygenase-2, expression of Toll-like receptors and lipid peroxidation; b) antineurogenic effects and reduced brain-derived neurotrophic factor (BDNF) levels; and c) apoptosis with reduced levels of Bcl-2 and BAG1 (Bcl-2 associated athanogene 1), and increased levels of caspase-3. Stress-induced inflammation, e.g. increased IL-1β, but not reduced neurogenesis, is sufficient to cause depression. Antidepressants a) reduce peripheral and central inflammatory pathways by decreasing IL-1β, TNFα and IL-6 levels; b) stimulate neuronal differentiation, synaptic plasticity, axonal growth and regeneration through stimulatory effects on the expression of different neurotrophic factors, e.g. trkB, the receptor for brain-derived neurotrophic factor; and c) attenuate apoptotic pathways by activating Bcl-2 and Bcl-xl proteins, and suppressing caspase-3. It is concluded that external stressors may provoke depression-like behaviors through activation of inflammatory, oxidative, apoptotic and antineurogenic mechanisms. The clinical efficacity of antidepressants may be ascribed to their ability to reverse these different pathways.

Abnormal cingulate and prefrontal cortical neurochemistry in major depression after electroconvulsive therapy

BACKGROUND

Metabolic changes after electroconvulsive therapy (ECT) have been described in depressed patients, but results are heterogeneous. To determine the concentrations of N-acetyl-aspartate (NAA), choline-containing compounds, creatine + phosphocreatine (tCr), and glutamate in the left dorsolateral prefrontal cortex (DLPFC) and left anterior cingulum of depressed patients before and after ECT, we used proton magnetic resonance spectroscopy.

METHODS

Metabolite concentrations in the DLPFC and anterior cingulum were determined in 25 patients with major depressive disorder (MDD) and 27 healthy control subjects using the point resolved spectroscopy sequence. Neuropsychological and clinical parameters were determined before and after nine sessions of right unilateral ultrabrief pulse ECT.

RESULTS

In the cingulum, baseline glutamate and NAA levels were decreased in depressed patients. High glutamate at baseline predicted a greater treatment response. After ECT, increased NAA levels were observed in responders to treatment and tCr levels were significantly decreased across all depressive patients. In the left DLPFC, NAA levels were significantly decreased in responders to ECT compared with nonresponders. Autobiographic memory was deteriorated in all patients after ECT.

CONCLUSIONS

Low glutamatergic state in depressive patients emphasizes the role of dysfunctional glutamatergic neurotransmission in the pathophysiology of MDD. The low NAA level at baseline in the patients supports neurodegenerative changes in MDD. N-acetyl-aspartate levels might serve as early surrogate marker for dynamic metabolic changes due to ECT, reflecting both neuroprotection and lowered neuronal viability. The tCr decrease in the cingulum suggests altered mitochondrial energy metabolism.

Connectivity between mitochondrial functions and psychiatric disorders

Mitochondria provide most of the energy production in cells. They are involved in the regulation of free radicals, calcium buffering, and redox signaling and take part in the intrinsic pathway of apoptosis. Mutations or polymorphisms of mitochondrial DNA, mitochondria-mediated oxidative stress, decrease of adenosine triphosphate production, changes of intracellular calcium and oxidative stress are concerned in various diseases. There is increasing evidence that impaired functions of mitochondria are associated with mood disorders. It is suggested that disturbed energetic metabolism and/or reactive oxygen species production take part in the pathophysiology of mood disorders and could participate in the therapeutic effects or side-effects of antidepressants and mood stabilizers.

Venlafaxine modulates depression-induced behaviour and the expression of Bax mRNA and Bcl-xl mRNA in both hippocampus and myocardium

OBJECTIVES

Major depressive disorder is associated with progressive brain changes and is frequently comorbid with cardiovascular disease. There may be shared pathophysiological pathways between cerebral and myocardial dysfunction that impact on apoptosis related proteins. Our aim was to examine behaviour changes of rats with chronic mild stress (CMS), explore the expression of Bax and Bcl-xl in the hippocampus and myocardium, and additionally evaluate the effects of venlafaxine on these molecular mechanisms.

METHODS

Rats were randomly divided into three groups. The behaviour was assessed using the open field and sucrose consumption tests. Gene expression was measured by RT-PCR.

RESULTS

In CMS, there was a significant reduction of movements and sucrose consumption, an increased Bax level and a decreased Bcl-xl level in both the hippocampus and myocardium. The venlafaxine group showed an increase in movements and sucrose consumption, as well as upregulated expression of Bcl-xl and downregulated expression of Bax in both the hippocampus and myocardium.

CONCLUSIONS

These results demonstrate that in CMS, there is an increase in pro-apoptotic pathways that is reversed by venlafaxine. This suggests that there are shared active biochemical pathways that may play a role in the process of neuroprogression that is seen in depression and cardiovascular disorders.

Dose-dependent modulation of apoptotic processes by fluoxetine in maturing neuronal cells: an in vitro study

OBJECTIVES

Recent studies indicate that the selective serotonin reuptake inhibitor (SSRI) fluoxetine is not solely effective by the instant inhibition of the serotonin transporter (SERT) but also by its influence on mitotic and/or apoptotic processes.

METHODS

To investigate the effects of the compound in vitro, we treated neurons from different brain areas with increasing concentrations of fluoxetine. Additionally, human embryonic kidney (HEK-293) cells and HEK-293 cells stably expressing the SERT were used. Cell viability was quantified by MTT-assay and apoptosis via fluorescence-activated cell-sorting analyses. Fluoxetine's effect on the γ-aminobutyric acid (GABA) receptor was electrophysiologically investigated to test the hypothesis if a GABA-mimetic effect exists that might lead - additionally to the well-known N-methyl-D-aspartate (NMDA)-antagonism - to increased apoptosis in immature neurons.

RESULTS

In hippocampal, cortical, and both types of HEK-293 cells, viability decreased and apoptosis increased in a dose-dependent manner (0.5-75 μM). In contrast, in mesencephalic and striatal cells the viability was unchanged or even slightly stimulated up to 20 μM fluoxetine. An anti-apoptotic effect of concentrations below 10 μM was observed in these cells. The GABA(A) receptor was directly activated by fluoxetine.

CONCLUSIONS

We conclude that fluoxetine affects apoptotic processes independently from SERT expression. Since especially the combined GABA-mimetic and NMDA-antagonistic effects increase apoptosis in developing neuronal cells, whereas both effects are neuroprotective in adult neurons we hypothesise that these mechanisms explain the discrepancy of in vitro and in vivo studies.

Recent advances in psychoneuroimmunology: Inflammation in psychiatric disorders

Psychiatric disorders are common and complex and their precise biological underpinnings remain elusive. Multiple epidemiological, molecular, genetic and gene expression studies suggest that immune system dysfunction may contribute to the risk for developing psychiatric disorders including schizophrenia, bipolar disorder, and major depressive disorder. However, the precise mechanisms by which inflammation-related events confer such risk are unclear. In this review, we examine the peripheral and central evidence for inflammation in psychiatric disorders and the potential molecular mechanisms implicated including inhibition of neurogenesis, apoptosis, the HPA-axis, the role of brain-derived neurotrophic factor and the interplay between the glutamatergic, dopaminergic and serotonergic neurotransmitter systems.

The beta3 adrenoceptor agonist, amibegron (SR58611A) counteracts stress-induced behavioral and neurochemical changes

These experiments were made to study the mechanisms underlying the antidepressant-like effects of the beta(3) adrenoceptor agonist amibegron (SR58611A). To this purpose, the expression levels of the hippocampal cyclic adenosine monophosphate (cAMP)-response element binding protein (CREB), brain-derived neurotrophic factor (BDNF), B-cell lymphoma-2 (Bcl-2) and Bax proteins were assessed, by using western blot analysis, in rats tested in the forced swim test (FST). Under basal conditions (no previous exposure to stressors), different groups of male Wistar rats received acutely or repeatedly (once/day for 7days) intraperitoneal (i.p.) injections of amibegron (1, 5 and 10mg/kg), the tricyclic antidepressant (TCA) clomipramine (50mg/kg), the selective serotonin reuptake inhibitor (SSRI) citalopram (15mg/kg) or their vehicles. The influence of stress-related conditions was studied in rats subjected to acute (4h) or repeated (4h/day for 7days) restraint stress, applied prior to the FST procedure. Compared to the control groups, both stressor procedures increased the immobility time in the FST and reduced hippocampal BDNF and Bcl-2/Bax ratio proteins expression, which were counteracted by amibegron (5 and 10mg/kg) treatment. Opposite effects were found in the CREB expression, since it was lower after acute and higher after repeated stress procedure, respectively. Again, these effects were reversed by amibegron treatment. Different results were obtained in animals treated with clomipramine or citalopram. Hence, it is likely that the observed behavioral effects of amibegron could be due, at least in part, to its action on hippocampal expression of neurotrophic and/or anti-apoptotic factors, supporting the hypothesis that beta(3) adrenoceptors may be a therapeutic target for the treatment of stress-related disorders.

Immunohistochemical expression of Bcl-2, p53 and caspase-9 in hypothalamus magnocellular centers of nNOS knockout mice following water deprivation

We studied the interactions between apoptosis regulator proteins (Bcl-2, p53 and caspase-9) and neuronal nitric oxide in vasopressinergic magnocellular centers of the hypothalamus using neuronal nitric oxide synthase (nNOS) gene knockout mice. nNOS gene deletion resulted in accumulation of Bcl-2, p53 and caspase-9 in the paraventricular (PVN) and supraoptic (SON) nuclei in controls. Dehydration increased the levels of all three apoptosis regulator proteins studied in nuclei of wild type mice. In the hypothalamus magnocellular centers of nNOS knockout mice, however, expression of Bcl-2, p53 and caspase-9 was unchanged after dehydration. The number of magnocellular neurons did not change in the SON and PVN of nNOS deficient mice compared to wild type, and after dehydration, cell death was not observed in either nucleus of wild type or knockout mice despite activation of apoptosis regulator protein expression. Thus, we demonstrated that gene disruption of nNOS prevents activation of Bcl-2, p53 and caspase-9 expression during water deprivation, and that nNOS deficiency did not affect survival of magnocellular neurons of the hypothalamus.

Resistance to the development of stress-induced behavioral despair in the forced swim test associated with elevated hippocampal Bcl-xl expression

Stress may predispose individuals toward depression through down-regulation of neurogenesis and increase in apoptosis in the brain. However, many subjects show high resistance to stress in relation to psychopathology. In the present study, we assessed the possibility that individual-specific patterns of gene expression associated with cell survival and proliferation may be among the molecular factors underlying stress resilience. Brain-derived neurotrophic factor (BDNF), anti-apoptotic B cell lymphoma like X (Bcl-xl) and pro-apoptotic bcl2-associated X protein (Bax) expression were determined in the hippocampus and frontal cortex of rats naturally differed in despair-like behavior in the forced swim test. In the hippocampus, BDNF messenger RNA (mRNA) level was significantly down-regulated 2h after the forced swim test exposure, and at this time point, Bcl-xl mRNA and protein levels were significantly higher in stressed than in untested animals. The ratios of hippocampal Bcl-xl to Bax mRNA negatively correlated with the total time spent immobile in the test. When animals were divided in two groups according to immobility responses in two consecutive swim sessions and designated as stress resilient if their immobility time did not increase in the second session as it did in stress sensitive rats, it was found that resilient rats had significantly higher Bcl-xl/Bax ratios in the hippocampus than stress sensitive animals. The data suggest that naturally occurring variations in the Bcl-xl/Bax ratio in the hippocampus may contribute to individual differences in vulnerability to stress-induced depression-like behaviors.

Neuronal damage and protection in the pathophysiology and treatment of psychiatric illness: stress and depression

The discovery that stress and depression, as well as other psychiatric illnesses, are characterized by structural alterations, and that these changes result from atrophy and loss of neurons and glia in specific limbic regions and circuits, has contributed to a fundamental change in our understanding of these illnesses. These structural changes are accompanied by dysregulation of neuroprotective and neurotrophic signaling mechanisms that are required for the maturation, growth, and survival of neurons and glia. Conversely, behavioral and therapeutic interventions can reverse these structural alterations by stimulating neuroprotective and neurotrophic pathways and by blocking the damaging, excitotoxic, and inflammatory effects of stress. Lifetime exposure to cellular and environmental stressors and interactions with genetic factors contribute to individual susceptibility or resilience. This exciting area of research holds promise and potential for further elucidating the pathophysiology of psychiatric illness and for development of novel therapeutic interventions.

Herbal formula SYJN protect PC12 cells from neurotoxicity induced by corticosterone

AIM OF THE STUDY

SYJN is a Chinese herbal formula, containing four herbs: Bupleurum chinense DC., Curcuma aromatica Salisb., Perilla frutescens (Linn.) Britt. and Acorus tatarinowii Schott. Previous studies on the formula in our laboratory revealed an antidepressant-like effect on animal models of behavioral despair. However,the mechanisms underlying such antidepressant-like effect are yet to be understood. The aim of this work was to verify the previously established antidepressant-like effects on cell level using corticosterone-induced neurotoxicity in rat pheochromocytoma (PC12) cells to see if SYJN possesses any neuroprotective properties.

MATERIALS AND METHODS

PC12 cells were treated with 200 microM corticosterone in the absence or the presence of various concentrations of SYJN for 48 h. Then, cell viability, apoptosis, intracellular Ca(2+) ([Ca(2+)]i) concentration and caspase-3 activity were determined.

RESULTS

Following the exposure of PC12 cells to 200 microM corticosterone for 48 h, there were reductions in cell survival rate but increases in lactate dehydrogenase (LDH) release. In parallel, corticosterone caused significant elevations in DNA fragmentation, [Ca(2+)]i concentration and caspase-3 activity. However, when the PC12 cells were incubated with SYJN at different concentrations (10, 50 and 100mg/L) in the presence of 200 microM corticosterone for 48 h, the above effects were evidently alleviated in a dose-dependent manner.

CONCLUSION

SYJN could generate a neuroprotective effect on corticosterone-induced neurotoxicity in PC12 cells, suggesting a possible action pathway of SYJN in vivo by decreasing the [Ca(2+)]i concentration and caspase-3 activity.

Aberrant functional connectivity of dorsolateral prefrontal and cingulate networks in patients with major depression during working memory processing

BACKGROUND

In patients with major depressive disorder (MDD), functional neuroimaging studies have reported an increased activation of the dorsolateral prefrontal cortex (DLPFC) during executive performance and working memory (WM) processing, and also an increased activation of the anterior cingulate cortex (ACC) during baseline conditions. However, the functional coupling of these cortical networks during WM processing is less clear.

METHOD

In this study, we used a verbal WM paradigm, event-related functional magnetic resonance imaging (fMRI) and multivariate statistical techniques to explore patterns of functional coupling of temporally dissociable dorsolateral prefrontal and cingulate networks. By means of independent component analyses (ICAs), two components of interest were identified that showed either a positive or a negative temporal correlation with the delay period of the cognitive activation task in both healthy controls and MDD patients.

RESULTS

In a prefronto-parietal network, a decreased functional connectivity pattern was identified in depressed patients comprising inferior parietal, superior prefrontal and frontopolar regions. Within this cortical network, MDD patients additionally revealed a pattern of increased functional connectivity in the left DLPFC and the cerebellum compared to healthy controls. In a second, temporally anti-correlated network, healthy controls exhibited higher connectivity in the ACC, the ventrolateral and the superior prefrontal cortex compared to MDD patients.

CONCLUSIONS

These results complement and expand previous functional neuroimaging findings by demonstrating a dysconnectivity of dissociable prefrontal and cingulate regions in MDD patients. A disturbance of these dynamic networks is characterized by a simultaneously increased connectivity of the DLPFC during task-induced activation and increased connectivity of the ACC during task-induced deactivation.

Antiapoptotic and neurotrophic effects of antidepressants: a review of clinical and experimental studies

Recent studies have strengthened the role of the abnormalities in neurotrophic pathways in the pathophysiology of depression. It has been shown that the depletion of growth factors, particularly brain-derived neurotrophic factor, may result in depression-like behavior in animals and may induce cellular changes that are reminiscent of those observed in depressed patients. Some authors even suggested that increased neuronal cell loss may contribute to the pathogenesis of depression. Hence, appreciable interest has been focused on the trophic and antiapoptotic effects of antidepressant drugs. In this paper, we put emphasis on the contribution of hippocampal atrophy, increased cell death and alterations in trophic factors to the pathogenesis of depression and their relationship to the potential of antidepressants to reverse these changes by modulating trophic factor cascades and preventing apoptosis. First, evidences for increased hippocampal atrophy and cell death in depression are discussed, followed by a review of selected studies of special interest that concern antiapoptotic action of antidepressant drugs. Next, depression-related neurotrophic abnormalities and their reversal by antidepressants are depicted. Finally, relationships among neurotrophins, antiapoptotic proteins and antioxidant enzymes in the pathology and treatment of depression are pointed out.

Estrogen affects levels of Bcl-2 protein and mRNA in medial amygdala of ovariectomized rats

The survival factor Bcl-2 is a cyclic AMP response element-binding protein (CREB) gene product implicated in mediating some of estrogen's effects on neuroprotection. Previously, we showed an effect of estradiol benzoate (E) on numbers of neuron-specific protein (NeuN)- and phosphorylated CREB (pCREB)-positive cells in medial (MeA), but not central (CeA), amygdala of ovariectomized rats. To determine whether these effects are accompanied by an E-induced increase in Bcl-2, we examined the effects of E on levels of Bcl-2 protein and mRNA in MeA and CeA of ovariectomized rats treated with E regimens resulting in moderate (2.5 microg E for 4 or 14 days) or high (10 microg E for 14 days) plasma estradiol levels. As a physiological control, we showed that all E treatments increased uterine wet weight relative to vehicle; 10 microg E for 14 days also increased uterine weight compared with that seen with lower E levels. Western blot analysis revealed that all E groups displayed an increase in uterine Bcl-2 protein levels compared with vehicle. We found that 2.5 microg and 10 microg E for 14 days increased levels of Bcl-2 gold immunolabeling compared with vehicle and 2.5 microg E for 4 days in MeA, but not CeA. We measured Bcl-2 mRNA levels in vehicle and 2.5 microg E-treated 14-day groups. There was a significant increase in Bcl-2 mRNA levels in MeA, but not CeA, of E-treated ovariectomized rats compared with vehicle controls. The E-induced increase in protein and mRNA levels of Bcl-2 in MeA may be important for neuroprotection in this region.

Gray matter reduction associated with psychopathology and cognitive dysfunction in unipolar depression: a voxel-based morphometry study

BACKGROUND

Functional neuroimaging studies on both cognitive processing and psychopathology in patients with major depression have reported several functionally aberrant brain areas within limbic-cortical circuits. However, less is known about the relationship between psychopathology, cognitive deficits and regional volume alterations in this patient population.

METHODS

By means of voxel-based morphometry (VBM) and a standardized neuropsychological test battery, we examined 15 patients meeting DSM-IV criteria for major depression disorder and 14 healthy controls in order to investigate the relationship between affective symptoms, cognitive deficits and structural abnormalities.

RESULTS

Patients with depression showed reduced gray matter concentration (GMC) in the left inferior temporal cortex (BA 20), the right orbitofrontal (BA 11) and the dorsolateral prefrontal cortex (BA 46). Reduced gray matter volume (GMV) was found in the left hippocampal gyrus, the cingulate gyrus (BA 24/32) and the thalamus. Structure-cognition correlation analyses revealed that decreased GMC of the right medial and inferior frontal gyrus was associated with both depressive psychopathology and worse executive performance as measured by the Wisconsin Card Sorting Test (WCST). Furthermore, depressive psychopathology and worse performance during the WCST were associated with decreased GMV of the hippocampus. Decreased GMV of the cingulate cortex was associated with worse executive performance.

LIMITATIONS

Moderate illness severity, medication effects, and the relatively small patient sample size should be taken into consideration when reviewing the implications of these results.

CONCLUSIONS

The volumetric results indicate that regional abnormalities in gray matter volume and concentration may be associated with both psychopathological changes and cognitive deficits in depression.

Stress downregulates hippocampal expression of the adhesion molecules NCAM and CHL1 in mice by mechanisms independent of DNA methylation of their promoters

Stress is an important physiological regulator of brain function in young and adult mammals. The mechanisms underlying regulation of the consequences of stress, and in particular severe chronic stress, are thus important to investigate. These consequences most likely involve changes in synaptic function of brain areas being part of neural networks that regulate responses to stress. Cell adhesion molecules have been shown to regulate synaptic function in the adult and we were thus interested to investigate a regulatory mechanism that could influence expression of three adhesion molecules of the immunoglobulin superfamily (NCAM, L1 and CHL1) after exposure of early postnatal and adult mice to repeated stress. We hypothesized that reduction of adhesion molecule expression after chronic stress, as observed previously in vivo, could be due to gene silencing of the three molecules by DNA methylation. Although adhesion molecule expression was reduced after exposure of C57BL/6 mice to stress, thus validating our stress paradigm as imposing changes in adhesion molecule expression, we did not observe differences in methylation of CpG islands in the promoter regions of NCAM, L1 and CHL1, nor in the promoter region of the glucocorticoid receptor in the hippocampus, the expression of which at the protein level was also reduced after stress. We must therefore infer that severe stress in mice of the C57BL/6 strain downregulates adhesion molecule levels by mechanisms that do not relate to DNA methylation.