Flattening the corticosterone rhythm attenuates 5-HT1A autoreceptor function in the rat: relevance for depression

Rosemary (Rosmarinus officinalis L.) hydrosol based on serotonergic synapse for insomnia

ETHNOPHARMACOLOGICAL RELEVANCE

Rosemary (Rosmarinus officinalis L.) has been widely used as a traditional remedy for insomnia, depression and anxiety in China and Western countries. Modern pharmacological studies have shown that rosemary has important applications in neurological disorders. However, the mechanism of action of rosemary hydrosol in the treatment of insomnia is not known.

AIMS OF THE STUDY

Insomnia is closely linked to anxiety and depression, and its pathogenesis is related to biology, psychology, and sociology. Rosemary is a natural plant that has been used to treat insomnia and depression and has good biological activity, but its material basis and mechanism for the treatment of insomnia are not clear. Here, we report on the role of aqueous extracts of rosemary in the treatment of insomnia.

MATERIALS AND METHODS

The study was based on network pharmacology, using a combination of RNA-sequencing, "quantity-effect" weighting coefficients, and pharmacodynamic experiments. DL-4-chlorophenylalanine (PCPA) was intraperitoneally injected into SD rats to replicate the insomnia model with a blank, model, diazepam, and rosemary hydrosol low-, medium-, and high-dose groups were set up for the experiment. The key pathways in the treatment of insomnia with rosemary hydrosol were analyzed by molecular docking, open field assay, ELISA, western-Blot, Rt-PCR, and immunohistochemical assay.

RESULTS

Rosemary hydrosol was analyzed by GC-MS to identify 19 components. 1579 differential genes were obtained by RNA-Seq analysis, 533 targets for rosemary hydrosol and 2705 targets for insomnia, and 29 key targets were obtained by intersection. The KEGG results were ranked by "quantity-effect" weighting coefficients, resulting in serotonergic synapse was the key pathway for the treatment of insomnia with rosemary hydrosol. Molecular docking results showed that 1,7,7-trimethylbicyclo[2.2.1] heptan-2-one, 3-methyl-4-isopropylphenol, caryophyllene, and citronellol of rosemary hydrosol acted synergistically to achieve a therapeutic effect on insomnia. Caryophyllene acts on the HTR1A target by upregulating 5-HT1AR, leading to increased 5-HT release, and upregulation of ADCY5, cAMP, PKA and GABAA at serotonergic synapses; citronellol upregulated ADCY5 and 1,7,7-trimethylbicyclo[2.2.1] heptan-2-one, and 3-methyl-4-isopropylphenol up-regulated GABAA to improve insomnia symptoms. In open-field experiments, ELISA kits (5-HT, GABA, and DA), Western-blotting, Rt-PCR and immunohistochemical assay experiments, insomnia rats in the low-, medium- and high-dose groups of rosemary hydrosol showed different degrees of improvement compared with the model group.

CONCLUSIONS

It was shown that rosemary hydrosol may exert its therapeutic effects on insomnia through serotonergic synapses by combining RNA-Seq, "quantity-effect" weighting coefficients network pharmacology and pharmacodynamic experiments. We have provided a preliminary theoretical study for the development of rosemary hydrosol additive into a beverage for the treatment of insomnia, but it needs to be studied in depth. This study was conducted in rats and the results have limitations and may not apply to humans.

Hidden variables in stress neurobiology research

Among the central goals of stress neurobiology research is to understand the mechanisms by which stressors change neural circuit function to precipitate or exacerbate psychiatric symptoms. Yet despite decades of effort, psychiatric medications that target the biological substrates of the stress response are largely lacking. We propose that the clinical advancement of stress response-based therapeutics for psychiatric disorders may be hindered by 'hidden variables' in stress research, including considerations of behavioral study design (stressors and outcome measures), individual variability, sex differences, and the interaction of the body's stress hormone system with endogenous circadian and ultradian rhythms. We highlight key issues and suggest ways forward in stress neurobiology research that may improve the ability to assess stress mechanisms and translate preclinical findings.

Chronically dysregulated corticosterone impairs dopaminergic transmission in the dorsomedial striatum by sex-divergent mechanisms

Major depressive disorder (MDD) is a leading cause of disability worldwide. Individuals with MDD exhibit decreased motivation and deficits in reward processing. In a subset of MDD patients, chronic dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis occurs, resulting in increased levels of the 'stress hormone' cortisol during the normal rest period (i.e., evening and night). However, the mechanistic relationship between chronically elevated resting cortisol and behavioral deficits in motivation and reward processing remains unclear. Given that women are diagnosed with MDD at twice the rate of men, it is important to understand whether the mechanisms linking cortisol to the symptoms of MDD differ by sex. In this study, we used subcutaneous implants to chronically elevate free plasma corticosterone (the rodent homolog of cortisol; 'CORT') during the rest period in male and female mice and examined changes in behavior and dopamine system function. We found that chronic CORT treatment impaired motivated reward-seeking in both sexes. In female but not male mice, CORT treatment reduced dopamine content in the dorsomedial striatum (DMS). In male but not female mice, CORT treatment impaired the function of the dopamine transporter (DAT) in DMS. From these studies, we conclude that chronic CORT dysregulation impairs motivation by impairing dopaminergic transmission in the DMS, but via different mechanisms in male and female mice. A better understanding of these sex-specific mechanisms could lead to new directions in MDD diagnosis and treatment.

Potential antidepressant effects of a dietary supplement from the chlorella and lion's mane mushroom complex in aged SAMP8 mice

Since the 1990s, the prevalence of mental illnesses, such as depression, has been increasing annually and has become a major burden on society. Due to the many side effects of antidepressant drugs, the development of a complementary therapy from natural materials is an urgent need. Therefore, this study used a complex extract of chlorella and lion's mane mushroom and evaluated its antidepressant effects. Six-month-old male senescence-accelerated mice prone-8 (SAMP8) were divided into positive control; negative control; and low, medium, and high-dose groups. All groups were treated with corticosterone (CORT) at 40 mg/Kg/day for 21- days to induce depression in the animals, and the effects of different test substances on animal behavior was observed. The positive control group was intraperitoneally injected with a tricyclic antidepressant (Fluoxetine, as tricyclic antidepressant), the control group was given ddH₂O, and the test substance groups were administered test samples once daily for 21 days. The open field test (OFT) and forced swimming test (FST) were applied for behavior analyses of depression animal models. The OFT results showed that the mice in the positive control and the medium-, and high-dose groups demonstrated a significantly prolonged duration in the central area and a significantly increased travel distance. In the FST, the positive control and the medium, and high-dose groups displayed significantly reduced immobility times relative to the control group. The blood analysis results showed significant decreases in triglyceride and blood urea nitrogen levels relative to the positive control and the medium- and high-dose groups. Notably, in the positive control and the medium- and high-dose groups, brain-derived neurotrophic factor (BDNF) increase by more than in the control group. In summary, medium and high dose of extract of chlorella and lion's mane mushroom could improve depression behavior in animals and have the potential to be antidepressant health care products.

Additive serotonergic genetic sensitivity and cortisol reactivity to lab-based social evaluative stress: Influence of severity across two samples

Prior work demonstrates that an additive serotonergic multilocus genetic profile score (MGPS) predicts amplified risk for depression following significant life stress, and that it interacts with elevations in the cortisol awakening response to predict depression. The serotonin system and HPA-axis have bidirectional influence, but whether this MGPS predicts acute cortisol reactivity, which might then serve as a mechanism for depression, is unknown. Our prior work suggests that depression risk factors predict blunted cortisol reactivity to explicit negative evaluative lab-based stress. Thus, we hypothesized that a 4-variant serotonergic MGPS (three SNPs from the original 5-variant version plus 5HTTLPR) would predict blunted cortisol reactivity to explicit negative evaluative stress versus a control. In Sample 1, growth curve modeling showed that the MGPS predicted heightened cortisol reactivity (p = 0.0001) in an explicitly negative evaluative Trier Social Stress Test variant (TSST) versus a control condition among non-depressed emerging adults (N = 152; 57% female). In Sample 2, 125 males completed the Socially Evaluative Cold Pressor Test (SECPT), an ambiguously negative evaluative manipulation; findings displayed a similar pattern but did not reach statistical significance (ps.075-.091). A participant-level meta-analysis of the two samples demonstrated a significant effect of negative evaluation severity, such that the MGPS effect size on reactivity increased linearly from control to SECPT to an explicitly negative evaluative TSST. Findings indicate that this MGPS contributes to sensitivity to social threat and that cortisol dysregulation in the context of social stress may be one mechanism by which this MGPS contributes to depression.

Male long-Evans rats: An outbred model of marked hypothalamic-pituitary-adrenal hyperactivity

Rat and mouse strains differ in behavioral and physiological characteristics, and such differences can contribute to explain discrepant results between laboratories and better select the most appropriate strain for a particular purpose. Differences in the activity of the hypothalamic-pituitary-adrenal (HPA) axis are particularly important given the pivotal role of this system in determining consequences of exposure to stressors. In this regard, Long-Evans (LE) rats are widely used in stress research, but there is no specific study aiming at thoroughly characterizing HPA activity in LE versus other extensively used strains. In a first experiment, LE showed higher resting ACTH and corticosterone levels only at certain points of the circadian rhythm, but much greater ACTH responsiveness to stressors (novel environment and forced swim) than Sprague-Dawley (SD) rats. Accordingly, enhanced corticotropin-releasing hormone (CRH) expression in the paraventricular nucleus of the hypothalamus and reduced expression of glucocorticoid receptors were observed in the hippocampal formation. Additionally, they are hyperactive in novel environments, and prone to adopt passive-like behavior when compared to SD rats. Supporting that altered HPA function has a marked physiological impact, we observed in another set of animals much lower thymus weight in LE than SD rats. Finally, to demonstrate that LE rats are likely to have higher HPA responsiveness to stressors than most strains, we studied resting and stress levels of HPA hormones in LE versus Wistar and Fischer rats, the latter considered an example of high HPA responsiveness. Again, LE showed higher resting and stress levels of ACTH than both Wistar and Fischer rats. As ACTH responsiveness to stressors in LE rats is stronger than that previously reported when comparing other rat strains and they are commercially available, they could be an appropriate model for studying the behavioral and physiological implications of a hyper-active HPA axis under normal and pathological conditions.

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Strain differences in hypothalamic-pituitary-adrenal (HPA) function were studied.

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Long-Evans (LE) rats show greater HPA response to stressors than other strains.

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CRH expression in critical brain areas is greater in LE than Sprague-Dawley (SD) rats.

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Glucocorticoid receptor expression was lower in the hippocampal formation of LE rats.

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LE rats are more active in novel environments but showed more passive coping.

Epilepsy Associated Depression: An Update on Current Scenario, Suggested Mechanisms, and Opportunities

Depression is one of the most frequent psychiatric comorbidities associated with epilepsy having a major impact on the patient's quality of life. Several screening tools are available to identify and follow up psychiatric disorders in epilepsy. Out of various psychiatric disorders, people with epilepsy (PWE) are at greater risk of developing depression. This bidirectional relationship further hinders pharmacotherapy of comorbid depression in PWE as some antiepileptic drugs (AEDs) worsen associated depression and coadministration of existing antidepressants (ADs) to alleviate comorbid depression has been reported to worsen seizures. Selective serotonin reuptake inhibitors (SSRIs) and selective serotonin and norepinephrine reuptake inhibitors (SNRIs) are first choice of ADs and are considered safe in PWE, but there are no high-quality evidences. Similar to observations in people with depression, PWE also showed pharmacoresistant to available SSRI/SNRIs, which further complicates the disease prognosis. Randomized double-blind placebo-controlled clinical trials are necessary to report efficacy and safety of available ADs in PWE. We should also move beyond ADs, and therefore, we reviewed common pathological mechanisms such as neuroinflammation, dysregulated hypothalamus pituitary adrenal (HPA) axis, altered neurogenesis, and altered tryptophan metabolism responsible for coexistent relationship of epilepsy and depression. Based on these common pertinent pathways involved in the genesis of epilepsy and depression, we suggested novel targets and therapeutic approaches for safe management of comorbid depression in epilepsy.

Corticosterone-induced Hippocampal 5-HT Responses were Muted in Depressive-like State

Interactions between the hypothalamic-pituitary-adrenal axis and the central 5-HT system in the depressive state remain largely unknown. The present study investigated corticosterone (CORT) regulations of extracellular 5-HT in the hippocampal CA3 in a mouse model of depression. Basal dialysate 5-HT, true extracellular 5-HT, 5-HT reuptake efficiency, and time courses of dialysate 5-HT following CORT injections at 10, 20, and 40 mg/kg were determined at baseline, depressive-like state and after subsequent fluoxetine (FLX) treatment using in vivo microdialysis in male C57BL/6 mice. Behavioral tests were used to determine behavioral phenotypes and therapeutic responses to FLX. Depressed mice showed decreased extracellular 5-HT, increased 5-HT reuptake efficiency, and absence of the increase in dialysate 5-HT response to CORT injections, which were all reversed in FLX-responsive mice. Surprisingly, the FLX nonresponsive mice continued to worsen behaviorally and exhibited lower extracellular 5-HT and higher 5-HT reuptake efficiency. Our study indicates that abolished-CORT induced 5-HT response, decreased extracellular 5-HT, and increased 5-HT reuptake efficiency might be the signature features associated with depressive-like state. Increased 5-HT reuptake efficiency was one of the underlying mechanisms, with target effectors remaining to be explored. The findings in the FLX nonresponsive mice suggest distinct neuromechanisms, which might be genetically predetermined.

Glucocorticoids in the Physiological and Transcriptional Regulation of 5-HT1A Receptor and the Pathogenesis of Depression

There is growing increase in the global prevalence of depression, but treatment outcome of this highly disabling disease is not satisfactory. Many patients are not benefitted by the currently prescribed antidepressants-together with this partial remission is very common. Improving treatment strategies and developing better therapeutic agents for treating depression is therefore highly needed. Stress-related epigenetic changes play a critical role in the pathogenesis as well as treatment of depression. Stressful events activate hypothalamic-pituitary-adrenal axis to increase circulating levels of glucocorticoids (GCs), and a greater sensitivity to this fright and flight response increases risk of depression. A role of serotonin (5-hydroxytryptamine; 5-HT) in responses to stress and in the pathogenesis and treatment of depression is well established. Substantial evidence supports a critical role of 5-HT1A receptors in these effects of 5-HT. The present article targets stress-induced higher and sustained increases of GCs and mediated influences on the physiological as well transcriptional regulation of 5-HT1A receptors to evaluate their causal role in the pathogenesis of depression. It is suggested that synthetic compounds with antagonist activity for GC receptors and agonist activity for 5-HT1A receptors may prove better therapeutic agents for treating depression.

Chronic fluoxetine reverses the effects of chronic corticosterone treatment on α2-adrenoceptors in the rat frontal cortex but not locus coeruleus

Disruption of the hypothalamic-pituitary-adrenal axis is an established finding in patients with anxiety and/or depression. Chronic corticosterone administration in animals has been proposed as a model for the study of these stress-related disorders and the antidepressant action. Alterations of the central noradrenergic system and specifically of inhibitory α₂-adrenoceptors seem to be part of the pathophysiology of depression and contribute to the antidepressant activity. The present study evaluates in male rats the effect of chronic corticosterone treatment during 35 days (16-20 mg kg^-1 day^-1) on the sensitivity of α₂-adrenoceptors expressed in the somatodendritic and terminal noradrenergic areas locus coeruleus (LC) and prefrontal cortex (PFC), respectively. Further, the effect of chronic fluoxetine treatment (5 mg kg^-1, i.p., since the 15th day) on the sensitivity of α₂-adrenoceptors was examined under control conditions and in corticosterone-treated rats. The α₂-adrenoceptor functionality was analysed in vitro by agonist-mediated [³⁵S]GTPγS binding stimulation and in vivo through the modulation of noradrenaline (NA) release evaluated by dual-probe microdialysis. The concentration-effect curves of the [³⁵S]GTPγS binding stimulation by the agonist UK14304 (5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine) demonstrated a desensitization of cortical α₂-adrenoceptors induced by corticosterone (-logEC₅₀ = 6.7 ± 0.2 vs 8.2 ± 0.3 in controls) that was reverted by fluoxetine treatment (-logEC₅₀ = 7.5 ± 0.3). Local administration of the α₂-adrenoceptor antagonist RS79948 ((8aR,12aS,13aS)-5,8,8a,9,10,11,12,12a,13,13a-decahydro-3-methoxy-12-(ethylsulfonyl)-6H-isoquino[2,1-g][1,6]naphthyridine) (0.1-100 μmol L^-1) into the LC induced a concentration-dependent NA increase in the PFC of the control group (E_max = 191 ± 30%) but non-significant effect was observed in corticosterone-treated rats (E_max = 133 ± 46%), reflecting a desensitization of α₂-adrenoceptors that control the firing of noradrenergic neurons. Fluoxetine treatment did not alter the corticosterone-induced desensitization in this area (E_max = 136 ± 19%). No effect of fluoxetine on α₂-adrenoceptor functionality was observed in control animals (E_max = 223 ± 30%). In PFC, the local administration of RS79948 increased NA in controls (E_max = 226 ± 27%) without effect in the corticosterone group (E_max = 115 ± 26%), suggesting a corticosterone-induced desensitization of terminal α₂-adrenoceptors. Fluoxetine administration prevented the desensitization induced by corticosterone in the PFC (E_max = 233 ± 33%) whereas desensitized α₂-adrenoceptors in control animals (E_max = -24 ± 10%). These data indicate that chronic corticosterone increases noradrenergic activity by acting at different α₂-adrenoceptor subpopulations. Treatment with the antidepressant fluoxetine seems to counteract these changes by acting mainly on presynaptic α₂-adrenoceptors expressed in terminal areas.

Cortisol awakening response and additive serotonergic genetic risk interactively predict depression in two samples: The 2019 Donald F. Klein Early Career Investigator Award Paper

BACKGROUND

The serotonin system and hypothalamic pituitary-adrenal (HPA)-axis are each implicated in the pathway to depression; human and animal research support these systems' cross-talk. Our work implicates a 5-variant additive serotoninergic multilocus genetic profile score (MGPS) and separately the cortisol awakening response (CAR) in the prospective prediction of depression; other work has shown that the serotonin transporter polymorphism 5HTTLPR predicts CAR and interacts with the CAR to predict depression.

METHODS

We tested the hypothesis that a 6-variant MGPS (original plus 5HTTLPR) would interact with CAR to predict prospective depressive episode onsets in 201 emerging adults using four annual follow-up interviews. We also tested whether MGPS predicted CAR. We attempted replication of significant findings in a sample of 77 early adolescents predicting depression symptoms.

RESULTS

In sample 1, MGPS did not significantly predict CAR. MGPS interacted with CAR to predict depressive episodes; CAR slopes for depression steepened as MGPS increased, for risk or protection. No single variant accounted for results, though CAR's interactions with 5HTTLPR and the original MGPS were both significant. In sample 2, the 6-variant MGPS significantly interacted with CAR to predict depression symptoms.

CONCLUSIONS

Higher serotonergic MGPS appears to sensitize individuals to CAR level-for better and worse-in predicting depression.

Antidepressant-like activities of live and heat-killed Lactobacillus paracasei PS23 in chronic corticosterone-treated mice and possible mechanisms

Emerging evidence indicates that ingestion of specific probiotics, known as "psychobiotics", confer beneficial effects on mental health. This study investigated antidepressant-like effects and possible underlying mechanisms of Lactobacillus paracasei PS23 (PS23), live or heat-killed, in a mouse model of corticosterone-induced depression using fluoxetine as standard drug. PS23 were orally gavaged to mice from day 1 to 41 or fluoxetine from day 17 to 41 and injected with corticosterone from day 17 to 37. After the last corticosterone treatment, anxiety- and depression-like behaviors were tested within 4 days. On day 42, serum and brain tissue were collected 24 min after forced swim stress. Abnormal behavioral changes induced by corticosterone were ameliorated by treatment with live PS23 in open field and sucrose preference tests, with heat-killed PS23 in open field, forced swim and sucrose preference tests, and with fluoxetine in open field and forced swim tests. Furthermore, both live and heat-killed PS23 and fluoxetine reversed corticosterone-reduced protein levels of brain-derived neurotropic factor, mineralocorticoid, and glucocorticoid receptors in the hippocampus. In addition, live PS23 also reverses corticosterone-reduced serotonin levels in hippocampus, prefrontal cortex and striatum; whereas heat-killed PS23 reverses corticosterone-reduced dopamine levels in hippocampus and prefrontal cortex. And fluoxetine normalized reduced corticosterone level in serum. These studies showed that both live and heat-killed PS23 can reverse chronic corticosterone-induced anxiety- and depression-like behaviors and that may provide insights into the mechanism and a potential psychobiotic for depression management.

The 5-HT7 receptor antagonist SB 269970 ameliorates corticosterone-induced alterations in 5-HT7 receptor-mediated modulation of GABAergic transmission in the rat dorsal raphe nucleus

RATIONALE

Chronic stress and corticosterone have been shown to affect serotonin (5-HT) neurotransmission; however, the influence of stress on the activity of the dorsal raphe nucleus (DRN), the main source of 5-HT in the forebrain, is not well understood. In particular, it is unknown if and how stress modifies DRN 5-HT₇ receptors, which are involved in the modulation of the firing of local inhibitory interneurons responsible for regulating the activity of DRN projection cells.

OBJECTIVES

Our study aimed to investigate the effect of repeated corticosterone injections on the modulation of the inhibitory transmission within the DRN by 5-HT₇ receptors and whether it could be reversed by treatment with a 5-HT₇ receptor antagonist.

METHODS

Male Wistar rats received corticosterone injections repeated twice daily for 14 days. Spontaneous inhibitory postsynaptic currents (sIPSCs) were then recorded from DRN projection cells in ex vivo slice preparations obtained 24 h after the last injection.

RESULTS

Repeated corticosterone administration resulted in decreased frequency, but not amplitude, of sIPSCs in DRN projection cells. There were no changes in the excitability of these cells; however, corticosterone treatment suppressed the 5-HT₇ receptor-mediated increase in sIPSC frequency. Administration of the 5-HT₇ receptor antagonist SB 269970 for 7 days beginning on the eighth day of corticosterone treatment reversed the detrimental effects of corticosterone on 5-HT₇ receptor reactivity and GABAergic transmission in the DRN.

CONCLUSIONS

Elevated corticosterone level reduces DRN 5HT₇ receptor reactivity and decreases GABAergic transmission within the DRN, which can be reversed by the 5-HT₇ receptor antagonist SB 269970.

Treadmill exercise alleviates depressive symptoms in rotenone-induced Parkinson disease rats

Parkinson disease (PD) is characterized by selective loss of the dopaminergic neurons. The symptoms of depression following PD are closely associated with reduced activity of the serotonergic system in the dorsal raphe. We explored the antidepressive effect of exercise and its possible mechanism using the rotenone-induced PD rats. PD rats were induced by subcutaneously injection with rotenone for 14 days. The rats in the exercise groups were made to run on a treadmill for 30 min once a day during 14 consecutive days. Forced swimming test, immunohistochemistry for serotonin (5-hydroxytryptamine, 5-HT), tryptophan hydroxylase (TPH), and western blot for serotonin 1A (5-HT1A) receptor were conducted. Injection of rotenone induced PD rats. PD rats showed depressive state and treadmill exercise ameliorated this depressive state. 5-HT, TPH, and 5-HT1A receptor expressions in the dorsal raphe were suppressed by rotenone injection and treadmill exercise increased the expressions of 5-HT, TPH, and 5-HT1A receptor in the rotenone-injected rats. The present results show that treadmill exercise ameliorated depressive symptoms in the rotenone-induced PD rats. The antidepressive effect of treadmill exercise might be ascribed to the enhancement of serotonergic function through upregulation of 5-HT1A expression in the dorsal raphe.

Effect of subchronic corticosterone administration on α2-adrenoceptor functionality in rat brain: an in vivo and in vitro study

RATIONALE

Noradrenergic system plays a critical role in the hypothalamic-pituitary-adrenal (HPA) axis regulation and the stress response. A dysregulated HPA axis may be indicative of an increased biological vulnerability for depression. In addition, a variety of studies have focused on specific alterations of α₂-adrenoceptors as a mechanism involved in the pathogenesis of mood disorders and antidepressant response.

OBJECTIVES

This study aimed to evaluate the effect of subchronic corticosterone administration on rat brain α₂-adrenoceptor functionality by in vitro [³⁵S]GTPγS binding stimulation assays and in vivo dual-probe microdialysis determination of extracellular noradrenaline concentrations.

RESULTS

Implantation of a time release corticosterone pellet during 14 days induced sustained changes in endocrine function. However, there were no differences in α₂-adrenoceptor agonist UK14304-induced stimulation of [³⁵S]GTPγS binding in prefrontal cortex (PFC) between corticosterone-treated and control rats. In the same way, the in vivo evaluation of α₂-adrenoceptor-mediated noradrenaline release responses to the α₂-adrenoceptor agonist clonidine local administration into the locus coeruleus (LC), and the PFC did not show differences between the groups.

CONCLUSIONS

The present results show that subchronic corticosterone administration does not induce changes on functionality of α₂-adrenoceptors neither in the LC nor in noradrenergic cortical terminal areas.

Corticosterone exposure augments sensitivity to the behavioral and neuroplastic effects of fluoxetine in C57BL/6 mice

Both genetic background and pre-existing stress play critical roles in the effects of antidepressant drugs. The current studies showed this principal by demonstrating that exposure to the stress hormone corticosterone (CORT) allowed behavioral and neurogenic effects to emerge following chronic treatment with fluoxetine of C57BL/6 mice, a strain ordinarily resistant to these effects. Adult male mice were implanted subcutaneously with 21-day slow-release CORT pellets (10 mg) or placebo and then co-treated with 5 mg/kg fluoxetine (b.i.d., i.p.) or saline for 14 days. Animals were then assessed for approach behavior in the novelty-induced hypophagia (NIH) test, hippocampal cell proliferation, corticosteroid receptor expression, and CORT plasma levels. Co-treatment of CORT with fluoxetine significantly reduced approach behavior in the novel environment of the NIH test and increased hippocampal cell proliferation whereas fluoxetine given alone was ineffective. CORT given alone did not alter approach behavior in the novel environment and caused a smaller increase of cell proliferation. The CORT effect was blocked by adrenalectomy and was likely due to increased adrenal feedback. Cell proliferation in CORT-treated animals was associated with reduced mineralocorticoid, but not glucocorticoid, receptor mRNA expression. Although the pellets were advertised to release CORT for 21 days, plasma CORT levels were increased at 1 day after implantation but were not sustained when measured at 7 days or longer intervals. Nevertheless, the transient CORT increase was sufficient to induce long-lasting behavioral and molecular changes when followed by fluoxetine treatment. These studies warrant further investigation into the role of glucocorticoids and environmental stress as adjunctive facilitators of the response to antidepressants, especially for treatment-resistant patients.

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C57BL/6J mice are not responsive to behavioral and neurogenic effects of chronic fluoxetine.

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CORT reduced anxiogenic behavior, increased hippocampal neurogenesis in response to fluoxetine.

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CORT pellets are not effective in sustaining elevated plasma CORT levels.

Antidepressant-Like Effects of Sanggenon G, Isolated from the Root Bark of Morus alba, in Rats: Involvement of the Serotonergic System

The root bark of Morus alba is commonly used as an alternative medicine due to its numerous health benefits in humans. However, the antidepressant effects of various active components from M. alba have not been fully elucidated. In this study, we aimed to determine whether sanggenon G, an active compound isolated from the root bark of M. alba, exhibited antidepressant-like activity in rats subjected to forced swim test (FST)-induced depression. Acute treatment of rats with sanggenon G (30 mg/kg, intraperitoneally (i.p.)) significantly reduced immobility time and increased swimming time without any significant change in climbing. Rats treated with sanggenon G also exhibited a decrease in the limbic hypothalamic-pituitary-adrenal (HPA) axis response to the FST, as indicated by attenuation of the corticosterone response and decreased c-Fos immunoreactivity in the hypothalamic paraventricular nucleus (PVN). In addition, the antidepressant-like effects of sanggenon G were significantly inhibited by WAY100635 (1 mg/kg, i.p.; a selective 5-hydroxytryptamine1A (5-HT1A) receptor antagonist), but not SCH23390 (0.05 mg/kg, i.p.; a dopamine D1 receptor antagonist). Our findings suggested that the antidepressant-like effects of sanggenon G were mediated by an interaction with the serotonergic system. Further studies are needed to evaluate the potential of sanggenon G as an alternative therapeutic approach for the treatment of depression.

Study protocol for the randomised controlled trial: antiglucocorticoid augmentation of anti-Depressants in Depression (The ADD Study)

BACKGROUND

Some patients with depression do not respond to first and second line conventional antidepressants and are therefore characterised as suffering from treatment refractory depression (TRD). On-going psychosocial stress and dysfunction of the hypothalamic-pituitary-adrenal axis are both associated with an attenuated clinical response to antidepressants. Preclinical data shows that co-administration of corticosteroids leads to a reduction in the ability of selective serotonin reuptake inhibitors to increase forebrain 5-hydroxytryptamine, while co-administration of antiglucocorticoids has the opposite effect. A Cochrane review suggests that antiglucocorticoid augmentation of antidepressants may be effective in treating TRD and includes a pilot study of the cortisol synthesis inhibitor, metyrapone. The Antiglucocorticoid augmentation of anti-Depressants in Depression (The ADD Study) is a multicentre randomised placebo controlled trial of metyrapone augmentation of serotonergic antidepressants in a large population of patients with TRD in the UK National Health Service.

METHODS/DESIGN

Patients with moderate to severe treatment refractory Major Depression aged 18 to 65 will be randomised to metyrapone 500 mg twice daily or placebo for three weeks, in addition to on-going conventional serotonergic antidepressants. The primary outcome will be improvement in Montgomery-Åsberg Depression Rating Scale score five weeks after randomisation (i.e. two weeks after trial medication discontinuation). Secondary outcomes will include the degree of persistence of treatment effect for up to 6 months, improvements in quality of life and also safety and tolerability of metyrapone. The ADD Study will also include a range of sub-studies investigating the potential mechanism of action of metyrapone.

DISCUSSION

Strengths of the ADD study include broad inclusion criteria meaning that the sample will be representative of patients with TRD treated within the UK National Health Service, longer follow up, which to our knowledge is longer than any previous study of antiglucocorticoid treatments in depression, and the range of mechanistic investigations being carried out. The data set acquired will be a rich resource for a range of research questions relating to both refractory depression and the use of antiglucocorticoid treatments.

TRIAL REGISTRATION

Current Controlled Trials: ISRCTN45338259; EudraCT Number: 2009-015165-31.

Mineralocorticoid receptor antagonist spironolactone prevents chronic corticosterone induced depression-like behavior

High level of serum corticosteroid is frequently associated with depression, in which a notable HPA (hypothalamus-pituitary-adrenal) axis hyperactivity is often observed. There are two types of corticosteroid receptors expressed in the hippocampus that provide potent negative feedback regulation on the HPA axis but dysfunction during depression, i.e. the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR). The balance between hippocampal MR and GR during chronic stress plays an important role in the occurrence of depression. The aim of this study is to explore if chronic corticosterone administration would induce depression-like behavior and affect the expression and function of hippocampal MR and GR, in addition to assess whether manipulation of corticosteroid receptors would modulate depressive behaviors. Hence, mice were treated with corticosterone (40 mg/kg) for 21 days followed by assessment in a battery of depression-like behaviors. The results show that chronic corticosterone-treated animals displayed an increased immobility time in a forced-swimming test, decreased preference to sucrose solution and novel object recognition performance, and enhanced hippocampal serotonin but decreased MR expression in both hippocampus and hypothalamus. On the other hand, co-administration of MR antagonist, spironolactone (25mg/kg, i.p. × 7 days) in corticosteroid-treated animals reduced immobility time in a forced-swimming test and improved performance in a novel object recognition test. In conclusion, we demonstrate that chronic corticosterone treatment triggers several depression-like behaviors, and in parallel, down-regulates MR expression in the hippocampus and hypothalamus. Administration of an MR antagonist confers an anti-depressant effect in chronic corticosterone-treated animals.

Transient increase in alcohol self-administration following a period of chronic exposure to corticosterone

Stressful life events and chronic stressors have been associated with escalations in alcohol drinking. Stress exposure leads to the secretion of glucocorticoids (cortisol in the human; corticosterone (CORT) in the rodent). To model a period of heightened elevations in CORT, the present work assessed the effects of chronic exposure to the stress hormone CORT on alcohol self-administration. Male Long Evans rats were trained to self-administer a sweetened alcohol solution (2% sucrose/15% alcohol) resulting in moderate levels of daily alcohol intake (0.5-0.7 g/kg). Following stable baseline operant self-administration, rats received CORT in the drinking water for 7 days. A transient increase in alcohol self-administration was observed on the first self-administration session following CORT exposure, and behavior returned to control levels by the second session. Control experiments determined that this increase in alcohol self-administration was specific to alcohol, unrelated to general motor activation, and functionally dissociated from decreased CORT levels at the time of testing. These results indicate that repeated exposure to heightened levels of stress hormone (e.g., as may be experienced during stressful episodes) has the potential to lead to exacerbated alcohol intake in low to moderate drinkers. Given that maladaptive drinking patterns, such as escalated alcohol drinking following stressful episodes, have the potential to put an individual at risk for future drinking disorders, utilization of this model will be important for examination of neuroadaptations that occur as a consequence of CORT exposure in order to better understand escalated drinking following stressful episodes in nondependent individuals.

Prolonged restraint stress increases IL-6, reduces IL-10, and causes persistent depressive-like behavior that is reversed by recombinant IL-10

Altered inflammatory cytokine profiles are often observed in individuals suffering from major depression. Recent clinical work reports on elevated IL-6 and decreased IL-10 in depression. Elevated IL-6 has served as a consistent biomarker of depression and IL-10 is proposed to influence depressive behavior through its ability to counterbalance pro-inflammatory cytokine expression. Clinical and animal studies suggest a role for IL-10 in modifying depressive behavior. Murine restraint stress (RST) is regularly employed in the study of behavioral and biological symptoms associated with depressive disorders. While responses to acute RST exposure have been widely characterized, few studies have examined the ongoing and longitudinal effects of extended RST and fewer still have examined the lasting impact during the post-stress period. Consistent with clinical data, we report that a protocol of prolonged murine RST produced altered cytokine profiles similar to those observed in major depressive disorder. Parallel to these changes in circulating cytokines, IL-10 mRNA expression was diminished in the cortex and hippocampus throughout the stress period and following cessation of RST. Moreover, chronic RST promoted depressive-like behavior throughout the 28-day stress period and these depressive-like complications were maintained weeks after cessation of RST. Because of the correlation between IL-10 suppression and depressive behavior and because many successful antidepressant therapies yield increases in IL-10, we examined the effects of IL-10 treatment on RST-induced behavioral changes. Behavioral deficits induced by RST were reversed by exogenous administration of recombinant IL-10. This work provides one of the first reports describing the biological and behavioral impact following prolonged RST and, taken together, this study provides details on the correlation between responses to chronic RST and those seen in depressive disorders.

Chronic effects of corticosterone on GIRK1-3 subunits and 5-HT1A receptor expression in rat brain and their reversal by concurrent fluoxetine treatment

Dysregulation of the serotonergic system and abnormalities of the hypothalamic-pituitary-adrenal axis have been demonstrated in major depression. Animal studies indicate that 5-HT1A receptor expression may be reduced by long-term administration of corticosterone. However, similar studies on the regulation of GIRK channels, one of the most important effectors of the neuronal 5-HT1A receptor, are limited. In order to address these issues, slow-release corticosterone pellets were implanted subcutaneously to adrenal intact male rats (200mg pellets, 35 days release). Starting on day 15, animals were treated for 21 days with fluoxetine (5mg/kg/day, i.p.), or vehicle. Using in situ hybridization histochemistry and receptor autoradiography, we found that chronic corticosterone treatment was accompanied by a significant decrease on the mRNAs coding for mineralocorticoid receptors in hippocampal areas. Under these conditions, 5-HT1A receptor mRNA expression decreased in dorsal raphe nucleus and dentate gyrus. However, 5-HT1A receptor levels, as measured by [(3)H]-8-OH-DPAT binding, diminished significantly only in dentate gyrus. It is noteworthy that chronic treatment with fluoxetine reversed the alterations on 5-HT1A receptor mRNA levels only in dorsal raphe. Finally, chronic corticosterone treatment produced an increase on the mRNA coding for the GIRK2 subunit in several hypothalamic and thalamic areas, which was reversed by fluoxetine. Measurements of cell density and volume of the granular layer of the dentate gyrus did not reveal significant changes after corticosterone or corticosterone plus fluoxetine treatments. These data are relevant for a better understanding of the differential regulation of pre- and postsynaptic 5-HT1A receptors by corticosterone flattened rhythm.

Changes in 5-HT1A receptor expression in the oculomotor nucleus in a rat model of post-traumatic stress disorder

Post-traumatic stress disorder (PTSD) is an anxiety disorder that develops after exposure to a life-threatening traumatic experience. Mental disorder appears after the traumatic stress incident and affects the movement of the eye muscle dominated by the oculomotor nucleus, an important nuclear group of the brainstem. It has been reported that dysfunction of the neurotransmitter 5-hydroxytryptamine (5-HT) can lead to the instability of the internal environment in response to stress and plays an important role in the pathology of PTSD and that the 5-HT1A receptor (5-HT1AR) is critically involved in regulating mood and anxiety levels. In this study, the 5-HT1AR expression in the oculomotor nucleus was examined in rats with single-prolonged stress (SPS), a well established post-traumatic stress disorder animal model. Our results show that the expression of 5-HT1AR in the oculomotor nucleus neurons gradually increased 1, 4, and 7 days after exposure to SPS in comparison to the normal control group, measured by immunohistochemistry, western blotting, and reverse transcription polymerase chain reaction (RT-PCR). The expression of 5-HT1AR reached its peak 7 days after the SPS exposure and then decreased 14 days after. There is also a change in the ultrastructure in the oculomotor nucleus neuron upon SPS treatment which was observed by transmission electron microscopy. These results suggest that SPS can induce a change of the 5-HT1AR expression in the oculomotor nucleus, which may be one of the molecular mechanisms that lead to PTSD.

Ingestion of theanine, an amino acid in tea, suppresses psychosocial stress in mice

The antistress effect of theanine (γ-glutamylethylamide), an amino acid in tea, was investigated using mice that were psychosocially stressed from a conflict among male mice in conditions of confrontational housing. Two male mice were housed in the same cage separated by a partition to establish a territorial imperative. When the partition was removed, the mice were co-housed confrontationally. As a marker for the stress response, changes in the adrenal gland were studied in comparison to group-housed control mice (six mice in a cage). Significant adrenal hypertrophy was observed in mice during confrontational housing, which was developed within 24 h and persisted for at least 1 week. The size of cells in the zona fasciculata of the adrenal gland, from which glucocorticoid is mainly secreted, increased (∼1.11-fold) in mice during confrontational housing, which was accompanied by a flattened diurnal rhythm of corticosterone and ACTH in blood. The ingestion of theanine (>5 μg ml(-1)) prior to confrontational housing significantly suppressed adrenal hypertrophy. An antidepressant, paroxetin, suppressed adrenal hypertrophy in a similar manner in mice during confrontational housing. In mice that ingested theanine, behavioural depression was also suppressed, and a diurnal rhythm of corticosterone and ACTH was observed, even in mice that were undergoing confrontational housing. Furthermore, the daily dose of theanine (40 μg ml(-1)) blocked the counteracting effects of caffeine (30 μg ml(-1)) and catechin (200 μg ml(-1)). The present study demonstrated that theanine prevents and relieves psychosocial stress through the modulation of hypothalamic-pituitary-adrenal axis activity.

5-HT(1A) receptor and apoptosis contribute to interferon-α-induced "depressive-like" behavior in mice

Interferon-α (IFN-α)-induced "depressive-like" behavior is a major limitation for the treatment of hepatitis C virus (HCV), especially for patients with psychiatric disorders. Recently, serotonin 1A (5-HT(1A)) receptor and cellular apoptosis are involved in mechanism(s) contributing to depression. To gain insight into this mechanism(s), we used C57BL/6J mice to examine the impact of IFN-α on the modulation of 5-HT(1A) receptor and cellular apoptosis and their relationship. Our results showed that repeated administration of IFN-α (6 MIU/kg, s.c.) induced "depressive-like" behavior of mice in the forced swim test, tail suspension test and sucrose preference test. Besides, the depressive mice exhibited a notable downregulation of 5-HT(1A) receptor and upregulation of cleaved caspase-3 and Bax/Bcl-2 ratio. These changes could be blocked by the 5-HT(1A) receptor agonist 8-OH-DPAT (0.5 mg/kg, i.p., 30 min before IFN-α administration), but not by the standard antidepressant imipramine (10 mg/kg, i.p., 30 min before IFN-α administration) although both of them could ameliorate the depressive-like behavior of mice. These findings indicated that repeated injection with IFN-α provoked "depressive-like" behavior through cellular apoptosis, which could be ameliorated by the activation of 5-HT(1A) receptor.

Pre-gestational stress reduces the ratio of 5-HIAA to 5-HT and the expression of 5-HT1A receptor and serotonin transporter in the brain of foetal rat

Background

Many studies have found that stress before or during pregnancy is linked to an increased incidence of behavioural disorders in offspring. However, few studies have investigated hypothalamic-pituitary-adrenal (HPA) axis activity and the serotonergic system as a consequence of pregestational stress. In the present study, we investigated the effect of pre-gestational stress on HPA axis activity in maternal rats and their foetuses and examined whether changes in HPA axis activity of maternal rats produced functional changes in the serotonergic system in the brain of foetuses.

Results

We used the behavioural tests to assess the model of chronic unpredictable stress (CUS) in maternal rats. We found the activity in the open field and sucrose consumption was lower for rats with CUS than for the controls. Body weight but not brain weight was higher for control foetuses than those from the CUS group. Serum corticosterone and corticotrophin-releasing hormone levels were significantly higher for mothers with CUS before pregnancy and their foetuses than for the controls. Levels of 5-hydroxytryptamine (5-HT) were higher in the hippocampus and hypothalamus of foetuses in the CUS group than in the controls, and 5-hydroxyindoleacetic acid (5-HIAA) levels were lower in the hippocampus in foetuses in the CUS group than in the control group. Levels of 5-HIAA in the hypothalamus did not differ between foetuses in the CUS group and in the control group. The ratio of 5-HIAA to 5-HT was significantly lower for foetuses in the CUS group than in the control group. Levels of 5-HT1A receptor were significantly lower in the foetal hippocampus in the CUS group than in the control group, with no significant difference in the hypothalamus. The levels of serotonin transporter (SERT) were lower in both the foetal hippocampus and foetal hypothalamus in the CUS group than in the control group.

Conclusions

Our data demonstrate that pre-gestational stress alters HPA axis activity in maternal rats and their foetuses, which is associated with functional changes in 5-HT activity (5-HT, 5-HIAA and ratio of 5-HIAA to 5-HT), as well as the levels of the 5-HT1A receptor and SERT in the hippocampus and hypothalamus of foetuses.

Role for monoaminergic systems in the antidepressant-like effect of ethanol extracts from Hemerocallis citrina

ETHNOPHARMACOLOGICAL RELEVANCE

Hemerocallis citrina, a traditional herbal medicine, has been used for the improvement of emotions in Eastern-Asia countries.

AIM OF THE STUDY

Herein, we explored the antidepressant-like effect and its monoaminergic mechanism of the ethanol extracts from Hemerocallis citrina (HCE).

MATERIALS AND METHODS

Effect of HCE (90, 180 and 360 mg/kg, p.o.) on the immobility time was assessed in the mouse forced swim test (FST) and tail suspension test (TST), and locomotor activity was evaluated in the open-field test (OFT). Additionally, the monoamine neurotransmitters serotonin (5-HT), noradrenaline (NA) and dopamine (DA) levels involved in the antidepressant-like effect of HCE were also measured in the mice brain regions of frontal cortex and hippocampus.

RESULTS

HCE (90, 180 and 360 mg/kg, p.o.) administration significantly reduced the immobility time in both the FST and TST without accompanying changes in locomotor activity in the OFT. The pretreatment of mice with WAY 100635 (0.1 mg/kg, s.c., a 5-HT(1A) receptor antagonist), cyproheptadine (3 mg/kg, i.p., a 5-HT(2) receptor antagonist), prazosin (62.5 μg/kg, i.p., an α(1)-adrenoceptor antagonist), yohimbine (1 mg/kg, i.p., an α(2)-adrenoceptor antagonist), propranolol (5 mg/kg, i.p., a β-adrenoceptor antagonist) or sulpiride (50 mg/kg, i.p., a dopamine D(2) receptor antagonist), but not SCH23390 (0.05 mg/kg, s.c., a dopamine D(1) receptor antagonist) prevented the antidepressant-like effect of HCE (360 mg/kg, p.o.) in the TST. In addition, HCE enhanced 5-HT and NA levels in the frontal cortex and hippocampus as well as elevated DA levels in the frontal cortex.

CONCLUSION

The results indicate that the antidepressant-like effect of HCE is dependent on the serotonergic (5-HT(1A) and 5-HT(2) receptors), noradrenergic (α(1)-, α(2)- and β-adrenoceptors) and dopaminergic (D(2) receptor) systems as well as the elevation of 5-HT, NA and DA levels in the mouse brain.

The HPA axis modulates the CNS melanocortin control of liver triacylglyceride metabolism

The central melanocortin system regulates lipid metabolism in peripheral tissues such as white adipose tissue. Alterations in the activity of sympathetic nerves connecting hypothalamic cells expressing melanocortin 3/4 receptors (MC3/4R) with white adipocytes have been shown to partly mediate these effects. Interestingly, hypothalamic neurons producing corticotropin-releasing hormone and thyrotropin-releasing hormone co-express MC4R. Therefore we hypothesized that regulation of hypothalamo-pituitary adrenal (HPA) and hypothalamo-pituitary thyroid (HPT) axes activity by the central melanocortin system could contribute to its control of peripheral lipid metabolism. To test this hypothesis, we chronically infused rats intracerebroventricularly (i.c.v.) either with an MC3/4R antagonist (SHU9119), an MC3/4R agonist (MTII) or saline. Rats had been previously adrenalectomized (ADX) and supplemented daily with 1mg/kg corticosterone (s.c.), thyroidectomized (TDX) and supplemented daily with 10 μg/kgL-thyroxin (s.c.), or sham operated (SO). Blockade of MC3/4R signaling with SHU9119 increased food intake and body mass, irrespective of gland surgery. The increase in body mass was accompanied by higher epididymal white adipose tissue (eWAT) weight and higher mRNA content of lipogenic enzymes in eWAT. SHU9119 infusion increased triglyceride content in the liver of SO and TDX rats, but not in those of ADX rats. Concomitantly, mRNA expression of lipogenic enzymes in liver was increased in SO and TDX, but not in ADX rats. We conclude that the HPA and HPT axes do not play an essential role in mediating central melanocortinergic effects on white adipose tissue and liver lipid metabolism. However, while basal hepatic lipid metabolism does not depend on a functional HPA axis, the induction of hepatic lipogenesis due to central melanocortin system blockade does require a functional HPA axis.

Functional status of somatodendritic serotonin 1A autoreceptor after long-term treatment with fluoxetine in a mouse model of anxiety/depression based on repeated corticosterone administration

Most preclinical studies investigating the effects and the mechanism of action of antidepressants have been performed in naive rodents. This is inappropriate because antidepressants act on specific symptoms of the pathological condition, such as distress and anxiety. We have developed a mouse model of anxiety/depression based on addition of corticosterone to drinking water. This model is highly reproducible and easy to set up compared with unpredictable chronic mild stress. The serotonin 1A (5-HT(1A)) autoreceptor is known to play a role in mood disorders and their treatments. An increase in somatodendritic 5-HT(1A) autoreceptor density in the dorsal raphe (DR) attenuates the therapeutic activity of selective serotonin-reuptake inhibitors (SSRIs), whereas their functional desensitization promotes activation of brain serotonergic transmission, thereby representing an adaptive change relevant to their therapeutic effect. Here we assessed the effects of sustained administration of the SSRI fluoxetine on 5-HT(1A) autoreceptor sensitivity in mice administered with corticosterone. Fluoxetine attenuated hypothermia induced by the 5-HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin, decreased DR 5-HT neuronal activity, and decreased 5-HT release in both vehicle- and corticosterone-pretreated mice. However, such desensitization was more pronounced in corticosterone-pretreated mice. This change had an overall effect on serotonergic tone because we found a greater firing rate of 5-HT neurons associated with an enhancement of 5-HT outflow in the DR of corticosterone-pretreated mice in response to fluoxetine compared with the corresponding group of vehicle-pretreated mice. These results provide cellular explanations for the antidepressant effects produced by SSRIs in subjects with pathological conditions but not in naive animals or healthy volunteers.

Cysteamine attenuates the decreases in TrkB protein levels and the anxiety/depression-like behaviors in mice induced by corticosterone treatment

OBJECTIVE

Stress and glucocorticoid hormones, which are released into the circulation following stressful experiences, have been shown to contribute significantly to the manifestation of anxiety-like behaviors observed in many neuropsychiatric disorders. Brain-derived neurotrophic factor (BDNF) signaling through its receptor TrkB plays an important role in stress-mediated changes in structural as well as functional neuroplasticity. Studies designed to elucidate the mechanisms whereby TrkB signaling is regulated in chronic stress might provide valuable information for the development of new therapeutic strategies for several stress-related psychiatric disorders.

MATERIALS AND METHODS

We examined the potential of cysteamine, a neuroprotective compound to attenuate anxiety and depression like behaviors in a mouse model of anxiety/depression induced by chronic corticosterone exposure.

RESULTS

Cysteamine administration (150 mg/kg/day, through drinking water) for 21 days significantly ameliorated chronic corticosterone-induced decreases in TrkB protein levels in frontal cortex and hippocampus. Furthermore, cysteamine treatment reversed the anxiety and depression like behavioral abnormalities induced by chronic corticosterone treatment. Finally, mice deficient in TrkB, showed a reduced response to cysteamine in behavioral tests, suggesting that TrkB signaling plays an important role in the antidepressant effects of cysteamine.

CONCLUSIONS

The animal studies described here highlight the potential use of cysteamine as a novel therapeutic strategy for glucocorticoid-related symptoms of psychiatric disorders.

Long-term continuous corticosterone treatment decreases VEGF receptor-2 expression in frontal cortex

OBJECTIVE

Stress and increased glucocorticoid levels are associated with many neuropsychiatric disorders including schizophrenia and depression. Recently, the role of vascular endothelial factor receptor-2 (VEGFR2/Flk1) signaling has been implicated in stress-mediated neuroplasticity. However, the mechanism of regulation of VEGF/Flk1 signaling under long-term continuous glucocorticoid exposure has not been elucidated.

MATERIAL AND METHODS

We examined the possible effects of long-term continuous glucocorticoid exposure on VEGF/Flk1 signaling in cultured cortical neurons in vitro, mouse frontal cortex in vivo, and in post mortem human prefrontal cortex of both control and schizophrenia subjects.

RESULTS

We found that long-term continuous exposure to corticosterone (CORT, a natural glucocorticoid) reduced Flk1 protein levels both in vitro and in vivo. CORT treatment resulted in alterations in signaling molecules downstream to Flk1 such as PTEN, Akt and mTOR. We demonstrated that CORT-induced changes in Flk1 levels are mediated through glucocorticoid receptor (GR) and calcium. A significant reduction in Flk1-GR interaction was observed following CORT exposure. Interestingly, VEGF levels were increased in cortex, but decreased in serum following CORT treatment. Moreover, significant reductions in Flk1 and GR protein levels were found in postmortem prefrontal cortex samples from schizophrenia subjects.

CONCLUSIONS

The alterations in VEGF/Flk1 signaling following long-term continuous CORT exposure represents a molecular mechanism of the neurobiological effects of chronic stress.

Recovery from disrupted ultradian glucocorticoid rhythmicity reveals a dissociation between hormonal and behavioural stress responsiveness

Ultradian release of glucocorticoids is thought to be essential for homeostasis and health. Furthermore, deviation from this pulsatile release pattern is considered to compromise resilience to stress-related disease, even after hormone levels have normalised. In the present study, we investigate how constant exposure to different concentrations of corticosterone affects diurnal and ultradian pulsatility. The rate of recovery in pulsatile hypothalamic-pituitary-adrenal (HPA) activity after withdrawal of exogenous corticosterone is also examined. Finally, the behavioural and neuroendocrine responsiveness to an audiogenic stressor is studied. Adrenally intact male rats were subcutaneously implanted with vehicle, 40% or 100% corticosterone pellets for 7 days. The continuous release of corticosterone from these implants abolished diurnal and ultradian corticosterone variation, as measured with high-frequency automated blood sampling. Pellet removal on post-surgery day 8 allowed rapid recovery of endogenous rhythms in animals previously exposed to daily average concentrations (40%) but not after exposure to high concentrations (100%) of corticosterone. Behavioural and neuroendocrine responsiveness to stress was distinctly different between the treatment groups. Audiogenic stimulation 1 day after pellet removal resulted in a similar corticosterone response in animals previously exposed to 40% corticosterone or vehicle. The 40% pellet group, however, showed less and shorter behavioural activity (i.e. locomotion, risk assessment) to noise stress compared to 100% corticosterone and vehicle-treated animals. In conclusion, unlike the animals impanted with 100% corticosterone, we find that basal HPA axis activity in the 40% group, which had mean daily levels of circulating corticosterone in the physiological range, rapidly reverts to the characteristic pulsatile pattern of corticosterone secretion. Upon reinstatement of the ultradian rhythm, and despite the fact that these animals did not differ from controls in their response to noise stress, they did show substantial changes in their behavioural response to stress.

Metabotropic glutamate receptor 7: at the interface of cognition and emotion

Understanding the complex interaction between stress and genetics that leads to the manifestation of disorders such as depression, anxiety, and cognitive dysfunction is one of the key areas of research in modern neuroscience. Growing evidence suggests that the glutamatergic system may be a relevant therapeutic target for such disorders. Glutamate is the neurotransmitter at the vast majority of excitatory synapses in the brain, and metabotropic glutamate (mGlu) receptor subtypes (mGlu(1) receptor-mGlu(8) receptor) act as important pre- and postsynaptic regulators of neurotransmission in the central nervous system (CNS), providing a mechanism by which fast synaptic responses through ligand-gated cation channels can be fine-tuned. Thus mGlu receptors are poised to participate in a wide variety of functions of the CNS. The presynaptic mGlu(7) receptor shows the highest evolutionary conservation within the family and it is thought to regulate neurotransmitter release. The mGlu(7) receptor is also the most widely distributed of the presynaptic mGlu receptors and is present at a broad range of synapses that are postulated to be critical for both normal CNS function and a range of psychiatric and neurological disorders. A growing body of evidence suggests that the mGlu(7) receptor is a key player in shaping synaptic responses at glutamatergic synapses as well as being a key regulator of inhibitory GABAergic transmission. The development of selective pharmacological and genetic tools has allowed for the unravelling of mGlu(7) receptor function in a host of physiological and behavioural processes. Knockout mice and siRNA knockdown has pointed to a role of the mGlu(7) receptor in anxiety, extinction of fear and aversion learning, spatial memory and the hormonal response to stress. In addition, these studies are largely supported by pharmacological manipulation of mGlu(7) receptor using the selective modulator N,N'-dibenzhydrylethane-1,2-diamine dihydrochloride (AMN082), although paradoxical effects with this agonist have also emerged. Together these data suggest that the mGlu(7) receptor is an important regulator of glutamatergic function, of fear and aversion and cognition and thus this receptor represents an innovative therapeutic target for stress-related disorders at the interface of cognition and anxiety.

Icariin attenuates chronic mild stress-induced dysregulation of the LHPA stress circuit in rats

Chronic mild stress (CMS) is suggested to develop dysregulation of the limbic-hypothalamic-pituitary-adrenal (LHPA) stress circuit. Icariin, a major constituent of flavonoids isolated from Epimedium brevicornum, has been previously confirmed to rescue the HPA axis abnormalities in animal models of depression. However, antidepressant treatment of icariin on corticotropin-releasing factor (CRF) system within the LHPA stress circuit and its interaction with serotonergic receptor are still seldom studied in CMS model of animals. The present study further investigated the effects of CMS procedure and subsequent icariin treatment on mRNA and protein levels of CRF, CRF receptor 1 (CRFR1) and CRF binding protein (CRFBP), as well as sucrose intake in rats. Moreover, the levels of cyclic adenosine 3',5'-monophosphate (cAMP) response element binding protein (CREB), glucocorticoid receptor (GR) and 5-hydroxytryptamine 1A receptor (5-HTR1A) in hypothalamus, hippocampus and frontal cortex were simultaneously evaluated for their participations in CRF system in this model. We found that CMS procedure significantly increased CRF expression levels in the brain regions, and decreased GR and 5-HTR1A in hippocampus and frontal cortex, with sucrose intake reduction representing the hedonic deficit in rats. Icariin restored these alterations in CMS rats. These results confirmed the hypothesis that icariin exerted antidepressant-like effect via its regulation of central CRF system. And hippocampus was suggested as an important neural area controlling the LHPA stress circuit in icariin-treated CMS rats. These findings for the first time proved that the potential molecular mechanism of antidepressant action of icariin was targeted on the interaction of the LHPA stress circuit and serotonergic function in CMS rats.

Influence of metyrapone treatment during pregnancy on the development and maturation of brain monoaminergic systems in the rat

AIM

This study examines the effect of reducing the corticosterone levels of gestating rat dams on the postnatal development and maturation of monoaminergic systems in their offspring's brains.

METHODS

Metyrapone, an inhibitor of CORT synthesis, was administered to pregnant rats from E0 to E17 of gestation. Monoamine concentrations were determined in male and female offspring at postnatal days (PN) 23 and 90 in the hippocampus, hypothalamus and striatum.

RESULTS

Reducing maternal corticosterone (mCORT) during gestation led to alterations in dopamine and serotonin levels in all three brain areas studied at PN 23. Alterations persisted until at least PN 90 in the serotonergic systems; the dopamine content of the hippocampus also remained modified. Reduced mCORT during gestation also led to alterations in the development and maturation of the hypothalamic noradrenergic systems. Sexually dimorphic responses were observed in all these monoaminergic systems at different times.

CONCLUSION

These results suggest that while they are still developing, brain monoaminergic systems are particularly sensitive to epigenetic influences. An adequate foetal level of CORT is required for the normal ontogeny of brain monoaminergic systems. The present data also provide that during the critical period of brain development, maternal CORT plays an important role in the sexual differentiation of monoaminergic systems, with particular influence on brain serotonergic neurones.

Neuropsychological functioning in health and mood disorder: Modulation by glucocorticoids and their receptors

Numerous studies have shown that disturbances in hypothalamic-pituitary-adrenal (HPA) axis function and consequent hypercortisolaemia occur in a significant proportion of patients with mood disorders. This dysfunction has been proposed to be an exacerbating factor of depressive symptoms and may predict symptomatic relapse. Glucocorticoids are also known to have a specific role in learning and memory processes. In this review we present a brief overview of the relationship between HPA axis dysfunction and neuropsychological impairment in mood disorders and the specific links between glucocorticoids and cognition in health and illness states. Finally we examine the neuropsychological effects of drugs that specifically target glucocorticoid receptor function.

Antidepressant-like effect of the extract of Rosmarinus officinalis in mice: involvement of the monoaminergic system

Rosemary, Rosmarinus officinalis L. (Labiatae) has several therapeutic applications in folk medicine in curing or managing a wide range of diseases, including depression. In this study, the effect of the hydroalcoholic extract of the stems and leaves of this plant was investigated in two behavioral models, the forced swimming test (FST) and tail suspension test (TST) in mice. The extract of R. officinalis produced an antidepressant-like effect, since the acute treatment of mice with the extract by p.o. route significantly reduced the immobility time in the FST (100 mg/kg) and TST (10-100 mg/kg), as compared to a control group, without accompanying changes in ambulation in the open-field test. Moreover, the repeated administration (14 days) of the hydroalcoholic extract of R. officinalis by p.o. route also produced an antidepressant-like effect in the TST (100-300 mg/kg). The pretreatment of mice with p-chlorophenylalanine (PCPA, 100 mg/kg, i.p., an inhibitor of serotonin synthesis, for 4 consecutive days), NAN-190 (0.5 mg/kg, i.p., a 5-HT(1A) receptor antagonist), ketanserin (5 mg/kg, i.p., a 5-HT(2A) receptor antagonist), 1-(m-chlorophenyl) biguanide (mCPBG, 10 mg/kg, i.p., a 5-HT(3) receptor agonist), prazosin (1 mg/kg, i.p., an alpha(1-)adrenoceptor antagonist), SCH23390 (0.05 mg/kg, s.c., a dopamine D(1) receptor antagonist) or sulpiride (50 mg/kg, i.p., a dopamine D(2) receptor antagonist), but not yohimbine (1 mg/kg, i.p., an alpha(2-)adrenoceptor antagonist) was able to reverse the anti-immobility effect of the extract (10 mg/kg, p.o.) in the TST. The combination of MDL72222, (0.1 mg/kg, i.p., a 5-HT(3) receptor antagonist) with a sub-effective dose of the extract of R. officinalis (1 mg/kg, p.o.) produced an anti-immobility effect in the TST. The results suggest that the antidepressant action of the extract of R. officinalis is mediated by an interaction with the monoaminergic system and that this plant should be further investigated as an alternative therapeutic approach for the treatment of depression.

Elevated plasma corticosterone level and depressive behavior in experimental temporal lobe epilepsy

Depression is frequently reported in epilepsy patients; however, mechanisms of co-morbidity between epilepsy and depression are poorly understood. An important mechanism of depression is disinhibition within the hypothalamo-pituitary-adrenocortical (HPA) axis. We examined the functional state of the HPA axis in a rat model of co-morbidity between temporal lobe epilepsy and depression. Epilepsy was accompanied by the interictal elevation of plasma corticosterone, and by the positively combined dexamethasone/corticotropin releasing hormone test. The extent of the HPA hyperactivity was independent of recurrent seizures, but positively correlated with the severity of depressive behavior. We suggest that the observed hyperactivity of the HPA axis may underlie co-morbidity between epilepsy and depression.

5-HT(1A) receptor function in major depressive disorder

Dysfunction of the serotonin 1A receptor (5-HT(1A)) may play a role in the genesis of major depressive disorder (MDD). Here we review the pharmacological, post-mortem, positron emission tomography (PET), and genetic evidence in support of this statement. We also touch briefly on two MDD-associated phenotypes, cognitive impairment and somatic pain. The results of pharmacological challenge studies with 5-HT(1A) receptor agonists are indicative of blunted endocrine responses in depressed patients. Lithium, valproate, selective serotonin reuptake inhibitors (SSRIs), tricyclic antidepressants (TCAs), and other treatment, such as electroconvulsive shock therapy (ECT), all increase post-synaptic 5-HT(1A) receptor signaling through either direct or indirect effects. Reduced somatodendritic and postsynaptic 5-HT(1A) receptor numbers or affinity have been reported in some post-mortem studies of suicide victims, a result consistent with well-replicated PET analyses demonstrating reduced 5-HT(1A) receptor binding potential in diverse regions such as the dorsal raphe, medial prefrontal cortex (mPFC), amygdala and hippocampus. 5-HT(1A) receptor knockout (KO) mice display increased anxiety-related behavior, which, unlike in their wild-type counterparts, cannot be rescued with antidepressant drug (AD) treatment. In humans, the G allele of a single nucleotide polymorphism (SNP) in the 5-HT(1A) receptor gene (HTR1A; rs6295), which abrogates a transcription factor binding site for deformed epidermal autoregulatory factor-1 (Deaf-1) and Hes5, has been reported to be over-represented in MDD cases. Conversely, the C allele has been associated with better response to AD drugs. We raise the possibility that 5-HT(1A) receptor dysfunction represents one potential mechanism underpinning MDD and other stress-related disorders.

TRH and TRH-like peptide expression in rat following episodic or continuous corticosterone

Sustained abnormalities of glucocorticoid levels have been associated with neuropsychiatric illnesses such as major depression, posttraumatic stress disorder (PTSD), panic disorder, and obsessive compulsive disorder. The pathophysiological effects of glucocorticoids may depend not only on the amount of glucocorticoid exposure but also on its temporal pattern, since it is well established that hormone receptors are down-regulated by continuously elevated cognate hormones. We have previously reported that TRH (pGlu-His-Pro-NH2) and TRH-like peptides (pGlu-X-Pro-NH2) have endogenous antidepressant-like properties and mediate or modulate the acute effects of a single i.p. injection of high dose corticosterone (CORT) in rats. For these reasons, two accepted methods for inducing chronic hyperglucocorticoidemia have been compared for their effects on brain and peripheral tissue levels of TRH and TRH-like peptides in male, 250 g, Sprague-Dawley rats: (1) the dosing effect of CORT hemisuccinate in drinking water, and (2) s.c. slow-release pellets. Overall, there were 93% more significant changes in TRH and TRH-like peptide levels in brain and 111% more in peripheral tissues of those rats ingesting various doses of CORT in drinking water compared to those with 1-3 s.c. pellets. We conclude that providing rats with CORT in drinking water is a convenient model for the pathophysiological effects of hyperglucocorticoidemia in rodents.

Strain differences in proliferation of progenitor cells in the dentate gyrus of the adult rat and the response to fluoxetine are dependent on corticosterone

This paper investigates the role of differences in adrenal cortical function on the proliferation rate of progenitor cells in the dentate gyrus of the hippocampus in adult Sprague–Dawley (SD) and Lister-Hooded (LH) male rats. SD rats had around 60% more cells labeled with Ki67 (an index of mitosis) than LH rats under basal conditions. Bilateral adrenalectomy (ADX) increased levels in both strains, but by unequal amounts, such that post-ADX numbers of Ki67-labeled cells were similar in both strains. Daily injections of 5 mg/kg corticosterone for 7 days reduced levels to similar values in ADX rats of both strains. The activity of progenitor cells in either strain did not respond to daily i.p. injections of fluoxetine (10 mg/kg) for 14 days, but an equivalent dose administered by osmotic minipump stimulated proliferation in both by a similar proportional amount, such that strain differences persisted. S.c. implantation of a corticosterone pellet (75 mg), which flattens the diurnal rhythm in corticosterone, prevented fluoxetine delivered by minipump from activating progenitor cell mitosis in SD rats, as it had in the LH strain in a previous study. These results show that much, if not all, of the marked strain differences between SD and LH rats in progenitor cell activity, and hence rates of neurogenesis in the dentate gyrus may be ascribed to corresponding differences in adrenal cortical activity.

Corticosteroid-serotonin interactions in the neurobiological mechanisms of stress-related disorders

Among psychiatric disorders, depression and generalized anxiety are probably the most common stress-related illnesses. These diseases are underlain, at least partly, by dysfunctions of neurotransmitters and neurohormones, especially within the serotoninergic (5-HT) system and the hypothalamo-pituitary-adrenal (HPA) axis, which are also the targets of drugs used for their treatment. This review focuses on the nature of the interactions between central 5-HT and corticotrope systems in animal models, in particular those allowing the assessment of serotoninergic function following experimental manipulation of the HPA axis. The review provides an overview of the HPA axis and the 5-HT system organization, focusing on the 5-HT(1A) receptors, which play a pivotal role in the 5-HT system regulation and its response to stress. Both molecular and functional aspects of 5-HT/HPA interactions are then analyzed in the frame of psychoaffective disorders. The review finally examines the hippocampal neurogenesis response to experimental paradigms of stress and antidepressant treatment, in which neurotrophic factors are considered to play key roles according to the current views on the pathophysiology of depressive disorders.

Gene expression patterns in brain cortex of three different animal models of depression

Animal models represent a very useful tool for the study of depressive-like behavior and for the evaluation of the therapeutic efficacy of antidepressants. Nevertheless, gene expression patterns of these different animal models and whether genes classically associated with human major depression are present in these genetic profiles remain unknown. Gene expression was evaluated in three animal models of depression: acute treatment with reserpine, olfactory bulbectomy and chronic treatment with corticosterone. Gene expression analysis was carried out using the Affymetrix GeneChip technology. The results were evaluated using the GeneChip Operating software (Gcos 1.3) and analyzed with the GeneSpring GX v7.3 bioinformatics software (Agilent) and dChip 2005 software. Expression changes were validated with quantitative real-time polymerase chain reaction (RT-PCR) assays. Many transcripts were differentially expressed in the cortex of depressed-like animals in each model. Gene ontology analysis showed that significant gene changes were clustered primarily into functional neurochemical pathways associated with apoptosis and neuronal differentiation. When expression profiles were compared among the three models, the number of transcripts differentially expressed decreased and only two transcripts (complement component 3 and fatty acid-binding protein 7) were differentially expressed in common. Both genes were validated with RT-PCR. Moreover, five (Htr2a, Ntrk3, Crhr1, Ntrk2 and Crh) of the genes classically related to human major depression were differentially expressed in at least one of these models. The different animal models of depression share relevant characteristics although gene expression patterns are different among them. Moreover, some of the classical genes related to human major depression are differentially expressed in these models.

Chronic low dose corticosterone exposure decreased hippocampal cell proliferation, volume and induced anxiety and depression like behaviours in mice

A dysregulated hypothalamic-pituitary-adrenal axis (HPA) has been implicated in major depressive disorder and most commonly used animal models of depression have been shown to elevate circulating levels of plasma corticosterone. We have compared the effects of chronic and acute corticosterone administration on hippocampal cell proliferation (as measured by BrdU immunohistochemistry), hippocampal volume and the appearance of anxiety (light dark box) and depression (forced swim test) like behaviours in CD1 mice. We have also examined the effects of chronic administration of fluoxetine and imipramine on these parameters. Chronic (14 days) but not acute treatment with corticosterone resulted in reduced hippocampal cell proliferation and granule cell layer volume, these changes were prevented by co-administration of imipramine and fluoxetine. In contrast, acute and 7 day but not 14 or 21 day treatment with corticosterone gave rise to a "depressed" phenotype in the forced swim test. Mice treated for 14 days with corticosterone also developed an anxious phenotype in the light dark box but only upon repeated testing. The results presented here demonstrate that moderately elevated corticosterone for a prolonged period is sufficient to induce cellular changes in the hippocampus that are prevented by chronic administration of antidepressants.