Hypothalamo-pituitary-adrenocortical axis, glucocorticoids, and neurologic disease

Stress, a Brief Update

Stress is fundamental for health and adaptation; it is an evolutionarily conserved response that involves several systems in the organism. The study of the stress response could be traced back to the end of the nineteenth century with George Beard's or Claude Bernard's work and, from that moment on, several studies that have allowed the elucidation of its neurobiology and the consequences of suffering from it were consolidated. In this theoretical review, we discuss the most relevant researches to our knowledge on the study of stress response, from the concept of stress, its neurobiology, the hormonal response during stress, as well as its regulation, the effects of acute and chronic stress, stress from cognition, the different stress responses during life, as well as its relationship with different psychiatric disorders. Taken together, the reviewed research updates the classic perspective on stress, increasing the factors that should be considered in research to explore the effects of stress on health.

Exploring the role of biologics in depression

Depression is a chronic and prevalent neuropsychiatric disorder; clinical symptoms include excessive sad mood, anhedonia, increased anxiety, disturbed sleep, and cognitive deficits. The exact etiopathogenesis of depression is not well understood. Studies have suggested that tumor necrosis factor-alpha (TNF-α) and interleukins (ILs) perform vital roles in the pathogenesis and treatment of depression. Increasing evidence suggests the upregulation of TNF-α and ILs expression in patients with depression. Therefore, biologics like TNF inhibitors (etanercept, infliximab, adalimumab) and IL inhibitors (ustekinumab) have become key compounds in the treatment of depression. Interestingly, treatment with an antidepressant has been found to decrease the TNF-α level and improve depression-like behaviors in several preclinical and clinical studies. In the current article, we have reviewed the recent findings linking TNF-α and the pathogenesis of depression proving TNF-α inhibitors as potential new therapeutic agents. Animal models and clinical studies further support that TNF-α inhibitors are effective in ameliorating depression-like behaviors. Moreover, studies showed that peripheral injection of TNF-α exhibits depressive symptoms. These symptoms have been improved by treatment with TNF-α inhibitors. Hence suggesting TNF-α inhibitors as potential new antidepressants for the management of depressive disorder.

Major Depression: One Brain, One Disease, One Set of Intertwined Processes

Major depressive disorder (MDD) is a heterogeneous disease affecting one out of five individuals and is the leading cause of disability worldwide. Presently, MDD is considered a multifactorial disease with various causes such as genetic susceptibility, stress, and other pathological processes. Multiple studies allowed the formulation of several theories attempting to describe the development of MDD. However, none of these hypotheses are comprehensive because none of them can explain all cases, mechanisms, and symptoms of MDD. Nevertheless, all of these theories share some common pathways, which lead us to believe that these hypotheses depict several pieces of the same big puzzle. Therefore, in this review, we provide a brief description of these theories and their strengths and weaknesses in an attempt to highlight the common mechanisms and relationships of all major theories of depression and combine them together to present the current overall picture. The analysis of all hypotheses suggests that there is interdependence between all the brain structures and various substances involved in the pathogenesis of MDD, which could be not entirely universal, but can affect all of the brain regions, to one degree or another, depending on the triggering factor, which, in turn, could explain the different subtypes of MDD.

Differential responses of stressful elements to predatory exposure in behavior-lateralized mice

BACKGROUND

Predatory stress as a psychological stressor can elicit the activation of the hypothalamic-pituitary-adrenal (HPA) axis, which is involved in the dialogue of the neuroimmunoendocrine network. The brain has been proven to regulate the activity of the HPA axis by way of lateralization. In the present study, we probed the pivotal elements of the HPA circuitry including CRH, GR and a multifunctional cytokine in behavior-lateralized mice to determine their changes when the animals were subjected to predator exposure.

METHODS

Behavior-lateralized mice were classified into left-pawed and right-pawed mice through a paw-preference test. Thereafter, mice in the acute stress group received a single 60-min cat exposure, and mice in the chronic group received daily 60-min cat exposure for 14 consecutive days. The plasma CS and TNF-α were determined by ELISA, the hypothalamic CRH mRNA and hippocampal GR mRNA were detected by real-time PCR, and the hippocampal GR protein was detected by western blot analysis.

RESULTS

The results revealed that the levels of plasma CS were significantly elevated after chronic predatory exposure in both right-pawed and left-pawed mice; the right-pawed mice exhibited a higher plasma CS level than the left-pawed mice. Similarly, the acute or chronic cat exposure could induce the release of plasma TNF-α, and the left-pawed mice tended to show a higher level after the acute stress. Chronic stress significantly upregulated the expression of hypothalamic CRH mRNA in both left-pawed and right-pawed mice. Normally, the left-pawed mice exhibited a higher GR expression in the hippocampus than the right-pawed mice. After the cat exposure, the expression of GR in both left-pawed and right-pawed mice was revealed to be greatly downregulated.

CONCLUSION

Our findings indicate that predatory stress can invoke a differential response of stressful elements in behavior-lateralized mice. Some of these responses shaped by behavioral lateralization might be helpful for facilitating adaption to various stimuli.

Neuroprotective, Neurotrophic and Anti-oxidative Role of Bacopa monnieri on CUS Induced Model of Depression in Rat

Major depression is a life threatening neuropsychiatric disorder that produces mental illness and major cause of morbidity. The present study was conducted to evaluate the neuroprotective, neurotrophic and antioxidant potential of Bacopa monnieri extract (BME) on chronic unpredictable stress (CUS) induced behavioral depression in rats. Behavioral tests were carried out for investigation of antidepressant like effects of BME, and potential mechanism was assessed by determining neurotrophin level and hippocampal neurogenesis. Depressive-like behavior was assessed by shuttle-box escape test, forced swim test and tail suspension test. Effect of BME on hypothalamic-pituitary-adrenal (HPA) axis was evaluated by measuring the plasma level of adrenocorticotropic hormone (ACTH) and corticosterone. The expression of brain derived neurotrophic factor (BDNF), neuronal marker doublecortin (DCX) in the hippocampus were measured and hippocampal neurogenesis was investigated by 5-bromo-2-deoxyuridine/neuronal nuclei (BrdU/NeuN). In addition, effects of BME on oxidative stress markers were also measured in the hippocampus of CUS exposed rats. The results indicated that BME significantly able to attenuate the depressive-like behaviors, normalized the levels of ACTH, corticosterone, and up-regulate the expression of BDNF, DCX and BrdU/NeuN in CUS induced rats compared to BME treated rats. It is also found that BME significantly increased the activity of antioxidant enzymes on CUS induced rats. These findings revealed that BME exerted neuroprotective effects possibly by promoting hippocampal neurogenesis with elevation of BDNF level and antioxidant defense against oxidative stress.

Pathogenetic and Therapeutic Applications of Tumor Necrosis Factor-α (TNF-α) in Major Depressive Disorder: A Systematic Review

Major depressive disorder (MDD) is characterized by mood, vegetative, cognitive, and even psychotic symptoms and signs that can cause substantial impairments in quality of life and functioning. Up to now, the exact pathogenesis of MDD remains poorly understood. Recent research has begun to reveal that the pro-inflammatory cytokines, particularly, tumor necrosis factor-α (TNF-α), play an integral role in the pathophysiology of depressive disorders and the mechanism of antidepressant treatment. On the base of several observations: it is found that subsets of MDD patients have enhanced plasma levels TNF-α; antidepressant treatments had linked with the decline of TNF-α; central administration of TNF-α gives rise to sickness behavior which shares features with depression; and a blockade of it can ameliorate depressive symptomatology in animal models and clinical trials. In this review article, we focus on recent evidence linking TNF-α and MDD looking at data from animal and clinical studies, illustrating the pathophysiological role, susceptibility and its therapeutic application in depression. We conclude by discussing future directions for research, in particular the opportunities for the development of novel therapeutics that target TNF-α. This will be very important for designing preventative strategies and for the identification of new drug targets and preventative strategies.

Cytokines and glucocorticoid receptors are associated with the antidepressant-like effect of alarin

Little is known about the physiological or pharmacological properties of alarin, a new neuropeptide belonging to the galanin family. We previously showed that alarin has an antidepressant-like effect and is associated with a decrease in the hyperactivity of hypothalamic-pituitary-adrenal (HPA) axis that is observed in patients with depression using unpredictable chronic mild stress (UCMS) mouse model of depression. However, the mechanisms underlying these effects have not been uncovered. Inflammatory cytokines are reportedly associated with depression. Animal studies and cytokine immune therapy in humans suggest that pro-inflammatory cytokines induce depressive symptomatology and potently activate the HPA axis, whereas anti-inflammatory cytokines may decrease activation. Thus, we first determined the levels of inflammatory cytokines in the blood and brain to evaluate whether the antidepressant-like effect of alarin in UCMS-treated mice is related to its regulation of these inflammatory cytokines. Pro-inflammatory cytokines disrupt the function and/or expression of glucocorticoid receptors (GRs), which mediate the negative feedback of glucocorticoids on the HPA axis to keep it from being overactivated. We next explored the expression level of GRs in the brains of mice subjected to UCMS and to the administration of alarin. We found that intracerebroventricular administration of alarin significantly ameliorated depression-like behaviors in the UCMS-treated mice. Alarin restored the UCMS-induced an increase in the levels of the pro-inflammatory cytokines interleukin (IL)-6 and tumor necrosis factor α and a decrease in the anti-inflammatory cytokine IL-10 level in the blood, prefrontal cortex, hippocampus and hypothalamus. Alarin also reversed the UCMS-induced down-regulation of GR expression in these brain regions. Thus, the antidepressant-like effects of alarin may be mediated by restoring altered pro-inflammatory and anti-inflammatory cytokine levels and GR expression to decrease HPA axis hyperactivity. Our findings provide additional knowledge to interpret the pathophysiology of depression.

Depressive symptoms are associated with tumor necrosis factor alpha in systemic lupus erythematosus

BACKGROUND

Tumor necrosis factor alpha (TNF-α) is deeply related to pathogenesis of neurodevelopmental disorders, especially depression. The aim of this study was to explore potential relationships between sera TNF-α levels and mood and anxiety disorders in systemic lupus erythematosus (SLE) patients.

METHODS

We included 153 consecutive SLE patients (women 148; median age 30; range 10-62) and 40 (women 37; mean age 28.5; range 12-59) age- and sex-matched healthy controls. Mood and anxiety disorders were determined through Beck Depression and Beck Anxiety Inventory. SLE patients were further assessed for clinical and laboratory SLE manifestations. TNF-α levels were measured by enzyme-linked immunosorbent assay using commercial kits.

RESULTS

Depressive symptoms were identified in 70 (45.7 %) SLE patients and in 10 (25 %) healthy controls (p < 0.001). Anxiety symptoms were identified in 93 (60.7 %) SLE patients and in 16 controls (40 %) (p < 0.001). Sera TNF-α levels were increased in SLE patients with depressive symptoms (p < 0.001) and with anxiety symptoms (p = 0.014). A direct correlation between the severity of depressive symptoms and sera TNF-α levels (r = 0.22; p = 0.003) was observed. TNF-α levels were significantly increased in patients with active disease (p = 0.012). In addition, we observed a correlation between sera TNF-α levels and disease activity (r = 0.28; p = 0.008). In the multivariate analysis, sera TNF-α levels were independently associated with depressive symptoms (t = 3.28; 95 % CI 1.08-2.2; p = 0.002).

CONCLUSIONS

Sera TNF-α levels are increased in SLE patients with mood and anxiety disorders. In SLE, sera TNF-α levels are independently associated with mood disorders. The etiology of mood disorders is still debated in SLE, but our findings suggest the presence of immunological basis for depression in SLE.

The importance of cytokines and autoantibodies in depression

The relationship between depression and immunity has been widely discussed. Cytokines, such as TNF-α, play an important role in immune system; these cytokines interact with virtually every pathophysiologic domain relevant to depression, including neurotransmitter metabolism, neuroendocrine function, and synaptic plasticity. Antibodies have also been implicated in the pathophysiology of depression. The association between decreased serotonin levels and excessive glutamatergic activity forms the first biochemical basis for cytokine-induced depression. Cytokines and antibodies (anti-ribosomal-P and anti-N-methyl-D-aspartate receptor antibodies) are deeply related to pathogenesis of neurodevelopmental disorders, especially depression. Tumor necrosis factor alpha (TNF-α) may underlie the mechanism of depression by an activation of the hypothalamo-pituitary-adrenocortical (HPA) axis, an activation of neuronal serotonin transporters and the stimulation of the indoleamine 2,3-dioxygenase which leads to tryptophan depletion. In the last 20 years since the initial reports of neural-immune interactions in depression, studies have shown a clear association between activation of the immune system mediated by proinflammatory cytokines. Genes encoding cytokines are highly polymorphic and single nucleotide polymorphisms, associated with increased or reduced cytokine production, have been described. To date, there are only few studies that investigated the relationship between depression and proinflammatory cytokines in patients with autoimmune diseases. Although an associative link between neuroinflammation and mood disorders is widely accepted, further studies are necessary to establish the cause-effect relationship. In this paper, we review the role of cytokines, focusing on TNF-α and antibodies in the depression and hypothesize how TNF-α may underlie and mediate the inflammatory process depression in patients with autoimmune disease.

Nobiletin Ameliorates the Deficits in Hippocampal BDNF, TrkB, and Synapsin I Induced by Chronic Unpredictable Mild Stress

Background. Our previous study has demonstrated that nobiletin could reverse the behavioral alterations in stressed mice. However, the relation of its antidepressant-like action with neurotrophic molecular expression remains unknown. This study aimed to explore the antidepressant-like mechanism of nobiletin related to the neurotrophic system in rats exposed to chronic unpredictable mild stress (CUMS). Methods. Depressive-like anhedonia (assessed by sucrose preference) and serum corticosterone secretion were evaluated in the CUMS, followed by brain-derived neurotrophic factor (BDNF), its tropomyosin-related kinase receptor B (TrkB), and the downstream target synapsin I expressions in the hippocampus. Results. Anhedonia, which occurred within week 2, was rapidly ameliorated by nobiletin. While fluoxetine needed additional 2 weeks to improve the anhedonia. In addition, nobiletin administration for 5 weeks significantly ameliorated CUMS-induced increase in serum corticosterone levels. Furthermore, we also found that CUMS-induced deficits of hippocampal BDNF, TrkB, and synapsin I were ameliorated by nobiletin. Conclusions. Taken together, these findings suggest that nobiletin produces rapidly acting antidepressant-like responses in the CUMS and imply that BDNF-TrkB pathway may play an important role in the antidepressant-like effect of nobiletin.

Antidepressant-like behavioral, neurochemical and neuroendocrine effects of naringenin in the mouse repeated tail suspension test

Our previous study demonstrated that the citrus bioflavonoid naringenin ameliorated behavioral alterations via the central serotonergic and noradrenergic systems in the tail suspension test (TST) induced mice. To better understand its pharmacological activity, mice were submitted to three 6min-TSTs one week apart (Day 1: test, Day 7: retest 1, Day 14: retest 2) followed by hippocampal glucocorticoid receptor (GR), monoamine neurotransmitters and serum corticosterone measurement. The results suggested that repeated TST detected the gradual increase in the efficacy of naringenin over time, additionally 1-day (20 mg/kg), 7-day (10, 20 mg/kg) and 14-day (5, 10, 20 mg/kg) naringenin treatment markedly decreased the immobility time. Moreover, administration of naringenin for 14 days (20 mg/kg) increased hippocampal serotonin (5-HT), norepinephrine (NE) and GR levels, and reduced serum corticosterone levels in mice exposed to the repeated TST. Overall, the present study indicated that the re-exposure would facilitate the detection of the anti-immobility effects of antidepressant drugs in the mouse TST, and clearly demonstrated that the antidepressant-like effect of naringenin may be mediated by an interaction with neuroendocrine and neurochemical systems.

Correlation between brain interstitial and total serum cortisol levels in traumatic brain injury. A preliminary study

INTRODUCTION

Brain cortisol availability has never been evaluated in patients with traumatic brain injury (TBI). Cerebral microdialysis is a well-established technique for monitoring brain metabolism in neurocritically ill patients, which may be used to measure interstitial cortisol. The objective of this preliminary study was to measure brain interstitial cortisol and its correlation with total serum cortisol in patients with TBI.

METHODS

We prospectively studied 6 patients with severe TBI admitted to the Intensive Care Unit of our tertiary University Hospital in which multimodal neuromonitoring including cerebral microdialysis with a high cut-off of 100 k-Da and 20-mm long membrane was used. Serum and brain interstitial cortisol microdialysis samples were obtained every 8 h and analyzed afterwards.

RESULTS

Linear regression analysis of total serum cortisol and brain interstitial cortisol in the whole population showed a moderate correlation (R2=0.538, p<0.001, no.=118). However, intra-individual correlation showed a great variability, with correlation coefficients ranging from a R2=0.091 to R2=0.680.

CONCLUSION

Our prospective and preliminary study showed a moderate correlation of brain interstitial cortisol and total serum cortisol values in patients with diffuse TBI. However, intra-individual analysis showed a great variability. These results suggest that total serum cortisol may not reflect brain cortisol availability in half of TBI patients.