Dopaminergic function and the cortisol response to dexamethasone in psychotic depression

1. It has been hypothesized that psychotic symptoms in depression may be due to increased dopamine activity secondary to hypothalamic-pituitary-adrenal (HPA) axis overactivity. 2. To test this hypothesis, the authors examined the cortisol response to dexamethasone suppression test (DST, 1 mg orally) and multihormonal responses to apomorphine (APO, 0.75 mg s.c.)--a dopamine agonist--in 150 drug-free hospitalized patients with DSM-IV major depressive episode with psychotic features (MDEP, n=35), major depressive episode without psychotic features (MDE, n=74), or schizophrenia paranoid type (SCZ, n=41), and 27 hospitalized healthy controls (HCs). 3. MDEPs showed increased activity of the HPA system (i.e. higher post-DST cortisol levels) than HCs, SCZs and MDEs. However, there were no differences in adrenocorticotropic hormone (ACTH), cortisol, prolactin and growth hormone (GH) responses to APO between MDEPs and MDEs and HCs. On the other hand, SCZs showed lower APO-induced ACTH stimulation and a higher rate of blunted GH than HCs, MDEs and MDEPs, suggesting a functional alteration of the hypothalamic dopamine receptors in SCZs. 4. In the total sample and in each diagnostic group, DST suppressors and non-suppressors showed no differences in hormonal responses to APO. 5. These results suggest a lack of causal link between HPA axis hyperactivity and dopamine dysregulation. In contrast to schizophrenia, psychotic symptoms in depression seem not to be related to dopamine function dysregulation.     

Mineralocorticoid receptor function in major depression

BACKGROUND: Negative feedback regulation of the hypothalamic-pituitary-adrenal axis occurs through a dual-receptor system of mineralocorticoid receptors (MR) and glucocorticoid receptors (GR). Their affinity for cortisol and their distribution in the brain differ. Studies using an MR antagonist have demonstrated that MR is active throughout the circadian rhythm. Because major depression is accompanied by increased glucocorticoid secretion and insensitivity to glucocorticoid feedback, and because glucocorticoids are capable of down-regulating MR and GR, we expected that major depression would be accompanied by decreased MR activity. METHODS: To test this hypothesis, we administered spironolactone, an MR antagonist, to individuals with major depression and matched control subjects and assessed levels of corticotropin and cortisol secretion in response to this acute challenge. Studies were conducted in the morning, the time of peak activation of the hypothalamic-pituitary-adrenal axis. All patients were currently depressed and free of all medications. All controls were free of all psychiatric diagnoses and of all medications. RESULTS: Spironolactone treatment resulted in a significant increase in cortisol secretion levels in both groups. Depressed patients demonstrated higher cortisol secretion levels than control subjects. In addition, depressed patients demonstrated a different pattern of increase in cortisol secretion levels after spironolactone administration. Furthermore, a significant effect of spironolactone treatment on corticotropin secretion levels can be observed in depressed patients, whereas controls show no such effect. CONCLUSIONS: Despite high baseline cortisol levels, patients with major depression show high functional activity of the MR system. Paired with the body of evidence regarding decreased sensitivity to GR agonists, these data suggest an imbalance in the MR/GR ratio. The balance of MR and GR is known to affect brain serotonin systems and may play an etiologic role in serotonin receptor changes observed in patients with major depression.     

Delta sleep-inducing peptide response to human corticotropin-releasing hormone (CRH) in major depressive disorder. Comparison with CRH-induced corticotropin and cortisol secretion

Twenty-four subjects (12 patients with major depressive disorder and 12 controls matched for sex and age) received 100 micrograms synthetic human corticotropin-releasing hormone (hCRH) as an iv bolus dose. Healthy subjects exhibited a slight, but sustained, increase of plasma delta sleep-inducing peptide (DSIP) concentrations, whereas a marked reduction of DSIP levels was found in depressives. Compared to controls, depressed patients showed a significant attenuation of corticotropin (ACTH) responses, whereas cortisol secretion in response to hCRH was normal. Basal DSIP and cortisol concentrations were highly correlated and were higher in depressives than in controls. Both were negatively correlated with the DSIP responses to hCRH. These findings are compatible with the hypothesis that hypothalamic-pituitary-adrenal (HPA) overactivity in the depressive state is primarily due to central hypersecretion of CRH and support the view of a modulatory function of DSIP in the complex regulatory mechanism of the HPA system and of its pathophysiological significance for aberrant HPA axis function in major depressive disorder.     

Function of the adrenal cortex in patients with major depression

Failure to suppress cortisol secretion after administration of dexamethasone occurs in up to 50% of depressed patients. To test whether this hypothalamic-pituitary-adrenal (HPA) overactivity is associated with adrenocortical hyperresponsiveness, we performed dexamethasone suppression tests (DSTs) and adrenocorticotropic hormone (ACTH) stimulation tests in depressed subjects and subjects with other psychiatric disorders. Three groups were defined: depressed nonsuppressors, depressed suppressors, and other suppressors. While predexamethasone and postdexamethasone cortisol concentrations were greater in the depressed nonsuppressor group, ACTH concentrations did not differ among groups. After receiving alpha-ACTH[1-24] (4.2 micrograms/kg), depressed nonsuppressors had greater increases in stimulated cortisol secretion than the other groups. These results demonstrate that in a subgroup of depressed patients, HPA overactivity is associated with adrenocortical hyperresponsiveness.     

Characterization and functional significance of glucocorticoid receptors in patients with major depression: modulation by antidepressant treatment

Hyperactivity of the hypothalamic pituitary adrenal (HPA) axis in patients with major depression is one of the most consistent findings in biological psychiatry. Experimental data support the idea that glucocorticoid-mediated feedback via glucocorticoid receptors (GR) is impaired in major depression. The aim of the present work was to assess the putative changes in GR density of peripheral blood mononuclear cells (PBMCs) in a group of patients with major depression and to determine modulation of these GR sites by antidepressant treatment. In addition, susceptibility of PBMCs to glucocorticoid effects was also studied using a functional end-point analysis in vitro, such as cortisol inhibition of mitogen-induced lymphocyte proliferation. Cortisol levels were also measured before and after dexamethasone suppression test (DST). The results showed a decrease in GR density in depressed patients compared with healthy subjects, mainly in those patients that showed basal cortisol levels in the upper normal range and were refractory to DST. Regarding the functional significance of this variation, two representative groups emerged from our study: a) free-medication patients with GR function comparable to healthy controls, and b) patients showing diminished GR activity. These results suggest a lack of relationship between GR density and cortisol-induced inhibition of lymphocyte proliferation. Patients treated with different antidepressant drugs showed a marked increase in the number of GR sites per cell compared to non-treated. Interestingly, this increase was even higher than in normal subjects. Hence, restoration of GR density after an efficient antidepressant treatment could be an index of an effective modulatory action of drugs on GR expression and highlights the possibility that GR levels might be used as markers of a successful treatment.     

Lack of effect of HPA axis hyperactivity on hormonal responses to d-fenfluramine in major depressed patients: implications for pathogenesis of suicidal behaviour

There is evidence for inhibitory effects of adrenocorticosteroids on serotonergic (5-HT) activity. However, in depression the relationship between altered cortisol levels and brain 5-HT function remains to be clarified. The aim of this study was to investigate whether hypothalamic-pituitary-adrenal (HPA) axis hyperactivity is associated with 5-HT dysfunction in depressed patients, especially in those with suicidal behaviour. Cortisol levels following the dexamethasone suppression test (DST, 1 mg PO) and prolactin, corticotropin and cortisol responses to the d-fenfluramine test (d-FEN, 45 mg PO) - a specific 5-HT releaser/uptake inhibitor - were measured in 71 drug-free DSM-IV major depressed inpatients (40 with a history of suicide attempt, 31 without) and 34 hospitalized healthy control subjects. Depressed patients showed higher post-DST cortisol levels but similar responses to d-FEN compared with control subjects. Hormonal responses to d-FEN were not correlated with cortisol levels (basal or post-DST). Among the depressed patients, DST suppressors and DST nonsuppressors exhibited no significant difference in endocrine responses to d-FEN. However, patients with a history of suicide attempt, when compared with patients without such a history, showed lower hormonal responses to d-FEN but comparable basal and post-DST cortisol levels. Taken together these results suggest that, in depression, HPA axis hyperactivity is not responsible for the reduced 5-HT activity found in patients with a history of suicidal behavior.     

Alpha 2-adrenergic receptor function in depression. The cortisol response to yohimbine

There is evidence that the abnormalities in hypothalamic-pituitary-adrenal (HPA) axis function observed in patients with depression may be related to changes in central neurotransmitter receptor function. To evaluate this possibility further, the alpha 2-adrenergic receptor antagonist yohimbine hydrochloride, which increases brain norepinephrine turnover, was administered to 40 patients with DSM-III major depression (18 melancholic, 22 nonmelancholic) and 16 healthy controls. Plasma free 3-methoxy-4-hydroxyphenylglycol (MHPG) level was measured as an index of noradrenergic function, and plasma cortisol level was used to assess the HPA response. Baseline cortisol levels were elevated in melancholic depressed patients, but not in nonmelancholic patients, when compared with healthy controls. The cortisol response to yohimbine was significantly greater in depressed patients than in controls, despite similar MHPG responses between groups. Since there is evidence that stimulation of postsynaptic alpha 2-adrenergic receptors inhibits HPA axis function, the abnormally increased cortisol response to the alpha 2-antagonist yohimbine suggests a relative subsensitivity of postsynaptic alpha 2-adrenergic receptors in depression.     

Sex specific associations between common glucocorticoid receptor gene variants and hypothalamus-pituitary-adrenal axis responses to psychosocial stress.

BACKGROUND: Alterations in glucocorticoid (GC) signaling have been associated with a number of psychiatric disorders. Genetic variation of the glucocorticoid receptor (GR) might be one of the factors underlying susceptibility to stress related disease. METHODS: We investigated 206 healthy subjects and assessed associations between four common GR gene (NR3C1) polymorphisms (ER22/23EK, N363S, BclI, 9beta) and hypothalamic-pituitary-adrenal (HPA) axis responses to psychosocial stress (Trier Social Stress Test, TSST) and glucocorticoid sensitivity measured by a dexamethasone suppression test (DST). RESULTS: Male 9beta AG carriers displayed the highest adrenocorticotropic hormone (ACTH) and total cortisol TSST responses (for ACTH: main effect genotype p = .02) whereas male BclI GG carriers showed diminished responses. Remarkably, the BclI GG genotype in women (all using oral contraceptives) was associated with the highest total cortisol TSST responses, resulting in a significant sex by genotype interaction (p = .03). Following the DST, male 9beta AG carriers had elevated ACTH levels (sex by genotype interaction p = .03). CONCLUSIONS: We observed significant sex specific associations between GR gene polymorphisms and HPA axis responses to psychosocial stress as well as GC sensitivity. These findings support the relevance of GR gene polymorphisms in HPA axis regulation. Genetic variations of the GR might constitute a risk factor in development of HPA axis related disorders.     

Childhood trauma,HPA axis activity and antidepressant response in patients with depression

Childhood trauma is among the most potent contributing risk factors for depression and is associated with poor treatment response. Hypothalamic-pituitary-adrenal (HPA) axis abnormalities have been linked to both childhood trauma and depression, but the underlying mechanisms are poorly understood. The present study aimed to investigate the link between childhood trauma, HPA axis activity and antidepressant response in patients with depression. As part of the Wellcome Trust NIMA consortium, 163 depressed patients and 55 healthy volunteers were included in this study. Adult patients meeting Structured Clinical Interview for Diagnostic and Statistical Manual Version-5 criteria for major depression were categorised into subgroups of treatment responder (n = 42), treatment non-responder (n = 80) and untreated depressed (n = 41) based on current depressive symptom severity measured by the 17-item Hamilton Rating Scale for Depression and exposure to antidepressant medications established by Antidepressant Treatment Response Questionnaire. Childhood Trauma Questionnaire was obtained. Baseline serum C-reactive protein was measured using turbidimetric detection. Salivary cortisol was analyzed at multiple time points during the day using the ELISA technique. Glucocorticoid resistance was defined as the coexistence of hypercortisolemia and inflammation. Our results show that treatment non-responder patients had higher exposure to childhood trauma than responders. No specific HPA axis abnormalities were found in treatment non-responder depressed patients. Untreated depressed showed increased diurnal cortisol levels compared with patients on antidepressant medication, and higher prevalence of glucocorticoid resistance than medicated patients and controls. The severity of childhood trauma was associated with increased diurnal cortisol levels only in individuals with glucocorticoid resistance. Therefore, our findings suggest that the severity of childhood trauma experience contributes to a lack of response to antidepressant treatment. The effects of childhood trauma on increased cortisol levels are specifically evident in patients with glucocorticoid resistance and suggest glucocorticoid resistance as a target for the development of personalized treatment for a subgroup of depressed patients with a history of childhood trauma rather than for all patients with resistance to antidepressant treatment.     

Corticotropin and cortisol response to human CRH as a probe for HPA system integrity in major depressive disorder

To explore the integrity of the hypothalamic-pituitary-adrenal (HPA) system in major depressive disorder, 12 patients and normal controls matched for sex, age, and body weight received 100 micrograms synthetic human corticotropin-releasing hormone (hCRH) as an i.v. bolus dose. Compared to controls, depressed patients showed an elevation in baseline cortisol and a significant attenuation of net adrenocorticotropin (ACTH) responses, while cortisol secretion in response to hCRH was normal. These abnormalities in HPA axis function and apparent discordances in the interrelationships of ACTH and cortisol baseline and net stimulation responses between depressed patients and normal controls indicate, at least in part, a derangement of the glucocorticoid-dependent negative feedback circuitry and support the hypothesis that HPA hyperactivity in depression involves neurotransmitter-mediated hypothalamic hypersecretion of CRH.     

HPA axis dysfunction in unmedicated major depressive disorder and its normalization by pharmacotherapy correlates with alteration of neural activity in prefrontal cortex and limbic/paralimbic regions

Dysregulation of the hypothalamic-pituitary-adrenocortical (HPA) axis is one of the most prominent neurobiological findings in major depressive disorder (MDD). The relationship of regional brain metabolism to HPA axis dysfunction in depressed patients, however, is still unclear. In this study, to examine the clinical pharmacotherapeutic effects on HPA axis function and brain metabolism in MDD patients, we performed the combined dexamethasone (DEX)/corticotropin-releasing hormone (CRH) test on 24 antidepressant-free patients with MDD a few days after positron emission tomography (PET) with a radiotracer, [(18)F]-fluorodeoxyglucose (FDG). Moreover, 10 patients who responded to pharmacotherapy were re-tested. 75% of unmedicated MDD patients exhibited a heightened cortisol response to the DEX/CRH test, and thus were defined as non-suppressors. Non-suppressors showed a marked hypometabolism in the medial prefrontal cortex as compared with suppressors. After successful pharmacotherapy, enhanced cortisol responsiveness normalized. Prior to treatment of the unmedicated MDD, a significant hypometabolism in various frontal regions and a significant hypermetabolism in the right hippocampus and parahippocampal gyrus were observed compared with controls. Metabolic activity in treatment responders showed a normalizing pattern in almost all the areas that had been characterized by metabolic abnormality at baseline except for the medial prefrontal cortex. These results indicate that depressed patients remitted with antidepressant treatment were accompanied by resolution of HPA dysregulation and alteration of regional glucose metabolism in the prefrontal cortical, limbic and paralimbic regions.     

Acute cortisol administration increases sleep depth and growth hormone release in patients with major depression

Acute administration of cortisol increases non-rapid-eye movement (non-REM) sleep, suppresses rapid-eye movement (REM) sleep and stimulates growth hormone (GH) release in healthy subjects. This study investigates whether cortisol has similar endocrine and electrophysiological effects in patients with depression who typically show a pathological overactivity of the hypothalamus-pituitary-adrenal (HPA) system. Fifteen depressed inpatients underwent the combined dexamethasone/corticotropin-releasing hormone test followed by three consecutive sleep EEG recordings in which the patients received placebo (saline) and hourly injections of cortisol (1mg/KG BW). Cortisol increased duration and intensity of non-REM sleep in particular in male patients and stimulated GH release. The activity of the HPA axis appeared to influence the cortisol-induced effects on non-REM sleep and GH levels. Stimulation of delta sleep was less pronounced in patients with dexamethasone nonsuppression. In contrast, REM sleep parameters were not affected by the treatment. These data demonstrate that the non-REM sleep-promoting effects of acute cortisol injections observed in healthy controls could be replicated in patients with depression. Our results suggest that non-REM and REM sleep abnormalities during the acute state of the disease are differentially linked to the activity of the HPA axis.     

Noradrenergic function and the cortisol response to dexamethasone in depression

Abnormalities of the hypothalamic-pituitary-adrenal (HPA) axis and the noradrenergic system have been reported in depression. To study possible interrelations between these two systems, plasma free 3-methoxy-4-hydroxyphenylglycol (MPHG) was compared with the cortisol response to dexamethasone in 64 depressed patients. Postdexamethasone cortisol nonsuppressors had higher baseline plasma free MHPG values than did cortisol suppressors. Increased severity of some depressive symptoms was associated with increased postdexamethasone cortisol levels. These results indicate that depressed patients with dexamethasone nonsuppression have increased noradrenergic turnover.     

Glucocorticoid receptors in major depression: relevance to pathophysiology and treatment.

Hyperactivity of the hypothalamic--pituitary--adrenal (HPA) axis has been reliably observed in patients with major depression. One of the primary features of this HPA axis hyperactivity is reduced sensitivity to the inhibitory effects of the glucocorticoid dexamethasone on the production of adrenocorticotropic hormone and cortisol during the dexamethasone suppression test and, more recently, the dexamethasone--corticotropin-releasing hormone test. Because the effects of glucocorticoids are mediated by intracellular receptors including, most notably, the glucocorticoid receptor (GR), a number of studies have considered the possibility that the number and/or function of GRs are reduced in depressed patients. Moreover, whether antidepressants act by reversing these putative GR changes has been examined. The extant literature on GR receptors in major depression was reviewed along with studies examining the impact of antidepressants on the GR. The data support the hypothesis that the function of the GR is reduced in major depression in the absence of clear evidence of decreased GR expression. The data also indicate that some antidepressants have direct effects on the GR, leading to enhanced GR function and increased GR expression. Hypotheses regarding the mechanism of these receptor changes involve relevant second messenger pathways that regulate GR function. The findings indicate that the GR is an important molecular target in major depression. Further elucidation of the biochemical and molecular mechanisms involved in GR changes in major depression is an exciting frontier that will no doubt lead to new insights into the pathophysiology and treatment of affective disorders.     

Salivary cortisol in women with and without perimenstrual mood changes

An increase in the activity of the hypothalamic–pituitary–adrenal axis (HPA axis) is frequently associated with major depression. During the premenstrual phase of their reproductive cycle some women experience depressive mood changes that are proposed to be of similar intensity to that experienced during periods of major depression. This study examined the secretion of cortisol, the end-product in the HPA axis, at different stages of the menstrual cycle in women with and without premenstrual depression. Women who experienced only mild physical and emotional changes in the premenstrual phase of their cycle had a significantly higher cortisol secretion on a premenstrual day (measured hourly) compared to a postmenstrual day. Those who were significantly more depressed premenstrually showed the opposite pattern of cortisol secretion with significantly lower levels on the premenstrual day compared with the postmenstrual day. Across the menstrual cycle, women who were significantly more depressed premenstrually also had lower evening cortisol levels in their premenstrual phase. The results of this study indicate that, unlike major depression where the underlying neurological changes are manifest as overactivity of the HPA axis, premenstrual depressive changes are associated with reduced HPA axis activity. Premenstrual depression may, therefore, be similar neurologically to seasonal affective disorder, which is associated with underactivity of the HPA axis.     

Endocrine responses to growth hormone-releasing hormone, thyrotropin-releasing hormone and corticotropin-releasing hormone in depression

To explore and to compare hypothalamic-pituitary-somatotropic (HPS), hypothalamic-pituitary-thyroid (HPT) and hypothalamic-pituitary-adrenocortical (HPA) axis function in depression, 30 subjects (15 patients with a major depressive episode and individually matched controls) received 50 micrograms growth hormone-releasing hormone-44 amide at 9:00, 200 micrograms thyrotropin-releasing hormone (TRH) at 9:00 and 100 micrograms human corticotropin-releasing hormone (CRH) at 18:00 on consecutive days as an i.v. bolus dose. Compared with controls, depressed patients showed blunted growth hormone (GH) responses to GHRH, decreased TRH-induced thyrotropin (TSH) release and reduced corticotropin (ACTH) but normal cortisol secretion following CRH. ACTH secretion following CRH and TRH-induced TSH release were positively correlated across depressed patients and controls but no significant correlations between GH responses to GHRH and TRH-induced TSH release or ACTH and cortisol secretion following CRH administration were demonstrated. Our findings suggest that altered HPT and HPA axis function associated with depression are triggered by factors that are at least partly different from those that cause HPS system dysfunction. We conclude that the pathophysiological process resulting in aberrant neuroendocrine secretory dynamics associated with depression may primarily occur at a suprapituitary site, and that HPS, HPT and HPA axis dysfunction may be precipitated by complex central and peripheral regulatory mechanisms involving largely independent factors.     

Dexamethasone-induced effects on lymphocyte distribution and expression of adhesion molecules in treatment-resistant depression

Alterations in immune function are associated with major depression and have been related to changes in endocrine function. We investigated whether alterations in immune function were associated with altered basal hypothalamic-pituitary-adrenal (HPA) function (salivary cortisol) and lymphocyte sensitivity to dexamethasone (DEX) intake (1 mg PO). The latter was explored by comparing the impact of DEX-induced changes on peripheral lymphocyte redistribution and expression of adhesion molecules (beta2 integrins and L-selectin). The study included 36 inpatients with treatment-resistant major depression (unipolar subtype) and 31 matched healthy controls. The dexamethasone suppression test (DST) was carried out and used to classify 10 patients as HPA axis non-suppressors. The latter presented significantly higher post-DEX salivary cortisol levels than DST suppressors, 82.0 vs. 8.9 nM l(-1) h(-1). No differences in basal salivary cortisol levels were found between patients and controls. Changes in cell redistribution (CD4(+), CD8(+), CD19(+), CD56(+) and HLADR(+) cells) after DEX administration were more prominent in controls than in patients, but the effects of DEX varied dependent on whether patients exhibited DEX-induced suppression of cortisol secretion. Glucocorticoid-induced suppression of adhesion molecule expression was also generally less marked in patients than controls. Our data indicate that alterations in immune function and steroid regulation associated with depression are not related to elevated basal levels of cortisol and further suggest that lymphocyte steroid resistance is associated with drug-resistant depression.     

Combined DEX/CRH test among Japanese patients with major depression

There is compelling evidence for an important role of the hypothalamus-pituitary-adrenal (HPA) axis abnormalities in the pathophysiology of major depressive disorder. Growing evidence has suggested that the combined dexamethasone (DEX)/CRH test is much more sensitive than the conventional DEX suppression test in order to detect HPA axis abnormalities. However, little data is currently available on DEX/CRH results for Asian populations, which prompted us to examine the sensitivity of the DEX/CRH test among Japanese subjects with major depression. The DEX/CRH test was administered in 20 inpatients with major depressive episode and 30 healthy controls. Significantly increased cortisol responses were observed for the patients, compared to the controls. There was a substantial difference in the distribution of non-suppressor, intermediate suppressor, and suppressor, which were defined in terms of cortisol response, was observed between the patients and controls (10, 60, and 30% in the patients vs. 0, 27, and 73% in the controls, P<0.01). Responses of ACTH showed a trend in the same direction. Within the depressed patients, individuals with a history of attempted suicide, in particular, tended to have enhanced responses to the DEX/CRH test, compared to those without such a history. Our results confirmed that the DEX/CRH test is a sensitive test to detect HPA axis abnormalities among Japanese patients with major depression. In addition, a possible relationship between suicidal acts and enhanced HPA axis abnormalities was suggested.     

Glucocorticoids, cytokines and brain abnormalities in depression

Major depression (MD) is a common psychiatric disorder with a complex and multifactor aetiology. Potential mechanisms associated with the pathogenesis of this disorder include monoamine deficits, hypothalamic-pituitary-adrenal (HPA) axis dysfunctions, inflammatory and/or neurodegenerative alterations. An increased secretion and reactivity of cortisol together with an altered feedback inhibition are the most widely observed HPA abnormalities in MD patients. Glucocorticoids, such as cortisol, are vital hormones that are released in response to stress, and regulate metabolism and immunity but also neuronal survival and neurogenesis. Interestingly depression is highly prevalent in infectious, autoimmune and neurodegenerative diseases and at the same time, depressed patients show higher levels of pro-inflammatory cytokines. Since communication occurs between the endocrine, immune and central nervous system, an activation of the inflammatory responses can affect neuroendocrine processes, and vice versa. Therefore, HPA axis hyperactivity and inflammation might be part of the same pathophysiological process: HPA axis hyperactivity is a marker of glucocorticoid resistance, implying ineffective action of glucocorticoid hormones on target tissues, which could lead to immune activation; and, equally, inflammation could stimulate HPA axis activity via both a direct action of cytokines on the brain and by inducing glucocorticoid resistance. In addition, increased levels of pro-inflammatory cytokines also induce the production of neurotoxic end products of the tryptophan-kynurenine pathway. Although the evidence for neurodegeneration in MD is controversial, depression is co-morbid with many other conditions where neurodegeneration is present. Since several systems seem to be involved interacting with each other, we cannot unequivocally accept the simple model that glucocorticoids induce neurodegeneration, but rather that elevated cytokines, in the context of glucocorticoid resistance, are probably the offenders. Chronic inflammatory changes in the presence of glucocorticoid resistance may represent a common feature that could be responsible for the enhanced vulnerability of depressed patients to develop neurodegenerative changes later in life. However, further studies are needed to clarify the relative contribution of glucocorticoids and inflammatory signals to MD and other disorders.     

HPA axis activation in major depression and response to fluoxetine: a pilot study

Hypothalamic-pituitary-adrenal (HPA) axis activation is a frequently observed phenomenon in major depression. However, whether this activation has any implications for treatment is unknown. To address this question, we examined baseline response to metyrapone and 6-week response to fluoxetine. Premenopausal women (n = 20) who met criteria for major depression with no other confounding Axis I disorders, medications, or medical illnesses and were not taking hormonal contraceptives were evaluated with an evening metyrapone challenge before the onset of treatment. Twenty-one normal women were also studied with the evening metyrapone challenge. The depressed patients then entered an open label treatment with fluoxetine for 6 weeks. Subjects were classified as responders if they demonstrated a 50% or greater decrease in Hamilton Depression Rating Scale rating. As a group, the depressed women demonstrated significantly increased ACTH secretion compared to control women before the onset of treatment, during the metyrapone challenge. Before treatment, women who were non-responders to fluoxetine showed increased HPA axis activation compared to controls, while the fluoxetine responders did not differ significantly from normal subjects in their ACTH levels during metyrapone challenge. These results suggest that overactivity of the HPA axis may be one factor associated with slower response to fluoxetine. This may reflect the greater severity of subjects with HPA axis dysregulation or the need to normalize the HPA axis with medications for optimal response.