Stimulation of the pituitary-adrenal axis with a low dose [Arg8]-vasopressin in depressed patients and healthy subjects

Sex differences in stress-related disorders: Major depressive disorder, bipolar disorder, and posttraumatic stress disorder

Stress-related disorders, such as mood disorders and posttraumatic stress disorder (PTSD), are more common in women than in men. This sex difference is at least partly due to the organizing effect of sex steroids during intrauterine development, while activating or inhibiting effects of circulating sex hormones in the postnatal period and adulthood also play a role. Such effects result in structural and functional changes in neuronal networks, neurotransmitters, and neuropeptides, which make the arousal- and stress-related brain systems more vulnerable to environmental stressful events in women. Certain brainstem nuclei, the amygdala, habenula, prefrontal cortex, and hypothalamus are important hubs in the stress-related neuronal network. Various hypothalamic nuclei play a central role in this sexually dimorphic network. This concerns not only the hypothalamus-pituitary-adrenal axis (HPA-axis), which integrates the neuro-endocrine-immune responses to stress, but also other hypothalamic nuclei and systems that play a key role in the symptoms of mood disorders, such as disordered day-night rhythm, lack of reward feelings, disturbed eating and sex, and disturbed cognitive functions. The present chapter focuses on the structural and functional sex differences that are present in the stress-related brain systems in mood disorders and PTSD, placing the HPA-axis in the center. The individual differences in the vulnerability of the discussed systems, caused by genetic and epigenetic developmental factors warrant further research to develop tailor-made therapeutic strategies.

The human hypothalamus in mood disorders: The HPA axis in the center

There are no specific structural neuropathological hallmarks found in the brain of mood disorders. Instead, there are molecular, functional and structural alterations reported in many brain areas. The neurodevelopmental underpinning indicated the presence of various genetic and developmental risk factors. The effect of genetic polymorphisms and developmental sequalae, some of which may start in the womb, result in functional changes in a network mediated by neurotransmitters and neuropeptides, which make the emotion- and stress-related brain systems more vulnerable to stressful events. This network of stress-related neurocircuits consists of, for instance, brainstem nuclei, the amygdala, habenula, prefrontal cortex and hypothalamus. Various nuclei of the hypothalamus form indeed one of the crucial hubs in this network. This structure concerns not only the hypothalamo-pituitary-adrenal (HPA) axis that integrate the neuro-endocrine-immune responses to stress, but also other hypothalamic nuclei and systems that play a key role in the symptoms of depression, such as disordered day-night rhythm, lack of reward feelings, disturbed eating, sex, and disturbed cognitive functions. The present review will focus on the changes in the human hypothalamus in depression, with the HPA axis in the center. We will discuss the inordinate network of neurotransmitters and neuropeptides involved, with the hope to find the most vulnerable neurobiological systems and the possible development of tailor-made treatments for mood disorders in the future.

Hypothalamic-pituitary-adrenal axis function during perinatal depression

Abnormal function of the hypothalamic-pituitary-adrenal (HPA) axis is an important pathological finding in pregnant women exhibiting major depressive disorder. They show high levels of cortisol pro-inflammatory cytokines, hypothalamic-pituitary peptide hormones and catecholamines, along with low dehydroepiandrosterone levels in plasma. During pregnancy, the TH2 balance together with the immune system and placental factors play crucial roles in the development of the fetal allograft to full term. These factors, when altered, may generate a persistent dysfunction of the HPA axis that may lead to an overt transfer of cortisol and toxicity to the fetus at the expense of reduced activity of placental 11β-hydroxysteroid dehydrogenase type 2. Epigenetic modifications also may contribute to the dysregulation of the HPA axis. Affective disorders in pregnant women should be taken seriously, and therapies focused on preventing the deleterious effects of stressors should be implemented to promote the welfare of both mother and baby.

Disruption of fetal hormonal programming (prenatal stress) implicates shared risk for sex differences in depression and cardiovascular disease

Comorbidity of major depressive disorder (MDD) and cardiovascular disease (CVD) represents the fourth leading cause of morbidity and mortality worldwide, and women have a two times greater risk than men. Thus understanding the pathophysiology has widespread implications for attenuation and prevention of disease burden. We suggest that sex-dependent MDD-CVD comorbidity may result from alterations in fetal programming consequent to the prenatal maternal environments that produce excess glucocorticoids, which then drive sex-dependent developmental alterations of the fetal hypothalamic-pituitary-adrenal (HPA) axis circuitry impacting mood, stress regulation, autonomic nervous system (ANS), and the vasculature in adulthood. Evidence is consistent with the hypothesis that disruptions of pathways associated with gamma aminobutyric acid (GABA) in neuronal and vascular development and growth factors have critical roles in key developmental periods and adult responses to injury in heart and brain. Understanding the potential fetal origins of these sex differences will contribute to development of novel sex-dependent therapeutics.

Effect of arginine vasopressin on the behavioral activity in the behavior despair depression rat model

Arginine vasopressin (AVP), a nonapeptide posterior hormone of the pituitary, is mainly synthesized and secreted in the hypothalamic paraventricular nucleus (PVN) and supraoptic nucleus (SON). Large numbers of studies have reported that AVP plays a role in depression. The present study was to investigate by which level, brain or periphery, AVP affects the behavioral activity in the behavior despair depression rat model. The results showed that (1) either forced swimming or tail suspension significantly increased AVP concentration not only in the brain (PVN, SON, frontal of cortex, hippocampus, amygdala, lumber spinal cord) but also in the periphery (posterior pituitary and serum); (2) intraventricular injection (icv) of AVP decreased the animal immobility time, whereas V₁ receptor antagonist d(CH₂)₅Tyr(Me)AVP (icv) increased the animal immobility time in a dose-dependent manner not only in FST but also in TST, but the V₂ receptor antagonist d(CH₂)₅[D-Ile, Ile, Ala-NH₉]AVP did not change the animal immobility time in FST or TST; (3) V₁, not V₂ receptor antagonist could inhibit the animal immobility time decrease induced by AVP (icv); (4) neither AVP nor its receptor antagonist (including V₁ and V₂ receptor antagonist) influenced the animal immobility time in both FST and TST. The data suggested that AVP in the brain rather than the periphery played a role in the behavior despair depression by V₁, not V₂ receptors, which behavior despair might have a positive feedback effect on central AVP and blood AVP might have a negative feedback on central AVP in the depressive process.

Sexual differentiation of the human brain: relation to gender identity, sexual orientation and neuropsychiatric disorders

During the intrauterine period a testosterone surge masculinizes the fetal brain, whereas the absence of such a surge results in a feminine brain. As sexual differentiation of the brain takes place at a much later stage in development than sexual differentiation of the genitals, these two processes can be influenced independently of each other. Sex differences in cognition, gender identity (an individual's perception of their own sexual identity), sexual orientation (heterosexuality, homosexuality or bisexuality), and the risks of developing neuropsychiatric disorders are programmed into our brain during early development. There is no evidence that one's postnatal social environment plays a crucial role in gender identity or sexual orientation. We discuss the relationships between structural and functional sex differences of various brain areas and the way they change along with any changes in the supply of sex hormones on the one hand and sex differences in behavior in health and disease on the other.

Hypothalamic vasopressin and oxytocin mRNA expression in relation to depressive state in Alzheimer's disease: a difference with major depressive disorder

Arginine vasopressin (AVP) and oxytocin (OXT), produced in the hypothalamic paraventricular (PVN) and supraoptic nucleus (SON), are considered to be involved in the pathophysiology of major depressive disorder (MDD). The objective of this study was to determine, for the first time, the relationship between AVP and OXT gene expression and depressive state in Alzheimer's disease (AD). Post-mortem brain tissue was obtained from six control subjects, and from a prospectively studied cohort of 23 AD patients, using the DSM-IIIR and the Cornell Scale for Depression in Dementia to determine depression diagnosis and severity. The amount of AVP and OXT mRNA was determined by in situ hybridisation. AD patients did not differ from controls with respect to the amount of AVP or OXT mRNA in the PVN or SON. Also, no differences were found between depressed and nondepressed AD patients and no relationship was found between the depression severity and AVP or OXT mRNA expression. The results indicate that AVP and OXT gene expression in the PVN and SON is unchanged in depressed AD patients compared to nondepressed AD patients. This is in contrast with the enhanced AVP gene expression in MDD, suggesting a difference in pathophysiology between MDD and depression in AD.

Vasopressin-neurophysin and DST in major depression: relationship with suicidal behavior

The purpose of the present study was to assess if AVP-neurophysin is associated with hypercortisolemia and suicidal behaviour in depressed patients. The study included 28 patients subgrouped into suicide attempters (n=13) and nonattempters (n=15). We assessed basal AVP-neurophysins concentrations and post-dexamethasone (DST) cortisol levels. Concentrations of AVP-neurophysins did not differ between DST suppressors and nonsuppressors: 0.29+/-0.13 ng/ml vs 0.36+/-0.21 ng/ml, (F=1.1, df=1, 27, p=0.30). Suicide attempters did not differ from nonattempters for AVP-neurophysins levels. Our results fail to support a role of AVP in the early cortisol escape.

Lithium, arginine vasopressin and the dex/CRH test in mood disordered patients

The impact of lithium on arginine vasopressin (AVP) release has implications for our understanding of the pathophysiology and treatment of mood disorders and for the interpretation of neuroendocrine studies. In this secondary analysis of neuroendocrine, data from 23 patients with chronic major depressive disorder, 41 patients with bipolar disorder and 18 healthy controls, we examine the relationship between lithium therapy, AVP levels and the cortisol response to the dexamethasone/corticotropin-releasing hormone (dex/CRH) test. These data demonstrate that patients taking lithium have elevated post-dexamethasone AVP levels compared to both healthy controls and patients not on lithium.

The stress system in depression and neurodegeneration: focus on the human hypothalamus

The stress response is mediated by the hypothalamo-pituitary-adrenal (HPA) system. Activity of the corticotropin-releasing hormone (CRH) neurons in the hypothalamic paraventricular nucleus (PVN) forms the basis of the activity of the HPA-axis. The CRH neurons induce adrenocorticotropin (ACTH) release from the pituitary, which subsequently causes cortisol release from the adrenal cortex. The CRH neurons co-express vasopressin (AVP) which potentiates the CRH effects. CRH neurons project not only to the median eminence but also into brain areas where they, e.g., regulate the adrenal innervation of the autonomic system and affect mood. The hypothalamo-neurohypophysial system is also involved in stress response. It releases AVP from the PVN and the supraoptic nucleus (SON) and oxytocin (OXT) from the PVN via the neurohypophysis into the bloodstream. The suprachiasmatic nucleus (SCN), the hypothalamic clock, is responsible for the rhythmic changes of the stress system. Both centrally released CRH and increased levels of cortisol contribute to the signs and symptoms of depression. Symptoms of depression can be induced in experimental animals by intracerebroventricular injection of CRH. Depression is also a frequent side effect of glucocorticoid treatment and of the symptoms of Cushing's syndrome. The AVP neurons in the hypothalamic PVN and SON are also activated in depression, which contributes to the increased release of ACTH from the pituitary. Increased levels of circulating AVP are also associated with the risk for suicide. The prevalence, incidence and morbidity risk for depression are higher in females than in males and fluctuations in sex hormone levels are considered to be involved in the etiology. About 40% of the activated CRH neurons in mood disorders co-express nuclear estrogen receptor (ER)-alpha in the PVN, while estrogen-responsive elements have been found in the CRH gene promoter region, and estrogens stimulate CRH production. An androgen-responsive element in the CRH gene promoter region initiates a suppressing effect on CRH expression. The decreased activity of the SCN is the basis for the disturbances of circadian and circannual fluctuations in mood, sleep and hormonal rhythms found in depression. Neuronal loss was also reported in the hippocampus of stressed or corticosteroid-treated rodents and primates. Because of the inhibitory control of the hippocampus on the HPA-axis, damage to this structure was expected to disinhibit the HPA-axis, and to cause a positive feedforward cascade of increasing glucocorticoid levels over time. This 'glucocorticoid cascade hypothesis' of stress and hippocampal damage was proposed to be causally involved in age-related accumulation of hippocampal damage in disorders like Alzheimer's disease and depression. However, in postmortem studies we could not find the presumed hippocampal damage of steroid overexposure in either depressed patients or in patients treated with synthetic steroids.

Increased arginine vasopressin mRNA expression in the human hypothalamus in depression: A preliminary report

BACKGROUND

Elevated arginine vasopressin (AVP) plasma levels have been observed in major depression, particularly in relation to the melancholic subtype. Two hypothalamic structures produce plasma vasopressin: the supraoptic nucleus (SON) and the paraventricular nucleus (PVN). The aim of this study was to establish which structure is responsible for the increased vasopressin plasma levels in depression.

METHODS

Using in situ hybridization, we determined the amount of vasopressin messenger ribonucleic acid (mRNA) in the PVN and SON in postmortem brain tissue of nine depressed subjects (six with the melancholic subtype) and eight control subjects.

RESULTS

In the SON, a 60% increase of vasopressin mRNA expression was found in depressed compared with control subjects. In the melancholic subgroup, AVP mRNA expression was significantly increased in both the SON and the PVN compared with control subjects.

CONCLUSIONS

We found increased AVP gene expression in the SON in depressed subjects. This might partly explain the observed increased vasopressin levels in depression.

Vasopressin as a target for antidepressant development: an assessment of the available evidence

Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis is one of the key biological abnormalities described in major depressive disorder, occurring in 30-50% of depressed subjects. Corticotropin-releasing hormone (CRH) and vasopressin (AVP) are the main regulators of this stress system, with the two neuropeptides acting synergistically in bringing about adrenocorticotropin (ACTH) release from the anterior pituitary and cortisol from the adrenal gland. Based on the demonstration of elevated cerebrospinal fluid levels of CRH in depressives, and other evidence, it has been postulated that excess CRH and the resultant increased HPA forward drive form the basis of neuroendocrine dysregulation in depression. However, there is an accumulating body of evidence to support a significant role for AVP in the regulation of pituitary-adrenal activity in health and also in depressive disorder. This review, based on a Medline search from 1980 to 2001, focuses on the functional neuroanatomy, receptor pharmacology, VP synergism with CRH, and the data from clinical and pre-clinical studies that support an important role for AVP in the pathophysiology of major depression. We suggest that future antidepressants may target the vasopressinergic system.

Cushing’s disease and melancholia

Striking similarities exist in the endocrinology of Cushing's disease and melancholic depression.Laboratory abnormalities, which have been found in both, include raised urinary,plasma and salivary cortisol, non-suppression of cortisol in the dexamethasone suppression test and adrenocorticotrophin (ACTH) hypersecretion. The hypercortisolism can be so severe in melancholic depression that it is difficult to distinguish from Cushing's disease and has been described as a "pseudo-Cushing's" state. Cerebrospinal fluid corticotrophin-releasing hormone (CRH) levels have been found to be lower in patients with Cushing's disease than in depressed subjects. Dynamic endocrine tests may help to distinguish between the two disorders.An exaggerated response to synacthen has been found in both but a reduced ACTH response to CRH occurs in depression, unlike those with Cushing's disease who show ACTH hyper-responsiveness. Other tests, which may help to distinguish between the two disorders,include the dexamethasone-CRH test, the naloxone test, the insulin-induced hypoglycemia test and the desmopressin stimulation test. Similarities in psychiatric symptoms have been recognised for many years. More recently, the physical complications of melancholic depression have been noted. These include osteoporosis, an increased risk of death from cardiovascular disease, hypertension, a redistribution of fat to intra abdominal sites and insulin resistance. Cushing's disease shares these physical complications and we propose that the common underlying factor is excessive plasma glucocorticoids. The increasing recognition of the physical complications and the increased morbidity and mortality in those who suffer from depression underscores the necessity for early detection and treatment of this illness and screening for undetected physical complications.

Hypothalamo-pituitary-adrenal cortical responses to low-dose physostigmine and arginine vasopressin administration: sex differences between major depressives and matched control subjects

Of heuristic value in understanding the neurochemistry of major depression is whether the hypothalamo-pituitary-adrenocortical (HPA) axis hyperactivity that occurs in this illness can be related to putative neurotransmitter dysfunction(s). Cholinergic neurotransmission stimulates hypothalamic corticotropin releasing hormone (CRH) and arginine vasopressin (AVP) secretion, both of which stimulate pituitary corticotropin (ACTH) secretion, but whether the HPA axis in humans is activated only by doses of cholinergic agonists that produce noxious side effects remains controversial. To test the hypothesis of increased cholinergic sensitivity in major depression, physostigmine (PHYSO), a reversible cholinesterase inhibitor, was administered to patients and control subjects at a dose that elevated plasma ACTH, cortisol, and AVP concentrations but produced few or no side effects. Exogenous AVP also was administered to determine if it would augment the effect of low-dose PHYSO on the HPA axis. Twelve premenopausal or estrogen-replaced female major depressives, 12 individually matched female control subjects, eight male major depressives, and eight matched male control subjects underwent four test sessions 5-7 days apart: PHYSO (8 microg/kg IV), AVP (0.08 U/kg IM), PHYSO + AVP, and saline control. Serial blood samples were taken before and after pharmacologic challenge and analyzed for ACTH1-39, cortisol, and AVP. Estradiol and testosterone were also measured at each test session. PHYSO (8 microg/kg) significantly increased plasma ACTH, cortisol, and AVP, while producing no side effects in approximately half the subjects and predominantly mild side effects in the other half. These hormone increases following PHYSO occurred primarily in the female depressives and the male control subjects and were not significantly related to the presence or absence of side effects. The greater the ACTH and AVP responses to PHYSO, the stronger their correlation, suggesting that AVP may have been acting as a secretagogue for ACTH. Administered AVP significantly increased the secretion of ACTH in the patients and control subjects to a similar degree, and AVP given after PHYSO did not augment the HPA axis response to a greater degree in the depressives than in the control subjects. Plasma estradiol and testosterone were within the normal range for all four groups of subjects and were not significantly related to their HPA axis hormone responses. The study results support the hypothesis of heightened cholinergic sensitivity in premenopausal female, but not in male, patients with major depression. The low dose of PHYSO used may represent a useful paradigm for central cholinergic stimulation of the HPA axis.

Vasopressin and the regulation of hypothalamic-pituitary-adrenal axis function: implications for the pathophysiology of depression

The role of arginine vasopressin (AVPNP) in the control of adrenocorticotropic hormone (ACTH) secretion is explored, and in particular, its involvement in various stress response paradigms which may be of relevance in our understanding of the pathophysiology of depression. VP is released from two sites in the hypothalamus; the parvicellular division of the paraventricular nucleus (PVN), where corticotropin releasing hormone (CRH) is also formed, and from the magnocellular neurons of the supraoptic nucleus (SON) and the PVN. The intricate interaction with CRH, the other main ACTH secretagogue, and with glucocorticoids, the inhibitory feedback component of hypothalamic-pituitary-adrenal-axis (HPA) activity, is outlined. That VP plays an important role in the stress response is now beyond doubt. Examination of the impact of psychological stressors on the differential expression of VP and CRH at a hypothalamic and pituitary level has been facilitated by advances in molecular biological techniques. Of importance has been the cloning of the V1b receptor gene, the receptor at which AVP is active in the anterior pituitary. Chronic stress paradigms, associated with HPA hyperresponsiveness, and ACTH release following a novel superimposed stress, have been found with relative consistency to show a shift in the CRH:AVP ratio. This may relate to differing feedback sensitivity of AVP to glucocorticoid feedback restraint and the greater responsivity of AVP over CRH to chronic stimulatory stress input. Evidence for functionally distinct pools of ACTH releasing corticotropes, and the finding that AVP levels more closely correlate with ACTH levels than do CRH levels, suggest a more dynamic role for AVP in activity of the stress axis, and a primarily permissive function for CRH. The renewed interest in the role of VP in HPA axis activity may have important implications for furthering our understanding of psychiatric conditions such as depression, where significant dysregulation of this axis is seen. Elevated baseline cortisol, dexamethasone non-suppression and blunted CRH/ACTH release have been consistently documented. The possible contribution of VP to this hyperactivity, despite its known synergy with CRH, has been largely neglected. In animal models there is clear evidence that chronic psychological stressors increase the ratio of AVP to CRH production. Psychosocial stressors are intrinsically linked with depressive illness. The finding of elevated levels of AVP in postmortem studies of depressives and the lowering of CSF AVP levels by antidepressants, raises the question of the precise role of AVP in the overactivity of the HPA in depression, a finding that is currently attributed to overdrive of its HPA regulatory companion, CRH.

Correlation between vasopressin baseline and TSH-blunting in depressives

A blunted thyrotropin (TSH) response is a predictor of a good response to antidepressant drug treatment in depressives and neuroleptic treatment in paraphrenic patients (Larger et al 1986). The aim of the following study was to elucidate possible relationships between different endocrine systems and to shed light on the pathogenetic hypotheses of TSH-blunting. In order to evaluate especially hypothalamic activity in severe depression we were interested in the vasopressin system as another hormonal system underlying hypothalamic control. Thirty-four patients who met the criteria for major depression according to DSM-III-R were subjected to the thyrotropin-releasing hormone (TRH) test. We also took baseline readings of the cortisol, neurophysinI (hNpI, reflecting vasopressin plasma levels), and neurophysinII (hNpII, reflecting oxytocin plasma levels) levels. Likelihood ratio tests were done with logistic regression models to analyze the phenomenon of TSH-blunting. We observed that the likelihood of a blunted TSH response increases with higher levels of hNpI and low levels of cortisol, but is unrelated to hNpII levels.

Stimulation of the pituitary-adrenal system with graded doses of CRH and low dose vasopressin infusion in depressed patients and healthy subjects: a pilot study

A corticotropin-releasing hormone (CRH) stimulation test with four cumulative doses of human CRH (0.01, 0.06, 0.2 and 1 microgram/kg body weight) and infusion of a low dose of [Arg8]-vasopressin (0.004 U/kg body weight/30 min) was performed in five depressed patients and six healthy subjects. Plasma samples for the measurement of cortisol, ACTH and beta-endorphin were taken at regular intervals and considered as measures of pituitary-adrenal function. A dose-response relationship between CRH and the hormones measured was found in patients and controls. Depressed patients already responded to the lowest dose of CRH with respect to cortisol release, whereas ACTH and beta-endorphin responded to the second and third doses, respectively. In control subjects the cortisol and ACTH response started after the third dose of CRH, whereas beta-endorphin responded significantly to the highest dose only. When both groups were compared, differences in response were found to the higher doses of CRH with respect to cortisol, ACTH and, less markedly, beta-endorphin and to the lowest dose of CRH with respect to cortisol. Although numbers are small, the data show 'blunting' of the ACTH response to the higher doses of CRH in patients with an enhanced cortisol response of the adrenals to lower and higher doses of CRH. There was no significant difference in response when CRH was used with vasopressin as compared to treatment with CRH alone. Thus, in this design vasopressin did not contribute significantly to CRH activity. The data suggest that pituitary cell sensitivity might be changed in depression as part of HPA dysfunction.