Clinical and magnetic resonance imaging correlates of hypothalamic-pituitary-adrenal axis function in depression and Alzheimer's disease

The role of metabolic derangements and glucocorticoid excess in the aetiology of cognitive impairment in type 2 diabetes. Implications for future therapeutic strategies

Dementia is becoming increasingly common in western societies and carries with it a substantial clinical, social and economic burden. It is now well established that type 2 diabetes is a risk factor for dementia and it is likely that this association has a multifactorial aetiology. There is a relative paucity of data on interventions to improve cognitive function in people with type 2 diabetes. Two small randomized controlled trials have suggested that better glycaemic control, over a relatively short time period, can improve or prevent decline in cognitive function. There is also increasing interest in the link between intracerebral insulin and cognitive impairment. Several studies have suggested that relative and/or absolute deficiency of insulin may occur in Alzheimer's dementia and, although one small randomized trial was essentially negative, randomized trials are currently underway to investigate the impact of thiazolidinediones on cognitive function in dementia. The hypothalamic-pituitary-adrenal axis is also activated in people with type 2 diabetes and there are data linking increased cortisol concentrations with cognitive impairment. Inhibition of the 11 beta-hydroxysteroid dehydrogenase type 1 enzyme, which generates cortisol from inactive cortisone in many tissues including the brain, is an attractive therapeutic target to enhance cognition. Large-scale epidemiological and intervention studies are now underway, which should enhance our understanding and management of cognitive impairment in type 2 diabetes.

A comparison of neurocognitive impairment in younger and older adults with major depression

BACKGROUND

Neurocognitive impairment is a well-recognized feature of depression that has been reported in younger and older adults. Similar deficits occur with ageing and it is unclear whether the greater deficits in late-life depression are an ageing-related phenomenon or due to a difference in the nature of late-life depression itself. We hypothesized that ageing alone would not fully explain the increased neurocognitive impairment in late-life depression but that differences in the illness explain the greater decrements in memory and executive function.

METHOD

Comparison of the neuropsychological performance of younger (<60 years) and older (60 years) adults with major depressive disorder (MDD) and healthy comparison subjects. Scores for each depression group were normalized against their respective age-matched control group and the primary comparisons were on four neurocognitive domains: (i) attention and executive function; (ii) verbal learning and memory; (iii) visuospatial learning and memory; and (iv) motor speed.

RESULTS

We recruited 75 subjects with MDD [<60 years (n=44), 60 years (n=31)] and 82 psychiatrically healthy comparison subjects [<60 years (n=42), 60 years (n=40)]. The late-life depression group had greater impairment in verbal learning and memory and motor speed but not in executive function. The two depressed groups did not differ in depression severity, global cognitive function, intelligence or education.

CONCLUSIONS

Late-life depression is associated with more severe impairment in verbal learning and memory and motor speed than depression in earlier adult life and this is not due to ageing alone.

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

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

Pathways linking late-life depression to persistent cognitive impairment and dementia

There is a strong association between late-life depression, cognitive impairment, cerebrovascular disease, and poor cognitive outcomes, including progressive dementia, especially Alzheimer's disease. While neuroimaging evidence suggests that cerebrovascular disease plays a prominent role, it seems that depression alone may also confer substantial risk for developing Alzheimer's disease. The relationships between the prominent cerebrovascular changes, other structural abnormalities, specific forms of cognitive dysfunction, and increased risk for developing Alzheimer's disease among those with late-life depression have been difficult to reconcile. The varied findings suggest that there are likely multiple pathways to poor cognitive outcomes. We present a framework outlining multiple, non-mutually exclusive etiologic links between depression, cognitive impairment, and progressive decline, including dementia. Importantly, the model is both testable and falsifiable. Going forward, using models such as this to inform research should accelerate knowledge acquisition on the depression/dementia relationship that may be useful for dementia prevention, monitoring the impact of depression treatment on clinical status and course of illness.

12-month cognitive outcomes of major and minor depression in older medical patients

OBJECTIVE

To examine the temporal relationship between depression diagnoses and cognitive function in older medical patients.

DESIGN

Prospective cohort study with repeated follow-up assessments at 3, 6, and 12 months after hospitalization.

SETTING

The medical services of two acute care hospitals in Montreal, Quebec, Canada.

PARTICIPANTS

Two hundred eighty-one medical inpatients aged 65 and older without apparent cognitive impairment at study entry.

MEASUREMENTS

Diagnostic Interview Schedule for depression and Mini-Mental State Examination (MMSE) for cognitive function.

RESULTS

At study entry, 121 (43.1%) and 51 (18.1%) patients, respectively, met Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition criteria for major or minor depression. Based on a mixed effects regression model, depression diagnoses were associated with poorer cognitive function, independent of age, education, baseline cognitive and physical function, cardiovascular diseases and other comorbidities, previous history of depression and antidepressant treatment, and fluctuation in the severity of depression symptoms over time. On average across three follow-up assessments, patients with major or minor depression, respectively, had a 0.8 (95% confidence interval: 0.1-1.5) and 1.0 (0.3-1.8) point lower performance on the MMSE than those without depression. In contrast, there was no significant association when depression diagnoses and cognitive function were assessed over shorter intervals or cross-sectionally. A general linear regression model yielded consistent results, with adjusted effect estimates of 0.9 (0.03-0.8) for major and 1.5 (0.5-2.5) for minor depression over 12 months.

CONCLUSION

A diagnosis of major or minor depression at hospital admission is an independent risk factor for poorer cognitive function during the subsequent 12 months in older medical patients.

Role of insulin metabolism disturbances in the development of Alzheimer disease: mini review

Alzheimer disease (AD) is the most common form of dementia. Different pathogenic processes have been studied that underlie characteristic changes of AD, including A beta protein aggregation, tau phosphorylation, neurovascular dysfunction, and inflammatory processes. Insulin exerts pleiotropic effects in neurons, such as the regulation of neural proliferation, apoptosis, and synaptic transmission. In this setting, any disturbance in the metabolism of insulin in the central nervous system (CNS) may put unfavorable effects on CNS function. It seems that disturbances in insulin metabolism, especially insulin resistance, play a role in most pathogenic processes that promote the development of AD. In this article, the relationships of disturbances in the metabolism of insulin in CNS with A beta peptides aggregation, tau protein phosphorylation, inflammatory markers, neuron apoptosis, neurovascular dysfunction, and neurotransmitter modulation are discussed, and future research directions are provided.

Reduction in rat phosphatidylethanolamine binding protein-1 (PEBP1) after chronic corticosterone treatment may be paralleled by cognitive impairment: a first study

Chronic stress is associated with hippocampal atrophy and cognitive dysfunction. This study investigates how long-lasting administration of corticosterone as a mimic of experimentally induced stress affects psychometric performance and the expression of the phosphatidylethanolamine binding protein (PEBP1) in the adult hippocampus of one-year-old male rats. Psychometric investigations were conducted in rats before and after corticosterone treatment using a holeboard test system. Rats were randomly attributed to 2 groups (n = 7) for daily subcutaneous injection of either 26.8 mg/kg body weight corticosterone or sesame oil (vehicle control). Treatment was continued for 60 days, followed by cognitive retesting in the holeboard system. For protein analysis, the hippocampal proteome was separated by 2D electrophoresis (2DE) followed by image processing, statistical analysis, protein identification via peptide mass fingerprinting and gel matching and subsequent functional network mapping and molecular pathway analysis. Differential expression of PEBP1 was additionally quantified by Western blot analysis. Results show that chronic corticosterone significantly decreased rat hippocampal PEBP1 expression and induced a working and reference memory dysfunction. From this, we derive the preliminary hypothesis that PEBP1 may be a novel molecular mediator influencing cognitive integrity during chronic corticosterone exposure in rat hippocampus.

Social support and enhanced suppression of adrenocorticotropic hormone and cortisol responses to hypothalamic-pituitary-adrenal function and thyrotropin-releasing hormone tests in patients with major depressive disorder

The results of the thyrotropin-releasing hormone (TRH) stimulation test and the combined dexamethasone/corticotropin-releasing hormone (DEX/CRH) test are believed to correlate with social support status in patients with major depressive disorder. We studied 41 consecutive patients hospitalized for major depressive disorder and tested their responses to DEX/CRH and TRH on hospital days 4-7. DeltaMAX TSH and DeltaMAX cortisol were measured. Multiple regression analysis found that social support questionnaire (SSQ-A) and SSQ-B scores were significantly related to DeltaMAX cortisol and DeltaMAX TSH, respectively, at the time of admission. Social support might contribute partially to the TRH and DEX/CRH test results in patients with major depressive disorder.

Relationship between body mass index and gray matter volume in 1,428 healthy individuals

OBJECTIVE

To investigate any correlation between BMI and brain gray matter volume, we analyzed 1,428 healthy Japanese subjects by applying volumetric analysis and voxel-based morphometry (VBM) using brain magnetic resonance (MR) imaging, which enables a global analysis of brain structure without a priori identification of a region of interest.

METHODS AND PROCEDURES

We collected brain MR images from 690 men and 738 women, and their height, weight, and other clinical information. The collected images were automatically normalized into a common standard space for an objective assessment of neuroanatomical correlations in volumetric analysis and VBM with BMI.

RESULTS

Volumetric analysis revealed a significant negative correlation in men (P < 0.001, adjusting for age, lifetime alcohol intake, history of hypertension, and diabetes mellitus), although not in women, between BMI and the gray matter ratio, which represents the percentage of gray matter volume in the intracranial volume. VBM revealed that, in men, the regional gray matter volume of the bilateral medial temporal lobes, anterior lobe of the cerebellum, occipital lobe, frontal lobe, precuneus, and midbrain showed significant negative correlations with BMI, while those of the bilateral inferior frontal gyri, posterior lobe of the cerebellum, frontal lobes, temporal lobes, thalami, and caudate heads showed significant positive correlations with BMI.

DISCUSSION

Global loss and regional alterations in gray matter volume occur in obese male subjects, suggesting that male subjects with a high BMI are at greater risk for future declines in cognition or other brain functions.

Enhanced suppression of adrenocorticotropic hormone and cortisol responses to hypothalamic-pituitary-adrenal function and thyrotropin-releasing hormone tests after stressful life events in patients with major depressive disorder

BACKGROUND

It is commonly believed that there exists a relationship between the outcome of thyrotropin-releasing hormone (TRH) test, the combined dexamethasone/corticotropin-releasing hormone (DEX/CRH) test and stressful life events (SLEs) in major depressive disorder.

OBJECTIVE

SLEs influence the TRH and DEX/CRH tests in major depressive disorder when administered at the time of admission and improvement.

METHODS

The TRH and DEX/CRH tests were administered to patients hospitalized for major depressive disorders - on the 4th through the 7th hospital day and at the time of improvement. We measured DeltaMAX TSH, DeltaMAX ACTH, ACTH AUC, DeltaMAX cortisol, cortisol AUC, DeltaMAX ACTH/DeltaMAX TSH and DeltaMAX cortisol/DeltaMAX TSH.

RESULTS

SLEs were significantly negatively associated with DeltaMAX ACTH, ACTH AUC and cortisol AUC at the time of admission. However, these relationships lost significance at the time of improvement. The sample (41 patients at the time of admission, 18 patients at the time of improvement) was relatively small, which may have contributed to false-negative results.

CONCLUSION

SLEs may be negatively associated with the outcome of the DEX/CRH tests in major depressive disorder. The hypothalamic-pituitary-adrenal axis in the DEX/CRH test was modulated by SLEs.

Major depression in late life is associated with both hypo- and hypercortisolemia

BACKGROUND

In younger adults, depression has been associated with hypercortisolemia. In older depressed patients, however, both low and high cortisol levels have been reported. We examined the possibility of a U-shaped association between depression and cortisol in older people, suggesting both hypo- and hyperactivity of the hypothalamic-pituitary-adrenal axis. We also examined whether this might represent different depression subtypes.

METHODS

This population-based study included 1185 subjects aged 65 and older. Depression was measured at both diagnostic (major depression) and symptomatic (subthreshold depression) levels of caseness. Plasma concentrations of cortisol (CORT) and corticosteroid binding globulin (CBG) were determined. From these (CORT/CBG), a free cortisol index (FCI) was computed.

RESULTS

The association between cortisol and major depression was U-shaped (B CORT = -9.50 [SE 3.85] p = .014; B CORT(2) = .008 [SE .003] p = .021). Hypocortisolemic depression (lower cortisol tertile) was associated with female sex, joint diseases, and smoking. Hypercortisolemic (upper cortisol tertile) depression was associated with older age, male sex, cardiovascular diseases, nonsteroidal antiinflammatory use, and (borderline significant) cognitive impairment.

CONCLUSIONS

In older people, the association between cortisol and major depression is U-shaped. Hypo- and hypercortisolemic depression may represent different depression subtypes, requiring different clinical management.

Antidepressant-induced neurogenesis in the hippocampus of adult nonhuman primates

New neurons are generated in the adult hippocampus of many species including rodents, monkeys, and humans. Conditions associated with major depression, such as social stress, suppress hippocampal neurogenesis in rodents and primates. In contrast, all classes of antidepressants stimulate neuronal generation, and the behavioral effects of these medications are abolished when neurogenesis is blocked. These findings generated the hypothesis that induction of neurogenesis is a necessary component in the mechanism of action of antidepressant treatments. To date, the effects of antidepressants on newborn neurons have been reported only in rodents and tree shrews. This study examines whether neurogenesis is increased in nonhuman primates after antidepressant treatment. Adult monkeys received repeated electroconvulsive shock (ECS), which is the animal analog of electroconvulsive therapy (ECT), the most effective short-term antidepressant. Compared with control conditions, ECS robustly increased precursor cell proliferation in the subgranular zone (SGZ) of the dentate gyrus in the monkey hippocampus. A majority of these precursors differentiated into neurons or endothelial cells, while a few matured into glial cells. The ECS-mediated induction of cell proliferation and neurogenesis was accompanied by increased immunoreactivity for the neuroprotective gene product BCL2 (B cell chronic lymphocytic lymphoma 2) in the SGZ. The ECS interventions were not accompanied by increased hippocampal cell death or injury. This study demonstrates that ECS is capable of inducing neurogenesis in the nonhuman primate hippocampus and supports the possibility that antidepressant interventions produce similar alterations in the human brain.

Late-life depressive symptoms are associated with both hyperactivity and hypoactivity of the hypothalamo-pituitary-adrenal axis

OBJECTIVE

Although depression has been associated with hyperactivity of the hypothalamo-pituitary-adrenal (HPA) axis, recent studies among depressed elderly have found decreased cortisol levels, which may be due to underlying physical frailty associated with HPA-axis hypoactivity. The authors examined the relationship between urinary cortisol level and late-life depressive symptoms. The authors also explored whether hypo- and hypercortisolemic depressive symptoms are qualitatively different.

METHODS

Data are from 881 community-dwelling participants, average age 74.2 years, of the Aging in the Chianti Area Study. Depressive symptoms were assessed using the Center for Epidemiologic Studies Depression Scale (CES-D) scale and cortisol levels were determined in 24-hour urine samples.

RESULTS

Mean urinary cortisol level was 98.9 microg/24 hours (SD=47.8), and 31% of the sample had significant depressive symptoms (CES-D > or =16). There was no linear association between urinary cortisol level and depressive symptoms; however, there was a nonlinear association between urinary cortisol level and depressive symptoms. Older persons in the lowest and highest urinary cortisol deciles were 2.2 and 1.9 times more likely to have significant depressive symptoms than older persons in all other deciles. Depressed persons with low cortisol presented more physical frailty than depressed persons with high cortisol.

CONCLUSION

Late-life depressive symptoms are associated with both hyperactivity and hypoactivity of the HPA axis, which suggests distinct mechanisms for these associations.

The associations among hippocampal volume, cortisol reactivity, and memory performance in healthy young men

In aged and pathological populations, reduced hippocampal volume is frequently described in association with impairment of hippocampus-dependent cognitive processes and chronically elevated cortisol levels. Recent studies in young healthy subjects show a negative association between hippocampal volume and memory. The aim of the present study was to investigate the associations among hippocampal volume, cortisol levels and memory performance in a group of healthy young men. Hippocampal volume was determined by manual segmentation of high-resolution 3D Magnetic Resonance Images from 13 subjects. Stress-induced cortisol levels in response to the "Trier Social Stress Test" (TSST) as well as the cortisol response to awakening (CRA) over four weeks were assessed. Declarative memory performance was tested before and after exposure to the TSST. The results show that larger hippocampal volume was associated with a significantly stronger cortisol increase in response to the TSST and a significantly greater CRA. Moreover, larger hippocampal volume was associated with significantly lower memory performance before the TSST. Our results challenge the direction of the frequently observed relationships among hippocampal volume, cortisol reactivity and memory performance and question the relevance of findings in clinical and aged subjects for young healthy populations.

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.

Plasma cortisol and progression of dementia in subjects with Alzheimer-type dementia

OBJECTIVE

Studies of subjects with dementia of the Alzheimer type have reported correlations between increases in activity of the hypothalamic-pituitary-adrenal (HPA) axis and hippocampal degeneration. In this study, the authors sought to determine whether increases in plasma cortisol, a marker of HPA activity, were associated with clinical and cognitive measures of the rate of disease progression in subjects with Alzheimer-type dementia.

METHOD

Thirty-three subjects with very mild and mild Alzheimer-type dementia and 21 subjects without dementia were assessed annually for up to 4 years with the Clinical Dementia Rating scale and a battery of neuropsychological tests. Plasma was obtained at 8 a.m. on a single day and assayed for cortisol. Rates of change over time in the clinical and cognitive measures were derived from growth curve models.

RESULTS

In the subjects with dementia, but not in those without dementia, higher plasma cortisol levels were associated with more rapidly increasing symptoms of dementia and more rapidly decreasing performance on neuropsychological tests associated with temporal lobe function. No associations were observed between plasma cortisol levels and clinical and cognitive assessments obtained at the single assessment closest in time to the plasma collection.

CONCLUSIONS

Higher HPA activity, as reflected by increased plasma cortisol levels, is associated with more rapid disease progression in subjects with Alzheimer-type dementia.

Inflammation and depression: is there a causal connection with dementia?

Epidemiological studies show that there is a correlation between chronic depression and the likelihood of dementia in later life. There is evidence that inflammatory changes in the brain are pathological features of both depression and dementia. This suggests that an increase in inflammation-induced apoptosis, together with a reduction in the synthesis of neurotrophic factors caused by a rise in brain glucocorticoids, may play a role in the pathology of these disorders. A reduction in the neuroprotective components of the kynurenine pathway, such as kynurenic acid, and an increase in the neurodegenerative components, 3- hydroxykynurenine and quinolinic acid, contribute to the pathological changes. Such changes are postulated to cause neuronal damage and thereby predispose chronically depressed patients to dementia.

Plasma cortisol and progression of dementia in subjects with Alzheimer-type dementia

OBJECTIVE

Studies of subjects with dementia of the Alzheimer type have reported correlations between increases in activity of the hypothalamic-pituitary-adrenal (HPA) axis and hippocampal degeneration. In this study, the authors sought to determine whether increases in plasma cortisol, a marker of HPA activity, were associated with clinical and cognitive measures of the rate of disease progression in subjects with Alzheimer-type dementia.

METHOD

Thirty-three subjects with very mild and mild Alzheimer-type dementia and 21 subjects without dementia were assessed annually for up to 4 years with the Clinical Dementia Rating scale and a battery of neuropsychological tests. Plasma was obtained at 8 a.m. on a single day and assayed for cortisol. Rates of change over time in the clinical and cognitive measures were derived from growth curve models.

RESULTS

In the subjects with dementia, but not in those without dementia, higher plasma cortisol levels were associated with more rapidly increasing symptoms of dementia and more rapidly decreasing performance on neuropsychological tests associated with temporal lobe function. No associations were observed between plasma cortisol levels and clinical and cognitive assessments obtained at the single assessment closest in time to the plasma collection.

CONCLUSIONS

Higher HPA activity, as reflected by increased plasma cortisol levels, is associated with more rapid disease progression in subjects with Alzheimer-type dementia.

The neuropsychological profile of psychotic major depression and its relation to cortisol

BACKGROUND

Our study described the neuropsychological profile of psychotic major depression (PMD) compared to nonpsychotic major depression (NPMD) patients and psychiatrically healthy controls (HC). We predicted that higher cortisol levels would be associated with greater cognitive deficits.

METHODS

Twenty-nine PMDs, 24 NPMDs, and 26 HCs were recruited at Stanford University Medical Center. Psychiatric ratings, cortisol levels from 1800-0900 hours, and neuropsychological test data were obtained.

RESULTS

PMDs had more severe cognitive impairments compared with NPMDs and HCs with the exception of simple verbal attention. PMDs had elevated mean cortisol levels from 1800 to 0100 hours which were significantly correlated with poorer verbal memory and psychomotor speed performance. Cortisol slopes from 1800 to 0100 hours were also significantly correlated with verbal memory and working memory.

CONCLUSIONS

While PMDs' ability to attend passively to information appears intact, they have more difficulty processing, manipulating, and encoding new information. Elevated cortisol levels, as seen in PMD patients, are associated with poorer cognitive performance especially related to verbal memory for lists of words and working memory.

Cognitive dysfunction, hippocampal atrophy and glucocorticoid feedback in Alzheimer's disease

BACKGROUND

The hippocampal formation is damaged early in Alzheimer's disease (AD). An association between temporal lobe volume and cognitive function has been shown in several studies. Increased limbic-hypothalamic-pituitary-adrenal (LHPA) axis function has been suggested to be related to hippocampal atrophy and cognitive impairment. Our hypothesis was that there is a clear link between hippocampal volume -- notably of the CA1 region -- memory (episodic and visuospatial) and decreased feedback sensitivity in the LHPA axis in AD.

METHODS

Sixteen medication-free outpatients with mild to moderate AD were included. Hippocampal volume was measured with magnetic resonance imaging. Dexamethasone suppression tests were performed using .5 mg and .25 mg dexamethasone. Three different components in the neuropsychological battery -- Rey 15 item memory test, Alzheimer's Disease Assessment Scale (ADAS) word recall and spatial span from Wechsler Adult Intelligence Scale - Revised neuropsychological instrument (WAIS-R NI) -- were found to represent episodic and visuospatial memory.

RESULTS

Low hippocampal CA1 volume and high post-dexamethasone cortisol levels in combination were significantly associated with Rey 15 item memory and spatial span test outcomes. No association was found between LHPA feedback and hippocampal volume.

CONCLUSIONS

Low hippocampal volume and a disturbed negative feedback in the LHPA axis link to specific cognitive impairments in Alzheimer's disease.

Physiological correlates of cognitive functioning in an elderly population

Cognitive decline in old age is not universal or inevitable. Associations have been observed with neuroendocrine function, but the relevance of other physiological processes is unclear. We predicted that impairment of memory in an ageing population would be related to the dysregulation of neuroendocrine and cardiovascular responses. One hundred and thirty-nine participants (65-80 years) were recruited from general practice in London. Two standardised verbal paired-associates recall tasks were administered in order to determine declarative memory performance, and a fluid intelligence task (matrix reasoning) was also performed. Salivary cortisol samples were collected every 10 min, while blood pressure and heart rate were measured before, during and after each task. Illness history and medication use were obtained from medical records. Multiple linear regression analysis, adjusted for age, gender, education, chronic illness, and medication use, revealed that cortisol responses were inversely related to memory performance. Additionally, superior memory was associated with more effective post-task recovery of heart rate (in both men and women) and diastolic blood pressure recovery in men. Cardiovascular recovery effects were independent of covariates, and of levels of heart rate and blood pressure measured during tasks themselves. These associations were also independent of subjective ratings of stress and perceived performance. Neither neuroendocrine nor cardiovascular responses were related to performance of the reasoning task. We conclude that memory in the elderly is associated both with hypothalamic-pituitary-adrenocortical function and cardiovascular regulation. Disturbances of neuroendocrine and hemodynamic function may be related to greater vulnerability to cognitive decline.

Brain glucose metabolism in the early and specific diagnosis of Alzheimer's disease. FDG-PET studies in MCI and AD

The demographics of aging suggest a great need for the early diagnosis of dementia and the development of preventive strategies. Neuropathology and structural MRI studies have pointed to the medial temporal lobe (MTL) as the brain region earliest affected in Alzheimer's disease (AD). MRI findings provide strong evidence that in mild cognitive impairments (MCI), AD-related volume losses can be reproducibly detected in the hippocampus, the entorhinal cortex (EC) and, to a lesser extent, the parahippocampal gyrus; they also indicate that lateral temporal lobe changes are becoming increasingly useful in predicting the transition to dementia. Fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) imaging has revealed glucose metabolic reductions in the parieto-temporal, frontal and posterior cingulate cortices to be the hallmark of AD. Overall, the pattern of cortical metabolic changes has been useful for the prediction of future AD as well as in distinguishing AD from other neurodegenerative diseases. FDG-PET on average achieves 90% sensitivity in identifying AD, although specificity in differentiating AD from other dementias is lower. Moreover, recent MRI-guided FDG-PET studies have shown that MTL hypometabolism is the most specific and sensitive measure for the identification of MCI, while the utility of cortical deficits is controversial. This review highlights cross-sectional, prediction and longitudinal FDG-PET studies and attempts to put into perspective the value of FDG-PET in diagnosing AD-like changes, particularly at an early stage, and in providing diagnostic specificity. The examination of MTL structures, which has so far been exclusive to MRI protocols, is then examined as a possible strategy to improve diagnostic specificity. All told, there is considerable promise that early and specific diagnosis is feasible through a combination of imaging modalities.

Plasma cortisol levels, brain volumes and cognition in healthy elderly men

PURPOSE

In ageing animals, exposure to chronic high levels of glucocorticoids is associated with cognitive impairment and hippocampal atrophy. However, there are few studies examining relationships among glucocorticoids, brain volumes and cognitive function in healthy older humans. This study examined the hypotheses that higher plasma cortisol levels and altered sensitivity to glucocorticoids are associated with worse cognition and more brain atrophy in elderly men.

MATERIALS AND METHODS

Ninety-seven healthy men aged 65-70 had plasma cortisol measured at 09:00, 14:30 h, and post-dexamethasone (0.25mg, 09:00 h), and had dermal sensitivity to glucocorticoids measured. They also underwent cognitive testing, with scores adjusted for estimated prior mental ability, and had MRI measurements of intracranial area (a validated estimate of intracranial capacity), and hippocampus, temporal lobe and frontal lobe volumes.

RESULTS

Plasma cortisol levels at 09:00 h were significantly and negatively correlated with a summary General Cognitive Factor accounting for 51% of the variance of cognitive function (rho=-0.22, p=0.035), and specific cognitive tests: delayed paragraph recall (rho=-0.28, p=0.036) and processing speed (rho=-0.23, p=0.026). Regional brain volumes adjusted for intracranial area generally did not correlate with cortisol levels. Tissue glucocorticoid sensitivity did not correlate with any measure of cognition or brain volume.

CONCLUSIONS

In healthy older men, higher plasma cortisol levels are associated with worse ageing-related overall cognitive change but not ageing-related brain atrophy.

The stress system in the human brain in depression and neurodegeneration

Corticotropin-releasing hormone (CRH) plays a central role in the regulation of the hypothalamic-pituitary-adrenal (HPA)-axis, i.e., the final common pathway in the stress response. The action of CRH on ACTH release is strongly potentiated by vasopressin, that is co-produced in increasing amounts when the hypothalamic paraventricular neurons are chronically activated. Whereas vasopressin stimulates ACTH release in humans, oxytocin inhibits it. ACTH release results in the release of corticosteroids from the adrenal that, subsequently, through mineralocorticoid and glucocorticoid receptors, exert negative feedback on, among other things, the hippocampus, the pituitary and the hypothalamus. The most important glucocorticoid in humans is cortisol, present in higher levels in women than in men. During aging, the activation of the CRH neurons is modest compared to the extra activation observed in Alzheimer's disease (AD) and the even stronger increase in major depression. The HPA-axis is hyperactive in depression, due to genetic factors or due to aversive stimuli that may occur during early development or adult life. At least five interacting hypothalamic peptidergic systems are involved in the symptoms of major depression. Increased production of vasopressin in depression does not only occur in neurons that colocalize CRH, but also in neurons of the supraoptic nucleus (SON), which may lead to increased plasma levels of vasopressin, that have been related to an enhanced suicide risk. The increased activity of oxytocin neurons in the paraventricular nucleus (PVN) may be related to the eating disorders in depression. The suprachiasmatic nucleus (SCN), i.e., the biological clock of the brain, shows lower vasopressin production and a smaller circadian amplitude in depression, which may explain the sleeping problems in this disorder and may contribute to the strong CRH activation. The hypothalamo-pituitary thyroid (HPT)-axis is inhibited in depression. These hypothalamic peptidergic systems, i.e., the HPA-axis, the SCN, the SON and the HPT-axis, have many interactions with aminergic systems that are also implicated in depression. CRH neurons are strongly activated in depressed patients, and so is their HPA-axis, at all levels, but the individual variability is large. It is hypothesized that particularly a subgroup of CRH neurons that projects into the brain is activated in depression and induces the symptoms of this disorder. On the other hand, there is also a lot of evidence for a direct involvement of glucocorticoids in the etiology and symptoms of depression. Although there is a close association between cerebrospinal fluid (CSF) levels of CRH and alterations in the HPA-axis in depression, much of the CRH in CSF is likely to be derived from sources other than the PVN. Furthermore, a close interaction between the HPA-axis and the hypothalamic-pituitary-gonadal (HPG)-axis exists. Organizing effects during fetal life as well as activating effects of sex hormones on the HPA-axis have been reported. Such mechanisms may be a basis for the higher prevalence of mood disorders in women as compared to men. In addition, the stress system is affected by changing levels of sex hormones, as found, e.g., in the premenstrual period, ante- and postpartum, during the transition phase to the menopause and during the use of oral contraceptives. In depressed women, plasma levels of estrogen are usually lower and plasma levels of androgens are increased, while testosterone levels are decreased in depressed men. This is explained by the fact that both in depressed males and females the HPA-axis is increased in activity, parallel to a diminished HPG-axis, while the major source of androgens in women is the adrenal, whereas in men it is the testes. It is speculated, however, that in the etiology of depression the relative levels of sex hormones play a more important role than their absolute levels. Sex hormone replacement therapy indeed seems to improve mood in elderly people and AD patients. Studies of rats have shown that high levels of cumulative corticosteroid exposure and rather extreme chronic stress induce neuronal damage that selectively affects hippocampal structure. Studies performed under less extreme circumstances have so far provided conflicting data. The corticosteroid neurotoxicity hypothesis that evolved as a result of these initial observations is, however, not supported by clinical and experimental observations. In a few recent postmortem studies in patients treated with corticosteroids and patients who had been seriously and chronically depressed no indications for AD neuropathology, massive cell loss, or loss of plasticity could be found, while the incidence of apoptosis was extremely rare and only seen outside regions expected to be at risk for steroid overexposure. In addition, various recent experimental studies using good stereological methods failed to find massive cell loss in the hippocampus following exposure to stress or steroids, but rather showed adaptive and reversible changes in structural parameters after stress. Thus, the HPA-axis in AD is only moderately activated, possibly due to the initial (primary) hippocampal degeneration in this condition. There are no convincing arguments to presume a causal, primary role for cortisol in the pathogenesis of AD. Although cortisol and CRH may well be causally involved in the signs and symptoms of depression, there is so far no evidence for any major irreversible damage in the human hippocampus in this disorder.

A meta-analysis of cortisol response to challenge in human aging: importance of gender

An increased cortisol response to challenge is associated with a variety of age-related disorders such as Alzheimer's disease, depression, diabetes, metabolic syndrome, and hypertension. Among the healthy elderly, an increased cortisol response to challenge may be a risk factor for developing these age-related disorders. We searched Pubmed, Embase, PsychInfo, Biosis, and Digital Dissertations (January 1966-June 2003) and included 45 parallel-group (young vs. old subjects) studies that used either a pharmacological or psychological challenge in healthy volunteers and measured cortisol response to challenge. We calculated effect sizes (Cohen's d) for the standardized mean differences between groups. Compared to younger controls (n=670, mean age 28 years +/-5), older subjects (n=625, 69+/-6) showed a larger cortisol response to challenge defined as stronger response to stimulation or less inhibition after a suppression test (d=0.42, 95% confidence interval (CI), 0.26-0.57). The effect of age on cortisol release was significantly stronger in women (d=0.65, 95% CI 0.34-0.97) than men (d=0.24, 95% CI 0.02-0.47). Our results demonstrate that aging increases the cortisol response to challenge. This effect of age on cortisol response is almost three-fold stronger in women than men. Prospective studies should explore whether the higher cortisol response in the elderly is a risk factor for developing neuropsychiatric and medical disorders.

Cognition in mania and depression: psychological models and clinical implications

Affective disorders, including bipolar disorder and major depressive disorder, are highly prevalent throughout the world and are extremely disabling. Diagnostic and Statistical Manual criteria and psychological models strongly implicate cognitive dysfunctions as being integral to our understanding of these disorders. We review the findings from studies that have used neurocognitive tests and functional imaging techniques to explore abnormal cognition in affective disorders. In particular, we highlight the evidence for cognitive dysfunctions that persist into full clinical remission, and the recent trend toward the use of "hot" processing tasks, involving emotionally charged stimuli, as a means of differentiating between the cognitive underpinnings of mania and depression. The clinical relevance of these developments is discussed.

Insulin resistance, affective disorders, and Alzheimer's disease: review and hypothesis

Affective disorders (ad) and Alzheimer's disease (AD) have been associated for almost a century, and various neurophysiologic factors have been implicated as common biologic markers. Yet, links between ad and AD still await elucidation. We propose that insulin resistance (IR) is one of the missing links between ad and AD. IR with hyperinsulinemia and subsequent impairment of glucose metabolism especially in ad patients may promote neurodegeneration and facilitate the onset of AD. According to our hypothesis, IR may persist even into ad remission in some patients. Persistent regional hypometabolism and vascular changes resulting from long-standing IR may lead to currently irreversible structural changes. Evidence in support of the hypothesis is reviewed and clinical implications suggested.

Habituation to stress and dexamethasone suppression in rats with selective basal forebrain cholinergic lesions

Previous studies suggest a role for basal forebrain cholinergic neurons in enhancing the inhibitory influence of the hippocampus and medial prefrontal cortex (mPFC) on glucocorticoid stress responses mediated by the hypothalamic-pituitary-adrenocortical (HPA) axis. An inhibitory action of the basal forebrain cholinergic (BFC) system may occur through facilitation of stress-related information processing and maintenance of glucocorticoid receptor (GR) expression and negative feedback signaling in these target regions. The current study investigated the possibility that BFC input to the hippocampus contributes to habituation of the glucocorticoid response following repeated exposure to a stressor. Cholinergic lesions were made by microinjections of the immunotoxin 192 IgG-saporin into the medial septum/vertical limb of the diagonal band, and 3 weeks later rats were subjected to six daily sessions of restraint stress. Blood samples taken before, during and after acute stress revealed a significant increase in peak activation and protracted elevation of corticosterone in cholinergic lesioned rats. After 5 days of repeated stress, however, both groups habituated to the stressor, as indicated by similarly low corticosterone profiles throughout both the response and recovery period. Against that habituated background, rats were administered a dexamethasone challenge on day 6, so that feedback status could be examined. Dexamethasone-induced suppression of endogenous corticosterone before, during, and after stress was significantly attenuated in lesioned rats. The profile of dysfunction in glucocorticoid regulation after selective cholinergic lesions in young animals may be relevant to the adrenocortical hyperactivity and negative feedback deficits seen in conditions such as normal aging and Alzheimer's dementia, in which integrity of the basal forebrain cholinergic system is compromised.

HPA axis and memory

The hormones of the hypothalamus-pituitary-adrenal (HPA) axis influence memory in situations of acute and chronic stress. The present review tries to summarize the current state of knowledge by describing the enhancing as well as the impairing effects of stress or glucocorticoid (GC) treatment documented in animals and humans. GCs secreted during the acquisition of a stressful task facilitate consolidation. However, acute stress (or GC treatment) unrelated to the task impairs performance. The effects of acute stress are additionally modulated by gender, age and the emotional valence of the learning material. Chronic stress in rodents has mostly impairing effects on memory and hippocampal integrity. However, other regions of the brain, such as the prefrontal cortex, are also sensitive to stress. In humans, similar observations have been reported in several patient populations as well as in older subjects. The potential to reverse these effects using behavioural or pharmacological approaches needs to be explored.

Effects of cholinergic lesions produced by infusions of 192 IgG-saporin on glucocorticoid receptor mRNA expression in hippocampus and medial prefrontal cortex of the rat

Principal neurons in the hippocampus and prefrontal cortex of the rat have been identified as targets for glucocorticoids involved in the hypothalamic-pituitary-adrenocortical stress response. Alterations in mRNA expression for glucocorticoid receptors in each of these regions have been shown to affect the negative feedback response to corticosterone following an acute stressor. Both decreases in forebrain glucocorticoid receptors and in the efficiency of adrenocortical feedback have been observed in normal aging, and have been selectively induced with experimental lesions or manipulations in neurotransmitter systems. The current study investigated the possibility that a loss of cholinergic support from cells in the basal forebrain, a hallmark of aging, contributes to the selective age-related loss of glucocorticoid receptor mRNA expression at cholinoceptive target sites that include the hippocampus and medial prefrontal cortex. Lesions of the basal forebrain cholinergic system in young adult rats were made by microinjections of the immunotoxin 192 IgG-saporin into the medial septum/vertical limb of the diagonal band and substantia innominata/nucleus basalis. Basal levels of circulating glucocorticoids were unaffected by the lesions. Analysis of both mineralocorticoid and glucocorticoid receptor mRNA expression revealed a significant decrease in glucocorticoid receptor mRNA in the hippocampus and medial prefrontal cortex, with spared expression at subcortical sites and no detectable change in mineralocorticoid receptor mRNA in any of the examined regions. Thus, rats with lesions of the basal forebrain cholinergic system recapitulate some of the detrimental effects of aging associated with glucocorticoid-mediated stress pathways in the brain.

Reversal of cycloheximide-induced memory disruption by AIT-082 (Neotrofin) is modulated by, but not dependent on, adrenal hormones

RATIONALE

AIT-082 (Neotrofin), a hypoxanthine derivative, has been shown to improve memory in both animals and humans. In animals, adrenal hormones modulate the efficacy of many memory-enhancing compounds, including piracetam and tacrine (Cognex).

OBJECTIVE

To investigate the role of adrenal hormones in the memory-enhancing action of AIT-082.

METHODS

Plasma levels of adrenal hormones (corticosterone and aldosterone) in mice were significantly reduced by surgical or chemical (aminoglutethimide) adrenalectomy or significantly elevated by oral administration of corticosterone. The effects of these hormone level manipulations on the memory-enhancing activity of AIT-082 and piracetam were evaluated using a cycloheximide-induced amnesia/passive avoidance model.

RESULTS

As previously reported by others, the memory enhancing action of piracetam was abolished by adrenalectomy. In contrast, the memory enhancement by 60 mg/kg AIT-082 (IP) was unaffected. However, a sub-threshold dose of AIT-082 (0.1 mg/kg, IP) that did not improve memory in control animals did improve memory in adrenalectomized animals. These data suggested that, similar to piracetam and tacrine, the memory enhancing action of AIT-082 might be inhibited by high levels of adrenal hormones. As expected, corticosterone (30 and 100 mg/kg) inhibited the action of piracetam, however no dose up to 100 mg/kg corticosterone inhibited the activity of AIT-082.

CONCLUSIONS

These data suggest that while AIT-082 function is not dependent on adrenal hormones, it is modulated by them. That memory enhancement by AIT-082 was not inhibited by high plasma corticosterone levels may have positive implications for its clinical utility, given that many Alzheimer's disease patients have elevated plasma cortisol levels.

Magnetic resonance imaging, Down's syndrome and Alzheimer's disease: research and clinical implications

BACKGROUND

The diagnosis of Alzheimer's disease (AD) remains at times difficult to make using available neuropsychological measures. Neuro-imaging is a relatively new form of detecting the changes associated with dementia. The present study investigated the role of magnetic resonance imaging (MRI) in diagnosing AD in adults with Down's syndrome (DS).

METHODS

Subjects with DS and Alzheimer-type dementia were matched to non-demented controls with DS. Magnetic resonance imaging findings (i.e. volumetric and two-dimensional scans) were compared between the two groups in order to show a relationship between the changes of AD and structural MRI abnormalities.

RESULTS

Specific structural abnormalities which are seen in non-intellectually disabled subjects with dementia are also found in individuals with both DS and AD. However, such findings cannot be used to diagnose clinical AD with good accuracy in adults with DS. A number of practical issues of patient compliance and over-sedation are demonstrated by the findings.

CONCLUSIONS

Magnetic resonance imaging has an important but limited role to play in the management of AD in the population with DS. If intravenous sedation is used, medical support is essential to prevent a serious mishap.

Cortisol and dehydroepiandosterone sulfate plasma levels and their relationship to aging, cognitive function, and dementia

We have studied the relationship between dehydroepiandrosterone sulfate (DHEAS), cortisol, and cognitive function in a population of demented patients (n=29), age-matched controls (n=46), and younger subjects (n=11). All were submitted to morning collection of blood for determination of plasma cortisol and DHEAS measured by 125I radioimmunoassay. DHEAS levels and cortisol/DHEAS ratios were significantly different among groups with higher DHEAS levels and lower cortisol/DHEAS ratios in younger people (Bonferroni p<.05). Cortisol levels were associated to the presence of dementia (Odds ratio=.93; 95% CI,.86-1.01). There was no difference between DHEAS levels of demented and age-matched controls; however, demented patients showed a trend for higher cortisol/DHEAS ratios than age-matched controls and the latter showed higher ratio values than younger subjects. DHEAS and cortisol plasma values were significantly correlated in all individuals (p<.01). In this study cortisol was independently associated to the presence of dementia.

Salivary cortisol day profiles in elderly with mild cognitive impairment

It is unknown whether hypothalamus-pituitary-adrenal (HPA) axis dysfunction is associated with the memory impairments observed among elderly participants with mild cognitive impairment (MCI), a group considered at increased risk for Alzheimer's disease (AD). Therefore, salivary cortisol levels were measured at six points over the course of the day while at-home in MCI participants (n=16), normal elderly (n=28), and young controls (n=14). Results revealed that MCI participants did not show elevated salivary cortisol levels. The 9 a.m. cortisol level of the MCI group was significantly lower than the 9 a.m. level of the young controls, but did not differ from those of the normal elderly group. In contrast to the other two groups, within the MCI group mean cortisol levels were inversely related to immediate recall of paragraphs. No association was observed between mean cortisol levels and performance in paired associates and digit span. Whether cortisol levels, in conjunction with other factors, such as hippocampal volume, will lead to improved prediction of future decline to AD in participants with MCI remains to be established in longitudinal studies.

Effects of rapid tryptophan depletion on salivary and plasma cortisol in Alzheimer's disease and the healthy elderly

Serotonergic function is reduced in dementia of Alzheimer type (DAT) and abnormalities in the hypothalamic-pituitary-adrenal (HPA) axis are also common. There is considerable interaction between the two systems. Effects of lowering brain serotonin on salivary and plasma cortisol were assessed in patients with DAT and in control subjects. A double-blind, cross-over design involving administration of two nutritionally balanced amino acid mixtures with or without tryptophan was used. Salivary and plasma cortisol were measured at intervals before and after the drink. DAT patients had higher salivary cortisol than controls. Despite a reduction of approximately 70% in plasma free tryptophan after 4 h in both groups, there was no effect on salivary or plasma cortisol. We conclude that, in subjects with DAT and healthy elderly subjects, acute tryptophan depletion had no effect on cortisol secretion.

Effects of hydrocortisone administration on cognitive function in the elderly

Previous studies have found adverse effects of both acute and chronic elevations of corticosteroids on cognitive function in humans and that cortisol levels may predict cognitive decline in elderly subjects. However, no previous studies have directly investigated the effects of hydrocortisone on cognitive functioning in the healthy elderly. Sixteen healthy elderly subjects took part in a placebo-controlled, double-blind, cross-over trial. Hydrocortisone 20 mg or placebo was administered twice, 12 h and 1 h before cognitive testing. On each occasion, a battery of neuropsychological tests was performed which included tests of attention, working memory, declarative memory and executive function. Salivary cortisol levels at the time of testing were elevated approximately 10-fold following hydrocortisone compared with placebo. No significant effects were found on memory or a range of other cognitive functions. The lack of effect of this regime of hydrocortisone is in contrast to studies in younger subjects. The elderly may be less sensitive to cognitive effects of short-term increases in cortisol levels, possibly due to an age-related downregulation of hippocampal glucocorticoid receptors.

Structural changes in the brain in depression and relationship to symptom recurrence

Depression is an important public health problem affecting about 15% of the general population; however, little is known about possible changes in the brain that might underlie the disorder. Neuroimaging has been a powerful tool to map actual changes in the brain structure of depressed patients that might be directly related to their symptoms of depression. Some imaging studies of brain structure have shown smaller hippocampal volume with the chronicity of depression correlating to a reduction in volume. Although the meaning of these findings is unclear, other studies have shown increased amygdala volume. Studies have found reductions in volume of the frontal cortex, with some studies showing specific reductions in subregions of the frontal cortex, including the orbitofrontal cortex. Findings of an increase in white matter lesions in elderly patients with depression have been replicated and correlated with late-onset depression, as well as impairments in social and cognitive function. These findings point to alterations in a circuit of brain regions hypothesized to include the frontal cortex, hippocampus, amygdala, striatum, and thalamus, that underlie symptoms of depression.

Role of calcium regulation in pathophysiology model of schizophrenia and possible interventions

Recent advances into the neuroscience research related to pathophysiology of schizophrenia have been impressive. While some are based on pre-existing theories and models, others have explored on a molecular level attempting to integrate the concepts of the past and present. However, given the complex multifactorial etiology of schizophrenia attempts to improve the current treatment modalities raise more questions than answers. In the cascade model of the hypotheses, the focus will be on a common factor/marker for the disease, to address the possible stepwise correlation between the various theories. Homeostasis of calcium, its relation to the release of glutamate, dopamine and nitric oxide will be discussed in detail with the potential for interventions aimed at every stage. Although this hypothesis emphasizes the role of calcium as a common factor, other potential causes such as autoantibodies to the receptors, such as NMDA (and GABA) cannot be ruled out.

History of depression as a risk factor for dementia: an updated review

OBJECTIVE

This review updates an earlier meta-analysis of the data on history of depression as a risk factor for dementia. It also considers the available evidence on the hypotheses proposed to explain the association between history of depression and dementia.

METHOD

A meta-analysis was carried out on results from seven case-control and six prospective studies. A qualitative review was carried out on the evidence related to the hypotheses to explain the association.

RESULTS

The meta-analysis found evidence to support an association from both case-control studies (estimated relative risk 2.01; 95% CI 1.16-3.50) and prospective studies (estimated relative risk 1.87; 95% CI 1.09-3.20). However, the evidence did not clearly support any one hypothesis explaining the association. The most likely contenders are: (i) depression can be an early prodrome of dementia, (ii) depression brings forward the clinical manifestation of dementing diseases, and (iii) depression leads to damage to the hippocampus through a glucocorticoid cascade.

CONCLUSIONS

The possibility that history of depression is a risk factor for dementia needs to be taken seriously and explanations of the association need to be further researched.

Neither major depression nor glucocorticoid treatment affects the cellular integrity of the human hippocampus

In major depression, decreased hippocampal volume has been attributed to hypercortisolemia, a frequent sign of the disorder, because in animals an excess of corticosteroids has led to dendritic atrophy, astrogliosis and loss of neurons in this brain region. The present study is the first to investigate the structural integrity of the human hippocampus in major depression and following glucocorticoid treatment. Post-mortem hippocampal tissue from 15 patients who had had major depression or bipolar affective disorder, 10 patients who had been treated with glucocorticoids and 16 controls was assessed using haematoxylin-eosin, Nissl and Bodian staining. The patterns of reactive astrogliosis (glial fibrillary acidic protein, GFAP), synaptic density (synaptophysin), synaptic reorganization (growth-associated protein B-50) and early signs of Alzheimer's disease (Alz-50) were examined immunocytochemically. Multivariate analysis, with the patients' age, tissue fixation time and postmortem delay as covariates, was performed. There was no evidence of neuronal cell loss or other major morphological alterations in any of the groups, nor was there a significant change in the distribution pattern of synaptophysin or Alz-50. Changes in B-50 and GFAP staining were observed in the steroid-treated and depressed patients in areas CA1 and CA2 only. The human hippocampus in major depression and after glucocorticoid treatment does not reveal any major morphological changes or signs of neuronal cell death, but does show subtle alterations in B-50 and GFAP expression in selected parts of the pyramidal cell layer.

Stress hormone-related psychopathology: pathophysiological and treatment implications

Stress is commonly associated with a variety of psychiatric conditions, including major depression, and with chronic medical conditions, including diabetes and insulin resistance. Whether stress causes these conditions is uncertain, but plausible mechanisms exist by which such effects might occur. To the extent stress-induced hormonal alterations (e.g., chronically elevated cortisol levels and lowered dehydroepiandrosterone [DHEA] levels) contribute to psychiatric and medical disease states, manipulations that normalize these hormonal aberrations should prove therapeutic. In this review, we discuss mechanisms by which hormonal imbalance (discussed in the frameworks of "allostatic load" and "anabolic balance") might contribute to illness. We then review certain clinical manifestations of such hormonal imbalances and discuss pharmacological and behavioural treatment strategies aimed at normalizing hormonal output and lessening psychiatric and physical pathology.

Stress-level cortisol treatment impairs inhibitory control of behavior in monkeys

Most studies of cortisol-induced cognitive impairments have focused on hippocampal-dependent memory. This study investigates a different aspect of cognition in a randomized placebo-controlled experiment with monkeys that were treated with cortisol according to a protocol that simulates a prolonged stress response. Young adult and older adult monkeys were assigned randomly to placebo or chronic treatment with cortisol in a 2 x 2 factorial design (n = 8 monkeys per condition). Inhibitory control of behavior was assessed with a test shown previously in primates to reflect prefrontal cortical dysfunction. Failure to inhibit a specific goal-directed response was evident more often in older adults. Treatment with cortisol increased this propensity in both older and young adult monkeys. Age-related differences in response inhibition were consistent across blocks of repeated test trials, but the treatment effects were clearly expressed only after prolonged exposure to cortisol. Aspects of performance that did not require inhibition were not altered by age or treatment with cortisol, which concurs with effects on response inhibition rather than nonspecific changes in behavior. These findings lend support to related reports that cortisol-induced disruptions in prefrontal dopamine neurotransmission may contribute to deficits in response inhibition and play a role in cognitive impairments associated with endogenous hypercortisolism in humans.

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.

Corticosteroids and cognition

The brain is a major target organ for corticosteroids. It has been observed that excessive circulatory levels of endogenous and exogenous corticosteroids are frequently associated with cognitive impairment in a wide variety of clinical disease states. Cognition and low levels of corticosteroids have been less well studied. In this paper we review the literature on glucocorticosteroid effects on cognition and delineate specific functions that appear to be causally affected. We draw a possible connection to specific areas of brain perturbation, including the hippocampus and frontal lobe regions. The possibility that cognitive dysfunction caused by glucocorticoids can be pharmacologically managed is introduced.

The association between depressive symptoms and cognitive decline in community-dwelling elderly persons

OBJECTIVE

To investigate whether depressive symptoms predict specific types of cognitive decline in order to elucidate the association between late life depression and cognitive decline.

BACKGROUND

Mechanisms underlying the association between late life depression and cognitive decline are still unclear.

METHOD

Six hundred and forty-one elderly persons of the Longitudinal Aging Study Amsterdam (LASA) aged 70-85 were examined by means of two measurement occasions over a period of 3 years. Depressive symptoms were assessed by means of the CES-D. Various cognitive functions were examined using neuropsychological tests.

RESULTS

Depressive symptoms were associated with decline in speed of information processing over a 3-year period, whereas there was no association between depression and increasing memory impairment or global mental deterioration.

CONCLUSION

These findings suggest that depressive symptoms are associated with subcortical pathology, most probable white matter lesions.

The neurobiology of the stress cascade and its potential relevance for schizophrenia

This review explores the neurobiology of stress and its possible role in the etiology of schizophrenia. Major life events may play a role in onset and relapse in schizophrenia. Other data suggest that early stress exposure increases schizophrenia risk, especially in individuals with latent vulnerability. Animal research has led to an elucidation of the mechanisms by which stress and cortisol are toxic to the hippocampus and impair cognition. Associations among these factors have been found in a variety of human conditions, including psychiatric illness and normal aging. These mechanisms are plausible in schizophrenia, which is characterized by a degree of cortisol dysregulation, hippocampal abnormality, and cognitive impairment. Characterization of the role of the stress cascade in schizophrenia has implications for novel pharmacologic and other treatment, especially for cognitive symptoms, which are debilitating and largely refractory to treatment.

Epidemiology of dementia: concepts and overview

This article reviews current knowledge about the prevalence and incidence of dementia and the risk and protective factors for dementia. Relevant epidemiologic concepts and methodological issues are reviewed, focusing on the implications of designing and interpreting epidemiologic studies of dementia and illustrating the integrative role of epidemiology.

Does the insulin-like growth factor system interact with prostaglandins and proinflammatory cytokines during neurodegeneration?

Prostaglandins and proinflammatory cytokines are implicated in the etiology of neurodegenerative diseases, such as Alzheimer's disease. Signaling cascades initiated by these factors may result in reactive oxygen species generation and cell death. The insulin-like growth factors (IGF) are ubiquitous polypeptides involved in all aspects of growth and development. Additionally, the IGF are regarded as survival factors that display potent antiapoptotic activity. Interfering with IGF production, distribution, or signaling may result in greater susceptibility to apoptotic stimuli. In neurodegenerative conditions, the IGF appear to be antagonized by prostaglandins and proinflammatory cytokines. In this review, the relationship among specific prostaglandins, the proinflammatory factors, tumor necrosis factor, interleukin-1, and interleukin-6, and the IGF system will be investigated.