Morphologische Ver�nderungen im Diencephalon und Telencephalon nach St�rungen des Regelkreises Adenohypophyse-Nebennierenrinde

Serum cortisol is negatively related to hippocampal volume, brain structure, and memory performance in healthy aging and Alzheimer's disease

Objective

Elevated cortisol levels have been frequently reported in Alzheimer's disease (AD) and linked to brain atrophy, especially of the hippocampus. Besides, high cortisol levels have been shown to impair memory performance and increase the risk of developing AD in healthy individuals. We investigated the associations between serum cortisol levels, hippocampal volume, gray matter volume and memory performance in healthy aging and AD.

Methods

In our cross-sectional study, we analyzed the relationships between morning serum cortisol levels, verbal memory performance, hippocampal volume, and whole-brain voxel-wise gray matter volume in an independent sample of 29 healthy seniors (HS) and 29 patients along the spectrum of biomarker-based AD.

Results

Cortisol levels were significantly elevated in patients with AD as compared to HS, and higher cortisol levels were correlated with worse memory performance in AD. Furthermore, higher cortisol levels were significantly associated with smaller left hippocampal volumes in HS and indirectly negatively correlated to memory function through hippocampal volume. Higher cortisol levels were further related to lower gray matter volume in the hippocampus and temporal and parietal areas in the left hemisphere in both groups. The strength of this association was similar in HS and AD.

Conclusion

In AD, cortisol levels are elevated and associated with worse memory performance. Furthermore, in healthy seniors, higher cortisol levels show a detrimental relationship with brain regions typically affected by AD. Thus, increased cortisol levels seem to be indirectly linked to worse memory function even in otherwise healthy individuals. Cortisol may therefore not only serve as a biomarker of increased risk for AD, but maybe even more importantly, as an early target for preventive and therapeutic interventions.

Synaptic Mechanisms Regulating Mood State Transitions in Depression

Depression is an episodic form of mental illness characterized by mood state transitions with poorly understood neurobiological mechanisms. Antidepressants reverse the effects of stress and depression on synapse function, enhancing neurotransmission, increasing plasticity, and generating new synapses in stress-sensitive brain regions. These properties are shared to varying degrees by all known antidepressants, suggesting that synaptic remodeling could play a key role in depression pathophysiology and antidepressant function. Still, it is unclear whether and precisely how synaptogenesis contributes to mood state transitions. Here, we review evidence supporting an emerging model in which depression is defined by a distinct brain state distributed across multiple stress-sensitive circuits, with neurons assuming altered functional properties, synapse configurations, and, importantly, a reduced capacity for plasticity and adaptation. Antidepressants act initially by facilitating plasticity and enabling a functional reconfiguration of this brain state. Subsequently, synaptogenesis plays a specific role in sustaining these changes over time.

Cortisol on Circadian Rhythm and Its Effect on Cardiovascular System

The synthesis and secretion of cortisol are controlled by the hypothalamic–pituitary–adrenal axis. Cortisol exhibits a proper 24-h circadian rhythm that affects the brain, the autonomic nervous system, the heart, and the vasculature that prepares the cardiovascular system for optimal function during these anticipated behavioral cycles. A literature search was conducted using databases such as Google Scholar, PubMed, and Scopus. Relevant search terms included “circadian rhythm and cardiovascular”, “cortisol”, “cortisol and acute coronary syndrome”, “cortisol and arrhythmias”, “cortisol and sudden cardiac death”, “cortisol and stroke”, and “cardioprotective agents”. A total of 120 articles were obtained on the basis of the above search. Lower levels of cortisol were seen at the beginning of sleep, while there was a rise towards the end of sleep, with the highest level reached at the moment the individual wakes up. In the present review, we discuss the role of 11β-hydroxysteroid dehydrogenase (11β-HSD1), which is a novel molecular target of interest for treating metabolic syndrome and type-2 diabetes mellitus. 11β-HSD1 is the major determinant of cortisol excess, and its inhibition alleviates metabolic abnormalities. The present review highlights the role of cortisol, which controls the circadian rhythm, and describes its effect on the cardiovascular system. The review provides a platform for future potential cardioprotective therapeutic agents.

Excessive daytime sleepiness and its predictors among medical and health science students of University of Gondar, Northwest Ethiopia: institution-based cross-sectional study

Background

Excessive daytime sleepiness (EDS) is a condition of sleepiness when a person would not be expected to sleep. University students are prone to EDS due to the competitive learning environment and fragmented night sleep. No study was conducted in Ethiopia on EDS. Therefore, this study aimed to determine EDS and its predictors among University of Gondar (UoG) Medical and Health Science students.

Methods

Institution-based cross-sectional study was carried out on 383 Medical and Health Science students of UoG who were recruited using a computer-generated simple random sampling technique. We used a validated Epworth daytime sleepiness tool to collect data. Epi-Info™ 7 and Stata 14 were used for data entry and analysis, respectively. Bivariable and multivariable binary logistic regression analyses were performed to find out predictors. Odds ratio with 95% uncertainty interval were computed. In the final model, a variable with a p < 0.05 was declared as a predictor of EDS.

Results

Three hundred and eighty-three students completed the questionnaire. Males were 69.97% and the mean age of participants was 20.79 (±1.83) years. In the current study, the prevalence of EDS was 31.07% (95% UI: 26.62–35.91). The odds of getting EDS was 1.83 (AOR = 1.83, 95% UI: 1.14–2.96) and 1.84 (AOR = 1.84, 95% UI: 1.13–3.00) higher among students who reported night sleep behaviour disorders and depression, respectively.

Conclusion

This study revealed that EDS is high and predicted by depression and night sleep behaviour disorders. These findings suggest the need to set preventive strategies such as counselling of students to reduce depression and night sleep behaviour disorders. Further studies particularly qualitative studies are required to find out more factors affecting EDS.

Chronic stress and hippocampal dendritic complexity: Methodological and functional considerations

The current understanding of how chronic stress impacts hippocampal dendritic arbor complexity and the subsequent relationship to hippocampal-dependent spatial memory is reviewed. A surge in reports investigating hippocampal dendritic morphology is occurring, but with wide variations in methodological detail being reported. Consequently, this review systematically outlines the basic neuroanatomy of relevant hippocampal features to help clarify how chronic stress or glucocorticoids impact hippocampal dendritic complexity and how these changes occur in parallel with spatial cognition. Chronic stress often leads to hippocampal CA3 apical dendritic retraction first with other hippocampal regions (CA3 basal dendrites, CA1, dentate gyrus, DG) showing dendritic retraction when chronic stress is sufficiently robust or long lasting. The stress-induced reduction in hippocampal CA3 apical dendritic arbor complexity often coincides with impaired hippocampal function, such as spatial learning and memory. Yet, when chronic stress ends and a post-stress recovery period ensues, the atrophied dendritic arbors and poor spatial abilities often improve. However, this process differs from a simple reversal of chronic stress-induced deficits. Recent reports suggest that this return to baseline-like functioning is uniquely different from non-stressed controls, emphasizing the need for further studies to enhance our understanding of how a history of stress subsequently alters an organism's spatial abilities. To provide a consistent framework for future studies, this review concludes with an outline for a quick and easy reference on points to consider when planning chronic stress studies with the goal of measuring hippocampal dendritic complexity and spatial ability.

Prolonged secretion of cortisol as a possible mechanism underlying stress and depressive behaviour

Stress is associated with the onset of depressive episodes, and cortisol hypersecretion is considered a biological risk factor of depression. However, the possible mechanisms underlying stress, cortisol and depressive behaviours are inconsistent in the literature. This study examined the interrelationships among stress, cortisol and observed depressive behaviours in female rhesus macaques for the first time and explored the possible mechanism underlying stress and depressive behaviour. Female monkeys were video-recorded, and the frequencies of life events and the duration of huddling were analysed to measure stress and depressive behaviour. Hair samples were used to measure chronic cortisol levels, and the interactions between stress and cortisol in the development of depressive behaviour were further evaluated. Significant correlations were found between stress and depressive behaviour measures and between cortisol levels and depressive behaviour. Stress was positively correlated with cortisol levels, and these two factors interacted with each other to predict the monkeys’ depressive behaviours. This finding extends the current understanding of stress/cortisol interactions in depression, especially pertaining to females.

A critical review of chronic stress effects on spatial learning and memory

The purpose of this review is to evaluate the effects of chronic stress on hippocampal-dependent function, based primarily upon studies using young, adult male rodents and spatial navigation tasks. Despite this restriction, variability amongst the findings was evident and how or even whether chronic stress influenced spatial ability depended upon the type of task, the dependent variable measured and how the task was implemented, the type and duration of the stressors, housing conditions of the animals that include accessibility to food and cage mates, and duration from the end of the stress to the start of behavioral assessment. Nonetheless, patterns emerged as follows: For spatial memory, chronic stress impairs spatial reference memory and has transient effects on spatial working memory. For spatial learning, however, chronic stress effects appear to be task-specific: chronic stress impairs spatial learning on appetitively motivated tasks, such as the radial arm maze or holeboard, tasks that evoke relatively mild to low arousal components from fear. But under testing conditions that evoke moderate to strong arousal components from fear, such as during radial arm water maze testing, chronic stress appears to have minimal impairing effects or may even facilitate spatial learning. Chronic stress clearly impacts nearly every brain region and thus, how chronic stress alters hippocampal spatial ability likely depends upon the engagement of other brain structures during behavioral training and testing.

The effects of chronic glucocorticoid exposure on dendritic length, synapse numbers and glial volume in animal models: implications for hippocampal volume reductions in depression

Glucocorticoids (GCs) are hormones secreted by the adrenal glands as an endocrine response to stress. Although the main purpose of GCs is to restore homeostasis when acutely elevated, animal studies indicate that chronic exposure to these hormones can cause damage to the hippocampus. This is indicated by reductions in hippocampal volume, and changes in neuronal morphology (i.e., decreases in dendritic length and number of dendritic branch points) and ultrastructure (e.g., smaller synapse number). Smaller hippocampal volume has been also reported in humans diagnosed with major depressive disorder or Cushing's disorder, conditions in which GCs are endogenously and chronically elevated. Although a number of studies considered neuron loss as the major factor contributing to the volume reduction, recent findings indicated that this is not the case. Instead, alterations in dendritic, synaptic and glial processes have been reported. The focus of this paper is to review the GC effects on the cell number, dendritic morphology and synapses in an effort to better understand how these changes may contribute to reductions in hippocampal volume. Taken together, the data from animal models suggest that hippocampal volumetric reductions represent volume loss in the neuropil, which, in turn, under-represent much larger losses of dendrites and synapses.

Corticosteroids: sculptors of the hippocampal formation

The influence of corticosteroids on hippocampus-dependent learning and memory processes is now indisputable. On the other hand, closer scrutiny of early studies together with interpretations from newer studies would suggest that the proposition that corticosteroid-induced hippocampal cell death accounts fully for the associated cognitive deficits is only partially correct. Firstly, it is now clear that a specific sub-population of hippocampal neurons, the granule cells of the dentate gyrus, is more sensitive to changes in the corticosteroid environment; this fact raises the interesting question of what might be the unique properties of granule cells that render them more vulnerable to these hormones, since virtually all hippocampal cells express corticosteroid receptors. Secondly, from a critical analysis of the available data, the picture that emerges is that corticosteroids, by acting through two distinct receptors, influence not only cell birth and death, but probably also cell differentiation. Mineralocorticoid receptor (MR) occupation appears to be essential for the survival of existing and newly generated granule neurons. In contrast, while glucocorticoid receptors (GR) can induce loss of neurons in the absence of MR activation, it appears that their occupation usually results in less drastic effects involving only dendritic atrophy and loss of synaptic contacts. This revised scheme of corticosteroid actions on hippocampal structure should explain earlier observations that many of the cognition- impairing effects of corticosteroids are reversible.

Circuits and systems in stress. I. Preclinical studies

This paper reviews the preclinical literature related to the effects of stress on neurobiological and neuroendocrine systems. Preclinical studies of stress provide a comprehensive model for understanding neurobiological alterations in post-traumatic stress disorder (PTSD). The pathophysiology of stress reflects long-standing changes in biological stress response systems and in systems involved in stress responsivity, learning, and memory. The neural circuitry involved includes systems mediating hypothalamic-pituitary-adrenal (HPA) axis, norepinephrine (locus coeruleus), and benzodiazepine, serotonergic, dopaminergic, neuropeptide, and central amino acid systems. These systems interact with brain structures involved in memory, including hippocampus, amygdala, and prefrontal cortex. Stress responses are of vital importance in living organisms; however excessive and/or repeated stress can lead to long-lasting alterations in these circuits and systems involved in stress responsiveness. Intensity and duration of the stressor, and timing of the stressor in life, have strong impact in this respect.

Stress and depression: possible links to neuron death in the hippocampus

Recent intriguing reports have shown an association between major depression and selective and persistent loss of hippocampal volume, prompting considerable speculation as to its underlying causes. In this paper we focus on the hypothesis that overt hippocampal neuron death could cause this loss and review current knowledge about how hippocampal neurons die during insults. We discuss (a) the trafficking of glutamate and calcium during insults; (b) oxygen radical generation and programmed cell death occurring during insults; (c) neuronal defenses against insults; (d) the role of energy availability in modulating the extent of neuron loss following such insults. The subtypes of depression associated with hippocampal atrophy typically involve significant hypersecretion of glucocorticoids, the adrenal steroids secreted during stress. These steroids have a variety of adverse affects, direct and indirect, in the hippocampus. Thus glucocorticoids may play a contributing role toward neuron death. We further discuss how glucocorticoids cause or exacerbate cellular changes associated with hippocampal neuron loss in the context of the events listed above.

Do glucocorticoids contribute to brain aging?

The hippocampus, an area with abundant glucocorticoid receptors, continues to be the focus of research on effects of glucocorticoids on the aging brain. Based on recent studies, the primary structural change found during aging is synaptic loss, rather than neuronal loss. High levels of glucocorticoids are associated with synaptic loss in the hippocampus, hippocampal atrophy, and cognitive decline during aging in some individuals. However, increasing levels of glucocorticoid are not always found since early experiences can alter sensitivity to negative feedback and the level of activation of the hypothalamic-pituitary-adrenal axis in aged individuals. New ways in which glucocorticoids may contribute to brain aging are discussed, including decreased responses to glucocorticoids possibly as a result of decreased glucocorticoid receptors and also altered regulation of neuronal turnover in the dentate gyrus. Decreased responsiveness of glial fibrillary acidic protein to glucocorticoids during aging could facilitate reactive gliosis and loss of synapses by altering neuron-astrocyte interactions. Neuronal turnover is regulated by glucocorticoids in the dentate gyrus where ongoing neurogenesis may be important for hippocampal-based memory formation in adulthood. Although the age-related decline in neurogenesis can be reversed by removal of adrenal steroids, the death of dentate granule neurons is also greatly increased by this treatment. Recent studies show age-related resistance to induced apoptosis and neurogenesis in the dentate gyrus following adrenalectomy, which is associated with increased expression of transforming growth factor-beta1. Therefore, the contribution of glucocorticoids to brain aging depends on the physiological and cellular context and some of these effects are reversible.

Adrenalectomy causes loss of zinc ions in zinc-enriched (ZEN) terminals and decreases seizure-induced neuronal death

Chelatable zinc ions from synaptic vesicles have been suggested to be involved in neuronal death caused by stroke, epilepsy and head trauma. Elevated glucocorticoid concentration exacerbates such neuron loss, while low levels protect. We have tested the notion that the neuroprotective effect of prior glucocorticoid reduction is mediated by a reduction of zinc ions contained in zinc-enriched (ZEN) synaptic vesicles. The level of vesicular zinc ions was evaluated by toluene sulfonamide quinoline (TSQ) fluorometry and zinc autometallography (ZnS(AMG)) 10 and 30 days, respectively, after adrenalectomy. The hippocampus showed significant vesicular zinc ion depletion following adrenalectomy. After the kainate injection, adrenalectomized rats showed proconvulsive seizure behavior, i.e. shortened latency to seizure onset time and increased seizure score. Additionally they showed decreased hippocampal CA3 neuronal death as compared to control animals. The present data suggest that zinc ions released from damaged ZEN terminals are involved in seizure-induced neuronal death.

Stress and the aging hippocampus

The "glucocorticoid cascade hypothesis" of hippocampal aging has stimulated a great deal of research into the neuroendocrine aspects of aging and the role of glucocorticoids, in particular. Besides strengthening the methods for investigating the aging brain, this research has revealed that the interactions between glucocorticoids and hippocampal neurons are far more complicated than originally envisioned and involve the participation of neurotransmitter systems, particularly the excitatory amino acids, as well as calcium ions and neurotrophins. New information has provided insights into the role of early experience in determining individual differences in brain and body aging by setting the reactivity of the hypothalamopituitary-adrenal axis and the autonomic nervous system. As a result of this research and advances in neuroscience and the study of aging, we now have a far more sophisticated view of the interactions among genes, early development, and environmental influences, as well as a greater appreciation of events at the cellular and molecular levels which protect neurons, and a greater appreciation of pathways of neuronal damage and destruction. While documenting the ultimate vulnerability of the brain to stressful challenges and to the aging process, the net result of this research has highlighted the resilience of the brain and offered new hope for treatment strategies for promoting the health of the aging brain.

Effects of microgravity and bone morphogenetic protein II on GFAP in rat brain

This study evaluated effects of bone morphogenetic protein II (BMP) on glial fibrillary acidic protein (GFAP) in the brain of female Fischer 344 rats during 14 days of spaceflight. GFAP mRNA decreased in vehicle-implanted rats flown on the space shuttle by 53 and 48% in the stratum moleculare and stratum lacunosum moleculare hippocampal subregions, respectively. GFAP mRNA was not significantly affected by BMP implantation during spaceflight. Rats returning from space exhibited a 56% increase in serum corticosterone. BMP treatment did not additively increase corticosterone elevations in microgravity but appeared to increase serum corticosterone and reduce GFAP mRNA in the stratum moleculare in control rats. These data suggest that exposure to microgravity reduces GFAP expression in hippocampal astrocytes.

Effects of corticosterone treatment and rehabilitation on the hippocampal formation of neonatal and adult rats. An unbiased stereological study

Elevations in the plasma levels of glucocorticoids are associated with cognitive impairments that have been ascribed to loss of neurons in the hippocampal formation. However, recent studies have strongly challenged this view. In order to clarify this issue, we have employed for the first time the optical fractionator and the Cavalieri principle, two unbiased stereological tools, to estimate respectively the total number of neurons and the volumes of the main subdivisions of the hippocampal formation of rats submitted to corticosterone treatment for different periods, either neonatally or in adulthood. A significant reduction in the number of neurons and in the volumes of the layers of the dentate gyrus and CA3 hippocampal field was found in rats exposed to glucocorticoids in the neonatal period; furthermore, animals treated with corticosterone from birth until 180 days of age had also a reduction in the volume of the stratum radiatum of the CA1 hippocampal field. Conversely, when the exposure occurred only during adulthood, no significant neuronal loss was observed, but there were significant reductions in the volume of layers in the dentate gyrus and CA3 hippocampal field. To search for signs of structural recovery, we incorporated a group of rats submitted to corticosterone treatment during the neonatal period in which the hormonal conditions were restored thenceforth. In this group we found a significant increase in the volume of the molecular layer of the dentate gyrus when compared with rats that were kept under corticosteroid treatment. In conclusion, these data provide a sound structural basis for the cognitive deficits observed during, and following, exposure to increased levels of glucocorticoids.

Steroid hormones and their receptors in the brain

Steroid hormones regulate several important functions of the brain by altering the expression of particular genes through their receptors. First in this paper the localization of glucocorticoid receptor immunoreactivity and mRNA in the brain was examined. Second biphasic effects of glucocorticoid on the hippocampus was described and particular emphasis was given on the apoptosis. Third the significance of estrogen receptor in the sexually dimorphic areas was discussed. These results suggest that steroids modulate the gene expression along with the alteration of cell structures in a different manner in a tissue-specific pattern.

Stress effects on morphology and function of the hippocampus

The hippocampal formation, which contains high levels of adrenal steroid receptors, is vulnerable to insults such as stroke, seizures, and head trauma, and it is also sensitive and vulnerable to the effects of stress. We have discovered that the hippocampus of rodents and tree shrews shows atrophy of pyramidal neurons in the CA3 region. Psychosocial stress and restraint stress produce atrophy over approximately 3-4 weeks. Atrophy is blocked by inhibiting adrenal steroid formation and by blocking the actions of excitatory amino acids using Dilantin or NMDA receptor inhibitors. Glucocorticoid administration also blocks CA3 atrophy, but Dilantin administration blocks this as well, indicating that excitatory amino acid release mediates the atrophy, which likely involves disassembly of the dendritic cytoskeleton. Studies with in vivo microdialysis in several laboratories have shown that glutamate release in the hippocampus increases in stress and that stress-induced glutamate release is reduced by adrenalectomy. Recent electron microscopy of mossy fiber terminals on CA3 neurons has revealed a depletion of synaptic vesicles as a result of repeated stress. The mossy fiber terminals appear to be responsible for driving atrophy of CA3 neurons, which involves principally atrophy of the apical dendrites. These results are discussed in relation to data from MRI showing atrophy of the whole human hippocampus in Cushing's disease, recurrent depressive illness, PTSD, and normal aging as well as dementia.

Magnetic resonance imaging-based measurement of hippocampal volume in posttraumatic stress disorder related to childhood physical and sexual abuse--a preliminary report

We have previously reported smaller hippocampal volume and deficits in short-term memory in patients with combat-related posttraumatic stress disorder (PTSD) relative to comparison subjects. The purpose of this study was to compare hippocampal volume in adult survivors of childhood abuse to matched controls. Magnetic resonance imaging was used to measure volume of the hippocampus in adult survivors of childhood abuse (n = 17) and healthy subjects (n = 17) matched on a case-by-case basis for age, sex, race, handedness, years of education, body size, and years of alcohol abuse. All patients met criteria for PTSD secondary to childhood abuse. PTSD patients had a 12% smaller left hippocampal volume relative to the matched controls (p < .05), without smaller volumes of comparison regions (amygdala, caudate, and temporal lobe). The findings were significant after controlling for alcohol, age, and education, with multiple linear regression. These findings suggest that a decrease in left hippocampal volume is associated with abuse-related PTSD.

Roles of steroid hormones and their receptors in structural organization in the nervous system

Due to their chemical properties, steroid hormones cross the blood-brain barrier where they have profound effects on neuronal development and reorganization both in invertebrates and vertebrates, including humans mediated through their receptors. Steroids play a crucial role in the organizational actions of cellular differentiation representing sexual dimorphism and apoptosis, and in the activational effects of phenotypic changes in association with structural plasticity. Their sites of action are primarily the genes themselves but some are coupled with membrane-bound receptor/ion channels. The effects of steroid hormones on gene transcription are not direct, and other cellular components interfere with their receptors through cross-talk and convergence of the signaling pathways in neurons. These genomic and non-genomic actions account for the divergent effects of steroid hormones on brain function as well as on their structure. This review looks again at and updates the tremendous advances made in recent decades on the study of the role of steroid (gonadal and adrenal) hormones and their receptors on developmental processes and plastic changes in the nervous system.

Neurotrophin expression modulated by glucocorticoids and oestrogen in immortalized hippocampal neurons

We have used reverse transcription followed by polymerase chain reaction amplification to investigate changes in expression of nerve growth factor (NGF) mRNA in immortalized hippocampal neurons after treatment with the glucocorticoids dexamethasone and corticosterone, the glucocorticoid antagonist RU38486, and the gonadal steroids progesterone and 17-beta oestradiol. We found that NGF mRNA levels rise after application of either dexamethasone or corticosterone, and that this rise is prevented by the antagonist. Thus, neurotrophin expression is modulated by the physiological glucocorticoid and is mediated by type II glucocorticoid receptors. Progesterone has no effect, while 17-beta oestradiol suppresses NGF mRNA in a postnatally-derived cell line but does not change levels in an embryonic line. An increase in neurotrophin expression is therefore not a general response to steroid hormone application, and may be a specific defence against the presence of metabolically endangering glucocorticoids.

Chronic psychosocial stress induces morphological alterations in hippocampal pyramidal neurons of the tree shrew

The effect of sustained psychosocial stress on the morphology of hippocampal pyramidal neurons was analysed in male tree shrews after 14, 20, and 28 days of social confrontation. A variety of physiological changes such as constantly elevated levels of urinary cortisol and norepinephrine and reduced body weight, which are indicative of chronic stress were observed in the subordinate, but not in the dominant males. Light microscopic analysis of Nissl-stained hippocampal sections showed that the staining intensity of the nucleoplasm in the CA1 and CA3 pyramidal neurons was increased after prolonged psychosocial stress, indicating a change in the nuclear chromatin structure. These alterations were observed only in subordinate animals and increased in a time dependent manner in accordance with the length of the stress period. There was, however, neither a reduction in density nor a degeneration of pyramidal neurons in chronically stressed animals. Mechanisms which may possibly account for the observed alterations are discussed.

Long-term exposure to high levels of corticosterone aggravates AF64A-induced cholinergic hypofunction in rat hippocampus in vivo

Male Sprague-Dawley rats were bilaterally adrenalectomized and corticosterone (CORT) was substituted as subcutaneous pellets in two groups of animals: low- (L-CORT: 1 x 25 mg pellet) or high-level of CORT (H-CORT: 4 x 100 mg pellet). Between 14 and 19 days after CORT substitution, ethylcholine aziridinium (AF64A) was intracerebroventricularly (i.c.v.) injected in the CORT long-term exposed rats and the dose- and time-dependent effect of this treatment was measured on choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activities in hippocampus and septum and on serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA) and noradrenaline (NA) levels in hippocampus. Rats were killed at 2, 4, 7 and 14 days after AF64A treatment. Starting 4 days after the i.c.v. administration of 0.5 or 1.0 nmol of AF64A, an aggravation of the reduction of ChAT activity was measured in the hippocampus of the H-CORT animals compared to the L-CORT ones. In the septum of the H-CORT rats, the activity of ChAT increased within the first week after the infusion of the toxin, while no significant effect was observed in the L-CORT group. As we observed with ChAT, AF64A induced a severe inhibition of AChE activity in the hippocampus of the H-CORT rats compared to the L-CORT ones. In the septum, an increase of AChE activity was observed in both groups of CORT-exposed animals. In the hippocampus of H-CORT animals, the exacerbation of the inhibition of ChAT and AChE activity was accompanied by a parallel decrease in the content of 5-HT and 5-HIAA starting 4 days after AF64A injections. Finally, NA content in hippocampus was not affected by the toxin in the CORT-substituted animals. These data demonstrate that: (1) long-term exposure to supraphysiological levels of CORT enhances the cholinodisruption induced in hippocampus by AF64A, at doses of 0.5 and 1.0 nmol/side; (2) high circulating plasma CORT concentrations impair hippocampal cholinergic neuronal capacity to recover from damage; and (3) the degree of inhibition of the serotoninergic system is augmented in H-CORT animals, most probably due to an adaptation of the serotoninergic neurons to the larger withdrawal of cholinergic function observed in this group.

Potential behavioral modification of glucocorticoid damage to the hippocampus

Glucocorticoids (GCs), the adrenal steroids secreted during stress, can damage the hippocampus, a principal neural target site for GCs. The extent of cumulative exposure to GCs influences the rate of neuron loss in the aging hippocampus, such that stress can accelerate senescent hippocampal degeneration. Moreover, under circumstances where GC exposure is insufficient to damage neurons, the hormones impair the capacity of neurons to survive neurological insults such as hypoxia-ischemia, seizure, or hypoglycemia. Considerable progress has been made in understanding how GCs endanger hippocampal neurons. The effect is a direct one, in that the endangerment is mediated by GC receptors and occurs in cultured hippocampal neurons. The endangerment is energetic in nature--the insults worsened by GCs represent energetic crises, and the GC endangerment is prevented by supplementation of neurons with energy substrates. As the likely mechanism by which GCs induce an energetic vulnerability, the steroids inhibit glucose transport in hippocampal neurons and glia. As a result of this effect of GCs upon energetics is that neurons are less capable of the costly task of containing the damaging fluxes of glutamate and calcium triggered by the neurological insults. Thus, following such insults, GCs disrupt glutamate removal and elevate synaptic glutamate concentrations, enhance the magnitude and duration of the subsequent mobilization of free cytosolic calcium, and exacerbate the magnitude of calcium-dependent degenerative events. Thus, stress has the capacity to damage the hippocampus and exacerbate the toxicity of some common neurological disorders; nevertheless, some behavioral interventions are known to cause sustained diminution of GC concentrations, and thus have the potential to protect the hippocampus from these deleterious effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of acute and short-term administration of cholinomimetic drugs on corticosterone secretion in the rat

Centrally acting cholinomimetic drugs have been proposed for the therapy of cognitive disorders in aged subjects. Among the possible adverse side effects of this class of compounds, of great relevance is the stimulatory action on the adrenocortical axis, in view of the toxicity of glucocorticoids for hippocampal neurons and the immune system. The aim of the present study was to evaluate in conscious male rats the effect of acute and short-term administration of three novel cholinomimetic drugs on the release of corticosterone. The potent agonist of muscarinic receptors RU 35963 strikingly increased corticosterone levels after acute but not after short-term (6 days) administration. Similar results were obtained after administration of the reversible inhibitor of cholinesterase, eptastigmine. In contrast to RU 35963 and eptastigmine, acute administration of a choline precursor, L-alpha-glycerylphosphorylcholine, only slightly affected plasma corticosterone concentrations after both acute and short-term administration. It is concluded that activation of adrenocortical function by cholinomimetic drugs is a short-lasting event which does not represent an important side effect of these compounds when given on a long-term basis.

Glucocorticoid modulation of neurotrophin expression in immortalized mouse hippocampal neurons

To see whether glucocorticoid hormones can influence the regulation of neurotrophin expression in hippocampal neurons, we have used reverse-transcription followed by polymerase chain reaction to investigate changes in the mRNA levels of nerve growth factor (NGF) and neurotrophin-3 (NT-3) in immortalized hippocampal neurons after dexamethasone application. Our results show that NGF mRNA levels rise in both embryonic and postnatal neurons, but with different time courses, while NT-3 levels rise in the embryonic but not in the postnatally derived cell line. Modulation of NT expression by glucocorticoids may therefore be developmentally regulated.

The effect of aging on stress responsiveness and central corticosteroid receptors in the brown Norway rat

The present study examined the stress responsiveness of the hypothalamic-pituitary-adrenal axis in relation to the properties of corticosteroid receptors in the brain and pituitary of old (30 months) and young (3 months) male Brown Norway rats. Adrenocorticotropin hormone (ACTH) and corticosterone (B) were measured following exposure to novelty and to a conditioned emotional stimulus in blood samples sequentially obtained from chronically cannulated animals. Mineralocorticoid (MR) and glucocorticoid (GR) receptors were quantified by radioligand binding assay and in situ hybridization. The receptor binding constants were determined in tissue of rats that were adrenalectomized 24 hours previously, whereas gene expression was measured in the brain of intact animals. Aged Brown Norway rats showed a small but significant elevation in basal circulating ACTH level. The conditioned emotional stimulus, rather than the exposure to novelty, triggered a more than two-times higher ACTH response in the aged compared to the young rat. The termination of the stress-induced ACTH response seemed to proceed more efficiently in the aged rat. Basal and stress-induced total plasma B level did not differ in the young and old rats. The latter showed a 65% lower binding capacity of corticosteroid-binding globulin (CBG). Interestingly, in the aged rat the stress-induced rise in free circulating plasma B level was not elevated, but only prolonged. The hippocampus of aged rats displayed a decrease of maximally 44% in the apparent Bmax of MR, but no change in GR number. The Bmax of GR showed a 40% reduction in the hypothalamus and a 50% reduction in the anterior pituitary. GR affinity was considerably increased in the anterior pituitary, but was unchanged in the hippocampus and hypothalamus. Old age affected MR and GR gene expression differentially. GR mRNA was significantly reduced in cell field CA3 (-42%), CA4 (-41%) and the dentate gyrus (-26%) of the dorsal hippocampus, but did not change either in hippocampal cell field CA1 or in the hypothalamic paraventricular nucleus (PVN) of the old rat. There was no significant difference in MR mRNA between young and aged rats in the different cell fields of the hippocampus. The aged rat, therefore, is characterized by site- and receptor-specific changes in binding constants as well as by changes in receptor transcription and translation. The data demonstrate that in the old Brown Norway rats, a conditioned emotional stimulus results in enhanced pituitary ACTH release.(ABSTRACT TRUNCATED AT 400 WORDS)

Cortisol reduces plasticity in the kitten visual cortex

We investigated the effect of elevated levels of cortisol on plasticity in the visual cortex of the cat. Animals were given daily injections of cortisol i.m. for 20 days starting around 35 days of age. After 10 days they were monocularly deprived, and after an additional 10 days recordings were made from the visual cortex to construct an ocular dominance histogram. The results were compared with those from normal animals of the same age, and with animals monocularly deprived for the same period but not treated with cortisol. Cortisol reduced the ocular dominance shift in a dose-dependent manner, but did not totally abolish it even at the highest doses used. Two other series of animals were recorded, one slightly later in the critical period and one slightly earlier, with care taken to give cortisol before the animals were exposed to light in the morning. In both cases, cortisol reduced the ocular dominance shift but did not abolish it. To interpret these results, we measured levels of plasma cortisol in normal cats of various ages. Average levels were fairly constant between birth and 12 months of age (0.5-1 microgram/dl), and increased slightly after that, but there was a large variation between animals. Thus elevated levels of cortisol can have a substantial effect on plasticity in the visual cortex of the cat, but the decline of the critical period for plasticity between 6 weeks and 3-5 months of age does not seem to be due to a rise in cortisol levels during this time.

Postnatal handling attenuates certain neuroendocrine, anatomical, and cognitive dysfunctions associated with aging in female rats

Hippocampal degeneration with aging is associated with increased hypothalamic-pituitary-adrenal (HPA) activity and, in male rats, both are attenuated by postnatal handling. Considering the important sex differences in the effects of handling and in HPA responses to stress in older rats, we have examined the effects of postnatal handling on aging in females. Female, Long-Evans rats were handled (H) during the first 3 weeks of life and later compared with nonhandled (NH) controls at various ages. Handling resulted in permanently increased hippocampal type II, glucocorticoid receptor binding. Relative to H females, NH females showed increased basal corticosterone levels in later life and hypersecreted corticosterone following stress at all ages examined. Both effects are similar to those reported in males. However, unlike males, H and NH females did not differ in corticosterone levels achieved during stress, a finding that may be related to sex-dependent effects of handling on pituitary transcortin receptors. There were no differences in hippocampal neuron density in 6-month-old animals. However, the older NH animals showed considerable neuron loss in the CA1 and CA3 hippocampal cellfields. There was little or no neuron loss in the H animals. Finally, the NH animals exhibited age-related spatial memory impairments, such that by 24 months of age the performance of the NH females was profoundly worse than that of the younger NHs and same-aged H animals. These data suggest that early handling permanently alters CNS systems that regulate hypothalamic-pituitary-adrenal (HPA) function, although the effect may depend on the gender of the animal. In both males and females, however, handling appears to prevent (or minimize) increased adrenal secretion in later life and to attenuate hippocampal cell loss and spatial memory impairments.

Individual variations in hippocampal dentate degeneration following adrenalectomy

Corticosterone appears to have two markedly different effects on cells of the hippocampus in rats. On one hand, elevated levels of corticosterone contribute to the degeneration of pyramidal cells. On the other hand, elimination of corticosterone by adrenalectomy may cause degeneration of dentate granule cells (Sloviter, Valiquette, Abrams, Ronk, Sollas, Paul, & Neubort, 1989). However, the latter response is variable. Low levels of corticoids from accessory adrenal tissue not consistently detectable by radioimmunoassay may provide sufficient hormone to maintain granule cell viability. We describe simple measures that predict which individual adrenalectomized rats have degeneration of the granule cell layer. Body weight gain after adrenalectomy is positively correlated with granule cell layer area at sacrifice 3 months after surgery. Also, short-term loss of body weight when saline drinking water is replaced with tap water predicts the degree of degeneration of the granule cell layer. These observations may aid further study of this striking effect of adrenal hormones on brain anatomy.

Exposure to excess glucocorticoids alters dendritic morphology of adult hippocampal pyramidal neurons

We have used Golgi-impregnated tissue to demonstrate that exposure to excess glucocorticoids alters dendritic morphology in a specific population of neurons in the adult rat hippocampus. Daily injection of 10 mg of corticosterone for 21 days resulted in decreased numbers of apical dendritic branch points and decreased total apical dendritic length measured in a 100-microns-thick section in CA3 pyramidal cells compared to sham-injected and non-injected controls. In contrast, no changes were observed in CA3 pyramidal cell basal dendritic morphology. Furthermore, no changes were observed in the dendritic morphology of CA1 pyramidal cells or granule cells of the dentate gyrus. Cross-sectional cell body area of any of the 3 cell types examined in this study was unaffected by corticosterone treatment. Finally, qualitative analysis of Nissl-stained tissue from the same brains revealed increased numbers of darkly staining, apparently shrunken CA3 pyramidal cells in corticosterone treated compared to control brains. The changes in dendritic morphology we have observed may be indicative of neurons in the early stages of degeneration, as prolonged exposure to high levels of corticosterone has been shown by others to result in a loss of CA3 pyramidal cells. Additionally, these results suggest possible structural alterations which may occur under physiological conditions in which corticosterone levels are chronically elevated such as in aged animals.

Cortisol reactivity and cognitive performance in a continuous mental task paradigm

The after-effects of fatigue or stress on the performance of cognitive tests have been particularly difficult to demonstrate. In this study we examined whether salivary cortisol, used as an index of stress evoked by the continuous performance of mental tasks, reflected individual differences in cognitive performance. In a within-subject experiment in which 24 subjects were exposed to 4 hours of continuous mental activity and to a control session, significantly higher cortisol levels were found during the continuous task session. Cognitive performance was assessed before and after each session. The relevant test parameters involved aspects of verbal memory, concept shifting and divided attention. When subjects were divided into two groups based on the magnitude of individual cortisol responses to the continuous tasks, it was found that the subgroup with higher cortisol responses decreased in attention compared with their attention after the control session. In contrast, the performance of the subgroup with no or lower cortisol responses did not differ between the two sessions. There was no evidence of similar effects on verbal memory or concept shifting.

Central action of adrenal steroids during stress and adaptation

Corticosteroids interact with receptors in the central nervous system. These receptors display heterogeneity and can be distinguished as corticosterone- and aldosterone-binding mineralocorticoid receptors and dexamethasone-binding glucocorticoid receptors. Ligand specificity of mineralocorticoid receptors for either corticosterone or aldosterone seems to be determined by co-localized transcortin and the enzyme, 11 beta-hydroxysteroid dehydrogenase. Aldosterone-selective mineralocorticoid receptors appear to be present in the circumventricular organs and the AV3V region of the hypothalamus and mediate behavior that is driven by salt appetite. Highest concentrations of mineralocorticoid receptors are found in neurons of the hippocampus. These limbic mineralocorticoid receptor sites mediate tonic influences of corticosterone on brain processes. Glucocorticoid receptors bind corticosterone with a tenfold lower affinity than do mineralocorticoid receptors, and are widely distributed in neuronal and glial cells of the brain. Glucocorticoid receptors are involved in the termination of the stress response (negative feedback). Studies involving measurement of glucocorticoid receptor mRNA and binding sites have revealed that glucocorticoid receptors are subject to autoregulation. After ADX, glucocorticoid receptor concentration increases, but is reduced after chronic stress, chronic administration of glucocorticoids, and at senescence. A diminished glucocorticoid receptor concentration may compromise the negative feedback action exerted by glucocorticoids after stress. After ADX, mineralocorticoid receptor binding is acutely up-regulated and reaches its maximum between 7 and 24 hours post-ADX. Mineralocorticoid receptor mRNA level shows a transient increase following ADX. Long-term ADX has no effect on the mineralocorticoid receptor concentration, but, interestingly, chronic dexamethasone treatment results in an up-regulation of mineralocorticoid receptors. Mineralocorticoid receptor level is decreased at senescence, but this age-related decrement can be reversed by chronic treatment with the ACTH4-9 analog, ORG 2766. Functionally, mineralocorticoid receptors and glucocorticoid receptors are involved in different aspects of the organization of the stress response, and in conjunction they control the stress responsiveness of the animal.

Dexamethasone and corticosterone receptor sites. Differential topographic distribution in rat hippocampus revealed by high resolution autoradiography

High resolution light microscopic autoradiography was used, together with regional surveys and combined acridine orange staining, to define in rat hippocampus cellular and subcellular sites of concentration and retention of 3H dexamethasone and to compare the topographic pattern of labeling with that of 3H corticosterone. Nuclear uptake of 3H dexamethasone in the hippocampus is demonstrated for the first time in vivo. With 3H dexamethasone, strongest nuclear radioactive labeling was observed in certain glial cells throughout the hippocampus, followed by strong nuclear labeling in most neurons in area CA1 and in the adjacent dorsolateral subiculum and weak nuclear labeling in granule cells of the dentate gyrus. Neurons in areas CA2, CA3, CA4, and in the dorsomedial subiculum and indusium griseum showed little or no nuclear labeling after 3H dexamethasone. With 3H corticosterone, strongest nuclear labeling was observed in neurons in area CA2 and in the dorsomedial subiculum and indusium griseum, followed by area CA1, then CA3 and CA4; the dentate gyrus contained scattered strongly labeled cells among cells with intermediate nuclear labeling. At the subcellular level, evidence for both nuclear and cytoplasmic accumulation of label was found. The results indicate that dexamethasone and corticosterone have both nuclear and cytoplasmic binding sites and that particular patterns of target cell distribution exist, characteristic for each agent. This suggests a differential regulation of cellular functions for the two compounds. Corticosterone nuclear binding appears to be more extensive and encompasses regions with dexamethasone binding. Whether in certain of these common regions corticosterone binds to the same receptor as dexamethasone, which seems possible, or to different receptors, remains to be clarified.

Chemical adrenalectomy reduces hippocampal damage induced by kainic acid

Glucocorticoids (GCs), the adrenal steroids secreted during stress, have numerous catabolic effects which include damage to neurons of the hippocampus, a principal neural target site for the steroids. In the rat, the extent of GC exposure over the lifespan is a major determinant of the rate of hippocampal neuron death during aging. GCs also modulate the severity of hippocampal damage in the rat following insults such as seizure or hypoxia-ischemia. As evidence, exogenous GCs exacerbate, while adrenalectomy attenuates hippocampal damage after these insults. Thus, it is possible that diminution of endogenous GC secretion might protect the human hippocampus after similar neurological insults; adrenalectomy under such circumstances is obviously not a viable clinical option. We demonstrate the protective effects of transient chemical adrenalectomy with the GC synthesis inhibitor, metyrapone. Rats were microinfused with the excitotoxin kainic acid in order to induce status epilepticus seizures; this insult caused a significant GC stress-response. Attenuation of that response with metyrapone reduced the CA3 hippocampal damage produced by kainic acid. Metyrapone did not change the intensity of seizures, but rather, apparently, changed the capacity of neurons to withstand the seizure. Thus, metyrapone, which is used safely and efficaciously in other clinical contexts, might prove protective of the brain following seizure in the human.

Neurotrophic ACTH analogue promotes plasticity of type I corticosteroid receptor in brain of senescent male rats

Age-related changes were studied in the concentration of type-I and type-II corticosteroid receptors in the hippocampus of young adult (3 months) and aged (28.5 to 30.5 months) male rats. Using 3H-labelled ligands, in vitro binding of type-I and type-II corticosteroid receptors in the soluble cell fraction (cytosol) revealed an age-related decrease in concentration of both receptor types of 52% and 28%, respectively. Infusion of young and aged male rats for 2 weeks with the ACTH4-9 [adrenocorticotropin4-9] peptide analogue ORG 2766 (0.5 micrograms/0.5 microliter/hr) resulted in only a minor increase (+8%) in the number of type-I receptors in young rats. In the aged animals, however, the type-I receptor concentration was 68% higher than in the vehicle-treated aged animals. In contrast, no effect of the peptide treatment was noted on the concentration of type-II receptors in either young or aged rats. Furthermore, no effect was found for either age or treatment with peptide on the affinity of type-I and type-II receptors for their respective ligands. Binding of 3H-labelled ligands to brain sections of young and aged rats was performed using in vitro autoradiography. Quantitative image analysis of the film showed that in senescence there is a marked reduction in both type-I (62-75%) and type-II (29-56%) receptor concentrations in the hippocampal subregions (CA1, CA2, CA3 and dentate gyrus) as well as in the lateral septum. Treatment of aged rats with ORG 2766 selectively reversed the age-associated reduction in type-I receptors, while the peptide did not affect the type-II receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of acute and chronic stress on the neural retina of young, mid-age, and aged Fischer-344 rats

Male Fischer-344 rats at 5 (young), 11 (mid-age) and 18 (aged) months of age were exposed either to a single, 1-h period of acute stress, or to daily 4-h periods (chronic) of escapable footshock stress for 6 months, and subsequently allowed a one month interval without stress. The influence of age and exposure to stress on the neural retina was examined by histopathologic and morphometric methods. Age changes in the retina of unstressed control animals included reduction in the thickness of the outer nuclear layer (ONL; photoreceptor nuclei) and of the retina, especially in the peripheral areas. The superior hemisphere was more severely affected than the inferior retina. Exposure to acute stress did not influence retinal histopathology. However, in mid-age and aged rats exposed to chronic stress, the ONL and retinal thicknesses were reduced significantly. Our results indicate for the first time that exposure of rats to chronic stress produces changes in retinal morphology that are associated commonly with aging, such as extensive loss of peripheral photoreceptor cells. In addition, the results show that the effects of chronic stress exposure are greatest in aged rats. The effect of light exposure on the aging retina was not investigated since all rats were exposed to the same total photoperiod.

Gender and chronic stress effects on the neural retina of young and mid-aged Fischer-344 rats

Young (5 months) and mid-aged (11 months) male and female Fischer rats were exposed to daily (5 days/week) chronic escapable foot-shock stress for 6 months. Following a subsequent 1-month rest period, by which time the animals were 12 and 18 months old, neural retinas were evaluated histopathologically and morphometrically. A significant reduction in the thickness of the retina occurred in the mid-aged, as compared to the young animals. A severe age-related loss in photoreceptor cells, particularly in the peripheral zones of the retina, occurred in a pattern resembling that described for aging humans. The effect of stress was to increase photoreceptor loss in a pattern resembling that of age-related cell loss. Stress-associated photoreceptor cell death was observed in males and females of both ages, but was more pronounced and statistically significant for mid-aged males (a five-fold increase in cell loss over females). The results demonstrated that exposure of rats to chronic escapable foot-shock stress exacerbates retinal changes commonly associated with aging and that the deleterious effects of chronic stress exposure were greater in the older age, male group.

Glucocorticoid toxicity in the hippocampus: temporal aspects of neuronal vulnerability

Glucocorticoids, the adrenocortical hormones secreted during stress, can be cumulatively toxic to hippocampal neurons, and this steroid-induced neuron loss has a role in functional impairments of the senescent hippocampus. The glucocorticoids, through their varied catabolic actions, appear to non-specifically induce metabolic vulnerability in the hippocampal neurons. As such, a wide variety of unrelated toxic insults which damage the hippocampus have their toxicity exacerbated by glucocorticoid treatment and attenuated by adrenalectomy. The present report demonstrates such a synergy between corticosterone (CORT), the species-specific glucocorticoid of rats, and 3-acetylpyridine (3-AP), a neurotoxic antimetabolite which inhibits ATP synthesis. When microinfused into Ammon's horn, 3-AP destroys dentate gyrus neurons preferentially. Administration of CORT at a concentration producing titers equivalent to those seen after prolonged stress, prior to and following 3-AP infusion, caused a 5-fold increase in the volume of hippocampal damage induced by the toxin. Conversely, adrenalectomy prior to microinfusion reduced the toxin's potency by more than 60%. Both the history of elevated CORT (i.e. prior to the 3-AP infusion) and the elevated CORT titers in the aftermath of the infusion contributed to the exaggerated damage. Finally, as little as 24 h of elevated CORT prior to and following the microinfusion could significantly potentiate toxin-induced damage. These studies present further evidence for CORT compromising the capacity of hippocampal neurons to survive a variety of toxic insults. Furthermore, the time-course of this effect suggests the relatively rapid metabolic actions of CORT as critical to this endangerment.