Corticosterone impairs hippocampal neuronal calcium regulation--possible mediating mechanisms

Neurobiology of zinc and its role in neurogenesis

BACKGROUND

Zinc (Zn) has a diverse role in many biological processes, such as growth, immunity, anti-oxidation system, homeostatic, and repairing. It acts as a regulatory and structural catalyst ion for activities of various proteins, enzymes, and signal transcription factors, as well as cell proliferation, differentiation, and survival. The Zn ion is essential for neuronal signaling and is mainly distributed within presynaptic vesicles. Zn modulates neuronal plasticity and synaptic activity in both neonatal and adult stages. Alterations in brain Zn status results in a dozen neurological diseases including impaired brain development. Numerous researchers are working on neurogenesis, however, there is a paucity of knowledge about neurogenesis, especially in neurogenesis in adults. Neurogenesis is a multifactorial process and is regulated by many metal ions (e.g. Fe, Cu, Zn, etc.). Among them, Zn has an essential role in neurogenesis. At the molecular level, Zn controls cell cycle, apoptosis, and binding of DNA and several proteins including transcriptional and translational factors. Zn is needed for protein folding and function and Zn acts as an anti-apoptotic agent; organelle stabilizer; and an anti-inflammatory agent. Zn deficiency results in aging, neurodegenerative disease, immune deficiency, abnormal growth, cancer, and other symptoms. Prenatal deficiency of Zn results in developmental disorders in humans and animals.

CONCLUSION

Both in vitro and in vivo studies have shown an association between Zn deficiency and increased risk of neurological disorders. This article reviews the existing knowledge on the role of Zn and its importance in neurogenesis.

Relationship between the hippocampal shape abnormality and serum cortisol levels in first-episode and drug-naïve major depressive disorder patients

BACKGROUND

We aimed to investigate the relationship between the hippocampal shape deformations and the serum cortisol levels in first-episode and drug-naïve major depression disorder (MDD) patients.

METHODS

Thirty first-episode and drug-naïve MDD patients and 40 healthy subjects were recruited. High-resolution T1-weighted imaging and morning blood samples for cortisol measurement were obtained from all MDD patients and healthy subjects. In the hippocampal shape analysis, we compared the hippocampal shape between MDD patients and healthy subjects and evaluated the linear correlation between hippocampal shape deformations and the serum cortisol levels in MDD patients and healthy subjects.

RESULTS

MDD patients showed significant inward deformations predominantly in the cornu ammonis (CA) 1 and subiculum in bilateral hippocampi compared to healthy subjects (false discovery rate (FDR) corrected, P < .05). Furthermore, in MDD patients, a significant linear correlation between inward deformations and high cortisol levels were found predominantly in the CA1 and subiculum, extending into the CA2-3 (FDR-corrected, P < .05), whereas no significant linear correlation was observed in healthy subjects.

CONCLUSIONS

The serum cortisol levels are therefore considered to be associated with hippocampal shape abnormalities in MDD.

The time-dependent health and biochemical effects in rats exposed to stainless steel welding dust and its soluble form

Welding processes that generate fumes containing toxic metals, such as hexavalent chromium (Cr(VI)), manganese (Mn), and nickel (Ni), have been implicated in lung injury, inflammation, and lung tumor promotion in animal models. The principal objective of this study was to determine the dynamics of toxic effects of inhalation exposure to morphologically rated welding dust from stainless steel welding and its soluble form in TSE System with a dynamic airflow. We assessed the pulmonary toxicity of welding dust in Wistar rats exposed to 60.0 mg/m³ of respirable-size welding dust (mean diameter 1.17 µm) for 2 weeks (6 h/day, 5 days/week); the aerosols were generated in the nose-only exposure chambers (NOEC). An additional aim included the study of the effect of betaine supplementation on oxidative deterioration in rat lung during 2 weeks of exposure to welding dust or water-soluble dust form. The animals were divided into eight groups (n = 8 per group): control, dust, betaine, betaine + dust, soluble-form dust, soluble-form dust + betaine, saline and saline + betaine groups. Rats were euthanized 1 or 2 weeks after the last exposure for assessment of pulmonary toxicity. Differential cell counts, total protein concentrations and cellular enzyme (lactate dehydrogenase-LDH) activities were determined in bronchoalveolar lavage (BAL) fluid, and corticosterone and thiobarbituric acid reactive substances (TBARS) concentrations were assessed in serum. The increase in polymorphonuclear (PMN) leukocytes in BAL fluid (a cytological index of inflammatory responses of the lung) is believed to reflect pulmonary toxicity of heavy metals. Biomarkers of toxicity assessed in bronchoalveolar fluids indicate that the level of the toxic effect depends mainly on the solubility of studied metal compounds; biomarkers that showed treatment effects included: total cell, neutrophil and lymphocyte counts, total protein concentrations, and cellular enzyme (lactate dehydrogenase) activity. Betaine supplementation at 250 mg/kg/day in all study rats groups attenuated stress indices, and corticosterone and TBARS serum levels, and simultaneously stimulated increase of polymorphonuclear cells in BALF of rats. The study confirmed deleterious effect of transitory metals and particles during experimental inhalation exposure to welding dusts, evidenced in the lungs and brain by increased levels of total protein, higher cellular influx, rise of LDH in BALF, elevated TBARS and increased corticosterone in serum of rats. Our result confirm also the hypothesis about the effect of the welding dusts on the oxidative stress responsible for disturbed systemic homeostasis and impairment of calcium regulation.

A Mechanistic Basis for the Beneficial Effects of Caloric Restriction On Longevity and Disease: Consequences for the Interpretation of Rodent Toxicity Studies

Caloric restriction in rodents has been repeatedly shown to increase life span while reducing the severity and retarding the onset of both spontaneous and chemically induced neoplasms. These effects of caloric restriction are associated with a spectrum of biochemical and physiological changes that characterize the organism's adaptation to reduced caloric intake and provide the mechanistic basis for caloric restriction's effect on longevity. Here, we review evidence suggesting that the primary adaptation appears to be a rhythmic hypercorticism in the absence of elevated adrenocorticotropin (ACTH) levels. This characteristic hypercorticism evokes a spectrum of responses, including reduced body temperature and increased metabolic efficiency, decreased mitogenic response coupled with increased rates of apoptosis, reduced inflammatory response, reduced oxidative damage to proteins and DNA, reduced reproductive capacity, and altered drug-metabolizing enzyme expression. The net effect of these changes is to (1) decrease growth and metabolism in peripheral tissues to spare energy for central functions, and (2) increase the organism's capacity to withstand stress and chemical toxicity. Thus, caloric restriction research has uncovered an evolutionary mechanism that provides rodents with an adaptive advantage in conditions of fluctuating food supply. During periods of abundance, body growth and fecundity are favored over endurance and longevity. Conversely, during periods of famine, reproductive performance and growth are sacrificed to ensure survival of individuals to breed in better times. This phenomena can be observed in rodent populations that are used in toxicity testing. Improvements over the last 30 years in animal husbandry and nutrition, coupled with selective breeding for growth and fecundity, have resulted in several strains now exhibiting larger animals with reduced survival and increased incidence of background lesions. The mechanistic data from caloric restriction studies suggest that these large animals will also be more susceptible to chemically induced toxicity. This creates a problem in comparing tests performed on animals of different weights and comparing data generated today with the historical database. The rational use of caloric restriction to control body weight to within preset guidelines is a possible way of alleviating this problem.

Review : The Vicious Circle of Stress and Anticholinesterase Responses

After either acute psychological stress or exposure to acetylcholinesterase (AChE) inhibitors, long-lasting deleterious changes of a similar nature occur in the mammalian brain. We explored the molecular and neurophysiological mechanisms preceding these convergent delayed consequences in vivo and in perfused hippocampal brain slices. In stressed mice, we observed a disruption of the blood-brain barrier, which leads to efficient brain penetrance of anti-AChEs. This increase in penetrance of anti-AChEs, and consequently in acetylcholine (ACh) levels, induces a cascade of c-fos-mediated transcriptional responses dependent on intracellular Ca2+ accumulation. Consequently, the capacity for synthesis and vesicle packaging of ACh is suppressed simultaneously with enhanced AChE production that potentiates ACh hydrolysis. This bimodal decrease in ACh bioavailability, which is independent of the hypothalamic-pituitary-adrenal axis, then ter minates the initial neurophysiological excitation. In vivo, this AChE overexpression leads to enzyme accu mulation that is evident for more than 80 hr. The overexpressed enzyme can protect the brain from sustained hyperexcitability and from increased susceptibility to seizure activity and neuronal toxicity. However, exper imental accumulation of AChE in brain neurons through transgenic manipulations leads to a slowly pro gressive deterioration in cognitive and neuromotor faculties. The transcriptional consequences of stress and anti-AChEs may therefore be beneficial in the short term but deleterious in the long term. NEURO SCIENTIST 5:173-183, 1999

Chronic Psychosocial Stress and Negative Feedback Inhibition: Enhanced Hippocampal Glucocorticoid Signaling despite Lower Cytoplasmic GR Expression

Chronic subordinate colony housing (CSC), a pre-clinically validated mouse model for chronic psychosocial stress, results in increased basal and acute stress-induced plasma adrenocorticotropic hormone (ACTH) levels. We assessed CSC effects on hippocampal glucocorticoid (GC) receptor (GR), mineralocorticoid receptor (MR), and FK506 binding protein (FKBP51) expression, acute heterotypic stressor-induced GR translocation, as well as GC effects on gene expression and cell viability in isolated hippocampal cells. CSC mice showed decreased GR mRNA and cytoplasmic protein levels compared with single-housed control (SHC) mice. Basal and acute stress-induced nuclear GR protein expression were comparable between CSC and SHC mice, as were MR and FKBP51 mRNA and/or cytoplasmic protein levels. In vitro the effect of corticosterone (CORT) on hippocampal cell viability and gene transcription was more pronounced in CSC versus SHC mice. In summary, CSC mice show an, if at all, increased hippocampal GC signaling capacity despite lower cytoplasmic GR protein expression, making negative feedback deficits in the hippocampus unlikely to contribute to the increased ACTH drive following CSC.

Restraint stress increases hemichannel activity in hippocampal glial cells and neurons

Stress affects brain areas involved in learning and emotional responses, which may contribute in the development of cognitive deficits associated with major depression. These effects have been linked to glial cell activation, glutamate release and changes in neuronal plasticity and survival including atrophy of hippocampal apical dendrites, loss of synapses and neuronal death. Under neuro-inflammatory conditions, we recently unveiled a sequential activation of glial cells that release ATP and glutamate via hemichannels inducing neuronal death due to activation of neuronal NMDA/P2X₇ receptors and pannexin1 hemichannels. In the present work, we studied if stress-induced glia activation is associated to changes in hemichannel activity. To this end, we compared hemichannel activity of brain cells after acute or chronic restraint stress in mice. Dye uptake experiments in hippocampal slices revealed that acute stress induces opening of both Cx43 and Panx1 hemichannels in astrocytes, which were further increased by chronic stress; whereas enhanced Panx1 hemichannel activity was detected in microglia and neurons after acute/chronic and chronic stress, respectively. Moreover, inhibition of NMDA/P2X₇ receptors reduced the chronic stress-induced hemichannel opening, whereas blockade of Cx43 and Panx1 hemichannels fully reduced ATP and glutamate release in hippocampal slices from stressed mice. Thus, we propose that gliotransmitter release through hemichannels may participate in the pathogenesis of stress-associated psychiatric disorders and possibly depression.

The Antidepressant-like Effect of Ethanol Extract of Daylily Flowers ( Jīn Zhēn Huā) in Rats

According to the prediction of the 2008 World Health Organization (WHO) report, depression will be the highest burden disease by the year 2030. Daylily flower ( Jīn Zhēn Huā ; the flower of Hemerocallis fulva) is traditionally used for soothing in Chinese dietary therapy. The major flavonoid of daylily flowers, rutin, is also characterized to be an antidepressant. In this study, we investigated the antidepressant effects of ethanol extract of daylily flowers (DFEtoH) and rutin by forced swimming test (FST) and neurotransmitter metabolism of brain regions (frontal cortex, hippocampus, striatum, and amygdala). Results show that either short- or long-term tests, the extract and rutin significantly reduce the immobility time and increased swimming time of FST, which are compared with the vehicle (P < 0.05). The extract and rutin also increase the serotonin, norepinephrine, and dopamine concentration of these brain regions (P < 0.05). In long-term tests, the daylily flowers extract markedly increased serotonin concentration and reduced serotonin turnover rate in these brain regions but not frontal cortex. In conclusion, present data illustrated that DFEtoH does have antidepressant-like effects possibly via the regulation of serotonergic system. Moreover, rutin might be playing a very important role in the antidepressant-like effects of DFEtoH.

Glucocorticoids increase excitotoxic injury and inflammation in the hippocampus of adult male rats

BACKGROUND/AIMS

Stress exacerbates neuron loss in many CNS injuries via the actions of adrenal glucocorticoid (GC) hormones. For some injuries, this GC endangerment of neurons is accompanied by greater immune cell activation in the CNS, a surprising outcome given the potent immunosuppressive properties of GCs.

METHODS

To determine whether the effects of GCs on inflammation contribute to neuron death or result from it, we tested whether nonsteroidal anti-inflammatory drugs could protect neurons from GCs during kainic acid excitotoxicity in adrenalectomized male rats. We next measured GC effects on (1) chemokine production (CCL2 and CINC-1), (2) signals that suppress immune activation (CX3CL1, CD22, CD200, and TGF-β), and (3) NF-κB activity.

RESULTS

Concurrent treatment with minocycline, but not indomethacin, prevented GC endangerment. GCs did not substantially affect CCL2, CINC-1, or baseline NF-κB activity, but they did suppress CX3CL1, CX3CR1, and CD22 expression in the hippocampus - factors that normally restrain inflammatory responses.

CONCLUSIONS

These findings demonstrate that cellular inflammation is not necessarily suppressed by GCs in the injured hippocampus; instead, GCs may worsen hippocampal neuron death, at least in part by increasing the neurotoxicity of CNS inflammation.

Glucocorticoid signaling in myeloid cells worsens acute CNS injury and inflammation

Glucocorticoid stress hormones (GCs) are well known for being anti-inflammatory, but some reports suggest that GCs can also augment aspects of inflammation during acute brain injury. Because the GC receptor (GR) is ubiquitously expressed throughout the brain, it is difficult to know which cell types might mediate these unusual "proinflammatory" GC actions. We examined this with cell type-specific deletion or overexpression of GR in mice experiencing seizure or ischemia. Counter to their classical anti-inflammatory actions, GR signaling in myeloid cells increased Iba-1 and CD68 staining as well as nuclear p65 levels in the injured tissue. GCs also reduced levels of occludin, claudin 5, and caveolin 1, proteins central to blood-brain-barrier integrity; these effects required GR in endothelial cells. Finally, GCs compromised neuron survival, an effect mediated by GR in myeloid and endothelial cells to a greater extent than by neuronal GR.

Impact of corticosterone treatment on spontaneous seizure frequency and epileptiform activity in mice with chronic epilepsy

Stress is the most commonly reported precipitating factor for seizures in patients with epilepsy. Despite compelling anecdotal evidence for stress-induced seizures, animal models of the phenomena are sparse and possible mechanisms are unclear. Here, we tested the hypothesis that increased levels of the stress-associated hormone corticosterone (CORT) would increase epileptiform activity and spontaneous seizure frequency in mice rendered epileptic following pilocarpine-induced status epilepticus. We monitored video-EEG activity in pilocarpine-treated mice 24/7 for a period of four or more weeks, during which animals were serially treated with CORT or vehicle. CORT increased the frequency and duration of epileptiform events within the first 24 hours of treatment, and this effect persisted for up to two weeks following termination of CORT injections. Interestingly, vehicle injection produced a transient spike in CORT levels – presumably due to the stress of injection – and a modest but significant increase in epileptiform activity. Neither CORT nor vehicle treatment significantly altered seizure frequency; although a small subset of animals did appear responsive. Taken together, our findings indicate that treatment of epileptic animals with exogenous CORT designed to mimic chronic stress can induce a persistent increase in interictal epileptiform activity.

The effect of different maternal deprivation paradigms on the expression of hippocampal glucocorticoid receptors, calretinin and calbindin-D28k in male and female adolescent rats

Maternal deprivation (MD) is a well-established protocol used to investigate neurobiological changes that are associated with the etiology of and vulnerability to stress-related diseases in animal models. The resulting psychophysiological effects, the timing and duration of these adverse stimuli, and the method by which they exert their effects on the animals remain unclear. This study characterized differences in the hippocampal expression of glucocorticoid receptors (GRs) and the calcium-binding proteins calretinin (CALR) and calbindin-D28k (CALB) in male and female rats that underwent different MD paradigms during the stress hyporesponsive period (SHRP). Both GRs and the two calcium-binding proteins were much more abundant in females than in males. MD paradigms had a significant effect on CALR and CALB expression in both males and females but affected GR levels only in males. Additionally, expression of the two calcium-binding proteins in the hippocampus responded differently to MD-induced stress, especially in females. Taken together, these results indicate that females are able to modulate their response to stress better than males.

Zinc signaling through glucocorticoid and glutamate signaling in stressful circumstances

Humans and animals are constantly exposed to environmental stress. The hypothalamic-pituitary-adrenal (HPA) axis responds to stress, followed by glucocorticoid secretion from the adrenal glands. This response serves to maintain homeostasis in the living body through energy mobilization or to restore it. The brain is an important target for glucocorticoids. The hippocampus participates in the regulation of the HPA axis. Stress activates glutamatergic neurons in the hippocampus, and serious stress induces dyshomeostasis of extracellular glutamate. This dyshomeostasis, which is potentiated by glucocorticoids, modifies cognitive and emotional behavior. On the other hand, zinc is necessary for glucocorticoid signaling and is released from glutamatergic (zincergic) neurons to modulate synaptic glutamate signaling. Stress also induces dyshomeostasis of extracellular zinc, which may be linked to dyshomeostasis of extracellular glutamate. Thus, glucocorticoid signaling might also contribute to dyshomeostasis of extracellular zinc. It is likely that zinc signaling participates in cognitive and emotional behavior through glucocorticoid and glutamate signaling under stressful circumstances. This Mini-Review analyzes the relationship among signals of glucocorticoid, glutamate, and zinc under stressful circumstances to elucidate the significance of the zinc signaling in response to stress.

Long-term continuous corticosterone treatment decreases VEGF receptor-2 expression in frontal cortex

OBJECTIVE

Stress and increased glucocorticoid levels are associated with many neuropsychiatric disorders including schizophrenia and depression. Recently, the role of vascular endothelial factor receptor-2 (VEGFR2/Flk1) signaling has been implicated in stress-mediated neuroplasticity. However, the mechanism of regulation of VEGF/Flk1 signaling under long-term continuous glucocorticoid exposure has not been elucidated.

MATERIAL AND METHODS

We examined the possible effects of long-term continuous glucocorticoid exposure on VEGF/Flk1 signaling in cultured cortical neurons in vitro, mouse frontal cortex in vivo, and in post mortem human prefrontal cortex of both control and schizophrenia subjects.

RESULTS

We found that long-term continuous exposure to corticosterone (CORT, a natural glucocorticoid) reduced Flk1 protein levels both in vitro and in vivo. CORT treatment resulted in alterations in signaling molecules downstream to Flk1 such as PTEN, Akt and mTOR. We demonstrated that CORT-induced changes in Flk1 levels are mediated through glucocorticoid receptor (GR) and calcium. A significant reduction in Flk1-GR interaction was observed following CORT exposure. Interestingly, VEGF levels were increased in cortex, but decreased in serum following CORT treatment. Moreover, significant reductions in Flk1 and GR protein levels were found in postmortem prefrontal cortex samples from schizophrenia subjects.

CONCLUSIONS

The alterations in VEGF/Flk1 signaling following long-term continuous CORT exposure represents a molecular mechanism of the neurobiological effects of chronic stress.

Ameliorative effect of Yokukansan on social isolation-induced aggressive behavior of zinc-deficient young mice

Yokukansan, a traditional Japanese medicine has been used to cure neuropsychological disorders. In the present study, the effect of Yokukansan on social isolation-induced aggressive behavior was examined in zinc-deficient mice, which were fed a zinc-deficient diet and a drinking water containing Yokukansan for 2 weeks. In the resident-intruder test, the rate of mice that exhibited aggressive behavior in zinc-deficient mice, which was significantly higher than that in the control mice, was significantly decreased by administration of Yokukansan. The basal level of serum glucocorticoid, which was significantly higher in zinc-deficient mice, was lowered by administration of Yokukansan. On the other hand, serum glucocorticoid levels after the resident-intruder test were almost the same between the control and zinc-deficient mice. However, administration of Yokukansan to zinc-deficient mice significantly increased serum glucocorticoid level after the resident-intruder test and the significant difference in the rate of serum corticosterone level after the test to the basal level between the control and zinc-deficient mice was abolished. Dietary zinc deficiency increases the basal levels of serum glucocorticoid, while may insufficiently increase serum glucocorticoid levels in the resident-intruder test. The concentrations of glutamate and GABA (γ-aminobutyric acid) in the brain were significantly higher in zinc-deficient mice, while Yokukansan ameliorated the significant increases. These results indicate that Yokukansan ameliorates social isolation-induced aggressive behavior of zinc-deficient mice, probably via amelioration of abnormal glucocorticoid secretion. The ameliorative effect seems to be linked to the modification of glutamatergic neuron activity after administration of Yokukansan.

Red mold rice promoted antioxidase activity against oxidative injury and improved the memory ability of zinc-deficient rats

Zn deficiency is a common disease leading to memory impairment with increasing age. This study evaluated the protection effects of red mold rice (RMR) administration and Zn supplementation against memory and learning ability impairments from oxidative stress caused by Zn deficiency. Rats (4 weeks old) were induced to be Zn deficiency by a Zn-deficient diet for 12 weeks. After that, rats were administered Zn, 1xRMR, 5xRMR, and various dosages of RMR plus Zn, respectively. Decreases of antioxidant enzyme activities in the hippocampus and cortex were observed, and the levels of Ca, Fe, and Mg were increased in the hippocampus and cortex of Zn-deficient rats, leading to memory and learning ability injury. However, the administration of RMR (1- or 5-fold dosage) and with or without Zn significantly improved the antioxidase and neural activity to maintain cortex and hippocampus functions. This study demonstrates that RMR is a possible functional food for the prevention or cure of neural injury associated with Zn deficiency.

Insight into zinc signaling from dietary zinc deficiency

Zinc is necessary for not only brain development but also brain function. Zinc homeostasis in the brain is tightly regulated by the brain barrier system and is not easily disrupted by dietary zinc deficiency. However, histochemically reactive zinc as revealed by Timm's staining is susceptible to zinc deficiency, suggesting that the pool of Zn(2+) can be reduced by zinc deficiency. The hippocampus is also susceptible to zinc deficiency in the brain. On the other hand, zinc deficiency causes abnormal glucocorticoid secretion from the adrenal cortex, which is observed prior to the decrease in extracellular zinc concentration in the hippocampus. The hippocampus is enriched with glucocorticoid receptors and hippocampal functions are changed by abnormal glucocorticoid secretion. Zinc deficiency elicits neuropsychological symptoms and affects cognitive performance. It may also aggravate glutamate excitotoxicity in neurological diseases. Abnormal glucocorticoid secretion is associated with these symptoms in zinc deficiency. Furthermore, the decrease in Zn(2+) pool may cooperate with glucocorticoid action in zinc deficiency. Judging from susceptibility of Zn(2+) pool in the brain to zinc deficiency, it is possible that the decrease in Zn(2+) pool in the peripheral tissues triggers abnormal glucocorticoid secretion. To understand the importance of zinc as a signaling factor, this paper analyzes the relationship among the changes in hippocampal functions, abnormal behavior and pathophysiological changes in zinc deficiency, based on the data from experimental animals.

Behavior in the forced swim test and neurochemical changes in the hippocampus in young rats after 2-week zinc deprivation

Abnormal behavior in zinc deficiency and its cause are poorly understood. In the present paper, behavior in the forced swim test and neurochemical changes in the brain associated with its behavior were studied focused on abnormal corticosterone secretion in zinc deficiency. The effect of chronic corticosterone treatment was also studied. Immobility time in the forced swim test was increased in young rats fed a zinc-deficient diet for 2 weeks, as well as corticosterone (40mg/kg/dayx14 days)-treated control rats. The basal Ca(2+) levels in the hippocampus, which were determined by fluo-4FF, AM, were increased in both brain slices from zinc-deficient and corticosterone-treated rats. Serum glucose level was decreased in zinc deficiency and hippocampal glucose metabolism, which is determined by [(14)C]2-deoxyglucose uptake, was elevated. Hippocampal ATP level was not decreased, whereas, the concentrations of glutamate, GABA and glutamine in the hippocampus, unlike the whole brain, were decreased in zinc deficiency. However, the decrease in these amino acids was restored by adrenalectomy prior to zinc deficiency. These results suggest that glucose is insufficient for the synthesis of amino acids in the hippocampus of zinc-deficient rats. It is likely that the neurochemical and metabolic changes in the hippocampus, which may be associated with abnormal corticosterone secretion, is the base of abnormal behavior associated with neuropsychological symptoms in zinc deficiency.

Curcumin protects PC12 cells from corticosterone-induced cytotoxicity: possible involvement of the ERK1/2 pathway

Antiglucocorticoid therapy in depressed patients is effective, which indicates that glucocorticoids play a key role in the occurrence of depression. Our previous work demonstrated the efficacy of curcumin in treating depression in rat and mouse models. We characterized the protective effects of curcumin against corticosterone-induced cytotoxicity in PC12 cells and explored the mechanisms of these protective effects in association with the phosphorylation and expression of ERK1/2 in PC12 cells. MTT assay showed that curcumin significantly protected PC12 cells from corticosterone-induced cytotoxicity. Curcumin at concentrations from 10(-8) to 10(-6) M rescued PC12 cells from corticosterone-induced cytotoxicity. Cell viability was increased more than 20% with curcumin treatment. Western blot analysis showed that corticosterone increased ERK1/2 phosphorylation in PC12 cells and curcumin 10(-9) M to 10(-6) M significantly inhibited corticosterone-induced ERK1/2 phosphorylation in PC12 cells in a dose-dependent manner. These results suggest that curcumin is able to protect PC12 cells which may be associated with inhibition of ERK phosphorylation.

Blocking glucocorticoid and enhancing estrogenic genomic signaling protects against cerebral ischemia

Glucocorticoids (GCs) and estrogen can modulate neuron death and dysfunction during neurological insults. Glucocorticoids are adrenal steroids secreted during stress, and hypersecretion of GCs during cerebral ischemia compromises the ability of hippocampal and cortical neurons to survive. In contrast, estrogen can be neuroprotective after cerebral ischemia. Here we evaluate the protective potential of a herpes viral vector expressing a chimeric receptor (ER/GR), which is composed of the ligand-binding domain of the GC receptor (GR) and the DNA-binding domain of the estrogen receptor-alpha (ER). This novel receptor can transduce an endangering GC signal into a protective estrogenic one. Using an in vitro oxygen glucose deprivation model (OGD), GCs exacerbated neuron death in primary cortical cultures, and this worsening effect was completely blocked by ER/GR expression. Moreover, blocking GC actions with a vector expressing a dominant negative GC receptor promoted neuron survival during postischemia, but not preischemia. Thus, gene therapeutic strategies to modulate GC and estrogen signaling can be beneficial during an ischemic insult.

Effects of the glucocorticoid antagonist, mifepristone, on the consequences of withdrawal from long term alcohol consumption

BACKGROUND

Studies were carried out to test the hypothesis that administration of a glucocorticoid Type II receptor antagonist, mifepristone (RU38486), just prior to withdrawal from chronic alcohol treatment, would prevent the consequences of the alcohol consumption and withdrawal in mice.

MATERIALS AND METHODS

The effects of administration of a single intraperitoneal dose of mifepristone were examined on alcohol withdrawal hyperexcitability. Memory deficits during the abstinence phase were measured using repeat exposure to the elevated plus maze, the object recognition test, and the odor habituation/discrimination test. Neurotoxicity in the hippocampus and prefrontal cortex was examined using NeuN staining.

RESULTS

Mifepristone reduced, though did not prevent, the behavioral hyperexcitability seen in TO strain mice during the acute phase of alcohol withdrawal (4 hours to 8 hours after cessation of alcohol consumption) following chronic alcohol treatment via liquid diet. There were no alterations in anxiety-related behavior in these mice at 1 week into withdrawal, as measured using the elevated plus maze. However, changes in behavior during a second exposure to the elevated plus maze 1 week later were significantly reduced by the administration of mifepristone prior to withdrawal, indicating a reduction in the memory deficits caused by the chronic alcohol treatment and withdrawal. The object recognition test and the odor habituation and discrimination test were then used to measure memory deficits in more detail, at between 1 and 2 weeks after alcohol withdrawal in C57/BL10 strain mice given alcohol chronically via the drinking fluid. A single dose of mifepristone given at the time of alcohol withdrawal significantly reduced the memory deficits in both tests. NeuN staining showed no evidence of neuronal loss in either prefrontal cortex or hippocampus after withdrawal from chronic alcohol treatment.

CONCLUSIONS

The results suggest mifepristone may be of value in the treatment of alcoholics to reduce their cognitive deficits.

Attenuation of abnormal glutamate release in zinc deficiency by zinc and Yokukansan

The mechanism of the abnormal increase in extracellular glutamate concentration in the hippocampus induced with 100mM KCl in zinc deficiency is unknown. In the present study, the changes in glutamate release (exocytosis) and GLT-1, a glial glutamate transporter, expression were studied in young rats fed a zinc-deficient diet for 4 weeks. Exocytosis at mossy fiber boutons was enhanced as reported previously and GLT-1 protein was increased in the hippocampus. The enhanced exocytosis is thought to increase extracellular glutamate concentration. However, the basal concentration of extracellular glutamate in the hippocampus was not increased by zinc deficiency, suggesting that GLT-1 protein increased serves to maintain the basal concentration of extracellular glutamate. The enhanced exocytosis was attenuated in the presence of 100microM ZnCl(2), which attenuated the abnormal increase in extracellular glutamate induced with high K(+) in zinc deficiency. The present study indicates that zinc attenuates abnormal glutamate release in zinc deficiency. The enhanced exocytosis was also attenuated in slices from zinc-deficient rats administered Yokukansan, a herbal medicine, in which the abnormal increase in extracellular glutamate induced with high K(+) was attenuated. It is likely that Yokukansan is useful for prevention or cure of abnormal glutamate release. The enhanced exocytosis in zinc deficiency is a possible mechanism on abnormal increase in extracellular glutamate in the hippocampus induced with high K(+).

LY294002 inhibits glucocorticoid-induced COX-2 gene expression in cardiomyocytes through a phosphatidylinositol 3 kinase-independent mechanism

Glucocorticoids induce COX-2 expression in rat cardiomyocytes. While investigating whether phosphatidylinositol 3 kinase (PI3K) plays a role in corticosterone (CT)-induced COX-2, we found that LY294002 (LY29) but not wortmannin (WM) attenuates CT from inducing COX-2 gene expression. Expression of a dominant-negative mutant of p85 subunit of PI3K failed to inhibit CT from inducing COX-2 expression. CT did not activate PI3K/AKT signaling pathway whereas LY29 and WM decreased the activity of PI3K. LY303511 (LY30), a structural analogue and a negative control for PI3K inhibitory activity of LY29, also suppressed COX-2 induction. These data suggest PI3K-independent mechanisms in regulating CT-induced COX-2 expression. LY29 and LY30 do not inhibit glucocorticoid receptor transactivity. Both compounds have been reported to inhibit Casein Kinase 2 activity and modulate potassium and calcium levels independent of PI3K, while LY29 has been reported to inhibit mammalian Target of Rapamycin (mTOR), and DNA-dependent Protein Kinase (DNA-PK). Inhibitor of Casein Kinase 2 (CK2), mTOR or DNA-PK failed to prevent CT from inducing COX-2 expression. Tetraethylammonium (TEA), a potassium channel blocker, and nimodipine, a calcium channel blocker, both attenuated CT from inducing COX-2 gene expression. CT was found to increase intracellular Ca(2+) concentration, which can be inhibited by LY29, TEA or nimodipine. These data suggest a possible role of calcium instead of PI3K in CT-induced COX-2 expression in cardiomyocytes.

Enhancement of hippocampal mossy fiber activity in zinc deficiency and its influence on behavior

The extracellular concentration of glutamate in the hippocampus is increased by hippocampal perfusion with CaEDTA, a membrane-impermeable zinc chelator, suggesting that the activity of glutamatergic neurons in the hippocampus are influenced by the extracellular concentrations of zinc. In the present study, the relationship between the extracellular concentrations of zinc and mossy fiber activity in the hippocampus was examined in mice and rats fed a zinc-deficient diet for 4 weeks. Timm's stain, by which histochemically reactive zinc in the presynaptic vesicles is detected, was attenuated in the hippocampus in zinc deficiency. The extracellular signal of ZnAF-2, a membrane-impermeable zinc indicator, was also lower in the hippocampal CA3, suggesting that the basal extracellular concentrations of zinc are lower maintained in zinc deficiency. To check mossy fiber activity after 4-week zinc deprivation, the decrease in the signal of FM4-64, an indicator of presynaptic activity (exocytosis), at mossy fiber synapses was measured under the condition of spontaneous depolarization. The decrease was significantly facilitated by zinc deficiency, suggesting that the basal exocytosis at mossy fiber synapses is enhanced by zinc deficiency. On the other hand, the increase in anxiety-like behavior was observed in the open-field test after 4-week zinc deprivation. The present study demonstrates that the decrease in the basal extracellular concentrations of zinc may be linked to the enhancement of the basal mossy fiber activity in zinc deficiency. This decrease seems to be also involved in neuropsychological behavior in zinc deficiency.

Enhancement of social isolation-induced aggressive behavior of young mice by zinc deficiency

Neuropsychological behavior via activation of the hypothalamic-pituitary-adrenal (HPA) axis was analyzed using young mice fed a zinc-deficient diet for 2 weeks. Serum corticosterone concentration was significantly increased after 2-week zinc deprivation, whereas zinc concentration in the brain was not decreased. In the resident-intruder test, the rate of mice that exhibited aggressive behavior to the total mice was significantly higher in isolated zinc-deficient mice than in isolated control mice. The duration of aggressive behavior was more in isolated zinc-deficient mice. These results indicate that aggressive behavior of young mice elicited by social isolation is enhanced by zinc deficiency. On the other hand, social isolation-induced aggressive behavior was enhanced in isolated pair-fed mice with food restriction that can activate the HPA axis. Serum corticosterone concentration was also significantly higher in isolated zinc-deficient mice. To see the effect of the increased serum corticosterone on behavioral abnormality, neurotransmitter concentrations in brain tissue were checked. The concentrations of glutamate and GABA in brain tissue were significantly higher in both grouped and isolated zinc-deficient mice. Furthermore, the concentration of extracellular glutamate in the amygdala before the resident-intruder test was significantly higher in isolated zinc-deficient (aggressive) mice and the higher concentration was maintained during the test. The changes in neurotransmitter homeostasis, probably via the increase in serum corticosterone, seem to be linked to aggressive behavior elicited by social isolation in zinc deficiency.

Parvalbumin immunoreactivity and protein content alter in the hippocampus after adrenalectomy in seizure sensitive gerbils

OBJECTIVES

Neurons containing parvalbumin (PV), a calcium-binding protein, in the hippocampus, play an important role in hippocampal excitability in epilepsy. In this study, we examined temporal and spatial changes of PV immunoreactivity and protein content in the hippocampus after adrenalectomy (ADX) in seizure sensitive (SS) gerbils, which are hereditarily seizure-prone.

METHODS

PV distribution and change in SS gerbils after ADX were examined in the hippocampal CA1 region and in the dentate gyrus (DG) using immunohistochemistry and Western blot analysis.

RESULTS

PV immunoreactivity in sham-operated SS gerbils was detected in many CA1 pyramidal cells. Three hours after ADX, PV immunoreactivity significantly decreased in CA1 pyramidal cells and thereafter PV immunoreactivity began to increase by 4 days after ADX. Four days after ADX, PV immunoreactivity was significantly higher than that in the sham-operated SS gerbils. In the DG of sham-operated SS gerbils, PV immunoreactivity was mainly detected in polymorphic cells. Three hours after ADX, PV immunoreactivity in the DG significantly decreased in the polymorphic layer. Thereafter, PV-immunoreactive neurons decreased with time after ADX. Western blot analysis showed that change in PV protein content was similar to immunohistochemical data after ADX in SS gerbils.

CONCLUSION

Our results indicate that PV is changed in hippocampus after ADX and PV may be associated with the regulation of seizure activity.

Corticosterone disrupts glucose-, but not lactate-supported hippocampal PS-LTP

We previously reported that acute exposure of rat hippocampal brain slices to stress levels of corticosterone aggravated ischemic neuronal damage. The present study examined whether or not an acute stress level corticosterone exposure interferes with expression of rat hippocampal CA1 population spike long-term potentiation (PS-LTP) in slices supplemented either with glucose or lactate. Exposure of glucose-supplemented (5mM) slices to corticosterone (1microM) for 90min significantly diminished their ability to generate and maintain PS-LTP compared to equicaloric lactate-supplemented (10mM) slices (p<0.05). Moreover, this diminished expression of LTP in glucose-supplemented slices was ameliorated by either treatment with RU38486 (5microM), a potent corticosterone receptor antagonist or with10mM glucose. These results suggest that lactate may serve as an effective alternate energy substrate during exposure to elevated levels of corticosterone, allowing maintenance of glucocorticoid-sensitive neuronal functions such as synaptic potentiation during metabolically critical periods when glucose utilization is compromised.

Hippocampal calcium dyshomeostasis and long-term potentiation in 2-week zinc deficiency

On the basis of abnormal neuropsychological behavior in the open-field test after 2-week zinc deprivation, neurochemical response was examined in young mice fed a zinc-deficient diet for 2 weeks. Serum corticosterone concentration was markedly higher in zinc-deficient mice than in the control mice. Basal signals of intracellular calcium (fluo-4 FF) were also significantly more in hippocampal slices from zinc-deficient mice. These results suggest that basal Ca2+ levels in hippocampal cells are increased by zinc deficiency. On the other hand, Schaffer collateral long-term potentiation (LTP) was unaffected by zinc deficiency; the averaged fEPSP after tetanic stimulation was 162+/-8% of baseline value in the control and 172+/-22% in zinc-deficient mice. In the Morris water maze, there was also no significant difference in learning behavior for the hidden platform task between the control and zinc-deficient mice. The present study indicates that Schaffer collateral LTP associated with spatial cognition performance are unaffected by calcium dyshomeostasis in the hippocampus elicited by 2-week zinc deprivation, which may be linked to the increased serum corticosterone concentration.

Anxiety-like behavior of young rats after 2-week zinc deprivation

The relationship between neuronal function in the brain and neuropsychological behavior were analyzed in young rats fed a zinc-deficient diet for 1-2 weeks. Serum zinc concentration was less than 50% of that of the control. However, zinc concentration in the hippocampal perfusate measured by the in vivo microdialysis was not decreased after 2-week zinc deprivation. Timm's stain, with which histochemically reactive zinc in the presynaptic vesicle is detected, was not also attenuated in the brain. On the other hand, serum corticosterone concentration, which was determined in the morning, was markedly increased after 2-week zinc deprivation and intracellular calcium signal, which was determined by fura-2 AM, was also increased in the hippocampus. In the hippocampus in zinc deficiency, intracellular free calcium concentration may be altered prior to the decrease in zinc concentration in the extracellular fluid. When rats were subjected to the open-field test, the frequency of line crossing and the time of grooming were decreased after 2-week zinc deprivation. In the plus-maze test, the time spent in the open arms was also decreased in zinc-deficient rats, suggesting that anxiety-like behavior is increased in zinc deficiency. The present study indicates that the increase in anxiety-like behavior in zinc deficiency may be linked to the increased concentration of basal free calcium in hippocampal cells, probably due to the increase in serum corticosterone concentration.

Hypobaric hypoxia-induced dendritic atrophy of hippocampal neurons is associated with cognitive impairment in adult rats

Simulated hypobaric hypoxia (HBH), resembling high altitude hypoxia severely affects the CNS and results in several physiological changes. The hippocampus is closely associated with learning and memory and an insult to this region affects cognition. Previous studies suggest that rapid or prolonged exposures to HBH are associated with psychomotor and cognitive impairments. The defense personnel, mountain climbers and rescue teams are exposed to such harsh environment and thus it demands a systematic study emphasizing the subtle effects of such extreme environments on cognitive function. Accordingly, this study evaluated the effect of hypobaric hypoxia on structural changes in the principal neurons of the hippocampus and learning in eight-arm radial maze. Adult male Wistar rats, subjected to simulated hypobaric hypoxia equivalent to an altitude of 6000 m for a period of 2 or 7 days, in a hypoxic chamber served as hypoxic group (HY). Rats housed in a similar chamber for the same period of time, without hypoxic exposure served as sham control (SC), while normal control (NC) group of rats were housed in standard laboratory conditions. The dendritic morphology of neurons in cornu ammonis region 1 (CA1) and cornu ammonis region 3 (CA3) was studied in Golgi-impregnated hippocampal sections. Exposure for 2 days to hypobaric hypoxia had minimal deleterious effects on the CA1 pyramidal neurons, while exposure for 7 days resulted in a significant decrease in the number of branching points, intersections and dendritic length. Unlike the CA1 pyramidal neurons, the CA3 neurons exhibited dendritic atrophy following both 2 and 7 days of hypoxic exposure. Further, hippocampal-dependent spatial learning was affected marginally following 2 day exposure, while 7 day exposure severely affected learning of the partially baited radial arm maze task. Our study suggests that dendritic atrophy in the hippocampus on exposure to HBH could be one of the bases for the cognitive deficits exhibited under such conditions.

Adolescence, glucocorticoids and alcohol

This review examines the evidence that glucocorticoids are involved, during both adolescence and adulthood, in the cognitive deficits caused by long-term alcohol consumption and in the mechanism(s) of alcohol dependence. During adolescence, the hypothalamopituitary-adrenal (HPA) axis undergoes well-characterized changes in basal activity and many of these are influenced by alcohol consumption. While the former have been fairly well studied, there is little information about whether alcohol effects on the HPA in adolescents differ from those in adults. The means by which glucocorticoids may influence alcohol-related neurotoxicity are presented, and potential differences between adolescence and adults in this regard noted. The substantial evidence for involvement of glucocorticoids in alcohol-induced cognitive deficits is described, with particular reference to the consequences of alcohol withdrawal. The use of immature organotypic cultures of rodent brain in the study of alcohol neurotoxicity is considered in detail, and the information obtained from this methodology concerning the role of glucocorticoid receptors and excitable membrane proteins in this neurotoxicity. The influence of glucocorticoids on alcohol consumption and possible contributions to alcohol dependence are then considered. In conclusion, more information concerning the effects of glucocorticoids on plasticity and alcohol neurotoxicity during the adolescent period is needed.

Neuroprotective effects of agmatine against cell damage caused by glucocorticoids in cultured rat hippocampal neurons

In the present study the neuroprotective effects of agmatine against neuronal damage caused by glucocorticoids were examined in cultured rat hippocampal neurons. Spectrophotometric measurements of lactate dehydrogenase activities, beta-tubulin III immunocytochemical staining, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate (dUTP) nick-end-labeling assay (TUNEL) labeling and caspase-3 assays were carried out to detect cell damage or possible involved mechanisms. Our results show that dexamethasone and corticosterone produced a concentration-dependent increase of lactate dehydrogenase release in 12-day hippocampal cultures. Addition of 100 microM agmatine into media prevented the glucocorticoid-induced increase of lactate dehydrogenase release, an effect also shared with the specific N-methyl-D-aspartate receptor antagonist MK801 and glucocorticoid receptor antagonists mifepristone and spironolactone. Arcaine, an analog of agmatine with similar structure as agmatine, also blocked glucocorticoid-induced increase of lactate dehydrogenase release. Spermine and putrescine, the endogenous polyamine and metabolic products of agmatine without the guanidino moiety of agmatine, have no appreciable effect on glucocorticoid-induced injuries, indicating a structural relevance for this neuroprotection. Immunocytochemical staining with beta-tubulin III confirmed the substantial neuronal injuries caused by glucocorticoids and the neuroprotective effects of agmatine against these neuronal injuries. TUNEL labeling demonstrated that agmatine significantly reduced TUNEL-positive cell numbers induced by exposure of cultured neurons to dexamethasone. Moreover, exposure of hippocampal neurons to dexamethasone significantly increased caspase-3 activity, which was inhibited by co-treatment with agmatine. Taken together, these results demonstrate that agmatine can protect cultured hippocampal neurons from glucocorticoid-induced neurotoxicity, through a possible blockade of the N-methyl-D-aspartate receptor channels or a potential anti-apoptotic property.

Stress increases vulnerability to inflammation in the rat prefrontal cortex

Inflammation could be involved in some neurodegenerative disorders that accompany signs of inflammation. However, because sensitivity to inflammation is not equal in all brain structures, a direct relationship is not clear. Our aim was to test whether some physiological circumstances, such as stress, could enhance susceptibility to inflammation in the prefrontal cortex (PFC), which shows a relative resistance to inflammation. PFC is important in many brain functions and is a target for some neurodegenerative diseases. We induced an inflammatory process by a single intracortical injection of 2 microg of lipopolysaccharide (LPS), a potent proinflammogen, in nonstressed and stressed rats. We evaluated the effect of our treatment on inflammatory markers, neuronal populations, BDNF expression, and behavior of several mitogen-activated protein (MAP) kinases and the transcription factor cAMP response element-binding protein. Stress strengthens the changes induced by LPS injection: microglial activation and proliferation with an increase in the levels of the proinflammatory cytokine tumor necrosis factor-alpha; loss of cells such as astroglia, seen as loss of glial fibrillary acidic protein immunoreactivity, and neurons, studied by neuronal-specific nuclear protein immunohistochemistry and GAD67 and NMDA receptor 1A mRNAs expression by in situ hybridization. A significant increase in the BDNF mRNA expression and modifications in the levels of MAP kinase phosphorylation were also found. In addition, we observed a protective effect from RU486 [mifepristone (11beta-[p-(dimethylamino)phenyl]-17beta-hydroxy-17-(1-propynyl)estra-4,9-dien-3-one)], a potent inhibitor of the glucocorticoid receptor activation. All of these data show a synergistic effect between inflammation and stress, which could explain the relationship described between stress and some neurodegenerative pathologies.

Shock stress protects mice against amphetamine-induced dopaminergic toxicity

The effect of tail shock (ten, 2.0 mA/0.15 s shocks) on amphetamine-induced dopaminergic toxicity in adult, male BALB/c mice was assessed. Fifteen minutes following a single shock session, mice received amphetamine (50-mg/kg) or saline as follows: Shock/Saline; NoShock/Saline; Shock/Amphetamine; No Shock/Amphetamine. Amphetamine caused a 60% dopamine depletion in the No Shock/Amphetamine group. Tail shock provided neuroprotection against amphetamine-induced dopamine depletion, an effect likely related to the stress response.

A 24 h corticosterone exposure exacerbates excitotoxic insult in rat hippocampal slice cultures independently of glucocorticoid receptor activation or protein synthesis

Elevations in circulating concentrations of glucocorticoids (GC) may increase the expression and/or sensitivity of ionotropic transmitter receptors in brain. For example, recent evidence suggests that acute and chronic GC exposure may alter the number and/or function of N-methyl-D-aspartate (NMDA)-type glutamate receptors, effects that may sensitize the brain to excitotoxic insults. The present studies examined the ability of short-term (24 h) corticosterone (CORT) exposure to potentiate NMDA-induced cytotoxicity in rat hippocampal slice cultures. Additional studies evaluated the role of mineralocorticoid (MR) and glucocorticoid receptor (GR) function, as well as de novo protein synthesis, in potentiation of toxicity by corticosterone exposure. Hippocampal slice cultures were exposed to NMDA (20 microM) for 24 h with cytotoxicity assessed by fluorescent detection of propidium iodide uptake. Exposure to NMDA caused significant propidium iodide uptake in each hippocampal region, while 24 h CORT (0.001-1 microM) exposure alone did not significantly increase propidium iodide uptake. Co-exposure of cultures to CORT and NMDA synergistically increased propidium iodide uptake in each hippocampal region, effects that were prevented by co-exposure to a non-toxic concentration of MK-801 (20 microM). In contrast, 24 h exposure with the MR antagonist spironolactone (1-10 microM), the GR antagonist RU-486 (1-10 microM), or the protein synthesis inhibitor cycloheximide (1 microM) failed to reduce the significant increase in propidium iodide uptake. These data suggest that relatively brief elevations in CORT levels may sensitize the hippocampus to injury independently of GC receptor activity and protein synthesis.

Corticosterone and dexamethasone potentiate cytotoxicity associated with oxygen-glucose deprivation in organotypic cerebellar slice cultures

Many patients display elevated levels of serum cortisol following acute ischemic stroke. Given that glucocorticoids may potentiate some forms of insult, these studies examined the effects of corticosterone or dexamethasone exposure on cytotoxicity following oxygen-glucose deprivation in the cerebellum, a brain region susceptible to stroke. In organotypic cerebellar slice cultures prepared from neonatal rat pups, 90-min of oxygen-glucose deprivation at 15 days in vitro resulted in significant cytotoxicity at 24-, 48-, and 72-h post-oxygen-glucose deprivation, as measured by uptake of propidium iodide. Exposure of cultures following oxygen-glucose deprivation to the antioxidant trolox (500 microM), but not to the glucocorticoid receptor antagonist RU486 (10 microM), completely blocked oxygen-glucose deprivation-induced cytotoxicity. Corticosterone (1 microM) or dexamethasone (10 microM) exposure alone did not significantly increase propidium iodide uptake above levels observed in control cultures. However, corticosterone or dexamethasone exposure after oxygen-glucose deprivation potentiated oxygen-glucose deprivation-mediated propidium iodide uptake at each time point. Trolox, as well as RU486, co-exposure of cultures to corticosterone or dexamethasone after oxygen-glucose deprivation abolished all cytotoxicity. In conclusion, these data demonstrated that glucocorticoid exposure modulated oxygen-glucose deprivation-mediated propidium iodide uptake, which likely involved glucocorticoid receptor activation and pro-oxidant effects.

Seizure-induced changes of mineralocorticoid and glucocorticoid receptors in the hippocampus in seizure sensitive gerbils

Abnormal corticosteroid hormone levels during stress and resultant mineralocorticoid receptor (MR)/glucocorticoid receptor (GR) imbalance enhance the vulnerability of specific hippocampal neurons. In the present study, we investigated the distribution of MR and GR in seizure resistant (SR) and seizure sensitive (SS) gerbils, and observed the seizure-induced changes of MR and GR in the hippocampus of SS gerbils using immunohistochemistry and western blot analysis. MR and GR immunoreactivities were higher in the SS pre-seizure gerbils than that in SR gerbils. In the SR gerbils, the immunodensity of GR was high compared to that of MR. The changes of MR and GR immunoreactivities were significant in the stratum pyramidale of the hippocampal CA1 region and the infrablade of the dentate gyrus after seizure on-set. MR immunoreactivity in the CA1 region was significantly increased at 12h after seizure on-set, thereafter MR immunoreactivity was decreased. MR immunoreactivity in the dentate gyrus was decreased time-dependently after seizure on-set. GR immunoreactivity was decreased in the CA1 region and dentate gyrus time-dependently after seizure on-set. At 12h after seizure on-set, differences in MR and GR immunodensity diminished in the CA1 region and dentate gyrus. This imbalance of MR and GR immunoreactivity in these regions may be associated with seizure generation in the Mongolian gerbil, which is a hereditary seizure model.

Acute and repeated restraint stress influences cellular damage in rat hippocampal slices exposed to oxygen and glucose deprivation

Several studies have shown that high corticosteroid hormone levels increase neuronal vulnerability. Here we evaluate the consequences of in vivo acute or repeated restraint stress on cellular viability in rat hippocampal slices suffering an in vitro model of ischemia. Cellular injury was quantified by measuring lactate dehydrogenase (LDH) and neuron-specific enolase released into the medium. Acute stress did not affect cellular death when oxygen and glucose deprivation (OGD) was applied both immediately or 24h after restraint. The exposure to OGD, followed by reoxygenation, resulted in increased LDH in the medium. Repeated stress potentiated the effect of OGD both, on LDH and neuron-specific enolase released to the medium. There was no effect of repeated stress on the release of S100B, an astrocytic protein. Additionally, no effect of repeated stress was observed on glutamate uptake by the tissue. These results suggest that repeated stress increases the vulnerability of hippocampal cells to an in vitro model of ischemia, potentiating cellular damage, and that the cells damaged by the exposure to repeated stress+OGD are mostly neurons. The uptake of glutamate was not observed to participate in the mechanisms responsible for rendering the neurons more susceptible to ischemic damage after repeated stress.

Corticosterone Increases Damage and Cytosolic Calcium Accumulation Associated With Ethanol Withdrawal in Rat Hippocampal Slice Cultures

BACKGROUND

Evidence suggests that stress hormones (i.e., glucocorticoids) may be increased during acute or chronic consumption of ethanol and during withdrawal from ethanol consumption, effects that may contribute to the development of cognitive impairment. The goal of the current studies was to examine the hypothesis that increased glucocorticoid levels in conjunction with ethanol exposure and withdrawal may cause hippocampal damage.

METHODS

Organotypic hippocampal slice cultures were exposed to 50 mM ethanol for 10 days and withdrawn for 1 day. After withdrawal, cytotoxicity and cytosolic Ca2+ accumulation were measured using the nucleic acid stain propidium iodide and Calcium Orange, AM, respectively. Cultures were also treated with nontoxic concentrations of corticosterone (0.001-1 microM) during ethanol exposure and withdrawal or only during withdrawal. Additional cultures were coexposed to corticosterone and RU486 (0.1-10.0 microM), spironolactone (0.1-10.0 microM), or MK-801 (20 microM) during ethanol exposure and/or withdrawal.

RESULTS

Ethanol withdrawal did not increase propidium iodide fluorescence and cytosolic Ca2+ levels. However, significant increases in propidium iodide fluorescence and in cytosolic Ca2+ accumulation were observed in cultures when corticosterone (> or = 100 nM) was exposed during ethanol treatment and/or withdrawal. These effects of corticosterone on ethanol withdrawal were attenuated by RU486 and MK-801 but not by spironolactone coexposure.

CONCLUSIONS

This report demonstrated that corticosterone exposure during ethanol treatment and/or withdrawal resulted in significant hippocampal damage, possibly via activation of glucocorticoid receptors and enhancement of the glutamatergic cascade. The findings from these studies suggest that glucocorticoids contribute to the neuropathological consequences of alcohol dependence in humans.

Choline exposure reduces potentiation of N-methyl-D-aspartate toxicity by corticosterone in the developing hippocampus

Exposure to high levels of glucocorticoids (GCs) may adversely affect neuronal viability, particularly in the developing hippocampus, via increased function or sensitivity of N-methyl-D-aspartate (NMDA)-type glutamate receptors. Conversely, choline supplementation in the developing brain may reduce the severity of subsequent insult. The present studies aimed to examine the extent to which short-term exposure to high concentrations of corticosterone would produce neuronal injury mediated by NMDA receptor activity. These studies also assessed the ability of choline to prevent this form of injury via interactions with nicotinic acetylcholine receptors (nAChRs) expressing the alpha7 subunit. Organotypic hippocampal slice cultures derived from neonatal rat were pre-treated for 72 h with corticosterone (100 nM) alone or with choline (0.1-10 mM), prior to a brief (1 h) NMDA exposure (5 microM). NMDA exposure produced significant cellular damage, reflected as increased fluorescence of the non-vital marker propidium iodide, in the CA1 region. While exposure to corticosterone alone did not produce damage, pre-treatment of cultures with corticosterone markedly exacerbated NMDA-induced toxicity. Pre-treatment with choline (> or =1 mM) alone or in combination with corticosterone markedly reduced subsequent NMDA toxicity, effects blocked by co-exposure to methyllycaconitine (100 nM), an antagonist active at nAChRs expressing the alpha7 subunit. These data suggest that even short-term exposure to high concentrations of GCs may adversely affect neuronal viability and that choline supplementation protects the brain from NMDA receptor-mediated damage, including that associated with hypercortisolemia.

(−)-nicotine ameliorates corticosterone's potentiation of N-methyl-d-aspartate receptor-mediated cornu ammonis 1 toxicity

Hypercortisolemia, long-term exposure of the brain to high concentrations of stress hormones (i.e. cortisol), may occur in patients suffering from depression, alcoholism, and other disorders. This has been suggested to produce neuropathological effects, in part, via increased function or sensitivity of N-methyl-d-aspartate (NMDA)-type glutamate receptors. Given that cigarette smoking is highly prevalent in some of these patient groups and nicotine has been shown to reduce toxic consequences of NMDA receptor function, it may be suggested that nicotine intake may attenuate the neurotoxic effects of hypercortisolemia. To investigate this possibility, organotypic hippocampal slice cultures derived from rat were pre-treated with corticosterone (0.001-1 microM) alone or in combination with selective glucocorticoid receptor antagonists for 72-h prior to a brief (1-h) NMDA exposure (5 microM). Pre-treatment with corticosterone (0.001-1 microM) alone did not cause hippocampal damage, while NMDA exposure produced significant cellular damage in the cornu ammonis (CA)1 subregion. No significant damage was observed in the dentate gyrus or CA3 regions following NMDA exposure. Pre-treatment of cultures with corticosterone (0.1-1 microM) markedly exacerbated NMDA-induced CA1 and dentate gyrus region damage. This effect in the CA1 region was prevented by co-administration of the glucocorticoid receptor antagonist RU486 (>or=1 microM), but not spironolactone (1-10 microM), a mineralocorticoid receptor antagonist. In a second series of studies, both acute and pre-exposure of cultures to (-)-nicotine (1-10 microM) significantly reduced NMDA toxicity in the CA1 region. Co-administration of cultures to (-)-nicotine (1-10 microM) with 100 nM corticosterone prevented corticosterone's exacerbation of subsequent CA1 insult. This protective effect of (-)-nicotine was not altered by co-exposure of cultures to 10 microM dihydro-beta-erythroidine but was blocked by co-exposure to 100 nM methyllycaconitine, suggesting the involvement of nicotinic acetylcholine receptors possessing the alpha7* subunit. The present studies suggest a role for hypercortisolemia in sensitizing the hippocampal NMDA receptor system to pathological activation and indicate that prolonged nicotine exposure attenuates this sensitization. Thus, it is possible that one consequence of heavy smoking in those suffering from hypercortisolemia may be a reduction of neuronal injury and sparing of cellular function.