Adrenalectomy regulates apoptotic-associated genes in rat hippocampus

Sex-Dependent Changes of miRNA Levels in the Hippocampus of Adrenalectomized Rats Following Acute Corticosterone Administration

We explored sex-biased effects of the primary stress glucocorticoid hormone corticosterone on the miRNA expression profile in the rat hippocampus. Adult adrenalectomized (ADX) female and male rats received a single corticosterone (10 mg/kg) or vehicle injection, and after 6 h, hippocampi were collected for miRNA, mRNA, and Western blot analyses. miRNA profiling microarrays showed a basal sex-biased miRNA profile in ADX rat hippocampi. Additionally, acute corticosterone administration triggered a sex-biased differential expression of miRNAs derived from genes located in several chromosomes and clusters on the X and 6 chromosomes. Putative promoter analysis unveiled that most corticosterone-responsive miRNA genes contained motifs for either direct or indirect glucocorticoid actions in both sexes. The evaluation of transcription factors indicated that almost 50% of miRNA genes sensitive to corticosterone in both sexes was under glucocorticoid receptor regulation. Transcription factor-miRNA regulatory network analyses identified several transcription factors that regulate, activate, or repress miRNA expression. Validated target mRNA analysis of corticosterone-responsive miRNAs showed a more complex miRNA-mRNA interaction network in males compared to females. Enrichment analysis revealed that several hippocampal-relevant pathways were affected in both sexes, such as neurogenesis and neurotrophin signaling. The evaluation of selected miRNA targets from these pathways displayed a strong sex difference in the hippocampus of ADX-vehicle rats. Corticosterone treatment did not change the levels of the miRNA targets and their corresponding tested proteins. Our data indicate that corticosterone exerts a sex-biased effect on hippocampal miRNA expression, which may engage in sculpting the basal sex differences observed at higher levels of hippocampal functioning.

Isoalantolactone induces intrinsic apoptosis through p53 signaling pathway in human lung squamous carcinoma cells

Isoalantolactone has recently been revealed to induce apoptosis in several types of cancer. However, little is reported on its anti-tumor potential on human lung cancer. Our present study was designed to investigate its effects on human lung squamous carcinoma SK-MES-1 cells. We found that Isoalantolactone induced cellular and DNA morphological changes and decreased the viability of SK-MES-1 cells. It significantly inhibited the growth of SK-MES-1 cells through apoptosis in a dose-dependent manner via activation of p53. It also induced cell cycle arrest at G1 phase. It can down-regulate Bcl-2 and up-regulate Bax, to induce dissipation of mitochondrial membrane potential and generation of reactive oxygen species. Caspase-3 was also activated by Isoalantolactone, with the cleavage of poly (ADP-ribose) polymerase. Our results reveal that Isoalantolactone induces intrinsic apoptosis in SK-MES-1 cells through p53 signaling pathway, which suggests that Isoalantolactone could be a potential leading compound for future development of anti-lung cancer drugs.

Dracorhodin perchlorate induces G1/G0 phase arrest and mitochondria-mediated apoptosis in SK-MES-1 human lung squamous carcinoma cells

Dracorhodin perchlorate (DP) has recently been revealed to induce apoptosis in various types of cancer. However, the antitumor potential and molecular mechanisms of DP in human lung cancer have not been previously reported. Therefore, the present study aimed to investigate the effects of DP on cell viability, the cell cycle and apoptosis, using an MTT assay, flow cytometry and western blot studies. DP was identified to induce cellular and DNA morphological changes, and decreased the viability of SK-MES-1 human lung squamous carcinoma cells. DP significantly inhibited the growth of SK-MES-1 cells by inducing apoptosis and G₁/G₀ cell cycle arrest in a dose-dependent manner via activation of p53 (P<0.05). Furthermore, DP promoted the significant upregulation of B cell lymphoma-2 (Bcl-2)-activated X protein and significant downregulation of Bcl-2 (P<0.05), inducing dissipation of the mitochondrial membrane potential (MMP). In addition, caspase-3 was activated by DP via the cleavage of its substrate, proteolytic cleavage of poly(ADP-ribose) polymerase. DP also induced caspase-independent apoptosis by significantly increasing the protein expression of the apoptosis-inducing factor (P<0.05), which is localized in mitochondria under the physiological conditions and released into the cytoplasm when MMP is dissipated. Furthermore, the present study demonstrated that DP significantly increased the generation of reactive oxygen species (P<0.05). In conclusion, the current study revealed that DP is able to induce cell cycle arrest and apoptosis in SK-MES-1 cells via activation of the mitochondrial pathway, indicating that DP may be a potential leading compound for the development of future lung cancer therapeutic regimes.

Novel aspects of glucocorticoid actions

Normal hypothalamic-pituitary-adrenal (HPA) axis activity leading to the rhythmic and episodic release of adrenal glucocorticoids (GCs) is essential for body homeostasis and survival during stress. Acting through specific intracellular receptors in the brain and periphery, GCs regulate behaviour, as well as metabolic, cardiovascular, immune and neuroendocrine activities. By contrast to chronic elevated levels, circadian and acute stress-induced increases in GCs are necessary for hippocampal neuronal survival and memory acquisition and consolidation, as a result of the inhibition of apoptosis, the facilitation of glutamatergic neurotransmission and the formation of excitatory synapses, and the induction of immediate early genes and dendritic spine formation. In addition to metabolic actions leading to increased energy availability, GCs have profound effects on feeding behaviour, mainly via the modulation of orexigenic and anorixegenic neuropeptides. Evidence is also emerging that, in addition to the recognised immune suppressive actions of GCs by counteracting adrenergic pro-inflammatory actions, circadian elevations have priming effects in the immune system, potentiating acute defensive responses. In addition, negative-feedback by GCs involves multiple mechanisms leading to limited HPA axis activation and prevention of the deleterious effects of excessive GC production. Adequate GC secretion to meet body demands is tightly regulated by a complex neural circuitry controlling hypothalamic corticotrophin-releasing hormone (CRH) and vasopressin secretion, which are the main regulators of pituitary adrenocorticotrophic hormone (ACTH). Rapid feedback mechanisms, likely involving nongenomic actions of GCs, mediate the immediate inhibition of hypothalamic CRH and ACTH secretion, whereas intermediate and delayed mechanisms mediated by genomic actions involve the modulation of limbic circuitry and peripheral metabolic messengers. Consistent with their key adaptive roles, HPA axis components are evolutionarily conserved, being present in the earliest vertebrates. An understanding of these basic mechanisms may lead to novel approaches for the development of diagnostic and therapeutic tools for disorders related to stress and alterations of GC secretion.

Acute Antiapoptotic Effects of Hydrocortisone in the Hippocampus of Neonatal Rats

Natural glucocorticoid hydrocortisone was suggested as a potent substitution for dexamethasone in the treatment of bronchopulmonary dysplasia in neonates. The aim of this study was to investigate whether hydrocortisone is able to affect the expression of apoptotic genes and the intensity of naturally occurring cell death in the developing rat hippocampus. Hormone treatment decreased procaspase-3 and active caspase-3 levels as well as DNA fragmentation intensity in the hippocampal formation of one-week-old rats in 6 h after injection. These changes were accompanied by an upregulation of antiapoptotic protein Bcl-XL, while expression of proapoptotic protein Bax remained unchanged. The action of hydrocortisone was glucocorticoid receptor-independent, as the selective glucocorticoid receptor agonist dexamethasone did not affect either apoptotic protein levels or DNA fragmentation intensity in the hippocampal region. The data are the first evidences for in vivo antiapoptotic effects of hydrocortisone in the developing hippocampus.

Neuroprotection provided by dietary restriction in rats is further enhanced by reducing glucocortocoids

Glucocorticoids (GC)--corticosterone (CORT) in rodents and cortisol in primates--are stress-induced hormones secreted by adrenal glands that interact with the hypothalamic pituitary axis. High levels of cortisol in humans are observed in neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD), as well as in diabetes, post-traumatic stress syndrome, and major depression. Experimental models of diabetes in rats and mice have demonstrated that reduction of CORT reduces learning and memory deficits and attenuates loss of neuronal viability and plasticity. In contrast to the negative associations of elevated GC levels, CORT is moderately elevated in dietary restriction (DR) paradigms which are associated with many healthy anti-aging effects including neuroprotection. We demonstrate here in rats that ablating CORT by adrenalectomy (ADX) with replenishment to relatively low levels (30% below that of controls) prior to the onset of a DR regimen (ADX-DR) followed by central administration of the neurotoxin, kainic acid (KA), significantly attenuates learning deficits in a 14-unit T-maze task. The performance of the ADX-DR KA group did not differ from a control group (CON) that did not receive KA and was fed ad libitum (AL). By contrast, the sham-operated DR (SHAM-DR KA) group, SHAM-AL KA group, and ADX-AL KA group demonstrated poorer learning behavior in this task compared to the CON group. Stereological analysis revealed equivalent DR-induced neuroprotection in the SH-DR KA and ADX-DR KA groups, as measured by cell loss in the CA2/CA3 region of the hippocampus, while substantial cell loss was observed in SH-AL and ADX-AL rats. A separate set of experiments was conducted with similar dietary and surgical treatment conditions but without KA administration to examine markers of neurotrophic activity, brain-derived neurotrophic factor (BDNF), transcriptions factors (pCREB), and chaperone proteins (HSP-70). Under these conditions, we noted elevations in both BDNF and pCREB in ADX DR rats compared to the other groups; whereas, HSP-70, was equivalently elevated in ADX-DR and SH-DR groups and was higher than observed in both SH-AL and ADX-AL groups. These results support findings that DR protects hippocampal neurons against KA-induced cellular insult. However, this neuroprotective effect was further enhanced in rats with a lower-than control level of CORT resulting from ADX and maintained by exogenous CORT supplementation. Our results then suggest that DR-induced physiological elevation of GC may have negative functional consequences to DR-induced beneficial effects. These negative effects, however, can be compensated by other DR-produced cellular and molecular protective mechanisms.

Resveratrol improves hippocampal atrophy in chronic fatigue mice by enhancing neurogenesis and inhibiting apoptosis of granular cells

Neuroimaging evidence showed structural and/or functional abnormalities existing in the central nervous system, especially the hippocampus, in chronic fatigue syndrome (CFS) patients. However, its pathophysiologic mechanisms are unclear in part due to the lack of an applicable animal model. We established a chronic fatigue murine model by six repeated injections of Brucella abortus antigen to mice, which was manifested as reduced daily running activity and hippocampal atrophy. Thereafter, resveratrol, a polyphenolic activator of sirtuin 1, was used for treatment in this model. Daily running activity was increased by more than 20%, and the hippocampus was enlarged after 4-week resveratrol therapy. Furthermore, resveratrol inhibited neuronal apoptosis and expression of hippocampal acetylated p53 in the fatigue mice. Resveratrol also improved neurogenesis and expression of brain-derived neurotrophic factor mRNA in the hippocampus. We concluded that repeated injection of B. abortus antigen could induce hypoactivity and hippocampal atrophy in mice. Resveratrol may be effective for improving fatigue symptoms and enlarging the atrophic hippocampus by repressing apoptosis and promoting neurogenesis.

A novel animal model of hippocampal cognitive deficits, slow neurodegeneration, and neuroregeneration

Long-term adrenalectomy (ADX) results in an extensive and specific loss of dentate gyrus granule cells in the hippocampus of adult rats. This loss of granule cells extends over a period of weeks to months and ultimately results in cognitive deficits revealed in a number of tasks that depend on intact hippocampal function. The gradual nature of ADX-induced cell death and the ensuing deficits in cognition resemble in some important respects a variety of pathological conditions in humans. Here, we characterize behavioural and cellular processes, including adult neurogenesis, in the rat ADX model. We also provide experimental evidence for a neurogenic treatment strategy by which the lost hippocampal cells may be replaced, with the goal of functional recovery in mind.

Dietary restriction and brain health

The benefits of dietary restriction (DR) on health and aging prevention have been well recognized. Recent studies suggest that DR may enhance brain functions including learning and memory, synaptic plasticity, and neurogenesis, all of which are associated with brain health. Under the stress stimulated by DR, a favorable environment is established for facilitating neuronal plasticity, enhancing cognitive function, stimulating neurogenesis and regulating inflammatory response. DR-induced expressions of factors such as heat shock proteins (HSPs), neurotrophic factors, and Sirtuin1 (SIRT1) are responsible for the effect of DR on the brain. Due to the difficulty in practising long-term DR in human, the potential mimics of DR are also discussed.

Nicotinamide prevents the long-term effects of perinatal asphyxia on apoptosis, non-spatial working memory and anxiety in rats

There is no established treatment for the long-term effects produced by perinatal asphyxia. Thus, we investigated the neuroprotection provided by nicotinamide against the effects elicited by perinatal asphyxia on hippocampus and behaviour observed at 30-90 days of age. Asphyxia was induced by immersing foetuses-containing uterine horns, removed from ready-to-deliver rats into a water bath at 37 degrees C for 20 min. Caesarean-delivered siblings were used as controls. Saline or nicotinamide (0.8 mmol/kg, i.p.) was administered to control and asphyxia-exposed animals 24, 48, and 72 h after birth. The animals were examined for morphological changes in hippocampus, focusing on delayed cell death and mossy fibre sprouting, and behaviour, focusing on cognitive behaviour and anxiety. At the age of 30-45 days, asphyxia-exposed rats displayed (1) increased apoptosis, assessed in whole hippocampus by nuclear Hoechst staining, and (2) increased mossy fibre sprouting, restricted to the stratum oriens of dorsal hippocampus, assessed by Timm's staining. Rats from the same cohorts displayed (3) deficits in non-spatial working memory, assessed by a novel object recognition task, and (4) increased anxiety, assessed by an elevated plus-maze test when examined at the age of 90 days. Nicotinamide prevented the effects elicited by perinatal asphyxia on apoptosis, working memory, and anxiety.

Desipramine prevents stress-induced changes in depressive-like behavior and hippocampal markers of neuroprotection

Extracellular signal-regulated kinases (ERKs) are widely implicated in multiple physiological processes. Although ERK1/2 has been proposed as a common mediator of antidepressant action in naive rodents, it remains to be determined whether the ERK1/2 pathway plays a role in depressive disorder. Here, we investigated whether chronic restraint stress (14 days) and antidepressant treatment [desipramine (DMI), 10 mg/kg intraperitoneally] induce changes in animal behavior and hippocampal levels of phospho-ERK1/2 and its substrate phospho-cAMP response element-binding protein (CREB). The results indicated that stress-induced depressive-like behaviors were correlated with an increase in P-ERK1/2 and P-CREB in the hippocampus evaluated by immunoblot analysis. As an indication of CREB activity, we evaluated changes in mRNA levels of its target genes. Brain-derived neurotrophic factor (BDNF) mRNA was reduced by stress, an effect prevented by DMI only in the CA3 area of hippocampus. Bcl-2 mRNA was reduced in all hippocampal regions by stress, an effect independent of DMI treatment. However, immunoblot from hippocampal extracts revealed that stress increased BCL-2 levels, an effect prevented by chronic DMI. These results suggest that ERKs and BDNF may be altered in depressive disorder, modifications that are sensitive to DMI action. In contrast, the stress-induced increase in BCL-2 may correspond to a neuroprotective response.

Plasticity of hippocampus following perinatal asphyxia: effects on postnatal apoptosis and neurogenesis

Asphyxia during delivery produces long-term deficits in brain development, including hippocampus. We investigated hippocampal plasticity after perinatal asphyxia, measuring postnatal apoptosis and neurogenesis. Asphyxia was performed by immersing rat fetuses with uterine horns removed from ready-to-deliver rats into a water bath for 20 min. Caesarean-delivered pups were used as controls. The animals were euthanized 1 week or 1 month after birth. Apoptotic nuclear morphology and DNA breaks were assessed by Hoechst and TUNEL assays. Neurogenesis was estimated by bromodeoxyuridine/MAP-2 immunocytochemistry, and the levels and expression of proteins related to apoptosis and cell proliferation were measured by Western blots and in situ hybridization, respectively. There was an increase of apoptosis in CA1, CA3, and dentate gyrus (DG) and cell proliferation and neurogenesis in CA1, DG, and hilus regions of hippocampus 1 week after asphyxia. The increase of apoptosis in CA3 and cell proliferation in the suprapyramidal band of DG was still observed 1 month following asphyxia. There was an increase of BAD, BCL-2, ERK2, and bFGF levels in whole hippocampus and bFGF expression in CA1 and CA2 and hilus at P7 and P30. There was a concomitant decrease of phosphorylated-BAD (Ser112) levels. The increase of BAD levels supports the idea of delayed cell death after perinatal asphyxia, whereas the increases of BCL-2, ERK2, and bFGF levels suggest the activation of neuroprotective and repair pathways. In conclusion, perinatal asphyxia induces short- and long-term regionally specific plastic changes, including delayed cell death and neurogenesis, involving pro- and antiapoptotic as well as mitogenic proteins, favoring hippocampal functional recovery.

Adrenalectomy promotes a permanent decrease of plasma corticoid levels and a transient increase of apoptosis and the expression of Transforming Growth Factor beta1 (TGF-beta1) in hippocampus: effect of a TGF-beta1 oligo-antisense

BACKGROUND

Corticosterone reduction produced by adrenalectomy (ADX) induces apoptosis in dentate gyrus (DG) of the hippocampus, an effect related to an increase in the expression of the pro-apoptotic gene bax. However it has been reported that there is also an increase of the anti-apoptotic gene bcl-2, suggesting the promotion of a neuroprotective phenomenon, perhaps related to the expression of transforming growth factor beta1 (TGF-beta1). Thus, we have investigated whether TGF-beta1 levels are induced by ADX, and whether apoptosis is increased by blocking the expression of TGF-beta1 with an antisense oligonucleotide (ASO) administered intracerebrally in corticosterone depleted rats.

RESULTS

It was observed an increase of apoptosis in DG, 2 and 5 days after ADX, in agreement with a reduction of corticosterone levels. However, the effect of ADX on the number of apoptotic positive cells in DG was decreased 5 days after the lesion. In CA1-CA3 regions, the effect was only observed 2 days after ADX. TGF-beta1 mRNA levels were increased 2 days after ADX. The sustained intracerebro-ventricular administration of a TGF-beta1 ASO via an osmotic mini pump increased apoptosis levels in CA and DG regions 5 days after ADX as well as sham-operated control animals. No significant effect was observed following a scrambled-oligodeoxynucleotide treatment.

CONCLUSION

The changes in both the pattern and the magnitude of apoptotic-cell morphology observed 2 and 5 days after ADX suggest that, as a consequence of the reduction of corticosteroids, some trophic mechanisms restricting cell death to a particular time window are elicited. Sustained intracerebral administration of TGF-beta1 ASO increased the apoptosis promoted by ADX, suggesting that TGF-beta1 plays an anti-apoptotic role in vivo in hippocampus.

Temporal and region-dependent changes in muscarinic M4 receptors in the hippocampus and entorhinal cortex of adrenalectomized rats

Long-term adrenalectomy induces a dramatic loss of cells in the dentate gyrus and CA1-CA4 fields of the hippocampus resulting in an impairment of cognitive functions such as spatial learning, memory and exploratory behaviour. Muscarinic M1 and M4 receptor levels in the hippocampus and entorhinal cortex of adult male Wistar rats were examined 3, 14, 30, 90, and 150 days after adrenalectomy. Receptor levels in the entorhinal cortex and the hippocampus were determined by quantitative autoradiography using 125I-M1-toxin-1 and 125I-M4-toxin-1, M1 and M4 subtype selective antagonists, respectively. Moreover, the level of hippocampal M1 and M4 muscarinic receptors were evaluated 1 month after adrenalectomy by immunoblot analysis. Adrenalectomy induced apoptotic processes were examined by analysing apoptotic markers using Western blot analysis. No significant changes were observed in the level of muscarinic M1 receptors in the entorhinal cortex, the dentate gyrus and in the different CA fields of the hippocampus of adrenalectomized (ADX) rats. However, M4 receptors showed a significant decrease in the entorhinal cortex (at 3 days), dentate gyrus and CA4 (at 14 days), CA3 (at 30 days), and CA2 and CA1 (at 90 days) after adrenalectomy. Moreover, a decrease in the level of M4 receptors was detected in ADX rats 1 month after adrenalectomy as compared with sham groups using M4 specific antibody. Apoptotic markers such as PARP and p53 were significantly increased whereas Bcl-2 marker was decreased in ADX rat brain homogenates compared to controls. Our results show that M1 and M4 receptors are differentially affected by adrenalectomy and indicate that these subtypes have different functions in the hippocampus. Our data on time and region-dependent decreases in hippocampal M4 receptors indicate that the M4 receptor subtype is influenced by adrenal hormones and suggest that the M4 receptor might be linked to memory function in the hippocampus.

Perindopril regulates beta-agonist-induced cardiac apoptosis

Administration of the beta-adrenergic agonist isoproterenol results in cardiac apoptosis. The effect of short-term beta-adrenergic stimulation by isoproterenol on the activity of plasma, lung, and left ventricular (LV) angiotensin I-converting enzyme (ACE) activity and its association with the development of cardiac apoptosis was investigated. beta-Adrenergic stimulation for 24 hours produced an early increase only in the proapoptotic proteins bax and bcl-XS without changes in the levels of the antiapoptotic protein bcl-XL. The ratio between these bcl family proteins was indicative of apoptosis and correlated with an early and significant increase (300%) in DNA laddering. However, after 5 days of the beta-adrenergic stimulation, the ratio changed in favor of antiapoptotic proteins and correlated with the absence of DNA fragmentation. In addition, LV and plasma ACE activities increased markedly with isoproterenol over the study period up to 5 days. ACE activity also regulated expression of the antiapoptotic gene bcl-XL. The administration of perindopril (an ACE inhibitor) prevented the observed increase in bax and bcl-XS levels and attenuated (50% decrease, P<0.05) the effect of isoproterenol on DNA fragmentation. Thus, early and transient cardiac apoptosis triggered by the beta-adrenergic agonist isoproterenol is reversed in the presence of perindopril.

Neuropathological Studies on Cycloate-Induced Neuronal Cell Death in the Rat Brain

The herbicide cycloate (carbamothioic acid, ethyl(cyclohexyl)-S-ethyl ester) given as a single oral dose to rats, caused selective neuronal cell death in two regions in the rat forebrain, the pyramidal neurons of layers II-III throughout the pyriform cortex and in granule cells of the caudal ventro-lateral dentate gyrus. Male Alderley Park rats, 6-8-week-old, were given a single oral dose of either 0 or 2000 mg/kg cycloate and killed for neuropathological investigation 1, 2, 3, 7, 14 or 28 days after dosing, using a regime of perfusion fixation with modified Karnovsky's fixative, followed by routine paraffin embedding. Seven transverse levels of brain were examined from each rat. Cycloate-induced neuronal cell death was seen in the pyriform cortex 1 day after dosing and persisted through to Day 28, the lesion was more marked in the rostral compared to the caudal region of the pyriform cortex. Neuronal cell death was also observed in the ventro-lateral caudal dentate gyrus on Days 1-14, day after dosing. In the early stages, Days 1-3 and to a lesser extent Day 7, the neuronal cell death resembled apoptosis, characterized by condensation of nuclear material, cell shrinkage and strong cytoplasmic eosinophilia. By Days 14 and 28 and to a lesser extent Day 7, the cell death resembled necrosis, i.e. karyorrhectic nuclei with pale irregular cytoplasm. Microglial accumulation was associated with the neuronal cell injury. In control brains, an occasional apoptotic body was seen in both the pyriform cortex and dentate gyrus. Our results demonstrate that cycloate is a novel neurotoxicant, which following a single large oral dose induces a cell specific and highly localized forebrain lesion. The time course data analyzed temporally, suggests that cycloate may cause an up regulation of apoptosis in selected regions of the adult brain.

Gene expression profiles associated with survival of individual rat dentate cells after endogenous corticosteroid deprivation

Removal of circulating corticosterone by adrenalectomy (ADX) leads to apoptosis after 3 days in a small population of rat dentate granule neurons, whereas most surrounding cells remain viable. Interestingly, a specific expression profile is triggered in surviving granule cells that may enhance their survival. Hippocampal slices prepared 1, 2 or 3 days after ADX or sham operation were stained ex vivo with Hoechst 33258, which serves to identify apoptotic neurons. After electrophysiological analysis, multiple gene expression in surviving individual granule cells was assessed by linear antisense RNA amplification and hybridization to slot blots containing various neuronal cDNAs. Hierarchical clustering and principal component analysis was performed on two physiological variables and 14 mRNA ratios from ADX cells from every time point. Our results indicate that surviving 3-day ADX granule cells display lower membrane capacitance, lower relative N-methyl-d-aspartate (NMDA) R1 mRNA expression and higher relative mineralocorticoid receptor (MR), alpha1A voltage-gated Ca-channel, Bcl-2 and NMDA R2C mRNA expression. Some 1- and 2-day ADX cells cluster with these 3-day survivors; therefore, one or more components of their mRNA expression profile may represent predictive markers for apoptosis resistance. The functional relevance of two candidate genes was tested by in vivo local over-expression in the same model system; of these, Bcl-2 conferred partial protection when induced shortly before ADX. Therefore, removal of corticosteroids triggers a specific gene expression profile in surviving dentate granule cells; key components of this profile may be associated with their survival.

Altered expression of p53 mRNA in the brain and pituitary during repeated immobilization stress: negative correlation with glucocorticoid receptor mRNA levels

In our previous study, apparent reduction of glucocorticoid receptor (GR) mRNA was seen in the hippocampus and the hypothalamic paraventricular nucleus (PVN) during repeated immobilization (IMO) stress, but not following starvation. Our laboratory has also shown that the sp1 activates, whereas tumour suppressor p53 represses the promoter activity of GR gene. In an attempt to reveal the possibility that transcription factors such as sp1 and/or p53 are involved in the regulation of GR mRNA expression in the hippocampus and in the PVN in vivo, we examined the expression of GR mRNA, p53 mRNA, and sp1 mRNA in the hippocampus and in the PVN during repeated IMO and following starvation. In addition, the expression of these mRNAs was examined in the anterior pituitary, another GR-rich area. GR mRNA in all subfields of the hippocampus was robustly decreased, while GR mRNA in the anterior pituitary was increased, 24 h following 4 x IMO (2 h daily, for 4 consecutive days) and immediately after 5 x IMO. GR mRNA in the PVN was significantly decreased immediately after 5 x IMO, but not at 24 h after 4 x IMO. Conversely, p53 mRNA in the PVN and hippocampus was increased, whereas p53 mRNA in the anterior pituitary was decreased, 24 h following 4 x IMO and immediately after 5 x IMO. Sp1 mRNA was unchanged in all areas examined following repeated IMO. Following 4 days of starvation, neither GR mRNA, p53 mRNA nor sp1 mRNA showed any changes in the PVN and the hippocampus, except there was a minor decrease in GR mRNA in CA1-2. In the anterior pituitary, 4 days of starvation induced a minor, but significant increase in GR mRNA, whereas it decreased p53 mRNA. Overall, regression analyses revealed a negative correlation between GR mRNA levels and p53 mRNA levels in CA1-2 and dentate gyrus of the hippocampus and in the anterior pituitary. GR mRNA in the PVN also showed a tendency towards the negative correlation with p53 mRNA levels. The results raise the possibility that p53 negatively regulates GR mRNA expression in the PVN, the hippocampus and the anterior pituitary during repeated immobilization stress.

Chronic intermittent cold stress activates ovarian sympathetic nerves and modifies ovarian follicular development in the rat

We studied the effects of a chronic intermittent cold stress regime on sympathetic nerve activation and ovarian physiology. This paradigm (4 degrees C for 3 h/day, Monday-Friday, for 3 or 4 wk) does not affect basal plasma levels of corticosterone. After 3 wk of stress, we detected a decrease in noradrenaline (NA) in the ovary, but after 4 wk, this ovarian neurotransmitter concentration increased over that of unstressed control rats. To analyze whether this effect on NA is preceded by an activation of the neurotrophic factor system responsible for growth and survival of sympathetic neurons, we measured both nerve growth factor (NGF) (by enzyme immunoassay) and the intraovarian levels of its low affinity receptor mRNA (by reverse transcription-polymerase chain reaction). The activation of sympathetic nerves was followed by an increase in NGF concentration without affecting the ovarian levels of either NGF or the mRNA of its receptor. Interestingly, follicular development changed during the stress procedure; after 3 or 4 wk of stress, we found a decrease in preantral healthy follicles without a compensatory increase in atresia. Concomitantly with the increase in NA and NGF in the ovary, we observed that a new population of follicles with hypertrophied thecal cell layers appeared after 4 wk of stress. These results suggest that chronic stress, through an intraovarian neurotrophin-mediated sympathetic activation, produces changes in follicular development that could lead to an impairment of reproductive function.

Corticosterone differentially regulates bax, bcl-2 and bcl-x mRNA levels in the rat hippocampus

It has previously been shown that adrenalectomy (ADX) produces apoptosis in the granule cell of the dentate gyrus (DG), and that this effect is prevented by corticosterone replacement. Thus, we have investigated how this phenomenon takes place in rat hippocampus using in situ hybridization. The expression of the pro-apoptotic gene bax was measured in the pyramidal cell fields and in the DG. After 5 days of ADX, there was a significant increase in bax mRNA levels in the suprapyramidal layer of the DG, an effect prevented by corticosterone replacement. The mRNA of the anti-apoptotic bcl-2 gene was expressed in CA3 and DG. ADX increased bcl-2 mRNA levels, but only in the suprapyramidal layer of the DG, an effect that was prevented by corticosterone administration. It is concluded that the up-regulation of bax may explain the apoptosis observed in DG after ADX, while the bcl-2 induction may correspond to a compensatory mechanism protecting the cells from death.