Synergy between chronic corticosterone treatment and cerebral ischemia in producing damage in noncalbindinergic neurons

A Comparative Study of Two Models of Intraluminal Filament Middle Cerebral Artery Occlusion in Rats: Long-Lasting Accumulation of Corticosterone and Interleukins in the Hippocampus and Frontal Cortex in Koizumi Model

Recently, we have shown the differences in the early response of corticosterone and inflammatory cytokines in the hippocampus and frontal cortex (FC) of rats with middle cerebral artery occlusion (MCAO), according to the methods of Longa et al. (LM) and Koizumi et al. (KM) which were used as alternatives in preclinical studies to induce stroke in rodents. In the present study, corticosterone and proinflammatory cytokines were assessed 3 months after MCAO. The most relevant changes detected during the first days after MCAO became even more obvious after 3 months. In particular, the MCAO-KM (but not the MCAO-LM) group showed significant accumulation of corticosterone and IL1β in both the ipsilateral and contralateral hippocampus and FC. An accumulation of TNFα was detected in the ipsilateral hippocampus and FC in the MCAO-KM group. Thus, unlike the MCAO-LM, the MCAO-KM may predispose the hippocampus and FC of rats to long-lasting bilateral corticosterone-dependent distant neuroinflammatory damage. Unexpectedly, only the MCAO-LM rats demonstrated some memory deficit in a one-trial step-through passive avoidance test. The differences between the two MCAO models, particularly associated with the long-lasting increase in glucocorticoid and proinflammatory cytokine accumulation in the limbic structures in the MCAO-KM, should be considered in the planning of preclinical experiments, and the interpretation and translation of received results.

Ischemic Stroke, Glucocorticoids, and Remote Hippocampal Damage: A Translational Outlook and Implications for Modeling

Progress in treating ischemic stroke (IS) and its delayed consequences has been frustratingly slow due to the insufficient knowledge on the mechanism. One important factor, the hypothalamic-pituitary-adrenocortical (HPA) axis is mostly neglected despite the fact that both clinical data and the results from rodent models of IS show that glucocorticoids, the hormones of this stress axis, are involved in IS-induced brain dysfunction. Though increased cortisol in IS is regarded as a biomarker of higher mortality and worse recovery prognosis, the detailed mechanisms of HPA axis dysfunction involvement in delayed post-stroke cognitive and emotional disorders remain obscure. In this review, we analyze IS-induced HPA axis alterations and supposed association of corticoid-dependent distant hippocampal damage to post-stroke brain disorders. A translationally important growing point in bridging the gap between IS pathogenesis and clinic is to investigate the involvement of the HPA axis disturbances and related hippocampal dysfunction at different stages of SI. Valid models that reproduce the state of the HPA axis in clinical cases of IS are needed, and this should be considered when planning pre-clinical research. In clinical studies of IS, it is useful to reinforce diagnostic and prognostic potential of cortisol and other HPA axis hormones. Finally, it is important to reveal IS patients with permanently disturbed HPA axis. Patients-at-risk with high cortisol prone to delayed remote hippocampal damage should be monitored since hippocampal dysfunction may be the basis for development of post-stroke cognitive and emotional disturbances, as well as epilepsy.

A Comparative Study of Koizumi and Longa Methods of Intraluminal Filament Middle Cerebral Artery Occlusion in Rats: Early Corticosterone and Inflammatory Response in the Hippocampus and Frontal Cortex

Two classical surgical approaches for intraluminal filament middle cerebral artery occlusion (MCAO), the Longa et al. (LM) and Koizumi et al. methods (KM), are used as alternatives in preclinical studies to induce stroke in rodents. Comparisons of these MCAO models in mice showed critical differences between them along with similarities (Smith et al. 2015; Morris et al. 2016). In this study, a direct comparison of MCAO-KM and MCAO-LM in rats was performed. Three days after MCAO, infarct volume, mortality rate, neurological deficit, and weight loss were similar in these models. MCAO-LM rats showed an increase in ACTH levels, while MCAO-KM rats demonstrated elevated corticosterone and interleukin-1β in blood serum. Corticosterone accumulation was detected in the frontal cortex (FC) and the hippocampus of the MCAO-KM group. IL1β beta increased in the ipsilateral hippocampus in the MCAO-KM group and decreased in the contralateral FC of MCAO-LM rats. Differences revealed between MCAO-KM and MCAO-LM suggest that corticosterone and interleukin-1β release as well as hippocampal accumulation is more expressed in MCAO-KM rats, predisposing them to corticosterone-dependent distant neuroinflammatory hippocampal damage. The differences between two models, particularly, malfunction of the hypothalamic-pituitary-adrenal axis, should be considered in the interpretation, comparison, and translation of pre-clinical experimental results.

Vulnerability to stroke: implications of perinatal programming of the hypothalamic-pituitary-adrenal axis

Chronic stress is capable of exacerbating each major, modifiable, endogenous risk factor for cerebrovascular and cardiovascular disease. Indeed, exposure to stress can increase both the incidence and severity of stroke, presumably through activation of the hypothalamic-pituitary-adrenal (HPA) axis. Now that characterization of the mechanisms underlying epigenetic programming of the HPA axis is well underway, there has been renewed interest in examining the role of early environment on the evolution of health conditions across the entire lifespan. Indeed, neonatal manipulations in rodents that reduce stress responsivity, and subsequent life-time exposure to glucocorticoids, are associated with a reduction in the development of neuroendocrine, neuroanatomical, and cognitive dysfunctions that typically progress with age. Although improved day to day regulation of the HPA axis also may be accompanied by a decrease in stroke risk, evidence from rodent studies suggest that an associated cost could be increased susceptibility to inflammation and neuronal death in the event that a stroke does occur and the individual is exposed to persistently elevated corticosteroids. Given its importance in regulation of health and disease states, any long-term modulation of the HPA axis is likely to be associated with both benefits and potential risks. The goals of this review article are to examine (1) the clinical and experimental data suggesting that neonatal experiences can shape HPA axis regulation, (2) the influence of stress and the HPA axis on stroke incidence and severity, and (3) the potential for neonatal programming of the HPA axis to impact adult cerebrovascular health.

The role of parvalbumin and calbindin D28k in experimental scrapie

AIMS

Prion diseases are generally characterized by pronounced neuronal loss. In particular, a subpopulation of inhibitory neurones, characterized by the expression of the calcium-binding protein parvalbumin (PV), is selectively destroyed early in the course of human and experimental prion diseases. By contrast, nerve cells expressing calbindin D28 k (CB), another calcium-binding protein, as well as PV/CB coexpressing Purkinje cells, are well preserved.

METHODS

To evaluate, if PV and CB may directly contribute to neuronal vulnerability or resistance against nerve cell death, respectively, we inoculated PV- and CB-deficient mice, and corresponding controls, with 139A scrapie and compared them with regard to incubation times and histological lesion profiles.

RESULTS

While survival times were slightly but significantly diminished in CB-/-, but not PV-/- mice, scrapie lesion profiles did not differ between knockout mice and controls. There was a highly significant and selective loss of isolectin B(4)-decorated perineuronal nets (which specifically demarcate the extracellular matrix surrounding the 'PV-expressing' subpopulation of cortical interneurones) in scrapie inoculated PV+/+, as well as PV-/- mice. Purkinje cell numbers were not different in CB+/+ and CB-/- mice.

CONCLUSIONS

Our results suggest that PV expression is a surrogate marker for neurones highly vulnerable in prion diseases, but that the death of these neurones is unrelated to PV expression and thus based on a still unknown pathomechanism. Further studies including the inoculation of mice ectopically (over)expressing CB are necessary to determine whether the shortened survival of CB-/- mice is indeed due to a neuroprotective effect of this molecule.

2006 Curt P. Richter award winner: Social influences on stress responses and health

Both positive and negative social interactions can modulate the hypothalamic-pituitary-adrenal (HPA) axis and influence recovery from injuries and illnesses, such as wounds, stroke, and cardiac arrest. Stress exacerbates neuronal death following stroke and cardiac arrest, and delays cutaneous wound healing, via a common mechanism involving stress-induced increases in corticosterone, acting on glucocorticoid receptors. In contrast, hamsters and mice that form social bonds are buffered against stress and heal cutaneous wounds more quickly than socially isolated animals, presumably because the physical contact experienced by the pairs releases oxytocin, which in turn suppresses the HPA axis and facilitates wound healing. Social housing also decreases stroke-induced neuronal death and improves functional recovery, but the mechanism appears to involve suppressing the inflammatory response that accompanies stroke, rather than alterations in HPA axis activity. An interaction between the HPA axis and immune system determines stroke outcome in neonatally manipulated mice that exhibit life-long dampening of the HPA axis. Taken together, these studies provide support for the detrimental effects of stress and identify potential mechanisms underlying the well-documented clinical observation that social support positively influences human health.

Role of IL-1 in poststroke depressive-like behavior in mice

BACKGROUND

Poststroke depression (PSD) leads to impaired functional recovery and increased mortality, yet physiological mechanisms are unknown. The present study investigates the roles of glucocorticoids and interleukin-1 (IL-1) in poststroke anhedonia.

METHODS

Adult male mice underwent middle cerebral artery occlusion (MCAO), and were recovered 7 days. Mice were treated with metyrapone (100 mg/kg intraperitoneally), mifepristone (50 mg/kg subcutaneously), or vehicle injections on reperfusion days 4-7. A separate cohort of mice was implanted with cannulae and was administered IL-1 receptor antagonist (IL-1ra) or vehicle (6 microg intracerebroventricularly) on reperfusion days 6 and 7. After the final injection or infusion, sucrose consumption was recorded for 6 hours.

RESULTS

Mice in the sham-treated group consumed significantly more sucrose solution than water, whereas MCAO-treated mice consumed similar amounts of each, suggesting anhedonia among MCAO-treated mice. A separate experiment assessed whether stroke-induced increases in corticosteroids or IL-1 contribute to anhedonia. Only IL-1ra restored sucrose consumption in MCAO-treated mice. Vehicle-MCAO-treated mice drank significantly less sucrose solution than did both IL-1ra and vehicle-sham treatment groups, whereas IL-1ra-MCAO-treated mice drank similar amounts to both sham-treated groups.

CONCLUSIONS

Poststroke anhedonia, a symptom of depression in human beings, can be reproduced in a mouse model of stroke and appears to involve altered IL-1 transmission in the brain.

Microglial activation and neuronal apoptosis in Bornavirus infected neonatal Lewis rats

Lewis rats neonatally infected with Borna disease virus have a behavioral syndrome characterized by hyperactivity, movement disorders, and abnormal social interactions. Virus is widely distributed in brain; however, neuropathology is focused in dentate gyrus, cerebellum, and neocortex where granule cells, Purkinje cells and pyramidal cells are lost through apoptosis. Although a transient immune response is present, its distribution does not correlate with sites of damage. Neuropathology is instead colocalized with microglial proliferation and expression of MHC class I and class II, ICAM, CD4 and CD8 molecules. Targeted pathogenesis in this system appears to be linked to microglial activation and susceptibility of specific neuronal populations to apoptosis rather than viral tropism or virus-specific immune responses.

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.

Redistribution of glucose-6-phosphate dehydrogenase in response to cerebral ischemia in rat brain

Glucose-6-phosphate dehydrogenase (G6PD), a cytoplasmic enzyme, plays a protective role during oxidative stress in eucaryotic cells, since they provide coenzymes and substrates to the primary antioxidant enzymes. The redistribution of G6PD in the hippocampus was studied post-ischemia (PI). There was a characteristic localisation of G6PD in pyramidal cell layers of the rat hippocampus. In hippocampus CA1 cells were stained weakly whereas CA3 cells showed strong histochemical staining. Ischemia induced up-regulation of G6PD in the hippocampus was in a specific manner. First, the activity increased in the whole hippocampus (at 4 hours PI) which persisted 6 hrs PI in CA1 area. However G6PD activity decreased in the CA3 area & dentate gyrus. At 10 & 24 hrs PI, activity decreased in CA1 area but normalised in CA3 area & dentate gyrus compared to controls. This suggests that the sensitive CA1 neurons are transiently capable of generating an anti-oxidative arsenal to cope with the oxidative stress in the first few hours PI. We can conclude that the brain contains inducible endogenous mechanisms that are capable of enhancing the ability of neurons to withstand lethal ischemic challenge.

Acute hypoxia-induced alterations of calbindin-D28k immunoreactivity in cerebellar Purkinje cells of the guinea pig fetus at term

Purkinje cells (PCs) are vulnerable to hypoxic/ischemic insults and rich in calcium and calcium-buffering/sequestering systems, including calcium-binding proteins (CaBPs). Calbindin-D28k is an EF-hand CaBP, which is highly expressed in PCs where it acts primarily as a cellular Ca++ buffer. Elevation of [Ca++] in the cytosol and nuclei of PCs is pivotal in hypoxic/ischemic cell death. We hypothesize that hypoxia results in decreased concentration, or availability of calbindin-D28k in PCs, thereby decreasing their buffering capacity and resulting in increase of intracellular and intranuclear [Ca++]. Cerebellar tissues from normoxic fetuses were compared to fetuses obtained from term pregnant guinea pigs exposed to hypoxia [7% FiO2] for 60 min. The pregnant guinea pigs were either killed upon delivery immediately following hypoxia (Hx0h) or were subsequently allowed to recover for 24 h (Hx24h) or 72 h (Hx72h). Fetal brain hypoxia was documented biochemically by a decrease in brain tissue levels of ATP and phosphocreatine. Compared to normoxic fetuses, there is a predominantly somatodendritic loss or decrease of calbindin-D28k immunohistochemical staining in PCs of Hx0h (p < 0.005), Hx24h (p < 0.05), and Hx72h (p < 0.005) fetuses. Hypoxia-induced alterations of calbindin-D28k immunoreactivity are qualitatively similar at all time points and include a distinctive intranuclear localization in subpopulations of PCs. A similar trend is demonstrated by immunoblotting. Subpopulations of TUNEL+/calbindin-D28k- PCs lacking morphologic features of apoptosis or necrosis are demonstrated in Hx24h and Hx72h fetuses. The present study demonstrates an abrogating effect of perinatal hypoxia on calbindin-D28k immunoreactivity in cerebellar PCs. The perturbation of this Ca++ buffer protein in hypoxia-induced neuronal injury may herald delayed cell death or degeneration.

Glucocorticoids, stress, and their adverse neurological effects: relevance to aging

Glucocorticoids, the adrenal steroids secreted during stress, while critical for successful adaptation to acute physical stressors, can have a variety of deleterious effects if secreted in excess. It has come to be recognized that glucocorticoid excess can have adverse effects in the nervous system, particularly the hippocampus. These effects include disruption of synaptic plasticity, atrophy of dendritic processes, compromising the ability of neurons to survive a variety of coincident insults and, at an extreme, overt neuron death. This review considers the current cellular and molecular bases underlying these adverse glucocorticoid actions, and their relevance to brain aging.