Cardiac arrest and cardiopulmonary resuscitation dysregulates the hypothalamic-pituitary-adrenal axis

Corticotropin-Releasing Factor Aggravates Ischemic Stroke Injury by the Inflammatory Activation of Microglia

Ischemic stroke is the second leading cause of death worldwide. Therefore, exploring effective and emerging molecular targets for ischemic stroke is a primary task of basic and clinical research. The aim of the present study was to investigate the function of corticotropin-releasing factor (CRF) in ischemic stroke and its related mechanisms, to provide a reference for the treatment of ischemic stroke. CRF, antalarmin, or astressin-2B were used to activate or block the CRF1 (CRF receptor 1) or CRF2 (CRF receptor 2) in BV2 cells and adult male mice, thus constructing a distal middle cerebral artery occlusion (dMCAO) model. CRF not only accelerated microglial activity by promoting transcription and production of inflammatory factors, but also promoted the transformation of activated BV2 cells from a neuroprotective phenotype (M2) to cytotoxic phenotype (M1), and these effects were mediated by the TLR4/NF-κB signaling pathway. These effects can be blocked by antalarmin but not by astressin-2B. CRF significantly aggravated the neurological deficit, increased infarction volume, and exacerbated neuronal injuries. Additionally, CRF significantly improved the levels of TNF-α and phospho-NF-κB in the ischemia penumbra. Finally, CRF significantly increased the number of CD16/Iba-1-positive cells and decreased the number of CD206/Iba-1-positive cells in the ischemia penumbra. These results provide evidence of the proinflammatory role of CRF in an ischemic stroke model and a possible underlying mechanism, which may facilitate the elucidation of potential treatment approaches for ischemic stroke.

Global cerebral ischemia in adolescent male Long Evans rats: Effects of vanillic acid supplementation on stress response, emotionality, and visuospatial memory

The developmental period is critical in delineating plastic response to internal and external events. However, neurobehavioural effects of global cerebral ischemia (GCI) in the maturing brain remain largely unknown. This study characterised the effects of GCI experienced at puberty on adulthood (1) hippocampus CA1 neuronal damage, (2) cognitive and emotional impairments, and (3) glucocorticoid receptor (GR) expression. Effects of adolescent exposure to the phenol vanillic acid (VA) on post-ischemic outcomes were also determined. Male Long Evans rats (n = 35) were supplemented for 21 consecutive days (postnatal days 33-53) with VA (91 mg/kg) or nut paste vehicle (control) prior to a 10-min GCI or sham surgery. As adults, rats were tested in the Open Field Test (OFT), Elevated-Plus Maze (EPM), and Barnes Maze (BM). GR expression was determined in the basolateral amygdala (BLA), CA1, and paraventricular nucleus (PVN), and brain injury assessed via CA1 neuronal density. Adolescent GCI exposure induced extensive hippocampal CA1 injury, which was not prevented by VA supplementation. Behaviourally, GCI increased EPM exploration while having no impact on spatial memory. VA intake increased OFT peripheral exploration. Notably, while no delayed changes in CA1 and PVN GR immunoreactivity were noted, both treatments separately increased BLA GR expression when compared with sham-nut paste rats. Age at GCI occurrence plays a critical role on post-ischemic impairments. The observation of minimal functional impairments despite important CA1 neuronal damage supports use of compensatory mechanisms. Our findings also show daily VA supplementation during adolescence to have no protective effects on post-ischemic outcomes, contrasting adult intake.

The evaluation of pituitary damage associated with cardiac arrest: An experimental rodent model

The pituitary gland plays an important endocrinal role, however its damage after cardiac arrest (CA) has not been well elucidated. The aim of this study was to determine a pituitary gland damage induced by CA. Rats were subjected to 10-min asphyxia and cardiopulmonary resuscitation (CPR). Immunohistochemistry and ELISA assays were used to evaluate the pituitary damage and endocrine function. Samples were collected at pre-CA, and 30 and 120 min after cardio pulmonary resuscitation. Triphenyltetrazolium chloride (TTC) staining demonstrated the expansion of the pituitary damage over time. There was phenotypic validity between the pars distalis and nervosa. Both CT-proAVP (pars nervosa hormone) and GH/IGF-1 (pars distalis hormone) decreased over time, and a different expression pattern corresponding to the damaged areas was noted (CT-proAVP, 30.2 ± 6.2, 31.5 ± 5.9, and 16.3 ± 7.6 pg/mg protein, p < 0.01; GH/IGF-1, 2.63 ± 0.61, 0.62 ± 0.36, and 2.01 ± 0.41 ng/mg protein, p < 0.01 respectively). Similarly, the expression pattern between these hormones in the end-organ systems showed phenotypic validity. Plasma CT-proAVP (r = 0.771, p = 0.025) and IGF-1 (r = −0.775, p = 0.024) demonstrated a strong correlation with TTC staining area. Our data suggested that CA induces pathological and functional damage to the pituitary gland.

Social influences on microglial reactivity and neuronal damage after cardiac arrest/cardiopulmonary resuscitation

Social isolation presents a risk factor and worsens outcome to cerebrovascular diseases; however, the underlying mechanisms remain underspecified. This study examines the effect of social environment on microglial reactivity after global cerebral ischemia, to test the hypothesis that social isolation leads to greater microglial responses. Adult female and male mice were pair-housed or socially isolated for one week prior to cardiac arrest/cardiopulmonary resuscitation (CA/CPR) or the sham procedure, and following either 2 or 24 h of reperfusion, microglia samples were enriched and analyzed for gene expression. At the 2-hour time point, microglia from both females and males exhibited ischemia-induced inflammation, characterized by the gene expression increase of tumor necrosis factor alpha (TNF-α), interleukin 1 beta (IL-1β) and interleukin 6 (IL-6), regardless of the housing conditions. However, at 24 h post-ischemia, social housing attenuated microglial pro-inflammatory gene expression in a sex-specific manner. At this time point, the ischemia-induced increased expression of IL-1β and IL-6 was attenuated by social interaction in microglia from male mice, while among female mice social attenuation of the inflammatory response was observed in the microglial expression of cell surface protein major histocompatibility complex II (MHC II). A second study examined behavioral and physiological measures 96 h after ischemic injury. At this time point, female and male mice displayed increased locomotion and exploratory behavior following CA/CPR relative to controls. Regardless of sex, ischemia also elicited neuroinflammation and neurodegeneration, both of which were modulated by the social environment. Hippocampal nitric oxide (iNOS), cortical TNF-α, and counts of Fluoro-Jade C positive stained cells in the CA1 region of the hippocampus, were increased in the isolated CA/CPR group relative to sham controls and the pair-housed CA/CPR groups. Together, these data indicate that female and male mice exhibit similar outcome measures and social modulation at 96 h post-ischemic injury, nonetheless, that social environment influences microglial reactivity to global cerebral ischemia in a sex-specific manner.

CRHR1 exacerbates the glial inflammatory response and alters BDNF/TrkB/pCREB signaling in a rat model of global cerebral ischemia: implications for neuroprotection and cognitive recovery

This study examined the impact of corticotropin-releasing hormone type 1 receptor (CRHR1) blockade using Antalarmin (ANT) on the expression of markers of neuroplasticity and inflammation, as well as neuroprotection and behavioral recovery following global cerebral ischemia. Male Wistar rats (N=50) were treated with ANT (2μg/2μl; icv) or a vehicle solution prior to a sham or four vessel (4VO) occlusion. Seven days post ischemia, anxiety was assessed in the Elevated Plus Maze and Open Field tests, and fear and spatial learning in a Y-Maze Passive Avoidance Task and the Barnes Maze. Thirty days post ischemia, brain derived neurotrophic factor (BDNF) and tropomyosin receptor kinase B (TrkB) receptor expression, hippocampal neuronal death and inflammation were determined by analyzing immunoreactivity (ir) of neuron-specific nuclear protein (NeuN), microglia (IBA1, ionized calcium binding adaptor molecule 1), astrocytes (GFAP, glial fibrillary acidic protein) and TNFα (tumor necrosis factor alpha) a pro-inflammatory cytokine. Our findings revealed that ANT improved behavioral impairments, while conferring neuroprotection and blunting neuroinflammation in all hippocampal sub-regions post ischemia. We also observed reduced BDNF and TrkB mRNA and protein levels at the hippocampus, and increased expression at the hypothalamus and amygdala post ischemia, site-specific alterations which were regularized by pre-ischemic CRHR1 blockade. These findings support that CRHR1 actively contributes to altered brain plasticity, neuronal inflammation and injury and recovery of function following ischemic brain insults.

Alterations in the corticotropin-releasing hormone (CRH) neurocircuitry: Insights into post stroke functional impairments

Although it is well accepted that changes in the regulation of the hypothalamic-pituitary adrenal (HPA) axis may increase susceptibility to affective disorders in the general population, this link has been less examined in stroke patients. Yet, the bidirectional association between depression and cardiovascular disease is strong, and stress increases vulnerability to stroke. Corticotropin-releasing hormone (CRH) is the central stress hormone of the HPA axis pathway and acts by binding to CRH receptors (CRHR) 1 and 2, which are located in several stress-related brain regions. Evidence from clinical and animal studies suggests a role for CRH in the neurobiological basis of depression and ischemic brain injury. Given its importance in the regulation of the neuroendocrine, autonomic, and behavioral correlates of adaptation and maladaptation to stress, CRH is likely associated in the pathophysiology of post stroke emotional impairments. The goals of this review article are to examine the clinical and experimental data describing (1) that CRH regulates the molecular signaling brain circuit underlying anxiety- and depression-like behaviors, (2) the influence of CRH and other stress markers in the pathophysiology of post stroke emotional and cognitive impairments, and (3) context and site specific interactions of CRH and BDNF as a basis for the development of novel therapeutic targets. This review addresses how the production and release of the neuropeptide CRH within the various regions of the mesocorticolimbic system influences emotional and cognitive behaviors with a look into its role in psychiatric disorders post stroke.

Endocannabinoid CB1 receptor activation upon global ischemia adversely impact recovery of reward and stress signaling molecules, neuronal survival and behavioral impulsivity

Global cerebral ischemia in rodents, which mimics cardiac arrest in humans, is associated with a surge in endocannabinoids and increased transmission of dopamine and glutamate leading to excitotoxic cell death. The current study assessed the role of CB1 receptor activation at the moment of an ischemic insult on ensuing regulation of stress and reward signaling molecules, neuronal injury and anxiety-like behavior. Male Wistar rats were separated into 4 groups (n=10/group); sham and ischemic rats administered the CB1 endocannabinoid receptor antagonist AM251 (2mg/kg, i.p.) 30min prior to global cerebral ischemia, and vehicle-treated counterparts. The effects of CB1 receptor blockade on corticotropin-releasing hormone (CRH), vesicular glutamate transporter 2 (vGluT2), tyrosine hydroxylase (TH) and dopamine receptor 1 (DRD1) signaling expression, together with CA1 neuronal damage and anxiety-like behaviors were assessed. Our findings show attenuated CA1 injury and behavioral deficits in AM251-treated ischemic rats. AM251-pretreatment also partially or completely reversed ischemia-induced alterations in TH-ir expression at the hippocampus, ventral tegmental area (VTA), nucleus accumbens (NAc) and basolateral amygdala (BLA), normalized DRD1-ir at the medial forebrain bundle, and diminished BLA and PVN-CRH expression. All groups showed comparable vGluT2 expression at the BLA and PVN-parvocellular subdivision. These findings support a determinant role of CB1 receptor activation at time of ischemia on functional recovery. They also support "state-dependent" effects of endocannabinoids, raising considerations in the development of effective molecules to regulate HPA axis function and mood disorders following cardiac arrest and stroke.

Pharmacological stimulation of hypoxia inducible factor-1α facilitates the corticosterone response to a mild acute stressor

While both glucocorticoids (the principal output of the hypothalamic-pituitary-adrenal axis) and oxidative stress have been implicated in outcomes due to an excessive or prolonged stress response, the precise mechanisms linking these two systems remain poorly elucidated. One potential mediator between the hypothalamic-pituitary-adrenal axis and oxidative stress is the hypoxia inducible factor-1 (HIF-1) pathway. HIF-1 is an oxygen-responsive transcription factor with diverse effects including changes in cellular metabolism. The experiments in this manuscript sought to determine if pharmacological stimulation of HIF-1α via administration of dimethyloxalylglycine (DMOG) would facilitate the corticosterone response to a mild acute stressor. DMOG administration significantly increased plasma corticosterone 5 min after an acute airpuff without changing baseline plasma corticosterone or plasma corticosterone level two hours post-startle. DMOG administration also reduced hippocampal gene expression of the pro-translocation co-chaperone for the glucocorticoid receptor, FKBP4, two hours after airpuff startle. At this same two-hour time point, hippocampal expression of FKBP5, an anti-translocation co-chaperone of the glucocorticoid receptor, in the DMOG-treated group was also positively correlated with plasma corticosterone levels. These data indicate that there is significant crosstalk between the hypothalamic-pituitary-axis and the HIF-1 pathway and extend the current knowledge of glucocorticoid and hypoxia interactions in an ethologically relevant stress model.

Microemboli alter the acute stress response and cause prolonged expression of MCP-1 in the hippocampus

Microvascular ischemia is linked to cardiovascular disease pathology, as well as alterations in mood and cognition. Ischemia activates the hypothalamic-pituitary-adrenal (HPA) axis and through chronic activation, alters HPA axis function. Dysregulation of the HPA axis can lead to the chronic release of glucocorticoids, a hyper-inflammatory cerebral response, cell damage, and changes in behavior. Although the interactions between injury and HPA axis activity have been established in global ischemia, HPA-related repercussions of diffuse ischemic damage and subsequent inflammation have not been assessed. The current study used a rat model of microsphere embolism (ME) ischemia to test the hypothesis that microvascular ischemia would lead to long term alterations in HPA axis function and inflammatory activity. Furthermore, given the pro-inflammatory nature of chronic stress, we assessed the implications of chronic stress for gene expression of inflammatory factors and key components of the glucocorticoid receptor response, following microvascular ischemia. Results indicated that ME altered the response to an acute stress fourteen days following ME injury and increased hippocampal expression of monocyte chemoattractant protein 1 (Mcp-1) as long as 4 weeks following ME injury, without concomitant effects on gene expression of the glucocorticoid receptor or its co-chaperones. Furthermore, no exacerbative effects of chronic stress exposure were observed following ME injury beyond the effects of ME injury alone. Together, these results indicate that ME injury is sufficient to alter both HPA axis activity and cerebral inflammation for a prolonged period of time following injury.

Meloxicam blocks neuroinflammation, but not depressive-like behaviors, in HIV-1 transgenic female rats

Adolescents living with human immunodeficiency virus (HIV) comprise approximately 12% of the HIV-positive population worldwide. HIV-positive adolescents experience a higher rate of clinical depression, a greater risk of sexual and drug abuse behaviors, and a decreased adherence to highly active antiretroviral therapies (HAART). Using adolescent HIV-1 transgenic rats (HIV-1 tg) that display related immune response alterations and pathologies, this study tested the hypothesis that developmental expression of HIV-1-related proteins induces a depressive-like phenotype that parallels a decrease in hippocampal cell proliferation and an increase in pro-inflammatory cytokine expression in the hippocampus. Consistent with this hypothesis, adolescent HIV-1 tg rats demonstrated a depressive-like behavioral phenotype, had decreased levels of cell proliferation, and exhibited elevated expression of monocyte chemotactic protein-1 (Mcp-1) in the hippocampus relative to controls. Subsequently, we tested the ability of meloxicam, a selective COX-2 inhibitor, to attenuate behavioral deficits via inflammatory mechanisms. Daily meloxicam treatments did not alter the behavioral profile despite effectively reducing hippocampal inflammatory gene expression. Together, these data support a biological basis for the co-morbid manifestation of depression in HIV-positive patients as early as in adolescence and suggest that modifications in behavior manifest independent of inflammatory activity in the hippocampus.

Neural effects of inflammation, cardiovascular disease, and HIV: Parallel, perpendicular, or progressive?

The pervasive reach of the inflammatory system is evidenced by its involvement in numerous disease states. Cardiovascular disease, marked by high levels of circulating inflammatory mediators, affects an estimated 83.6 million Americans. Similarly, human immunodeficiency virus (HIV) produces a paradoxical state of generalized immune activity despite widespread immunosuppression, and affects 35 million people worldwide. Patients living with HIV (PLWH) suffer from inflammatory conditions, including cardiovascular disease (CVD), at a rate exceeding the general population. In this combined disease state, immune mechanisms that are common to both CVD and HIV may interact to generate a progressive condition that contributes to the exacerbated pathogenesis of the other to the net effect of damage to the brain. In this review, we will outline inflammatory cell mediators that promote cardiovascular risk factors and disease initiation and detail how HIV-related proteins may accelerate this process. Finally, we examine the extent to which these comorbid conditions act as parallel, perpendicular, or progressive sequela of events to generate a neurodegenerative environment, and consider potential strategies that can be implemented to reduce the burden of CVD and inflammation in PLWH.

Evidence of lasting dysregulation of neuroendocrine and HPA axis function following global cerebral ischemia in male rats and the effect of Antalarmin on plasma corticosterone level

Abnormal function of the neuroendocrine stress system has been implicated in the behavioral impairments observed following brain ischemia. The current study examined long-term changes in stress signal regulation 30days following global cerebral ischemia. Experiment 1 investigated changes in the expression of corticotropin releasing hormone (CRH) and its subtype 1 receptor (CRHR1), glucocorticoid receptors (GR) in the paraventricular nucleus of the hypothalamus (PVN), the central nucleus of the amygdala (CeA), and the CA1 subfield of the hippocampus. Tyrosine hydroxylase (TH) was determined at the locus coeruleus (LC). Experiment 2 investigated the role of central CRHR1 activation on corticosterone (CORT) secretion at multiple time intervals following global ischemia after exposure to an acute stressor. Findings from Experiment 1 demonstrated a persistent increase in GR, CRH and CRHR1 immunoreactivity (ir) at the PVN, reduced GR and CRHR1 expression in pyramidal CA1 neurons, and increased LC TH expression in ischemic rats displaying working memory errors in the radial arm Maze. Findings from Experiment 2 revealed increased CORT secretion up to 7 days, but no longer present 14 and 21 days post ischemia. However upon an acute restraint stress induced 27 days following reperfusion, ischemic rats had increased plasma CORT secretions compared to sham-operated animals, suggesting HPA axis hypersensitivity. Antalarmin (2 μg/2 μl) pretreatment significantly attenuated post ischemic elevation of basal and stress-induced CORT secretion. These findings support persistent neuroendocrine dysfunctions following brain ischemia likely to contribute to emotional and cognitive impairments observed in survivors of cardiac arrest and stroke.

Microembolism infarcts lead to delayed changes in affective-like behaviors followed by spatial memory impairment

Microvascular disease is defined by microvascular events including arterial wall thickening, microvascular lesions, and microembolic stroke. Characteristics of microvascular disease are observed in the vast majority of patients presenting with late-life depression, and changes in affective behavior may precede microvascular-associated changes in cognitive decline. The current study used a microsphere injection model to test the hypothesis that microembolism infarcts induce depressive-like behaviors in rodents. Further, the study sought to determine whether microembolism-induced changes in affective-like behavior preceded deficits in spatial memory. Microbeads were injected into the internal carotid artery to generate microembolic lesions and behavior was assessed at either a short recovery (SR) time point (4-6 days post-surgery) or long recovery (LR) time point (14-17 days post-surgery). A separate cohort of rats was used to assess spatial memory in the Barnes Maze at the LR time point and beyond (35 days post-surgery). Microembolism infarcts led to an increase in anxiety- and depressive-like behaviors at the LR, but not the SR, time point as evidenced by reduced time in the center of the open field, reduced consumption of a sucrose solution, increased latency to approach a novel female at 14 days and impaired spatial memory at 33 days. A thorough analysis of histological markers and lesion volume revealed that gross histological damage was not predictive of behavioral outcomes, suggesting that alterations in neuronal function may underlie behavioral deficits. Collectively, these data demonstrate that microembolism infarcts are sufficient to induce changes in affective-like behavior and these changes precede alterations in spatial memory.

Heart rate variability predicts cell death and inflammatory responses to global cerebral ischemia

This study examines the relationship between autonomic functioning and neuropathology following cardiac arrest (CA) in mice. Within 24 h of CA, parasympathetic cardiac control, as indexed by high frequency (HF) heart rate variability, rapidly decreases. By day 7 after CA, HF heart rate variability was inversely correlated with neuronal damage and microglial activation in the hippocampus. Thus, by virtue of its sensitivity to central insult, HF heart rate variability may offer an inexpensive, non-invasive method of monitoring neuropathological processes following CA. The inverse linear relationships between heart rate variability and brain damage after CA also may partially explain why low heart rate variability is associated with increased morbidity and mortality in myocardial infarction patients.

Differential effects of voluntary and forced exercise on stress responses after traumatic brain injury

Voluntary exercise increases levels of brain-derived neurotrophic factor (BDNF) after traumatic brain injury (TBI) when it occurs during a delayed time window. In contrast, acute post-TBI exercise does not increase BDNF. It is well known that increases in glucocorticoids suppress levels of BDNF. Moreover, recent work from our laboratory showed that there is a heightened stress response after fluid percussion injury (FPI). In order to determine if a heightened stress response is also observed with acute exercise, at post-injury days 0-4 and 7-11, corticosterone (CORT) and adrenocorticotropic hormone (ACTH) release were measured in rats running voluntarily or exposed to two daily 20-min periods of forced running wheel exercise. Forced, but not voluntary exercise, continuously elevated CORT. ACTH levels were initially elevated with forced exercise, but decreased by post-injury day 7 in the control, but not the FPI animals. As previously reported, voluntary exercise did not increase BDNF in the FPI group as it did in the control animals. Forced exercise did not increase levels of BDNF in any group. It did, however, decrease hippocampal glucocorticoid receptors in the control group. The results suggest that exercise regimens with strong stress responses may not be beneficial during the early post-injury period.

Effects of acute restraint-induced stress on glucocorticoid receptors and brain-derived neurotrophic factor after mild traumatic brain injury

We have previously reported that experimental mild traumatic brain injury results in increased sensitivity to stressful events during the first post-injury weeks, as determined by analyzing the hypothalamic-pituitary-adrenal (HPA) axis regulation following restraint-induced stress. This is the same time period when rehabilitative exercise has proven to be ineffective after a mild fluid-percussion injury (FPI). Here we evaluated effects of stress on neuroplasticity. Adult male rats underwent either an FPI or sham injury. Additional rats were only exposed to anesthesia. Rats were exposed to 30 min of restraint stress, followed by tail vein blood collection at post-injury days (PID) 1, 7, and 14. The response to dexamethasone (DEX) was also evaluated. Hippocampal tissue was collected 120 min after stress onset. Brain-derived neurotrophic factor (BDNF) along with glucocorticoid (GR) and mineralocorticoid (MR) receptors was determined by Western blot analysis. Results indicated injury-dependent changes in glucocorticoid and mineralocorticoid receptors that were influenced by the presence of dexamethasone. Control and FPI rats responded differentially to DEX in that GR increases after receiving the lower dose of DEX were longer lasting in the FPI group. A suppression of MR was found at PID 1 in vehicle-treated FPI and Sham groups. Decreases in the precursor form of BDNF were observed in different FPI groups at PIDs 7 and 14. These findings suggest that the increased sensitivity to stressful events during the first post-injury weeks, after a mild FPI, has an impact on hippocampal neuroplasticity.

Heightening of the stress response during the first weeks after a mild traumatic brain injury

The effects of a mild traumatic brain injury range from white matter disruption to affective disorders. We set out to determine the response to restraint-induced stress after a mild fluid-percussion injury (FPI), an experimental model for brain injury. Hypothalamic-pituitary-adrenal (HPA) axis regulation of corticosterone (CORT) and adrenocorticotropic hormone (ACTH) was determined during the first post-injury weeks, which corresponds to the same time period when rehabilitative exercise has been shown to be ineffective after a mild FPI. Adult male rats underwent either an FPI or sham injury. Additional rats were only exposed to anesthesia. HPA regulation was evaluated by measuring the effects of dexamethasone (DEX) treatment on CORT and ACTH. Tail vein blood was collected following 30-min restraint stress, at post-injury days (PID) 1, 7 and 14, prior to (0 min) and at 30, 60, 90 and 120 min after stress onset. Results from these studies indicate that the stress response was significantly more pronounced after FPI in that CORT and ACTH restraint-induced increases were more pronounced and longer lasting compared to controls. DEX suppression of CORT and ACTH was observed in all groups, suggesting that stress hyper-responsiveness after mild FPI is not attributable to reduced sensitivity of CORT feedback regulation. The increased sensitivity to stressful events in the first two post-injury weeks after a mild FPI may have a negative impact on early rehabilitative therapies.

Social interaction modulates autonomic, inflammatory, and depressive-like responses to cardiac arrest and cardiopulmonary resuscitation

Psychological factors, including depression and social isolation, are important determinants of cardiovascular health. The current study uses a well-validated mouse model of cardiac arrest/cardiopulmonary resuscitation (CA/CPR) to examine the effect of social environment on several pathophysiological and behavioral responses to cerebral ischemia. Male experimental mice were either housed in pairs with an ovariectomized female or socially isolated for the duration of the experiment. Cardiac arrest increased the mRNA expression of the proinflammatory cytokines TNF-α, IL-1β, and IL-6, as well as the microglia marker MAC-1; expression of each of these factors, except IL-6, was further increased among socially isolated mice. Furthermore, socially isolated animals exposed to the CA/CPR procedure displayed significantly higher levels of neuronal cell death and microglia staining within the hippocampus at 7 d following surgery. Social isolation also exacerbated CA/CPR-induced depressive-like behavior and cardiac autonomic dysregulation. In the absence of ischemic damage, social environment had no significant effect on the expression of neuronal cell death, autonomic cardiac control, or behavior. Together, these data suggest that social factors influence the pathophysiological trajectory following cardiac arrest.