Long-term depression in Purkinje neurons is persistently impaired following cardiac arrest and cardiopulmonary resuscitation in mice

The role of serum/glucocorticoid-regulated kinase 1 in brain function following cerebral ischemia

Cardiopulmonary arrest (CA) is a major cause of death/disability in the U.S. with poor prognosis and survival rates. Current therapeutic challenges are physiologically complex because they involve hypoperfusion (decreased cerebral blood flow), neuroinflammation, and mitochondrial dysfunction. We previously discovered novel serum/glucocorticoid-regulated kinase 1 (SGK1) is highly expressed in brain of neurons that are susceptible to ischemia (hippocampus and cortex). We inhibited SGK1 and utilized pharmacological (specific inhibitor, GSK650394) and neuron-specific genetic approaches (shRNA) in rodent models of CA to determine if SGK1 is responsible for hypoperfusion, neuroinflammation, mitochondrial dysfunctional, and neurological deficits after CA. Inhibition of SGK1 alleviated cortical hypoperfusion and neuroinflammation (via Iba1, GFAP, and cytokine array). Treatment with GSK650394 enhanced mitochondrial function (via Seahorse respirometry) in the hippocampus 3 and 7 days after CA. Neuronal injury (via MAP2, dMBP, and Golgi staining) in the hippocampus and cortex was observed 7 days after CA but ameliorated with SGK1-shRNA. Moreover, SGK1 mediated neuronal injury by regulating the Ndrg1-SOX10 axis. Finally, animals subjected to CA exhibited learning/memory, motor, and anxiety deficits after CA, whereas SGK1 inhibition via SGK1-shRNA improved neurocognitive function. The present study suggests the fundamental roles of SGK1 in brain circulation and neuronal survival/death in cerebral ischemia-related diseases.

Cutaneous burn injury induces neuroinflammation and reactive astrocyte activation in the hippocampus of aged mice

BACKGROUND

By 2050, one in six people globally will be 65 or older. Confusion and delirium are significant complications after burn injury, especially in the elderly population. The etiology is still unknown, however complications may be driven by pro-inflammatory activation of astrocytes within the hippocampus (HPC) after burn injury. Reduced levels of phosphorylated cyclic-AMP response binding element (pCREB), caused by elevated systemic pro-inflammatory cytokines, could lead to cognitive decline and memory impairment.

METHODS

To examine the effects of remote injury on neuroinflammation in advanced age, young and aged mice were subjected to a 15 % total body surface area scald burn or sham injury, and euthanized after 24 h. Expression of ccl2 and tnfa were measured by qPCR in the whole brain and HPC. Astrocyte activation was measured by immunofluorescence within the HPC. pCREB was measured by immunohistochemistry in the dentate gyrus.

RESULTS

We saw an 80-fold increase in ccl2 and a 30-fold elevation in tnfa after injury in the whole brain of aged mice compared to young groups and aged sham mice (p < 0.05 and p < 0.05, respectively). Additionally, there was a 30-fold increase in ccl2 within isolated HPC of aged injured mice when compared to sham injured animals (p < 0.05). When investigating specific HPC regions, immunofluorescence staining showed a >20 % rise in glial fibrillary acidic protein (GFAP) positive astrocytes within the cornu ammonis 3 (CA3) of aged injured mice when compared to all other groups (p < 0.05). Lastly, we observed a >20 % decrease in pCREB staining by immunohistochemistry in the dentate gyrus of aged mice compared to young regardless of injury (p < 0.05).

CONCLUSIONS

These novel data suggest that remote injury in aged, but not young, mice is associated with neuroinflammation and astrocyte activation within the HPC. These factors, paired with an age related reduction in pCREB, could help explain the increased cognitive decline seen in burn patients of advanced age. To our knowledge, we are the first group to examine the impact of advanced age combined with burn injury on inflammation and astrocyte activation within the brain.

Repetitive anodal transcranial direct current stimulation improves neurological recovery by preserving the neuroplasticity in an asphyxial rat model of cardiac arrest

BACKGROUND

Non-shockable rhythms present an increasing proportion of out-of-hospital cardiac arrest (CA) patients, but are associated with poor prognosis and received limited therapeutic effect of targeted temperature management (TTM). Previous study showed repetitive anodal transcranial direct current stimulation (tDCS) improved neurological outcomes in animals with ventricular fibrillation. Here, we examine the effectiveness of tDCS on neurological recovery and the potential mechanisms in a rat model of asphyxial CA.

METHOD

Cardiopulmonary resuscitation was initiated after 5 min of untreated asphyxial CA. Animals were randomized to three experimental groups immediately after successful resuscitation (n = 12/group, 6 males): no-treatment control (NTC) group, TTM group, and tDCS group. Post resuscitation hemodynamics, quantitative electroencephalogram (EEG), neurological deficit score, and 96-h survival were evaluated. Brain tissues of additional animals undergoing same experimental procedure was harvested for enzyme-linked immunoassay-based quantification assays of neuroplasticity-related biomarkers and compared with the sham-operated rats (n = 6/group).

RESULTS

We observed that after resuscitation tDCS-treated animals exhibited significantly higher mean arterial pressure and left ventricular ejection fraction than NTC group and showed greatly improved EEG characteristics including weighted-permutation entropy and gamma band power, and neurologic deficit scores and 96-h survival rates compared to NTC and TTM groups. Furthermore, neuroplastic biomarkers including microtubule-associated protein 2, growth-associated protein 43, postsynaptic density protein 95 and synaptophysin, were significantly higher in tDCS group when compared with NTC and TTM groups.

CONCLUSION

In this rat model of asphyxial CA, repetitive anodal tDCS commenced after resuscitation improved neurological recovery, and it may exert a neuroprotective effect by preserving the neuroplasticity.

Oximetry-Guided normoxic resuscitation following canine cardiac arrest reduces cerebellar Purkinje neuronal damage

BACKGROUND

Animal studies indicate that maintaining physiologic O₂ levels (normoxia) immediately after restoration of spontaneous circulation (ROSC) from cardiac arrest (CA) results in less hippocampal neuronal death compared to animals ventilated with 100% O₂. This study tested the hypothesis that beneficial effects of avoiding hyperoxia following CA are apparent in the cerebellum and therefore not limited to one brain region.

METHODS

Adult beagles were anesthetized and mechanically ventilated. Ventricular fibrillation CA was induced by electrical myocardial stimulation and cessation of ventilation. Ten min later, dogs were ventilated with 100% O₂ and resuscitated using 3 min of open chest CPR followed by defibrillation. Dogs were ventilated for 1 h with either 100% O₂ or with O₂ titrated rapidly to maintain hemoglobin O₂ saturation at 94-96%. FiO₂ was adjusted in both groups between one and 24 h post-arrest to maintain normoxic PaO₂ of 80-120 mm Hg. Following 24 h critical care, dogs were euthanized and cerebellum analyzed for histochemical measures of neuronal damage and inflammation.

RESULTS AND CONCLUSIONS

Hyperoxic resuscitation increased the number of injured Purkinje cells by 278% and the number of activated microglia/macrophages by 18% compared to normoxic resuscitation. These results indicate that normoxic resuscitation promotes favorable histopathologic outcomes in the cerebellum (in addition to hippocampus) following CA/ROSC. These findings emphasize the importance of avoiding unnecessary hyperoxia following CA/ROSC.

Effect of mild hypothermia on cerebral microcirculation in a murine cardiopulmonary resuscitation model

BACKGROUND

We hypothesized that mild hypothermia may improve brain microcirculation by reducing cerebral microvascular endothelial cells apoptosis, and this effect may be maximized by moving up the initiation of mild hypothermia from after return of spontaneous circulation (ROSC) to the start of cardiopulmonary resuscitation (CPR).

METHODS

A total of 35 rats were randomized into the intra-arrest hypothermia group (IAH), post-resuscitation hypothermia group (PRH), normothermia group (NT), or the sham control group. A craniotomy exposed the parietal cortex for visualization of microcirculation. Ventricular fibrillation was electrically induced and untreated for 8 minutes, followed by 8 minutes of precordial compression and mechanical ventilation. Hypothermia (33 ± 0.5°C) in the IAH and PRH group was induced and maintained for 6 hours at the beginning of CPR or after ROSC, respectively. At baseline, 1, 3, and 6 hours, hemodynamic parameters were measured and the pial microcirculations were visualized with a sidestream dark field imaging video microscope. Microvascular flow index and perfused microvessel density (PMD) were calculated. Rats were euthanized, and brain tissues were removed at 3 and 6 hours separately. Expression of Bax, Bcl-2, and Caspase 3 in brain microvascular endothelial cells was examined by Western blot.

RESULTS

Microvascular flow index and PMD were significantly reduced after cardiac arrest and resuscitation (all P < 0.05), and the former was largely preserved by hypothermia regardless when the hypothermia treatment was induced (P < 0.05). Bax and Caspase 3 increased and Bcl-2 decreased significantly after resuscitation, and hypothermia treatment reversed the trend partly (all P < 0.05). A moderate correlation was observed between MFI and those proteins (Bcl-2/BAX: 3 hours: r = 0.730, P = 0.002; 6 hours: r = 0.743, P = 0.002).

CONCLUSION

Mild hypothermia improves cerebral microcirculatory blood supply, partly by inhibiting endothelial cell apoptosis. Mild hypothermia induced simultaneously with CPR has shown no additional benefit in microcirculation or endothelial cell apoptosis.

Cofilin-actin rod formation in neuronal processes after brain ischemia

Functional impairment after brain ischemia results in part from loss of neuronal spines and dendrites, independent of neuronal death. Cofilin-actin rods are covalently linked aggregates of cofilin-1 and actin that form in neuronal processes (neurites) under conditions of ATP depletion and oxidative stress, and which cause neurite degeneration if not disassembled. ATP depletion and oxidative stress occur with differing severity, duration, and time course in different ischemic conditions. Here we evaluated four mouse models of brain ischemia to define the conditions that drive formation of cofilin-actin rods. Three of the models provide early reperfusion: transient middle cerebral artery occlusion (MCAo), transient bilateral common carotid artery occlusion (CCAo), and cardiac arrest / cardiopulmonary resuscitation (CA/CPR). Early reperfusion restores ATP generating capacity, but also induces oxidative stress. The fourth model, photothrombotic cortical infarction, does not provide reperfusion. Cofilin-actin rods were formed in each of these models, but with differing patterns. Where acute reperfusion occurred, rod formation was maximal within 4 hours after reperfusion. Where infarction occurred, rods continued to form for at least 24 hours after ischemic onset, and extended into the adjacent non-ischemic tissue. Interventions that limit cofilin-actin rod formation may help to preserve integrity of neuronal processes in permanent ischemia.

Cardiac Arrest Induces Ischemic Long-Term Potentiation of Hippocampal CA1 Neurons That Occludes Physiological Long-Term Potentiation

Ischemic long-term potentiation (iLTP) is a form of synaptic plasticity that occurs in acute brain slices following oxygen-glucose deprivation. In vitro, iLTP can occlude physiological LTP (pLTP) through saturation of plasticity mechanisms. We used our murine cardiac arrest and cardiopulmonary resuscitation (CA/CPR) model to produce global brain ischemia and assess whether iLTP is induced in vivo, contributing to the functionally relevant impairment of pLTP. Adult male mice were subjected to CA/CPR, and slice electrophysiology was performed in the hippocampal CA1 region 7 or 30 days later. We observed increased miniature excitatory postsynaptic current amplitudes, suggesting a potentiation of postsynaptic AMPA receptor function after CA/CPR. We also observed increased phosphorylated GluR1 in the postsynaptic density of hippocampi after CA/CPR. These data support the in vivo induction of ischemia-induced plasticity. Application of a low-frequency stimulus (LFS) to CA1 inputs reduced excitatory postsynaptic potentials in slices from mice subjected to CA/CPR, while having no effects in sham controls. These results are consistent with a reversal, or depotentiation, of iLTP. Further, depotentiation with LFS partially restored induction of pLTP with theta burst stimulation. These data provide evidence for iLTP following in vivo ischemia, which occludes pLTP and likely contributes to network disruptions that underlie memory impairments.