Ischemic neurons in rat brains after 6, 8, or 10 minutes of transient hypoxic ischemia

Rat model of asphyxia-induced cardiac arrest and resuscitation

Neurologic injury after cardiopulmonary resuscitation is the main cause of the low survival rate and poor quality of life among patients who have experienced cardiac arrest. In the United States, as the American Heart Association reported, emergency medical services respond to more than 347,000 adults and more than 7,000 children with out-of-hospital cardiac arrest each year. In-hospital cardiac arrest is estimated to occur in 9.7 per 1,000 adult cardiac arrests and 2.7 pediatric events per 1,000 hospitalizations. Yet the pathophysiological mechanisms of this injury remain unclear. Experimental animal models are valuable for exploring the etiologies and mechanisms of diseases and their interventions. In this review, we summarize how to establish a standardized rat model of asphyxia-induced cardiac arrest. There are four key focal areas: (1) selection of animal species; (2) factors to consider during modeling; (3) intervention management after return of spontaneous circulation; and (4) evaluation of neurologic function. The aim was to simplify a complex animal model, toward clarifying cardiac arrest pathophysiological processes. It also aimed to help standardize model establishment, toward facilitating experiment homogenization, convenient interexperimental comparisons, and translation of experimental results to clinical application.

Neurodegeneration, Myelin Loss and Glial Response in the Three-Vessel Global Ischemia Model in Rat

(1) Background: Although myelin disruption is an integral part of ischemic brain injury, it is rarely the subject of research, particularly in animal models. This study assessed for the first time, myelin and oligodendrocyte loss in a three-vessel model of global cerebral ischemia (GCI), which causes hippocampal damage. In addition, we investigated the relationships between demyelination and changes in microglia and astrocytes, as well as oligodendrogenesis in the hippocampus; (2) Methods: Adult male Wistar rats (n = 15) underwent complete interruption of cerebral blood flow for 7 min by ligation of the major arteries supplying the brain or sham-operation. At 10 and 30 days after the surgery, brain slices were stained for neurodegeneration with Fluoro-Jade C and immunohistochemically to assess myelin content (MBP+ percentage of total area), oligodendrocyte (CNP+ cells) and neuronal (NeuN+ cells) loss, neuroinflammation (Iba1+ cells), astrogliosis (GFAP+ cells) and oligodendrogenesis (NG2+ cells); (3) Results: 10 days after GCI significant myelin and oligodendrocyte loss was found only in the stratum oriens and stratum pyramidale. By the 30th day, demyelination in these hippocampal layers intensified and affected the substratum radiatum. In addition to myelin damage, activation and an increase in the number of microglia and astrocytes in the corresponding layers, a loss of the CA1 pyramidal neurons, and neurodegeneration in the neocortex and thalamus was observed. At a 10-day time point, we observed rod-shaped microglia in the substratum radiatum. Parallel with ongoing myelin loss on the 30th day after ischemia, we found significant oligodendrogenesis in demyelinated hippocampal layers; (4) Conclusions: Our study showed that GCI-simulating cardiac arrest in humans—causes not only the loss of pyramidal neurons in the CA1 field, but also the myelin loss of adjacent layers of the hippocampus.

Histopathological evaluation of the role of negative electrical charge on renal ischemia/reperfusion injuries on brain and heart tissues in rat

This study was performed to evaluate the role of electroacupuncture on kidney 1 (Ki1) acupoint to prevent the heart and brain injury following ischemia/reperfusion of both kidneys. 24 Sprague Dawley rats were randomly assigned into four equal groups. In the treatment 1 group, following anesthesia, acupuncture needles were inserted on Ki1 on the palm of both hindlimbs and connected to electroacupuncture unit for a 3.00 Hz direct current, 1 hr before surgery until the end of surgery. In treatment two groups, the electroacupuncture was also performed 48 and 24 hr before the operation, with the same protocol as treatment 1. Control 1 and control 2 groups had the same procedures like the treatment ones, except for acupuncture. Immediately after reperfusion, the samples of brains and hearts were taken and prepared for microscopic examination. Histopathological study of the heart in the control and treatment groups showed the breakage of myofibrils, hyaline necrosis, edema and disorganization of myocytes. The severity of cardiac lesions was decreased in both treatment groups in comparison with the controls. Brain in control and treatment groups showed ischemic necrosis, disorganization of the neurons in the hippocampus, and edema. The severity of lesions was reduced in the treatment groups and showed a significant difference between the control and treatment 1. It could be concluded that electroacupuncture on the Ki1 point could reduce the severity of damages induced by renal ischemia/reperfusion in the remote organs of the heart and brain.

Neuroprotective effects of the new Na channel blocker rs100642 in global ischemic brain injury

INTRODUCTION

RS100642, a mexiletine analogue, is a novel sodium channel blocker with neuroprotective and antioxidant activities. The protectivity of RS100642, which has been shown against focal cerebral ischemia, was investigated in global cerebral ischemia in this study.

MATERIAL AND METHODS

Global cerebral ischemia was induced for five minutes in adult male Wistar Albino rats via the 4-vessel occlusion method. Intravenous administration of 1 mg/kg RS100642 following reperfusion for 30 min (RS100642 group) was compared with a sham treatment group (ischemia group) and nonischemized group (control) histologically based on morphology and caspase-3 immunohistochemistry, and biochemically based both on measurement of oxidative stress including malondialdehyde (MDA) levels, superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT) activities and on assessment of apoptosis including caspase-3 and -8 activities and tumor necrosis factor α (TNF-α) levels at the end of 6 h.

RESULTS

While the RS100642 group had significantly lower MDA levels and higher SOD activities than the sham treatment group (p < 0.05), GPx and CAT activities of the RS100642 and sham treatment groups were similar (p > 0.05) and significantly lower than those of the controls (p < 0.05). Necrosis and caspase-3 activity and immunoreactivity in the RS100642 group were significantly lower than those in the sham treatment group (p < 0.05), while there was no significant difference between groups regarding caspase-8 and TNF-α (p > 0.05).

CONCLUSIONS

Na⁺ channel blockade by RS100642 has remarkable neuroprotective effects following global brain ischemia/reperfusion damage. Further research is required to determine the optimum dose and time of administration.

Long-Term Deficits in Cortical Circuit Function after Asphyxial Cardiac Arrest and Resuscitation in Developing Rats

Cardiac arrest is a common cause of global hypoxic-ischemic brain injury. Poor neurologic outcome among cardiac arrest survivors results not only from direct cellular injury but also from subsequent long-term dysfunction of neuronal circuits. Here, we investigated the long-term impact of cardiac arrest during development on the function of cortical layer IV (L4) barrel circuits in the rat primary somatosensory cortex. We used multielectrode single-neuron recordings to examine responses of presumed excitatory L4 barrel neurons to controlled whisker stimuli in adult (8 ± 2-mo-old) rats that had undergone 9 min of asphyxial cardiac arrest and resuscitation during the third postnatal week. Results indicate that responses to deflections of the topographically appropriate principal whisker (PW) are smaller in magnitude in cardiac arrest survivors than in control rats. Responses to adjacent whisker (AW) deflections are similar in magnitude between the two groups. Because of a disproportionate decrease in PW-evoked responses, receptive fields of L4 barrel neurons are less spatially focused in cardiac arrest survivors than in control rats. In addition, spiking activity among L4 barrel neurons is more correlated in cardiac arrest survivors than in controls. Computational modeling demonstrates that experimentally observed disruptions in barrel circuit function after cardiac arrest can emerge from a balanced increase in background excitatory and inhibitory conductances in L4 neurons. Experimental and modeling data together suggest that after a hypoxic-ischemic insult, cortical sensory circuits are less responsive and less spatially tuned. Modulation of these deficits may represent a therapeutic approach to improving neurologic outcome after cardiac arrest.

Enduring disturbances in regional cerebral blood flow and brain oxygenation at 24 h after asphyxial cardiac arrest in developing rats

BACKGROUND

Disturbances in cerebral blood flow (CBF) and brain oxygenation (PbO2) are present early after pediatric cardiac arrest (CA). CBF-targeted therapies improved neurological outcome in our CA model. To assess the therapeutic window for CBF- and PbO2-targeted therapies, we propose to determine if CBF and PbO2 disturbances persist at 24 h after experimental pediatric CA.

METHODS

Regional CBF and PbO2 were measured at 24 h after asphyxial CA in immature rats (n = 26, 6-8/group) using arterial spin label MRI and tissue electrodes, respectively.

RESULTS

In all regions but the thalamus, CBF recovered to sham values by 24 h; thalamic CBF was >32% higher after CA vs. sham. PbO2 values at 24 h after CA in the cortex and thalamus were similar to shams in rats who received supplemental oxygen, however, on room air, cortical PbO2 was lower after CA vs. shams.

CONCLUSION

CBF remains increased in the thalamus at 24 h after CA and PbO2 is decreased to hypoxic levels in cortex at 24 h after CA in rats who do not receive supplemental oxygen. Given the enduring disturbances in this model and the lack of routine CBF or PbO2 monitoring in patients, our data suggest the need for clinical correlation.

Cardiac Arrest-Induced Global Brain Hypoxia-Ischemia during Development Affects Spontaneous Activity Organization in Rat Sensory and Motor Thalamocortical Circuits during Adulthood

Normal maturation of sensory information processing in the cortex requires patterned synaptic activity during developmentally regulated critical periods. During early development, spontaneous synaptic activity establishes required patterns of synaptic input, and during later development it influences patterns of sensory experience-dependent neuronal firing. Thalamocortical neurons occupy a critical position in regulating the flow of patterned sensory information from the periphery to the cortex. Abnormal thalamocortical inputs may permanently affect the organization and function of cortical neuronal circuits, especially if they occur during a critical developmental window. We examined the effect of cardiac arrest (CA)-associated global brain hypoxia-ischemia in developing rats on spontaneous and evoked firing of somatosensory thalamocortical neurons and on large-scale correlations in the motor thalamocortical circuit. The mean spontaneous and sensory-evoked firing rate activity and variability were higher in CA injured rats. Furthermore, spontaneous and sensory-evoked activity and variability were correlated in uninjured rats, but not correlated in neurons from CA rats. Abnormal activity patterns of ventroposterior medial nucleus (VPm) neurons persisted into adulthood. Additionally, we found that neurons in the entopeduncular nucleus (EPN) in the basal ganglia had lower firing rates yet had higher variability and higher levels of burst firing after injury. Correlated levels of power in local field potentials (LFPs) between the EPN and the motor cortex (MCx) were also disrupted by injury. Our findings indicate that hypoxic-ischemic injury during development leads to abnormal spontaneous and sensory stimulus-evoked input patterns from thalamus to cortex. Abnormal thalamic inputs likely permanently and detrimentally affect the organization of cortical circuitry and processing of sensory information. Hypoxic-ischemic injury also leads to abnormal single neuron and population level activity in the basal ganglia that may contribute to motor dysfunction after injury. Combination of deficits in sensory and motor thalamocortical circuit function may negatively impact sensorimotor integration in CA survivors. Modulation of abnormal activity patterns post-injury may represent a novel therapeutic target to improve neurologic function in survivors.

Microdialysis Assessment of Cerebral Perfusion during Cardiac Arrest, Extracorporeal Life Support and Cardiopulmonary Resuscitation in Rats - A Pilot Trial

Cerebral metabolic alterations during cardiac arrest, cardiopulmonary resuscitation (CPR) and extracorporeal cardiopulmonary life support (ECLS) are poorly explored. Markers are needed for a more personalized resuscitation and post-resuscitation care. Aim of this study was to investigate early metabolic changes in the hippocampal CA1 region during ventricular fibrillation cardiac arrest (VF-CA) and ECLS versus conventional CPR. Male Sprague-Dawley rats (350g) underwent 8min untreated VF-CA followed by ECLS (n = 8; bloodflow 100ml/kg), mechanical CPR (n = 18; 200/min) until return of spontaneous circulation (ROSC). Shams (n = 2) were included. Glucose, glutamate and lactate/pyruvate ratio were compared between treatment groups and animals with and without ROSC. Ten animals (39%) achieved ROSC (ECLS 5/8 vs. CPR 5/18; OR 4,3;CI:0.7-25;p = 0.189). During VF-CA central nervous glucose decreased (0.32±0.1mmol/l to 0.04±0.01mmol/l; p<0.001) and showed a significant rise (0.53±0.1;p<0.001) after resuscitation. Lactate/pyruvate (L/P) ratio showed a 5fold increase (31 to 164; p<0.001; maximum 8min post ROSC). Glutamate showed a 3.5-fold increase to (2.06±1.5 to 7.12±5.1μmol/L; p<0.001) after CA. All parameters normalized after ROSC with no significant differences between ECLS and CPR. Metabolic changes during ischemia and resuscitation can be displayed by cerebral microdialysis in our VF-CA CPR and ECLS rat model. We found similar microdialysate concentrations and patterns of normalization in both resuscitation methods used. Institutional Protocol Number: GZ0064.11/3b/2011.

Comparison of different quantification methods to determine hippocampal damage after cerebral ischemia

BACKGROUND

Experimental stroke studies use multiple techniques to evaluate histopathological damage. Unfortunately, sensitivity and reproducibility of these techniques are poorly characterized despite pivotal influence on results.

METHOD

The present study compared several quantification methods to differentiate between two severities of global cerebral ischemia and reperfusion. Male Sprague-Dawley rats were randomized to moderate (10min) or severe (14min) ischemia by bilateral carotid occlusion (BCAO) with hemorrhagic hypotension. Neuronal cell count was determined in hippocampus at bregma -3.14mm and -3.8mm on day 3 and 28 post insult by counting neurons in the whole CA1 or in one to three defined regions of interest (ROI) placed in NeuN and Fluoro-Jade B stained sections.

RESULTS

In healthy rats hippocampal neurons were arranged uniformly, while distribution became inhomogeneous after ischemia. The number of NeuN and Fluoro-Jade B positive cells was dependent on localization. Differences between ischemia severities became more prominent at 28 days compared to 3 days. Fluoro-Jade B positive cell count increased at 28 days, staining rather injured not dying neurons.

COMPARISON WITH EXISTING METHODS

Placement of counting windows has a major influence on extent of differences between degree of neuronal injury and variations within groups.

CONCLUSIONS

The investigated quantification methods result in inconsistent information on the degree of damage. To obtain consistent and reliable results observation period should be extended beyond 3 days. Due to inhomogeneous distribution of viable neurons in CA1 after ischemia neuronal counting should not be performed in a single ROI window, but should be performed in multiple ROIs or the whole CA1 band.

Thalamocortical dysfunction and thalamic injury after asphyxial cardiac arrest in developing rats

Global hypoxia-ischemia interrupts oxygen delivery and blood flow to the entire brain. Previous studies of global brain hypoxia-ischemia have primarily focused on injury to the cerebral cortex and to the hippocampus. Susceptible neuronal populations also include inhibitory neurons in the thalamic reticular nucleus. We therefore investigated the impact of global brain hypoxia-ischemia on the thalamic circuit function in the somatosensory system of young rats. We used single neuron recordings and controlled whisker deflections to examine responses of thalamocortical neurons to sensory stimulation in rat survivors of 9 min of asphyxial cardiac arrest incurred on postnatal day 17. We found that 48-72 h after cardiac arrest, thalamocortical neurons demonstrate significantly elevated firing rates both during spontaneous activity and in response to whisker deflections. The elevated evoked firing rates persist for at least 6-8 weeks after injury. Despite the overall increase in firing, by 6 weeks, thalamocortical neurons display degraded receptive fields, with decreased responses to adjacent whiskers. Nine minutes of asphyxial cardiac arrest was associated with extensive degeneration of neurites in the somatosensory nucleus as well as activation of microglia in the reticular nucleus. Global brain hypoxia-ischemia during cardiac arrest has a long-term impact on processing and transfer of sensory information by thalamic circuitry. Thalamic circuitry and normalization of its function may represent a distinct therapeutic target after cardiac arrest.

Long-term neuropsychological, neuroanatomical, and life outcome in hippocampal amnesia

Focal bilateral hippocampal damage typically causes severe and selective amnesia for new declarative information (facts and events), a cognitive deficit that greatly impacts the ability to live a normal, fully independent life. We describe the case of 1846, a 48-year-old woman with profound hippocampal amnesia following status epilepticus and an associated anoxic episode at age 30. Patient 1846 has undergone extensive neuropsychological testing on many occasions over the 18 years since her injury, and we present data indicating that her memory impairment has remained severe and stable during that time. New, high-resolution, structural MRI studies of 1846's brain reveal substantial bilateral hippocampal atrophy resembling that of other well-known amnesic patients. In spite of severe amnesia 1846 lives a full and mostly independent adult life, facilitated by an extensive social support network of family and friends. Her case provides an example of a rare and unlikely positive outcome in the face of severe memory problems.

Triggered by asphyxia neurogenesis seems not to be an endogenous repair mechanism, gliogenesis more like it

We analyzed the long-term consequences of asphyxial cardiac arrest for hippocampal cell proliferation in rats to evaluate if the ischaemia-induced degenerated CA1 region may be repopulated by endogenous (stem) cells. Studies were performed in an asphyxial cardiac arrest model with 5 minutes of asphyxiation and three different survival times: 7, 21, and 90 days. Sham-operated non-asphyxiated rats served as control. Cell proliferation was studied by labeling dividing cells with 5-bromo-2'-deoxy-uridine (BrdU). The neurodegenerative/regenerative pattern at single cell levels was monitored by immunohistochemistry. Alterations of gene expression were analyzed by real-time quantitative RT-PCR. Analysis of BrdU-incorporation demonstrated an increase at 7, 21 as well as 90 days after global ischaemia in the hippocampal CA1 pyramidal cell layer. Similar results were found in the dentate gyrus. Differentiation of BrdU-positive cells, investigated by cell phenotype-specific double fluorescent labeling, showed increased neurogenesis only in the dentate gyrus of animals surviving the cardiac arrest for 7 days. The majority of newcomers, especially in the damaged CA1 region, consisted of glial cells. Moreover, asphyxia seemed to be able to induce the migration of microglia and astroglia from adjacent areas into the damaged area and/or the activation of resident cells. In addition, we show microglia proliferation/activation even 90 days after cardiac arrest. This morphological finding was confirmed by PCR analysis. The results indicate that asphyxia triggers cell proliferation in general and gliogenesis in particular - a possible pro-reparative event. Furthermore, from the finding of microglia proliferation up to 90 days after insult we conclude that delayed cell death processes take place which should be considered for further therapy strategies.

Post-cardiac arrest temperature manipulation alters early EEG bursting in rats

OBJECTIVES

Hypothermia improves outcomes after cardiac arrest (CA), while hyperthermia worsens injury. EEG recovers through periodic bursting from isoelectricity after CA, the duration of which is associated with outcome in normothermia. We quantified burst frequency to study the effect of temperature on early EEG recovery after CA.

METHODS

Twenty-four rats were divided into three groups, based on 6h of hypothermia (T=33 degrees C), normothermia (T=37 degrees C), or hyperthermia (T=39 degrees C) immediately post-resuscitation from 7-min asphyxial CA. Temperature was maintained using surface cooling and re-warming. Neurological recovery was defined by 72-h neurological deficit score (NDS).

RESULTS

Burst frequency was higher during the first 90min in rats treated with hypothermia (25.6+/-12.2min(-1)) and hyperthermia (22.6+/-8.3min(-1)) compared to normothermia (16.9+/-8.5min(-1)) (p<0.001). Burst frequency correlated strongly with 72-h NDS in normothermic rats (p<0.05) but not in hypothermic or hyperthermic rats. The 72-h NDS of the hypothermia group (74, 61-74; median, 25-75th percentile) was significantly higher than the normothermia (49, 47-61) and hyperthermia (43, 0-50) groups (p<0.001).

CONCLUSIONS

In normothermic rats resuscitated from CA, early EEG burst frequency is strongly associated with neurological recovery. Increased bursting followed by earlier restitution of continuous EEG activity with hypothermia may represent enhanced recovery, while heightened metabolic rate and worsening secondary injury is likely in the hyperthermia group. These factors may confound use of early burst frequency for outcome prediction.

Clinical neurophysiologic monitoring and brain injury from cardiac arrest

Electrophysiologic testing continues to play an important role in injury stratification and prognostication in patients who are comatose after cardiac arrest. As discussed previously, however, the adage about treating whole patients, not just the numbers, is relevant in this situation. EEG and SSEP can offer high specificity for discerning poor prognosis as long as they are applied to appropriate patient populations. As discussed previously, EEG and SSEP patterns change during the first hours to days after cardiac arrest and negative prognostic information should not be based solely on studies performed during the first 24 hours. Both electrophysiologic techniques also are susceptible to artifacts that may worsen the electrical patterns artificially and suggest a falsely poor prognosis. EEG is suppressed by anesthetic agents and hypothermia, both of which may produce ECS and burst suppression. Patients who experience respiratory arrest from a toxic ingestion of narcotics or barbiturates, in particular, may present with high-grade EEG patterns initially. Many patients also receive anesthetic medications at the time of tracheal intubation, which may linger beyond their normal half-life in patients who have hepatic or renal insufficiency or concurrent use of interacting medications. SSEP is much less susceptible to sedative anesthetic agents, but hypothermia is demonstrated to prolong evoked potential latencies. As therapeutic hypothermia becomes more common after cardiac arrest, the effect of temperature on electrophysiologic testing needs to be taken into account. The publications discussed previously also emphasize the need to adjust the prognostic value of electro-physiologic tests to the pretest probability of meaningful neurologic recovery in individual patients. Clearly, grade I EEG patterns and normal N20 potentials indicate a much better prognosis in patients who have a short du-ration of cardiac arrest, short duration of coma after resuscitation, and when the studies are performed within the first few days. In patients who remain in coma days after resuscitation and lack appropriate brainstem reflexes, however, even the most normal appearing electrophysiologic patterns do little to change the overall prognosis. Aside from prognostication, electrophysiologic testing holds great promise in defining the basic anatomy and physiology of coma emergence after cardiac arrest. In addition, quantitative EEG and automated evoked potentials have the potential to render these tools less subjective and arcane and more applicable for monitoring patients in the period during and immediately after resuscitation. Quantitative EEG also has great potential asa tool to define the time window for neuroprotective intervention and the means to track the response to such therapies in real time.

Regulated hypothermia reduces brain oxidative stress after hypoxic-ischemia

Regulated hypothermia produces a decrease in core temperature by lowering the brain's temperature set-point while maintaining thermoregulation at that lower set point. In contrast, forced hypothermia lowers core temperature by overwhelming the body's capacity to thermoregulate, but does not change the set-point. Regulated hypothermia has been shown to be cerebral protective in hibernating mammals. The effect of regulated hypothermia on the brain during reperfusion from hypoxic-ischemia has not been well studied. We induced regulated hypothermia with a neurotensin analogue (NT77) to determine whether it could reduce oxidative stress in the brain during reperfusion from asphyxial cardiac arrest (ACA) in rats. Mild hypothermia (32-34 degrees C) was induced by brief (4 h) external cooling (BC), NT77 or prolonged external cooling (24 h) (PC) 30 min after resuscitation from 8 min of ACA in rats. Malondialdehyde (MDA) levels in the brain were measured during reperfusion to quantitate oxidative stress.

RESULTS

MDA levels in the hippocampus were elevated at 16 h of normothermic reperfusion versus 48 h with BC reperfusion. There was no increase in hippocampal MDA levels in the NT77 and PC groups at 24-72 h of reperfusion. Regulated hypothermia induced by NT77 reduced oxidative stress in the hippocampus during reperfusion from hypoxic-ischemia in comparison to forced brief external cooling of the same duration. In addition, the duration of external cooling after resuscitation also alters oxidative stress in the brain during reperfusion.

Neurotensin-induced hypothermia improves neurologic outcome after hypoxic-ischemia

OBJECTIVE

External cooling is commonly used to force induction of mild hypothermia but requires equipment, has a slow onset of action, and must be prolonged to provide permanent neurologic benefits after hypoxic-ischemia. It is unknown whether the method for inducing mild hypothermia affects neurologic outcome after near-drowning. The objective of the study was to induce mild hypothermia with neurotensin analog NT77 or external cooling in a rat model of near-drowning. We hypothesize that NT77 would be more effective for improving neurologic outcome than external cooling of the same duration.

DESIGN

Rats were randomized to a normothermic control, neurotensin-induced hypothermia, brief external cooling, or prolonged external cooling group after asphyxial cardiac arrest.

SETTING

Laboratory investigation.

SUBJECTS

Forty-eight rats.

INTERVENTIONS

Mild hypothermia was induced by external cooling for 4 hrs (brief external cooling) or 24 hrs (prolonged external cooling) or by neurotensin-induced hypothermia administration 30 mins after asphyxial cardiac arrest in rats.

MEASUREMENTS

Outcome was assessed by a neurologic deficit score, the Morris water maze, and CA1 hippocampus histology 15 days after resuscitation.

MAIN RESULTS

Neurologic deficit score at 72 hrs after asphyxial cardiac arrest was lower with neurotensin-induced hypothermia (score, 0) and prolonged external cooling (score, 0) vs. normothermic control (score, 20) and brief external cooling (score, 18; p <.05). Latency time in the Morris water maze 15 days after asphyxial cardiac arrest was decreased with neurotensin-induced hypothermia (14+/-11 secs) and prolonged external cooling (18+/-9 secs) vs. normothermic control (74+/-17 secs) and brief external cooling (78+/-18 secs, p <.05). There was less ischemic neuronal damage with neurotensin-induced hypothermia (28+/-24%) and prolonged external cooling (21+/-14%) vs. normothermic control (61+/-32%) and brief external cooling (51+/-32%).

CONCLUSIONS

Neurotensin-induced hypothermia improved neurologic outcome after asphyxial cardiac arrest in rats vs. brief external cooling but was comparable to prolonged external cooling.

Neurological recovery by EEG bursting after resuscitation from cardiac arrest in rats

INTRODUCTION

The return of neurological function during the early period after resuscitation from cardiac arrest (CA) has not been evaluated systematically. We report the temporal analysis of EEG bursting pattern during the very early periods after resuscitation.

DESIGN/METHOD

A balanced group of good and poor outcome animals was selected from a population of rats subjected to either 5 or 7 min of asphyxial cardiac arrest (ACA) on the basis of a single criteria: 24 h neurobehavioral function based on the neurodeficit score (NDS). The EEGs of six consecutive good outcome rats (NDS > or = 60) and six consecutive poor outcome rats (NDS < 60) were selected for the study. The EEGs of these animals were given to two EEG examiners who were blinded to the selection process, the experimental conditions and the neurobehavioral recovery. The EEG bursting characteristics, such as rate, peak and duration of bursting were studied.

RESULTS

There was significantly higher EEG bursting in the good outcome animals (P < 0.05) and the burst complexes evolved into continuous activity by 90 min. Lower frequency bursting that persisted and failed to evolve into continuous activity was observed in the poor outcome group.

CONCLUSION

Increased EEG bursting during first 30-40 min after resuscitation from moderate to severe ACA was observed in rats with good neurological outcome at 24 h. Early EEG bursting patterns may provide additional prognostication after resuscitation from CA.

Direct visualization of trapped erythrocytes in rat brain after focal ischemia and reperfusion

Partial microcirculatory stasis after cerebral ischemia and reperfusion is a potential factor in delayed cell death. Sometimes described as the "no-reflow" phenomenon, limitations in current detection techniques have left the extent and spatial distribution of the phenomenon undetermined, which has led to some doubt as to its actual existence. The authors describe a new method, based on erythrocyte autofluorescence, that allows the erythrocytes trapped in the microvasculature, and thus blocking recirculation, to be directly visualized. Using this method, the authors have examined the spatial and temporal characteristics of this phenomenon in the rat intraluminal model of cerebral ischemia and reperfusion. Up to 15% of the capillaries in the ischemic penumbra remained occluded at least 2 hours after reperfusion. The amount of capillary bed showing trapped erythrocytes was more severe in the ischemic penumbra region than in the ischemic core. These results indicate that the no-reflow phenomenon may contribute to the developing damage in ischemic penumbra region, leading to additional injury after reperfusion.

Strain specific differences in a cardio-pulmonary resuscitation rat model

An asphyxial cardiac arrest rat model, originally developed for Sprague-Dawley rats, was transferred to a Wistar rat model. Several strain specific life support adjustments, i.e. ventilator settings, anaesthesia, and drug requirements, were necessary to stabilize the model for Wistar rats. Despite these arrangements numerous resuscitation related variables appeared different. Three groups were evaluated and compared: a temperature monitored Wistar group 1 (n=34), a temperature controlled Wistar group 2 (n=26) and a temperature controlled Sprague-Dawley group 3 (n=7). Overall, Wistar rats seem to have more sensitive cardio-circulatory system evidenced by a more rapid development of cardiac arrest (164 vs. 201 s), requiring higher adrenaline/epinephrine doses (10 vs. 5 microg/kg) and requiring more time for recovery after resuscitation (i.e. for return of blood pressure and blood gases). Without strict temperature control (as in groups 2+3 rats) group 1 rats went into spontaneous mild to moderate hypothermia during the first 24 h after restoration of spontaneous circulation (ROSC). Spontaneous hypothermia delayed the development of overall visible CA1 neuronal damage 24-48 h, but did not prevent it; therefore the model seemed to be suitable for future studies. Neuronal damages in the CA1 region in Wistar rats appeared to be more as shrunken cell bodies and pyknotic nuclei before resorption took place, whereas in Sprague-Dawley rats appeared in the same region.

Low-dose Carbicarb improves cerebral outcome after asphyxial cardiac arrest in rats

STUDY OBJECTIVE

Controversy surrounds the use of buffers during cardiac arrest to correct acidosis. The objective of this study was to determine whether attenuation or neutralization of cerebral acidosis by Carbicarb alters hippocampal glutamate levels, neuronal cell death, and neurologic deficits after reperfusion from asphyxial cardiac arrest in rats.

METHODS

Rats were prospectively randomized to either a control (n=45), low-dose Carbicarb (LDC; 3 mL/kg, n=45), or high-dose Carbicarb (HDC; 6 mL/kg, n=45) group in a blinded fashion during resuscitation after 8 minutes of asphyxial cardiac arrest. Microdialysis was used to assess brain pH and glutamate. A neurologic deficit score and neuronal cell death in the hippocampus were determined at day 7.

RESULTS

Resuscitation was greatest in LDC rats (42/45) and least in HDC rats (28/45) versus that in control rats (34/45). Brain pH was higher in the LDC and HDC rats 10 minutes after resuscitation and remained higher than that of control rats for 120 minutes after resuscitation. Glutamate levels at 10 to 120 minutes after reperfusion were lowest in the LDC rats. LDC rats had the lowest neurologic deficit score (1+/-2) versus that of control rats (13+/-8) and HDC rats (19+/-6). Hippocampal neuronal cell death was lowest in LDC rats (30+/-20) versus that in control rats (86+/-47) and HDC rats (233+/-85).

CONCLUSION

LDC administered during resuscitation from asphyxial cardiac arrest attenuated acidosis, improved resuscitation, and reduced neurologic deficits and the number of dead hippocampal neurons. Neutralization of cerebral acidosis with HDC increased the number of dead hippocampal neurons and neurologic deficits after resuscitation from cardiac arrest in rats.

Site of injury-directed induction of heme oxygenase-1 and -2 in experimental spinal cord injury: differential functions in neuronal defense mechanisms?

The heme oxygenase (HO) isozymes catalyze oxidation of the heme molecule to biliverdin and carbon monoxide (CO) with the release of chelated iron. Presently, we have defined, for the first time, propensity for site of injury-directed induction of isozymes--the stress-inducible isozyme, HO-1, responds distal (below) and the glucocorticoid (GC)-inducible HO-2 responds proximal (above) to the site of injury. We have also shown that reactive iron (Fe3+) and cGMP staining spatially resemble that of HO-1; which, in turn, colocalizes in motor neurons with transcription factors: Fas-associated protein containing death domain (FADD), tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) and p53. Spinal cord injury (SCI) was inflicted by clip compression for 30 min, and analyses were carried out after 4 h or 16 h. When compared with spinal cord segments proximal to the site of injury, northern blot analysis showed remarkably higher levels of HO-1 mRNA distal (below) to the site of injury at both time points. In contrast, HO-2 mRNA levels were elevated proximal (above) to the site of injury and more prominently at 16 h post SCI. Immunohistochemical analyses were carried out using 2 x 5 mm segments above and below the compression site. When compared with segments above the site of injury, the intensity of HO-1 immunostaining and the number of HO-1 positive neurons in the ventral horn motor neurons were prominently increased in segments below the injury. Western blot analysis confirmed the observations. HO-2 protein was mapped to the ventral horn motor neurons, oligodendrocytes, the Clarke's nucleus neurons and the ependymal cells. When compared with segments below the site of injury, neuronal HO-2 staining intensity was increased above the site of injury, and most notably at 16 h. These observations were also confirmed by western blotting and HO activity measurements. Tissue Fe3+ and cGMP staining were increased and prominently mapped below the site of injury, where cGMP colocalized with HO-1 in the nucleus of the motor neurons. Also, a site of injury-directed pattern of induction of FADD, TRAIL, and p53 immunoreactivity, and a widespread colocalization of the oncogenes with HO-1 protein, were found within motor neurons below the level of injury. We forward the hypothesis that HO-1 and HO-2 have different roles in the defense mechanisms of the injured nervous system. We hypothesize that HO-1 protects against further damage by contributing to controlled cell death through their intrinsic suicide program, while HO-2 is involved in suppression of inflammatory response by NO derived radicals.

Delayed, spontaneous hypothermia reduces neuronal damage after asphyxial cardiac arrest in rats

OBJECTIVE

Core temperature is reduced spontaneously after asphyxial cardiac arrest in rats. To determine whether spontaneous hypothermia influences neurologic damage after asphyxial arrest, we compared neurologic outcome in rats permitted to develop spontaneous hypothermia vs. rats managed with controlled normothermia.

INTERVENTIONS

Male Sprague-Dawley rats were asphyxiated for 8 mins and resuscitated. After extubation, a cohort of rats was managed with controlled normothermia (CN) by placement in a servo-controlled incubator set to maintain rectal temperature at 37.4 degrees C for 48 hrs. CN rats were compared with permissive hypothermia (PH) rats that were returned to an ambient temperature environment after extubation. Rats were killed at either 72 hrs (PH72hr, n = 14; CN72hr, n = 9) or 6 wks (PH6wk, n = 6, CN6wk, n = 6) after resuscitation. PH72 rats were historic controls for the CN72 rats, whereas PH6 and CN6 rats were randomized and studied contemporaneously.

MEASUREMENTS

A clinical neurodeficit score (NDS) was determined daily. A pathologist blinded to group scored 40 hematoxylin and eosin -stained brain regions for damage by using a 5-point scale (0 = none, 5 = severe). Quantitative analysis of CA1 hippocampus injury was performed by counting normal-appearing neurons in a defined subsection of CA1.

MAIN RESULTS

Mean rectal temperatures measured in the PH6wk rats (n = 6) were 36.9, 34.8, 35.5, 36.7, and 37.4 degrees C at 2, 8, 12, 24, and 36 hrs, respectively. Mortality rate (before termination) was lower in PH compared with CN (0/20 vs. 7/15; p < .005). PH demonstrated a more favorable progression of NDS (p = .04) and less weight loss (p < .005) compared with CN. Median histopathology scores were lower (less damage) in PH72hr vs. CN72hr for temporal cortex (0 vs. 2.5), parietal cortex (0 vs. 2), thalamus (0 vs. 3), CA1 hippocampus (1.5 vs. 4.5), CA2 hippocampus (0 vs. 3.5), subiculum (0 vs. 4), and cerebellar Purkinje cell layer (2 vs. 4) (all p < .05). There was almost complete loss of normal-appearing CA1 neurons in CN72hr rats (6 +/- 2 [mean +/- SD] normal neurons compared with 109 +/- 12 in naïve controls). In contrast, PH72hr rats demonstrated marked protection (97 +/- 23 normal-appearing neurons) that was still evident, although attenuated, at 6 wks (42 +/- 24 normal-appearing neurons, PH6wk).

CONCLUSION

Rats resuscitated from asphyxial cardiac arrest develop delayed, mild to moderate, prolonged hypothermia that is neuroprotective.

Hypothermia during reperfusion after asphyxial cardiac arrest improves functional recovery and selectively alters stress-induced protein expression

This study examined whether prolonged hypothermia induced 1 hour after resuscitation from asphyxial cardiac arrest would improve neurologic outcome and alter levels of stress-related proteins in rats. Rats were resuscitated from 8 minutes of asphyxia resulting in cardiac arrest. Brain temperature was regulated after resuscitation in three groups: normothermia (36.8 degrees C x 24 hours), immediate hypothermia (33 degrees C x 24 hours, beginning immediately after resuscitation), and delayed hypothermia (33 degrees C x 24 hours, beginning 60 minutes after resuscitation). Mortality and neurobehavioral deficits were improved in immediate and delayed hypothermia rats relative to normothermia rats. Furthermore, both immediate and delayed hypothermia improved neuronal survival in the CA1 region of the hippocampus assessed at 14 days. In normothermia rats, the 70-kDa heat shock protein (Hsp70) and 40-kDa heat shock protein (Hsp40) were increased within 12 hours after resuscitation in the hippocampus. Delayed hypothermia attenuated the increase in Hsp70 levels in the hippocampus but did not affect Hsp70 induction in the cerebellum. Hippocampal expression of Hsp40 was not affected by hypothermia. These data indicate that prolonged hypothermia during later reperfusion improves neurologic outcome after experimental global ischemia and is associated with selective changes in the pattern of stress-induced protein expression.

Prolonged severe hemorrhagic shock and resuscitation in rats does not cause subtle brain damage

OBJECTIVE

Some patients who survived severe hemorrhagic shock (HS) seem to exhibit persistent subtle neurobehavioral deficits. This finding is of concern if limited hypotensive fluid resuscitation is applied in hypotensive victims with penetrating trauma. This study was designed to determine whether subtle brain damage would occur in rats after severe prolonged HS. We hypothesized that rats surviving HS with mean arterial pressure (MAP) controlled at 40 mm Hg for 60 minutes would recover with slight permanent brain damage in terms of cognitive function without morphologic loss of neurons and that rats surviving HS with MAP at 30 mm Hg for 45 minutes (60 minutes were not tolerated) would have grossly abnormal brain function and loss of neurons.

METHODS

Under light nitrous oxide-halothane anesthesia, spontaneously breathing rats underwent MAP-controlled HS (HS phase I), volume resuscitation to normotension and invasive monitoring to 60 minutes (resuscitation phase II), and observation to 10 days with detailed assessment of cognitive function (observation phase III). Five conscious rats served as normal controls. Three treatment groups were compared: group 1, shams (11 of 12 rats survived to 10 days); group 2, HS at MAP 40 mm Hg for 60 minutes (10 of 17 rats survived); group 3, HS at 30 mm Hg for 45 minutes (10 of 14 rats survived).

RESULTS

On post-HS day 10, all normal controls and all survivors of all three groups were functionally normal with overall performance category = 1 (normal) (overall performance category 1 = normal, 5 = death) and neurologic deficit scores < or = 7% (neurologic deficit scores 0-10% = normal, 100% = brain death). Post-HS beam balance, beam walking, and Morris water maze test results in HS groups 2 and 3 showed latencies not significantly different from those in shams and normal controls. Light microscopic scoring of five selectively vulnerable brain regions and other regions in five coronal sections revealed no ischemic (pyknotic, shrunken, eosinophilic) neurons in any of the survivors to 10 days. There was no statistical difference between normal controls, sham animals, and both HS groups in the number of normal neurons counted in the hippocampal CA-1 region in the 10-day survivors. All nonsurvivors died with intestinal necrosis.

CONCLUSION

HS at MAP 40 mm Hg for 60 minutes or MAP 30 mm Hg for 45 minutes does not cause subtle functional or histologic brain damage in surviving rats. Controlling MAP at 30 mm Hg carries a risk of sudden cardiac arrest. These data suggest that limited fluid resuscitation, to maintain MAP at about 40 mm Hg, as recommended for victims of penetrating trauma with uncontrolled HS, is safe for the brain.

Mild protective and resuscitative hypothermia for asphyxial cardiac arrest in rats

It has been shown in dogs that mild hypothermia (34 degrees C) during or immediately after ventricular fibrillation cardiac arrest can improve cerebral outcome. The effect of mild hypothermia on outcome after 8 minutes of asphyxiation (5 minutes' cardiac arrest) was studied for the first time in rats. Restoration of spontaneous circulation was with external cardiopulmonary resuscitation and observation to 72 hours. Three groups of 10 rats each were studied. At 72 hours postarrest, compared with the normothermic control group 1, final overall performance categories (OPC) and neurological deficit scores (NDS) were numerically better in the resuscitative (post-arrest) hypothermia group 2 and significantly better in the protective (pre-intra-arrest) hypothermia group 3 (P < .05). Total brain histopathological damage scores (HDS) were 17 +/- 5 in group 1, 14 +/- 6 in group 2 (NS), and 6 +/- 2 in group 3 (P < .001 versus group 1). HDS correlated with OPC (r = .6, P < .05) and NDS (r = .7, P < .05). Mild hypothermia improved cerebral outcome after asphyxial cardiac arrest in rats, more when induced before than after arrest. The model's insult is within the therapeutic window, which makes it also suitable for screening other cerebral resuscitation potentials.