Characterization of neuroprotection from excitotoxicity by moderate and profound hypothermia in cultured cortical neurons unmasks a temperature-insensitive component of glutamate neurotoxicity

Targeted therapeutic hypothermia protects against noise induced hearing loss

Introduction

Exposure to occupational or recreational loud noise activates multiple biological regulatory circuits and damages the cochlea, causing permanent changes in hearing sensitivity. Currently, no effective clinical therapy is available for the treatment or mitigation of noise-induced hearing loss (NIHL). Here, we describe an application of localized and non-invasive therapeutic hypothermia and targeted temperature management of the inner ear to prevent NIHL.

Methods

We developed a custom-designed cooling neck collar to reduce the temperature of the inner ear by 3-4°C post-injury to deliver mild therapeutic hypothermia.

Results

This localized and non-invasive therapeutic hypothermia successfully mitigated NIHL in rats. Our results show that mild hypothermia can be applied quickly and safely to the inner ear following noise exposure. We show that localized hypothermia after NIHL preserves residual hearing and rescues noise-induced synaptopathy over a period of months.

Discussion

This study establishes a minimally-invasive therapeutic paradigm with a high potential for rapid translation to the clinic for long-term preservation of hearing health.

Co-culturing Immune Cells and Mouse-Derived Mixed Cortical Cultures with Oxygen-Glucose Deprivation to In Vitro Simulate Neuroinflammatory Interactions After Stroke

Studying interactions between neural cells and glial cells in vitro remains an essential tool for scientists worldwide, and with the addition of oxygen-glucose deprivation (OGD) can be particularly useful for identifying mechanisms related to ischemic stroke-related injury and repair. In developing these protocols in the lab, however, we discovered the limitation of co-culturing immune cells with pure neuronal cultures as the standard media for immune cells impair neuronal growth and vice versa. Thus, we optimized a mixed cortical cell culture system that does not require the use of glial-conditioned media to support the viability and growth of neurons but can nonetheless be used to quantify neuronal survival and dendritic arborization. The following methods provide a guide as to how to culture mixed cortical cells from mouse pups (postnatal day 0-2). Additionally, we demonstrate how to co-culture mixed cortical cells with immune cells (e.g., B cells) to study neuro-immune interactions in vitro.

Quantitative evaluation of extrinsic factors influencing electrical excitability in neuronal networks: Voltage Threshold Measurement Method (VTMM)

The electrical excitability of neural networks is influenced by different environmental factors. Effective and simple methods are required to objectively and quantitatively evaluate the influence of such factors, including variations in temperature and pharmaceutical dosage. The aim of this paper was to introduce ‘the voltage threshold measurement method’, which is a new method using microelectrode arrays that can quantitatively evaluate the influence of different factors on the electrical excitability of neural networks. We sought to verify the feasibility and efficacy of the method by studying the effects of acetylcholine, ethanol, and temperature on hippocampal neuronal networks and hippocampal brain slices. First, we determined the voltage of the stimulation pulse signal that elicited action potentials in the two types of neural networks under normal conditions. Second, we obtained the voltage thresholds for the two types of neural networks under different concentrations of acetylcholine, ethanol, and different temperatures. Finally, we obtained the relationship between voltage threshold and the three influential factors. Our results indicated that the normal voltage thresholds of the hippocampal neuronal network and hippocampal slice preparation were 56 and 31 mV, respectively. The voltage thresholds of the two types of neural networks were inversely proportional to acetylcholine concentration, and had an exponential dependency on ethanol concentration. The curves of the voltage threshold and the temperature of the medium for the two types of neural networks were U-shaped. The hippocampal neuronal network and hippocampal slice preparations lost their excitability when the temperature of the medium decreased below 34 and 33°C or increased above 42 and 43°C, respectively. These results demonstrate that the voltage threshold measurement method is effective and simple for examining the performance/excitability of neuronal networks.

Neuroprotective hypothermia - Why keep your head cool during ischemia and reperfusion

BACKGROUND

Targeted temperature management (TTM) is the induced cooling of the entire body or specific organs to help prevent ischemia and reperfusion (I/R) injury, as may occur during major surgery, cardiac resuscitation, traumatic brain injury and stroke. Ischemia and reperfusion induce neuronal damage by mitochondrial dysfunction and oxidative injury, ER stress, neuronal excitotoxicity, and a neuroinflammatory response, which may lead to activation of apoptosis pathways.

SCOPE OF REVIEW

The aim of the current review is to discuss TTM targets that convey neuroprotection and to identify potential novel pharmacological intervention strategies for the prevention of cerebral ischemia and reperfusion injury.

MAJOR CONCLUSIONS

TTM precludes I/R injury by reducing glutamate release and oxidative stress and inhibiting release of pro-inflammatory factors and thereby counteracts mitochondrial induced apoptosis, neuronal excitotoxicity, and neuroinflammation. Moreover, TTM promotes regulation of the unfolded protein response and induces SUMOylation and the production of cold shock proteins. These advantageous effects of TTM seem to depend on the clinical setting, as well as type and extent of the injury. Therefore, future aims should be to refine hypothermia management in order to optimize TTM utilization and to search for pharmacological agents mimicking the cellular effects of TTM.

GENERAL SIGNIFICANCE

Bundling knowledge about TTM in the experimental, translational and clinical setting may result in better approaches for diminishing I/R damage. While application of TTM in the clinical setting has some disadvantages, targeting its putative protective pathways may be useful to prevent I/R injury and reduce neurological complications.

Combination of therapeutic hypothermia and other neuroprotective strategies after an ischemic cerebral insult

Abrupt deprivation of substrates to neuronal tissue triggers a number of pathological events (the “ischemic cascade”) that lead to cell death. As this is a process of delayed neuronal cell death and not an instantaneous event, several pharmacological and non-pharmacological strategies have been developed to attenuate or block this cascade. The most promising neuroprotectant so far is therapeutic hypothermia and its beneficial effects have inspired researchers to further improve its protective benefit by combining it with other neuroprotective agents. This review provides an overview of all neuroprotective strategies that have been combined with therapeutic hypothermia in rodent models of focal cerebral ischemia. A distinction is made between drugs interrupting only one event of the ischemic cascade from those mitigating different pathways and having multimodal effects. Also the combination of therapeutic hypothermia with hemicraniectomy, gene therapy and protein therapy is briefly discussed. Furthermore, those combinations that have been studied in a clinical setting are also reviewed.

Time-dependent effects of hypothermia on microglial activation and migration

Background

Therapeutic hypothermia is one of the neuroprotective strategies that improve neurological outcomes after brain damage in ischemic stroke and traumatic brain injury. Microglial cells become activated following brain injury and play an important role in neuroinflammation and subsequent brain damage. The aim of this study was to determine the time-dependent effects of hypothermia on microglial cell activation and migration, which are accompanied by neuroinflammation.

Methods

Microglial cells in culture were subjected to mild (33 °C) or moderate (29 °C) hypothermic conditions before, during, or after lipopolysaccharide (LPS) or hypoxic stimulation, and the production of nitric oxide (NO), proinflammatory cytokines, reactive oxygen species, and neurotoxicity was evaluated. Effects of hypothermia on microglial migration were also determined in in vitro as well as in vivo settings.

Results

Early-, co-, and delayed-hypothermic treatments inhibited microglial production of inflammatory mediators to varying degrees: early treatment was the most efficient, and delayed treatment showed time-dependent effects. Delayed hypothermia also suppressed the mRNA levels of proinflammatory cytokines and iNOS, and attenuated microglial neurotoxicity in microglia-neuron co-cultures. Furthermore, delayed hypothermia reduced microglial migration in the Boyden chamber assay and wound healing assay. In a stab injury model, delayed local hypothermia reduced migration of microglia toward the injury site in the rat brain.

Conclusion

Taken together, our results indicate that delayed hypothermia is sufficient to attenuate microglial activation and migration, and provide the basis of determining the optimal time window for therapeutic hypothermia. Delayed hypothermia may be neuroprotective by inhibiting microglia-mediated neuroinflammation, indicating the therapeutic potential of post-injury hypothermia for patients with brain damages exhibiting some of the inflammatory components.

Therapeutic hypothermia in acute ischemic stroke

Induced hypothermia has been used for neuroprotection in cardiac and neurovascular procedures. Experimental and translational studies provide evidence for its utility in the treatment of ischemic cerebrovascular disease. Over the past decade, these principles have been applied to the clinical management of acute stroke. Varying induction methods, time windows, clinical indications, and adjuvant therapies have been studied. In this article the authors review the mechanisms and techniques for achieving therapeutic hypothermia in the setting of acute stroke, and they outline pertinent side effects and complications. The manuscript summarizes and examines the relevant clinical trials to date. Despite a reasonable amount of existing data, this review suggests that additional trials are warranted to define the optimal time window, temperature regimen, and precise clinical indications for induction of therapeutic hypothermia in the setting of acute stroke.

A Multiscale Approach to Blast Neurotrauma Modeling: Part II: Methodology for Inducing Blast Injury to in vitro Models

Due to the prominent role of improvised explosive devices (IEDs) in wounding patterns of U.S. war-fighters in Iraq and Afghanistan, blast injury has risen to a new level of importance and is recognized to be a major cause of injuries to the brain. However, an injury risk-function for microscopic, macroscopic, behavioral, and neurological deficits has yet to be defined. While operational blast injuries can be very complex and thus difficult to analyze, a simplified blast injury model would facilitate studies correlating biological outcomes with blast biomechanics to define tolerance criteria. Blast-induced traumatic brain injury (bTBI) results from the translation of a shock wave in-air, such as that produced by an IED, into a pressure wave within the skull-brain complex. Our blast injury methodology recapitulates this phenomenon in vitro, allowing for control of the injury biomechanics via a compressed-gas shock tube used in conjunction with a custom-designed, fluid-filled receiver that contains the living culture. The receiver converts the air shock wave into a fast-rising pressure transient with minimal reflections, mimicking the intracranial pressure history in blast. We have developed an organotypic hippocampal slice culture model that exhibits cell death when exposed to a 530 ± 17.7-kPa peak overpressure with a 1.026 ± 0.017-ms duration and 190 ± 10.7 kPa-ms impulse in-air. We have also injured a simplified in vitro model of the blood-brain barrier, which exhibits disrupted integrity immediately following exposure to 581 ± 10.0 kPa peak overpressure with a 1.067 ± 0.006-ms duration and 222 ± 6.9 kPa-ms impulse in-air. To better prevent and treat bTBI, both the initiating biomechanics and the ensuing pathobiology must be understood in greater detail. A well-characterized, in vitro model of bTBI, in conjunction with animal models, will be a powerful tool for developing strategies to mitigate the risks of bTBI.

Hypothermia and rewarming injury in hippocampal neurons involve intracellular Ca2+ and glutamate excitotoxicity

This study examines the causes of hypothermia and rewarming injury in CA1, CA3, and dentate neurons in rat hippocampal slice cultures. Neuronal death, assessed with propidium iodide or Sytox fluorescence, Fluoro-Jade labeling, and Cresyl Violet staining, depended on the severity and duration of hypothermia. More than 6 h at temperatures less than 12 °C followed by rewarming to 37 °C (profound hypothermia and rewarming, PH/RW) caused swelling and death in large number of neurons in CA1, CA3, and dentate. During PH, [ATP] decreased and [Ca(2+)](I) and extracellular [glutamate] increased, with neuron rupture and nuclear condensation following RW. The data support the hypothesis that neuronal death from PH/RW is excitotoxic, due to ATP loss, glutamate receptor activation and Ca(2+) influx. We found that antagonism of N-methyl-D-aspartate (NMDA) receptors, but not 2-amino-3-(5-methyl-3-oxo-1,2- oxazol-4-yl) propanoic acid or metabotropic glutamate receptors, decreased neuron death and prevented increases in [Ca(2+)](I) caused by PH/RW. Chelating extracellular Ca(2+) decreased PH/RW injury, but inhibiting L- and T-type voltage-gated Ca(2+) channels, K+ channels, Ca(2+) release from the endoplasmic reticulum, and reverse Na(+)/Ca(2+) exchange did not affect the Ca(2+) changes or cell death. We conclude that the mechanism of PH/RW neuronal injury in hippocampal slices primarily involves intracellular Ca(2+) accumulation mediated by NMDA receptors that activates necrotic, but not apoptotic processes.

Neuroprotection by Freezing Ischemic Penumbra Evolution Without Cerebral Blood Flow Augmentation With a Postsynaptic Density-95 Protein Inhibitor

Background and Purpose—

The purpose of this study was to determine whether neuroprotection is feasible without cerebral blood flow augmentation in experimental permanent middle cerebral artery occlusion.

Methods—

Rats were subjected to permanent middle cerebral artery occlusion by the suture occlusion method and were treated 1 hour thereafter with a single 5-minute intravenous infusion of the postsynaptic density-95 protein inhibitor Tat-NR2B9c (7.5 mg/kg) or saline (n=8/group). Arterial spin-labeled perfusion-weighted MRI and diffusion weighted MRI were obtained with a 4.7-T Bruker system at 30, 45, 70, 90, 120, 150, and 180 minutes postmiddle cerebral artery occlusion to determine cerebral blood flow and apparent diffusion coefficient maps, respectively. At 24 hours, animals were neurologically scored (0 to 5), euthanized, and the brains stained with 2–3-5-triphenyl tetrazolium chloride to ascertain infarct volumes corrected for edema. Additionally, the effects of Tat-NR2B9c on adenosine 5′-triphosphate levels were measured in vitro in neurons subjected to oxygen–glucose deprivation.

Results—

Final infarct volume was decreased by 30.3% in the Tat-NR2B9c-treated animals compared with controls ( P =0.028). There was a significant improvement in 24 hours neurological scores in the Tat-NR2B9c group compared with controls, 1.8±0.5 and 2.8±1.0, respectively ( P =0.021). Relative to controls, Tat-NR2B9c significantly attenuated diffusion-weighted imaging lesion growth and preserved the diffusion-weighted imaging/perfusion-weighted imaging mismatch (ischemic penumbra) without affecting cerebral blood flow in the ischemic core or penumbra. Tat-NR2B9c treatment of primary neuronal cultures resulted in 26% increase in cell viability and 34% greater adenosine 5′-triphosphate levels after oxygen–glucose deprivation.

Conclusions—

Preservation of adenosine 5′-triphosphate levels in vitro and neuroprotection in permanent middle cerebral artery occlusion in rats is achievable without cerebral blood flow augmentation using a postsynaptic density-95 protein inhibitor.

A closed-circuit neonatal xenon delivery system: a technical and practical neuroprotection feasibility study in newborn pigs

BACKGROUND

Asphyxia accounts for 23% of the 4 million annual global neonatal deaths. In developed countries, the incidence of death or severe disability after hypoxic-ischemic (HI) encephalopathy is 1-2/1000 infants born at term. Hypothermia (HT) benefits newborns post-HI and is rapidly entering clinical use. Xenon (Xe), a scarce and expensive anesthetic, combined with HT markedly increases neuroprotection in small animal HI models. The low-Xe uptake of the patient favors the use of closed-circuit breathing system for efficiency and economy. We developed a system for delivering Xe to mechanically ventilated neonates, then investigated its technical and practical feasibility in a previously described neonatal pig model approximating the clinical scenario of global HI injury, prolonged Xe delivery with and without HT as a potential therapy, subsequent neonatal intensive care unit management, and tracheal extubation.

METHODS

Sixteen newborn pigs underwent a global 45 min HI insult (4%-6% inspired oxygen reducing the electroencephalogram amplitude to <7 microV), then received 16 h 50% inspired Xe during normothermia (39.0 degrees C) or HT (33.5 degrees C). A conventional neonatal ventilator provided breaths of oxygen to a lower chamber compressing a hanging bag within. This bag communicated with the upper closed part of the breathing system containing soda lime, unidirectional valves, Xe/oxygen analyzers, and a tracheal tube connection. At each end-inspiration, this bag emptied fully and a bolus of oxygen, the driving gas, crossed from the lower to upper chamber via an additional valve. This mechanically substituted the gas uptake from the circle during the previous breath cycle (oxygen + small volume of Xe) with an equivalent volume of oxygen creating a slow-rising inspired oxygen concentration. This was offset by manual injection of Xe boluses, infrequently at steady state, due to the low-Xe uptake of the patient.

RESULTS

Total mean Xe usage was 0.18 (0.16-0.21) L/h with no differences between Xe-HT and Xe-NT groups, which had weights of 1767 (1657-1877) g and 1818 (1662-1974) g, respectively (95% CI). HT reduced heart rate in the cooled animals; 180 (165-195) vs 148 (142-155) bpm (P < 0.0001) with no differences in arterial blood pressure, oxygen saturation, arterial carbon dioxide tension, or weaning times between these groups.

CONCLUSION

We describe a closed-circuit Xe delivery system with automatic mechanical oxygen replenishment, which could be developed as a single use device. Gas exchange was maintained while Xe consumption was minimal (<$2/h at $10/L*). We have shown it is both feasible and cost-efficient to use this Xe delivery method in newborn pigs for up to 16 h with or without concurrent cooling after a severe HI insult.

PDZ protein interactions underlying NMDA receptor-mediated excitotoxicity and neuroprotection by PSD-95 inhibitors

In neuronal synapses, PDZ domains [postsynaptic density-95 (PSD-95)/Discs large/zona occludens-1] of PSD-95 proteins interact with C termini of NMDA receptor [NMDAR (NR)] subunits, linking them to downstream neurotoxic signaling molecules. Perturbing NMDAR/PSD-95 interactions with a Tat peptide comprising the nine C-terminal residues of the NR2B subunit (Tat-NR2B9c) reduces neurons' vulnerability to excitotoxicity and ischemia. However, NR subunit C termini may bind many of >240 cellular PDZs, any of which could mediate neurotoxic signaling independently of PSD-95. Here, we performed a proteomic and biochemical analysis of the interactions of all known human PDZs with synaptic signaling proteins including NR1, NR2A-NR2D, and neuronal nitric oxide synthase (nNOS). Tat-NR2B9c, whose interactions define PDZs involved in neurotoxic signaling, was also used. NR2A-NR2D subunits and Tat-NR2B9c had similar, highly specific, PDZ protein interactions, of which the strongest were with the PSD-95 family members (PSD-95, PSD-93, SAP97, and SAP102) and Tax interaction protein 1 (TIP1). The PSD-95 PDZ2 domain bound NR2A-NR2C subunits most strongly (EC50, approximately 1 microM), and fusing the NR2B C terminus to Tat enhanced its affinity for PSD-95 PDZ2 by >100-fold (EC50, approximately 7 nM). IC50 values for Tat-NR2B9c inhibiting NR2A-NR2C/PSD-95 interactions (approximately 1-10 microM) and nNOS/PSD-95 interactions (200 nM) confirmed the feasibility of such inhibition. To determine which of the PDZ interactions of Tat-NR2B9c mediate neuroprotection, one of PSD-95, PSD-93, SAP97, SAP102, TIP1, or nNOS expression was inhibited in cortical neurons exposed to NMDA toxicity. Only neurons lacking PSD-95 or nNOS but not PSD-93, SAP97, SAP102, or TIP1 exhibited reduced excitotoxic vulnerability. Thus, despite the ubiquitousness of PDZ domain-containing proteins, PSD-95 and nNOS above any other PDZ proteins are keys in effecting NMDAR-dependent excitotoxicity. Consequently, PSD-95 inhibition may constitute a highly specific strategy for treating excitotoxic disorders.

Temperature-dependent N-methyl-D-aspartate receptor-mediated cytotoxicity in cultured rat cortical neurons

Hypothermia protects against hypoxic or ischemic damage. However, the mechanisms by which brain cooling prevents hypoxic or ischemic damage are not clear. We examined whether hypothermia protects against excitotoxicity in cultured cortical cells. Exposure of cortical cell culture to 500 microM N-methyl-D-aspartate (NMDA) for 15 min at 32 degrees C or 37 degrees C did not induce neurotoxicity. On the other hand, reduction of temperature to 20 degrees C resulted in widespread neuronal disintegration by the following day. Moreover, intracellular calcium concentration increased markedly by adding NMDA to cells at 20 degrees C. These results suggest that profound hypothermia does not protect neurons from excitotoxicity by inhibiting NMDA receptor activity.

Motor impairment and neuronal damage following hypothermia in tropical amphibians

Although the induction of mild to moderate cerebral hypothermia in mammals can have neuroprotective activity, some deleterious effects have been described when inducing deep hypothermia during cooling of the brain. In the spinal cord, rapid deep cooling can induce seizure activity accompanied by release of the excitatory neurotransmitters, glutamate and aspartate. We used cold-sensitive tropical amphibians as a model to determine (a) the critical temperature inside the central nervous system necessary to induce seizures during rapid cooling; (b) the survival rate during slow deep cooling of the whole animal; and (c) whether deep cooling can cause neuronal cell damage. Seizures induced by deep rapid (<or=3 min) cooling of the spinal cord began when a critical temperature of 10.4 degrees C was reached. During slow (>or=30 min) deep cooling of the whole animal (12 h at 2-3 degrees C), around 70% of animals died. Spinal reflexes were enhanced when temperatures within the spinal cord reached between 9.0 degrees C and 11.6 degrees C. A fivefold increase in blood glucose level was observed during slow deep cooling. Recovery after slow deep cooling was accompanied by motor impairment and the main histological findings were condensation of the cytoplasm and nuclear pyknosis. Severe neuronal cell damage was characterized by swelling, vacuolated cytoplasm with distended neuronal bodies. These results indicate that deep cooling can easily induce neuronal cell damage in the central nervous system of cold-sensitive animals. They also warn us to the potential sequels associated with the use of deep brain cooling as a neuroprotective strategy.

Asynchronous administration of xenon and hypothermia significantly reduces brain infarction in the neonatal rat

BACKGROUND

Neonatal asphyxia causes long-term neurological and behavioural impairment in the developing brain. Concurrent administration of xenon and hypothermia synergistically reduces long-term damage in a rat model of neonatal asphyxia. This study sought to investigate whether asynchronous administration of xenon and hypothermia is capable of combining synergistically to provide neuroprotection.

METHODS

Seven-day-old rats were subjected to right common carotid artery occlusion followed by 90 min hypoxia with 8% oxygen. After a 1 h recovery period, rats received asynchronous administration of mild hypothermia (35 degrees C) and xenon (20%) with a 1 or 5 h gap between interventions, xenon (20%) alone, or mild hypothermia (35 degrees C) alone. Infarct volume in the brain was measured 4 days after injury.

RESULTS

Administration of hypothermia or xenon alone, 1 and 6 h after the hypoxic ischaemic insult, respectively, provided no neuroprotection. Asynchronous administration of xenon and hypothermia at a 1 h interval produced a significant reduction in infarct volume [93 (7) vs 74 (8); P < 0.05]. Reduction in infarct volume was also present when hypothermia and xenon were asynchronously administered with an intervening gap of 5 h [97 (5) vs 83 (3); P < 0.05].

CONCLUSIONS

This finding provides a rationale for investigating the combined use of hypothermia and xenon in a progressive manner for the management of neonatal asphyxia. Thus, hypothermia can be administrated at the site of delivery and xenon can be administered later.

Hypoxic-ischemic brain injury in infants with congenital heart disease dying after cardiac surgery

Cardiac surgery for congenital heart disease is performed increasingly earlier in infancy, including in the neonatal period. With increased survival of infants, there is growing concern about the long-term neurological sequelae of hypoxic-ischemic injury due to congenital heart disease itself prior to surgery, corrective surgery with the use of low-flow cardiopulmonary bypass (CPB) and/or deep hypothermic circulatory arrest (DHCA), and/or unstable hemodynamic factors postoperatively. In analyzing the neuropathology of 38 infants dying after cardiac surgery, we tested a set of questions related to the severity and patterns of brain injury, CPB, DHCA, and age of the infants at the time of surgery. In all infants dying after cardiac surgery, irrespective of the modality, cerebral white matter damage [periventricular leukomalacia (PVL) or diffuse white matter gliosis] was the most significant lesion in terms of severity and incidence, followed by a spectrum of gray matter lesions. There was no significant association between the duration of deep hypothermic circulatory arrest and the degree of severity of overall brain injury, and the pattern of brain injury was similar irrespective of the modality of cardiac surgery. There was no significant association between the age at the time of surgery (neonatal versus postneonatal) and the severity of overall brain injury. The patterns of brain injury were not age-related in the limited time-frame analyzed, except that infants who developed acute PVL after both closed and DHCA/CPB surgery (14/38 infants, 34%) were significantly younger at death (median age 13.0 days) compared to unaffected infants (median age at death 42.5 days) (P=0.031). This observation suggests that neonatal (<30 postnatal days), but not postneonatal (>30 postnatal days), brains are at risk for acute PVL, and likely reflects the vulnerability of immature (pre-myelinating) white matter to hypoxia-ischemia.

Prolonged hypothermia protects neonatal rat brain against hypoxic-ischemia by reducing both apoptosis and necrosis

Although hypothermia is an effective treatment for perinatal cerebral hypoxic-ischemic (HI) injury, it remains unclear how long and how deep we need to maintain hypothermia to obtain maximum neuroprotection. We examined effects of prolonged hypothermia on HI immature rat brain and its protective mechanisms using the Rice-Vannucci model. Immediately after the end of hypoxic exposure, the pups divided into a hypothermia group (30 degrees C) and a normothermia one (37 degrees C). Rectal temperature was maintained until they were sacrificed at each time point before 72h post HI. Prolonged hypothermia significantly reduced macroscopic brain injury compared with normothermia group. Quantitative analysis of cell death using H&E-stained sections revealed the number of both apoptotic and necrotic cells was significantly reduced by hypothermia after 24h post HI. Hypothermia seemed to decrease the number of TUNEL-positive cells. Immunohistochemistry and Western blot showed that prolonged hypothermia suppressed cytochrome c release from mitochondria to cytosol and activation of both caspase-3 and calpain in cortex, hippocampus, thalamus and striatum throughout the experiment. These results showed that prolonged hypothermia significantly reduced neonatal brain injury even when it was started after HI insult. Our results suggest that prolonged hypothermia protects neonatal brain after HI by reducing both apoptosis and necrosis.

Effects of epidural hypothermic saline infusion on locomotor outcome and tissue preservation after moderate thoracic spinal cord contusion in rats

Object. Regionally delivered hypothermia has advantages over systemic hypothermia for clinical application following spinal cord injury (SCI). The effects of local hypothermia on tissue sparing, neuronal preservation, and locomotor outcome were studied in a moderate thoracic spinal cord contusion model.

Methods. Rats were randomized to four treatment groups and data were collected and analyzed in a blinded fashion. Chilled saline was perfused into the epidural space 30 minutes postcontusion to achieve the following epidural temperatures: 24 ± 2.3°C (16 rats), 30 ± 2.4°C (13 rats), and 35 ± 0.9°C (13 rats). Hypothermia was continued for 3 hours when a 45-minute period of rewarming was instituted. In a fourth group a moderate contusion only was induced in 14 animals. Rectal (core) and T9–10 (epidural) temperatures were measured continuously. Locomotor testing, using the Basso-Beattie-Bresnahan (Ba-Be-Br) scale, was performed for 6 weeks, and rats were videotaped for subsequent analysis. The lesion/preserved tissue ratio was calculated throughout the entire lesion cavity and the total lesion, spinal cord, and spared tissue volumes were determined. The rostral and caudal extent of gray matter loss was also measured. At 6 weeks locomotor recovery was similar in all groups (mean Ba-Be-Br Scale scores 14.88 ± 3.71, 14.83 ± 2.81, 14.50 ± 2.24, and 14.07 ± 2.39 [p = 0.77] for all four groups, respectively). No significant differences in spared tissue volumes were found when control and treatment groups were compared, but gray matter preservation was reduced in the infusion-treated groups.

Conclusions. Regional cooling applied 30 minutes after a moderate contusive SCI was not beneficial in terms of tissue sparing, neuronal preservation, or locomotor outcome. This method of cooling may reduce blood flow in the injured spinal cord and exacerbate secondary injury.

Vulnerability of central neurons to secondary insults after in vitro mechanical stretch

Mild traumatic brain injuries are of major public health significance. Neurons in such injuries often survive the primary mechanical deformation only to succumb to subsequent insults. To study mechanisms of vulnerability of injured neurons to secondary insults, we used an in vitro model of sublethal mechanical stretch. Stretch enhanced the vulnerability of the neurons to excitotoxic insults, causing nuclear irregularities, DNA fragmentation, and death suggestive of apoptosis. However, the DNA degradation was not attributable to classical (caspase mediated) or caspase-independent apoptosis. Rather, it was associated with profound stretch-induced mitochondrial dysfunction and the overproduction of reactive oxygen species (ROS). Sublethally stretched neurons produced surprisingly high levels of ROS, but these in isolation were insufficient to kill the cells. To be lethal, the ROS also needed to combine with nitric oxide (NO) to form the highly reactive species peroxynitrite. Peroxynitrite was not produced after stretch alone and arose only after combining stretch with an insult capable of stimulating NO production, such as NMDA or an NO donor. This explained the exquisite sensitivity of sublethally stretched neurons to a secondary NMDA insult. ROS scavengers and NO synthase (NOS) inhibitors prevented cell death and DNA degradation. Moreover, inhibiting neuronal NOS activation by NMDA using peptides that perturb NMDA receptor-postsynaptic density-95 interactions also reduced protein nitration and cell death, indicating that the reactive nitrogen species produced were neuronal in origin. Our data explain the mechanism of enhanced vulnerability of sublethally injured neurons to secondary excitotoxic insults and highlight the importance of secondary mechanisms to the ultimate outcome of neurons in mild neurotrauma.

Post-ischemic hypothermia-induced tissue protection and diminished apoptosis after neonatal cerebral hypoxia–ischemia

Hypothermia is possibly the single most effective method of neuroprotection developed to date. However, the mechanisms are not completely understood. The aim of this study was to investigate the effects of post-ischemic hypothermia on brain injury and apoptotic neuronal cell death as well as related biochemical changes after neonatal hypoxia-ischemia (HI). Seven-day-old rats were subjected to left common carotid artery ligation and hypoxia (7.8%) for 1 h. Systemic hypothermia was induced immediately after hypoxia-ischemia, and body temperature was maintained at 30 degrees C for 10 h. The normothermic group was kept at 36 degrees C. Brain infarct volumes and neuronal loss in the CA1 area of the hippocampus were significantly reduced at 72 h post-HI in the hypothermia group. Cytochrome c release and activation of caspase-3 and -2 at 24 h post-HI were significantly diminished by hypothermia. The numbers of cytochrome c- and TUNEL-positive cells in the cortex and dentate gyrus of the hippocampus were significantly reduced in the hypothermia group compared with the normothermia group at 72 h post-HI. These results indicate that hypothermia may, at least partially, act through inhibition of the intrinsic pathway of caspase activation in the neonatal brain, thereby preventing apoptotic cell death.

Hypothermia and thiopentone sodium: individual and combined neuroprotective effects on cortical cultures exposed to prolonged hypoxic episodes

Because there are many conflicting reports on cerebroprotective effects of hypothermia and barbiturates, we examined the degree of neuroprotection at defined temperatures (normothermia, 37 degrees C; mild hypothermia, 32 degrees C; deep hypothermia, 22 degrees C; and profound hypothermia, 17 degrees C) and various concentrations (low, 4 microM; moderate, 40 microM; and high, 400 & microM) of thiopentone sodium (TPS), alone and in combination in cortical cultures exposed to prolonged hypoxia (24-48 hr). The survival rate of embryonic day (E)16 Wistar rat cortical neurons was evaluated on photomicrographs before and after experiments. During the 24-hr hypoxic period, the survival rate of neurons was maximal with combinations of mild hypothermia with 40 microM (91.6 +/- 0.7%) and 400 microM TPS (90.8 +/- 0.7%) or deep hypothermia combined with all concentrations of TPS (4 microM, 90.6 +/- 1.0%; 40 microM, 91.4 +/- 0.8%; 400 microM, 91.8 +/- 1.2%). During 48 hr hypoxia, the highest survival rate was seen with the combination of deep hypothermia and either 40 microM (90.9 +/- 0.6%) or 400 microM (91.1 +/- 1.4%) TPS. In the presence of profound hypothermia in combination with all concentrations of TPS, the survival rate was significantly reduced (P< 0.01) compared to combined application of either mild or deep hypothermia with TPS. In summary, maximal neuroprotection was attained with hypothermia and TPS in combination rather than applied individually, during prolonged hypoxic episodes (24- 48 hr). During a 24-hr hypoxic period, both mild and deep hypothermia combined with a clinically relevant concentration of TPS (40 microM) offered the highest neuroprotection. Only deep hypothermia provided maximal neuroprotection when combined with 40 microM TPS, during 48-hr hypoxia. Combination of profound hypothermia and TPS did not confer considerable neuroprotection during long lasting hypoxia.

Neuroprotective effect of hypothermia at defined intraischemic time courses in cortical cultures

Many experimental and clinical studies have shown that hypothermia confers cerebroprotective benefits against ischemic insults. Because of the many conflicting reports on hypothermic neuroprotection, we undertook this cellular study to identify the optimal temperature or a range of temperatures for maximal neuroprotection at different times (6-24 hr) during ischemic insults. Cultured Wistar rat cortical neurons were exposed to oxygen deprivation at defined times and temperatures (37 degrees C normothermia, 32 degrees C mild hypothermia, 27 degrees C moderate hypothermia, 22 degrees C deep hypothermia, and 17 degrees C profound hypothermia). The survival rate of neurons was evaluated by assessing viable neurons on photomicrographs. The normothermic group demonstrated a significantly lower survival rate of cultured neurons (6 hr, 80.3% +/- 2.7%; 12 hr, 56.1% +/- 2.1%; 18 hr, 34.2% +/- 1%; 24 hr, 18.1% +/- 2.2%) compared to hypothermic groups (P < 0.001). The survival rate for the profound hypothermic group was significantly reduced (P < 0.01) compared to other hypothermic groups (at 17 degrees C: 12 hr, 85.9% +/- 2.5%, 18 hr, 74.7% +/- 3.7%, 24 hr, 58.7% +/- 2.7%). Almost equal survival rates were observed among mild, moderate, and deep hypothermic groups following <18 hr exposure to hypoxia, but the deep hypothermic group showed a significantly higher survival rate (84.1% +/- 1.6%; P < 0.001) when subjected to hypoxia for 24 hr. In conclusion, hypothermia offers marked neuroprotection against hypoxia, but attenuation of neuronal cell death was less with profound hypothermia compared to mild, moderate, and deep hypothermia. Deep hypothermia affords maximal protection of neurons compared to mild and moderate hypothermia during long-lasting hypoxia (>18 hr).

Synaptic and non-synaptic AMPA receptors permeable to calcium

For a long time, alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA) receptors permeable to calcium have been considered to be either non-existent or as "atypical". There is now ample evidence that these receptors exist in numerous regions of the nervous system and in many neuronal as well as non-neuronal cell populations. This evidence has been accumulated by several methods, including electrophysiological recording, calcium imaging and cobalt-loading. Functional AMPA receptors permeable to calcium are already expressed at very early stages of embryonic development, well before the onset of synaptogenesis. They are probably involved in the paracrine signaling necessary for construction of the nervous system before becoming involved in synaptic transmission. In immature cells, cyclothiazide strongly increases the steady-state level of responses not only to AMPA, but also to kainate. Ingestion, during pregnancy, of food or drug substances that can cross the placental barrier and act upon the embryonic receptors may constitute a risk for normal development. In the adult nervous system, synaptic as well as non-synaptic (paracrine) AMPA receptors permeable to calcium are probably widely expressed in both glial and neuronal cells. They may also participate in controlling some aspects related to adult neurogenesis, in particular the migration of newly formed neurons.

Differential fall in ATP accounts for effects of temperature on hypoxic damage in rat hippocampal slices

Intracellular recordings, ATP and cytosolic calcium measurements from CA1 pyramidal cells in rat hippocampal slices were used to examine the mechanisms by which temperature alters hypoxic damage. Hypothermia (34 degrees C) preserved ATP (1.7 vs. 0.8 nM/mg) and improved electrophysiologic recovery of the CA1 neurons after hypoxia; 58% of the neurons subjected to 10 min of hypoxia (34 degrees C) recovered their resting and action potentials, while none of the neurons at 37 degrees C recovered. Increasing the glucose concentration from 4 to 6 mM during normothermic hypoxia improved ATP (1.3 vs. 0.8 nM/mg) and mimicked the effects of hypothermia; 67% of the neurons recovered their resting and action potentials. Hypothermia attenuated the membrane potential changes and the increase in intracellular Ca(2+) (212 vs. 384 nM) induced by hypoxia. Changing the glucose concentration in the artificial cerebrospinal fluid primarily affects ATP levels during hypoxia. Decreasing the glucose concentration from 4 to 2 mM during hypothermic hypoxia worsened ATP, cytosolic Ca(2+), and electrophysiologic recovery. Ten percent of the neurons subjected to 4 min of hypoxia at 40 degrees C recovered their resting and action potentials; this compared with 60% of the neurons subjected to 4 min of normothermic hypoxia. None of the neurons subjected to 10 min of hypoxia at 40 degrees C recovered their resting and action potentials. Hyperthermia (40 degrees C) worsens the electrophysiologic changes and induced a greater increase in intracellular Ca(2+) (538 vs. 384 nM) during hypoxia. Increasing the glucose concentration from 4 to 8 mM during 10 min of hyperthermic hypoxia improved ATP (1.4 vs. 0.6 nM/mg), Ca(2+) (267 vs. 538 nM), and electrophysiologic recovery (90 vs. 0%). Our results indicate that the changes in electrophysiologic recovery with temperature are primarily due to changes in ATP and that the changes in depolarization and Ca(2+) are secondary to these ATP changes. Both primary and secondary changes are important for explaining the improved electrophysiologic recovery with hypothermia.

Distinct roles of synaptic and extrasynaptic NMDA receptors in excitotoxicity

Excitatory synaptic activity governs excitotoxicity and modulates the distribution of NMDA receptors (NMDARs) among synaptic and extrasynaptic sites of central neurons. We investigated whether NMDAR localization was functionally linked to excitotoxicity by perturbing F-actin, a cytoskeletal protein that participates in targeting synaptic NMDARs in dendritic spines. Depolymerizing F-actin did not affect NMDA-evoked whole-cell currents. However, the number of dendritic NMDAR clusters and the NMDAR-mediated component of miniature spontaneous EPSCs were reduced, whereas the number of AMPA receptor clusters and AMPA receptor-mediated component of EPSCs was unchanged. This selective perturbation of synaptically activated NMDARs had no effect on neuronal death or the accumulation of (45)Ca(2+) evoked by applying exogenous NMDA or L-glutamate, which reach both synaptic and extrasynaptic receptors. However, it increased survival and decreased (45)Ca(2+) accumulation in neurons exposed to oxygen glucose deprivation, which causes excitotoxicity by glutamate release at synapses. Thus, synaptically and extrasynaptically activated NMDARs are equally capable of excitotoxicity. However, their relative contributions vary with the location of extracellular excitotoxin accumulation, a factor governed by the mechanism of extracellular neurotransmitter accumulation, not the synaptic activation of NMDARs.