Daqing Ma

Postoperative impairment of cognitive function in rats: a possible role for cytokine-mediated inflammation in the hippocampus.

Background: Postoperative cognitive dysfunction is being increasingly reported as a complication. The authors investigated the role of cytokine-mediated inflammation within the central nervous system in the development of cognitive dysfunction in a rat model. Methods: Adult rats were subjected to neuroleptic anesthesia (20 &mgr;g/kg fentanyl plus 500 &mgr;g/kg droperidol, intraperitoneal) for splenectomy or no surgery. On postanesthetic days 1, 3, and 7, cognitive function was assessed in a Y maze. To evaluate the immune response in the hippocampus, the authors measured glial activation, as well as transcription and expression of key proinflammatory cytokines interleukin 1&bgr; and tumor necrosis factor &agr;. To determine propensity for apoptosis, they measured expression of Bax and Bcl-2. Results: Cognitive function in splenectomized animals was impaired at days 1 and 3 after surgery compared with cognitive function in nonanesthetized rats. At all times, anesthetized rats that were not subjected to surgery were no different from control rats. Glial activation was observed in the hippocampus only in splenectomized rats at postsurgery days 1 and 3. Interleukin-1&bgr; messenger RNA (mRNA) was significantly increased at postsurgery days 1 and 3, with an increase in protein expression detected on day 1. There was a significant increase in tumor necrosis factor-&agr; mRNA on day 1 after surgery, although this was not associated with an increase in protein expression. The ratio of Bcl-2:Bax was significantly decreased in the splenectomized animals. Conclusion: These results suggest that splenectomy performed during neuroleptic anesthesia triggers a cognitive decline that is associated with a hippocampal inflammatory response that seems to be due to proinflammatory cytokine-dependent activation of glial cells.

Xenon and Hypothermia Combine to Provide Neuroprotection from Neonatal Asphyxia

Perinatal asphyxia can result in neuronal injury with long‐term neurological and behavioral consequences. Although hypothermia may provide some modest benefit, the intervention itself can produce adverse consequences. We have investigated whether xenon, an antagonist of the N‐methyl‐D‐aspartate subtype of the glutamate receptor, can enhance the neuroprotection provided by mild hypothermia. Cultured neurons injured by oxygen‐glucose deprivation were protected by combinations of interventions of xenon and hypothermia that, when administered alone, were not efficacious. A combination of xenon and hypothermia administered 4 hours after hypoxic‐ischemic injury in neonatal rats provided synergistic neuroprotection assessed by morphological criteria, by hemispheric weight, and by functional neurological studies up to 30 days after the injury. The protective mechanism of the combination, in both in vitro and in vivo models, involved an antiapoptotic action. If applied to humans, these data suggest that low (subanesthetic) concentrations of xenon in combination with mild hypothermia may provide a safe and effective therapy for perinatal asphyxia. Ann Neurol 2005;58:182–193

Xenon mitigates isoflurane-induced neuronal apoptosis in the developing rodent brain.

Background:Anesthetics, including isoflurane and nitrous oxide, an antagonist of the N-methyl-d-aspartate subtype of the glutamate receptor, have been demonstrated to induce apoptotic neurodegeneration when administered during neurodevelopment. Xenon, also an N-methyl-d-aspartate antagonist, not only lacks the characteristic toxicity produced by other N-methyl-d-aspartate antagonists, but also attenuates the neurotoxicity produced by this class of agent. Therefore, the current study sought to investigate xenons putative protective properties against anesthetic-induced neuronal apoptosis. Method:Separate cohorts (n = 5 or 6 per group) of 7-day-old rats were randomly assigned and exposed to eight gas mixtures: air, 75% nitrous oxide, 75% xenon, 0.75% isoflurane, 0.75% isoflurane plus 35% or 75% nitrous oxide, 0.75% isoflurane plus 30% or 60% xenon for 6 h. Rats were killed, and cortical and hippocampal apoptosis was assessed using caspase-3 immunostaining. In separate cohorts, cortices were isolated for immunoblotting of caspase 3, caspase 8, caspase 9, and cytochrome c. Organotypic hippocampal slices of postnatal mice pups were derived and cultured for 24 h before similar gas exposures, as above, and subsequently processed for caspase-3 immunostaining. Results:In vivo administration of isoflurane enhances neuronal apoptosis. When combined with isoflurane, nitrous oxide significantly increases whereas xenon significantly reduces apoptosis to a value no different from that of controls. In vitro studies corroborate the ability of xenon to attenuate isoflurane-induced apoptosis. Isoflurane enhanced expression of indicators of the intrinsic and common apoptotic pathways; this enhancement was increased by nitrous oxide but attenuated by xenon. Conclusions:The current study demonstrates that xenon prevents isoflurane-induced neonatal neuronal apoptosis.

Effects of Xenon on in Vitro and in Vivo Models of Neuronal Injury

Background Xenon, the “inert” gaseous anesthetic, is an antagonist at the N-methyl-d-aspartate (NMDA)-type glutamate receptor. Because of the pivotal role that NMDA receptors play in neuronal injury, the authors investigated the efficacy of xenon as a neuroprotectant in both in vitro and in vivo paradigms. Methods In a mouse neuronal–glial cell coculture, injury was provoked either by NMDA, glutamate, or oxygen deprivation and assessed by the release of lactate dehydrogenase into the culture medium. Increasing concentrations of either xenon or nitrogen (10–75% of an atmosphere) were coadministered and maintained until injury was assessed. In separate in vivo experiments, rats were administered N-methyl-dl-aspartate and killed 3 h later. Injury was quantified by histologic assessment of neuronal degeneration in the arcuate nucleus of the hypothalamus. Results Xenon exerted a concentration-dependent protection against neuronal injury provoked by NMDA (IC50 = 19 ± 6% atm), glutamate (IC50 = 28 ± 8% atm), and oxygen deprivation (IC50 = 10 ± 4% atm). Xenon (60% atm) reduced lactate dehydrogenase release to baseline concentrations with oxygen deprivation, whereas xenon (75% atm) reduced lactate dehydrogenase release by 80% with either NMDA- or glutamate-induced injury. In an in vivo brain injury model in rats, xenon exerted a concentration-dependent protective effect (IC50 = 78 ± 8% atm) and reduced the injury by 45% at the highest xenon concentration tested (75% atm). Conclusions Xenon, when coadministered with the injurious agent, exerts a concentration-dependent neuroprotective effect at concentrations below which anesthesia is produced in rodents. Unlike either nitrous oxide or ketamine (other anesthetics with NMDA antagonist properties), xenon is devoid of both neurotoxicity and clinically significant adverse hemodynamic properties. Studies are proposed to determine whether xenon can be used as a neuroprotectant in certain clinical settings.

The Neuroprotective Effect of Xenon Administration during Transient Middle Cerebral Artery Occlusion in Mice

Background Xenon has been shown to be neuroprotective in several models of in vitro and in vivo neuronal injury. However, its putative neuroprotective properties have not been evaluated in focal cerebral ischemia. The purpose of this study was to determine if xenon offers neuroprotection in a mouse model of middle cerebral artery occlusion. Methods C57BL/6 mice underwent 60 min of middle cerebral artery occlusion. The animals (n = 21 per group) were randomized to receive either 70% xenon + 30% O2, 70% N2O + 30% O2, or 35% xenon + 35% N2O + 30% O2. After 24 h, functional neurologic outcome (on three independent scales: four-point, general, and focal deficit scales) and cerebral infarct size were evaluated. Results The 70% xenon + 30% O2 group showed improved functional outcome (median [interquartile range], four-point scale: 2 [2], 70% xenon + 30% O2versus 3 [2], 70% N2O + 30% O2, P = 0.0061; general deficit scale: 9 [6], 70% xenon + 30% O2versus 10 [4], 70% N2O + 30% O2, P = 0.0346). Total cerebral infarct volumes were reduced in the 70% xenon + 30% O2 group compared with the 70% N2O + 30% O2 group (45 ± 17 mm3versus 59 ± 11 mm3, respectively; P = 0.0009). Conclusions In this model of transient focal cerebral ischemia, xenon administration improved both functional and histologic outcome.

Xenon Attenuates Cardiopulmonary Bypass–induced Neurologic and Neurocognitive Dysfunction in the Rat

Background With clinical data suggesting a role for excitatory amino acid neurotransmission in the pathogenesis of cardiopulmonary bypass (CPB)–associated brain injury, the current study was designed to determine whether xenon, an N-methyl-d-aspartate receptor antagonist, would attenuate CPB-induced neurologic and neurocognitive dysfunction in the rat. Methods Following surgical preparation, rats were randomly divided into four groups: (1) sham rats were cannulated but did not undergo CPB; (2) CPB rats were subjected to 60 min of CPB using a membrane oxygenator receiving a gas mixture of 30% O2, 65% N2, and 5% CO2; (3) CPB + MK801 rats received MK801 (0.15 mg/kg intravenous) 15 min prior to 60 min of CPB with the same gas mixture; and (4) CPB + xenon rats underwent 60 min of CPB using an oxygenator receiving 30% O2, 60% xenon, 5% N2, and 5% CO2. Following CPB, the rats recovered for 12 days, during which they underwent standardized neurologic and neurocognitive testing (Morris water maze). Results The sham and CPB + xenon groups had significantly better neurologic outcome compared to both the CPB and CPB + MK801 groups on postoperative days 1 and 3 (P < 0.05). Compared to the CPB group, the sham, CPB + MK801, and CPB + xenon groups had better neurocognitive outcome on postoperative days 3 and 4 (P < 0.001). By the 12th day, the neurocognitive outcome remained significantly better in the CPB + xenon group compared to the CPB group (P < 0.01). Conclusion These data indicate that CPB-induced neurologic and neurocognitive dysfunction can be attenuated by the administration of xenon, potentially related to its neuroprotective effect via N-methyl-d-aspartate receptor antagonism.

Xenon Preconditioning Reduces Brain Damage from Neonatal Asphyxia in Rats

Xenon attenuates on-going neuronal injury in both in vitro and in vivo models of hypoxic-ischaemic injury when administered during and after the insult. In the present study, we sought to investigate whether the neuroprotective efficacy of xenon can be observed when administered before an insult, referred to as ‘preconditioning’. In a neuronal–glial cell coculture, preexposure to xenon for 2 h caused a concentration-dependent reduction of lactate dehydrogenase release from cells deprived of oxygen and glucose 24 h later; xenons preconditioning effect was abolished by cycloheximide, a protein synthesis inhibitor. Preconditioning with xenon decreased propidium iodide staining in a hippocampal slice culture model subjected to oxygen and glucose deprivation. In an in vivo model of neonatal asphyxia involving hypoxic–ischaemic injury to 7-day-old rats, preconditioning with xenon reduced infarction size when assessed 7 days after injury. Furthermore, a sustained improvement in neurologic function was also evident 30 days after injury. Phosphorylated cAMP (cyclic adenosine 3′,5′-monophosphate)-response element binding protein (pCREB) was increased by xenon exposure. Also, the prosurvival proteins Bcl-2 and brain-derived neurotrophic factor were upregulated by xenon treatment. These studies provide evidence for xenons preconditioning effect, which might be caused by a pCREB-regulated synthesis of proteins that promote survival against neuronal injury.

Estrous cycle phase variations in visceromotor and cardiovascular responses to colonic distension in the anesthetized rat

Visceromotor and cardiovascular responses to colonic distension were measured in female rats, anesthetized with halothane in oxygen, in the proestrus, estrus, metestrus and diestrus phases of the estrous cycle. Ten rats were studied in each group and responses were measured at 5-min intervals for 60 min. A mixed model analysis of variance showed that there was no real change in either the visceral or cardiovascular response with time. There was a highly significant difference in visceromotor responses between the phases of the estrous cycle (P < 0.001). During the phase of proestrus the balloon pressure at which a response was triggered was much lower, with a mean value (95% confidence interval) of 18.7 (16.1, 21.8) mmHg, than the other phases with mean values (95% confidence interval) of 31.9 (27.4, 37.2) mmHg for estrus, 28.1 (24.2, 32.8) mmHg for metestrus, and 31.1 (26.7, 36.3) mmHg for diestrus. The mean arterial blood pressure increased in all groups (range 3.2, 5.4%) as a response to the stimulus, but there was no associated heart rate variability and no significant differences in cardiovascular changes between the groups (P = 0.6). The visceromotor responses measured during the phase of proestrus occurred at a significantly lower threshold than in the other phases of estrous.

Combination of Xenon and Isoflurane Produces a Synergistic Protective Effect against Oxygen–Glucose Deprivation Injury in a Neuronal–Glial Co-culture Model

SUSTAINED exposure to glutamate causes neuronal death by overactivation of its receptors, particularly those of the N-methyl-D-aspartate (NMDA) subtype. This process, denoted by the term excitotoxicity, is believed to play an important role in ongoing neuronal injury and death in acute insults, such as ischemic stroke and head trauma. Consequently, the neuroprotective effects of NMDA receptor antagonists, including xenon, have been investigated in a variety of both in vitro and in vivo models of neuronal injury of the type that may occur perioperatively. Notwithstanding their putative beneficial effects, the clinical use of NMDA antagonists has been hindered by the observation that several drugs of this class of compound produce neurotoxicity, characterized by distinctive behavioral and morphologic effects. Although xenon does not seem to have this side effect, it may be desirable to use lower concentrations because of the prohibitive cost of this gas and to permit adequate oxygenation. Therefore, we sought to investigate whether neuroprotective efficacy can be observed when this NMDA receptor antagonist is combined with another putative neuroprotective agent that acts by modulating the -aminobutyric acid (GABA) receptor. The neuronal damage from ischemia may also be a result of loss of inhibitory influences. In the brain, GABA acts as the major inhibitory neurotransmitter; an agonist of the A subtype of the GABA receptor (GABAA) has been shown to be neuroprotective in a transient forebrain ischemia model. Isoflurane potentiates activation of the GABAA receptors, 13 and its neuroprotective effect has been demonstrated previously. Because these anesthetics exert their neuroprotectant properties through different mechanisms, we hypothesized that in combination, their efficacy would be enhanced. To test our hypothesis, we studied the neuroprotective effect of the combination of xenon and isoflurane versus oxygen– glucose deprivation (OGD) injury in a neuronal–glial co-culture model.

Dexmedetomidine exerts dose-dependent age-independent antinociception but age-dependent hypnosis in Fischer rats.

Dexmedetomidine (Dex), an &agr;2-adrenoceptor agonist, is an effective analgesic and sedative drug in adults; however, little information is available about its efficacy in pediatric populations. Some anesthetics exhibit an age-dependent analgesic effect, e.g., nitrous oxide, being relatively ineffective in newborn rats. We investigated the analgesic and hypnotic efficacy of Dex using 6 cohorts of Fischer rats aged 7, 15, 19, 23, and 29 days and adults exposed to either Dex (10 or 50 &mgr;g/kg) or saline subcutaneously. Formalin plantar testing was used to mimic inflammatory pain, and its effect was assessed using immunohistochemical (c-Fos staining) and behavioral methods. The hypnotic action of Dex was assessed by loss of righting reflex. Formalin administration produced a typical nociceptive response in each age group; these nociceptive responses were significantly attenuated by Dex 50 &mgr;g/kg at all ages (P < 0.05), whereas Dex 10 &mgr;g/kg had little effect. Neonatal rats showed the greatest hypnotic sensitivity to Dex (P < 0.05).