Systematic studies on the effects of the NMDA receptor antagonist MK-801 on cerebral blood flow and responsivity, EEG, and blood-brain barrier following complete reversible cerebral ischemia

Acquisition and expression of sucrose conditioned flavor preferences following dopamine D1, opioid and NMDA receptor antagonism in C57BL/6 mice

The study of inbred mouse strains is a useful animal model to assess differences in ingestive behavior responses, including conditioned flavor preferences (CFP). C57BL/6, BALB/c and SWR inbred mice display differential sensitivity to dopamine (DA) D1, opioid and muscarinic cholinergic receptor antagonism of sucrose or saccharin intake as well as to muscarinic cholinergic antagonism of acquisition (learning) of sucrose-CFP. Given that DA D1, opioid and N-methyl-D-aspartate (NMDA) receptor antagonists differentially alter sucrose-CFP in BALB/c and SWR inbred mice, the present study examined whether systemic administration of naltrexone, SCH23390 or MK-801 altered acquisition and expression of sucrose-CFP in C57BL/6 mice. In acquisition experiments, male food-restricted C57BL/6 mice were treated with vehicle, naltrexone (1, 5 mg/kg), SCH23390 (50, 200 nmol/kg) or MK-801 (100, 200 µg/kg) 30 min prior to each of ten daily sessions in which they alternately consumed a flavored (CS+, e.g. cherry) 16% sucrose solution and a differently-flavored (CS-, e.g. grape) 0.05% saccharin solution followed by six two-bottle CS choice tests mixed in 0.2% saccharin without injections. SCH23390 and MK-801, but not naltrexone eliminated sucrose-CFP acquisition in food-restricted C57BL/6 mice. In expression experiments, food-restricted C57BL/6 mice underwent the ten training sessions without injections followed by two-bottle CS choice tests 30 min following vehicle, naltrexone (1, 5 mg/kg), SCH23390 (200, 800 nmol/kg) or MK-801 (100, 200 µg/kg). SCH23390 more effectively reduced the magnitude of sucrose-CFP expression than naltrexone or MK-801 in food-restricted C57BL/6 mice. Thus, dopamine D1 and NMDA receptor signaling is essential for learning of sucrose-CFP in C57BL/6 mice.

Effects of GABA(A) receptor blockade on regional cerebral blood flow and blood-brain barrier disruption in focal cerebral ischemia

In cerebral ischemia, transmission by the inhibitory neurotransmitter, γ-aminobutyric acid (GABA) is altered. This study was performed to determine whether blockade of GABA(A) receptor would affect regional cerebral blood flow (rCBF) and blood-brain barrier (BBB) permeability in a focal ischemic area of the brain. Rats were anesthetized with isoflurane and mechanically ventilated. Fifteen minutes after a permanent middle cerebral artery (MCA) occlusion, one half of the rats were infused with bicuculline 1mg/kg/min iv for 2 min followed by 0.1mg/kg/min iv to the end of the experiment. The other half were infused with normal saline. At one hour after MCA occlusion, rCBF was determined using ¹⁴C-iodoantipyrine and BBB permeability was determined by measuring the transfer coefficient (Ki) of ¹⁴C-α-aminoisobutyric acid. With MCA occlusion, rCBF was decreased in the ischemic cortex (IC) (-70%) in the control rats. In the bicuculline treated rats, the rCBF of the IC was lower (-48%) than the contralateral cortex but higher than the rCBF of the IC of the control rats (+55%). MCA occlusion increased Ki in the IC of the control rats (+72%) and bicuculline administration increased Ki further (+53%) in the IC. Blockade of GABA(A) receptors did not significantly affect rCBF or BBB permeability in the non-ischemic brain regions under isoflurane anesthesia. Our data demonstrated that blockade of GABA(A) receptors increased rCBF and enhanced the BBB disruption in focal cerebral ischemia. Our data suggest that GABA(A) receptors are involved, at least in part, in modulating rCBF and BBB disruption in focal cerebral ischemia.

Effects of blockade of ionotropic glutamate receptors on blood-brain barrier disruption in focal cerebral ischemia

To determine whether blockade of ionotropic glutamate receptors such as NMDA or AMPA receptors would attenuate blood-brain barrier (BBB) disruption in focal cerebral ischemia, 15 min before middle cerebral artery (MCA) occlusion, CGS-19755 or NBQX was injected intraperitoneally in rats. At 1 h after MCA occlusion, BBB permeability was determined by measuring the transfer coefficient (K(i)) of (14)C-α-aminoisobutyric acid and the volume of dextran distribution. With MCA occlusion, K(i) was increased in the ischemic cortex (IC) (316%). CGS-19755 attenuated the increase in K(i) in the IC (-46%), but NBQX did not significantly decrease it. The difference in the volume of dextran distribution between the IC and the contralateral cortex became insignificant with the blockade of NMDA or AMPA receptors. Our data demonstrated that blockade of NMDA or AMPA receptors could attenuate the BBB disruption in focal cerebral ischemia and suggest that ionotropic glutamate receptors are involved in part in BBB disruption.

Effects of exogenous excitatory amino acid neurotransmitters on blood-brain barrier disruption in focal cerebral ischemia

This study was performed to determine whether exogenous N-methyl-D: -aspartate (NMDA) or alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) would aggravate blood-brain barrier (BBB) disruption in focal cerebral ischemia in rats. Forty-five minutes after middle cerebral artery (MCA) occlusion, one of the following patches was applied to the exposed ischemic cerebral cortex of each rat: normal saline (control), 10(-5) M AMPA, 10(-4) M AMPA, 10(-5) M NMDA, or 10(-4) M NMDA. At 1 h after MCA occlusion, BBB permeability was determined by measuring the transfer coefficient (Ki) of (14)C-alpha-aminoisobutyric acid ((14)C-AIB). In all experimental groups, the Ki of the ischemic cortex (IC) was higher than that of the corresponding contralateral cortex (CC). The Ki of the IC of the animals treated with 10(-4) M AMPA or 10(-4) M NMDA was higher (+41%: P < 0.05 and +33%: P < 0.05, respectively) than that of the control animals. Our data demonstrated that exogenous NMDA or AMPA could further aggravate the BBB disruption in focal cerebral ischemia. Any insult increasing the release of excitatory neurotransmitters could further aggravate BBB disruption and brain edema during the ischemic period.

Transient NMDA receptor-mediated hypoperfusion following umbilical cord occlusion in preterm fetal sheep

Exposure to severe hypoxia leads to delayed cerebral and peripheral hypoperfusion. There is evidence in the very immature brain that transient abnormal glutaminergic receptor activity can occur during this phase of recovery. We therefore examined the role of N-methyl-D-aspartate (NMDA) receptor activity in mediating secondary hypoperfusion in preterm fetal sheep at 70% of gestation. Fetuses received either sham asphyxia or asphyxia and were studied for 12 h recovery. The specific, non-competitive NMDA receptor antagonist dizocilpine maleate (2 mg kg-1 bolus plus 0.07 mg kg h-1i.v.) or saline (vehicle) was infused from 15 min after asphyxia until 4 h. In the asphyxia-vehicle group abnormal epileptiform EEG transients were observed during the first 4 h of reperfusion, the peak of which corresponded approximately to the nadir in peripheral and cerebral hypoperfusion. Dizocilpine significantly suppressed this activity (2.7+/-1.3 versus 11.2+/-2.7 counts min-1 at peak frequency, P<0.05) and markedly delayed and attenuated the rise in vascular resistance in both peripheral and cerebral vascular beds observed after asphyxia, effectively preventing the initial deep period of hypoperfusion in carotid blood flow and femoral blood flow (P<0.01). However, while continued infusion did attenuate subsequent transient tachycardia, it did not prevent the development of a secondary phase of persistent but less profound hypoperfusion. In conclusion, the present studies suggest that in the immature brain the initial phase of delayed cerebral and peripheral hypoperfusion following exposure to severe hypoxia is mediated by NMDA receptor activity. The timing of this effect in the cerebral circulation corresponds closely to abnormal EEG activity, suggesting a pathological glutaminergic activation that we speculate is related to evolving brain injury.

Cerebral Blood Flow Thresholds for mRNA Synthesis After Focal Ischemia and the Effect of MK-801

BACKGROUND AND PURPOSE

MK-801 is a noncompetitive antagonist of N-methyl-d-aspartate subtype glutamate receptors with protective efficacy in experimental stroke. This study examined the impact of MK-801 on cerebral blood flow (CBF) and its relationship to gene expression changes during focal ischemia.

METHODS

Spontaneously hypertensive rats were subjected to surgical occlusion of the middle cerebral artery and ipsilateral common carotid artery after 30 minutes pretreatment with 5 mg/kg MK-801 or saline vehicle. After 2.5 hours of ischemia, regional CBF was evaluated by [14C]iodoantipyrine autoradiography and compared with distributions of gene expression changes evaluated by in situ hybridization detection of mRNAs encoding several immediate-early genes and the stress protein, hsp72.

RESULTS

MK-801 increased CBF in contralateral cortex from 93+/-15 to 187+/-37 mL/100 g per minute and produced a significant 25% reduction in the volume of ischemic cortex ipsilateral to occlusion. The extent of cortex failing to express inducible mRNAs correspondingly decreased, but the CBF threshold for mRNA synthesis remained unchanged (25 to 30 mL/100 g per minute). Widespread immediate-early gene expression in the neocortex became restricted to periinfarct regions after MK-801 treatment, and hybridization patterns in the striatum and hippocampus reflected the altered topography of cortical activation after drug treatment.

CONCLUSIONS

MK-801 alters ischemia-induced gene expression by 2 distinct mechanisms. Generalized increases in CBF reduce the volume of cortex falling below ischemic injury thresholds, protecting tissue and facilitating transcription of inducible genes proximal to the ischemic focus. In addition, MK-801 attenuates the signals that induce expression of immediate-early genes in cortical and subcortical regions remote from the middle cerebral artery territory.

Fructose-1,6-bisphosphate and MK-801 by aortic arch flush for cerebral preservation during exsanguination cardiac arrest of 20 min in dogs. An exploratory study

In our exsanguination cardiac arrest (CA) outcome model in dogs we are systematically exploring suspended animation (SA), i.e. preservation of brain and heart immediately after the onset of CA to enable transport and resuscitative surgery during CA, followed by delayed resuscitation. We have shown in dogs that inducing moderate cerebral hypothermia with an aortic arch flush of 500 ml normal saline solution at 4 degrees C, at start of CA 20 min no-flow, leads to normal functional outcome. We hypothesized that, using the same model, but with the saline flush at 24 degrees C inducing minimal cerebral hypothermia (which would be more readily available in the field), adding either fructose-1,6-bisphosphate (FBP, a more efficient energy substrate) or MK-801 (an N-methyl-D-aspartate (NMDA) receptor blocker) would also achieve normal functional outcome. Dogs (range 19-30 kg) were exsanguinated over 5 min to CA of 20 min no-flow, and resuscitated by closed-chest cardiopulmonary bypass (CPB). They received assisted circulation to 2 h, mild systemic hypothermia (34 degrees C) post-CA to 12 h, controlled ventilation to 20 h, and intensive care to 72 h. At CA 2 min, the dogs received an aortic arch flush of 500 ml saline at 24 degrees C by a balloon-tipped catheter, inserted through the femoral artery (control group, n=6). In the FBP group (n=5), FBP (total 1440 or 4090 mg/kg) was given by flush and with reperfusion. In the MK-801 group (n=5), MK-801 (2, 4, or 8 mg/kg) was given by flush and with reperfusion. Outcome was assessed in terms of overall performance categories (OPC 1, normal; 2, moderate disability; 3, severe disability; 4, coma; 5, brain death or death), neurologic deficit scores (NDS 0-10%, normal; 100%, brain death), and brain histologic damage scores (HDS, total HDS 0, no damage; >100, extensive damage; 1064, maximal damage). In the control group, one dog achieved OPC 2, one OPC 3, and four OPC 4; in the FBP group, two dogs achieved OPC 3, and three OPC 4; in the MK-801 group, two dogs achieved OPC 3, and three OPC 4 (P=1.0). Median NDS were 62% (range 8-67) in the control group; 55% (range 34-66) in the FBP group; and 50% (range 26-59) in the MK-801 group (P=0.2). Median total HDS were 130 (range 56-140) in the control group; 96 (range 64-104) in the FBP group; and 80 (range 34-122) in the MK-801 group (P=0.2). There was no difference in regional HDS between groups. We conclude that neither FBP nor MK-801 by aortic arch flush at the start of CA, plus an additional i.v. infusion of the same drug during reperfusion, can provide cerebral preservation during CA 20 min no-flow. Other drugs and drug-combinations should be tested with this model in search for a breakthrough effect.

Dose-response curve and optimal dosing regimen of cyclosporin A after traumatic brain injury in rats

Acute neuropathology following experimental traumatic brain injury results in the rapid necrosis of cortical tissue at the site of injury. This primary injury is exacerbated in the ensuing hours and days via the progression of secondary injury mechanism(s) leading to significant neurological dysfunction. Recent evidence from our laboratory demonstrates that the immunosuppressant cyclosporin A significantly ameliorates cortical damage following traumatic brain injury. The present study extends the previous findings utilizing a unilateral controlled cortical impact model of traumatic brain injury in order to establish a dose-response curve and optimal dosing regimen of cyclosporin A. Following injury to adult rats, cyclosporin A was administrated at various dosages and the therapy was initiated at different times post-injury. In addition to examining the effect of cyclosporin A on the acute disruption of the blood-brain barrier following controlled cortical impact, we also assessed the efficacy of cyclosporin A to reduce tissue damage utilizing the fluid percussion model of traumatic brain injury. The findings demonstrate that the neuroprotection afforded by cyclosporin A is dose-dependent and that a therapeutic window exists up to 24h post-injury. Furthermore, the optimal cyclosporin dosage and regimen markedly reduces disruption of the blood-brain barrier acutely following a cortical contusion injury, and similarly affords significant neuroprotection following fluid percussion injury. These findings clearly suggest that the mechanisms responsible for tissue necrosis following traumatic brain injury are amenable to pharmacological intervention.

Cerebral cortical muscarinic cholinergic and N-methyl-D-aspartate receptors mediate increase in cortical blood flow elicited by chemical stimulation of periaqueductal gray matter

The periaqueductal gray matter is implicated in the central processing of defensive reactions. We found previously that, when stimulated by N-methyl-D-aspartate, the caudal third of its lateral subdivision elicited an increase in blood flow over widespread cerebral neocortical areas and that a major proportion of the flow increase was inhibited by topical cortical application of scopolamine, an antagonist of muscarinic receptors. The present study was undertaken to elucidate the roles of cortical nicotinic and excitatory amino acid receptors in the mediation of the flow increase in 66 anaesthetized, cervically cordotomized, artificially ventilated rats with open cranial windows. We found that the flow increase (laser-Doppler flowmetry) was resistant to antagonists of non-N-methyl-D-aspartate receptors and of nicotinic receptors. The response was, however, attenuated to a substantial extent by topical and intravenous N-methyl-D-aspartate receptor antagonists, MK-801 and topical D(-)-2-amino-5-phosphonopentanoic acid. Combined topical application of the latter antagonist with scopolamine attenuated the flow increase to a further extent beyond that achieved with either of the antagonists alone. Topical applications of acetylcholine and N-methyl-D-aspartate individually increased the cortical blood flow. A modest synergism was observed between the actions of these two agonists.Overall, we suggest that in the face of stimuli which provoke defensive reactions, the periaqueductal gray matter may elicit an increase in cortical blood flow by utilizing the cortical acetylcholine-muscarinic receptor system and the cortical excitatory amino acid-N-methyl-D-aspartate receptor system. The vasomotor actions of these two transmitter-receptor systems may operate independently of each other as well as in harmony with each other.

Exacerbation of damage and altered NF-kappaB activation in mice lacking tumor necrosis factor receptors after traumatic brain injury

Tumor necrosis factor alpha (TNFalpha) is widely expressed in both neurons and glia and has been shown to be upregulated after traumatic brain injury (TBI). TNFalpha receptor activation results in activation of the transcription factor nuclear factor kappaB (NF-kappaB), which may serve an antiapoptotic role via the induction of target genes manganese superoxide dismutase (MnSOD) and/or calbindin. In the present study, we used a controlled cortical impact model of TBI with pertinent lines of transgenic mice to combine both morphological characterization and molecular analysis to elucidate the role of TNFalpha after TBI. Measurements of both the lesion volume and the blood-brain barrier breach indicated exacerbations in mice rendered genetically deficient in both the p55 and p75 TNFalpha receptors (TNFR-KO) compared with wild-type animals. Additionally, animals genetically altered to overexpress MnSOD showed a significant decrease in lesion volume compared with that of control littermates, whereas no alterations were observed in mice lacking the calcium-binding protein calbindin D28k. Analysis of NF-kappaB activation and relative levels of MnSOD revealed delayed responses in the injured cortex of TNFR-KO animals compared with wild-type animals, implying that endogenous TNFalpha may be neuroprotective after TBI.

Does glutamate mediate brain damage in acute encephalitis?

Cerebrospinal fluid (CSF) amino acid neurotransmitter concentrations in 23 patients with acute encephalitis were compared with those in patients with acute brain infarction, multiple sclerosis and controls. The concentration of glutamate was significantly higher in encephalitis (5.2+/-6.7 micromol/l) and stroke patients (9.6+/-14.2 micromol/l) than in MS patients (1.6+/-0.9 micromol/l) and controls (1.7+/-0.8 micromol/l; p < 0.001). The concentration of glycine was significantly higher in encephalitis (11.0+/-4.7 micromol/l) than in stroke (7.6+/-3.2 micromol/l) and MS patients (6.3+/-2.1 micromol/l) or controls (5.6+/-1.8 micromol/l; p < 0.002). Taurine levels were significantly lower in encephalitis patients than in the other groups (p = 0.04). The correlation of high glutamate levels with poor outcome was almost significant (Kendall tau 0.63, p = 0.06). Our observations suggest that exicitotoxic neurotransmission may play an important role in the series of events that lead to neuronal damage in encephalitis.

Mechanisms of cerebral injury in perinatal asphyxia and strategies for prevention

We have investigated the mechanisms of hypoxic brain cell injury in the immature animal by examining (1) the role of excitatory amino acid neurotransmitter receptors, (2) the receptor-mediated increase in intracellular Ca2+, and (3) the generation of oxygen free radicals. We examined the effect of brain tissue hypoxia on the NMDA receptor-ion channel complex including the glutamate, Mg2+, spermine, CPP, and the non-NMDA receptor kainate sites. Brain tissue hypoxia resulted in modification of the NMDA receptor ion channel and its modulatory sites. Hypoxia increased the affinity of both the ion channel and the glutamate recognition site. Pretreatment of animals with the glutamate antagonist CPP prevented hypoxia-induced modification of the channel. Similarly, pretreatment of animals with Mg2+, a blocker of the NMDA receptor ion channel, prevented the hypoxia-induced modification of the receptor. In addition, an increased agonist-dependent entry of Ca2+ into synaptosomes was observed in hypoxic animals compared with normoxic animals. Increased free radical generation in the cerebral cortex during hypoxia was demonstrated using spin labeling technique and electron spin resonance spectroscopy. We conclude that hypoxia-induced modification of the NMDA receptor-ion channel complex leads to increased intracellular Ca2+ potentiating free radical generation and resulting in hypoxic cell injury.

Polydeoxyribonucleotide (defibrotide) protects against post-ischemic behavioral, electroencephalographic and neuronal damage in the gerbil

The effectiveness of defibrotide, a single-stranded polydeoxyribonucleotide compound, in preventing damage caused by cerebral ischemia was studied. Global ischemia was induced in anesthetized gerbils by bilateral carotid artery occlusion for 10 min. Defibrotide (100 mg/kg) or saline was injected, i.v., immediately after reperfusion. The following parameters were evaluated simultaneously: (1) electroencephalographic (EEG) spectral power, recorded before, during and after the ischemic period; (2) body temperature, monitored with a rectal thermistor probe after reperfusion for 120 min; (3) spontaneous motility, evaluated through a photocell system and quantified in terms of total distance travelled in 30 min, 1 h after recirculation and at periods over 15 days; (4) mnemonic functions assessed by passive avoidance test from 3 to 15 days after ischemia; (5) histological examination, 7 days after reperfusion, counting CA1 hippocampal neuronal cells. The ischemia-induced complete flattening of spectral power was significantly reversed (P < 0.01) by post-ischemic treatment with defibrotide between 30 and 90 min after ischemia. A complete recovery of total EEG spectral power was seen in the defibrotide group at 6 h and the saline ischemic group at 1 day. Seven days after bilateral carotid occlusion, there was a significant decrease in spectral power (-70% +/- 6) together with a loss of the number of CA1 cells in the saline ischemic group (-64%). Treatment with defibrotide significantly protected against the decrease in spectral power (-30% +/- 7) and cell loss (-9%). Finally, the number of animals found to be protected against the ischemia-induced flattening was significantly larger for defibrotide-treated gerbils than for saline-treated animals throughout the experiment except for the third day. Body temperature was significantly decreased only at 30 min after reperfusion in both ischemic and sham-operated groups. Defibrotide reduced ischemia-induced hypermotility but only 6 h after the insult. The ischemia-induced impairment of memory was partially reversed within 3 days in the defibrotide-treated animals and fully reversed within 7 days in the defibrotide group and 15 days in the saline group. Our results demonstrate that defibrotide, even when administered after the post-ischemic period, possesses anti-ischemic properties. The mechanism by which defibrotide protects the ischemic reperfused brain is still largely unknown. However, a neuroprotection via adenosine A1 and A2 subtype receptor interaction can be put forward.

Effects of excitatory amino acids on cerebral oxygen consumption and blood flow in rat

This investigation tested the importance of excitatory amino acids' effects on regional cerebral O2 consumption and the concomitant changes in cerebral blood flow (rCBF) in isoflurane anesthetized rats. In the glutamate or N-methyl-D-aspartate (NMDA) groups, 10(-2) M glutamate or NMDA was topically applied to the right cortex and the left cortex was used as a control. One mg/kg dizocilpine maleate (MK-801), a non-competitive NMDA receptor antagonist, was administered (iv) to the MK-801 group and saline was given to the control group. Cortical rCBF was determined using 14C-iodoantipyrine and regional O2 extraction was measured microspectrophotometrically. Cerebral O2 consumption increased 77% after glutamate (contralateral cortex: 9.0 +/- 1.1 ml O2/min/100 g, glutamate treated cortex: 15.9 +/- 3.9), while a 46% increase was observed with the same concentration of NMDA (contralateral cortex: 9.8 +/- 2.0, NMDA treated cortex: 14.3 +/- 5.5). After MK-801, the O2 consumption decreased to 37% of the control value (control cortex: 7.0 +/- 1.3, MK-801 treated cortex: 2.6 +/- 3.9). MK-801 significantly decreased cerebral O2 extraction from 7.1 +/- 1.3 ml O2/100 ml (control cortex) to 5.3 +/- 0.6 (MK-801 treated cortex). However, there was no significant difference in cerebral O2 extraction between treated and contralateral cortex in either the glutamate or NMDA groups. The increase in O2 consumption caused by glutamate or NMDA was coupled with increased rCBF. Glutamate increased rCBF from 95 +/- 5 ml/min/100 g (contralateral cortex) to 165 +/- 31 (treated cortex), while NMDA increased rCBF from 114 +/- 12 (contralateral cortex) to 178 +/- 60 (treated cortex). MK-801 decreased O2 consumption with a lesser decrease of rCBF. The rCBF was 48 +/- 9 in the MK-801 treated cortex and 99 +/- 22 in the control cortex. Some substances produced by the activation of NMDA receptors may be related to the coupling of cerebral metabolism and blood flow, since after blockade of NMDA receptors with MK-801, this relationship is uncoupled. These findings suggest that glutamatergic processes have a major effect on cerebral O2 consumption and that this is at least partly due to NMDA receptors.

Effect of the novel high-affinity glycine-site N-methyl-D-aspartate antagonist ACEA-1021 on 125I-MK-801 binding after subdural hematoma in the rat: an in vivo autoradiographic study

Acute subdural hematoma (SDH) complicates 20% of severe human head injuries and causes death or severe disability in 60% of these cases, due to brain swelling and high intracranial pressure. Although the mechanisms for these phenomena are unknown, previous studies have implicated excitatory amino acid-mediated mechanisms in both humans and animal models. The authors therefore performed in vivo autoradiography using 125I-MK-801, a high-affinity noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, as a tracer to evaluate NMDA ion channel activation spatially and temporally as a factor causing cytotoxic swelling. Acute SDH was induced in 16 anesthetized rats using 0.4 ml autologous venous blood. Fifty microcuries of 125I-MK-801 was injected via an aortic arch cannula 30 minutes after onset of SDH. The effect of a new putatively neuroprotective drug, ACEA-1021, a glycine-specific binding site NMDA antagonist, on 125I-MK-801 binding was tested on five animals "Nonspecific" 125I-MK-801 binding in the rat brain was assessed by pretreatment with "cold" (nonradiolabeled) MK-801 in five more animals. Four hours later the animals were sacrificed and brain sections were apposed to radiation-detecting high-sensitivity photographic film with precalibrated plastic standards for 4 weeks. A striking and highly significant 1.7- to 4.8-fold increase in 125I-MK-801 binding was seen in the penumbra of viable tissue surrounding the ischemic zone beneath the acute SDH, when compared to contralateral hemisphere binding (p < 0.001). The MK-801 pretreatment markedly reduced 125I-MK-801 uptake in this penumbral zone (4.73 +/- 0.36 nCi/mg control vs. 2.85 +/- 0.08 nCi/mg cold MK-801; p < 0.0001), indicating that the increased binding in the penumbra of the lesion was due to NMDA ion channel activation. Pretreatment with ACEA-1021 reduced 125I-MK-801 uptake by 28% (3.41 +/- 0.26 nCi/mg vs. 4.73 +/- 0.36 nCi/mg; p < 0.05), indicating that this agent prevents opening of the NMDA ion channel and, thus, exposure of its receptor for MK-801 binding. These studies show intense foci of penumbral NMDA receptor-mediated ion channel activation after onset of SDH, which is markedly reduced by an NMDA antagonist. Such agents are thus likely to reduce cell swelling after SDH occurs.

Postischemic therapy with MK-801 (dizocilpine) in a primate model of transient focal brain ischemia

The purpose of this study was to develop a primate model for assessing EEG, behavior and histology, and to test the effect of NMDA receptor blockade in transient focal ischemia. Squirrel monkeys (Saimiri sciureus) under halothane anesthesia were subjected to 110 min of transient focal ischemia (n = 15) by temporary clip occlusion of the MCA. An eight-lead EEG was recorded. Neurobehavioral testing was done in a subgroup of animals (n = 6). Brain temperature (37.5 degrees C) was monitored and controlled to avoid hypothermia or intergroup temperature differences, and blood pressure was regulated to 60 mmHg. The entire brain was subserially sectioned, and 52 standardized coronal sections encompassing the infarct were examined histologically 2 wk after the ischemia. Animals were randomized to receive either (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801) 1 mg/kg of maleate salt or carrier solution, 20 min and again at 12 h after the onset of ischemia. Cingulate and retrosplenial cortex were examined for NMDA-antagonist-induced neuronal necrosis. No reduction, or trend toward reduction of neurobehavioral deficit was seen with MK-801. MCA occulsion reduced EEG power over the ischemic hemisphere. MK-801 appeared to cause brain activation, and globally increased power at several frequencies. MK-801 did not reduce infarction in either neocortex (p > 0.05) or striatum (p > 0.05). No selective neuronal necrosis was seen in the cingulate or retrosplenial cortex. We conclude that MK-801 given 20 min after the onset of transient ischemia offers no significant neuroprotective effect against either neurobehavioral deficit or ischemic infarction in this model of transient focal ischemia. Further experiments in unanesthetized animals are necessary to determine if MK-801-induced necrosis exists in the gyrencephalic brain, but the enhancement of primate brain electrical activity by MK-801 suggests that brain activation occurs in primates as it does in rodents.

Cerebral ischemia in gerbils: effects of acute and chronic treatment with adenosine A2A receptor agonist and antagonist

Despite significant progress in understanding of the potential of adenosine A1 receptor-based therapies in treatment of cerebral ischemia and stroke, very little is known about the effect of selective stimulation of adenosine A2A receptors on the outcome of a cerebrovascular arrest. In view of a major role played by adenosine A2 receptors in the regulation of cerebral blood flow, we have investigated the effect of both acute and chronic administration of the selective adenosine receptor agonist 2-[(2-aminoethylamino)-carbonylethylphenylethylamino]-5'-N- ethylcarboxoamidoadenosine (APEC) and antagonist 8-(3-chlorostyryl)caffeine (CSC) on the outcome of 10 min ischemia in gerbils. Acute treatment with APEC improved recovery of postischemic blood flow and survival without affecting neuronal preservation in the hippocampus. Acute treatment with CSC had no effect on the cerebral blood flow but resulted in a very significant protection of hippocampal neurons. Significant improvement of survival was present during the initial 10 days postischemia. Due to subsequent deaths of animals treated acutely with CSC, the end-point mortality (14 days postischemia) in this group did not differ statistically from that seen in the controls. It is, however, possible that the late mortality in the acute CSC group was caused by the systemic effects of brain ischemia that are not subject to the treatment with this drug. Chronic treatment with APEC resulted in a statistically significant improvement in all studied measures. Although chronic treatment with CSC improved postischemic blood flow, its effect on neuronal preservation was minimal and statistically insignificant. Mortality remained unaffected. The results indicate that the acute treatment with adenosine A2A receptor antagonists may have a limited value in treatment of global ischemia. However, since administered CSC has no effect on the reestablishment of postischemic blood flow, treatment of stroke with adenosine A2A receptor antagonists may not be advisable. Additional studies are necessary to elucidate whether chronically administered drugs acting at adenosine A2 receptors may be useful in treatment of stroke and other neurodegenerative disorders.

Reduction of vasogenic edema and infarction by MK-801 in rats after temporary focal cerebral ischemia

Blood-brain barrier permeability alteration, vasogenic brain edema, and infarction, which are more extensive after 3 hours of temporary middle cerebral artery occlusion (MCAO) and 3 hours of reperfusion than after 6 hours of permanent MCAO, develop in rats after prolonged focal cerebral ischemia. Protective effects of excitatory amino acid receptor antagonists have been previously demonstrated after temporary global ischemia and permanent focal ischemia in rats. The purpose of this study was to evaluate the effectiveness of MK-801, a noncompetitive N-methyl-D-aspartate receptor antagonist, in temporary middle cerebral artery occlusion in rats maintained at physiological levels of brain temperature. Rats were anesthetized with chloral hydrate (350 mg/kg, intraperitoneally). The MCAO of rats was occluded by cannulation with a nylon suture for 3 hours, followed by 3 hours of reperfusion accomplished by withdrawing the suture. MK-801 (1 mg/kg, intravenously) or saline (S) was injected immediately before the onset of MCAO. Water content (MK-801, n = 6; S, n = 6), Evans blue dye extravasation (MK-801, n = 6; S, n = 6), infarct volume (MK-801, n = 10; S, n = 10), histology (MK-801, n = 6; S, n = 6), and neurological deficit (MK-801, n = 15; S, n = 18) were measured at the end of 3 hours of reperfusion. Brain temperature was monitored during the experiment. The infarction area (measured by 2, 3, 5-triphenyltetrazolium chloride staining) was reduced (P < 0.001) in the MK-801-treated rats, as was the infarct volume and the severity of neuronal damage (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Ketamine alters calcium and magnesium in brain tissue following experimental head trauma in rats

We previously reported that the N-methyl-D-aspartate receptor antagonists dizocilpine maleate and ketamine improved the neurological severity score (NSS) after head trauma in rats. Other investigators have reported increased calcium and decreased magnesium following head trauma in untreated rats. The present study was designed to determine whether ketamine influences the concentrations of calcium and magnesium in brain tissue following head trauma. Eighty-six male Sprague-Dawley rats (180 +/- 15 g) were divided into eight groups. Groups A (no head injury) and C (head injury) received no treatment. Groups B (no head injury) and D-H (head injury) received ketamine. In groups D, E, and F, ketamine, 180 mg/kg i.p., was given 1, 2, and 4 h after head trauma, respectively. In groups G and H, ketamine, 120 and 60 mg/kg, respectively, was given 1 h after head trauma. After we killed the rats at 48 h, cortical slices were taken to measure tissue calcium and magnesium content by the inductively coupled plasma atomic emission spectroscopy method. In the contused hemispheres, calcium increased and magnesium decreased (p < 0.0001). Among the head-injured groups, the increase in brain tissue calcium was smaller in groups receiving 60 mg/kg of ketamine at 1 h or 180 mg/kg of ketamine at 1, 2, or 4 h than in the group not receiving ketamine. The decrease in brain tissue magnesium was smaller in the groups receiving 180 mg/kg of ketamine at 1 and 2 h than in the group not receiving ketamine.(ABSTRACT TRUNCATED AT 250 WORDS)

MK-801 (dizocilpine) protects the brain from repeated normothermic global ischemic insults in the rat

We investigated the neuroprotective potential of MK-801 (dizocilpine), a noncompetitive N-methyl-D-aspartate (NMDA) antagonist, in the setting of three 5-min periods of global cerebral ischemia separated by 1-h intervals in halothane-anesthetized rats. Each ischemic insult was produced by bilateral carotid artery occlusions plus hypotension (50 mm Hg). Brain temperature was maintained at normothermic levels (36.5-37.0 degrees C) throughout the experiment. MK-801 (3 mg/kg) (n = 6) or saline (n = 6) was injected intraperitoneally 45 min following the end of the first ischemic insult. Following 7-day survival, quantitative neuronal counts of perfusion-fixed brains revealed severe ischemic damage in hippocampal CA1 area, neocortex, ventrolateral thalamus, and striatum of untreated rats. By contrast, significant protection was observed in MK-801-treated rats. In area CA1 of the hippocampus, numbers of normal neurons were increased 11- to 14-fold by MK-801 treatment (p < 0.01). The ventrolateral thalamus of MK-801-treated rats showed almost complete histologic protection, and neocortical damage was reduced by 71% (p < 0.01). The degree of MK-801 protection of striatal neurons was less complete than that seen in other vulnerable structures, amounting to 63% for central striatum (p = 0.02, Mann-Whitney U test) and 48% in the dorsolateral striatum (NS). A repeated-measures analysis of variance demonstrated a highly significant overall protective effect of MK-801 treatment (F1,10 = 37.2, p = 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

MRI and MRS studies on the time course of rat brain lesions and the effect of drug treatment: volume quantification and characterization of tissue heterogeneity by parameter selection

Magnetic resonance imaging has been used to follow the time course of lesions induced in the rat brain as an animal model for characterization of the volume of the lesion. The dispersion in spin-spin relaxation has been used to characterize the nature of the brain lesion. Parameter selective estimation of T2, quantitative determination of the lesion size and volume selective in vivo proton spectroscopy have been employed for the purpose. The work has been carried out on rats which were subject to lesioning by ibotenic acid as a model for excitotoxicity and also on rats which received doses of ibotenic acid and subsequent doses of the NMDA antagonist drug MK 801 (dizocilpine). The time course of the progress of the lesions in untreated animals and the effect of neuroprotection by MK 801 was continuously monitored in all test animals. Further, a relatively new inhalation anesthetic agent, isoflurane, has been employed. A more logical and semiquantitative T2 bandwidth demarkation useful in distinguishing different degrees of lesioning from the onset and up to the 'edema' stage through penumbra (mild lesion), medium degree lesion and severe lesion has been proposed.

Effects of intrathecal strychnine and bicuculline on nerve compression-induced thermal hyperalgesia and selective antagonism by MK-801

We studied the effects of intrathecally administered strychnine (STR; glycine antagonist; 10 or 30 micrograms) and bicuculline (BIC; GABAA antagonist 1 or 3 micrograms) on the thermal hyperalgesia which occurs following sciatic nerve constriction injury in rats. Following unilateral application of loose ligatures around the sciatic nerve, all rats typically displayed an ipsilateral thermal hyperalgesia on day 7. Intrathecal STR or BIC administered just after the nerve lesion and on days 1 and 2 after the nerve lesion significantly enhanced in a dose-dependent fashion the magnitude of the thermal hyperalgesia normally observed on day 7, as compared to intrathecal saline (for STR: 30 micrograms > 10 micrograms > or = saline; for BIC: 30 micrograms > 10 micrograms > or = saline, p < 0.05). Intrathecal MK-801, an N-methyl-D-aspartate antagonist, was without effect upon the response latency of the normal or sham operated paw, but selectively reversed the hyperalgesia. These results suggest that the loss of a spinal STR- and BIC-sensitive inhibition augments development of the hyperalgesia induced by chronic nerve compression.

MK-801 is neuroprotective but does not improve survival in severe forebrain ischemia

The effects of MK-801 on postischemic recovery, survival and neuronal preservation in the cortex, hippocampus and striatum were studied in Mongolian gerbils. The drug was administered 30 min prior to 20 of min forebrain ischemia induced by bilateral ligation of the carotids. Neurological recovery and survival were monitored for 7 days. At the end of the monitoring period neuronal damage was analyzed in the brains of the survivors in both groups. Treatment with MK-801 did not improve either neurological recovery or end-point survival. However, significant (P < 0.01) neuronal protection was observed in the hippocampi and striata of the drug treated animals while cortical neurons were not significantly protected. These findings demonstrate that protection against ischemic neuronal damage can be observed without concomitant improvement in either postischemic neurological recovery or survival. Protection of selectively vulnerable brain regions, often used as the predictor of the therapeutic potential of an agent, does not appear to correlate well with postischemic survival in this animal model of ischemia.

Hippocampal CA3 lesion prevents postconcussive metabolic dysfunction in CA1

Immediately following fluid-percussion (F-P) brain injury, the hippocampus exhibits a marked increase in its local CMRglc (LCMRglc; mumol/100 g/min) as determined using [14C]2-deoxy-D-glucose autoradiography. This injury-induced increase in metabolism is followed in 6 h by a subsequent decrease in LCMRglc. These two postinjury metabolic states may be the result of ionic disruptions following trauma via stimulation of glutamate-gated ion channels. To determine if endogenous glutamate innervation to the CA1 region of the hippocampus can provide an anatomical basis for this proposed mechanism, it was removed by kainic-acid-induced destruction of CA3, and the effect on CA1 metabolism following concussive injury was studied. Five days before a lateral F-P injury (3.5-4.5 atm), kainic acid (0.5 microgram) or vehicle was stereotaxically injected into the left ventricle of 65 rats. Histological inspection indicated that kainic acid produced severe cell loss primarily in the CA3 region of the hippocampus ipsilateral to the injection. The metabolic results indicated that immediately following injury, animals with an intact hippocampus exhibited an increase in LCMRglc to 84.6 +/- 5 within the CA1 region, representing a 81.5% increase over controls. However, in the CA3-lesioned animals, CA1 showed no evidence of an injury-induced hypermetabolism, with LCMRglc remaining at control levels (51.4 +/- 3.9). At 6 h postinjury, the intact hippocampus exhibited a reduction of LCMRglc to rates of 40.7 +/- 4.7 within the CA1 region, representing a 17.9% reduction compared with controls. In contrast, CA3-lesioned animals exhibited less of an injury-induced decrease in LCMRglc within the CA1 region, exhibiting a mean rate of 43.4 +/- 4.5, representing only a 12.5% reduction compared with controls. These results indicate that the removal of the CA3 projection to CA1 protects the CA1 cells from the metabolic dysfunction typically seen following injury. This supports our previous work indicating the important role glutamate plays in the ionic flux and subsequent metabolic changes that follow traumatic brain injury.

Protective effect of the NMDA antagonist MK-801 on photochemically induced spinal lesions in the rat

Photochemically induced ischemic lesions in the rat spinal cord were studied using neurological tests and morphological evaluation in order to investigate ischemia-mediated pathophysiological mechanisms in traumatic spinal cord injury. One week after ischemic lesioning, animals were severely impaired with 85% decrease of performance in neurological tests. During the next 2 weeks considerable recovery occurred. Pretreatment with the noncompetitive N-methyl-D-aspartate antagonist MK-801 at a dose of 0.5-1.0 mg/kg significantly improved the recovery of function after spinal ischemia while lower doses exerted no protection. Morphologically, no dose-response effect on the extent of tissue necrosis was found, but a significant difference between groups with severe neurological deficit versus mildly affected groups was observed. Immunohistochemical staining for glial fibrillary acidic protein in the area close to the lesion revealed extensive gliosis, while neurofilament immunohistochemistry showed an irregular pattern of fiber loss with large variability between animals. The degree of gliosis or loss of neurofilament immunoreactivity in nonnecrotic tissue was not affected by MK-801. These results suggest that excessive stimulation of N-methyl-D-aspartate receptors participates in the development of spinal cord ischemia and possibly also participates after traumatic spinal cord injury.

MK-801 prevents the post-ischemic cerebral hypoperfusion, but not the dysfunction of the vagal baroreflex in dogs

Pretreatment with MK-801, a non-competitive N-methyl-D-aspartate (NMDA) antagonist, failed to protect the vagal component of reflex bradycardia from 5-min global cerebral ischemia in dogs under pentobarbital anesthesia. On the other hand, MK-801 completely prevented the development of the post-ischemic cerebral hypoperfusion without affecting the cerebral blood flow in sham-operated animals. The results suggest that NMDA receptors may participate in the development of the secondary disturbance of the cerebral circulation, but are not involved in the post-ischemic dysfunction of the baroreflex system.

The acute effects of MK-801 on cerebral blood flow and tissue partial pressures of oxygen and carbon dioxide in conscious and alpha-chloralose anaesthetized rats

The dynamic effects of the non-competitive N-methyl-D-aspartate receptor antagonist, MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine] , on cerebral blood flow and tissue partial pressures of oxygen and carbon dioxide were investigated in the striatal and occipital regions of conscious and anaesthetized rats by mass spectrometry. MK-801 (0.5 and 5 mg/kg, i.p.) induced a large increase in the blood flow of both cerebral regions of conscious rats, without significant changes in local tissue partial pressures of oxygen and carbon dioxide. The increase in cerebral blood flow was maximal within 30 min after injection. Its amplitude was independent of the dose of MK-801, but cerebral blood flow remained elevated for up to 4 h after 5 mg/kg MK-801, while it progressively decreased towards its basal level in rats given 0.5 mg/kg MK-801. The amplitude and time-course of the vascular changes were similar in the two cerebral regions studied. The difference in the changes in tissue partial pressure of oxygen induced by MK-801 and by a 6% CO2 inhalation suggests that the MK-801-induced rise in cerebral blood flow in conscious rats is, at least partly, due to an increase in oxidative metabolism. In contrast, MK-801 induced either no changes or decreases in cerebral blood flow in alpha-chloralose-anaesthetized rats. The present results should be taken into account not only to determine the mechanisms by which N-methyl-D-aspartate receptor antagonists may exert their neuroprotective effects but also to further elucidate the sites of action of MK-801 in the central nervous system.

The effect of the NMDA receptor antagonist MK-801 on cerebral blood flow and infarct volume in experimental focal stroke

The non-competitive N-methyl-D-aspartate receptor/channel antagonist dizocilipine maleate (MK-801) has been reported to reduce infarct volume in a variety of focal stroke models. We examined the effect of MK-801 on infarct volume and cerebral blood flow in temporary and permanent focal ischemia in rats. In Wistar rats exposed to permanent right common carotid artery and 2 h of transient right middle cerebral and left common carotid artery occlusion followed by 22 h of reperfusion, MK-801 reduced infarct volume by 73% (P less than 0.05) and significantly increased cerebral blood flow to the ischemic core throughout the 2-h period of ischemia. In spontaneously hypertensive rats (SHRs) exposed to permanent right common carotid artery occlusion and 2 h of transient right middle cerebral artery occlusion followed by 22 h of reperfusion, MK-801 decreased infarct volume by 13% (P greater than 0.05) and increased cerebral blood flow to the penumbral region. In SHRs subjected to permanent right common carotid and middle cerebral artery occlusion MK-801 reduced infarct volume by 18% at 3 h (P greater than 0.05), by 25% at 6 h (P less than 0.01) and by 18% at 24 h (P less than 0.05). MK-801-treated SHRs had no difference in cerebral blood flow to the ischemic core, but increased cerebral blood flow to penumbral zones as compared with untreated SHRs. These results suggest that the protective effect of MK-801, at least in part, relates to improved cerebral blood flow.

Protection after transient focal cerebral ischemia by the N-methyl-D-aspartate antagonist dextrorphan is dependent upon plasma and brain levels

Dextrorphan is a dextrorotatory morphinan and a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist. We studied the dose response characteristics of dextrorphan's neuroprotective efficacy and side effects, correlating these beneficial and adverse responses with plasma and brain levels in a rabbit model of transient focal cerebral ischemia. Thirty-three rabbits, anesthetized with halothane, underwent occlusion of the left internal carotid and anterior cerebral arteries for 1 h, followed by 4.5 h of reperfusion. One hour after the onset of ischemia, they were treated with an i.v. infusion of varying dextrorphan doses or normal saline. After killing, the brains were analyzed for ischemic high signal intensity using magnetic resonance imaging (MRI) and for ischemic neuronal damage with histopathology. A separate group of 12 anesthetized ischemic rabbits received similar doses of dextrorphan, correlating plasma with brain dextrorphan levels. Twenty-six additional dextrorphan unanesthetized, nonischemic rabbits received infusions of dextrorphan to correlate behavioral side effects with dextrorphan dose and levels. Compared with controls, dextrorphan 15 mg/kg group had significantly less cortical ischemic neuronal damage (5.3 versus 33.2%, p = 0.01) and a reduction in cortical MRI high signal area (9.1 versus 41.2%, p = 0.02). The dextrorphan 10 mg/kg rabbits showed less cortical ischemic neuronal damage (27.2%) and less MRI high signal (34.8%) but this was not statistically significant (p = 0.6). Dextrorphan 5 mg/kg had no benefit on either neocortical ischemic neuronal damage (35.8%) or MRI high signal (42.9%). The protective effect of dextrorphan was correlated with plasma free dextrorphan levels (r = -0.50, p less than 0.02 for ischemic neuronal damage; r = -0.66, p less than 0.001 for ischemic MRI high signal). All the rabbits with plasma levels greater than 2,000 ng/ml had less than 12% cortical ischemic neuronal damage and less than 34% MRI high signal. All rabbits with plasma levels greater than 3,000 ng/ml showed less than 7% ischemic neuronal damage and less than 11% MRI high signal. Plasma levels of approximately 2,500 ng/ml correlated with brain dextrorphan levels of approximately 6,000 ng/g. Unanesthetized rabbits with plasma levels of approximately 2,500 ng/ml demonstrated loss of the righting reflex. These results demonstrate that systemic treatment with dextrorphan after 1 h focal ischemia can significantly protect against cerebral damage if adequate plasma and brain levels of dextrorphan are achieved. The brain levels necessary to obtain in vivo protection are similar to concentrations that prevent glutamate or NMDA-induced injury in neuronal culture.

The effects of a competitive NMDA receptor antagonist (CGS-19755) on cerebral blood flow and pH in focal ischemia

We report the effects of intravenous infusion of CGS-19755, a potent competitive N-methyl-D-aspartate (NMDA) antagonist, on local cerebral pH (LCpH) and local CBF (LCBF) in rats with occluded left middle cerebral and common carotid arteries. LCpH and LCBF were determined simultaneously by a double-label autoradiographic technique 4 h after vascular occlusion in three groups: no treatment, carrier infused, and a group receiving CGS-19755 at 10 mg/kg bolus immediately after occlusion followed by infusion at 5 mg kg-1 h-1 for 4 h. Compared with rats receiving carrier, several cortical structures on the side of occlusions showed significantly higher CBF in rats receiving CGS-19755. This drug also corrected the pH in several left cortical structures to values significantly higher than in the rats receiving carrier. The correction in LCpH was not limited to those regions showing significant elevations in LCBF. In the nonoccluded hemisphere, CGS-19755 significantly increased the hemispheric mean blood flow from 122 +/- 17 to 221 +/- 64 ml 100 g-1 min-1 (mean +/- SD of all structures, p less than 0.01) without any changes in LCpH. Cortical but not basal ganglia infarct volume was significantly smaller in rats receiving CGS-19755 than in the carrier-treated group. These results suggest that, at least partially, the neuroprotective effect of CGS-19755 in ischemia may be related to changes in CBF and pH in addition to its antagonist effect on the NMDA receptor.

Effects of dextromethorphan on regional cerebral blood flow in focal cerebral ischemia

Dextromethorphan (DM), a noncompetitive NMDA antagonist, has been demonstrated to reduce ischemic neuronal damage and edema, but DM's influence on cerebral blood flow has not been extensively studied. In this investigation, it is shown that DM has significant effects on regional cerebral blood flow (rCBF) patterns in a rabbit model of focal cerebral ischemia. rCBF was measured using radioactive microspheres following a 1 h permanent occlusion of the left internal carotid, anterior cerebral, and middle cerebral arteries in rabbits. Somatosensory evoked potentials (SEPs) were used to assess the degree of ischemia; only animals where SEPs were completely abolished were used for a frequency distribution analysis of rCBF. It was found that there were significantly more regions with lower flows in animals treated with normal saline (NS) (n = 7) compared to animals treated with DM (n = 7) (p less than 0.05, ipsilateral left side; p less than 0.001, contralateral right side). The frequency distribution medians were 27.5 ml 100 g-1 min-1 (left) and 70.0 ml 100 g-1 min-1 (right) in the NS group vs. 34.5 ml 100 g-1 min-1 (left) and 80.5 ml 100 g-1 min-1 (right) in the DM group. The left and right hemispheric regional means were 29.4 +/- 20 and 74.3 +/- 23 ml 100 g-1 min-1, respectively, in the NS group vs. 34.4 +/- 16 and 91.0 +/- 28 ml 100 g-1 min-1, respectively, in the DM group.(ABSTRACT TRUNCATED AT 250 WORDS)

The excitatory amino acid receptor antagonist MK-801 prevents the hypersensitivity induced by spinal cord ischemia in the rat

Protection by the NMDA receptor antagonist MK-801 against transient spinal cord ischemia-induced hypersensitivity was studied in rats. The spinal ischemia was initiated by vascular occlusion resulting from the interaction between the photosensitizing dye Erythrosin B and an argon laser beam. The hypersensitivity, termed allodynia, where the animals reacted by vocalization to nonnoxious mechanical stimuli in the flank area, was consistently observed during several days after induction of the ischemia. Pretreatment with MK-801 (0.1-0.5 mg/kg, iv) 10 min before laser irradiation dose dependently prevented the occurrence of allodynia. The neuroprotective effect of MK-801 was not reduced by maintaining normal body temperature during and after irradiation. There was a significant negative correlation between the delay in the administration of MK-801 after irradiation and the protective effect of the drug. Histological examination revealed slight morphological damage in the spinal cord in 38% of control rats after 1 min of laser irradiation without pretreatment with MK-801. No morphological abnormalities were observed in rats after pretreatment with MK-801 (0.5 mg/kg). The present results provide further evidence for the involvement of excitatory amino acids, through activation of the NMDA receptor, in the development of dysfunction following ischemic trauma to the spinal cord.

Effects of MK-801 on cerebral regional oxygen consumption in focal cerebral ischemia in rats

This investigation tested in rats whether MK-801, an N-methyl-D-aspartate receptor antagonist, would improve the balance of oxygen supply and consumption in the focal ischemic area of the brain induced by occlusion of the middle cerebral artery. Fifteen minutes after middle cerebral artery occlusion, 5 mg/kg MK-801 was administered intravenously to the MK-801 group (n = 12), and normal saline was given to the control group (n = 12). One hour after the occlusion in each group, regional cerebral blood flow was determined in six rats using [14C]iodoantipyrine, and regional arterial and venous oxygen saturations were determined using a microspectrophotometric technique in the other six rats. In both groups of animals, the cerebral blood flow of the ischemic cortex was significantly lower than that of the contralateral cortex (36 +/- 16 [SD] and 67 +/- 14 ml/min/100 g for the control group; 33 +/- 10 and 58 +/- 11 ml/min/100 g for the MK-801 group, respectively). Oxygen extraction was significantly higher in the ischemic cortex (8.8 +/- 2.1 ml O2/100 ml blood) than in the contralateral cortex (5.6 +/- 0.3) for the control group. However, for the MK-801 group, there was no significant difference between the ischemic cortex (6.1 +/- 1.0) and the contralateral cortex (5.7 +/- 1.1). Oxygen extraction in the ischemic cortex of the MK-801 group was significantly lower than that of the control group. Calculated ischemic regional oxygen consumption was similar to the nonischemic values in the control group, whereas the ischemic value was reduced to 61% of the value of the contralateral cortex in the MK-801 group.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of asphyxial brain damage, and possible pharmacologic interventions, in the fetus

An examination of the cellular and molecular mechanisms of neuronal cell damage may lead to the design of pharmacologic interventions during presumed or actual fetal asphyxia. Hypoxia-ischemia in its severest form results in insufficient adenosine 5'-triphosphate production. The most important effect of this is failure of adenosine 5'-triphosphate-dependent membrane functions, which maintain ionic homeostasis, that is, ionic pumping. There is K+ efflux and Na+ influx across the cell membrane, depolarization of the cell membrane, opening of the voltage-dependent calcium channels, and entrance of Ca++ into the cell. Cytosolic Ca++ is also increased by Ca++ efflux from the mitochondria and the sarcoplasmic reticulum. Ca++ is a toxin in high cytosolic concentrations; it activates phospholipases A and C, which cause membrane breakdown and release of free fatty acids, including arachidonic acid. The membrane is damaged, lysis occurs, and the neuron dies. High cytosolic Ca++ also causes release of excitatory amino acids (especially glutamate), which overwhelm the suppressant neurotransmitters, causing seizures, increased metabolism, and aggravation of the insufficient adenosine 5'-triphosphate availability. Thromboxane A2 is generated from arachidonic acid, increasing smooth muscle tone and thereby worsening the ischemia. Cyclooxygenase activity also results in formation of oxygen-free radicals that contribute to cell membrane damage, lysis, and death. Possibilities for pharmacologic interventions include (1) calcium channel blockers and antagonists, (2) excitatory neurotransmitter blockers, (3) oxygen-free radical scavengers (e.g., superoxide dismutase), (4) cyclooxygenase or prostaglandin synthesis inhibitors, and (5) seizure suppressants (e.g., phenobarbital). Some of these treatments have been shown experimentally to limit neuronal death in the adult and fetus, and after more investigative work they may be applicable to clinical practice.

Effects of dextromethorphan on rat brain during ischemia and reperfusion assessed by magnetic resonance spectroscopy

Using proton and phosphorus magnetic resonance spectroscopy, we evaluated the metabolic effects of preischemic administration of the N-methyl-D-aspartate antagonist dextromethorphan (50 mg/kg i.p.) during global forebrain ischemia and subsequent reperfusion in rats. Dextromethorphan-treated animals (n = 10) showed less lactate formation during ischemia than untreated animals (n = 11, p less than 0.001). During reperfusion, the lactate level in the treated group was reduced (p less than 0.05). Tissue pH declined less in the treated group during ischemia (p less than 0.01). There was no difference in the phosphocreatine/inorganic phosphate peak height ratio between groups. During ischemia, the N-acetylaspartate resonance peaks decreased in both groups. Histologic damage assessed in the hippocampal CA1 region 7 days after the ischemic insult was more severe in the untreated group (p less than 0.05). There was a significant correlation between end-ischemic tissue pH and hippocampal damage (r = -0.73, p less than 0.05). In the dextromethorphan-treated animals, 90% of the rats survived compared with 47% of the untreated animals (p less than 0.05). These results support findings in previous studies that dextromethorphan attenuates ischemic damage.