Dextromethorphan protects against cerebral injury following transient focal ischemia in rabbits

Dextromethorphan attenuates hypoxia-induced neuronal dysfunction in rat neocortical slices

We investigated the effects of the antitussive dextromethorphan (DM; 100 microM) on the extracellular DC potential, extracellular calcium concentration ([Ca2+]o) and on stimulus-evoked field potential (FP) responses in rat neocortical slices during hypoxia. DM significantly reduced the amplitude of the anoxic depolarization (AD) and the associated [Ca2+]o decrease by 47.6% and 48.5%, respectively, but did not change the onset latency and the duration of the AD. DM did not affect the preservation or recovery of excitatory synaptic transmission and significantly suppressed paired-pulse inhibition in the postanoxic recovery phase. These results indicate that DM exerts its potential neuroprotective action by reducing the hypoxia-induced depolarization and Ca2+ influx.

NBQX (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline) did not affect recovery of high energy phosphates and pH in early reperfusion in a rat model of transient forebrain ischemia. Or: an in vivo 31P NMR spectroscopy study

The new non-NMDA (N-methyl-D-aspartate) receptor antagonist NBQX (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline) has previously been shown to exert a neuroprotective effect in animal models of cerebral ischemia when administered in the post-ischemic phase. In this investigation the effect of NBQX on acidosis and energy recovery in early reperfusion after 10 min of transient forebrain ischemia with the 2-vessel occlusion model in the rat was studied with 31P NMR spectroscopy. In the intervention group the animals received a bolus dose of NBQX 30 mg.kg-1 i.v. at the start of reperfusion. 31P NMR spectroscopy was used to measure intracellular pH, ATP and phosphocreatine continuously in-vivo during, and after, the ischemic event. The recovery of high energy phosphates and pH was followed during 30 min of reperfusion. Pre-ischemic levels of phosphocreatine were reached after approximately 9-10 min in both groups. Although a slight improvement could be seen in the intervention group there was no significant difference in the rate of recovery between the two groups. ATP reached 90% of preischemic levels after about 8 min without significant difference between the two groups. With respect to the recovery of intracellular pH, no difference could be shown. Our results do not contradict previously published results, but suggest that the potential protective effect of NBQX is not mediated through improved recovery of energy metabolism in early reperfusion.

Protection against focal cerebral ischemia following exposure to a pulsed electromagnetic field

There is evidence that electromagnetic stimulation may accelerate the healing of tissue damage following ischemia. We undertook this study to investigate the effects of low frequency pulsed electromagnetic field (PEMF) exposure on cerebral injury in a rabbit model of transient focal ischemia (2 h occlusion followed by 4 h of reperfusion). PEMF exposure (280 V, 75 Hz, IGEA Stimulator) was initiated 10 min after the onset of ischemia and continued throughout reperfusion (six exposed, six controls). Magnetic resonance imaging (MRI) and histology were used to measure the degree of ischemic injury. Exposure to pulsed electromagnetic field attenuated cortical ischemia edema on MRI at the most anterior coronal level by 65% (P < 0.001). On histologic examination, PEMF exposure reduced ischemic neuronal damage in this same cortical area by 69% (P < 0.01) and by 43% (P < 0.05) in the striatum. Preliminary data suggest that exposure to a PEMF of short duration may have implications for the treatment of acute stroke.

Glutamate-mediated injury in focal cerebral ischemia: the excitotoxin hypothesis revised

Neuronal injury following focal cerebral ischemia is widely attributed to the excitotoxic effects of glutamate. However, critical analysis of published data on glutamate toxicity in vitro and the comparison of these data with in vivo release of glutamate and the therapeutic effect of glutamate antagonists raises doubts about a neurotoxic mechanism. An alternative explanation for glutamate-mediated injury is hypoxia due to peri-infarct spreading depression-like depolarizations. These depolarizations are triggered in the core of the ischemic infarct and spread at irregular intervals into the peri-infarct surrounding. In ischemically uncompromised tissue, the metabolic workload associated with spreading depression is coupled to an increase in blood flow and oxygen supply, assuring maintenance of oxidative respiration. In the penumbra region of focal ischemia, the hemodynamic constraints of collateral blood circulation prevail the adequate adjustment of oxygen delivery, leading to transient episodes of relative tissue hypoxia. The hypoxic episodes cause a suppression of protein synthesis, a gradual deterioration of energy metabolism and a progression of irreversibly damaged tissue into the penumbra zone. The generation of peri-infarct spreading depressions and the associated metabolic workload can be suppressed by NMDA and non-NMDA antagonists. As a result, the penumbral inhibition of protein synthesis and the progressing energy failure is also prevented, and the volume of ischemic infarct decreases. Interventions to improve ischemic resistance should therefore aim at improving the oxygen supply or reducing the metabolic workload in the penumbra region.

Do N-methyl-D-aspartate antagonists have disproportionately greater effects on brain swelling than on ischemic damage in focal cerebral infarction?

Using a frozen section technique, we have assessed the effects of N-methyl-D-aspartate (NMDA) antagonist upon brain swelling caused by ischemic brain edema in a rat model of focal cerebral infarction. Although pretreatment with the competitive NMDA antagonist, D-CPPene or the noncompetitive NMDA antagonist, CNS 1102 reduced both the volumes of infarction and ischemic edema in the cerebral hemisphere, mean reduction in brain edema was proportionately similar to decrease in infarct volume in the same animals (correlation coefficient, r = 0.82, p < 0.001). There was, therefore, no evidence of disproportionately greater effects with NMDA antagonist upon brain edema.

A review of brain retraction and recommendations for minimizing intraoperative brain injury

Brain retraction is required for adequate exposure during many intracranial procedures. The incidence of contusion or infarction from overzealous brain retraction is probably 10% in cranial base procedures and 5% in intracranial aneurysm procedures. The literature on brain retraction injury is reviewed, with particular attention to the use of intermittent retraction. Intraoperative monitoring techniques--brain electrical activity, cerebral blood flow, and brain retraction pressure--are evaluated. Various intraoperative interventions--anesthetic agents, positioning, cerebrospinal fluid drainage, operative approaches involving bone resection or osteotomy, hyperventilation, induced hypotension, induced hypertension, mannitol, and nimodipine--are assessed with regard to their effects on brain retraction. Because brain retraction injury, like other forms of focal cerebral ischemia, is multifactorial in its origins, a multifaceted approach probably will be most advantageous in minimizing retraction injury. Recommendations for operative management of cases involving significant brain retraction are made. These recommendations optimize the following goals: anesthesia and metabolic depression, improvement in cerebral blood flow and calcium channel blockade, intraoperative monitoring, and operative exposure and retraction efficacy. Through a combination of judicious retraction, appropriate anesthetic and pharmacological management, and aggressive intraoperative monitoring, brain retraction should become a much less common source of morbidity in the future.

A dose-response study of dextrorphan in permanent focal ischemia

The dose-response curve and time window of efficacy for dextrorphan in permanent focal brain ischemia leading to infarction was studied in the rat. With pretreatment, the maximum effective dose of 20 mg/kg reduced the eventual infarct volume by greater than 50%. Delayed drug administration, up to 45 min following permanent middle cerebral artery occlusion, significantly reduced infarct size.

Focal cerebral ischemia in the cat: pretreatment with a kappa-1 opioid receptor agonist, CI-977

The effects of the kappa-1 opioid receptor agonist (5R)-(5 alpha,7 alpha,8 beta)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro[4,5]dec-8-yl]-4- benzofuranacetamide monohydrochloride (CI-977) upon ischemic brain damage have been examined in 15 halothane-anesthetized cats. Focal cerebral ischemia was produced by permanent occlusion of one middle cerebral artery (MCA), and the animals killed 6 h later. The amount of early ischemic brain damage was assessed in coronal sections at 16 predetermined stereotactic planes. Pretreatment with CI-977 (0.3 mg/kg i.v. followed by continuous infusion at 0.15 mg/kg/h until death), initiated 15 min prior to MCA occlusion, significantly reduced the volume of ischemic brain damage (from 2345 +/- 675 mm3 of the cerebral hemisphere in vehicle-treated cats to 1569 +/- 370 mm3 in CI-977-treated cats; P < 0.01). These data indicate that the kappa-1 opioid agonist CI-977 is neuroprotective in a model of focal cerebral ischemia in a gyrencephalic species where key systemic variables have been assessed throughout the entire post-ischemic period.

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.

Changes in amino acid neurotransmitters and cerebral blood flow in the ischemic penumbral region following middle cerebral artery occlusion in the rat: correlation with histopathology

We simultaneously measured neurotransmitter amino acids by the microdialysis technique and cortical CBF by laser-Doppler flowmetry in the ischemic penumbral cortex of rats subjected to 2-h normothermic (36.5-37.5 degrees C) transient middle cerebral artery (MCA) clip-occlusion. Brains were perfusion-fixed 3 days later and infarct volume measured. CBF (% of preischemic values) fell to 32 +/- 2% (mean +/- SD) during ischemia and rose to 157 +/- 68% during recirculation. Extracellular glutamate levels increased from a baseline value of 7 +/- 3 microM to a peak value of 180 +/- 247 microM 20-30 min following onset of ischemia but subsequently returned to near baseline levels after 70 min of ischemia despite ongoing MCA occlusion. The threshold CBF for moderate glutamate release was 48%. Massive glutamate release was seen during the first 60 min of MCA occlusion in the two animals showing the largest infarcts and occurred at CBF values < or = 20% of control levels. Mean CBF during ischemia exhibited an inverse relationship with infarct volume, and the magnitude of glutamate release during ischemia was positively correlated with infarct volume. Extracellular gamma-aminobutyrate and glycine changes were similar to those of glutamate but showed no significant correlation with infarct volume. These results suggest that (a) accumulation of extracellular glutamate is an important determinant of injury in the setting of reversible MCA occlusion and (b) reuptake systems for neurotransmitter amino acids may be functional in the penumbra during transient focal ischemia.

Pharmacologic management of neonatal cerebral ischemia and hemorrhage: old and new directions

New developments in pharmacologic management of cerebral ischemia and hemorrhage are reviewed. A number of agents with diverse modes of action have now been shown to be neuroprotective in adult and neonatal animal models when administered either before or after a hypoxic-ischemic insult. As experience improves with these agents in hypoxic-ischemic injury and periventricular-intraventricular hemorrhage in human neonates, there is reason to be optimistic that effective neuroprotective strategies will soon be clinically available.

Efficacy of D-CPPene, a competitive N-methyl-D-aspartate antagonist in focal cerebral ischemia in the rat

The effect of a novel and potent competitive N-methyl-D-aspartate (NMDA) antagonist D-(E)-4-(3-phosphonoprop-2-enyl)piperazine-2-carboxylic acid (D-CPPene) upon ischemic brain damage has been examined in a rat model of focal cerebral ischemia. Focal cerebral ischemia was produced by permanent occlusion of the left middle cerebral artery (MCA). The animals were sacrificed 24 h after MCA occlusion and the amount of ischemic brain damage was assessed at 8 predetermined coronal planes. Pretreatment with D-CPPene (1.5, 4.5 or 15 mg/kg, i.v.), initiated 15 min prior to MCA occlusion (followed by constant infusion at 1, 3 or 10 mg/kg/h), produced dose-dependent reductions in the volumes of infarction; the dose of 4.5 mg/kg being the most effective (reduced by 37%; P < 0.01). These results indicate that systemic administration of the competitive NMDA antagonist D-CPPene has neuroprotective effects in a model of focal cerebral ischemia and define the dose dependency of its neuroprotective effects.

Inhibition of glutamate release in rat hippocampus by kynurenic acid does not protect CA1 cells from forebrain ischemia

We assessed the effect of a broad spectrum glutamatergic receptor antagonist, kynurenic acid (500 mg/kg) on ischemia-induced hippocampal glutamate release and neuronal damage. Kynurenic acid significantly decreased glutamate release during ischemia but had no effect on the hippocampal lesion. Some protection was observed in the cortex and in the striatum. These data suggested that the extracellular accumulation of glutamate during forebrain ischemia does not play a major role in the hippocampus.

Excitatory amino acid antagonists and their potential for the treatment of ischaemic brain damage in man

1. A wide range of therapeutic strategies has been explored in humans and experimental animals with the aim of improving outcome after brain ischaemia but few have shown convincing clinical benefit. 2. The massive increase in the extracellular concentration of glutamate which occurs in cerebral ischaemia is a key component in the sequence of neurochemical events which leads to neuronal death. Pharmacological blockade of the action of glutamate at the N-methyl-D-aspartate (NMDA) receptor, (the glutamate receptor subtype principally involved in the neurotoxic effects of the amino acid) provides a novel therapeutic approach to cerebral ischaemia. 3. The effects of NMDA receptor antagonists in animal models of focal cerebral ischaemia are uniquely consistent, viz, a marked reduction in the amount of irreversible ischaemic damage irrespective of the species, the model of cerebral ischaemia, when the animals are sacrificed after the ischaemic episode, whether ischaemia is permanent or temporary and followed by reperfusion and which particular NMDA antagonist was employed. 4. NMDA receptor antagonists have marked effects on brain function in normal animals. The balance between these potential adverse effects and the anti-ischaemic efficacy of these drugs will ultimately determine the clinical utility of this class of drugs. 5. The data which are reviewed provide the basis for the current clinical evaluation of NMDA receptor antagonists in stroke and head trauma.

The significance of brain temperature in focal cerebral ischemia: histopathological consequences of middle cerebral artery occlusion in the rat

The purpose of this study was to determine the effect of selective modulation of brain temperature in the experimental settings of permanent and reversible middle cerebral artery (MCA) occlusion in Sprague-Dawley rats. Three models of proximal MCA occlusion were used, in which the effect of brain-temperature modulations could be studied. These included (a) permanent MCA occlusion with an initial 30-min period of hypotension (30 or 36 degrees C x 4 h), (b) permanent MCA occlusion alone (30, 36, or 39 degrees C x 2 h), and (c) 2 h of reversible MCA occlusion (30, 36, or 39 degrees C x 2 h). In the transient MCA occlusion series, intra- and postischemic cortical blood flow was assessed using a laser-Doppler flowmeter placed over the dorsolateral cortex. After a 3-day survival, all rats were perfusion fixed for histopathological analysis and the determination of infarct volume. In animals with permanent MCA occlusion plus hypotension, no significant difference in infarct volume was demonstrated between the 30 and 36 degrees C groups. In rats with permanent MCA occlusion without hypotension, significant differences in infarct volume were again not demonstrable, but an interaction between infarct area and temperature class was shown by repeated-measures analysis, indicating that hypothermia altered the topographic pattern of the cortical infarct. With 2 h of reversible MCA occlusion, there was a statistically significant reduction in infarct volume in the 30 degrees C group compared to 39 degrees C rats. Although intra- and postischemic CBF were not significantly different among the three temperature groups, the cortical infarct volume was positively correlated with postischemic CBF. The postischemic CBF, in turn, was positively correlated to the intraischemic brain temperature and was negatively correlated to CBF during the ischemic period. These findings demonstrate that moderate manipulations of brain temperature have a greater influence on the resulting cortical infarction in the setting of transient focal ischemia than in the context of permanent vascular occlusion.

The effect of the kappa-opioid receptor agonist CI-977 in a rat model of focal cerebral ischaemia

The effect of a novel, highly potent and selective kappa-opioid receptor agonist CI-977 upon ischaemic brain damage and brain swelling has been examined in a rat model of focal cerebral ischaemia. Focal ischaemia was produced by the permanent occlusion of the left middle cerebral artery (MCA) during a brief period of halothane anaesthesia. The animals were sacrificed 24 h after MCA occlusion and the amount of ischaemic brain damage and swelling was assessed in coronal sections at 8 predetermined stereotactic planes. Treatment with CI-977 (0.03, 0.3 or 3 mg/kg), initiated 30 min prior to MCA occlusion (and at multiple times thereafter) produced dose-dependent reductions in the volumes of infarction and of brain swelling, with the most marked reductions being noted with CI-977 (0.3 mg/kg) in both infarction (reduced by 38% from controls; P less than 0.02) and swelling (reduced by 31%; P less than 0.002). There was an excellent correlation between the volume of brain swelling and ischaemic damage which was similar with saline-treated and CI-977-treated animals (overall correlation coefficient r = 0.896). These results indicate that CI-977 is effective in reducing infarction in a model of focal cerebral ischaemia, and that the reduction in brain swelling occurs in parallel with the reduction in ischaemic damage.

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.

Postischemic blockade of AMPA but not NMDA receptors mitigates neuronal damage in the rat brain following transient severe cerebral ischemia

Glutamatergic transmission is an important factor in the development of neuronal death following transient cerebral ischemia. In this investigation the effects of N-methyl-D-aspartate (NMDA) and non-NMDA receptor antagonists on neuronal damage were studied in rats exposed to 10 min of transient cerebral ischemia induced by bilateral common carotid occlusion combined with hypotension. The animals were treated with a blocker of the ionotropic quisqualate or alpha-amino-3-hydroxy-5-methyl-4-isoxazole (AMPA) receptor, 2.3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX), given postischemia as an intraperitoneal bolus dose of 30 mg kg-1 followed by an intravenous infusion of 75 micrograms min-1 for 6 h, or with the noncompetitive NMDA receptor blocker dizocilpine (MK-801) given 1 mg kg-1 i.p. at recirculation and 3 h postischemia, or with the competitive NMDA receptor antagonist DL-(E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid (CGP 40116), 5 mg kg-1, given intraperitoneally at recirculation. Treatment with NBQX provided a significant reduction of neuronal damage in the hippocampal CA1 area by 44-69%, with the largest relative decrease in the temporal part of the hippocampus. In neocortex a significant decrease in the number of necrotic neurons was also noted. No protection could be seen following postischemic treatment with dizocilpine or CGP 40116. Our data demonstrate that AMPA but not NMDA receptor antagonists decrease neuronal damage following transient severe cerebral ischemia in the rat and that the protection by NBQX may be dependent on the severity of the ischemic insult. We propose that the AMPA receptor-mediated neurotoxicity could be due to ischemia-induced changes in the control mechanisms of AMPA receptor-coupled processes or to changes of AMPA receptor characteristics.

Dextromethorphan alters cerebral blood flow and protects against cerebral injury following focal ischemia

The effects of the N-methyl-D-aspartate (NMDA) antagonist dextromethorphan (DM) on regional cerebral blood flow (rCBF) and cerebral injury were studied in a rabbit model of transient focal ischemia. Anesthetized rabbits underwent 2 h occlusion of the left internal carotid, middle cerebral and anterior cerebral artery, followed by 4 h of reperfusion. Ten minutes after the onset of ischemia they were treated with either i.v. DM 20 mg/kg followed by 10 mg/kg/h (n = 6) or normal saline (NS, n = 5). Control rabbits received DM (n = 3) or NS (n = 2) infusion without arterial occlusion. DM attenuated the sharp, post-ischemic rise in rCBF seen during reperfusion within the ischemic core of NS controls (DM 31% pre-ischemic value, NS 92%). DM also improved the delayed post-ischemic hypoperfusion compared with controls. DM infusion without arterial occlusion did not change rCBF values. Compared with NS controls, DM treated animals demonstrated recovery of the somatosensory evoked potential (DM 96% pre-ischemic values, NS 24%), 76% reduction in cortical edema and 92% decrease in cortical ischemic neuronal damage. We conclude that DM's effect on CBF may contribute to its neuroprotective action.

Neurocytotoxicity: pharmacological implications

Recent data suggest that brain damage in ischemia, hypoglycemia, and several other brain diseases is caused by excitotoxic mechanisms which are triggered by presynaptic release of glutamate and related excitatory amino acids, and which involve an abnormal postsynaptic influx of calcium into cells containing a high density of glutamate receptors. This contention is supported by results demonstrating reduction of infarct size in focal ischemia due to middle cerebral artery (MCA) occlusion, and amelioration of neuronal necrosis in hypoglycemic coma, by antagonist which block the NMDA type of glutamate receptor. These results underscore the pathogenetic role of calcium influx into energy-compromised cells since the NMDA receptor-linked ion channel has a high conductance to calcium. The issue has been clouded by the inability of NMDA antagonists to ameliorate brain damage due to cardiac arrest, or to forebrain ischemia in rats and gerbils. In these conditions, however, an AMPA receptor blocker (NBQX) has been found efficacious. These results demonstrate that the pathophysiology of ischemic lesions is different in the cardiac arrest type of ischemia and in lesions due to MCA occlusion, and demand an explanation of the differences in therapeutic response. Tentatively, the cardiac arrest type of ischemia is so dense that multiple calcium conductances are activated in the energy-deprived tissue, explaining why any drug which acts on only one of them (such as an NMDA antagonist) cannot prevent cellular calcium overload. Furthermore the ultimate brain damage, which is often conspicuously delayed, may be secondary to upregulation of synaptic efficacy, causing increased calcium cycling and calcium-related damage. In this situation, an AMPA receptor blocker may be efficacious because it blocks "fast" excitation and Na+ influx, an "upstream" event which causes "downstream" calcium influx via multiple pathways. In the perifocal ("penumbra") zone of a stroke lesion, the situation is different since depolarisation is initially moderate and/or intermittent. Furthermore, since ATP is still produced (albeit at a reduced rate) the problem is one of a disturbed pump/leak relationship. Then, blockade of a major calcium-carrying channel by NMDA receptor blockers, or of the trigger to depolarisation by an AMPA receptor antagonist, may improve the pump/leak relationship and carry cells in the penumbra over a critical period.

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.

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)

Focal cerebral ischemia in the cat: pretreatment with a competitive NMDA receptor antagonist, D-CPP-ene

The effects of the competitive N-methyl-D-aspartate (NMDA) receptor antagonist D-(E)-4-(3-phosphonoprop-2-enyl)piperazine-2-carboxylic acid (D-CPP-ene; SDZ EAA 494) upon ischemic brain damage have been examined in anesthetized cats. Focal cerebral ischemia was produced by permanent occlusion of the middle cerebral artery (MCA) and the animals were killed 6 h later. The amount of early ischemic brain damage was assessed in coronal sections at 16 predetermined stereotaxic planes. Pretreatment with D-CPP-ene (15 mg/kg i.v. followed by continuous infusion at 0.17 mg/kg/min until death), 15 min prior to MCA occlusion, significantly reduced the volume of ischemic brain damage (from 20.6 +/- 9.9% of the cerebral hemisphere in vehicle-treated cats to 7.2 +/- 4.4% in drug-treated cats; p less than 0.01). The competitive NMDA receptor antagonist D-CPP-ene is as effective as noncompetitive NMDA antagonists in reducing the amount of ischemic brain damage in this model of focal cerebral ischemia in a gyrencephalic species.

Stereotactic heavy-charged-particle Bragg-peak radiation for intracranial arteriovenous malformations

BACKGROUND

Heavy-charged-particle radiation has several advantages over protons and photons for the treatment of intracranial lesions; it has an improved physical distribution of the dose deep in tissue, a small angle of lateral scattering, and a sharp distal falloff of the dose.

METHODS

We present detailed clinical and radiologic follow-up in 86 patients with symptomatic but surgically inaccessible cerebral arteriovenous malformations that were treated with stereotactic helium-ion Bragg-peak radiation. The doses ranged from 8.8 to 34.6 Gy delivered to volumes of tissue of 0.3 to 70 cm3.

RESULTS

Two years after radiation treatment, the rate of complete obliteration of the lesions, as detected angiographically, was 94 percent for lesions smaller than 4 cm3, 75 percent for those of 4 to 25 cm3, and 39 percent for those larger than 25 cm3. After three years, the rates of obliteration were 100, 95, and 70 percent, respectively. Major neurologic complications occurred in 10 patients (12 percent), of whom 8 had permanent deficits. All these complications occurred in the initial stage of the protocol, before the maximal dose of radiation was reduced to 19.2 Gy. In addition, hemorrhage occurred in 10 patients from residual malformations between 4 and 34 months after treatment. Seizures and headaches were less severe in 63 percent of the 35 and 68 percent of the 40 patients, respectively, who had them initially.

CONCLUSIONS

Given the natural history of these inaccessible lesions and the high risks of surgery, we conclude that heavy-charged-particle radiation is an effective therapy for symptomatic, surgically inaccessible intracranial arteriovenous malformations. The current procedure has two disadvantages: a prolonged latency period before complete obliteration of the vascular lesion and a small risk of serious neurologic complications.

Protection by NMDA antagonists against selective cell loss following transient ischaemia

We have administered antagonists acting competitively or noncompetitively at the N-methyl-D-aspartate receptor after a short period of incomplete ischaemia and evaluated selective neuronal loss in the CA1 region of the rat hippocampus. The competitive antagonists D-(-)-2-amino-7-phosphonoheptanoate (2APH); 100 or 330 mg/kg; 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonate (CPP); 3.3 or 10 mg/kg; and CGS 19755 (cis-4-phosphonomethyl-2-piperidine carboxylate) 3.3 or 10 mg/kg; and the noncompetitive antagonists MK801 [+)5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate), 0.3, 1, or 3 mg/kg, and dextrorphan, 2, 6, 18, or 54 mg/kg, were administered intraperitoneally 15 min and 5 h after a 10-min incomplete ischaemia period; additionally MK801 (1 or 3 mg/kg) and CGS 19755 (10 or 30 mg/kg) were administered 5 and 10 h postischaemia. Seven days after ischaemia, the brains were fixed by perfusion. CA1 pyramidal cell counts were performed on Nissl-stained sections using an ocular grid piece. Ventilated (no ischaemia) control animals had a mean of 406 +/- 13 CA1 neurones/3 grid lengths. Ischaemia reduced this mean to 157 +/- 23. A significant protective effect against this cell loss was seen after two injections (at 15 min and 5 h postischaemia) of 2APH, CPP (10 mg/kg), CGS 19755 (10 mg/kg), MK801 (1 mg/kg), and dextrophan (54 mg/kg). Delayed injection (5 and 10 h postischaemia) of CGS 19755 (10 and 30 mg/kg) and MK801 (1 and 3 mg/kg) did not provide any protection against pyramidal cell loss.

Ischemic flow threshold for extracellular glutamate increase in cat cortex

Extracellular glutamate (Glu), cerebral blood flow (CBF), and auditory-evoked potentials (AEPs) were measured concurrently using microdialysis and hydrogen clearance in the auditory cortex of anesthetized cats during global ischemia of various severities. A threshold-type relationship was observed between extracellular Glu and CBF: Glu increased at CBF levels below about 20 ml/100 g/min. The Glu increase was related to the impairment of AEPs. The results suggest that Glu neurotoxicity is an important factor for ischemic neuronal injury even in penumbra.

Pretreatment with the NMDA antagonist dextrorphan reduces cerebral injury following transient focal ischemia in rabbits

We studied the efficacy of systemic pre-treatment with dextrorphan (DX), a clinically tested N-methyl-D-aspartate (NMDA) antagonist, in a rabbit model of transient focal cerebral ischemia. Rabbits were treated with either a 24 mg/kg i.v. loading dose followed by 12 mg/kg/h i.v. infusion of 0.48% DX in normal saline (NS), or with an equivalent volume of NS alone. One and 1/2 h after starting the drug or NS, the rabbits underwent a 1 h occlusion of the left internal carotid and anterior cerebral arteries, followed by 4 h of reperfusion. The DX-treated rabbits had significantly less neocortical ischemic neuronal damage (7.4%) than the normal saline group (31.6%) and demonstrated a significant decrease in ischemic cortical edema. DX may prove useful in the treatment of clinical cerebrovascular disease.

Non-competitive N-methyl-D-aspartate antagonists protect against sound-induced seizures in DBA/2 mice

Non-competitive antagonists of the N-methyl-D-aspartate (NMDA) receptor have been evaluated as anticonvulsants against sound-induced seizures in DBA/2 mice. The ED50 values for protection against sound-induced clonic seizures 15 min following the intracerebroventricular (i.c.v.) and intraperitoneal (i.p.) administration are: MK-801, ED50 = 0.5 nmol (i.c.v.); 0.14 mumol/kg (i.p.); phencyclidine, ED50 = 14 nmol (i.c.v.); 1.9 mumol/kg (i.p.); dextrorphan, ED50 = 35 nmol (i.c.v.); 18.5 mumol/kg (i.p.); tiletamine, ED50 = 40 nmol (i.c.v.); 5.6 mumol/kg (i.p.); SKF-10047, ED50 = 50 nmol (i.c.v.); 23.5 mumol/kg (i.p.); dextromethorphan, ED50 = 70 nmol (i.c.v.); 28.0 mumol/kg (i.p.); ketamine, ED50 = 110 nmol (i.c.v.); 15.5 mumol/kg (i.p.). The anticonvulsant effects of ketamine and tiletamine are of short duration (10-30 min), whereas the anticonvulsant effects of MK-801 and dextromethorphan last for 45 min or longer. The effects of phencyclidine, SKF-10047 and dextrorphan are of intermediate duration. Mild to moderate behavioural excitation is associated with the anticonvulsant activity of all the non-competitive NMDA antagonists. For MK-801, phencyclidine, dextrorphan, SKF-10047 and ketamine there is a close correlation between their relative anticonvulsant potencies and their potencies for displacing [3H]MK-801. The anticonvulsant effect is likely to be primarily mediated via NMDA antagonism at the PCP/MK-801 site.