Nimodipine pretreatment improves cerebral blood flow and reduces brain edema in conscious rats subjected to focal cerebral ischemia

Review : Neuroprotection in Brain Ischemia: An Update (Part II

Ischemic brain injury produced by stroke or cardiac arrest is a major cause of human neurological disability. Steady advances in the neurosciences have elucidated the pathophysiological mechanisms of brain ischemia and have suggested many therapeutic approaches to achieve neuroprotection of the acutely ischemic brain that are directed at specific injury mechanisms. In the second portion of this two-part review, the following potential therapeutic approaches to acute ischemic injury are considered: 1) modulation of nonglutamatergic neurotransmission, including monoaminergic systems (dopamine, norepinephrine, serotonin), γ-aminobutyric acid, and adenosine; 2) mild-to-moderate therapeutic hypothermia; 3) calcium channel antagonism; 4) an tagonism of oxygen free radicals; 5) modulation of the nitric oxide system; 6) antagonism of cytoskeletal proteolysis; 7) growth factor administration; 8) therapy directed at cellular mediators of injury; and 9) the rationale for combination pharmacotherapy. The Neuroscientist 1:164-175, 1995

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.

Venous thrombosis in children

Venous thromboembolic (VTE) events are being increasingly diagnosed in systemic and cerebral vessels in children. Systemic VTE are increasing in children as a result of therapeutic advances and improved clinical acumen in primary illnesses that previously caused mortality. The epidemiology of systemic VTE has been studied in international registries. In children older than 3 months, teenagers are the largest group developing VTE. The most common etiologic factor is the presence of central venous lines. Clinical studies have determined the most sensitive diagnostic method for diagnosing upper system VTE are ultrasound for jugular venous thrombosis and venography for intrathoracic vessels. However, the most sensitive diagnostic methods for lower system VTE and pulmonary embolism (PE) have not been established. Treatment studies for VTE consist of inadequately powered randomized controlled trials or prospective cohort studies. The long-term outcome of systemic VTE, post-thrombotic syndrome, has been reported in children. Cerebral sinovenous thrombosis (CSVT) is becoming increasingly diagnosed in children due to the recognition of the associated subtle clinical symptoms and improved cerebrovascular imaging. The etiology of CSVT includes thrombophilia, head and neck infections, and systemic illness. Estimates of the incidence and outcome of childhood CSVT have recently become available through the Canadian Pediatric Ischaemic Stroke Registry. Clinical studies have not yet been carried out in children to determine the best method of diagnosis or treatment. There have only been case-series studies carried out in the treatment of CSVT. Properly designed clinical trials are urgently required in children with systemic VTE/PE and CSVT to define the best methods of diagnosis, treatment and long-term management.

Effects of brain oedema in the measurement of ischaemic brain damage in focal cerebral infarction

In a model of focal cerebral ischaemia, enlargement of ischaemic tissue by ischaemic brain oedema is one of the major problems in the measurement of infarction volume. To minimize an error of this overestimation, several methods have been proposed. However, there has been no attempt to compare these methods to elucidate their eligibility in the measurement of ischaemic area. The authors used three different morphometric analyses in the measurement of infarction volume to assess the antiischaemic affects of a competitive NMDA antagonist, D-CPPene in MCA occlusion model of the rat: a direct measurement, the Swanson's method, and a measurement using a diagram. Post-occlusion treatment of D-CPPene (4.5 mg/kg, i.v. +3 mg/kg/h, i.v.) produced reduction of infarction volume to about 40% compared to the control (P < 0.05). The volume of infarction determined by the direct measurement was much larger than that by Swanson's or diagram method (P < 0.05), about 70% larger in the control and by two times in the treated. However, there was no significant difference in the measured volume between the Swanson's and diagram methods. The protection rate, which was calculated as % = (infarct volume of the control--that of the treated/infarct volume of the control) x 100%, was larger in the Swanson's and diagram methods than in the direct measurement. In conclusion, it is confirmed that the direct measurement at the peak time of ischaemic brain oedema brings about not only an overestimation of infarction volume but lower protection rate also, compared to the methods designed to minimize the overestimation. Our results also demonstrate the diagram method is useful in reducing overestimation of infarct volume that may be caused by ischaemic brain oedema, though this method was not designed for the purpose of avoiding oedema at first.

Mild traumatic brain injury in sports: neuropsychology's contribution to a developing field

Mild traumatic brain injuries are common at all levels of athletic competition. Although once considered a "routine part of the game," a significant amount of attention has recently been placed on these injuries at the professional, college, and high school levels. This paper reviews the epidemiology of sports-related brain injuries, the pathophysiology of the injuries, and the role of neuropsychology in this newly emerging area. Issues related to the adequacy of neuropsychological test instruments and approaches are discussed in light of future directions for research.

Hyperbaric oxygen reduces infarct volume in rats by increasing oxygen supply to the ischemic periphery

OBJECTIVE

Hyperbaric oxygen (HBO) increases oxygen supply to anoxic areas. To examine the therapeutic effect of HBO on ischemic stroke, we measured infarct volume as well as cerebral blood flow (CBF), oxygen supply, and lipid peroxidation in the ischemic periphery.

DESIGN

Prospective experimental study in rats.

SETTING

Experimental laboratory in a university teaching hospital.

SUBJECTS

Thirty-eight adult rats.

INTERVENTION

The rats were anesthetized (1% halothane) and intubated. Focal ischemia was induced by ligating the right middle cerebral and right common carotid arteries. Nineteen animals were exposed to 2 hrs of HBO (100% oxygen, 3 atmospheres absolute), initiated 10 mins after the onset of ischemia. The remaining animals were kept at ambient pressure and used as controls.

MEASUREMENTS AND MAIN RESULTS

At the initiation of ischemia, CBF measured by a laser-Doppler flow probe placed in the ischemic periphery was reduced to 47%+/-11% and 51%+/-15% of normal levels in animals exposed or not to HBO, respectively. These altered values were not affected further by administration of HBO and remained stable throughout a 2-hr observation period. Arterial oxygen pressure and content were significantly increased to 1571+/-130 torr (209.41+/-17.32 kPa; p < .0001) and 1.03+/-0.04 mmol/dL (p < 0.0001), respectively, in HBO-treated animals compared with nontreated animals (139+/-14 torr [18.53+/-1.87 kPa] and 0.86+/-0.04 mmol/dL, respectively). The calculated increase in the oxygen supply to the ischemic periphery was 20%. The infarct volume of HBO-treated animals measured 24 hrs after the onset of focal cerebral ischemia was significantly reduced by 18% (HBO-treated, 132+/-13 mm3 vs. nontreated, 161+/-29 mm3; p = .02). Lipid peroxidation was unchanged after 120 mins of HBO administration in the cerebral cortex where the laser-Doppler flow probe was placed.

CONCLUSIONS

HBO at 3 atmospheres absolute reduced infarct volume by increasing oxygen supply to the ischemic periphery without aggravating lipid peroxidation, suggesting that HBO can be useful in treating stroke victims.

Investigation of estrogen status and increased stroke sensitivity on cerebral blood flow after a focal ischemic insult

Recently the authors have shown that female stroke-prone spontaneously hypertensive rats (SHRSPs) in proestrus (high endogenous estrogen), sustain more than 20% smaller infarcts after middle cerebral artery occlusion (MCAO) compared with SHRSPs in metestrus (low endogenous estrogen). Because estrogen has vasodilator properties, the authors investigated whether the estrous state influences cerebral blood flow (CBF) after MCAO. CBF was measured 2.5 hours after a distal MCAO by [14C]iodo-antipyrine autoradiography in conscious SHRSPs either in metestrus or in proestrus. There were no significant differences in CBF when analyzed either at predetermined anatomic regions or by cumulative distribution analysis of areas with flow <25 mL/100 g/min. As a positive internal control, the authors compared results in SHRSPs with those in their normotensive reference strain, Wistar Kyoto rat. SHRSPs displayed more severe and widespread ischemia than Wistar Kyoto rats. Thus, the absence of demonstrable CBF differences between estrous states appears to be unrelated to the CBF measurement paradigm. In conclusion, the smaller infarct size afforded in proestrus in SHRSPs is unlikely to be due to an influence on CBF.

Ischemic cell death in brain neurons

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell death occurs by a necrotic pathway characterized by either ischemic/homogenizing cell change or edematous cell change. Death also occurs via an apoptotic-like pathway that is characterized, minimally, by DNA laddering and a dependence on caspase activity and, optimally, by those properties, additional characteristic protein and phospholipid changes, and morphological attributes of apoptosis. Death may also occur by autophagocytosis. The cell death process has four major stages. The first, the induction stage, includes several changes initiated by ischemia and reperfusion that are very likely to play major roles in cell death. These include inhibition (and subsequent reactivation) of electron transport, decreased ATP, decreased pH, increased cell Ca(2+), release of glutamate, increased arachidonic acid, and also gene activation leading to cytokine synthesis, synthesis of enzymes involved in free radical production, and accumulation of leukocytes. These changes lead to the activation of five damaging events, termed perpetrators. These are the damaging actions of free radicals and their product peroxynitrite, the actions of the Ca(2+)-dependent protease calpain, the activity of phospholipases, the activity of poly-ADPribose polymerase (PARP), and the activation of the apoptotic pathway. The second stage of cell death involves the long-term changes in macromolecules or key metabolites that are caused by the perpetrators. The third stage of cell death involves long-term damaging effects of these macromolecular and metabolite changes, and of some of the induction processes, on critical cell functions and structures that lead to the defined end stages of cell damage. These targeted functions and structures include the plasmalemma, the mitochondria, the cytoskeleton, protein synthesis, and kinase activities. The fourth stage is the progression to the morphological and biochemical end stages of cell death. Of these four stages, the last two are the least well understood. Quite little is known of how the perpetrators affect the structures and functions and whether and how each of these changes contribute to cell death. According to this description, the key step in ischemic cell death is adequate activation of the perpetrators, and thus a major unifying thread of the review is a consideration of how the changes occurring during and after ischemia, including gene activation and synthesis of new proteins, conspire to produce damaging levels of free radicals and peroxynitrite, to activate calpain and other Ca(2+)-driven processes that are damaging, and to initiate the apoptotic process. Although it is not fully established for all cases, the major driving force for the necrotic cell death process, and very possibly the other processes, appears to be the generation of free radicals and peroxynitrite. Effects of a large number of damaging changes can be explained on the basis of their ability to generate free radicals in early or late stages of damage. Several important issues are defined for future study. These include determining the triggers for apoptosis and autophagocytosis and establishing greater confidence in most of the cellular changes that are hypothesized to be involved in cell death. A very important outstanding issue is identifying the critical functional and structural changes caused by the perpetrators of cell death. These changes are responsible for cell death, and their identity and mechanisms of action are almost completely unknown.

Current concepts. Concussion in sports

This is a special report of the findings of the Concussion Workshop, sponsored by the AOSSM in Chicago in December 1997. Here follows a listing of the members of the workshop: Julian Bailes, MD, American Association of Neurological Surgeons; Arthur Boland, MD, AOSSM; Charles Burke III, MD, National Hockey League; Robert Cantu, MD, American College of Sports Medicine; Letha “Etty” Griffin, MD, National Collegiate Athletic Association; David Hovda, PhD, Neuroscientist, UCLA School of Medicine; Mary Lloyd Ireland, MD, American Academy of Orthopaedic Surgeons; James Kelly, MD, American Academy of Neurology; Greg Landry, MD, American Academy of Pediatrics; Mark Lovell, PhD, Neuropsychology Specialist, Henry Ford Health Systems; James Mathews, MD, American College of Emergency Physicians; Michael McCrea, PhD, Neuropsychology Specialist, Waukesha Memorial Hospital; Douglas McKeag, MD, American Medical Society for Sports Medicine; Dennis Miller, ATC, National Athletic Trainers Association; Jeffrey Minkoff, MD, AOSSM; Stephen Papadopoulus, MD, Congress of Neurological Surgeons; Elliott Pellman, MD, National Football League; Richard Quincy, MS, PT, ATC, Sports Physical Therapy, El Pomar Sports Center; Herbert Ross, DO, American Osteopathic Academy of Sports Medicine; Bryan Smith, MD, National Collegiate Athletic Association; and Edward Wojtys, MD, Workshop Chairman, AOSSM.

The views in this report do not necessarily represent the views of the entire group comprising the Concussion Workshop Group.

Nimodipine and perfusion changes after stroke

BACKGROUND AND PURPOSE

Meta-analysis of previous trials of oral nimodipine in acute stroke has suggested a benefit when commenced within 12 hours of onset. We sought to study the effect of oral nimodipine on reperfusion after acute stroke and the relation between reperfusion and outcome.

METHODS

Fifty patients with acute middle cerebral artery territory cortical infarction were blindly randomized within 12 hours of onset to either oral nimodipine (30 mg every 6 hours) or placebo. Treatment was continued for 2 weeks. Cerebral blood flow was assessed with the use of 99mTc-hexamethylpropyleneamine oxime single-photon emission CT before therapy, 24 hours later, and at 3 months. Hypoperfusion was measured by a validated volumetric technique. Neurological impairment and functional outcome were assessed with the Canadian Neurological Scale and Barthel Index, respectively. Tissue loss was measured with CT at 3 months. Four patients were excluded from analysis for technical reasons.

RESULTS

Twenty-three patients received nimodipine, and 23 received placebo. In the nimodipine group, there was early reperfusion that was not maintained at outcome (P=0.01). In the placebo group, mean infarct hypoperfusion volumes showed no overall change. Nonnutritional reperfusion in nimodipine-treated patients was associated with adverse neurological (P=0.05) and functional outcome (P=0.06). There was, however, no difference in clinical outcome between the 2 groups.

CONCLUSIONS

Oral nimodipine administered within 12 hours enhanced acute reperfusion, but this was largely nonnutritional. Larger studies using a shorter treatment delay are required to evaluate the clinical efficacy of nimodipine in acute ischemic stroke.

Mechanisms of motor dysfunction after transient MCA occlusion: persistent transmission failure in cortical synapses is a major determinant

BACKGROUND AND PURPOSE

Failure of prompt motor recovery after spontaneous recirculation or thrombolytic therapy may be due to an unsatisfactory restoration of synaptic activity within cortex and/or blockade of electrical impulses at the severely ischemic subcortical region.

METHODS

Afferent, efferent, and synaptic activities were focally examined within the rat sensorimotor cortex by recording the somatosensory-evoked potential (SEP) and motor area response evoked by stimulation of premotor afferents (PmEP) intracortically and the motor-evoked potential (MEP) generated by stimulation of the forelimb area from the brain stem. The effect of ischemia on electrical activity in the cortex and on axonal conduction in the subcortical region was studied differentially by proximal or distal occlusion of the MCA.

RESULTS

MEP consisted of direct and indirect waves generated by direct activation of pyramidal axons and indirect excitation of pyramidal neurons via cortical synapses, respectively. MEP, PmEP, and SEP disappeared on proximal occlusion. Following reperfusion after 1 to 3 hours of ischemia, the direct wave of MEP readily recovered but the indirect wave showed no improvement, suggesting a restored axonal conduction but impaired cortical synaptic transmission. The synaptic defect, which also caused a poor recovery in PmEP and SEP and on electrocorticogram, was persistent and detected 24 hours after 1 hour of proximal occlusion.

CONCLUSIONS

Our data suggest that motor dysfunction is caused by loss of cortical excitability and blockade of motor action potentials at the subcortical level during ischemia. After brief transient ischemia, axonal conduction readily recovers; however, a persistent transmission failure at cortical synapses leads to motor dysfunction.

Effects of treatment with nilvadipine on cerebral ischemia in rats

The protective effects of a Ca2+ antagonist, nilvadipine, on focal cerebral ischemia were studied in male spontaneously hypertensive rats. The animals received either nilvadipine (3mg x kg(-1) x day(-1)) or a vehicle subcutaneously. Group 1 (n=11) was treated for 7 days, and Group 2 (n=11) for 14 days. The middle cerebral artery was occluded on the 6th (Group 1) or 13th (Group 2) day of the treatment, and neuropathological outcomes were quantified 24 hours later. The mean arterial blood pressure was significantly reduced with nilvadipine to normal levels. The % infarct volumes of Groups 1 (37+/-2) and 2 (34+/-3) were significantly less than those of their controls (39+/-3 [n=11] and 40+/-4 [n=12], respectively), although the difference between Groups 1 and 2 was not significant. When infarct areas were compared in each of 8 coronal sections, the infarct size had decreased in the 5 posterior sections in Group 2, but only in 2 sections of Group 1. A significant decrease in the edema volumes was observed in Group 2, but not in Group 1. Thus, nilvadipine provided protective effects against cerebral ischemia in rats having chronic hypertension, and the effects were dependent on the duration of treatment.

Augmented neuronal death in CA3 hippocampus following hyperventilation early after controlled cortical impact

Minimizing secondary injury after severe traumatic brain injury (TBI) is the primary goal of cerebral resuscitation. For more than two decades, hyperventilation has been one of the most often used strategies in the management of TBI. Laboratory and clinical studies, however, have verified a post-TBI state of reduced cerebral perfusion that may increase the brain's vulnerability to secondary injury. In addition, it has been suggested in a clinical study that hyperventilation may worsen outcome after TBI.

OBJECT

Using the controlled cortical impact model in rats, the authors tested the hypothesis that aggressive hyperventilation applied immediately after TBI would worsen functional outcome, expand the contusion, and promote neuronal death in selectively vulnerable hippocampal neurons.

METHODS

Twenty-six intubated, mechanically ventilated, isoflurane-anesthetized male Sprague-Dawley rats were subjected to controlled cortical impact (4 m/second, 2.5-mm depth of deformation) and randomized after 10 minutes to either hyperventilation (PaCO2 = 20.3 +/- 0.7 mm Hg) or normal ventilation groups (PaCO2 = 34.9 +/- 0.3 mm Hg) containing 13 rats apiece and were treated for 5 hours. Beam balance and Morris water maze (MWM) performance latencies were measured in eight rats from each group on Days 1 to 5 and 7 to 11, respectively, after controlled cortical impact. The rats were killed at 14 days postinjury, and serial coronal sections of their brains were studied for contusion volume and hippocampal neuron counting (CA1, CA3) by an observer who was blinded to their treatment group. Mortality rates were similar in both groups (two of 13 in the normal ventilation compared with three of 13 in the hyperventilation group, not significant [NS]). There were no differences between the groups in mean arterial blood pressure, brain temperature, and serum glucose concentration. There were no differences between groups in performance latencies for both beam balance and MWM or contusion volume (27.8 +/- 5.1 mm3 compared with 27.8 +/- 3.3 mm3, NS) in the normal ventilation compared with the hyperventilation groups, respectively. In brain sections cut from the center of the contusion, hippocampal neuronal survival in the CA1 region was similar in both groups; however, hyperventilation reduced the number of surviving hippocampal CA3 neurons (29.7 cells/hpf, range 24.2-31.7 in the normal ventilation group compared with 19.9 cells/hpf, range 17-23.7 in the hyperventilation group [25th-75th percentiles]; *p < 0.05, Mann-Whitney rank-sum test).

CONCLUSIONS

Aggressive hyperventilation early after TBI augments CA3 hippocampal neuronal death; however, it did not impair functional outcome or expand the contusion. These data indicate that CA3 hippocampal neurons are selectively vulnerable to the effects of hyperventilation after TBI. Further studies delineating the mechanisms underlying these effects are needed, because the injudicious application of hyperventilation early after TBI may contribute to secondary neuronal injury.

SNX-111, a novel, presynaptic N-type calcium channel antagonist, is neuroprotective against focal cerebral ischemia in rabbits

Cytosolic Ca2+ overload has been proposed as a main cause of neuronal injury during cerebral ischemia. SNX-111, a synthetic product of the naturally occurring omega-conotoxin MVIIA, is a novel, presynaptic N-type Ca2+ channel antagonist and has been reported to be neuroprotective against cerebral ischemia. We studied the neuroprotective effects of SNX-111 in a rabbit model of focal cerebral ischemia. New Zealand white male rabbits (2.5-3.5 kg) were given 1 mg/kg/h i.v. SNX-111 (n=8) or normal saline (n=8) 10 min after onset of a 2-h period of transient focal cerebral ischemia induced by occlusion of the left middle cerebral, anterior cerebral and internal carotid arteries followed by 4 h reperfusion. SNX-111 significantly attenuated overall cortical ischemic neuronal damage by 44% (saline, 38.7+/-3.0%; SNX-111, 21.5+/-6.0%, P<0.05) and regions of hyperintensity on T2-weighted MRI by 30% (saline, 70.6+/-4.0%; SNX-111, 49.3+/-11.0%, P<0.05). No significant difference in (regional cerebral blood flow) rCBF or MAP (mean arterial blood pressure) was found between SNX-111- and saline-treated rabbits suggesting that neuroprotection is due to a cellular effect. We conclude that SNX-111 reduces ischemic injury in this model. Its use as a clinical neuroprotective agent for cerebrovascular surgery or stroke should be investigated further.

Identification of calcium channels involved in neuronal injury in rat hippocampal slices subjected to oxygen and glucose deprivation

The presynaptic Ca2+-influx affecting glutamate release during neuropathological processes is mediated via voltage-sensitive calcium channels (VSCCs). There is controversy, however, over the fractional contribution of the specific channel types involved. We have addressed this by investigating the protective effects of various VSCC blockers on oxygen and glucose-deprived rat hippocampal slices. The viability of treated and non-treated slices was assayed electrophysiologically by measuring the evoked population spike (PS) amplitude in the stratum pyramidale of the CA1 region and by imaging slices loaded with fluorochrome dyes specific for dead (ethidium homodimer) and live (calcein) cells using confocal microscopy. PS amplitudes were significantly (P < 0.01) depressed from 4.4 +/- 0.2 mV (n = 38) to 0.2 +/- 0.1 mV (n = 40) after the deprivation insult. Responses from deprived slices treated with omega-conotoxin MVIIC (100 nM; 4.2 +/- 0.5 mV; n = 20) were not significantly different from control, non-deprived slice responses. In contrast, deprived slices treated with either L-type (0.1 or 1 microM nimodipine) or N-type (0.1 or 3 microM omega-conotoxin MVIIA) blockers showed no significant protection. The viability of CA1 neurons as revealed by the fluorescence live/dead confocal viability assay was consistent with the electrophysiological measurements. By comparison with previous studies using P- and Q-type blockers to attempt neuroprotection against the same deprivation insult, the rank order in which specific Ca2+-channel types contribute to neuronal death due to oxygen and glucose deprivation was determined to be Q > N >> P > L.

Time-course and treatment response with SNX-111, an N-type calcium channel blocker, in a rodent model of focal cerebral ischemia using diffusion-weighted MRI

Diffusion-weighted magnetic resonance imaging (DWI) is capable of noninvasively imaging acute cerebral ischemia. We demonstrate the utility of this technique by evaluating SNX-111, a novel N-type calcium channel blocker with potential neuroprotective properties, in a rodent model of transient focal ischemia. Twenty-four Sprague-Dawley rats weighing between 310-350 g underwent occlusion of the middle cerebral artery (MCAO) for 105 min followed by 22.5 h of reperfusion. Thirty minutes following MCAO, animals were randomized to receive SNX-111 5 mg/kg intravenously over 1 h vs. placebo. DWI and T2-weighted MRIs (T2W) were performed at 0.5, 1.5 and 24 h after the onset of ischemia. Area fractions of increased signal intensity on the DWI and T2W images were measured. DWI area fractions at 1.5 and 24 h were also normalized to the initial, pre-treatment scans. Apparent diffusion coefficients (ADC) were calculated from fitted maps. Tri-phenyl tetrazolium chloride (TTC) staining was performed on brains at 24 h and infarct area fractions were measured. SNX-111 treated animals showed significantly improved 1.5-h DWI scan ratios compared to controls (ratios of 1.06 +/- 0.25 vs. 2.98 +/- 0.78 SNX vs. controls respectively, P < 0.05). A trend toward improved DWI ratios was seen by 24 h in the SNX-111 group (2.5 +/- 0.75 vs. 4.12 +/- 1.6, N.S.) DWI, T2W and TTC area fractions at 24 h also showed trends favoring a neuroprotective effect of SNX-111. Bright areas on DWI corresponded to ADC decreases of about 30% compared to the non-ischemic hemisphere. These decreases were the same in both treatment groups and at each time point. DWI, T2W and TTC area fractions at 24 h were strongly correlated (r = 0.98, DWI and TTC; r = 0.99, T2W and TTC; r = 0.97, T2W and DWI, P < 0.0001). We conclude that in this ischemic model, SNX-111 provides early neuroprotection and that serial DWI is a useful way of demonstrating this.

The effects of gamma 2-melanocyte-stimulating hormone and nimodipine on cortical blood flow and infarction volume in two rat models of middle cerebral artery occlusion

We observed that the pro-opiomelanocortin-derived neuropeptide, gamma 2-melanocyte-stimulating hormone (gamma 2-MSH), has various peripheral and central hemodynamic effects in the rat, including a marked enhancing effect on cerebral blood flow. This hemodynamic profile might be of interest in the pharmacotherapeutic approach to acute cerebral ischemia. Being an adrenocorticotropin (ACTH) analogue, gamma 2-MSH might also possess direct neuronal protective properties. Therefore, in two rat models of focal cerebral ischemia we studied the effects of gamma 2-MSH, with nimodipine, a Ca2+ channel antagonist, as a reference compound, on parasagittal laser-Doppler-assessed cortical blood flow and infarction volume. In isoflurane-anesthetized Wistar and F344 rats i.v. bolus infusions (four in total) of gamma 2-MSH or nimodipine or their vehicle controls were given 1 h before, 1 min after, and 1 h and 2 h after occlusion of the middle cerebral artery. We used both an intravasal and an extravasal middle cerebral artery occlusion technique because pilot experiments had shown differences in the severity of ischemia with the two techniques. gamma 2-MSH (100 nmol/kg in 1 min) increased cortical blood flow significantly but transiently, both pre- and post-ischemically, whereas nimodipine (20 micrograms/kg in 1 min) increased cortical blood flow only pre-ischemically in both models of middle cerebral artery occlusion. gamma 2-MSH had no effect on cortical and striatal infarction volume, while nimodipine caused a significant reduction of cortical infarction volume in the extravasal middle cerebral artery occlusion model. To conclude, despite its hemodynamic and possible neuroprotective properties, gamma 2-MSH did not prevent ischemic neuronal damage after middle cerebral artery occlusion in rats. This might be partly due to the short half-life of the peptide, leading to a transient increase in cortical blood flow and short neuronal exposure time, suggesting that prolonged infusion of the neuropeptide might be required. The results with nimodipine support the notion that it attenuates cortical ischemic damage, independently of effects on cerebral hemodynamics.

Treatment of focal cerebral ischemia with synthetic oligopeptide corresponding to lectin domain of selectin

BACKGROUND AND PURPOSE

Synthetic oligopeptides with amino acid sequences of the lectin domain of selectin block selectin-mediated cell adhesion in vitro, which may be applied to a therapeutic intervention to attenuate acute inflammatory reactions. To evaluate the efficacy of such treatment against ischemic brain injury, the effects of administering a selectin oligopeptide that selectively blocks selectin-mediated cell adhesion on histological outcome and on cerebral blood flow (CBF) were studied in models of rodent focal cerebral ischemia.

METHODS

Spontaneously hypertensive rats were anesthetized with halothane. Permanent focal cerebral ischemia was induced by tandem left middle cerebral artery (MCA) and common carotid artery (CCA) occlusion. Focal cerebral ischemia with partial reperfusion was introduced by reperfusing the CCA after 2 hours of tandem MCA/CCA occlusion. A synthetic oligopeptide (amino acid residues 23-30 from N terminal) of E-selectin was dissolved in physiological saline and was injected intravenously at a dosage of 2 mg/kg or 10 mg/kg before artery occlusion. Control animals received equivalent volumes of physiological saline or 10 mg/kg of synthetic oligopeptide with a scrambled amino acid sequence. Twenty-four hours after the occlusion, seven coronal brain slices were stained with 2,3,5-triphenyltetrazolium chloride, and the volume of ischemic injury was calculated. In a separate set of animals, regional CBF was monitored with laser-Doppler flowmetry at the dorsolateral cerebral cortex during 2-hour ischemia and 30 minutes after partial reperfusion.

RESULTS

The volume of ischemic injury did not differ among groups in permanent ischemia. In ischemia with partial reperfusion, 10 mg/kg selectin oligopeptide, but not the same dosage of scrambled oligopeptide, significantly reduced the volume of ischemic injury (95 +/- 13, 73 +/- 11, 55 +/- 6, and 111 +/- 14 mm3 for saline [n = 11]; 2 mg/kg [n = 10] and 10 mg/kg [n = 16] selectin oligopeptide and 10 mg/kg scrambled oligopeptide [n = 6], respectively; P < .01 by one-way ANOVA followed by the Tukey test). Laser-Doppler flowmetry demonstrated a larger increase in CBF after reperfusion of the CCA in the 10-mg/kg selectin oligopeptide group.

CONCLUSIONS

Our data demonstrate that administration of a synthetic oligopeptide corresponding to the lectin domain of selectin decreases the size of ischemic injury after transient, but not after permanent, focal cerebral ischemia as evaluated at 24 hours after onset of ischemia. These effects were associated with an improved CBF at the dorsolateral cerebral cortex after partial reperfusion.

Ischemia and lesion induced imbalances in cortical function

Cortical structures are often critically affected by ischemic and traumatic lesions which may cause transient or permanent functional disturbances. These disorders consist of changes in the membrane properties of single cells and alterations in synaptic network interactions within and between cortical areas including large-scale reorganizations in the representation of the peripheral input. Prominent functional modifications consisting of massive membrane depolarizations, suppression of intracortical inhibitory synaptic mechanisms and enhancement of excitatory synaptic transmission can be observed within a few minutes following the onset of cortical hypoxia or ischemia and probably represent the trigger signals for the induction of neuronal hyperexcitability, irreversible cellular dysfunction and cell death. Pharmacological manipulation of these early events may therefore be the most effective approach to control ischemia and lesion induced disturbances and to attenuate long-term neurological deficits. The complexity of secondary structural and functional alterations in cortical and subcortical structures demands an early and powerful intervention before neuronal damage expands to intact regions. The unsatisfactory clinical experience with calcium and N-methyl-D-aspartate antagonists suggests that this result might be achieved with compounds that show a broad spectrum of actions at different ligand-activated receptors, voltage-dependent channels and that also act at the vascular system. Whether the same therapy strategies developed for the treatment of ischemic injury in the adult brain may be applied for the immature cortex is questionable, since young cortical networks with a high degree of synaptic plasticity reveal a different response pattern to hypoxic and ischemic insults. Age-dependent molecular biological, morphological and physiological parameters contribute to an enhanced susceptibility of the immature brain to these noxae during early ontogenesis and have to be investigated in more detail for the development of adequate clinical therapy.

Imidazoline receptor agonist drugs: a new approach to the treatment of systemic hypertension

The imidazoline receptors have recently been discovered to be involved in central nervous system control of blood pressure (I-1 receptor) and in neuroprotection for cerebral ischemia (I-2 receptor). A new class of central-acting antihypertensive agents has been developed, the imidazoline receptor agonists (rilmenidine and moxonidine), which control blood pressure effectively without the adverse effects of sedation and mental depression that are usually associated with central-acting antihypertensives. This new generation of central-acting antihypertensive agents are highly selective for the imidazoline receptor, while having a low affinity for alpha 2-adrenergic receptors.

Severe controlled cortical impact in rats: assessment of cerebral edema, blood flow, and contusion volume

Controlled cortical impact (CCI) is a contemporary model of experimental cerebral contusion. We examined the cerebrovascular and neuropathologic effects of a severe CCI in rats. The utility of magnetic resonance imaging (MRI) for the assessment of contusion volume after severe CCI was also established. Severe CCI (3.0 mm depth, 4 m/sec velocity) to the left (L) parietal cortex was produced in anesthetized (isoflurane/N2O/O2), intubated, and mechanically ventilated male Sprague-Dawley rats (n = 58). Physiologic parameters were controlled. The time course of alterations in edema [L-R% brain water (% BW) in 3-mm coronal sections through injured and contralateral hemispheres, wet-dry weight] was evaluated at 2 h, 24 h, 48 h, and 7 days posttrauma. Local cerebral blood flow (ICBF, measured in 8 structures in each hemisphere by autoradiography) was evaluated at 2 h, 24 h, and 7 days. Contusion volume (measured by histology and image analysis) was assessed at 14 days and measured in 6 rats by both MRI and histology. The survival rate after severe CCI was 96.2%. The L-R difference in % BW increased to 1.69 +/- 0.18% at 2 h, 3.00 +/- 0.08% at 24 h, 2.69 +/- 0.09% at 48 h, and 0.94 +/- 0.21% at 7 days. These values all differed from the control (p < 0.05). The % BW was greater at 24 h and 48 h than at 2 h and 7 days (p < 0.05). Marked reductions in ICBF were limited to structures in the injured hemisphere and were observed in the parietal cortex (2 and 24 h), subcortical white matter (2 and 24 h), and hippocampus (2 h), (p < 0.05) vs control rats. In the contusion core, ICBF was 19.4 +/- 8.8 mL 100 g-1 min-1 at 24 h (p = 0.011 vs normal). Necrosis was seen in large portions of the parietal cortex and subcortical white matter, and portions of the hippocampus and thalamus. Contusion volume was 47.8 +/- 9.2 mm3, which represented 14.4 +/- 2.1% of the traumatized hemisphere. Estimates of contusion volume by MRI and histology were closely correlated (r = 0.941, p < 0.017). Severe CCI in rats is accompanied by contusion, reproducible edema, and marked hypoperfusion, involving over 14% of the injured hemisphere, and can be produced with minimal mortality. T2-weighted MRI successfully and noninvasively identifies contusion volume in this model.

Basic fibroblast growth factor increases regional cerebral blood flow and reduces infarct size after experimental ischemia in a rat model

BACKGROUND AND PURPOSE

The aim of this study was to ascertain whether basic fibroblast growth factors (bFGF) caused reduction in size of cerebral infarcts in Sprague-Dawley rats with experimental ischemia.

METHODS

In the first experiment we induced permanent occlusion of the left middle cerebral artery (MCA). Within 5 minutes after MCA occlusion, we infused bFGF (100 ng in 0.1 mL of saline) in the bFGF-treated group (n = 14) and 0.1 mL of saline alone in the control group (n = 7) into the common carotid artery ipsilateral to MCA occlusion. We harvested the brains 24 hours after MCA occlusion and determined infarct size planimetrically as a percentage of hemisphere size. In the second experiment cerebral blood flow (CBF) was continuously measured for 120 minutes after MCA occlusion in the bFGF-treated group (n = 9) and in the control group (n = 8) with the use of laser-Doppler flowmetry.

RESULTS

Infarct size in the bFGF-treated group decreased significantly in comparison with that in the control group (repeated-measures ANOVA, P < .0001). CBF in the transitional areas between the MCA and the anterior cerebral artery significantly increased in the bFGF-treated group in comparison with that in the control group (repeated-measures ANOVA, P < .005). An approximate 58% decrease in infarct size and a 40% increase in regional CBF were seen on bFGF treatment.

CONCLUSIONS

The present study suggested that intracarotid administration of bFGF (100 ng) can reduce infarct size after MCA occlusion. It was speculated that the increased CBF in the penumbral areas of MCA may contribute to contraction of infarct size.

The effect of chlormethiazole on neuronal damage in a model of transient focal ischaemia

1. The effect of chlormethiazole has been studied in a transient middle cerebral artery (MCA) occlusion model of cerebral ischaemia in the rat. The MCA was occluded for 1 h by use of an intraluminal suture technique, with reperfusion for 24 h following removal of the occluding filament. Neuronal damage was determined by measurement of the area of necrosis following Cresyl Violet staining of sections taken through the ischaemic region. 2. In the initial experiment, occlusion of the MCA produced a large volume of ischaemic damage in both cortex and striatum, characterized by necrosis and pyknosis (total volume of damage, 287 +/- 13 mm3, n = 9). Rats injected with chlormethiazole (1000 mumol kg-1, i.p.) 60 min before occlusion had a reduced volume of damage in both regions (104 +/- 11 mm3; n = 9; P < 0.001). 3. In a subsequent study systemic physiological parameters (heart rate, blood pressure, blood pH, blood gases and rectal temperature) were measured throughout the ischaemic period. 4. Chlormethiazole (1000 mumol kg-1) pretreatment produced little change in systemic physiology and the neuroprotective effect of the drug when given 60 min prior to the MCA occlusion was confirmed. Chlormethiazole was also neuroprotective when given 10 min following the start of reperfusion (control group: 244 +/- 52 mm3, n = 10; chlormethiazole pretreatment group: 102 +/- 23 mm3, n = 10; P < 0.001; chlormethiazole post-ischaemia group: 122 +/- 16 mm3; P < 0.001, n = 10). 5. It is concluded that chlormethiazole is an effective neuroprotective agent in this model of transient focal ischaemia. The observation that chlormethiazole is protective when given after reperfusion indicates that the effect of the drug is unlikely to be due to an alteration of intra-ischaemic cerebral blood flow, but is more probably a direct effect on the development of ischaemic damage.

A photothrombotic 'ring' model of rat stroke-in-evolution displaying putative penumbral inversion

BACKGROUND AND PURPOSE

To facilitate reproducible and rigorous study of a tissue zone at risk of encroaching ischemic damage, we propose a new model in which the potentially compromised tissue lies within rather than perifocal to an ischemic locus. The perimeter of the "zone at risk" is defined by a photothrombotically produced cortical lesion in the shape of a toroid (or "ring").

METHODS

The exposed crania of erythrosin B-injected rats were irradiated with a 514.5-nm laser beam, configured as a 5-mm-diameter ring, to yield a ring-shaped lesion caused by photochemically induced platelet occlusion of cortical vasculature. Developing perfusion deficits in the interior region were revealed by carbon black infusion. Tissue damage and infarct volumes were assessed by light and electron microscopy, and blood-brain barrier integrity was assessed with Evans blue dye and horseradish peroxidase as tracers.

RESULTS

For rats injected with 17 mg/kg erythrosin B and irradiated for 2 minutes with a ring beam intensity of 0.92 W/cm2 (beam power of 65 mW), carbon black infusion at times up to 4 hours demonstrated a shallow cortical ring lesion encircling a fully patent zone at risk, which by 24 hours evinced an essentially complete perfusion deficit. At times up to 24 hours, the ring lesion was penetrated at the pial surface by distal branches of the middle cerebral and anterior cerebral arteries. Stereotaxically based histopathological assessment showed that by 24 hours the lesion spanned the cortical thickness. Lesion volume increased from 14.5 +/- 8.0 mm3 (mean +/- SD) (n = 8) to 46.2 +/- 15.6 mm3 (n = 8) between 4 and 24 hours after irradiation (P < .01), but the anteroposterior lesion diameter did not change significantly between 4 hours (6.00 +/- 1.03 mm; n = 9) and 24 hours (6.75 +/- 1.15 mm; n = 9).

CONCLUSIONS

The present model of slowly developing but inevitable cortical tissue death in a sequestered area should facilitate more precise observations of the evolution of tissue metabolic responses, from the impending onset of ischemia to the threshold of irreversible damage. This system may prove efficient for evaluating treatments intended to salvage a penumbral region.

Protection of focal ischemic infarction by rilmenidine in the animal: evidence that interactions with central imidazoline receptors may be neuroprotective

Rilmenidine and idazoxan reduce the volume of focal ischemic infarctions produced by occlusion of the middle cerebral artery in the rat by 33% and 29%, respectively, by preserving neurons within the ischemic penumbra. In contrast, the alpha 2-selective antagonist SKF-86466 is without effect. The neuroprotective action of rilmenidine is dose dependent and parallels its antihypertensive actions. Neuroprotection cannot be attributed to changes in cerebral blood flow. We conclude that the neuroprotection produced by rilmenidine is attributable to an interaction with imidazoline receptors (IRs). However, the mechanism of action is not obvious. If it results from an action within the penumbra (direct), it is mediated by mitochondrial I-2 receptors on astrocytes, since cortical neurons are devoid of IRs. Neuroprotection might occur by selectively stimulating Ca2+ uptake into astrocytes, and thereby reducing Ca2+ uptake into neurons. Alternatively, rilmenidine may act indirectly to activate pathways in the brain that are neuroprotective. Neuroprotection may be a therapeutic target for rilmenidine and allied agents that act at central IRs.

Effects of neutropenia on edema, histology, and cerebral blood flow after traumatic brain injury in rats

Neutrophils accumulate during the acute inflammatory response to brain injury, but their role in the injury process remains controversial. We tested the hypothesis that neutrophils contribute to cerebral edema, tissue injury, and disturbed cerebral blood flow (CBF) (hyperemia or ischemia) during the first 24 h after traumatic brain injury. Wistar rats (n = 51) were injected with either vinblastine sulfate to induce neutropenia or the saline vehicle. Five days later, under halothane anesthesia, right hemispheric trauma was produced by weight drop (10 g x 5 cm) onto exposed dura. At 24 h after trauma, brain water (wet-dry weight), traumatic infarct size (percent of hemispheric section infarcted), or local CBF (lCBF, 14C-iodoantipyrine autoradiography) was assessed. Vinblastine treatment produced profound neutropenia on the day of trauma (absolute neutrophil count 0.024 +/- 0.008 x 10(9)/L vs 1.471 +/- 0.322 x 10(9)/L, p < 0.05 in neutropenic vs saline, respectively, mean +/- SEM). Neutropenia did not reduce the development of brain edema in the injured hemisphere (brain water 82.38 +/- 0.29% vs 82.73 +/- 0.37% in neutropenic and saline, respectively, mean +/- SEM) or traumatic infarct size (34.5 +/- 3.3% vs 33.2 +/- 2.1% in neutropenic vs saline respectively). In contrast, neutropenic rats exhibited 52%, 41%, and 57% reductions in lCBF in the frontal cortex, parietal cortex, and amygdala, respectively, of the injured hemisphere 24 h after trauma (all p < 0.05 vs nonneutropenic controls). These data suggest that neutrophils and the acute inflammatory process contribute to the level of CBF observed 24 h after trauma, but effects on edema or early posttraumatic infarct size could not be demonstrated.

Laser Doppler flowmetry of focal ischaemia and reperfusion in deep brain structures in rats

Monitoring cerebral blood flow during focal ischaemia and reperfusion with established techniques such as hydrogen clearance and autoradiography is difficult. Laser Doppler flowmetry is a new technique, it allows one to continuously measure blood flow in small tissue samples. The objective of this study was to compare laser Doppler flowmetry with hydrogen clearance using a new single fiber probe to obtain measurements in deep brain structures and then to show the temporal profile of cerebral blood flow during focal ischaemia and after reperfusion. First, the single fiber laser Doppler method was compared with the hydrogen clearance method in ten Wistar rats. Second, focal cerebral ischaemia was induced in fifteen Wistar rats using a model of middle cerebral artery occlusion based on the intravascular insertion of a nylon suture; reperfusion occurred after withdrawal of the suture. The laser Doppler probe was placed in the lateral caudatoputamen, and local cerebral blood flow was measured continuously before and during occlusion as well as after reperfusion. The relative blood flow values obtained by the laser Doppler method and the hydrogen clearance method showed a good correlation (r = 0.76) and a linear relationship. A rapid decrease in laser Doppler flowmetry to 42 +/- 16% of former baseline values was seen with occlusion of the middle cerebral artery; during occlusion cerebral blood flow remained at this level. Reperfusion resulted in a heterogeneous pattern of cerebral blood flow as laser Doppler flowmetry values ranged from 25% to 134% of baseline values. The effects of middle cerebral artery occlusion and reperfusion on cerebral blood flow can be monitored on-line with laser Doppler flowmetry.(ABSTRACT TRUNCATED AT 250 WORDS)

L-arginine infusion promotes nitric oxide-dependent vasodilation, increases regional cerebral blood flow, and reduces infarction volume in the rat

BACKGROUND AND PURPOSE

We previously reported that L-arginine infusion increased pial vessel diameter by nitric oxide-dependent mechanisms, improved regional cerebral blood flow (rCBF) distal to middle cerebral artery (MCA) occlusion, and reduced infarction volume in spontaneously hypertensive rats when administered intraperitoneally before and after MCA occlusion. In this report we extend our findings (1) by examining the time course of L-arginine on rCBF and pial vessel diameter under basal conditions and on rCBF after MCA occlusion and (2) by reproducing the protective effect of L-arginine on infarct volume when given intravenously immediately after the onset of MCA occlusion in both normotensive and hypertensive models of focal cerebral ischemia.

METHODS

Changes in pial vessel diameter (closed cranial window) and rCBF (laser-Doppler flowmetry) were measured over time after L-arginine infusion into anesthetized Sprague-Dawley rats. rCBF was also measured distal to MCA occlusion in a brain region showing rCBF reductions in the range of 80% of baseline. The effects of infusing L-arginine (300 mg/kg for 10 minutes beginning 5 minutes after occlusion) were assessed on infarction volume in Sprague-Dawley rats after proximal MCA occlusion and in spontaneously hypertensive rats after common carotid artery plus distal MCA occlusion.

RESULTS

L-Arginine (300 mg/kg IV) elevated rCBF by 20% when measured in the dorsolateral cortex of Sprague-Dawley rats and caused L-nitroarginine-methyl ester-inhibitable increases in pial vessel diameter. L-Arginine (> or = 30 mg/kg IV) increased blood flow distal to MCA occlusion by 50%. These effects were sustained throughout the observation period (70 to 105 minutes). Changes in mean arterial blood pressure were not observed. L-Arginine (300 mg/kg IV) reduced infarction volume by 35% and 28% in Sprague-Dawley and spontaneously hypertensive rats, respectively, when examined 24 hours after vessel occlusion.

CONCLUSIONS

These studies extend our previous findings by demonstrating that exogenous L-arginine induces sustained rCBF increases in normal brain as well as in a marginally perfused brain region distal to MCA occlusion. Our data in Sprague-Dawley rats support the conclusion that L-arginine-induced increases in rCBF can decrease infarction volume. We conclude that nitric oxide-mediated mechanisms increase rCBF and decrease infarction volume after MCA occlusion in both normotensive and hypertensive animals.

(S)-emopamil attenuates acute reduction in regional cerebral blood flow following experimental brain injury

We examined the effects of (S)-emopamil, a phenylalkylamine calcium channel blocker with serotonin receptor antagonist properties, on regional cerebral blood flow (rCBF) following experimental brain injury in the rat. Animals were subjected to fluid percussion brain injury of moderate severity (2.1 atm), and received (S)-emopamil (20 mg/kg, i.p., n = 10) or saline (n = 10) at 20 minutes postinjury and 2.5 hours after the first injection of the drug. Consecutive rCBF measurements were performed: (1) prior to injury, (2) 15 minutes, (3) 90 minutes, and (4) 4 hours postinjury, using the radiolabeled microsphere technique. Brain injury produced an acute and significant reduction of rCBF at 15 minutes postinjury in all the regions examined (p < 0.05). At 90 minutes postinjury, rCBF remained significantly depressed in the forebrain regions. All brain regions showed a recovery of rCBF to normal by 4 hours following injury in saline-treated animals, with the exception of injured left parietal cortex and bilateral hippocampi, where rCBF remained significantly depressed. A significant attenuation of the trauma-induced reduction in rCBF was observed at 70 minutes after the first administration of (S)-emopamil in the forebrain regions and cerebellum (p < 0.05). Following the second (S)-emopamil injection, the significant improvement in rCBF observed in left injured cortex was maintained. These results suggest that (S)-emopamil may be efficacious in reversing post-traumatic alterations in rCBF, which may contribute to the post-traumatic pathophysiologic sequelae.

Effect of the kappa-1 opioid agonist CI-977 on ischemic brain damage and cerebral blood flow after middle cerebral artery occlusion in the rat

The effects of the kappa-1 opioid agonist CI-977 upon the volume of ischemic brain damage (defined using quantitative neuropathology) and local cerebral blood flow (CBF) (defined using quantitative [14C]iodoantipyrine autoradiography) have been examined at 4 h and 30 min, respectively, after permanent middle cerebral artery (MCA) occlusion in halothane-anesthetised rats. Treatment with CI-977 (0.3 mg/kg, s.c.) 30 min before and 30 min after occlusion of the MCA reduced the volume of infarction in the cerebral hemisphere (reduced by 27% when compared to vehicle; P < 0.05) and cerebral cortex (reduced by 32%; P < 0.05), despite a marked and sustained hypotension, with only minimal effect on damage in the caudate nucleus. In the hemisphere contralateral to the occluded MCA, treatment with CI-977 (0.3 mg/kg, s.c.) 30 min prior to the induction of ischemia failed to demonstrate any significant effect on either the level of local CBF in any of the 25 regions examined or on the volume of low CBF determined by frequency distribution analysis. In the hemisphere ipsilateral to MCA occlusion, CI-977 failed to produce statistically significant alterations in either the level of local CBF in 23 of the 25 regions or on the volume of low CBF, but areas of hyperemia were observed in both the medial caudate nucleus and lateral thalamus (local CBF increased by 65% and 86%, respectively, when compared to vehicle).(ABSTRACT TRUNCATED AT 250 WORDS)

Magnetic resonance imaging findings associated with cardiac arrest

BACKGROUND AND PURPOSE

The frequency and prognostic significance of neuroradiological findings after cardiac arrest are unknown. Using healthy volunteers as control subjects, we studied the magnetic resonance imaging (MRI) findings associated with cardiac arrest, adjusted for confounding factors.

METHODS

The presence of cerebral infarcts, leukoaraiosis, atrophy, and edema on ultra-low-field MRI was assessed in 88 community volunteers and 52 cardiac arrest survivors enrolled in a placebo-controlled, randomized, double-blind trial of nimodipine in out-of-hospital ventricular fibrillation.

RESULTS

Cardiac arrest was an independent risk factor for the presence of infarcts in a logistic regression model adjusted for age, sex, and history of myocardial infarction, stroke, coronary heart disease, cardiac failure, and hypertension (odds ratio, 3.6; 95% confidence interval, 1.3 to 9.9; P = .01). Leukoaraiosis was associated with increasing age but not with cardiac arrest. Adjusted for age, the delay of advanced life support had an inverse correlation with the degree of atrophy in placebo-treated patients (r = -.62, P < .0001) but not in patients treated with nimodipine (r = -.10, P = .43). Lack of age-related atrophy, possibly implicating the presence of brain edema, predicted poor outcome after cardiac arrest (odds ratio, 4.6; 95% confidence interval, 1.4 to 15.8; P = .01).

CONCLUSIONS

Cardiac arrest was associated with deep cerebral infarcts but not with leukoaraiosis. MRI findings did not predict the functional outcome at 1 year. Nimodipine treatment had no significant effect on the MRI findings, but delayed resuscitation was associated with probable brain edema only in placebo-treated patients.

Excitatory amino acid-mediated cytotoxicity and calcium homeostasis in cultured neurons

A large body of evidence suggests that disturbances of Ca2+ homeostasis may be a causative factor in the neurotoxicity induced by excitatory amino acids (EAAs). The route or routes by which an increase in intracellular calcium concentration ([Ca2+]i) is mediated in vivo are presently not clarified. This may partly reflect the complexity of intact nervous tissue in combination with the relative unspecific action of the available "calcium antagonists," e.g., blockers of voltage-sensitive calcium channels. By using primary cultures of cortical neurons as a model system, it has been found that all EAAs stimulate increases in [Ca2+]i but via different mechanisms. By using the drug dantrolene, it has been shown that 2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propionate (AMPA) apparently exclusively stimulates Ca2+ influx through agonist-operated calcium channels and voltage-operated calcium channels. Increased [Ca2+]i due to exposure to kainate (KA) is for the major part caused by influx, as in the case of AMPA, but a small part of the increase in [Ca2+]i may be attributed to a release of Ca2+ from intracellular stores. Quisqualate (QA) stimulates Ca2+ release from an intracellular store that is independent of Ca2+ influx; presumably this store is activated by inositol phosphates. The increase in [Ca2+]i due to exposure to glutamate or N-methyl-D-aspartate (NMDA) may be compartmentalized into three components, one of which is related to influx and the other two to Ca2+ release from internal stores. Only one of the latter stores is dependent on Ca2+ influx with regard to release of Ca2+, whereas the other is activated by some other second messengers or, alternatively, directly coupled to the receptor. In muscles dantrolene is known to inhibit Ca2+ release from the sarcoplasmic reticulum, and also in neurons dantrolene inhibits an equivalent release from one or more hitherto unidentified internal Ca2+ pool(s). By using this drug it has been possible to show to what extent these Ca2+ stores are involved in the toxicity observed subsequent to exposure to the EAAs. It turned out that dantrolene, even under conditions allowing Ca2+ influx, inhibited toxicity induced by QA, NMDA, and glutamate, whereas that induced by AMPA or KA was unaffected. In combination with the findings that dantrolene inhibited release from the intracellular stores activated by QA, NMDA, and glutamate, it may be concluded that Ca2+ influx per se is not the primary event causing toxicity following exposure to these EAAs in these neurons. However, it may certainly be involved in the cases of toxicity induced by AMPA and KA.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Novel pharmacologic therapies in the treatment of experimental traumatic brain injury: a review

Delayed or secondary neuronal damage following traumatic injury to the central nervous system (CNS) may result from pathologic changes in the brain's endogenous neurochemical systems. Although the precise mechanisms mediating secondary damage are poorly understood, posttraumatic neurochemical changes may include overactivation of neurotransmitter release or re-uptake, changes in presynaptic or postsynaptic receptor binding, or the pathologic release or synthesis of endogenous "autodestructive" factors. The identification and characterization of these factors and the timing of the neurochemical cascade after CNS injury provides a window of opportunity for treatment with pharmacologic agents that modify synthesis, release, receptor binding, or physiologic activity with subsequent attenuation of neuronal damage and improvement in outcome. Over the past decade, a number of studies have suggested that modification of postinjury events through pharmacologic intervention can promote functional recovery in both a variety of animal models and clinical CNS injury. This article summarizes recent work suggesting that pharmacologic manipulation of endogenous systems by such diverse pharmacologic agents as anticholinergics, excitatory amino acid antagonists, endogenous opioid antagonists, catecholamines, serotonin antagonists, modulators of arachidonic acid, antioxidants and free radical scavengers, steroid and lipid peroxidation inhibitors, platelet activating factor antagonists, anion exchange inhibitors, magnesium, gangliosides, and calcium channel antagonists may improve functional outcome after brain injury.

Attenuation of ischemic and postischemic damage to brain metabolism and circulation by a novel Ca2+ channel antagonist, NC-1100, in spontaneously hypertensive rats

We investigated the effect of a newly synthesized Ca2+ channel antagonist, NC-1100, on cerebral blood flow (CBF) and metabolism in spontaneously hypertensive rats. The rats received a bolus injection of 0.2 or 1.0 mg/kg NC-1100 i.v. and 1-h cerebral ischemia was then induced by bilateral carotid artery occlusion (group 1). The rats in group 2 were continuously infused with NC-1100 0.03 or 0.1 mg/kg per min, starting immediately after bilateral carotid artery occlusion, for the 1 h of ischemia and following 3-h recirculation. Group 1: during ischemia, CBF in all rats decreased to 6-8% of the resting values. At 1 h cerebral ischemia, brain tissue lactate increased 11.5-, 10.1- and 9.8-fold of the normal control given vehicle or NC-1100, 0.2 and 1.0 mg/kg, respectively. The ATP levels were better preserved by NC-1100 administration; 0.61 +/- 0.04 (mean +/- S.E.M.), 0.80 +/- 0.09 and 0.97 +/- 0.14 mmol/kg (P < 0.05 vs. vehicle), respectively. Group 2: during recirculation, CBF in NC-1100-treated rats returned to 83-90% of the resting values, but to only 65% in the vehicle group. Postischemic brain lactate at 3 h was less well preserved and ATP was dose dependently better preserved in NC-1100- than vehicle-treated rats. It is considered that pre- as well as postischemic administration of a Ca2+ channel antagonist, NC-1100, is beneficial to attenuate and also ameliorate the metabolic and circulatory derangement in the ischemic brain.

L-arginine dilates rat pial arterioles by nitric oxide-dependent mechanisms and increases blood flow during focal cerebral ischaemia

L-Arginine (> or = 30 mg kg-1, i.v.), but not D-arginine (300 mg kg-1) administered 5 min after unilateral common carotid/middle cerebral artery occlusion increased regional cerebral blood flow (rCBF) within the dorsolateral ischaemic cortex in spontaneously hypertensive rats. L-Arginine (300 mg kg-1) increased rCBF from 22 +/- 2.7 to 33 +/- 4% of baseline as measured by laser-Doppler flowmetry. This increase may explain the ability of L-arginine to reduce infarct size following focal cerebral ischaemia, as reported previously. The mechanism appears to be mediated by nitric oxide since topical L-NAME (1 microM), a nitric oxide synthase inhibitor, decreased pial arteriole calibre from 115 +/- 2.2 to 106 +/- 0.9% of baseline following L-arginine infusion (300 mg kg-1).

Evaluation of a novel calcium channel blocker, (S)-emopamil, on regional cerebral edema and neurobehavioral function after experimental brain injury

The authors investigated the effects of a novel calcium channel blocker, (S)-emopamil, on cerebral edema and neurobehavioral and memory function following experimental fluid-percussion brain injury in the rat. Two independent experiments were performed to evaluate the effects of this compound on cardiovascular variables and postinjury cerebral edema (increases in tissue water content), and on cognitive deficits and neurological motor function following brain injury. Treatment with (S)-emopamil significantly reduced focal brain edema at 48 hours after brain injury. Profound memory dysfunction induced by brain injury was significantly attenuated following (S)-emopamil treatment. In addition, (S)-emopamil also attenuated the deficits in motor function that were observed over a 2-week period following brain injury. These results suggest that changes in calcium homeostasis may play an important role in the pathogenesis of trauma to the central nervous system and that the calcium channel blocker (S)-emopamil might be a useful compound for the treatment of traumatic brain injury.

Ion homeostasis in rat brain in vivo: intra- and extracellular [Ca2+] and [H+] in the hippocampus during recovery from short-term, transient ischemia

Changes in intra- and extracellular [Ca2+] and [H+], together with alterations in tissue PO2 and local blood flow, were measured in areas CA1 and CA3 of the hippocampus during recovery (up to 8 h) after an 8-min period of low-flow ischemia. Restoration of blood supply was followed by an immediate rise in flow and tissue PO2 above normal, with large fluctuations in both persisting for up to 4 h. In area CA1, [Ca2+]i decreased rapidly from an ischemic mean value of 30 microM to a control mean level of 73.1 nM in 20-30 min, whereas normalization of [Ca2+]e took approximately 1 h. Recovery of [Ca2+]i was accelerated by preischemic administration of a calcium antagonist, nifedipine, and a free radical scavenger, N-tert-butyl-alpha-phenylnitrone (PBN), but not by MK-801, a blocker of N-methyl-D-aspartate receptors. There was a secondary rise in [Ca2+]i in many cells beginning approximately 2 h after reperfusion. This was attenuated somewhat by PBN but not clearly influenced by either nifedipine or MK-801. Changes of [Ca2+]i in area CA3 were much smaller and slightly slower than in area CA1 and were not affected by the drugs mentioned above. In both areas CA1 and CA3, pHe and pHi fell during ischemia to an average value of 6.2, from which there was a rapid initial recovery in the first 5-10 min when blood flow was restored. Thereafter tissue pH rose slowly and did not reach control levels for approximately 1 h, and in some microareas not at all. It is concluded that (a) effective mechanisms for restoring normal [Ca2+]i remain intact after 8 min of low-flow ischemia; (b) in neurons of area CA1, some insidious change in the homeostasis of calcium triggers a secondary rise in its free cytosolic concentration, which may be causally related to activation of irreversible cell damage; and (c) the changes in [Ca2+]i and [Ca2+]e during and following 8 min of ischemia can be adequately accounted for by movements of a fixed pool of Ca between intra- and extracellular compartments, and possible mechanisms are discussed.

The CBF threshold and dynamics for focal cerebral infarction in spontaneously hypertensive rats

Two strategies were used to estimate the blood flow threshold for focal cerebral infarction in spontaneously hypertensive rats (SHRs) subjected to permanent middle cerebral artery and common carotid artery occlusion (MCA/CCAO). The first compared the volume of cortical infarction (24 h after ischemia onset) to the volumes of ischemic cortex (image analysis of [14C]iodoantipyrine CBF autoradiographs) perfused below CBF values less than 50 (VIC50) and less than 25 ml 100 g-1 min-1 (VIC25) at serial intervals during the first 3 h of ischemia. The infarct process becomes irreversible within 3 h in this model. In the second, measurements of CBF at the border separating normal from infarcted cortex at 24 h after ischemia onset were used as an index of the threshold. During the first 3 h of ischemia, VIC50 increased slightly to reach a maximum size at 3 h that closely matched the 24 h infarct volume. VIC25, in contrast, consistently underestimated the infarct volume by a factor of 2-3. CBF at the 24 h infarct border averaged 50 ml 100 g-1 min -1. Taken together, the results indicate that the CBF threshold for infarction in SHRs approaches 50 ml 100 g-1 min-1 when ischemia persists for greater than or equal to 3 h. This threshold value is approximately three times higher than in primates. Since cortical neuronal density is also threefold greater in rats than in primates, the higher injury threshold in the rat may reflect a neuronal primacy in determining the brain's susceptibility to partial ischemia.

Failure of GM1 ganglioside to influence outcome in experimental focal ischemia

BACKGROUND AND PURPOSE

Reports of improved short-term (less than 72 hours) outcome in experimental models of mechanical and ischemic central nervous system injury suggest that exogenous ganglioside administration may confer a protective effect on neural tissue. We studied the effect of the monosialoganglioside GM1 on cerebral infarction and edema in spontaneously hypertensive rats subjected to permanent focal cerebral ischemia.

METHODS

GM1 or normal saline was injected intramuscularly once a day for 3 days before and 30 and 120 minutes after occlusion of the right middle and common carotid arteries. Following a 24-hour survival period, the volume of infarction was measured by computer-assisted image analysis, and the extent of edema was assessed by measurements of tissue water content and hemispheric volume.

RESULTS

Infarct volume was similar among the GM1-treated (n = 10) and saline-treated (n = 10) rats (212 +/- 10 versus 220 +/- 13 microliters, respectively). In a second series of experiments, the brain water content and edema volume of the ischemic right hemisphere in GM1-treated rats (n = 10) did not differ from saline-treated controls (n = 10).

CONCLUSIONS

GM1 ganglioside does not effectively reduce cerebral infarction caused by permanent focal ischemia.

Reduction in focal cerebral ischemia by agents acting at imidazole receptors

Treatment with the alpha 2-adrenergic antagonist idazoxan (IDA) can provide protection from global cerebral ischemia. However, IDA also recognizes another class of receptors, termed imidazole (IM) receptors, which differ from alpha 2-adrenergic receptors and are responsible for the hypotensive actions of some centrally acting agents such as the oxazole rilmenidine (RIL). We therefore sought to determine whether RIL, an agent highly selective for IM receptors, offered protection from focal cerebral ischemia elicited in rat by ligation of the middle cerebral artery (MCA). We compared the effects of RIL with the effects of IDA and the selective non-IM alpha 2-antagonist SKF 86466 (SKF). In addition, we examined whether the neuroprotective effects of RIL and IDA could be attributed to changes in local CBF (LCBF). The MCA was occluded and animals either received immediate administration of drug while arterial pressure was maintained for 1 h or had local CBF increased to 200% of control for 1 h by hypercapnia or hypertension. RIL elicited a significant dose-dependent preservation of tissue to 33% of control at optimal dose (0.75 mg/kg). IDA (3 mg/kg) significantly reduced the size of ischemic infarction by 22%. In contrast, SKF (15 mg/kg) as well as doubling of LCBF did not preserve ischemic tissue. We conclude that both RIL and IDA can reduce focal ischemic infarction but that the mechanism does not appear secondary to antagonism of alpha 2-adrenergic receptors or elevation of LCBF. Occupation of IM receptors, either in the ischemic zone or at remote brain sites, may be responsible for neuroprotection of RIL and IDA.

The effects of dizocilpine (MK-801), phencyclidine, and nimodipine on infarct size 48 h after middle cerebral artery occlusion in the rat

The effects of the calcium channel blocker nimodipine and the non-competitive NMDA-antagonists MK-801 and phencyclidine (PCP) on infarct size 48 h after occlusion of the middle cerebral artery (MCA-O) were evaluated in the rat. Nimodipine was given at a dose of 0.3 mg/kg s.c. 30 min prior and 8, 16, and 24 h after MCA-O. MK-801 (1 mg/kg i.p. or 10 mg/kg i.p.) or PCP (0.3, 1.0, 3.0, 10, or 30 mg/kg i.p.) were administered 30 min prior to ischemia. In additional experiments 30 mg/kg PCP was given 1, 3, or 5 h post ischemia. Nimodipine and 1 mg/kg MK-801 reduced cortical infarct volumes significantly by 50% and 55%, respectively, while cortical infarct size fell by 32% and total infarct volume was not altered significantly after administration of 10 mg/kg MK-801. Pretreatment with 10 or 30 mg/kg PCP reduced cortical infarction by 47-53% and total infarct volumes by 39-42%. Posttreatment with PCP was effective if started at 1 or 3 h post ischemia.