Lidocaine accelerates neuroelectrical recovery after incomplete global ischemia in rabbits

Comprehensive Perioperative Approach to Complex Spine Deformity Management

OBJECTIVE

Study perioperative strategies for optimizing neuroprotection in complex spine deformity correction surgery.

METHODS

We report the case of a patient with severe lumbar dextroscoliosis, thoracolumbar junction hyperkyphosis with a 40-degree Cobb angle levoconvex scoliosis who underwent spinal deformity correction with loss of neuromonitoring during surgery. We performed a literature review on perioperative management of complex spine deformity.

RESULTS

A 50-year-old man presented with lumbar pain and right L4 radiculopathy. Surgical intervention for deformity correction and decompression was indicated with T4-L4 posterior instrumentation L2/L3 and L3/L4 transforaminal lumbar interbody fusion. Surgery was aborted due to the loss of neuromonitoring. Postsurgery, the patient had left sensory deficit and the neurocritical care team clinically suspected and deduced the anatomic location of the spinal cord compression. Magnetic resonance imaging confirmed a T10-T11 hyperintensity suggestive of cord ischemia due to osteophyte compressing the spinal cord. The patient underwent a second corrective surgery with no intraoperative events and has no long-term neurological sequela.

CONCLUSIONS

This case illustrates that a comprehensive perioperative approach and individualized risk factor assessment is useful in complex spine deformity surgery. Further research is needed to determine how this individualized comprehensive approach can lead to intraoperative and postoperative countermeasures that improved spine surgery outcomes.

LEVEL OF EVIDENCE

Level V.

Lidocaine Attenuates Cognitive Impairment After Isoflurane Anesthesia by Reducing Mitochondrial Damage

Mitochondrial dysfunction has been proposed to be one of the earliest triggering events in isoflurane-induced neuronal damage. Lidocaine has been demonstrated to attenuate the impairment of cognition in aged rats induced by isoflurane in our previous study. In this study, we hypothesized that lidocaine could attenuate isoflurane anesthesia-induced cognitive impairment by reducing mitochondrial damage. H4 human neuroglioma cells and 18-month-old male Fischer 344 rats were exposed to isoflurane or isoflurane plus lidocaine. Cognitive function was tested at 14 days after treatment by the Barnes Maze test in male Fischer 344 rats. Morphology was observed under electron microscope, and mitochondrial transmembrane potential, electron transfer chain (ETC) enzyme activity, complex-I-IV activity, immunofluorescence and flow cytometry of annexin V-FITC binding, TUNEL assay, and Western blot analyses were applied. Lidocaine attenuated cognitive impairment caused by isoflurane in aged Fischer 344 rat. Lidocaine was effective in reducing mitochondrial damage, mitigating the decrease in mitochondrial membrane potential (Δ_Ψm), reversing isoflurane-induced changes in complex activity in the mitochondrial electron transfer chain and inhibiting the apoptotic activities induced by isoflurane in H4 cells and Fischer 344 rats. Additionally, lidocaine suppressed the ratio of Bax (the apoptosis-promoting protein) to Bcl-2 (the apoptosis-inhibiting protein) caused by isoflurane in H4 cells. Lidocaine proved effective in attenuating isoflurane-induced POCD by reducing mitochondrial damage.

Effects of anesthesia on cerebral blood flow, metabolism, and neuroprotection

Administration of anesthetic agents fundamentally shifts the responsibility for maintenance of homeostasis from the patient and their intrinsic physiological regulatory mechanisms to the anesthesiologist. Continuous delivery of oxygen and nutrients to the brain is necessary to prevent irreversible injury and arises from a complex series of regulatory mechanisms that ensure uninterrupted cerebral blood flow. Our understanding of these regulatory mechanisms and the effects of anesthetics on them has been driven by the tireless work of pioneers in the field. It is of paramount importance that the anesthesiologist shares this understanding. Herein, we will review the physiological determinants of cerebral blood flow and how delivery of anesthesia impacts these processes.

Do sodium channel blockers have neuroprotective effect after onset of ischemic insult?

OBJECTIVE

Cerebral ischemia causes a series of pathophysiologic events that may result in cerebral infarct. Some neurons are more vulnerable to ischemia, particularly pyramidal neurons in the hippocampal CA1 region. Pharmacologic intervention for treatment of cerebral ischemia aims to counteract secondary neurotoxic events or to interrupt the progression of this process. In the present study, we compare the neuroprotective effects of sodium channel blockers (mexiletine, riluzole and phenytoin) and investigate whether they have neuroprotective effect when given after ischemic insult.

METHODS

A transient global cerebral ischemia model was performed in this study by clipping bilateral common carotid arteries during 45 minutes. Riluzole (8 mg/kg), mexiletine (80 mg/kg) and phenytoin (200 mg/kg) were injected into the rats intraperitoneally 30 minutes before or after reperfusion. Lipid peroxidation levels and cerebral water contents were evaluated 24 hours after ischemia. Histopathologic assessment of hippocampal region was determined 7 days after ischemia.

RESULTS

Riluzole, mexiletine and phenytoin treatment after global ischemia significantly decreased water content of the ischemic brain (p<0.05 for each). No significant difference was observed in cerebral edema among the drug treatment groups (p>0.05). When pre-treatment and post-treatment groups were compared with each other, only riluzole pre-treatment group revealed better result for cerebral edema (p<0.05). Pre-treatment with these drugs revealed significantly better results for the malonyldialdehyde (MDA) level and the number of survival neuron on the hippocampal region than the post-treatment groups.

CONCLUSION

It is demonstrated that riluzole, mexiletine and phenytoin are potent neuroprotective agents in the rat model of transient global cerebral ischemia, but they are more effective when given before onset of the ischemia.

Effect of lidocaine on dynamic changes in cortical reduced nicotinamide adenine dinucleotide fluorescence during transient focal cerebral ischemia in rats

Rats were subjected to 90min of focal ischemia by occluding the left middle cerebral and both common carotid arteries. The dynamic changes in the formation of brain ischemic areas were analyzed by measuring the direct current (DC) potential and reduced nicotinamide adenine dinucleotide (NADH) fluorescence with ultraviolet irradiation. In the lidocaine group (n=10), 30min before ischemia, an intravenous bolus (1.5mg/kg) of lidocaine was administered, followed by a continuous infusion (2mg/kg/h) for 150min. In the control group (n=10), an equivalent amount of saline was administered. Following the initiation of ischemia, an area of high-intensity NADH fluorescence rapidly developed in the middle cerebral artery territory in both groups and the DC potential in this area showed ischemic depolarization. An increase in NADH fluorescence closely correlated with the DC depolarization. The blood flow in the marginal zone of both groups showed a similar decrease. Five minutes after the onset of ischemia, the area of high-intensity NADH fluorescence was significantly smaller in the lidocaine group (67% of the control; P=0.01). This was likely due to the suppression of ischemic depolarization by blockage of voltage-dependent sodium channels with lidocaine. Although lidocaine administration did not attenuate the number of peri-infarct depolarizations during ischemia, the high-intensity area and infarct volume were significantly smaller in the lidocaine group both at the end of ischemia (78% of the control; P=0.046) and 24h later (P=0.02). A logistic regression analysis demonstrated a relationship between the duration of ischemic depolarization and histologic damage and revealed that lidocaine administration did not attenuate neuronal damage when the duration of depolarization was identical. These findings indicate that the mechanism by which lidocaine decreases infarct volume is primarily through a reduction of the brain area undergoing NADH fluorescence increases which closely correlates with depolarization.

Intravenous antiarrhythmic doses of lidocaine increase the survival rate of CA1 neurons and improve cognitive outcome after transient global cerebral ischemia in rats

Brain ischemia is often a consequence of cardiac or neurologic surgery. Prophylactic pharmacological neuroprotection would be beneficial for patients undergoing surgery to reduce brain damage due to ischemia. We examined the effects of two antiarrhythmic doses of lidocaine (2 or 4 mg/kg) on rats in a model of transient global cerebral ischemia. The occlusion of both common carotid arteries combined with hypotension for 10 min induced neuronal loss in the CA1 region of the hippocampus (18±12 vs. 31±4 neurons/200 μm linear distance of the cell body layer, X±SD; P<0.01). Lidocaine (4 mg/kg) 30 min before, during and 60 min after ischemia increased dorsal hippocampal CA1 neuronal survival 4 weeks after global cerebral ischemia (30±9 vs. 18±12 neurons/200 μm; P<0.01). There was no significant cell loss after 10 min of ischemia in the CA3 region, the dentate region or the amygdalae; these regions were less sensitive than the CA1 region to ischemic damage. Lidocaine not only increased hippocampal CA1 neuronal survival, but also preserved cognitive function associated with the CA1 region. Using an active place avoidance task, there were fewer entrances into an avoidance zone, defined by relevant distal room-bound cues, in the lidocaine groups. The untreated ischemic group had an average, over the nine sessions, of 21±12 (X±SD) entrances into the avoidance zone per session; the 4 mg/kg lidocaine group had 7±8 entrances (P<0.05 vs. untreated ischemic) and the non-ischemic control group 7±5 entrances (P<0.01 vs. untreated ischemic). Thus, a clinical antiarrhythmic dose of lidocaine increased the number of surviving CA1 pyramidal neurons and preserved cognitive function; this indicates that lidocaine is a good candidate for clinical brain protection.

The combined neuroprotective effects of lidocaine and dexmedetomidine after transient forebrain ischemia in rats

BACKGROUND

We investigated whether coadministration of lidocaine and dexmedetomidine would reduce brain injury following transient forebrain ischemia in rats to a greater extent than either drug alone.

METHODS

Adult male Sprague-Dawley rats were anesthetized with halothane to maintain normocapnia and normoxia. Rats received subcutaneous injection of saline 1 ml/kg, lidocaine 10 mg/kg, dexmedetomidine 3 microg/kg, or lidocaine 10 mg/kg plus dexmedetomidine 3 microg/kg. Thirty minutes after the drug injection, forebrain ischemia was induced by hemorrhagic hypotension and occlusion of the bilateral carotid arteries, and was confirmed by isoelectric EEG. At the end of 10-min ischemia, rats were reperfused. The same dose of drugs was administered 3, 24, and 48 h after ischemia. Neurological examination was done at 1, 2, and 7 days after ischemia. Seven days after ischemia, the brain was stained with hematoxylin and eosin. We counted ischemic cells in the CA1 hippocampal region, striatum, and cerebral cortex. We also measured extracellular glutamate and norepinephrine concentration in hippocampal CA1 in the four groups.

RESULTS

As compared with saline-treated rats, rats receiving dexmedetomidine plus lidocaine showed less than neurological deficit scores at 2 and 7 days after ischemia, and had less ischemic cells in the CA1 region. However, administration of dexmedetomidine plus lidocaine did not alter the area under the glutamate concentration curve and norepinephrine concentration during ischemia in the CA1 region, compared with saline-treated rats.

CONCLUSIONS

Our results suggest coadministration of lidocaine and dexmedetomidine improves the neurological outcome without alteration of glutamate and norepinephrine concentrations during forebrain ischemia in rats.

Microbubbles

Gas embolism is a known complication of various invasive procedures, and its management is well established. The consequence of gas microemboli, microbubbles, is underrecognized and usually overlooked in daily practice. We present the current data regarding the pathophysiology of microemboli and their clinical consequences. Microbubbles originate mainly in extracorporeal lines and devices, such as cardiopulmonary bypass and dialysis machines, but may be endogenous in cases of decompression sickness or mechanical heart valves. Circulating in the blood stream, microbubbles lodge in the capillary bed of various organs, mainly the lungs. The microbubble obstructs blood flow in the capillary, thus causing tissue ischemia, followed by inflammatory response and complement activation. Aggregation of platelets and clot formation occurs as well, leading to further obstruction of microcirculation and tissue damage. In this review, we present evidence of the biological and clinical detrimental effects of microbubbles as demonstrated by studies in animal models and humans, and discuss management of the microbubble problem with regard to detection, prevention, and treatment.

Lidocaine attenuates apoptosis in the ischemic penumbra and reduces infarct size after transient focal cerebral ischemia in rats

Lidocaine is a local anesthetic and antiarrhythmic agent. Although clinical and experimental studies have shown that an antiarrhythmic dose of lidocaine can protect the brain from ischemic damage, the underlying mechanisms are unknown. In the present study, we examined whether lidocaine inhibits neuronal apoptosis in the penumbra in a rat model of transient focal cerebral ischemia. Male Wistar rats underwent a 90-min temporary occlusion of middle cerebral artery. Lidocaine was given as an i.v. bolus (1.5 mg/kg) followed by an i.v. infusion (2 mg/kg/h) for 180 min, starting 30 min before ischemia. Rats were killed and brain samples were collected at 4 and 24 h after ischemia. Apoptotic changes were evaluated by immunohistochemistry for cytochrome c release and caspase-3 activation and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) for DNA fragmentation. Cytochrome c release and caspase-3 activation were detected at 4 and 24 h after ischemia and DNA fragmentation was detected at 24 h. Double-labeling with NeuN, a neuronal marker, demonstrated that cytochrome c, caspase-3, and TUNEL were confined to neurons. Lidocaine reduced cytochrome c release and caspase-3 activation in the penumbra at 4 h and diminished DNA fragmentation in the penumbra at 24 h. Lidocaine treatment improved early electrophysiological recovery and reduced the size of the cortical infarct at 24 h, but had no significant effect on cerebral blood flow in either the penumbra or core during ischemia. These findings suggest that lidocaine attenuates apoptosis in the penumbra after transient focal cerebral ischemia. The infarct-reducing effects of lidocaine may be due, in part, to the inhibition of apoptotic cell death in the penumbra.

Gas embolism: pathophysiology and treatment

Based on a literature search, an overview is presented of the pathophysiology of venous and arterial gas embolism in the experimental and clinical environment, as well as the relevance and aims of diagnostics and treatment of gas embolism. The review starts with a few historical observations and then addresses venous air embolism by discussing pulmonary vascular filtration, entrapment, and the clinical occurrence of venous air emboli. The section on arterial gas embolism deals with the main mechanisms involved, coronary and cerebral air embolism (CAE), and the effects of bubbles on the blood-brain barrier. The diagnosis of CAE uses various techniques including ultrasound, perioperative monitoring, computed tomography, brain magnetic resonance imaging and other modalities. The section on therapy starts by addressing the primary treatment goals and the roles of adequate oxygenation and ventilation. Then the rationale for hyperbaric oxygen as a therapy for CAE based on its physiological mode of action is discussed, as well as some aspects of adjuvant drug therapy. A few animal studies are presented, which emphasize the importance of the timing of therapy, and the outcome of patients with air embolism (including clinical patients, divers and submariners) is described.

Neuroprotective strategies in epilepsy

Dr. Carlen reviews the evidence that seizures may cause cell death and discusses possible strategies for preventing seizure-induced brain damage.

The use-dependent sodium channel blocker mexiletine is neuroprotective against global ischemic injury

Mechanisms responsible for anoxic/ischemic cell death in mammalian CNS grey and white matter involve an increase in intracellular Ca2+, however the routes of Ca2+ entry appear to differ. In white matter, pathological Ca2+ influx largely occurs as a result of reversal of Na+-Ca2+ exchange, due to increased intracellular Na+ and membrane depolarization. Na+ channel blockade has therefore been logically and successfully employed to protect white matter from ischemic injury. In grey matter ischemia, it has been traditionally presumed that activation of agonist (glutamate) operated and voltage dependent Ca2+ channels are the primary routes of Ca2+ entry. Less attention has been directed towards Na+-Ca2+ exchange and Na+ channel blockade as a protective strategy in grey matter. This study investigates mexiletine, a use-dependent sodium channel blocker known to provide significant ischemic neuroprotection to white matter, as a grey matter protectant. Pentobarbital (65 mg/kg) anesthetized, mechanically ventilated Sprague-Dawley rats were treated with mexiletine (80 mg/kg, i.p.). Then 25 min later the animals were subjected to 10 min of bilateral carotid occlusion plus controlled hypotension to 50 Torr by temporary partial exsanguination. Animals were sacrificed with perfusion fixation after 7 days. Ischemic and normal neurons were counted in standard H&E sections of hippocampal CA1 and the ratio of ischemic to total neurons calculated. Mexiletine pre-treatment reduced hippocampal damage by approximately half when compared to control animals receiving saline alone (45 vs. 88% damage, respectively; P<0.001). These results suggest that mexiletine (and perhaps other drugs of this class) can provide protection from ischemia to grey matter as well as white matter.

Physical and Pharmacological Neuroprotection in Cardiac Surgery

Stroke and neurocognitive deficits may follow cardiac surgery and have been linked to perioperative cerebral embolism. Alteration of cardiopulmonary bypass (CPB) or surgical technique to reduce embolism is, therefore, a rational neuroprotective strategy. Pharmacological cerebral protection has been advocated as an ideal "back-stop" to such "physical" interventions. A series of relevant studies conducted at Green Lane Hospital, Auckland, New Zeatand is described. Doppler ultra sound was used to monitor cerebral embolism during left heart valve surgery. Subsequently, salvaged CPB circuits were used to investigate several unexpected sources of emboli. The efficacy of a novel left heart deairing technique was audited using the Doppler de vice. Finally, a randomized double-blind trial of lidocaine in cerebral protection during cardiac surgery was con ducted. Most cerebral emboli were recorded after aortic declamping. However, cerebral emboli counts increased during stable CPB when the hard shell venous reservoir (HSVR) was operated at lower blood volumes and when air was seen in the venous return line. In vitro 2 HSVRs were found to generate bubbles when operated at blood volumes in excess of the manufacturer's recom mended minimum. Air in the venous return line was found to readily transit the CPB circuit and vacuum- assisted venous drainage markedly exacerbated this phenomenon. The novel deairing technique was mark edly superiorto conventional methods. Lidocaine admin istered in a standard antiarrhythmic dose for 48 hours from induction of anesthesia reduced the incidence of neuropsychological deficits at 10 days and 10 weeks postoperatively.

The protective action of tetrodotoxin and (+/-)-kavain on anaerobic glycolysis, ATP content and intracellular Na+ and Ca2+ of anoxic brain vesicles

Because recent reports point to Na+ channel blockers as protective agents directed against anoxia-induced neuronal damage including protection of anaerobic glycolysis, the influences of tetrodotoxin (TTX) and (+/-)-kavain on anoxic rat brain vesicles were investigated with respect to lactate synthesis, vesicular ATP content and cytosolic free Na+ and Ca2+ ([Na+]i, [Ca2+]i), both of the latter determined fluorometrically employing SBFI and FURA-2, respectively. After anoxia, basal lactate production was increased from 2.9 to 9.8 nmol lactate/min/mg protein. Although lactate synthesis seemed to be stable for at least 45 min of anoxia, as deduced from the linearity of lactate production, the ATP content declined continuously with a half life (tau 1/2) of 14.5 min, indicating that anaerobic glycolysis was insufficient to cover the energy demand of anoxic vesicles. Correspondingly, [Na+]i and [Ca2+]i increased persistently after anoxia by 22.1 mmol/l Na+ and 274.9 nmol/l Ca2+, determined 6.3 min after onset. An additional stimulation of vesicles with veratridine accelerated the drop of ATP (tau 1/2 = 5.1 min) and provoked a massive Na+ overload, which levelled off to 119 mmol/l Na+ within a few minutes. Concomitantly, [Ca2+]i increased linearly with a rate of 355 nmol Ca2+/l/min. Despite the massive perturbation of ion homeostasis, lactate production was unaffected during the first 8 min of veratridine stimulation. However, complete inhibition of lactate synthesis took place 30 min after veratridine was added. The Na+ channel blockers TTX and (+/-)-kavain, if applied before anoxia, preserved vesicular ATP content, diminished anoxia-induced increases in [Na+]i and [Ca2+]i and prevented both the veratridine-induced increases of [Na+]i and [Ca2+]i and the inhibition of lactate production. The data indicate a considerable Na+ influx via voltage-dependent Na+ channels during anoxia, which speeds up the decline in ATP and provokes an increase in [Ca2+]i. A massive Na+ and Ca2+ overload induced by veratridine failed to influence lactate synthesis directly, but initiated its inhibition.

Cerebral protection by lidocaine during cardiac operations

BACKGROUND

Lidocaine improves outcome in animal brain injury models. Cardiac operations often cause postoperative neuropsychological (NP) impairment. We investigated cerebral protection by lidocaine in cardiac surgical patients.

METHODS

Sixty-five patients undergoing left heart valve procedures completed 11 preoperative NP tests, a self-rating inventory for memory, and inventories measuring depression and anxiety. These were repeated 10 days, 10 weeks, and 6 months postoperatively. Patients received a 48-hour double-blinded infusion of either lidocaine in a standard antiarrhythmic dose or placebo, beginning at induction of anesthesia. A postoperative deficit in any test was defined as decline by more than or equal to the group preoperative standard deviation. In addition, sequential postoperative percentage change scores were calculated for each patient in all NP tests and the inventories for memory, depression and anxiety.

RESULTS

Forty-two patients completed all three reviews, 8 completed two reviews, and 5 patients were reviewed once. Significantly more placebo patients had a deficit in at least one NP test at 10 days (p<0.025) and 10 weeks (p<0.05). The lidocaine group achieved superior sequential percentage change scores in 6 of the 11 NP tests (p<0.05) and in the memory inventory (p<0.025). There were no group differences in the remaining NP tests or the depression and anxiety inventories.

CONCLUSIONS

These data show that cerebral protection by lidocaine, which is unrelated to any effect on depression or anxiety, and is at a level that is noticed by the patients.

Neuroprotection--rationale for pharmacological modulation of Na(+)-channels

The primary factor detrimental to neurons in neurological disorders associated with deficient oxygen supply or mitochondrial dysfunction is insufficient ATP production relative to their requirement. As a large part of the energy consumed by brain cells is used for maintenance of the Na+ gradient across the cellular membrane, reduction of energy demand by down-modulation of voltage-gated Na(+)-channels is a rational strategy for neuroprotection. In addition, preservation of the inward Na+ gradient may be beneficial because it is an essential driving force for vital ion exchanges and transport mechanisms such as Ca2+ homeostasis and neurotransmitter uptake.

The effect of postinjury administration of polyethylene glycol-conjugated superoxide dismutase (pegorgotein, Dismutec) or lidocaine on behavioral function following fluid-percussion brain injury in rats

Previous studies in our laboratory have shown that polyethylene glycol-conjugated superoxide dismutase (PEG-SOD) or lidocaine treatment before experimental fluid-percussion brain injury in rats reduces the cortical hypoperfusion normally found in the early posttraumatic period. The purpose of the current study was to determine if posttreatment with PEG-SOD or lidocaine is also associated with changes in the trauma-induced suppression of motor and cognitive function that occurs following traumatic brain injury (TBI). Twenty-four hours after surgical preparation, rats were randomly assigned to a saline or drug posttreatment group, PEG-SOD (pegorgotein, Dismutec 10,000 IU/kg) or lidocaine (2 mg/kg), which was injected iv 30 min after moderate injury. PEG-SOD completely prevented beam walk deficits on days 1-5 postinjury while lidocaine similarly prevented beam walk deficits on days 2 through 5 postinjury. Both drugs produced a statistically insignificant trend for a decrease in beam balance duration deficits on days 1-5 postinjury and had no effect on cognitive function, as assessed by the Morris water maze, on days 11 through 15 postinjury. The mechanism by which PEG-SOD and lidocaine reduce posttraumatic motor deficits may be related to their free radical scavenging effect or previously reported effects on posttraumatic cerebral blood flow. To our knowledge, this is the first report of the effectiveness of these two agents in laboratory animals when administered after traumatic injury.

Na+ channels as targets for neuroprotective drugs

Drugs that block voltage-dependent Na+ channels are well known as local anaesthetics, antiarrhythmics and anticonvulsants. Recent studies show that these compounds also provide a powerful mechanism of cytoprotection in animal models of cerebral ischaemia, hypoxia or head trauma. In this article Charles Taylor and Brian Meldrum review evidence indicating that Na+ channel modulators are neuroprotective and describe recent ideas for the molecular sites of action of voltage-dependent Na+ channel blockers. Clinical trials with several compounds are now in progress for stroke and traumatic head injury, and the therapeutic potential for this group of compounds is discussed.

Lidocaine reduces the hypoxia-induced release of an excitatory amino acid analog from rat striatal slices in superfusion

1. Lidocaine has been extensively investigated as a potential neuroprotective drug against ischemia-induced neurodegeneration without reaching any satisfactory conclusion. 2. The present work evaluates the effect of lidocaine -17 microM- on the hypoxia-induced release of tritiated D-aspartate from rat striatal slices in superfusion. 3. Hypoxia resulted in a significant increase in the amount of D-aspartate released from striatal slices preloaded with the tritiated excitatory amino acid analog. 4. The addition of lidocaine to the superfusion solution resulted in a drastic reduction in the amount of D-aspartate release evoked by hypoxia, rendering it close to normal values.

Neuroprotective properties of lifarizine compared with those of other agents in a mouse model of focal cerebral ischaemia

1. Changes in the peripheral type benzodiazepine binding site density following middle cerebral artery occlusion in the mouse, have been used as a marker of neuronal damage. These sites can be identified using the selective ligand [3H]-PK 11195 located on non neuronal cells, macrophages and astroglia, within the CNS. Glial cell proliferation and macrophage invasion is an unvoidable sequelae to cerebral ischaemic injury, secondary to neuronal loss. Following occlusion of the left middle cerebral artery (left MCA) a reproducible lesion was found in the parietal cortex within 7 days which gave rise to a significant increase in [3H]-PK 11195 binding. 2. Treatment of animals with the sodium channel blocker, lifarizine, significantly reduced the ischaemia-induced increase in [3H]-PK 11195 binding when given either 30 min pre-ischaemia and three times daily for 7 days at 0.5 mg kg-1, i.p. (P < 0.01) or delayed until 15 min post-ischaemia and three times daily for 7 days at 0.5 mg kg-1, i.p. (P < 0.001). Lifarizine was an effective neuroprotective agent in this model of focal ischaemia in the mouse. 3. Lifarizine also showed a dose-related protection against the ischaemia-induced increase in [3H]-PK 11195 binding with significant protection at doses of 0.1 mg kg-1, i.p. (P < 0.05), 0.25 mg kg-1, i.p. (P < 0.01) or 0.5 mg kg-1, i.p. (P < 0.01) 15 min post-ischaemia and b.i.d. for 7 days. No significant change is seen in the Kd for [3H]-PK 11195. The first dose could be delayed for up to 4 h after cerebralartery cauterization and protection was maintained.4. Phenytoin (28 mg kg-1, i.v. 15 min and 24 h post-ischaemia) was also neuroprotective in this model(P<0.01). This agent is thought to interact with voltage-dependent sodium channels to effect its anticonvulsantactions and this mechanism may also underlie its neuroprotective actions in focal cerebralischaemia.5. Agents with other mechanisms of action were also shown to have significant neuroprotection in this model. The non-competitive NMDA antagonist, MK 801, showed significant neuroprotection in the model when given at 0.5 mg kg-1, i.p. 30 min pre-ischaemia with t.i.d. dosing for 7 days (P< 0.001). The dihydropyridine calcium antagonist, nimodipine was not protective when given using the same dosing protocol as MK 801, 0.5 mg kg-1 30 min pre-occlusion and three times daily for 7 days but showed significant protection when given at 0.05 mg kg-1 15 min post-ischaemia and three times daily for 7days. The lipid peroxidation inhibitor, tirilazad (single dose 1 mg kg-1, i.v.) showed significant neuroprotection when given 5 min post-ischaemia but not when the first dose was delayed for 4 h.

Postischemic cerebral blood flow recovery in the female: effect of 17 beta-estradiol

Female reproductive hormones are considered to be protective agents in atherosclerotic vascular disease and stroke. The present study determined if there are unique cerebrovascular responses in female animals to global cerebral ischemia and if 17 beta-estradiol is important to postischemic outcome in brain. Three groups of anesthetized, sexually mature rabbits were treated with normotensive four-vessel occlusion (6 min) and 3 h of reperfusion: females chronically instrumented with 17 beta-estradiol implants (EFEM; n = 8, plasma estradiol level = 365 +/- 48 pg/ml), untreated females (FEM; n = 8, estradiol = 13 +/- 3 pg/ml), and untreated males (M; n = 8, estradiol < limit of radioimmunoassay). CBF (microspheres) and somatosensory evoked potential (SEP) amplitude were measured during ischemia/reperfusion. Baseline hemispheric blood flow and regional flow distribution were not altered by chronic estradiol treatment. Hemispheric blood flow was equivalently reduced during ischemia in FEM and M (6 +/- 1 and 9 +/- 2 ml min-1 100 g-1, respectively); however postischemic hyperemia was greater in FEM than M (CBF = 257 +/- 27 and 183 +/- 27 ml min-1 100 g-1. However, EFEM experienced higher CBF during ischemia (e.g., 13 +/- 2 ml min-1 100 g-1) and less hyperemia (134 +/- 4 ml min-1 100 g-1 in hemispheres) in numerous brain regions than FEM. CBF at 3 h reperfusion was not different among the groups. Recovery of SEPs was incomplete and similar in all groups. We conclude that chronic exogenous 17 beta-estradiol treatment increases CBF during global incomplete ischemia and ameliorates postischemic hyperemia in the female animal.

Hippocampal slices: glutamate overflow and cellular damage from ischemia are reduced by sodium-channel blockade

We evaluated concentrations of excitatory amino acids released from slices into the superfusing solution and also evaluated extracellular field potential recordings and histological appearance of slice tissues to evaluate several sodium-channel modulating drugs as potential treatments for ischemia. The selective sodium-channel blocker tetrodotoxin (TTX, 1 microM) reduced glutamate release from deprivation of oxygen and D-glucose, while calcium-channel blockade was ineffective. Thus, during ischemia, we propose that glutamate may be released from the free cytosolic pool ('metabolic' glutamate) rather than by exocytosis. TTX (100-500 nM) and voltage-dependent sodium-channel blockers (phenytoin, 20-100 microM; lidocaine, 2-200 microM) each prevented damage to slices without blocking action potentials. The reduction of cellular depolarization and sodium loading during ischemia may explain the neuroprotective action of several sodium-channel modulating drugs in our in vitro studies and also in animal models.

Protective effects of antiarrhythmic agents against anoxic injury in CNS white matter

Irreversible anoxic injury is dependent on extracellular Ca2+ in mammalian CNS white matter, with a large portion of the pathologic Ca2+ influx occurring through reverse Na(+)-Ca2+ exchange, stimulated by increased intracellular [Na+]. This Na+ leak likely occurs via incompletely inactivated voltage-gated Na+ channels. This study reports that clinically used antiarrhythmic compounds, likely by virtue of their Na+ channel-blocking properties, significantly protect CNS white matter from anoxia at concentrations that cause little suppression of the preanoxic response. Rat optic nerves were pretreated with various agents for 60 min, then subjected to 60 min of anoxia in vitro. Functional recovery was measured electrophysiologically as the area under the compound action potential (CAP). Without drug, the CAP areas recovered to a mean of 32 +/- 12% of control after 1 h of reoxygenation. Recoveries using prajmaline 10 microM were 82 +/- 15% (p < 0.0001), and using tocainide 1 mM, 78 +/- 8% (p < 0.0001), with little suppression (< or = 10%) of the preanoxic response. Ajmaline (10-100 microM), disopyramide (10-300 microM) and bupivacaine (10-100 microM) were somewhat less effective, whereas verapamil produced 52 +/- 11% recovery before reduction of the preanoxic CAP was observed at 30 microM. Procainamide (100-300 microM) was ineffective. These results suggest that Na+ channel blockers, including commonly used antiarrhythmic agents, may be effective in protecting central white matter, which is a target for anoxic/ischemic injury in diseases such as stroke and spinal cord injury.

Actions of the novel neuroprotective agent, lifarizine (RS-87476), on voltage-dependent sodium currents in the neuroblastoma cell line, N1E-115

1. The actions of the neuroprotective agent, lifarizine (RS-87476-190), on voltage-dependent Na+ currents have been examined in the neuroblastoma cell line, N1E-115, using the whole-cell variant of the patch clamp technique. 2. At a holding potential of -80 mV, lifarizine reduced the peak Na+ current evoked by a 10 ms depolarizing step with an IC50 of 1.3 microM. At holding potentials of -100 and -60 mV the IC50 concentrations of lifarizine were 7.3 microM and 0.3 microM, respectively. 3. At a holding potential of -100 mV, most channels were in the resting state and the IC50 value for inhibition of Na+ current should correspond to the dissociation constant of lifarizine for resting channels (KR). KR was therefore estimated to be 7.3 microM. 4. In the absence of lifarizine, recovery from inactivation following a 20 s depolarization from -100 mV to 0 mV was complete within 2 s. However, in the presence of 3 microM lifarizine recovery took place in a biexponential fashion with time constants of 7 s and 79 s. 5. Lifarizine (1 microM) had no effect on steady-state inactivation curves when conditioning pre-pulses of 1 s duration were used. However, when pre-pulse durations of 1 min were used the curves were shifted to the left by lifarizine by about 10 mV. Analysis of the shifts induced by a range of lifarizine concentrations revealed that the apparent affinity of lifarizine for the inactivated state of the channel (K1) was 0.19 microM. 6. Lifarizine (1 microM) had no effect on chloramine-T-modified Na+ currents, suggesting no significant open channel interaction. 7. Taken together, these data show that lifarizine is a potent voltage-dependent inhibitor of Na+currents in NIE-115 cells and that the voltage-dependence arises from an interaction of the compound with the inactivated state of the channel. The possible contribution of Na+ current inhibition to the neuroprotective actions of lifarizine is discussed.

The effect of acute cocaine or lidocaine on behavioral function following fluid percussion brain injury in rats

One of the goals of our laboratory is to examine how the presence of drugs of abuse will influence traumatic brain injury. Previous studies in our laboratory have shown that cocaine or lidocaine treatment before experimental fluid percussion brain injury in rats reduces the cortical hypoperfusion normally found in the early posttraumatic period. The purpose of the current study was to determine if pretreatment with cocaine or lidocaine is also associated with changes in trauma-induced suppression of reflexes and motor and cognitive dysfunction that occurs following traumatic brain injury (TBI). Twenty-four hours after surgical preparation, rats were randomly assigned to a saline or drug pretreatment group, cocaine (0.5, 2, or 5 mg/kg) or lidocaine (2 mg/kg), which was injected via the tail vein. None of the drug pretreatments worsened injury. Lidocaine and cocaine decreased the duration of suppression of some neurological reflexes and reduced posttraumatic body weight losses. Lidocaine and cocaine both decreased postinjury motor deficits. Lidocaine and cocaine did not affect cognitive function on days 11-15 postinjury. The mechanism by which lidocaine improves acute neurological and motor function following brain injury is unknown, but may involve improved posttraumatic cortical blood flow, as seen in our previous study. Our results, along with other studies showing lidocaine to be neuroprotective in animal models of ischemia, suggest that studies of the effect of posttraumatic administration of lidocaine are warranted.

Damage from oxygen and glucose deprivation in hippocampal slices is prevented by tetrodotoxin, lidocaine and phenytoin without blockade of action potentials

In vitro ischemia (IVI) was simulated with rat hippocampal slices in medium lacking D-glucose, equilibrated with 95% nitrogen, 5% carbon dioxide. Within 5-8 min, synaptic potentials disappeared and a DC negative shift (5-15 mV) occurred. Prolonged application of 95% oxygen and D-glucose 12 min later did not allow synaptic potentials to recover. Slices pretreated with sodium channel blocking drugs allowed synaptic potentials to recover after IVI. Tetrodotoxin (TTX, 100-600 nM), the anticonvulsant phenytoin (5.0 to 100 microM) and the local anesthetic lidocaine (2.0 to 200 microM) each delayed or prevented negative DC shifts from IVI. Histological examination showed that drug treatments also prevented CA1 pyramidal cell damage from IVI. Neuroprotection occurred without blocking synaptic potentials or presynaptic fiber volleys, suggesting relevance for treatment of brain ischemia.

Na+ currents that fail to inactivate

Textbook accounts give the impression that Na+ channels are short-acting binary switches: depolarization opens them, but only for about one millisecond. In contrast to this simplified view, a small but significant fraction of the total Na+ current in neurons occurs because channels open after long delays or in long-duration bursts of openings. Such non-inactivating Na+ current acts physiologically in neurons to amplify synaptic potentials and enhance endogenous rhythmicity, and also to aid repetitive firing of action potentials. In glial cells it also may regulate Na(+)-K+ ATPase activity. The evidence for non-inactivating Na+ current in a variety of neurons and glia is reviewed, along with a brief discussion of its ion channel substrate and its relevance for neurological diseases and drug therapy.

Anaerobic glycolysis and postanoxic recovery of respiration of rat cortical synaptosomes are reduced by synaptosomal sodium load

Synaptosomes of rat cerebral cortex were used to study the effect of veratridine-induced Na+ load on postanoxic recovery of respiration and on aerobic and anaerobic ATP turnover, calculated from rates of oxygen consumption and lactate production. Non-stimulated synaptosomes: after onset of anoxia lactate synthesis of synaptosomes rose immediately from 0.8 to 17.7 nmol lactate/min/mg protein indicating an anaerobic ATP turnover of 17.7 nmol ATP/min/mg protein. This value accounts for 80% of ATP synthesized during oxygenated conditions and seems to cover the energetic demand of anoxic synaptosomes. This assumption was supported by linearity of lactate production throughout anoxia (90 min), by unaffected synaptosomal integrity and by complete recovery of postanoxic respiration after 90 min of anoxia. Stimulated synaptosomes: stimulation of oxygenated synaptosomes with 10(-5) mol/l veratridine enhanced ATP turnover 5-fold, due to activation of Na+/K+ ATPase, as a result of veratridine-induced Na+ influx. Consequently, if not limited in capacity, anaerobic ATP synthesis should be enhanced after addition of veratridine during anoxia. However, the opposite effect was observed. Veratridine reduced anaerobic glycolysis in a concentration-dependent manner. This inhibitory effect could be prevented by tetrodotoxin applied 5 min prior to veratridine. Inhibition of anaerobic glycolysis was independent of extrasynaptosomal glucose (1-30 mmol/l) and Ca2+ concentration (Ca(2+)-free and 1.2 mmol/l Ca2+). Veratridine stimulation of anoxic synaptosomes reduced also the recovery of postanoxic respiration. The data indicate that Na+ load inhibits anaerobic ATP synthesis, the only energy source during anaerobic conditions. To our knowledge, inhibition of anaerobic glycolysis due to increased Na+ influx has not been shown so far.