The effect of the calcium antagonist nimodipine on the gerbil model of experimental cerebral ischemia

Glutamate excitotoxicity: Potential therapeutic target for ischemic stroke

Glutamate-mediated excitotoxicity is an important mechanism leading to post ischemic stroke damage. After acute stroke, the sudden reduction in cerebral blood flow is most initially followed by ion transport protein dysfunction and disruption of ion homeostasis, which in turn leads to impaired glutamate release, reuptake, and excessive N-methyl-D-aspartate receptor (NMDAR) activation, promoting neuronal death. Despite extensive evidence from preclinical studies suggesting that excessive NMDAR stimulation during ischemic stroke is a central step in post-stroke damage, NMDAR blockers have failed to translate into clinical stroke treatment. Current treatment options for stroke are very limited, and there is therefore a great need to develop new targets for neuroprotective therapeutic agents in ischemic stroke to extend the therapeutic time window. In this review, we highlight recent findings on glutamate release, reuptake mechanisms, NMDAR and its downstream cellular signaling pathways in post-ischemic stroke damage, and review the pathological changes in each link to help develop viable new therapeutic targets. We then also summarize potential neuroprotective drugs and therapeutic approaches for these new targets in the treatment of ischemic stroke.

Neuroprotective effects by nimodipine treatment in the experimental global ischemic rat model : real time estimation of glutamate

OBJECTIVE

Glutamate is a key excitatory neurotransmitter in the brain, and its excessive release plays a key role in the development of neuronal injury. In order to define the effect of nimodipine on glutamate release, we monitored extracellular glutamate release in real-time in a global ischemia rat model with eleven vessel occlusion.

METHODS

TWELVE RATS WERE RANDOMLY DIVIDED INTO TWO GROUPS: the ischemia group and the nimodipine treatment group. The changes of extracellular glutamate level were measured using microdialysis amperometric biosensor, in coincident with cerebral blood flow (CBF) and electroencephalogram. Nimodipine (0.025 µg/100 gm/min) was infused into lateral to the CBF probe, during the ischemic period. Also, we performed Nissl staining method to assess the neuroprotective effect of nimodipine.

RESULTS

During the ischemic period, the mean maximum change in glutamate concentration was 133.22±2.57 µM in the ischemia group and 75.42±4.22 µM (p<0.001) in the group treated with nimodipine. The total amount of glutamate released was significantly different (p<0.001) between groups during the ischemic period. The %cell viability in hippocampus was 47.50±5.64 (p<0.005) in ischemia group, compared with sham group. But, the %cell viability in nimodipine treatment group was 95.46±6.60 in hippocampus (p<0.005).

CONCLUSION

From the real-time monitoring and Nissl staining results, we suggest that the nimodipine treatment is responsible for the protection of the neuronal cell death through the suppression of extracellular glutamate release in the 11-VO global ischemia model of rat.

The effects of the pre-treatment of intravenous nimodipine on Na(+)-K+/Mg+2 ATPase, Ca+2/Mg+2 ATPase, lipid peroxidation and early ultrastructural findings following middle cerebral artery occlusion in the rat

Excessive calcium influx has been implicated in the pathophysiology of ischemic cerebral damage. The effects of nimodipine, a calcium antagonist, on the Na(+)-K+/MG+2 ATPase activity, Ca+2/Mg+2 ATPase, lipid peroxidation, and early ultrastructural findings were examined at the acute stage of ischemia in the rat brain. Ischemia was produced by permanent unilateral occlusion of the middle cerebral artery. In Group I, the rats which had no ischemia and not received medication were used for determining Na(+)-K+/Mg+2 ATPase, Ca+2/Mg+2 ATPase, the extent of lipid peroxidation by measuring the malondialdehyde content and normal ultrastructural findings. In Group II, the rats which had only subtemporal craniectomy without occlusion and received saline solution were used for determining the effect of the surgical procedure on the biochemical indices and ultrastructural findings. In Group III, the rats received saline solution following the occlusion in the same amount of nimodipine and in the same duration as used in Group IV. In Group IV, nimodipine pre-treatment 15 min before occlusion (microgram kg-1 min-1 over a 10 min period) was applied i.v. Na(+)-K+/Mg+2 ATPase and Ca+2/Mg+2 ATPase activities decreased significantly and promptly as early as 10 min and remained at a lower level than the contralateral hemisphere in the same group and at the normal level in Group I. Nimodipine pre-treatment immediately attenuated the inactivation of Na(+)-K+/Mg+2 ATPase (p < 0.05) but there was no change on Ca+2/Mg+2 ATPase activity (p < 0.05). Malondialdehyde content increased significantly in Group III following ischemia as early as 30 min. Nimodipine pre-treatment decreased the malondialdehyde level in Group IV (p < 0.05). This study supports the possibility that nimodipine pre-treatment effects the membrane stabilizing properties via inhibiting the lipid peroxidation and subsequently restoring some membrane bound and lipid dependent enzymes' activity such as Na(+)-K+/Mg+2 ATPase and the ultrastructural findings.

SM-20220, a potent Na+/H+ exchange inhibitor, improves consciousness recovery and neurological outcome following transient cerebral ischaemia in gerbils

We studied the cerebroprotective effect of SM-20220 (N-(aminoiminomethyl)-1-methyl-1H-indole-2-carboxamide methanesulphonate), a newly synthesized Na+/H+ exchanger (NHE) inhibitor, in Mongolian gerbil global ischaemia. Transient cerebral ischaemia was induced by clipping both common carotid arteries for 30 min followed by 24h reperfusion. Intravenous administration of SM-20220 (0.3 or 1.0 mg kg(-1)) immediately after reperfusion significantly shortened the consciousness recovery time (P < 0.01). SM-20220 also improved the neurological outcome (McGraw's scale) after reperfusion. At the dose of 1.0 mg kg(-1), the mortality rate was significantly reduced at 24 h after reperfusion (P < 0.01). This study shows that NHE is involved in the aggravation of cerebral function, represented by consciousness recovery, and neurological outcome following transient forebrain ischaemia, and that its inhibitor may exert protective effects on post-ischaemic brain damage.

Effects of mannitol and glycerol on cerebral energy metabolism in gerbils

OBJECTIVES

To evaluate the effects of infusion with hyperosmolar solutions, mannitol and glycerol on the recovery of cerebral energy metabolism during ischemia and reperfusion in the gerbil brain.

MATERIALS AND METHODS

Sequential changes in cerebral energy metabolism following 90-min ischemia and up to 8 h after reperfusion were measured in 15 gerbils using 31P nuclear magnetic resonance (NMR) spectroscopy after 60-min infusion of 10% glycerol (0.5 g/kg; n=5), or 20% mannitol (1.0 g/kg; n=5), and compared with those gerbils receiving with saline (n=5). Gerbils were anesthetized by intraperitoneal injection of pentobarbital. Forebrain ischemia was induced by clipping of bilateral common carotid arteries for 90 min and reperfused. NMR spectroscopy was measured by a 6.34-Tesla JEOL spectrometer, before administration, 2, 4, 6, and 8 h after 90-min ischemia and reperfusion. Areas of inorganic phosphate (Pi), phosphocreatine (PCr), and beta-ATP peaks were measured to calculate parameters of cerebral energy metabolism, i.e., PCr/Pi and beta-ATP/Pi ratios. Intracellular pH (pHi) was calculated from chemical shifts of Pi relative to PCr.

RESULTS

PHi was higher in the mannitol group than in the glycerol and saline groups (P<0.05) 2 h after reperfusion. PCr/Pi ratio was higher 2, 4, and 8 h after reperfusion (P<0.01, P<0.05, P<0.01) in the mannitol group; and 6 h after reperfusion (P<0.05) in the glycerol group; than in the saline group. Beta-ATP/Pi ratio was higher 2 and 8 h after reperfusion (P<0.05) in the glycerol group; and 2 h after reperfusion (P<0.01) in the mannitol group, than in the saline group.

CONCLUSIONS

The mannitol group had improved pHi higher than the glycerol group 2 h after reperfusion (P<0.05), while the glycerol group had improved beta-ATP/Pi ratio higher than the mannitol group 6 h after reperfusion (P<0.05). Both mannitol and glycerol groups had improved parameters of cerebral energy metabolism during ischemia and up to 8 h after reperfusion in the gerbil brain.

The influence of nimodipine and MK-801 on the brain free arachidonic acid level and the learning ability in hypoxia-exposed rats

1. The influence of voltage dependent calcium channel blocker (VDCC), nimodipine and N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801 on the brain free arachidonic acid (FAA) level and on the learning ability in hypoxia-exposed rats was examined. 2. Some animals were decapitated after cerebral hypoxia had been obtained and the brain FAA level was determined by gas chromatography. The other animals were trained in a passive avoidance procedure and were exposed to hypoxic conditions immediately after the learning trial response had been acquired. A passive avoidance retention test was performed 24 hours later. 3. Various doses of nimodipine (0.03; 0.1; 0.3 and 1.0 mg/kg) and MK-801 (0.03; 0.1 and 0.3 mg/kg) had been injected 30 minutes before biochemical or behavioral procedures started. 4. It was found that hypoxia strongly increased the brain FAA level and impaired the retention of the passive avoidance response. 5. Pretreatment with 0.3 mg/kg and 1.0 mg/kg of nimodipine prevented the brain FAA accumulation. It has also been shown that all tested doses of nimodipine significantly improved the retention deficit in the animals exposed to hypoxia. 6. Neither the one of tested doses of MK-801 influenced significantly the increase of the brain FAA level and/or passive avoidance behavior in hypoxic animals. 7. These results confirm the hypothesis that the brain FAA accumulation and cognitive impairment, caused by hypoxia, are maybe associated with disturbances in calcium homeostasis and that nimodipine may be useful in ameliorating the hypoxia-induced brain tissue damage. Blocade of NMDA receptor-channel complex by MK-801 was not sufficient to prevent hypoxia-induced neuronal damage.

Nimodipine improves brain energy metabolism and blood rheology during ischemia and reperfusion in the gerbil brain

Whether nimodipine improves cerebral blood flow (CBF) and metabolism in cerebral ischemia remains a controversial issue. We investigated the effect of nimodipine on CBF, brain energy metabolism, using a laser-Doppler flowmeter and in vivo 31phosphorus nuclear magnetic resonance (31P NMR) spectroscopy, and blood rheology during forebrain ischemia and reperfusion in gerbils. Eighty-three adult gerbils received nimodipine (1 micrograms/kg/min), or an equal volume of the vehicle, or saline, over 60 min prior to a transient forebrain ischemia for 60 min. We measured sequential changes in phosphocreatine (PCr) / inorganic phosphate (Pi) ratio, beta-ATP/Pi ratio, and intracellular pH (pHi) during ischemia and reperfusion by 31P NMR spectroscopy, and the measurement of whole blood viscosity (WBV) at 60 min after reperfusion. CBF was measured continuously throughout the study by a laser-Doppler flowmeter. During forebrain ischemia, PCr/Pi and beta-ATP/Pi ratios were higher significantly in the nimodipine-treated group (p < 0.05 and 0.01) than in the vehicle- or saline-treated groups. During reperfusion, PCr/Pi and beta-ATP/Pi ratios recovered significantly only in the nimodipine-treated group (p < 0.05 and 0.01). The WBV at high shear rate (562.5 s-1) lowered significantly in the nimodipine-treated group (p < 0.05) compared with the vehicle- or saline-treated group. CBF was higher significantly only during administration of nimodipine in the nimodipine-treated group (p < 0.01) than other groups. Nimodipine improved brain energy metabolism and blood rheology during forebrain ischemia and reperfusion in the gerbil brain.

Neurochemical mechanisms in brain injury and treatment: a review

This article reviews cellular energy transformation processes and neurochemical events that take place at the time of brain injury and shortly thereafter emphasizing hypoxia-ischemia, cerebrovascular accident, and traumatic brain injury. New interpretations of established concepts, such as diffuse axonal injury, are discussed; specific events, such as free radical production, excess production of excitatory amino acids, and disruption of calcium homeostasis, are reviewed. Neurochemically-based interventions are also presented: calcium channel blockers, excitatory amino acid antagonists, free radical scavengers, and hypothermia treatment. Concluding remarks focus on the role of clinical neuropsychologists in validation of treatment interventions.

Neuronal protective effects of calcium antagonists in cerebral ischemia

We investigated the effects of calcium antagonists against ischemic injury in vivo and against excitotoxic damage in vitro. In vivo nimodipine protected significantly the CA1 hippocampal neurons from neurodegeneration after transient global ischemia in rats without changing the local cerebral blood flow. Furnidipine reduced the area of ischemia after permanent MCA-occlusion in mice. The results in vitro using the Ca(2+)-sensitive dye fura-2 showed that nimodipine reduced in a dose-dependent manner the elevation of [Ca2+]i in hippocampal neurons induced by K(+)-stimulation. The present in vitro and in vivo data show that calcium antagonists are potent agents in protecting neurons against the deleterious consequences of an excitotoxic or ischemic insult.

The effect of nimodipine on high-energy phosphates and intracellular pH during cerebral ischemia

Experimental and clinical studies suggest that the calcium channel blocker nimodipine may reduce cerebral ischemic injury. Using rapid acquisition phosphorus-31 nuclear magnetic resonance (31P NMR) spectroscopy, we examined the effect of nimodipine on cerebral energy metabolism during severe ischemia in gerbils. High-energy phosphates and intracellular pH were characterized at baseline and at 2-min intervals following bilateral common carotid artery (CCA) ligation. Serial forebrain spectroscopy was continued until phosphocreatine (PCr) and adenosine triphosphate (ATP) resonances disappeared. Controls (n = 10) were compared to gerbils receiving intraperitoneal nimodipine 30 min prior to carotid ligation, at the following doses: 0.5 mg/kg (n = 8), 1.0 mg/kg (n = 10), 2.0 mg/kg (n = 8), or 4.0 mg/kg (n = 4). In the control group, PCr and ATP peaks were undetectable after a mean of 5.4 +/- 0.47 min following CCA ligation. Compared with controls, the mean time for depletion of high-energy phosphates following carotid ligation was prolonged at nimodipine doses of 0.5 mg/kg and 1.0 mg/kg, but the differences did not reach statistical significance. In the 2.0 mg/kg group, however, ATP was preserved until 9.8 +/- 1.0 min following the onset of ischemia, significantly longer than the control group (p = 0.005, Mann-Whitney test). Nimodipine had no effect on the time course or severity of intracellular acidosis. In this model of severe ischemia, relatively high doses of nimodipine slowed the depletion of high-energy phosphates without altering intracellular acidosis. This suggests that nimodipine may provide cerebral protection by directly altering ischemic cellular metabolism.

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.

Protective effects of benidipine on arachidonic acid-induced acute cerebral ischemia in rats

Acute cerebral ischemia was produced in rats by injection of arachidonic acid (AA) into the internal carotid artery. Evans blue (EB) was intravenously injected and its extravasation into the brain was determined as an indicator of disturbances in the blood-brain barrier and endothelial cells. Control animals showed severe cerebral edema and marked blue staining of the brain. Benidipine (30 micrograms/kg, i.p.) suppressed the increase in cerebral water content and the extravasation of EB. Similarly nicardipine (100 micrograms/kg, i.p.) suppressed the elevation of water content and the extravasation of EB. Furthermore, both benidipine (30 micrograms/kg, i.p.) and nicardipine (100 micrograms/kg, i.p.) improved the neuronal injuries following AA-injection. An antiplatelet agent, ticlopidine (100 mg/kg, i.p.), and a thromboxane A2 synthetase inhibitor, OKY-1581 (3 mg/kg, i.p.), also suppressed the elevation of cerebral water content. A lipoxygenase inhibitor, AA-561 (200 mg/kg, p.o.), and a cyclooxygenase inhibitor, indomethacin (10 mg/kg, i.p.), did not prevent the increase in cerebral water content. Neither benidipine (3-30 micrograms/kg, i.v.) nor nicardipine (100 micrograms/kg, i.v.) inhibited the AgNO3-induced thrombus formation of the abdominal aorta, whereas ticlopidine (100 mg/kg, p.o.) and OKY-1581 (3 mg/kg, i.v.) prevented the thrombus formation. From the present results, it is suggested that benidipine, as well as nicardipine, may protect against AA-induced acute cerebral infarction via a mechanism independent of antithrombotic action.

Various Ca2+ entry blockers prevent glutamate-induced neurotoxicity

In the present study we investigated the effect of different Ca2+ entry blockers on the onset of neuronal damage induced by glutamate, kainate or alpha-amino-3-hydroxy-5-methyl-5-isoxazolo propionate (AMPA) in primary culture of rat cerebellar granule cells. We found that the dihydropyridine derivative, nifedipine used at 100 nM concentration, significantly counteracted the neuronal death induced by 15 min application of 50 microM glutamate. This effect was dependent on the presence of nifedipine before the exposure of granule cells to glutamate and was dose-related (IC50 = 10 nM). The nifedipine response was reproduced by isradipine and by verapamil with IC50 values of 9 and 100 nM, respectively. The activation of voltage sensitive Ca2+ channels elicited by 100 nM Bay K 8644, greatly enhanced glutamate-mediated neurotoxicity. Moreover, 100 nM isradipine was significantly active in blocking the neuronal death produced by 24 h exposure of cerebellar granule cells to 10 microM AMPA or 60 microM kainate. These results reveal a 'preventive' role of the Ca2+ entry blockers on the development of the neurodegeneration induced by overstimulation of various glutamate receptor subtypes.

Therapeutic window of halothane anesthesia for reversal of delayed neuronal injury in gerbils: relationship to postischemic motor hyperactivity

The effect of postischemic halothane anesthesia on locomotor activity and delayed neuronal injury in the hippocampal CA1 sector was examined in gerbils subjected to 5-min forebrain ischemia. Locomotor activity was assessed for 48 h after ischemia using an animal activity monitor, and CA1 injury was evaluated by counting the number of surviving neurons following 7 days of recirculation. Sham-treated animals exhibited a slight decrease of motor activity for about 1 day after surgery. Gerbils subjected to ischemia without postischemic halothane anesthesia developed significant motor hyperactivity (18 times higher than control activity) between 1.7 h and 6.7 h of recirculation. Surviving CA1 neurons in this group amounted to only 17% of those in the control animals. Postischemic halothane anesthesia during the initial 1.7 h of recirculation abolished subsequent motor hyperactivity and protected 84% of all CA1 neurons. Postischemic halothane anesthesia during 1.7 h-3.3 h of recirculation and 3.3-5 h of recirculation did not abolish motor hyperactivity except during the period of anesthesia, and did not protect hippocampal CA1 neurons (only 24% and 10% neuronal survival, respectively). These results demonstrate that the therapeutic window of halothane anesthesia for protection of hippocampal injury precedes the phase of locomotor hyperactivity, and that the appearance of the latter predicts delayed neuronal death.

A trial of the effect of nimodipine on outcome after head injury

We performed a randomised prospective double blind trial to study the effect of the calcium antagonist nimodipine on the outcome of head injured patients. The subjects were not obeying commands at the time of entry to the study, within 24 hours of injury. One hundred and seventy-five patients received nimodipine IV, 2 mg per hour for up to 7 days and 176 received placebo. The two groups were well matched for important prognostic features. Six months after injury 93 (53%) of the nimodipine group and 86 (49%) of the control group had a favourable outcome (moderate/good recovery). The relative increase in favourable outcomes (8%) was not significant but is compatible (95% C.I.) with an increase in favourable outcomes in treated patients by 33% or a decrease by 12%. Nimodipine was well tolerated and there were few adverse reactions; means of systolic and diastolic blood pressures and the intracranial pressure did not differ between the groups. It is unlikely that nimodipine has a marked effect on outcome (ie an increase in favourable outcome of greater than 15%) after head injury of this severity but the study does not exclude a modest but clinically useful benefit.

Failure of nimodipine to improve neurologic outcome after eighteen minutes of cardiac arrest in the cat

The calcium entry blocker nimodipine was administered to cats following resuscitation from 18 min of cardiac arrest to evaluate its effect on neurologic and neuropathologic outcome in a clinically relevant model of complete cerebral ischemia. Cardiac arrest (ventricular fibrillation) was maintained for 18 min and resuscitation was performed by a standardized protocol in 40 cats. Beginning at 5 min post-resuscitation, nimodipine, 10 micrograms/kg over 2 min followed by 1 microgram/kg per min for 10 h, or the same volume of placebo was administered in a randomized, blinded fashion. Neurologic deficits were scored at 2, 4, and 7 days post-resuscitation by observers blinded to the treatment group. Thirty cats were evaluated neurologically at 7 days post-resuscitation and were entered into data analysis (n = 15 per group). Neither neurologic deficit scores nor neuropathologic scores were significantly different between groups. The authors conclude that nimodipine administration in the manner and doses stated does not improve neurologic outcome in cats following resuscitation from cardiac arrest.

Prevention of postischemic hyperthermia prevents ischemic injury of CA1 neurons in gerbils

Halothane-anesthetized Mongolian gerbils were submitted to 5-min bilateral carotid artery occlusion. After ischemia, halothane anesthesia was continued for various periods of up to 85 min, and the degree of CA1 neuronal injury was estimated 7 days later by counting the number of surviving pyramidal cells. During ischemia and postischemic halothane anesthesia, rectal and cranial temperature was kept at control level (37.7 and 37.0 degrees C, respectively) using a feedback-controlled heating system. When anesthesia was discontinued after ischemia, transient hyperthermia occurred. In animals with 0- and 15-min postischemic halothane anesthesia, both cranial and rectal temperature rose by approximately 1.5 degrees C, and the number of surviving CA1 neurons amounted to less than 25% of control. After 45- or 85-min postischemic anesthesia, hyperthermia was significantly reduced and the number of surviving neurons increased to 65 and 89%, respectively. The protective effect of postischemic anesthesia was lost when anesthetized animals were submitted to the same hyperthermic profile as nonanesthetized ones, using a feedback-controlled heating system (16% surviving neurons in hyperthermia vs. 89% in normothermia, respectively). These observations demonstrate that postischemic anesthesia with 1% halothane protects against delayed neuronal death by preventing postischemic hyperthermia and not by its anesthetic effects.

Threshold of carotid artery back pressure for delayed neuronal injury in the hippocampus after bilateral common carotid artery occlusion in gerbils

The threshold of carotid artery back pressure for the development of neuronal injury in the hippocampus was determined in gerbils following bilateral carotid artery occlusion of 5 or 10 min. Arterial back pressure was measured during ischemia at the left carotid bifurcation distal to the vascular occlusion, and neuronal injury evaluated one week after ischemia by counting the number of surviving neurons in the left hippocampal CA1 sector. With an arterial back pressure below 5 mm Hg, the mean density of surviving neurons decreased from 199 +/- 16/mm (mean +/- SD) to less than 21/mm both after 5 and 10 min ischemia (P less than 0.05). With a back pressure of between 5 and 15 mm Hg, neuronal density was 117 +/- 77/mm (not significantly different from control) after 5 min, and 24 +/- 18/mm (P less than 0.05) after 10 min ischemia. Above 15 mm Hg neither 5 nor 10 min ischemia produced significant neuronal damage. Thus, at threshold arterial back pressure, induction of neuronal injury in the hippocampus depends on the duration of ischemia, indicating progressive impairment of microcirculation with longer periods of ischemia.

MK-801 is neuroprotective in gerbils when administered during the post-ischaemic period

The neuroprotective effects of the non-competitive N-methyl-D-aspartate receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) have been evaluated in the gerbil hippocampus when the drug was administered i.p. at various times during and after a 5 min period of transient forebrain ischaemia, induced by bilateral common carotid artery occlusion. A single dose of 1, 3 or 10 mg/kg of MK-801 gave significant protection of hippocampal CA1 and CA2 pyramidal neurons when administered during the occlusion and up to 24 h following the period of ischaemia. A dose of 0.3 mg/kg was effective when administered during the occlusion period but gave no protection at 30 min or 2 h post-ischaemia. Experiments in which MK-801 was administered in repeated doses indicated that significant protection was achieved with 1 mg/kg of MK-801 repeated post-ischaemically and with 1 mg/kg MK-801 supplemented with repeated doses of 0.3 mg/kg of MK-801. However 0.3 mg/kg of MK-801 followed by repeated doses of 0.03 mg/kg administered post-ischaemically was not neuroprotective. These results indicate that MK-801 can protect hippocampal neurons from ischaemia-induced neuronal degeneration when it is administered up to 24 h after the insult. These data provide further evidence that therapeutic intervention in the post-ischaemic period can successfully prevent neurodegenerative events, and that the delayed degeneration of hippocampal neurons following an ischaemic insult occurs by an N-methyl-D-aspartate receptor-mediated process.

Effects of nifedipine and felodipine on adenosine and inosine release from the hypoxemic rat cerebral cortex

The cerebral cortical cup technique has been used to study the effects of nifedipine and felodipine on adenosine and inosine release from the rat brain. After basal and hypoxia (8% 02)-evoked control levels of purine release had been established, these 1,4-dihydropyridine calcium antagonists were administered intraperitoneally (1 mg/kg). Both agents depressed basal levels of purine efflux and suppressed the hypoxia-evoked release of adenosine and inosine. An inhibition of the transporter that mediates purine efflux from brain cells is likely to account for the suppression of release from the cerebral cortex. A reduced release of adenosine into the interstitial space also explains the ability of both agents to block the increase in CBF evoked by hypoxic challenges.

Levallorphan and dynorphin improve motor dysfunction in Mongolian gerbils with unilateral carotid occlusion: the first application of the inclined plane method in the experimental cerebral ischemia

Levallorphan and dynorphin were effective on the motor dysfunction in the gerbil model of unilateral cerebral ischemia. The effect of opioids, levallorphan (mixed agonist-antagonist), dynorphin (kappa-receptor agonist) and naloxone (mu-receptor antagonist), on neurological impairment was evaluated using the unilateral cerebral ischemia model of gerbil. Motor function was evaluated quantitatively by using the inclined plane method. Both levallorphan-treated group and dynorphin-treated group showed a significant improvement of the motor dysfunction compared with saline-control group. On the other hand, naloxone-treated group did not differ from saline-control group. The beneficial effect of these opioids on motor dysfunction might be mediated by the kappa-opioid receptor. This study also showed the potential usefulness of the inclined plane method for the investigation on the cerebral ischemia.

Haemodynamic effectiveness of nimodipine on spastic brain vessels after subarachnoid haemorrhage evaluated by the transcranial Doppler method. A review of clinical studies

The authors review the literature reports and own results of a double-blind study of the effectiveness of nimodipine on prevention or treatment of spasm of cerebral arteries following subarachnoid haemorrhage (SAH). Spasm has been evaluated using the transcranial Doppler method (TCD). The patients were divided into two groups which received 2 resp. 3 mg/h nimodipine. The clinical outcome and also the incidence of spasm of both of the groups were not different, but spasm was less severe in the 3 mg/h group.