Neuroprotection of S(+) ketamine isomer in global forebrain ischemia

The non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist ketamine can block the action of excitotoxic amino acids in the central nervous system. S(+) ketamine has a 2-3 times higher anesthetic potency compared with the ketamine-racemate and also shows a higher neuroprotective efficacy in vitro. To determine the neuroprotective activity of S(+) ketamine compared with its R(-) stereoisomer in vivo, we examined the functional and neurohistological outcome in rats treated 15 min after global forebrain ischemia with S(+) ketamine in different dosages compared with R(-) ketamine. Influence of the treatment on regional cerebral blood flow (rCBF) and cortical oxygen saturation (HbO2) was monitored over 1 h after the ischemia using laser doppler flowmetry and microphotospectrometry respectively. Sixty and ninety mg/kg of S(+) ketamine but not R(-) ketamine significantly reduced neuronal cell loss in the cortex compared with the saline treated group. No significant neuroprotection was observed in the hippocampus. Although no significant change in rCBF was found, S(+) ketamine restored the cortical HbO2 to preischemic values. These results indicate that S(+) ketamine in higher dosages can reduce neuronal damage in the cortex after cerebral ischemia, possibly by improving the ratio of oxygen supply to consumption in the postischemic tissue.     

Zonisamide as a neuroprotective agent in an adult gerbil model of global forebrain ischemia: a histological, in vivo microdialysis and behavioral study

Brief periods of global cerebral ischemia are known to produce characteristic patterns of neuronal injury both in human studies and in experimental animal models. Ischemic damage to vulnerable areas such as the CA1 sector of the hippocampus is thought to result from excitotoxic amino acid neurotransmission. The objective of this study was to determine the ability of a novel sodium channel blocking compound, zonisamide, to reduce neuronal damage by preventing the ischemia-associated accumulation of extracellular glutamate. Using a gerbil model, animals were subjected to 5 min ischemic insults. Both pre- and post-ischemic drug administration (zonisamide 150 mg/kg) were studied. Histological brain sections were prepared using a silver stain at 7 and 28 days post ischemia. The animals sacrificed at 28 days also underwent behavioral testing using a modified Morris water maze. In vivo microdialysis was performed on a separate group of animals in order to determine the patterns of ischemia-induced glutamate accumulation in the CA1 sector of the hippocampus. Pyramidal cell damage scores in the CA1 region of the hippocampus were significantly reduced in animals pre-treated with zonisamide compared to saline-treated controls, both at 7 days (drug pre-treated: 0.812±0.28, n=8; controls: 1.625±0.24, n=8; ^*P<0.05) and 28 (drug pre-treated: 0.833±0.22, n=12; controls: 1.955±0.26, n=11; ^**P<0.01) days post ischemia. However, animals receiving zonisamide post-treatment did not display significant differences from controls. Behavioral studies also showed significant preservation of function in drug-treated animals. Microdialysis studies confirmed a reduction in glutamate release in drug-treated animals compared to saline-treated controls. Our data suggest that zonisamide is effective in reducing neuronal damage by a mechanism involving decreased ischemia-induced extracellular glutamate accumulation and interruption of excitotoxic pathways.     

蛇床子素在缺血再灌注脑损伤模型中的脑保护作用

目的研究蛇床子素（osthole）在缺血再灌注脑损伤中的脑保护作用。方法实验用SD大鼠55只随机分为假手术组、模型组和三个不同剂量给药组（Ost）,其中模型组和给药组采用四血管阻塞法大鼠全脑缺血模型（4VO模型）。各给药组于缺血15min再灌注后1h给予5mg／kg、25mg／kg、125mg／kg蛇床子素腹腔注射治疗。各实验组动物在进行神经功能学评分后,分别用于分析海马CA1区细胞组织形态学变化和caspase3蛋白半定量分析,评价蛇床子素在缺血再灌注脑损伤后的脑保护作用。结果缺血15min再灌注后1h给药的各蛇床子素治疗组大鼠的行为学评分和组织形态学分析结果均明显优于模型组（P〈0．01）并在25mg／kg剂量时表现出最大保护效果,其caspase3表达水平显著降低。结论蛇床子素在脑缺血再灌注脑损伤后有一定的脑保护作用。     

Neuroprotection by both NMDA and non-NMDA receptor antagonists in in vitro ischemia

We have investigated the relative contributions of oxygen and glucose deprivation to ischaemic neurodegeneration in organotypic hippocampal slice cultures. Cultures prepared from 10-day-old rats were maintained in vitro for 14 days and then deprived of either oxygen (hypoxia), glucose (hypoglycaemia), or both oxygen and glucose (ischaemia). Hypoxia alone induced degeneration selectively in CA1 pyramidal cells and this was greatly potentiated if glucose was removed from the medium. We have also characterised the effects of both pre-and post-treatment using glutamate receptor antagonists and the sodium channel blocker tetrodotoxin (TTX). Neuronal death following either hypoxia or ischaemia was prevented by pre-incubation with CNQX, MK-801 or tetrodotoxin. MK-801 or CNQX also prevented death induced by either hypoxia or ischaemia if added immediately post-insult, however, post-insult addition of TTX prevented hypoxic but not ischaemic damage. Organotypic hippocampal slice cultures are sensitive to both NMDA and non-NMDA glutamate receptor blockade and thus represent a useful in vitro system for the study of ischaemic neurodegeneration paralleling results reported using in vivo models of ischaemia.     

A model of global forebrain ischemia/reperfusion in the awake rat.

Anesthesia is an essential element during the induction of ischemia/reperfusion and cerebral blood flow (CBF) measurement in most animal models. Cerebral neuroprotection and intrinsic effects on CBF afforded by anesthetics are confounding variables in those models. A new model of global forebrain ischemia/reperfusion (GFIR) in awake rats is presented and characterized. Rats underwent permanent occlusion of the basilar, and the paired pterygopalatine, external carotid, and occipital arteries. Inflatable balloon occluders were inserted around both common carotids, the nine-vessel occlusion (9VO) preparation. A subgroup of 9VO rats underwent placement of a laser Doppler flowmetry (LDF) probe for measurement of cortical CBF. Twenty-four hours later, while awake, 9VO rats were subjected to 10 min of ischemia by occluding both common carotid arteries. Blood gases, glucose and hematocrit were analyzed before and during ischemia, and for up to 90 min during reperfusion. Behavioral observations and continuous LDF CBF and mean arterial blood pressure determinations during ischemia and reperfusion were made. Rats were rendered comatose and decerebrate rigidity was observed during 9VO. Following balloon deflation, rats immediately regained the righting reflex and achieved complete recovery in the next 24 h. Moderate hyperglycemia was observed at 5 min of ischemia and up to 90 min reperfusion in 9VO rats. LDF CBF decreased to 5% of baseline and remained unchanged during ischemia. The 9VO is a reproducible recovery model of GFIR. Behavioral and LDF CBF correlates are consistent and survival studies are feasible.     

A conformationally restricted analogue of -glutamate, the (2S,3R,4S) isomer of -α(carboxycyclopropyl)glycine, activates the NMDA-type receptor more markedly than NMDA in the isolated rat spinal cord

Depolarizing actions of 4 conformationally restricted L-glutamate analogues, (2S,3S,4S) isomer (L-CCG-I), (2S,3R,4R) isomer (L-CCG-II), (2S,3S,4R) isomer (L-CCG-III) and (2S,3R,4S) isomer (L-CCG-IV) of L-alpha-(carboxycyclopropyl)-glycine (L-CCG), were investigated in the isolated rat spinal cord by extracellular recordings of potential changes of motoneurones from the ventral roots, in order to study the interaction between the conformation of glutamate and its receptor subtype. The order of the depolarizing activity was quisqualate greater than L-CCG-IV = kainate greater than NMDA greater than L-CCG-I greater than L-CCG-III greater than L-CCG-II. The depolarization caused by L-CCG-IV was effectively blocked by the NMDA antagonists and Mg2+ ions, while the L-CCG-I response was not affected by these blockers. These results suggest that the NMDA-type receptor is activated by a folded form of L-glutamate.     

Neuroprotective effects of bilobalide, a component of the Ginkgo biloba extract (EGb 761), in gerbil global brain ischemia

The neuroprotective effect of Ginkgo biloba extract (EGb 761) against ischemic injury has been demonstrated in animal models. In this study, we compared the protective effect of bilobalide, a purified terpene lactone from EGb 761, and EGb 761 against ischemic injury. We measured neuronal loss and the levels of mitochondrial DNA (mtDNA)-encoded cytochrome oxidase (COX) subunit III mRNA in vulnerable hippocampal regions of gerbils. At 7 days of reperfusion after 5 min of transient global forebrain ischemia, a significant increase in neuronal death and a significant decrease in COX III mRNA were observed in the hippocampal CA1 neurons. Oral administration of EGb 761 at 25, 50 and 100 mg/kg/day and bilobalide at 3 and 6 mg/kg/day for 7 days before ischemia progressively protected CA1 neurons from death and from ischemia-induced reductions in COX III mRNA. In addition, both bilobalide and EGb 761 protected against ischemia-induced reductions in COX III mRNA in CA1 neurons prior to their death, at 1 day of reperfusion. These results suggest that oral administration of bilobalide and EGb 761 protect against ischemia-induced neuron death and reductions in mitochondrial gene expression.     

Effect of intracerebral norepinephrine depletion on outcome from severe forebrain ischemia in the rat

Manipulations of plasma catecholamine concentrations influence outcome from ischemic brain insults. It has been suggested that these effects are mediated by influences on brain catecholamine concentrations. This study examined whether major changes in brain norepinephrine concentrations can alter outcome from severe forebrain ischemia. Sprague-Dawley rats were administered 50 mg/kg i. p. N-(chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) or were left untreated (control). One week later, these rats were subjected to either 7 or 8 min of normothermic forebrain ischemia (bilateral carotid occlusion and MABP=30 mmHg) and allowed to recover for 4 days. Histologic damage was then evaluated. In other control and DSP-4-treated animals, hippocampal microdialysate norepinephrine concentrations were measured before, during and after 8 min of forebrain ischemia. Norepinephrine concentrations were also determined in brain homogenates from non-ischemic DSP-treated and control rats. A 95% depletion of norepinephrine was observed in brain homogenates from non-ischemic DSP-4-treated rats compared with control. During ischemia, microdialysate norepinephrine concentrations increased in control but not in DSP-4-treated rats (P=0.002). For plasma, intra-ischemic epinephrine concentrations increased 8-10-fold and returned to baseline values post-ischemia with no differences between groups. Plasma norepinephrine values remained unchanged in both groups. Histologic damage resulting from either 7 or 8 min of ischemia in hippocampal structures, caudoputamen, and neocortex was similar between DSP-4-treated and control groups. This study could not identify any effect of major changes in brain norepinephrine concentrations on ischemic brain damage. These data indicate that peripheral catecholamine effects on near-complete forebrain ischemic outcome are unlikely to be mediated by effects on central catecholamine concentrations.     

Intraseptal administration of (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid induces immediate early gene expression in lateral septal neurons

Prior work has shown that activation of metabotropic glutamate receptors can induce burst firing and a form of NMDA receptor independent long term potentiation in lateral septal slice preparations. To study this phenomenon in vivo we used the expression of immediate early gene products as markers for increased neuronal activity following intraseptal injection of the metabotropic agonist 1S,3R-ACPD. Intraseptal injection of 1S, 3R ACPD induced the expression of Fos-like, Jun 13-like and Krox24-like immunoreactivity in lateral septal neurons in a dose-dependent fashion. Immediate early gene product expression peaked at 4 to 6 h post-injection and then declined to baseline. Immediate early gene expression was diminished by co-injection of -AP3 and was not elicited by intraseptal injection of -AP4, cysteine sulfinic acid or DHPG. Immediate early gene expression was not diminished by chronic lithium treatment but was diminished by chronic treatment with the phospholipase A₂ inhibitor quinacrine. Co-injection of the phospholipase AZ inhibitor NDGA partially suppressed the induction of immediate early gene expression. Metabotropic glutamate receptors regulate lateral septal neuron excitability in vivo and some of their effects may be mediated by activation of phospholipase A₂. Alternatively, arachidonic acid may play a permissive role it the effects of metabotropic glutamate receptors on lateral septal neurons.     

Effects of transient forebrain ischemia on long-term enhancement of dopamine release in rat striatal slices

We studied the effects of transient forebrain ischemia in vivo on long-term enhancement of dopamine (DA) release from rat striatal slices. One hour after the high-frequency tetanic stimulation (HFTS) or l-glutamate (10⁻⁶ M) application in Mg²⁺-free medium to striatal slices, the high concentration of KCl (high K⁺)-evoked DA release was measured. Tetanic stimulation or l-glutamate application significantly potentiated the high-K⁺-evoked DA release. When striatal slices were prepared from rats exposed to 3 min of ischemia followed by 24-h survival, the enhancement of DA release by HFTS was unaffected by ischemia. In contrast, the enhancement of DA release by HFTS was impaired in rats exposed to 5 min or 10 min of ischemia. In addition, high K⁺-evoked DA release per se was significantly impaired by 10 min of ischemia. The enhancement of DA release elicited by pretreatment with l-glutamate was also impaired in the rats exposed to 5 min of ischemia. When striatal slices were prepared from rats exposed to 5 min of ischemia with 7-day survival, the enhancement of DA release by HFTS was still impaired. The present results indicate that the neuronal mechanisms of the enhancement of DA release may be more sensitive to impairement from short periods of ischemia. Furthermore, the results suggest that an impairment of long-term enhancement of DA release by ischemia may be related the dysfunction of motor performance in rats exposed to ischemia.     

Neuroprotection and glutamate attenuation by acetylsalicylic acid in temporary but not in permanent cerebral ischemia

To assess the effects of acetylsalicylic acid (ASA) on glutamate and interleukin-6 (IL-6) release in the striatum of rats suffering from cerebral ischemia, we used the microdialysis technique with probes implanted 2 h prior to stroke onset. A total of 36 rats were randomly assigned to either temporary (90 min, n=18) or permanent (n=18) middle cerebral artery occlusion (MCAO). Animals received either a bolus of 40 mg/kg ASA or saline as control 30 min after stroke onset. Permanent MCAO led to large infarct volumes with no differences between treatment with ASA (239.8+/-4.1 mm3) and saline (230.1+/-3.9 mm3, p=0.15). In contrast, ASA therapy in temporary ischemia (87.2+/-6.2 mm3) reduced infarct size significantly compared to placebo (155.6+/-4.8 mm3, p<0.0001). Only in temporary ischemia, ASA application reduced glutamate significantly at the time points 90, 120, and 150 min after MCAO. Pooled post-ischemic microdialysate concentrations of IL-6 in temporary MCAO were significantly higher after ASA treatment (215+/-81 pg/mL, p=0.0297) than in saline-treated rats (80+/-13 pg/mL). In the permanent MCAO group, no difference in IL-6 between the ASA (125+/-21 pg/mL) and saline group (68+/-34 pg/mL) was noted. No differences were seen for c-fos positive neurons in the penumbra and hippocampus between all groups. These results suggest that the neuroprotective effect of ASA is reflected by glutamate attenuation and IL-6 induction even if given after stroke onset, but only if reperfusion is achieved.     

C57BL/6 strain is most susceptible to cerebral ischemia following bilateral common carotid occlusion among seven mouse strains: selective neuronal death in the murine transient forebrain ischemia

Rats and gerbils have been used widely to investigate the molecular mechanism of selective neuronal death following transient global ischemia. Recently, the availability of transgenic mice has enabled us to examine the involvement of specific gene products in various pathophysiological conditions. However, there has been only limited information about the experimental model of cerebral ischemia in mice, particularly in regard of selective neuronal death. We examined whether bilateral carotid occlusion produced global forebrain ischemia in seven common mouse strains including C57BL/6, ICR, BALB/c, C3H, CBA, ddY and DBA/2, based on neurological signs, histological findings and cortical microcirculatory as well as India ink perfusion patterns. The C57BL/6 strain was found to be the most susceptible among seven strains. All C57BL/6 mice died within 6 h after permanent bilateral carotid occlusion. After transient bilateral carotid occlusion for 20 min, more than 90% of C57BL/6 mice showed typical neurological signs such as torsion of the neck and rolling fits, and developed selective neuronal death in the hippocampus and caudoputamen. Hypothermia prevented the neuronal death. Visualization of brain vasculature by India ink perfusion indicated that the susceptibility of the mice after bilateral carotid occlusion depended mainly on the degree of anastomosis between carotid and basilar arteries. Our results showed the feasibility of investigating selective neuronal death in transgenic mice with simple temporary occlusion of both common carotid arteries, when those from the C57BL/6 strain or inbred transgenic mice from other strains with the C57BL/6 strain in a back-cross manner are used.     

Effects of clomethiazole on radial-arm maze performance following global forebrain ischemia in gerbils

The functional and neuroanatomical protective effects of clomethiazole (CMZ) were examined in an animal model of global forebrain ischemia. Gerbils underwent sham-surgery or were rendered ischemic by the application of aneurysm clips to both carotid arteries for 6 min. Three treatment groups received CMZ (50 mg/kg, 100 mg/kg, or 150 mg/kg) 30 min before ischemia, and one group was given 150 mg/kg of CMZ 30 min after ischemia. Following recovery, the gerbils were tested in a radial-arm maze to assess memory functions. Histological evaluation was assessed blindly using a percentile scoring system. The results indicate that pre-ischemic treatment with 100 mg/kg and 150 mg/kgof CMZ reduced brain damage and working memory errors significantly. Treatment dosage of150 mg/kg of CMZ was the most effective in preventing neuronal damage in the hippocampus and eliminating the working memory deficit typically induced by ischemia.     

Lubeluzole inhibits accumulation of extracellular glutamate in the hippocampus during transient global cerebral ischemia

Increases in extracellular glutamate during cerebral ischemia may play an important role in neuronal injury. Lubeluzole is a novel neuroprotective drug, which in previous in vitro and focal ischemia studies has been shown to inhibit nitric oxide synthesis, to block voltage-gated Na+-ion channels, and to inhibit glutamate release. In this study, we investigated the ability of lubeluzole to inhibit glutamate accumulation during episodes of transient global cerebral ischemia. Twenty-five New Zealand white rabbits were randomized to one of four groups: a normothermic control group; a hypothermic group; a 1.25 mg/kg lubeluzole group; or a 2.5 mg/kg lubeluzole group. The animals were anesthetized, intubated, and ventilated before microdialysis probes were placed in the hippocampus. Lubeluzole was given intravenously 90 min before the onset of ischemia. Esophageal temperature was maintained at 38 degrees C in the control, and lubeluzole treated groups, while the animals in the hypothermia group were cooled to 30 degrees C. A 15-min period of global cerebral ischemia was produced by inflating a neck tourniquet. Glutamate concentrations in the microdialysate were determined using high-performance liquid chromatography (HPLC). During ischemia and early reperfusion, glutamate concentrations increased significantly in the control group and returned to baseline after 15 min of reperfusion. In the lubleuzole 2.5 mg/kg and hypothermia groups, glutamate levels were significantly lower (P<0.05) than in the control group and there was no significant change from baseline levels during the entire experiment. This study suggests that lubeluzole is effective in inhibiting extracellular glutamate accumulation during global cerebral ischemia, and has the potential to produce potent neuroprotection when instituted prior to an ischemic event.     

A comparison of strain-related susceptibility in two murine recovery models of global cerebral ischemia

Genetically engineered mice are increasingly important in stroke research. The strains on which these constructs are built are known to have inherent differential sensitivities to ischemic insults. This has been largely attributed to differences in vascular anatomy. This study compared the outcome from forebrain ischemia in two common murine background strains using two different types of ischemic insult. C57Bl/6 and SV129 mice were subjected to two vessel (bilateral carotid) occlusion (2VO) or 2VO plus systemic hypotension (2VO+Hypo; mean arterial pressure=30+/-2 mmHg) for 10-20 min. Ventilation and pericranial temperature were controlled. Cerebral blood flow (CBF) was determined by 14C-iodoantipyrine autoradiography. Histologic damage in forebrain structures was measured 3 days post-ischemia. During 2VO+Hypo, the EEG became isoelectric in all animals. During 2VO alone, EEG isoelectricity occurred in 73% of C57Bl/6 and 50% of SV129 mice. Forebrain CBF was reduced to a similar extent in both strains. Greater CBF variability was seen with 2VO alone versus 2VO+Hypo. CBF was less in the 2VO+Hypo model. SV129 mice had wider posterior communicating but smaller basilar artery diameters. With or without hypotension, SV129 mice had markedly less severe histologic damage than C57Bl/6 mice. A time-dependent increase in histologic damage was demonstrated in the 2VO+Hypo model but not with 2VO alone. The 2VO and 2VO+Hypo models produced similar magnitudes of histologic injury in C57Bl/6 mice subjected to 10-min ischemia. SV129 mice were resistant to ischemia in either model. The 2VO+Hypo model produced a more uniform severity of ischemia as defined by CBF and EEG examination. Despite this, the murine strain had a substantially greater impact on histologic outcome than did cerebrovascular anatomy or the type of model used to produce the ischemic insult.     

谷氨酸转运体在全脑缺血性癫痫中作用的研究

目的比较三种谷氨酸转运体在全脑缺血性癫痫中的动态变化特征,为癫痫治疗提供有意义靶点.方法SD大鼠以胸部压迫8分钟造成全脑缺血性癫痫模型,分对照组、假手术组、全脑缺血无癫痫组和全脑缺血癫痫组.后两组又根据脑缺血后时间分为6h,24h,48h,72h,5d,7d组.应用免疫组化法研究谷氨酸转运体EAAT-1,EAAT-2,EAAT-3在海马CA1及皮质区表达;研究病理形态变化,同时测定大鼠脑电图改变.结果大鼠癫痫发生率为64%,全脑缺血癫痫大鼠神经损害较无癫痫组严重.与全脑缺血无癫痫大鼠比较,癫痫大鼠海马CA1及皮质区EAAT-2显著持续降低及EAAT-3表达明显升高.结论大鼠癫痫发生与脑缺血严重程度密切相关.海马CA1及皮层区EAAT-2、EAAT-3表达变化是抗癫痫治疗的作用靶点.     

钾通道阻断剂TEA对大鼠全脑缺血后海马神经元损伤的保护作用

在大鼠四血管夹闭前脑缺血模型上,观察了侧脑室给予钾通道阻断剂四乙基铵（TEA）和4-氨基吡啶（4-AP）对脑缺血后海马CA1区锥体神经元迟发性死亡的保护作用。结果发现：再灌流30min后给予TEA组CA1区存活的锥体细胞数明显高于生理盐水对照组,而再灌流30min后给予4-AP组和缺血前30min给予TEA组的存活细胞数则与生理盐水对照组无明显差别。表明再灌流后给予TEA对脑缺血诱导的海马CA1区锥体神经元死亡具有明显的保护作用,提示钾通道可能在缺血后海马CA1区锥体细胞的迟发性死亡中发挥重要的作用。     

Systemic gabapentin and S(+)-3-isobutyl-γ-aminobutyric acid block secondary hyperalgesia

Gabapentin (GBP) and S(+)-3-isobutyl-γ-aminobutyric acid (IBG) are anticonvulsant agents which are effective against many clinical and experimental neuropathic pain states. We examined the efficacy of these agents in a new rat model of secondary mechanical hyperalgesia generated by a mild thermal injury. Under brief halothane anesthesia, an injury was induced by applying one heel to a hot surface (52.5°C) for 45 s. GBP, IBG or saline was injected i.p. just prior to the injury. Mean mechanical withdrawal threshold (MWT) was determined using von Frey hairs before and at 30 min intervals for 3 h following the injury. MWT outside the injury area decreased post-injury (secondary hyperalgesia, allodynia), but primary (site of injury) mechanical hyperalgesia was not observed. Secondary hyperalgesia exhibited a tendency toward recovery over time. Time to onset of the anti-allodynic effect of GBP was 30–60 min. The minimum effective GBP dose was 100 mg/kg; 300 mg/kg GBP totally inhibited the drop in MWT, but was accompanied by pronounced sedation. Anti-allodynic effects of IBG were apparent at the first post-injury measure of MWT (30 min). Thirty milligrams per kilogram was the minimum effective dose; 100 mg/kg IBG totally blocked the allodynia with minimal side effects. Our findings demonstrate a dose-dependent blockade of the mechanical sensitivity caused by a mild thermal injury by both GBP and IBG. Results indicate that IBG is more effective than GBP in this model at doses which do not cause sedation. These observations support the suggested use of these or related γ-amino acid analogues as an effective treatment for post-operative pain.     

Region-selective stress-induced increase of glutamate uptake and release in rat forebrain

The study describes stress-induced changes in high-affinity uptake and release of glutamate by synaptosomal preparations from several regions of rat brain. The results demonstrate that restraint stress can lead to increased glutamate uptake and release in limbic forebrain regions (frontal cortex, hippocampus and septum) but not in the striatum. The increase in glutamate uptake was evident after 30 min of stress. A plateau (140–150% of unhandled controls) was reached after 1 h and was maintained after 4 h of continuous stress. The stress-induced increase in glutamate uptake was observed with glutamate concentrations of up to 10 μM, but not with 500 μM. The results indicate that forebrain glutamatergic terminals are activated by stressful stimuli in a regionally selective manner, and suggest that enhanced high-affinity uptake is important in clearing increased levels of released glutamate.     

Neuroprotective effects of lamotrigine in global ischemia in gerbils. A histological, in vivo microdialysis and behavioral study

A sudden surge in the release of glutamate is currently believed to be an important initiating step in neuronal damage due to an ischemic insult. In this experiment, we tested the efficacy of neuroprotection with lamotrigine, a novel antiepileptic drug that blocks voltage gated sodium channels and inhibits the ischemia-induced release of glutamate in the gerbil forebrain model of cerebral ischemia. The medication was administered 30 min before and 30 min after the insult in two groups of animals. Histological assessment of neuronal damage was evaluated at 7 and 28 days after the ischemic insult. Animals evaluated at 28 days also underwent behavioral testing. Microdialysis was used in the same model to study the response of ischemia-induced glutamate in saline treated controls versus animals treated with lamotrigine 20 min before the insult. There was highly significant neuronal protection in animals who were treated with lamotrigine either before or after the insult. Protection was seen both at 7 and 28 days after the insult. Behavioral testing also showed significantly better recovery in both sets of animals in comparison to the saline-treated group. Microdialysis confirmed a significant attenuation of the ischemia-induced glutamate surge when compared to the saline-treated animals. Our morphological, behavioral and microdialysis experiments show that lamotrigine offers significant neuroprotection from the effects of transient forebrain ischemia in gerbils. Neuroprotection with post-ischemic therapy probably depends on preserving the capacity of the sodium/calcium exchanger to reduce intracellular calcium concentrations or persistent `toxicity' of glutamate in the reperfusion period on the already `primed' injured neurons. These concepts need further study.