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

Zonisamide Ameliorated the Apoptosis and Inflammation in Cerebellar Tissue of Induced Alcohol Addiction Animal Model

This study investigated the effects of zonisamide treatment on cerebellar tissues in an experimental alcohol addiction (AA) model and its potential mechanisms of action, particularly regarding apoptotic protease activating factor-1 (APAF-1) and tumor necrosis factor-alpha (TNF-α) expression. Thirty rats were divided into three groups: sham, ethanol (EtOH), and EtOH + zonisamide. AA was induced by administering 6 cc of EtOH orally every 8 h for 4 days. Zonisamide (100 mg/kg) was given to rats once daily before EtOH administration. Motor defects were evaluated using an open field maze. Serum TNF-α levels were measured from blood samples. Cerebellar sections were processed for histological examination and immunostained for APAF-1 and TNF-α. Protein interaction networks were constructed using Cytoscape, and functional annotations were performed with ShinyGO (version 0.80) software. The traveled area in the EtOH group was significantly reduced compared to the sham group (p = 0.0005). Rats in the EtOH + zonisamide group covered a larger area, with zonisamide treatment significantly improving locomotor ability compared to the EtOH group (p = 0.0463). Serum TNF-α levels were significantly elevated in the EtOH group compared to the sham group (p < 0.0001) and were significantly decreased in the EtOH + zonisamide group compared to the EtOH group (p = 0.0309). Regular cerebellar histological layers were observed in the sham group, while EtOH induction caused loss of cerebellar tissue integrity, neuronal degeneration, vascular dilatation and congestion, reduced myelin density, and neuropils in the EtOH group. Zonisamide treatment improved these pathologies, enhancing myelination and neuropil formation. Negative APAF-1 and TNF-α expressions were observed across cerebellar layers in the sham group. Due to EtOH toxicity, APAF-1 and TNF-α expression were upregulated in the EtOH group compared to the sham group (p < 0.001 for both). Zonisamide treatment downregulated these protein expressions in the EtOH + zonisamide group compared to the EtOH group (p < 0.001 and p = 0.0087, respectively). APAF-1 was primarily associated with AA through antifolate resistance, endopeptidases, and the interleukin-1 pathway, while TNF-α was predominantly enriched in infections and choline-binding, indicating zonisamide's impact on immune and inflammatory pathways. In conclusion, zonisamide treatment significantly mitigated ethanol-induced cerebellar damage and inflammation in an AA model. Zonisamide improved locomotor function and reduced serum TNF-α levels, as well as APAF-1 and TNF-α expression in cerebellar tissues. These findings suggest that zonisamide exerts its protective effects by modulating immune and inflammatory pathways, thereby preserving cerebellar integrity and function.

The Effect of Zonisamide and Ethanol on Various Types of Memory in Rats

Background: Antiepileptic drugs might be useful in the treatment of alcohol use disorder. One of these drugs is zonisamide, which has been found to decrease alcohol intake and cravings. An important structure in the pathophysiology of addiction is the hippocampus. Memory deficits, which frequently occur in alcoholics, are associated with ethanol-induced changes in hippocampal plasticity and neurogenesis. The aim of this study was to assess the potential protective effect of zonisamide on memory in rats receiving alcohol and after the discontinuation of its administration. Methods: Wistar rats (n = 43) were tested in four behavioral models, namely: Morris water maze (MWM), passive avoidance (PA), contextual fear conditioning (CFC), and cued fear conditioning (CuFC). Results: Zonisamide co-administered with ethanol impaired spatial memory in MWM, but the drug did not affect memory in PA. However, the beneficial effect of zonisamide was observed after the discontinuation of ethanol administration, which was associated with the improvement of associative memory in CFC and the alleviation of alcohol-induced locomotor disturbances in CuFC. Conclusion: Zonisamide has a differential influence on memory, which depends inter alia on type of the memory, length of ethanol administration, or its absence.

Traditional and Innovative Anti-seizure Medications Targeting Key Physiopathological Mechanisms: Focus on Neurodevelopment and Neurodegeneration

Despite the wide range of compounds currently available to treat epilepsy, there is still no drug that directly tackles the physiopathological mechanisms underlying its development. Indeed, antiseizure medications attempt to prevent seizures but are inefficacious in counteracting or rescuing the physiopathological phenomena that underlie their onset and recurrence, and hence do not cure epilepsy. Classically, the altered excitation/inhibition balance is postulated as the mechanism underlying epileptogenesis and seizure generation. This oversimplification, however, does not account for deficits in homeostatic plasticity resulting from either insufficient or excessive compensatory mechanisms in response to a change in network activity. In this respect, both neurodevelopmental epilepsies and those associated with neurodegeneration may share common underlying mechanisms that still need to be fully elucidated. The understanding of these molecular mechanisms shed light on the identification of new classes of drugs able not only to suppress seizures, but also to present potential antiepileptogenic effects or "disease-modifying" properties.

Pharmacological management of dementia with Lewy bodies with a focus on zonisamide for treating parkinsonism

INTRODUCTION

Dementia with Lewy bodies (DLB) has no approved symptomatic or disease-modifying treatments in the US and Europe, despite being the second most common cause of neurodegenerative dementia.

AREAS COVERED

Herein, the authors briefly review the DLB drug development pipeline, providing a summary of the current pharmacological intervention studies. They then focus on the anticonvulsant zonisamide, a benzisoxazole derivative with a sulfonamide group and look at its value for treating parkinsonism in DLB.

EXPERT OPINION

Several new compounds are being tested in DLB, the most innovative being those aimed at decreasing brain accumulation of α-synuclein. Unfortunately, new drug testing is challenging in terms of consistent diagnostic criteria and lack of reliable biomarkers. Few randomized controlled trials (RCTs) are well-designed, with enough power to detect significant drug effects. Levodopa monotherapy can treat the parkinsonism in DLB, but it can cause agitation or visual hallucination worsening. Two Phase II/III RCTs of DLB patients recently reported a statistically significant improvement in motor function in those receiving zonisamide as an adjunctive treatment to levodopa. New biomarker strategies and validated outcome measures for DLB or prodromal DLB may enhance clinical trial design for the development of specific disease-modifying treatments.

The effect of zonisamide on memory processes - A preclinical study

OBJECTIVE

Zonisamide is an antiepileptic drug with a perspective of a broader use. Although it is regarded as a relatively safe drug, zonisamide might cause disorders of the central nervous system. The study assessed the influence of zonisamide on spatial and emotional memory in adult Wistar rats.

METHODS

Morris water maze test was used to examine the effect of zonisamide administered p.o. as single dose (50 mg/kg or 100 mg/kg) or repeatedly (50 mg/kg) on spatial memory. The impact of zonisamide administered as above on emotional memory was assessed in the Passive avoidance test.

RESULTS

Zonisamide mainly in a high acute dose impaired the spatial memory, whereas when administered repeatedly, its effect was observed only in the initial phase of the study. Emotional memory disturbances were noted only during repeated administration of zonisamide.

CONCLUSION

Zonisamide may impair memory and learning processes in rats but the results are varied and depend on the type of memory.

The anti-parkinsonian drug zonisamide reduces neuroinflammation: Role of microglial Nav 1.6

Parkinson's disease (PD), the second most common age-related progressive neurodegenerative disorder, is characterized by dopamine depletion and the loss of dopaminergic (DA) neurons with accompanying neuroinflammation. Zonisamide is an-anti-convulsant drug that has recently been shown to improve clinical symptoms of PD through its inhibition of monoamine oxidase B (MAO-B). However, zonisamide has additional targets, including voltage-gated sodium channels (Na_v), which may contribute to its reported neuroprotective role in preclinical models of PD. Here, we report that Na_v1.6 is highly expressed in microglia of post-mortem PD brain and of mice treated with the parkinsonism-inducing neurotoxin MPTP. Administration of zonisamide (20 mg/kg, i.p. every 4 h × 3) following a single injection of MPTP (12.5 mg/kg, s.c.) reduced microglial Na_v 1.6 and microglial activation in the striatum, as indicated by Iba-1 staining and mRNA expression of F4/80. MPTP increased the levels of the pro-inflammatory cytokine TNF-α and gp91^phox, and this was significantly reduced by zonisamide. Together, these findings suggest that zonisamide may reduce neuroinflammation through the down-regulation of microglial Na_v 1.6. Thus, in addition to its effects on parkinsonian symptoms through inhibition of MAO-B, zonisamide may have disease modifying potential through the inhibition of Na_v 1.6 and neuroinflammation.

Neuroprotective Effect of Lacosamide on Hypoxic-Ischemic Brain Injury in Neonatal Rats

BACKGROUND AND PURPOSE

Lacosamide (LCM) is an antiepileptic drug that enhances the slow inactivation of sodium channels and modulates collapsin response mediator protein-2. LCM was recently demonstrated to exert a neuroprotective effect in a murine model of traumatic brain injury and status epilepticus. Assuming the same underlying excitotoxicity-related brain injury mechanism, we hypothesized that LCM would have a neuroprotective effect in hypoxic-ischemic brain injury.

METHODS

We divided rats into three groups at each testing session: pre- or postfed with LCM, fed with normal saline, and sham. A hypoxic-ischemic brain injury was induced by subjecting 7-day-old rats to right carotid artery coagulation followed by 2.5 h of exposure to 8% oxygen. The animals were killed on postnatal day 12 to evaluate the severity of brain damage. Open field testing was also performed between week 2 and week 6, and the Morris water maze test was performed in week 7 after hypoxia-ischemia.

RESULTS

The incidence of liquefactive cerebral infarction was lower in rats prefed with LCM at 100 mg/kg/dose, with the mortality rate being higher at higher doses (200 and 300 mg/kg/dose). The infarct areas were smaller in LCM-prefed rats in several brain regions including the hemisphere, hippocampus, cortex, and striatum. Spatial learning and memory function were better in LCM-prefed rats (p<0.05). No effect was observed in postfed rats.

CONCLUSIONS

This study suggests that LCM pretreatment exerts a neuroprotective effect on hypoxia-ischemia in neonatal rats. The obtained results suggest that LCM pretreatment could be used as an effective neuroprotective method for neonates under hypoxic-ischemic conditions including heart surgery.

Neuroprotection as a Potential Therapeutic Perspective in Neurodegenerative Diseases: Focus on Antiepileptic Drugs

Neuroprotection is conceived as one of the potential tool to prevent or slow neuronal death and hence a therapeutic hope to treat neurodegenerative diseases, like Parkinson's and Alzheimer's diseases. Increase of oxidative stress, mitochondrial dysfunction, excitotoxicity, inflammatory changes, iron accumulation, and protein aggregation have been identified as main causes of neuronal death and adopted as targets to test experimentally the putative neuroprotective effects of various classes of drugs. Among these agents, antiepileptic drugs (AEDs), both the old and the newer generations, have shown to exert protective effects in different experimental models. Their mechanism of action is mediated mainly by modulating the activity of sodium, calcium and potassium channels as well as the glutamatergic and GABAergic (gamma-aminobutyric acid) synapses. Neurological pathologies in which a neuroprotective action of AEDs has been demonstrated in specific experimental models include: cerebral ischemia, Parkinson's disease, and Alzheimer's disease. Although the whole of experimental data indicating that neuroprotection can be achieved is remarkable and encouraging, no firm data have been produced in humans so far and, at the present time, neuroprotection still remains a challenge for the future.

Delayed hyperoxic ventilation attenuates oxygen-induced free radical accumulation during early reperfusion after global brain ischemia

To compare the effect of immediate and delayed administration of oxygen on the accumulation of free radicals in ischemia-reperfusion animal models. Thirty-two adult male Mongolian gerbils with microdialysis probes implanted in the right hippocampal CA1 were divided randomly into four groups (eight each). One group was sham-operated (Sham group) whereas the other three groups were subjected to 10 min bilateral carotid artery occlusion (BCAO). BCAO-treated animals were then subjected to the following: (a) immediate 30% O2 (near normoxia, NO group), (b) immediate 100% O2 (hyperoxia, HO group), and (c) 30% O2 for 60 min, followed by 100% O2 for 60 min (delayed hyperoxia, DHO group). Hippocampal accumulation of hydroxyl radicals (•OH) during reperfusion was estimated by measuring 2,3-dihydroxybenzoic acid (DHBA) and 2,5-DHBA in microdialysis perfusate. Hippocampi were removed 2 h after perfusion to measure malondialdehyde, pyruvate dehydrogenase activity, indices of lipid peroxidation, and cellular respiration. At 24 h after BCAO, the histology of hippocampi was analyzed to rate the injury. Immediately after the onset of reperfusion, all groups showed markedly elevated DHBA, which returned to baseline over 1-2 h. Compared with the NO group, the HO group showed significantly higher peak DHBA and slower recovery. In contrast, the DHO group was not significantly different from the NO group in terms of the DHBA level. DHO animals also showed significantly lower hippocampal malondialdehyde accumulation and higher pyruvate dehydrogenase activity at 2 h after reperfusion versus the HO group. Histology analysis also showed animals in the DHO group with ameliorated injury compared with the HO group. Hydroxyl radical accumulation was more sensitive to O2 during early reperfusion. Delayed hyperoxia may re-establish oxidative metabolism while minimizing oxidative stress after CA.

Zonisamide attenuates hyperoxia-induced apoptosis in the developing rat brain

Oxygen therapy used in the treatment of perinatal hypoxia induces neurodegeneration in babies with immature antioxidant mechanisms. Zonisamide is a new antiepileptic drug used in childhood intractable seizures. Many studies demonstrated its neuroprotective effects. There is no study evaluating its effect on hyperoxic brain injury. The aim of this study was to investigate the neuroprotective effect of zonisamide on hyperoxia-induced neonatal brain injury. A total of 21 Wistar rat pups were used. The animals were divided into three groups: control group, hyperoxia group, and zonisamide-treated group. The zonisamide-treated group received an intraperitoneal injection of zonisamide. Zonisamide significantly preserved the number of neurons in CA1 and dentate gyrus parts of hippocampus, prefrontal, and parietal cortex. Zonisamide treatment also decreased the number of apoptotic neurons in all examined parts of hippocampus, prefrontal, and parietal cortex. We suggest that zonisamide treatment may be used as a neuroprotective agent in hyperoxic brain injury.

Zonisamide: newer antiepileptic agent with multiple mechanisms of action

Zonisamide (Zonegran, Eisai, Inc.) is a broad spectrum antiepileptic drug indicated for use as adjunctive therapy in the treatment of partial seizures. Zonisamide has multiple mechanisms of action, which may explain widespread reports of its utility in focal epilepsy and generalized epilepsy, and for nonseizure disorders such as headache and neuropathic pain. Zonisamide has been available in Japan since 1989 and became available in the USA in 2002. The rights to this drug in North America and Europe were recently acquired by Eisai Co. A review of the chemical properties, pharmacokinetics, metabolism, potential mechanisms of action, efficacy in seizure and nonseizure disorders, and tolerability was therefore thought to be timely.

A critical role of NO/cGMP/PKG dependent pathway in hippocampal post-ischemic LTP: modulation by zonisamide

Nitric oxide (NO) is an intercellular retrograde messenger involved in several physiological processes such as synaptic plasticity, hippocampal long-term potentiation (LTP), and learning and memory. Moreover NO signaling is implicated in the pathophysiology of brain ischemia. In this study, we have characterized the role of NO/cGMP signaling cascade in the induction and maintenance of post-ischemic LTP (iLTP) in rat brain slices. Moreover, we have investigated the possible inhibitory action of zonisamide (ZNS) on this pathological form of synaptic plasticity as well as the effects of this antiepileptic drug (AED) on physiological activity-dependent LTP. Finally, we have characterized the possible interaction between ZNS and the NO/cGMP/PKG-dependent pathway involved in iLTP. Here, we provided the first evidence that an oxygen and glucose deprivation episode can induce, in CA1 hippocampal slices, iLTP by modulation of the NO/cGMP/PKG pathway. Additionally, we found that while ZNS application did not affect short-term synaptic plasticity and LTP induced by high-frequency stimulation, it significantly reduced iLTP. This reduction was mimicked by bath application of NO synthase inhibitors and a soluble guanyl cyclase inhibitor. The effect of ZNS was prevented by either the application of a NO donor or drugs increasing intracellular levels of cGMP and activating PKG. These findings are in line with the possible use of AEDs, such as ZNS, as a possible neuroprotective strategy in brain ischemia. Moreover, these findings strongly suggest that NO/cGMP/PKG intracellular cascade might represent a physiological target for neuroprotection in pathological forms of synaptic plasticity such as hippocampal iLTP.

Zonisamide: aspects in neuroprotection

Zonisamide is widely used as an antiepileptic drug. Two studies published recently in Experimental Neurology focus on the drug's neuroprotective effect. In the present commentary, we discuss the significance of their findings and aspects of zonisamide in neuroprotection.

Zonisamide: review of pharmacology, clinical efficacy, tolerability, and safety

BACKGROUND

Zonisamide (ZNS), a sulphonamide derivative, is a new-generation anticonvulsant with multiple potential mechanisms that contribute to its antiepileptic efficacy and may also explain its as yet incompletely assessed utility for non-seizure disorders such as headaches, neuropathic pain, and weight loss.

OBJECTIVE

A review of the pharmacokinetics, pharmacodynamics, evidence for efficacy in different seizure types and non-seizure conditions, adverse effects, and tolerability of ZNS is presented.

METHODS

A review of all manuscripts published in the English literature on ZNS was performed in preparing this manuscript.

RESULTS/CONCLUSIONS

ZNS has a broad label for use in Japan, while the regulatory bodies in the USA and Europe have approved it for use only as an adjunctive therapy for partial seizures in adults. It has favorable pharmacokinetic characteristics, proven efficacy in seizure disorders, and is well tolerated in long-term use.

Clinical pharmacology and mechanism of action of zonisamide

Antiepileptic drugs (AEDs) suppress seizures by selectively modifying the excitability of neurons and blocking seizure firing with minimal disturbance of nonepileptic activity. All AEDs have been shown to work by at least one of 3 main mechanisms of action: through modulation of voltage-gated ion channels, enhancement of synaptic inhibition, and inhibition of synaptic excitation. Zonisamide is a novel AED that has a broad combination of complementary mechanisms of action, which may offer a clinical advantage over other antiepileptic agents. By altering the fast inactivation threshold of voltage-dependent sodium channels, zonisamide reduces sustained high-frequency repetitive firing of action potentials. Zonisamide also inhibits low-threshold T-type calcium channels in neurons, which may prevent the spread of seizure discharge across cells. In addition, zonisamide is a weak inhibitor of carbonic anhydrase. However, this mechanism is not believed to contribute to the antiepileptic activity of zonisamide. Although zonisamide also seems to alter dopamine, serotonin, and acetylcholine metabolism, it is not clear to what extent these effects on neurotransmitters are involved in the clinical actions of the drug. In addition to these actions, recent evidence suggests that zonisamide may exert neuroprotective actions, independent of its antiepileptic activity. These potential effects may be important in preventing neuronal damage caused by recurrent seizures. Therefore, it seems that the multiple pharmacological actions of zonisamide may contribute to the seizure reductions observed in a wide range of epilepsies and may help to preserve efficacy in individual patients despite possible changes in electrophysiological status.

Zonisamide for the treatment of Parkinson's disease

Zonisamide is an antiepileptic drug widely used to treat seizures worldwide. In addition to epilepsy, zonisamide may have beneficial efficacy in various neurological or psychiatric diseases. This article reviews the structure, mechanism of action, pharmacokinetics and possible antiparkinsonian action of zonisamide. A multicentered, randomized, double-blind, placebo-controlled study conducted in Japan provided data suggesting that zonisamide, as an add-on treatment, has efficacy in treating motor symptoms in patients with Parkinson's disease (PD). Zonisamide may be effective in reducing the duration of 'off' time in patients with PD treated with L-DOPA. The therapeutic doses of zonisamide for the treatment of PD are 50-100 mg/day, considerably lower than those for the treatment of epilepsy (200-400 mg/day). It is expected that zonisamide will be safe and tolerated in patients with PD, as it has been used as an antiepileptic for more than 15 years; however, further studies are required to evaluate its safety and tolerability in the treatment of PD. The pharmacological mechanisms of the beneficial actions of zonisamide in PD remain unclear. Various hypotheses have been proposed, but the supporting data are not yet sufficient to draw any conclusions. Further basic research is required to advance our understanding of the antiparkinsonian mechanism of zonisamide.

Serotonin but not zonisamide inhibits theophylline-induced epileptiform activity in guinea pig hippocampal CA3 neurons

To test the putative serotonin (5-HT)-like effect of zonisamide (ZNS) we employed xanthine-induced epileptiform activity in the hippocampus slice preparation from guinea pigs. In this model Na(+)- and T-type Ca(2+) channel blockers are hardly effective while 5-HT should be inhibitory. Bath application of 5-HT hyperpolarized neurons and abolished theophylline-induced epileptiform activity. In contrast, ZNS failed to alter epileptiform bursting. We conclude that 5-HT augmenting effects of ZNS are missing or are not sufficient to inhibit epileptiform activity in hippocampal slice preparations.

Interactions between zonisamide and conventional antiepileptic drugs in the mouse maximal electroshock test model

Despite the major advances in antiepileptic drug (AED) therapeutics, about one third of patients with epilepsy still do not have adequate seizure control with currently available AEDs when prescribed as monotherapy. Typically, in this setting polytherapy with two or more AEDs is used. Zonisamide (ZNS) is a new AED effective in the treatment of refractory epilepsy and since it is only prescribed in polytherapy regimens, its interactions with other AEDs is of particular importance. The aim of this study was to isobolographically determine interactions between ZNS and four conventional AEDs: carbamazepine (CBZ), phenytoin (PHT), phenobarbital (PB), and valproate (VPA), in the mouse maximal electroshock (MES)-induced seizure model. The total brain concentrations of conventional AEDs and ZNS were measured with immunofluorescence and high-pressure liquid chromatography (HPLC), respectively, in order to determine any pharmacokinetic contribution in any observed interactions. With isobolography, synergistic interactions were observed for the combination of ZNS plus VPA and ZNS plus PHT at the fixed-ratio of 1:1, while additivity was observed for their combinations at the remaining dose ratios of 1:3 and 3:1. In contrast, the interactions between ZNS and PB and between ZNS and CBZ, applied at the fixed-ratios of 1:3, 1:1 and 3:1 proved to be additive. None of these AED combinations were associated with motor and long-term memory impairment. Furthermore, whilst brain AED concentrations were unaffected by ZNS, PHT significantly increased and PB reduced brain ZNS concentrations. Thus, the resultant interactions between ZNS and PHT and between ZNZ and PB were consequent to both pharmacodynamic and pharmacokinetic components. Finally, one can conclude that because of the synergistic pharmacodynamic interaction between ZNS and VPA, this combination might be useful in clinical practice.

Zonisamide - a review of experience and use in partial seizures

Zonisamide is a modern antiepileptic drug (AED) that is distinguished from other AEDs by its unique structure and broad mechanistic profile. Preclinical studies have reported a range of potential mechanisms of action for zonisamide, such as blocking voltage-gated sodium channels, reduction of T-type calcium channel currents, and enhancement of gamma-aminobutyric acid (GABA)-mediated inhibition, which are indicative of its broad antiseizure effects. Zonisamide has a favorable linear pharmacokinetic profile, a long half-life, and a low incidence of protein-binding interactions with other AEDs. Hepatically metabolized through the cytochrome P450 pathway, zonisamide does not induce its own metabolism or liver enzymes. For more than 2 decades, zonisamide has been extensively used as monotherapy and adjunctive therapy for the treatment of partial and generalized seizures in pediatric and adult patients in Japan. Zonisamide was approved in the USA in 2000 as adjunctive therapy for partial seizures in adults. With over 2 million patient-years of exposure internationally, zonisamide has demonstrated safety and efficacy against a multitude of epilepsy and seizure types, including both partial and generalized seizures. This review focuses on the experience and use of zonisamide in partial seizures, as well as possible new uses for zonisamide.

Catalpol prevents the loss of CA1 hippocampal neurons and reduces working errors in gerbils after ischemia-reperfusion injury

Catalpol, an iridoid glycoside, contained richly in the roots of Rehmannia glutinosa, was found for the first time to be of neuroprotection in gerbils subjected to transient global cerebral ischemia. Catalpol (1 mg/kg ip) used immediately after reperfusion and repeatedly at 12, 24, 48 and 72 h significantly rescued neurons in hippocampal CA1 subfield and reduced working errors during behavioral testing. The neuroprotective efficacy of catalpol became more evident when the doses of catalpol were increased to 5 and 10mg/kg. In addition, it was exciting that the significant neuroprotection by catalpol was also evident when catalpol was applied up to 3 h after ischemia. But the neuroprotective efficacy of catalpol became weak when catalpol was given at 6h after ischemia. Of great encouragement was the finding that the neuroprotection of catalpol could be seen not only in a short post-ischemic period (12 days) but also in a long period (35 days). All these indicated that catalpol was truly neuroprotective rather than simply delayed the onset of neuronal damage and might be of therapeutic value for the treatment of global cerebral ischemia.

Antiepileptic drugs and neuroprotection: current status and future roles

There has been a growing interest in the use of antiepileptic drugs (AEDs) for neuroprotection, and in the possible role of AEDs in disease modification (i.e., antiepileptogenesis). Increased understanding of the mechanisms underlying brain injury has led to advances in the study of neuroprotection. However, defining the clinical paradigm and selecting appropriate outcomes to detect neuroprotective effects present challenges to clinicians studying the neuroprotective properties of drugs. Established AEDs, such as phenytoin, phenobarbital, and carbamazepine, have shown neuroprotective activity in an ischemic/hypoxic model of neuronal injury. Animal model studies also have suggested that newer AEDs, such as levetiracetam, topiramate, and zonisamide, may have neuroprotective or antiepileptogenic properties. However, the prevention of epileptogenesis by an AED has yet to be demonstrated in clinical trials. The future of neuroprotection may involve established and newer AEDs, as well as other compounds, such as immunophilins, caspase inhibitors, endocannabinoids, and antioxidants.

Differential effects of vigabatrin and zonisamide on the neuropeptide Y system in the hippocampus of seizure prone gerbil

Changed neuropeptide Y (NPY) system in the hippocampus has been reported in various experimental epileptic models. However, there have been little data concerning the alteration in the NPY system in the epileptic hippocampus following treatment of anti-epileptic drugs (AEDs). In the present study, therefore, we performed analyses of effects of vigabatrin (VGB) and zonisamide (ZNS) treatment on the NPY system in the hippocampus of the seizure sensitive (SS) gerbils. In SS gerbil, NPY immunoreactivity in the hippocampus was lower than that in seizure resistant gerbil. Following VGB treatment, the number of NPY immunoreactive neurons and NPY mRNA expression were increased in the hilus and the hippocampus proper. In contrast, ZNS treatment markedly elevated only the density of NPY immunoreactive fibers in the dentate gyrus, not in the hippocampus proper, as compared with saline-treated animals. These patterns were observed in the dose-dependent manners. These findings suggest that AEDs treatments may distinctly affect the NPY system in the SS gerbil hippocampus.

Cardiac arrest with cardiopulmonary resuscitation reduces dendritic spine density in CA1 pyramidal cells and selectively alters acquisition of spatial memory

The hippocampus is highly sensitive to ischemia and is one of the most extensively damaged regions of brain during cardiac arrest. Damage to hippocampus can subsequently lead to learning and memory deficits. The current study used the Morris water maze to characterize spatial learning and memory deficits elicited by 8 min of cardiac arrest with cardiopulmonary resuscitation (CA/CPR) in mice, which is associated with a 25-50% decrease in CA1 neurons. Mice were trained to navigate the water maze prior to CA/CPR or sham surgery (SHAM). They were retested in the water maze on days 7 and 8 postsurgery; both CA/CPR and SHAM groups were able to perform the task at presurgical levels. However, when the hidden platform was moved to a new location, the SHAM mice were able to adapt more quickly to the change and swam a shorter distance in search of the platform than did CA/CPR mice. Thus, CA/CPR did not affect the ability of mice to retain a previously learned platform location, but it did affect their ability to learn a new platform location. This behavioural impairment was correlated with dendritic spine density in the CA1 region of the hippocampus. Data presented here suggest that morphological changes, such as spine density, that occur in neurons that survive CA/CPR may be associated with cognitive impairments.

Neuroprotective properties of catalpol in transient global cerebral ischemia in gerbils: dose–response, therapeutic time-window and long-term efficacy

The present study evaluated for the first time the dose-effectiveness, therapeutic time-window and long-term efficacy of the neuroprotection of catalpol by behavioral and histological measures in gerbils subjected to transient global cerebral ischemia. Catalpol (1 mg/kg ip) used immediately after reperfusion and repeatedly at 12, 24, 48 and 72 h significantly rescued neurons in the hippocampal CA1 subfield and reduced cognitive impairment. The neuroprotective efficacy of catalpol became more evident at the doses of 5 and 10 mg/kg. Of great importance were the findings that the neuroprotective efficacy of catalpol still could be seen even when the treatment was delayed 3 h and when the observational period was lasted out 35 days after ischemia. It was reasonable to draw the conclusion that catalpol was truly neuroprotective rather than simply delayed the onset of neuronal damage. These results suggested that catalpol might be of therapeutic value for global cerebral ischemia.

Antiepileptic drugs in neuroprotection

Antiepileptic drugs (AEDs) are designed to prevent and suppress seizure activity. Their effects on calcium influx and molecular cascades contributing to necrotic and apoptotic neuronal death, however, suggests that they have functions other than just suppression of excitability. The neuroprotective effects of 20 AEDs currently in use or being investigated in Phase II - III clinical trials for treatment of epilepsy are reviewed. Data analyses is complicated by several factors. Firstly, the available data on the neuroprotective effects of different AEDs varies largely. Secondly, most of the evidence demonstrating neuroprotective effects comes from stroke models and it is uncertain whether these data can be extrapolated to other conditions, such as status epilepticus (SE) or traumatic brain injury. Thirdly, data obtained in adult animals cannot be extrapolated to young animals without caution. For example, AEDs protecting adult brain from stroke or SE-induced injury can cause apoptosis in immature brain. Finally, data comparison is complicated by the variability in study designs and methodologies between studies. With these caveats in mind, an analysis of the available data suggests that AEDs with different mechanisms of action can have mild-to-moderate neuroprotective effects. It is difficult, however, to associate the neuroprotective effects with a favourable functional outcome. For example, it is difficult to conclude that administration of AEDs during the latency phase would have an effect on the molecular cascades underlying epileptogenesis. The few favourable data demonstrating a decrease in the incidence of epilepsy after SE are probably related to the administration of AEDs during SE, which resulted in modification/alleviation of the insult itself and consequently, reduced its epileptogenecity. These experimental data, however, are clinically important because they show that early intervention of SE has an effect on long-term functional outcome. These observations emphasise the need to use additional outcome measures, such as markers of normal development or cognitive performance, when the benefits of neuroprotection achieved by the use of neuroprotective AEDs are assessed.

Postoperative seizures: epidemiology, pathology, and prophylaxis

The risk of epileptic seizures after craniotomy is extremely important but the incidence of postoperative epilepsy varies greatly, depending on the patient's conditions such as primary diseases, severity of surgical insult, and pre-existing epilepsy. Animal studies suggest that neurosurgical insults lead to seizures by two different mechanisms: One mechanism is mediated by free radical generation and the other by impaired ion balance across the cell membrane caused by ischemia or hypoxia. Conventional antiepileptic agents such as phenytoin, phenobarbital, carbamazepine, and valproic acid are promising for the prevention of early seizures, but the effect in preventing postoperative epilepsy is still controversial. Studies on the prophylactic effect of newer antiepileptic agents in craniotomized patients were very limited. Zonisamide, an antiepileptic agent with antiepileptogenic, free radical scavenging and neuroprotective actions in experimental animals, showed promising effects against postoperative epilepsy in a randomized double blind controlled trial. Prophylactic treatment for craniotomized patients significantly prevented the development of partial seizures during the follow-up period. Most recent studies have not supported the prophylactic use of antiepileptic agents in craniotomized patients, but further studies are required.

The role of taurine in cerebral ischemia: studies in transient forebrain ischemia and embolic focal ischemia in rodents

Sudden cessation of blood flow to the brain results in a series of events that either result in rapid loss of brain cells or delayed neuronal injury in certain vulnerable regions of the brain. Research over the last three decades has allowed for a better understanding of how neurons and other brain cells die from the effects of ischemia and hypoxia in the central nervous system. Excitatory and inhibitory neurotransmitters exist in a very precise balance for normal function of the brain. Ischemia very rapidly disrupts this balance resulting in a rapid build-up of excitatory neurotransmitters, especially glutamate in the extracellular space. The increased glutamate together with energy loss opens a number of different types of calcium and sodium channels resulting in the build-up of these ions in neurons, leading to cellular dysfunction and death. While most ischemia research has focused on antagonism of excitatory amino acids, there are some reports on enhancement and amplification of inhibitory responses in focal and global ischemia. The majority of work relates to potentiation of GABA, either endogenous or through GABA potentiating medications. Taurine has neuroinhibitory properties and may also have potential for neuroprotection in cerebral ischemia. This present review focuses on the role of taurine as a neuroprotective agent, possibly acting through several different inhibitory mechanisms. Taurine may inhibit neurotransmitter release and may result in normal intracellular osmolality. In transient global ischemia in gerbils, we studied in vivo microdialysis of amino acids before, during and after ischemia. We were able to show that taurine resulted in attenuation of glutamate during ischemia (however did not reach significance). In similar experiments, neuronal damage was assessed in the hippocampus. Our results show 48% damage in taurine treated animals, 60% in alanine treated animals and 69% in control groups (trend towards protection but again did not reach significance) Focal ischemia was induced by embolizing a thrombus into the distal internal carotid artery and origin of the middle cerebral artery. Again, in studies where we compared taurine to a placebo treated animal, there was no significant decrease in the amount of damage with taurine. There are reports in the literature that taurine may attenuate neuronal injury during ischemia. Our studies in two models of cerebral ischemia in rodents did not reveal neuronal protection. It is possible that higher doses or possibly prolonged use of taurine may show better results. Taurine may also potentially offer additive protective effects when used in combination with thrombolysis or other neuroprotective agents. Further studies are necessary to better understand the potential for taurine as a neuroprotective agent in cerebral ischemia.

The role of pharmacology in spinal cord protection during thoracic aortic reconstruction

Surgery of the thoracic aorta continues to have a significant risk of neurologic complication. Several strategies to minimize this risk are emerging. Pharmacologic protection from these complications continues to be researched, but at this point few medications are being used clinically. This article reviews the pathophysiology of ischemic spinal cord injury and summarizes the investigational pharmacology that may prevent these serious complications.

Antiischemic effects of topiramate in a transient global forebrain ischemia model: a neurochemical, histological, and behavioral evaluation

The mechanisms of action of the anticonvulsant topiramate (TPM) are indicative of a potential benefit during cerebral ischemia. TPM was studied in a transient global forebrain ischemia (TGFI) model in gerbils in which 40 mg/kg was administered before or after TGFI. Control groups were administered 0.9% normal saline similarly. The evaluation consisted of neurochemical, histological, and functional analyses. The data obtained indicates that unlike the focal cerebral ischemia model, TPM is not neuroprotective in TGFI. The difference in effect, which may be due to the difference in species or the type of ischemia, points to the need for caution when extrapolating animal data from this drug to humans.

DOPA cyclohexyl ester potently inhibits aglycemia-induced release of glutamate in rat striatal slices

Brain ischemic insult causes glutamate release and resultant neuronal cell death. We here show that L-3,4-dihydroxyphenylalanine (DOPA) is a positive regulatory factor for glutamate release elicited by a mild brain insult using in vitro superfused rat striatal slices as a model system. Glucose deprivation for 18 min elicited release of glutamate, DOPA and dopamine (DA). Either tetrodotoxin (TTX) (1 microM) or alpha-methyl-p-tyrosine (alpha-MPT) (1 mM), a tyrosine hydroxylase inhibitor reduced markedly each of these releases. NSD-1015 (20 microM), an aromatic L-amino acid decarboxylase inhibitor restored the inhibition by alpha-MPT of glutamate and DOPA but not DA release. DOPA cyclohexyl ester (DOPA CHE) (0.3-1 microM), a competitive DOPA antagonist, concentration-dependently suppressed aglycemia-induced glutamate release, the effect which was mimicked neither by S-sulpiride nor SCH23390, a DA D(1) or D(2) receptor antagonist, respectively. Zonisamide (1-1000 microM), an anticonvulsant or YM872 (1 microM), an alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) a receptor antagonist produced no effect on aglycemia-induced glutamate release. DOPA CHE thus showed a relatively potent inhibitory action on aglycemia-induced glutamate release among several neuroprotective agents tested.

Neuroprotective effect of tiagabine in transient forebrain global ischemia: an in vivo microdialysis, behavioral, and histological study

The neuroprotective effect of tiagabine was investigated in global ischemia in gerbils. Two groups of the animals received 15 mg/kg of tiagabine 30 min before ischemia. In the first group, the temperature was controlled at 37 degrees C from time of injection to 1 h after ischemia. In the second group, the temperature was left uncontrolled to see the hypothermic effect of tiagabine. Microdialysis was performed in CA1 region of hippocampus in half of the animals in each group to assess the levels of glutamate and gamma-amino-butyric acid (GABA). Animal behavior was also tested in 28-day groups in a radial-arm maze. Histology was done 7 and 28 days after ischemia in CA1 region of hippocampus to assess early and delayed effect of drug. A significant suppression of glutamate was noted in both groups (P<0.01). Behavioral results showed that in the temperature-uncontrolled treatment group, animals significantly reduced their working memory errors as compared to the temperature-controlled treatment group. Histology revealed a significant neuroprotection (P<0.001) in the temperature-uncontrolled treatment group. In the temperature-controlled treatment group, however, neuroprotection was insignificant (P>0.05). A third group of animals received the same dose of tiagabine 3 h after ischemia. Temperature was not controlled in this group. The animals were sacrificed after 7 days so no behavior testing was carried out. Histology showed no neuroprotection in this group (P>0.05). These results show that tiagabine offers a significant neuroprotection in global ischemia in gerbils when given 30 min before ischemia but not when given 3 h after ischemia.

Efficacy of current antiepileptics to prevent neurodegeneration in epilepsy models

Results of experiments performed in animal epilepsy models and human epilepsy during the past decade indicate that the epileptic brain is not a stable neuronal network, but undergoes modifications caused by the underlying etiology and/or recurrent seizures. In many forms of epilepsy, such as temporal lobe epilepsy, the underlying etiologic factor triggers a cascade of events (epileptogenesis) leading to spontaneous seizures and cognitive decline. In some patients, the condition progresses, due in part to recurrent seizures. The current treatment of epilepsy focuses exclusively on preventing or suppressing seizures, which are symptoms of the underlying disease. Now, however, we are beginning to understand the underlying neurobiology of the epileptic process, as well as factors that might predict the risk of progression in individual patients. Thus, there are new opportunities to develop neuroprotective and antiepileptogenic treatments for patients who, if untreated, would develop drug-refractory epilepsy associated with cognitive decline. These treatments might improve the long-term outcome and quality-of-life of patients with epilepsy. Here we review the available data regarding the neuroprotective effects of antiepileptic drugs (AEDs) at different phases of the epileptic process. Analysis of published data suggests that initial-insult modification and prevention of the progression of seizure-induced damage are candidate indications for treatment with AEDs. An understanding of the molecular mechanisms underlying the progression of epileptic process will eventually show what role AEDs have in the neuroprotective and antiepileptogenic treatment regimen.

Trimetazidine as a potential neuroprotectant in transient global ischemia in gerbils: a behavioral and histological study

The effect of Trimetazidine (TMZ) as a potential neuroprotectant against stroke was studied in the gerbil model of transient forebrain global ischemia. Animals were subjected to a 5-min period of ischemia and assessed 4 and 21 days later. Gerbils were divided into two groups: in group one, gerbils were treated with TMZ at a dose of 25 mg/kg given by intraperitoneal injection prior to ischemia. In group two, gerbils were treated with TMZ at a dose of 25 mg/kg given intraperitoneally after ischemia. Saline-injected gerbils served as controls. Histological evaluation of neuronal damage was carried out using the silver staining technique in gerbils 4 and 21 days after the start of the experimental protocol. Behavioral functions were assessed in gerbils from the 14th to the 21st day after the start of the experimental protocol using the Morris water maze test. Results obtained from this study showed no significant difference between saline treated TMZ-treated gerbils when TMZ was administered after ischemia. When TMZ was administered prior to ischemia, there was a reduction in neuronal damage although it did not reach statistical significance and a statistically significant improvement in behavior. We conclude that TMZ shows signs of promise as a neuroprotective agent, and further studies should look at pre-treatment with different doses and different times.

Intracerebral microdialysis and its clinical application: a review

In vivo intracerebral microdialysis is an important neurochemical technique that has been used extensively in the experimental setting. Relatively recently, techniques have been developed to utilize this method in human subjects. The past decade has seen the advent of clinical investigations utilizing in vivo microdialysis in a number of neuropathological states. This review summarizes the principles of in vivo microdialysis techniques, as applied to humans, while discussing the significance of recent investigations for future clinical development.

The technique of intracerebral microdialysis

Intracerebral microdialysis is an increasingly popular experimental technique. A brief description of the principles of microdialysis is presented and the terms relevant to the procedure are defined. The methodology involved in conducting intracerebral microdialysis is described in detail. Factors influencing the outcome of analysis such as external stimuli, perfusion fluid, perfusion rate, temperature, probe placement, membrane characteristics, and timing of sample collection are discussed. The importance of maintaining the uniformity of the above-mentioned factors is stressed.

An assessment of zonisamide as an anti-epileptic drug

A brief review of epilepsy as a disease, anti-epileptic drugs and methods of evaluation of anti-epileptic drugs are presented as a background for assessment of zonisamide, which has been approved by the FDA as add-on therapy for the treatment of partial seizures with or without secondary generalisation in adults. Chemically, zonisamide is classified as a sulphonamide and is unrelated to other anti-epileptic drugs. The mode of action of zonisamide remains unclear, but likely mechanisms are blockade of sodium and T-type calcium channels. It is also shown to have some neuroprotective effect against hypoxia and ischaemia. It has a liner pharmacokinetics with excellent oral bioavailability. Zonisamide has been approved for use in Japan for ten years prior to approval in USA and Europe. Clinical experience with zonisamide in Japan has documented its efficacy in the treatment of partial seizures (partial-onset generalised tonic-clonic, simple partial and/or complex partial seizures) and to a more variable extent, generalised tonic-clonic, generalised tonic (mainly seen in symptomatic generalised epilepsies including Lennox-Gastaut Syndrome) and compound/combination seizures. The efficacy and safety was confirmed in trials conducted in USA and Europe in adults as well as children. Zonisamide compares favourably with other newly introduced drugs and has the potential for development as a monotherapy for epilepsy.

Retrograde perfusion with a sodium channel antagonist provides ischemic spinal cord protection

BACKGROUND

Neuronal voltage-dependent sodium channel antagonists have been shown to provide neuroprotection in focal and global cerebral ischemic models. We hypothesized that retrograde spinal cord venous perfusion with phenytoin, a neuronal voltage-dependent sodium channel antagonist, would provide protection during prolonged spinal cord ischemia.

METHODS

In a rabbit model, spinal cord ischemia was induced for 45 minutes. Six groups of animals were studied. Controls (group I, n = 8) received no intervention during aortic cross-clamping. Group II (n = 8) received systemic phenytoin (100 mg). Group III (n = 4) received systemic phenytoin (200 mg). Group IV (n = 8) received retrograde infusion of room temperature saline (22 degrees C) only. Group V (n = 8) and group VI (n = 9) received retrograde infusion of 50 mg and 100 mg of phenytoin, respectively, (infusion rate: 0.8 mL x kg(-1) x min(-1) during the ischemic period). Mean arterial blood pressure was monitored continuously. Animals were allowed to recover for 24 hours before assessment of neurologic function using the Tarlov scale.

RESULTS

Tarlov scores (0 = complete paraplegia, 1 = slight lower limb movement, 2 = sits with assistance, 3 = sits alone, 4 = weak hop, 5 = normal hop) were as follows (mean +/- SEM): group I, 0.50 +/- 0.50; group II, 0.25 +/- 0.46; group IV, 1.63 +/- 0.56; group V, 4.13 +/- 0.23; and group VI, 4.22 +/- 0.22 (p < 0.0001 V, VI versus I, II, IV by analysis of variance). No differences in mean arterial blood pressure were observed. All animals in group III became profoundly hypotensive and died before the conclusion of the 45-minute ischemic time.

CONCLUSIONS

Retrograde venous perfusion of the spinal cord with phenytoin, a voltage-sensitive sodium channel blocker, is safe and provides significant protection during prolonged spinal cord ischemia.

Glial glutamate transporter GLT-1 down-regulation precedes delayed neuronal death in gerbil hippocampus following transient global cerebral ischemia

Glial (GLT-1 and GLAST) and neuronal (EAAC1) high-affinity transporters mediate the sodium dependent glutamate reuptake in mammalian brain. Their dysfunction leads to neuronal damage by allowing glutamate to remain in the synaptic cleft for a longer duration. The purpose of the present study is to understand their contribution to the ischemic delayed neuronal death seen in gerbil hippocampus following transient global cerebral ischemia. The protein levels of these three transporters were studied by immunoblotting as a function of reperfusion time (6 h to 7 days) following a 10 min occlusion of bilateral common carotid arteries in gerbils. In the vulnerable hippocampus, there was a significant decrease in the protein levels of GLT-1 (by 36-46%, P < 0.05; between 1 and 3 days of reperfusion) and EAAC1 (by 42-68%, P < 0.05; between 1 and 7 days of reperfusion). Histopathological evaluation showed no neuronal loss up to 2 days of reperfusion but an extensive neuronal loss (by approximately 84%, P < 0.01) at 7 days of reperfusion in the hippocampal CA1 region. The time frame of GLT-1 dysfunction (1-3 days of reperfusion) precedes the initiation of delayed neuronal death (2-3 days of reperfusion). This suggests GLT-1 dysfunction as a contributing factor for the hippocampal neuronal death following transient global cerebral ischemia. Furthermore, decreased EAAC1 levels may contribute to GABAergic dysfunction and excitatory/inhibitory imbalance following transient global ischemia.

The role of taurine in neuronal protection following transient global forebrain ischemia

Osmoregulation and post ischemic glutamate surge suppression (PIGSS) are important mechanisms in the neuroprotective properties of taurine. We studied the role of taurine in PIGSS following transient global forebrain ischemia (TGFI). A group of gerbils received a high dose of continuous intracerebral taurine during the peri-ischemic period. Beta-alanine was given similarly to a negative control group. The control group consisted of animals undergoing only TGFI. On the fourth day following commencement of drug administration, TGFI was induced. Concurrently, half the animals from each group receiving an agent had intracerebral microdialysis. All animals underwent histological assessment at day 7. The microdialysis and histological data was analyzed. Our results showed that taurine treatment did not cause PIGSS. The histological difference between the three groups was statistically insignificant. We conclude that intracerebral taurine in the dosage administered during peri-ischemic period, does not result in PIGSS or histologically evident neuroprotection.

Global ischemia and behavioural deficits

Global cerebral ischemia in rodents is an established model in experimental research on cerebral ischemia which is characterized morphologically by a selective neuronal damage in the hippocampus, striatum and cortex. Using this model many studies have been performed to examine the pathophysiology of ischemic neuronal damage. Based upon these results it has been analysed whether substances which interact with the pathophysiological processes reduce the ischemic neuronal damage. Besides the morphological changes global ischemia leads to functional changes which can be assessed by behavioural studies. The Morris water maze examines the animals' abilities to learn, remember and go to a place in space only defined by its position relative to distal extramaze cues. In this test ischemic animals display a deficit in spatial learning as revealed by an increase in latency and in swim distance in the escape trials and a deficit in spatial memory as shown by reduced quadrant time and crossings over the former platform position during the probe trial. In several studies it could be demonstrated that neuroprotective strategies which reduce ischemic neuronal damage also attenuate or even completely prevent the ischemia-induced behavioural deficits in the water maze. Transplantation of fetal tissue which can also be used to achieve morphological recovery following global ischemia results in an amelioration of the ischemia-induced deficit. Thus, the water maze can clearly show that transplanted tissue can be functionally relevant. Data from the water maze seem to be a valuable completion to morphology which is especially important with respect to the relevance of experimental studies for clinical trials.

Effect of traumatic brain injury on mouse spatial and nonspatial learning in the Barnes circular maze

Controlled cortical impact (CCI) is a relatively new model of traumatic brain injury in the mouse, which, in combination with behavioral and histological methods, has potential for elucidating underlying mechanisms of neurodegeneration using genetically altered animals. Previously, we have demonstrated impaired spatial learning in a water maze task following CCI injury at a moderate level. There are many difficulties associated with this task, however, such as stress, physical demand, and the multiple trials over days required for satisfactory training. As a potential alternative to the water maze, we adapted the Barnes circular maze to our mouse model and assessed spatial/nonspatial learning following injury. Mice were trained to locate a dark tunnel, hidden beneath one of 40 holes positioned around the perimeter of a large, flat, plastic disk, brightly illuminated by four overhead halogen lamps. Sham-operated animals rapidly acquired this task, exhibiting reduced latency to find the tunnel and a more efficient search strategy as compared with injured mice. This difference was not due to visuomotor deficits, as all mice performed equally well in a cued version of the same task. These results demonstrate spatial learning impairment following CCI injury in a task that offers an efficient alternative to the water maze.

Interaction between Ca2+, K+, carbamazepine and zonisamide on hippocampal extracellular glutamate monitored with a microdialysis electrode

1. Multiple components of hippocampal glutamate release were examined by study of Ca2+- and K+-evoked hippocampal extracellular glutamate release using an in vivo microdialysis glutamate biosensor in urethane-anaesthetized rats. In addition, the effects of the antiepileptic drugs, carbamazepine (CBZ) and zonisamide (ZNS) perfused through the probe on glutamate release were assessed. 2. Basal glutamate levels were below detection limits (approximately 0.1 microM). An increase in extracellular KCl (from 2.7 to 50 and 100 mM) increased extracellular hippocampal glutamate levels to 9.2+/-1.4 and 20.0+/-2.6 microM, respectively, calculated from the area under curve (AUC) for 60 min. 3. This KCl-evoked glutamate release consisted of three components: an initial transient rise, a late gentle rise, and late multiple phasic transient rises. 4. An increase in or removal of extracellular CaCl2 levels respectively enhanced and reduced the 50 mM KCl-evoked hippocampal glutamate release (AUC for 60 min) from 9.2+/-1.4 to 12.4+/-2.1 and 5.8+/-0.9 microM. 5. Perfusion with 100 microM CBZ or 1 mM ZNS inhibited both the 50 mM KCl-evoked hippocampal glutamate release (AUC for 60 min) from 9.2+/-1.4 to 5.5+/-1.1 and to 5.8+/-1.3 microM, respectively, as well as the stimulatory effects of Ca2+ on KCl-evoked hippocampal glutamate release. 6. These results suggest that both CBZ and ZNS may reduce epileptiform events by inhibiting excitatory glutamatergic transmission.