Reduction by lifarizine of the neuronal damage induced by cerebral ischaemia in rodents

The temporal and spatial changes of actin cytoskeleton in the hippocampal CA1 neurons following transient global ischemia

Transient global ischemia usually results in delayed neuronal death in selective brain regions, prior to which a rapid loss of dendritic spines has been widely reported in these regions. Dendritic spines are characterized by a highly branched meshwork of actin cytoskeleton (F-actin), which is extremely vulnerable to the ATP-depleted conditions such as hypoxia/ischemia. However, the ischemia-induced changes of F-actin are still not clarified in the vulnerable brain areas. This study was designed to examine the temporal and spatial alterations of F-actin in the CA1 subfield of rat hippocampus following reperfusion after global cerebral ischemia. Phalloidin staining and confocal microscopic examination showed that F-actin disappeared from the dentritic spines in the CA1 stratum radiatum, but aggregated into thread- or fiber-like structures on days 1.5-2 after ischemia. This was followed by a nearly complete loss of F-actin in the CA1 subfield on days 3-7 after ischemia. Colocalization analysis demonstrated that the F-actin threads or fibers were located mainly within the dentritic trunks. As revealed by Nissl and Fluoro-Jade B staining, the decrease of F-actin proceeded concurrently with the evolution of ischemic damage. Consistently, western blots detected a significant decrease of F-/G-actin ratio in the dissected CA1 subfield after ischemia. To our knowledge, this is the first report on the change of F-actin in the ischemic brain. Although the underlying mechanisms remain to be elucidated, our findings may provide an important structural clue for the neuronal dysfunction induced by ischemia.

Morphology of Rat Hippocampal CA1 Neurons Following Modified Two and Four-Vessels Global Ischemia Models

Background

An appropriate animal model of ischemia stroke is essential for evaluation of different therapeutic methods. Two and four-vessel global ischemia models are one of the most common types of transient cerebral ischemia.

Objectives

In this study, the morphology of rat hippocampal CA1 neurons in modified models of two and four-vessel ischemia and reperfusion were evaluated.

Materials and Methods

In this study, 20 Wistar rats were randomly divided into five groups. In group 2 and 3, both common carotid arteries were occluded for 10 minutes in either 3 or 24 hours of reperfusions, respectively. In group 4 and 5, both common carotid and vertebral arteries were occluded for 10 minutes in either 3 or 24 hours of reperfusions, respectively. Group 1 as control, underwent the whole surgery without any arteries occlusion. Hippocampi of the rats in all groups were processed and tissue sections were stained using the Nissl method. The morphology of CA1 neurons were studied under a light microscope and compared different groups.

Results

In all groups ischemic changes were apparently observed in hippocampus CA1 neurons. In two-vessel occlusion model, after 3 and 24 hours of reperfusions, ischemic cells accounted for 14.9% and 23.2%, respectively. In four-vessel occlusion model, after 3 and 24 hours of reperfusions, ischemic cells accounted for 7.6% and 44.9% (P < 0.0001), respectively.

Conclusions

Modified four-vessel occlusion model resulted in significant ischemic changes after 24 hours of reperfusion in CA1 neurons of rat hippocampus.

Sodium channel blocking activity of AM-36 and sipatrigine (BW619C89): in vitro and in vivo evidence

Sodium channel blockers are neuroprotective against cerebral ischemia in animal models. A novel neuroprotective compound AM-36, when screened for activity at the most common receptor and ion channel binding sites, revealed activity at site 2 Na+ channels. Studies then investigated this Na+ channel blocking activity in vitro and in vivo relative to other Na+ channel blockers, including the neuroprotective agent sipatrigine (BW619C89). AM-36 inhibited batrachotoxinin (BTX)-sensitive Na+ channel binding in rat brain homogenates with an IC50 of 0.28 microM. Veratridine (100 microM)-induced neurotoxicity in murine cerebellar granule cells was completely inhibited by AM-36 (1.7 microM) compared to only partial inhibition by sipatrigine (26 microM). Veratridine-stimulated glutamate release, as measured through a microdialysis probe in the cortex of anesthetised rats, was inhibited by 90% by superfusion of AM-36 (1000 microM). In the endothelin-1 (ET-1) model of middle cerebral artery occlusion (MCAo) in conscious rats, both AM-36 (6 mg/kg i.p.) and sipatrigine (10 mg/kg i.p.) 30 min post-MCAo significantly reduced cortical, but not striatal infarct volume. As the refractiveness of the striatum is likely to be dependent on the route and time of drug administration, AM-36 (1 mg/kg i.v.) was administered 3 or 5 h after MCAo and significantly reduced both cortical and striatal infarct volumes. The present studies demonstrate Na+ channel blocking activity of AM-36 both in vitro and in vivo, together with significant neuroprotection when administration is delayed up to 5 h following experimental stroke.

Limiting neurological damage after stroke: a review of pharmacological treatment options

Acute ischaemic stroke is a leading cause of death and a major cause of long term disability worldwide. Effective treatments for limiting the neurological damage after stroke have proven elusive. An improved understanding of the complicated cascade of cellular events following the onset of cerebral ischaemia has led to exploration of a number of avenues for early intervention. Reperfusion of the ischaemic territory using thrombolytic drugs has shown promise in clinical trials as a method for achieving tissue salvage. Antithrombotic and antiplatelet agents have not demonstrated efficacy as acute therapies, although the early use of aspirin (acetylsalicylic acid) appears to produce a reduction in early stroke recurrence. A wide variety of drugs which interfere at various points in the ischaemic cascade, so-called 'neuroprotective agents', have also been studied, but with mixed success. Of these, antagonists of voltage-gated calcium channels, antagonists at the N-methyl-D-aspartate (NMDA) receptor and scavengers of free radicals have been most extensively studied. Despite proving effective in animal models of cerebral ischaemia, these drugs have largely failed to fulfil their promise in clinical trials. While individual compounds have proven ineffective, combinations of drugs with different mechanisms of action may yet provide the best treatment for acute ischaemic stroke.

The importance of voltage-dependent sodium channels in cerebral ischaemia

Strategies for the treatment of thromboembolic stroke are based on restoring the blood flow as soon as possible and protecting the neurons from the deleterious consequences of cerebral ischaemia. Interest has focused on blockers of voltage-dependent Na+ channels as potential neuroprotective agents because they prevent neuronal death in various experimental models of cerebral ischaemia and act cytoprotectively in models of white matter damage. Although several Na+ blockers are currently being tested in various phases of clinical development, most of these agents are relatively weak and unspecific. I therefore consider it worthwhile to search for molecules which specifically block voltage-dependent Na+ channels for the treatment of cerebral ischaemia.

Ca2+ channel antagonists and neuroprotection from cerebral ischemia

Stroke is the third leading cause of death and the main disabling neurologic disease. The finding in experimental studies that neuronal death does not occur immediately after ischemic injury has encouraged the development of neuroprotective agents. Various Ca2+ channel antagonists, that is, L-type-selective or non-selective derivatives from classical Ca2+ channel antagonists, have been examined for their ability of neuroprotection through improvement of cerebral blood circulation or inhibition of Ca2+ overload induced by excessive glutamate release. Although some of the antagonists showed efficient neuroprotection in animal models, systemic hypotension limited the utility of these drugs, and none of the compounds showed beneficial effects in treatments for acute ischemic stroke in clinical trials. Drugs other than Ca2+ channel antagonists developed on the basis of the glutamate-Ca2+ overload hypothesis were shown also to lack clinical benefit. Recently, some mechanisms have been proposed to interpret neuronal death in relation to hyperexcitability or apoptosis after ischemic insult. In these hypotheses, activation of the Ca2+ channel types selectively expressed in neuronal tissues is proposed as a critical step of the pathways toward neurodegeneration. Thus, it is increasingly recognized that developing highly selective compounds for neuronal Ca2+ channels is not only important for treatment of stroke but also for elucidation of mechanisms that underlie neurodegeneration.

Rodent models of global cerebral ischemia: a comparison of two-vessel occlusion and four-vessel occlusion

1. Human stroke is a complex and heterogeneous phenomenon that may defy attempts to develop a unitary animal model with which to address all of the relevant issues. 2. Focal models are regarded by many to be the approach of choice, but both global and focal models of cerebral ischemia can be sources of useful and complementary insight. 3. Of the global models, four-vessel occlusion requires a preparatory operative procedure that may increase the risk of extraneous factors confounding the response to the ischemic insult itself. The procedures are only partly reversible, with the vertebral arteries remaining permanently occluded. 4. The two-vessel occlusion model is easier to perform in a single procedure, and the less-intrusive surgical intervention allows greater scope for recovery experiments. The occlusion is fully reversible. 5. Many classes of compounds with therapeutic potential have been identified in the laboratory, often on the basis of success in one class of animal model, but translating these successes into a clinical context has proved singularly difficult. If, in future, compounds of interest are tested across a range of the available models, the likelihood of subsequent clinical success may be enhanced.