Ischemic brain damage following transient and moderate compression of sensorimotor cortex in Sprague-Dawley and diabetic Goto-Kakizaki rats

Abstract

Several animal models have been developed to facilitate the investigation of biochemical, physiological, and neurological events after cerebral ischemia. In this study we present a new animal model which reliably describes morphological changes and neurological deficits produced by mild to moderate brain ischemia and which can be used to identify novel, potentially useful, neuroprotective agents.

In our experiments we found that short-lasting compression (30 min) of a specific brain area in the sensorimotor cortex caused a well-defined functional deficit seen as transient (5-7 days) contralateral paresis of the fore- and/or hindlimbs in Sprague-Dawley rats. The morphological changes and the functional outcome after the ischemic insult were dependent upon the duration of the compression as well as on the age and body temperature of the animals. Morphological changes were characterized using Nissl staining whereas the neurological deficit was characterized using a beam-walking test. Administration of neuroprotective agents like the non-competitive NMDA/glutamate receptor antagonist dizocilpine (MK-801), and the selective AMPA/glutamate receptor antagonist, LY326325, significantly improved the neurological recovery. LY326325 also reduced the number of injured cortical neurons.

Although classical antagonists are effective neuroprotectants their clinical usefulness is restricted by their high incidence of disturbing, psychomimetic side effects observed as psychosis-like experiences in humans. In this study we found that the NR2B subtype-specific NMDA receptor antagonist CP101,606, which is thought tomay be devoid of disturbing CNS side effects, effectively blocked both the morphological and neurological effects after focal cerebral ischemia. The magnitude of the brain damage was determined by using Fluoro-Jade, a novel fluorescent marker that detects degenerating cells. CP101,606 dose-dependently improved the rate of functional recovery and antagonized the ischemic brain injury in cerebral cortex, hippocampus, and thalamus at clinically relevant plasma concentrations.

Further characterization of the ischemic brain damage using Fluoro-Jade and TUNEL staining provided further evidence for the idea that mild to moderate cerebral ischemia does not induce necrotic brain damage but rather a pattern of scattered dead and/or dying brain neurons.

Hyperglycemia is thought to worsen the outcome of cerebral ischemia. In our model, GotoKakizaki (GK) rats, which display genetically determined, spontaneous diabetes (type 2 diabetes), developed a much more severe brain injury revealed as more severe neurological deficits and larger brain injuries (at least in cerebral cortex, thalamus, and hippocampus) than Wistar control rats. The brain damage was characterized by Fluoro-Jade and by the microglia cell marker, OX42. The surgical procedure by itself had no effects on blood glucose levels in Wistar rats but there was a marked increse in the diabetic GK rats.

Finally we found that the ischemic insult caused degeneration of Purkinje cells in GK, Wistar, and Sprague-Dawley rats seen as a bilateral degeneration of Purkinje cells as detected by Fluoro-Jade. The Purkinje cells damage was accompanied by co-localized activation of microglia that was detected by the immunohistochemical marker, OX42. We suggest that the Purkinje cell damage is not due to direct mechanical injury but rather to a synaptically mediated toxic event.

Taken together, our data suggest that transient, extradural compression of sensorimotor cortex represents a useful animal model of cerebral ischemia that can be used to study not only pathophysiological changes occurring after focal cerebral ischemia but also to investigate new therapies for stroke treatment.