Effects of naftidrofuryl oxalate on microsphere embolism-induced changes in tricarboxylic acid cycle intermediates of rats

The vasodilator naftidrofuryl attenuates short-term brain glucose hypometabolism in the lithium-pilocarpine rat model of status epilepticus without providing neuroprotection

Status epilepticus (SE) triggered by lithium-pilocarpine is a model of epileptogenesis widely used in rats, reproducing many of the pathological features of human temporal lobe epilepsy (TLE). After the SE, a silent period takes place that precedes the occurrence of recurrent spontaneous seizures. This latent stage is characterized by brain glucose hypometabolism and intense neuronal damage, especially at the hippocampus. Importantly, interictal hypometabolism in humans is a predictive marker of epileptogenesis, being correlated to the extent and severity of neuronal damage. Among the potential mechanisms underpinning glucose metabolism impairment and the subsequent brain damage, a reduction of cerebral blood flow has been proposed. Accordingly, our goal was to evaluate the potential beneficial effects of naftidrofuryl (25 mg/kg i.p., twice after the insult), a vasodilator drug currently used for circulatory insufficiency-related pathologies. Thus, we measured the effects of naftidrofuryl on the short-term brain hypometabolism and hippocampal damage induced by SE in rats. 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) positron emission tomography (PET) neuroimaging along with various neurohistochemical assays aimed to assess brain damage were performed. SE led to both severe glucose hypometabolism in key epilepsy-related areas and hippocampal neuronal damage. Although naftidrofuryl showed no anticonvulsant properties, it ameliorated the short-term brain hypometabolism induced by pilocarpine. Strikingly, the latter was neither accompanied by neuroprotective nor by anti-inflammatory effects. We suggest that naftidrofuryl, by acutely enhancing brain blood flow around the time of SE improves the brain metabolic state but this effect is not enough to protect from the damage induced by SE.

[The model of stroke induced by microsphere embolism in rats]

Cerebral infarction is induced by injecting 700-900 microspheres with a diameter of 50 microm into the right internal carotid artery of the rat. Approximately 82% of the rats with typical symptoms of stroke survived at fifteen hours after the injection of microspheres. Microsphere-induced cerebral embolism elicits the widespread formation of small emboli in the ipsilateral hemisphere and subsequent neuronal loss and/or the development of multiple infarct areas in the brain, particularly in the cortex, striatum, and hippocampus. Thus, this model is considered to mimic focal ischemia-induced human stroke or multi-infarct dementia. We have found that this model showed sustained decreases in cerebral blood flow and cerebral high-energy phosphates; accumulation of tissue lactate, glucose, and glycogen; changes in the activity of several enzymes in the tricarboxylic acid cycle; loss of mitochondrial phosphorylation activity; and decreases in neurotransmitters, acetylcholine, monoamines, and amino acids in the ipsilateral hemisphere. Accordingly, microsphere embolism is capable of inducing severe and sustained cerebral ischemia resulting in disturbances of the energy and neurotransmitter metabolism in the brain. Such ischemic damage leads to learning and memory dysfunction. This model provides useful information about the pathogenesis, prophylaxis, and therapeutics of cerebral ischemic diseases.

Effects of nefiracetam on cerebral adenylyl cyclase activity in rats with microsphere embolism-induced memory dysfunction

The effects of nefiracetam on the cerebral adenylyl cyclase (AC) activity of animals with microsphere embolism-induced memory dysfunction were examined. Sustained cerebral ischemia in the right cerebral hemisphere was induced by an injection of microspheres into the right internal carotid artery of rats. To examine learning and memory function, the water maze test was performed from day 7 to day 10 after the operation. The escape latency of the microsphere-embolized (ME) rat in the water maze task was longer than that of the sham-operated (Sham) rat, suggesting that spatial memory dysfunction occurred in the ME rat. Gsalpha and Gi(1/2)alpha protein levels in the cerebral cortex, striatum and hippocampus of the ME rat, when determined on day 11, were similar to those of the Sham rats. The basal AC activity in the striatum, but not in the other two regions, of the ME rat decreased. The AC activity in the presence of 10 microM colforsin daropate (Col), a direct stimulator of AC, was increased by approximately 20-fold in sham animals and 7- to 10-fold in the ME rat. Treatment of the ME rat with 10 mg/kg/d nefiracetam p.o. from day 1 to day 10 after the operation shortened the escape latency, restored the basal AC activity in the striatum, and reversed the Col-induced increases in AC in these three regions without any changes in the cerebral Gsalpha and Gi(1/2)alpha protein levels. These results suggest that nefiracetam-mediated activation of AC activity may contribute to the improvement of memory and learning function in sustained cerebral ischemia.