Taku Taguchi

Failure in learning task and loss of cortical cholinergic fibers in microsphere-embolized rats

Abstract The present study was undertaken to elucidate the pathological changes in learning and memory functions and in the metabolism of cortical cholinergic neurons following microsphere embolism in the rat. Microspheres (48 μm) were injected into the right internal carotid artery of rats. Learning and memory functions were measured 7 or more days after the embolism by active and passive avoidance, and water maze tasks. In the biochemical study, cortical acetylcholine and choline contents, and choline acetyltransferase activity were measured. Cortical acetylcholinesterase-containing fibers were quantitatively estimated in the embolized rat. The active and passive avoidance, and water maze tasks were impaired in the microsphere-embolized rat. In the histochemical study, the density of cortical acetylcholinesterase-containing fibers of the ipsilateral hemisphere of the microsphere-embolized rat was decreased, but cell density was unchanged. Furthermore, microsphere embolism decreased the cortical acetylcholine concentration and choline acetyltransferase activity and increased the choline concentration. The results suggest that microsphere embolism causes severe damage to cortical cholinergic neurons, which may be, at least in part, related to the impairment of learning and memory functions in the sustained brain ischemia.

Changes in cholinergic neurons and failure in learning function after microsphere embolism-induced cerebral ischemia

Central cholinergic neurons play an important role in learning and memory functions. The present study was undertaken to elucidate the pathological changes in learning function and acetylcholine metabolism of the cerebral cortex and hippocampus, following microsphere embolism in rats. Microspheres (48 microns) were injected into the right internal carotid artery of the rats. Learning function was determined using a passive avoidance task on the seventh day after the embolism. In the biochemical study, acetylcholine and choline contents, and choline acetyltransferase activity were measured in the cerebral cortex and hippocampus. Cortical acetylcholinesterase-containing fibers were quantitatively estimated in the embolized rat. Passive avoidance was impaired in the microsphere-embolized rat. Microsphere embolism decreased the acetylcholine concentration and choline acetyltransferase activity in the cerebral cortex and hippocampus. In the histochemical study, the length of cortical acetylcholinesterase-containing fibers was decreased, but cell density was unchanged in the ipsilateral hemisphere of the microsphere-embolized rat. The results suggest that microsphere embolism induces severe damage to cholinergic neurons, which may be related to the impairment of learning function in the ischemic brain.

Effects of naftidrofuryl oxalate on microsphere-induced changes in acetylcholine and amino acid content of rat brain regions

Effects of naftidrofuryl oxalate (naftidrofuryl) on neurotransmitter, acetylcholine, and amino acid content of brain regions following microsphere-induced cerebral embolism were examined to elucidate its possible therapeutic effects on ischemic brain. Rats received 900 microspheres (48 μm in diameter) via the right internal carotid artery, followed by ligation of the right common carotid artery; and histological and biochemical alterations were examined on the 3rd, 5th, and 28th days after embolism. The embolism induced increases in triphenyltetrazolium chloride-(TTC)-unstained areas and decreases in acetylcholine, glutamate, aspartate, and γ-aminobutyric acid (GABA) contents in the cerebral cortex, striatum, and hippocampus of the right hemisphere, suggesting that microsphere embolism causes severe damage to these brain regions. Hematoxylin-eosin staining of the right cortical sections after embolism showed degeneration and necrosis of nerve cells with chromatolytic nuclei and eosinophilic cytoplasm. Changes in neurotransmitters of the left hemisphere were relatively small. Treatment with naftidrofuryl of the embolized rats with stroke-like symptoms took place from postoperative day 1 to 28. Treatment resulted in a reduction in TTC-unstained areas, less morphological damage to cerebral cortex on the 3rd and 5th days, and an appreciable restoration of acetylcholine content of three brain regions of the right hemisphere throughout the experiment, but restoration of neurotransmitter amino acids was observed to a smaller degree. The results suggest that naftidrofuryl is capable of preventing the development of ischemia-induced, sustained damage to brain regions vulnerable to oxygen deficiency, particularly by improving impaired acetylcholine metabolism.

Reduction by ATP-Sensitive Potassium Channel Opener, YM934, of Experimental Myocardial Infarct Size in Anesthetized Dogs

The present study was undertaken to examine whether the ATP-sensitive potassium channel opener, YM934, would be effective in reducing infarct size in a model of myocardial infarction in anesthetized dogs. For this purpose the effects of nifedipine, a calcium channel blocker, and hydralazine, a vasodilator with unknown mechanisms, were also investigated for comparison. Severe, irreversible myocardial injury was produced by a 90-min occlusion of the proximal left anterior descending coronary artery followed by 5 h of reperfusion. Infusion of YM934 (0.1 μg/kg/min i.c.) during the last 15 min of pre-ischemia reduced the myocardial infarct size and attenuated the release of creatine kinase MB eluted from the hearts without alteration in hemodynamic parameters including regional myocardial blood flow. In contrast, the other vasodilators, hydralazine and nifedipine, did not reduce myocardial infarct size under the same coronary vasodilatory conditions. These observations indicate that intracoronary YM934 is cardioprotective and that this effect is independent of alterations in regional myocardial blood flow.

Cardioprotective effects of YM934, an ATP-sensitive potassium channel opener, on stunned myocardium in anesthetized dogs

The effects of YM934 [2-(3,4-dihydro-2,2-dimethyl-6-nitro-2H-1,4-benzoxazin-4-yl) pyridine N-oxide], an adenosine triphosphate (ATP)-sensitive potassium channel opener, on stunned myocardium were examined. Forty eight anesthetized dogs were subjected to 15 min of left anterior descending (LAD) coronary artery occlusion followed by 3 hours of reperfusion. To elucidate the possible contribution of the cardioprotective property of YM934 to stunned myocardium, a nonhypotensive dose of YM934 was directly injected into the LAD coronary artery before the ischemic insults. Intracoronary artery infusion (i.c.) of YM934 (0.1 microg/kg/min) produced a marked improvement in post-ischemic regional contractile dysfunction. The effects were not associated with improvement of hemodynamics, including regional myocardial blood flow during ischemia, heart rate and mean arterial blood pressure. The anatomic areas at risk expressed as a percentage of the left ventricle and regional myocardial blood flow were not significantly different between groups. The cardioprotective effect of YM934 was completely blocked by pretreatment with an ATP-sensitive potassium channel blocker, glibenclamide (1.0 mg/kg i.v. bolus). These results suggest that YM934 exerts cardioprotective effect on stunned myocardium through opening myocardial ATP-sensitive potassium channels.

Effects of an ATP-sensitive potassium channel opener, YM934, on hypoxia/reoxygenation injury of isolated canine cardiac cells

The cardioprotective effects of YM934, an ATP‐sensitive potassium channel opener (KCO), on isolated canine cardiomyocytes were examined. Exposure of isolated canine cardiomyocytes to YM934 (10 μM) resulted in an increase of potassium channel opening activity in whole cell patch clamp technique. Glibenclamide (1 μM) reversed the channel opening activity induced by YM934. Pretreatment of the cardiomyocytes with YM934 caused a potent inhibition KCL (20 mM)‐induced increase in [Ca2+]i. Cromakalim also inhibited the KCL‐induced increase in [Ca2+]i under the same experimental conditions. The ratio of alive to dead cells and the release of creatine kinase from isolated cardiomyocytes during a 120‐min hypoxia / 15‐min reoxygenation period were dose‐dependently (YM934; 0.1–10 μM) attenuated; 71–93% of the preischemic value for the ratio of alive/dead cells and 76–58% of the nontreated hearts for the release of creatine kinase. These results suggest that YM934 has a direct cardioprotective effect against ischemia/reperfusion injury of canine cardiac myocytes, possibly through opening ATP‐sensitive potassium channels. Drug Dev. Res. 48:113–120, 1999.