Histological Evidence for Neuroprotective Action of Nebracetam on Ischemic Neuronal Injury in the Hippocampus of Stroke-Prone Spontaneously Hypertensive Rats

Abstract

ABSTRACT-Theprotective effect of nebracetam on ischemic neuronal damage was histologically examined in the pyramidal cell layer of the hippocampal CAI subfield 7 days after operation using stroke-prone spontaneously hypertensive rats (SHRSP) subjected to 10-min bilateral carotid occlusion. Nebracetam (50 and 100 mg/kg), given orally 10 min after reperfusion, dose-dependently protected against ischemic delayed neuronal damage in the SHRSP with occlusion; however, the blood pressure remained unchanged following nebracetam administration. These findings further support the notion that nebracetam protects against ischemic delayed neuronal cell death in the hippocampus. Keywords:Nebracetam, Ischemic hippocampal damage, Stroke-prone spontaneously hypertensive rat *To whom correspondence should be addressed .Stroke-prone spontaneously hypertensive rats (SHRSP) are a genetically determined hypertensive strain derived from spontaneously hypertensive rats (1). When these animals are fed a high-salt diet, severe hypertension occurred and their life span was short because of end-organ damage (1). The SHRSP are useful for evaluating the potency and therapeutic value of antihypertensive agents (2, 3). We demonstrated that 10-min bilateral carotid occlusion in SHRSP gradually decreased the density of the pyramidal cells in the hippocampal CAI subfield and neuronal cell death reached a peak 7 days after the operation (4, 5). This two-vessel occlusion model of SHRSP has advantages over the four-vessel occlusion model of normal rats (6) because it avoids the coagulation of bilateral vertebral arteries. This point leads to the different dynamics of cerebral blood flow after reperfusion between our model and the four-vessel occlusion model. In this context, our model more closely simulated the post-ischemic conditions in humans. Therefore, the SHRSP with twovessel occlusion is useful for examining delayed neuronal cell death in the hippocampus caused by a transient forebrain ischemia (4, 5). Several lines of evidence have shown that nebracetam has a nootropic property (7 -12).This compound protected against hypoglycemia/hypoxiainduced striatal and hippocampal damages in vitro (8 -10) and decreased the disruption of spatial cognition and memory impairment evoked by various treatments in vivo (11,12). The present study histologically examined the protective effects of nebracetam against ischemic hippocampal neuronal damage using the two-vessel occlusion model of SHRSP. Male SHRSP maintained and bred at the Laboratory Animal Center for Biochemical Research, Nagasaki University School of Medicine were used. These animals were fed a high-salt and low-protein diet containing 0.8% NaCI and 20.8% of protein (Funabashi Farm Co., Chiba) and allowed water ad libitum. Three to four rats per group were housed in a cage in an air-conditioned room at 24 ± I °C , humidity of 65 _±:5 %, with a 12-hr light-dark schedule (lights on 7:00 a.m.). Twelve-to fourteen-weekold SHRSP, each weighing 260-290 g, were supplied for bilateral carotid occlusion. Ne...

Quantitative Analysis of Delayed Neuronal Death in the Hippocampal Subfields of SHRSP and SHR

“…TIR resulted in a large decrease in viable pyramidal cells in SHRSP, which confirmed the previous qualitative studies (Yamashita et al 1994;Nakashima et al 1995;Sakurai-Yamashita et al 2003). The present quantitative study indicated for the first time that the decrease was about a half in average.…”