Résumé
Previous experiments has shown that Ginsenoside Rb1 (GRb1), which is one of the most important active ingredients in ginseng (Panax ginseng C.A. Meyer), reduced infarct and neurologic deficit followed by the transient cerebral ischemia in rats. The mechanism of this neuroprotective function is unclear. In this study, we tested whether the neuroprotective effect of GRb1 is achieved through preventing the neuronal apoptosis and modulating expression of neuronal apoptosis inhibitory protein (NAIP). Focal cerebral ischemia was induced by the middle cerebral artery occlusion (MCAO) in Wistar rats. GRb1 (40 mg/kg, i.p.) was administered immediately after the onset of reperfusion. The rats with neurological deficits were randomly divided into 2 groups: the ischemia and the GRb1 group. Each group was again divided into subgroups according to the various reperfusion time (3 h, 12 h, 1, 2, 3, 5, 10 days, n=4 per time point). Apoptotic cells were analyzed using TUNEL. Immunohistochemical method was used to assess expression of NAIP. This results showed that the number of apoptotic cells elevated at 3 h of reperfusion, and peaked at 24 h, then declined, but the number of apoptotic cells at 10 d after ischemia was significantly more than those of control groups (P＜0.01). Compared with ischemia group, the apoptotic cells decreased at all subgroups of GRb1; however, the significant differences were only found from 12 h to 3 d of reperfusion. In normal and sham groups, NAIP weak immunostaining was diffusely present in the neurons of parenchyma. The number of NAIP-positive cells started to increase in ischemic regions at 3 h after ischemia, peaked at 12 h and declined up to 5 d of reperfusion. At 5 d after ischemia, the number of NAIP-positive cells was less than that of control group (P＜0.05). A few astrocytes strongly expressed NAIP in the ischemic area. In the GRb1 group, the number of NAIP-positive cells from 12 h to 10 d after ischemia was evidently higher than in the ischemia group. Thus, these results suggest that GRb1 has potential ability to prevent apoptosis, the mechanism of which is related to induce expression of NAIP.