Effects of NGF pretreatment on cerebral injury in gerbils

Objective

To investigate the effects and underlying mechanisms of different doses of nerve growth factor(NGF) pretreatment on neuron apoptosis and the expressions of the apoptosis-related protein, Bcl-2 and Bax, in the gerbil cerebral prefrontal cortex following global cerebral ischemia-reperfusion(I/R) injury.

Methods

Fifty-four gerbils were randomly divided into five groups, group C: sham operation(n = 6); group I/R(n = 12), group L(n = 12): low-dose NGF+I/R, group M(n = 12): medium-dose NGF+I/R and group H (n = 12): high-dose NGF+I/R. Groups I/R, L, M and H were further divided into 2 subgroups according to the duration of reperfusion(24 h and 72 h). The global cerebral I/R injury model was induced by bilateral carotid artery occlusion for 20 min, followed by removal of the clamps to permit reperfusion. In groups L, M and H, NGF was injected into the lateral ventricle 24 h prior to ischemia. Terminal deoxynucleotidyl transferase mediated dUTP-biotin nick end labeling(TUNEL) and immunohistochemical staining were performed to detect neuron apoptosis and the expressions of Bcl-2 and Bax protein in the cerebral cortex, respectively.

Results

In the I/R group and NGF pretreatment groups(L, M and H groups), reperfusion for 72 h caused higher percentages of both neurons exhibiting apoptosis and Bax positive cells(P < 0.01), but lower percentages of Bcl-2 positive cells compared with the corresponding 24 h reperfusion groups(P < 0.05). All NGF pretreatment groups exhibited lower percentages of neurons exhibiting apoptosis and Bax positive cells but a higher percentage of Bcl-2 positive-cells relative to the I/R group(P < 0.01). Moreover, the high-dose NGF pretreatment group had a greater decreased neuronal apoptosis and Bax protein expression and increased Bcl-2 protein expression than either the low-or medium-dose groups.

Conclusion

Neuron apoptosis participates in the progression of cerebral ischemia-reperfusion injury. The protective effect of NGF pretreatment against ischemia-reperfusion-induced neuron apoptosis seems to be both time- and dose-dependent. This anti-apoptosis mechanism may be associated with upregulation of Bcl- 2 protein expression and downregulation of Bax protein expression.