Biochemical studies on the mechanism of the action of nerve growth factor

研究了神经生长因子（NGF）对培养的P3基底前脑胆碱能神经元低亲和力NGF受体（lnfr）基因表达的影响，NGF可促进P3基底前脑胆碱能神经元分化。根据RT-PCR（逆转录聚合酶链反应）方法的结果，在添加100 ng/ml NGF 1天后，NGF处理的培养物中lnfr mRNA水平比对照培养物增加了2倍以上。这种增加在添加NGF后可维持3天。即使在1 ng/ml NGF （=40 pM）时，lnfr mRNA的表达也有所增加，这表明当NGF浓度接近高亲和NGF受体的Kd值时，培养的胆碱能神经元中lnfr mRNA水平上调。此外，免疫组织化学染色显示，与对照组相比，ngf处理培养的胆碱能神经元单克隆抗lnfr抗体染色更强。我们的研究结果表明，NGF可以在培养的P3基底前脑胆碱能神经元中上调lnfr mRNA和蛋白水平的表达，这一机制可能在增强NGF对P3基底前脑胆碱能神经元的作用中起重要作用。

We examined the effect of nerve growth factor (NGF) on the expression of the low-affinity NGF receptor (LNGFR) gene in cultured P3 basal forebrain cholinergic neurons, on which NGF acts to promote differentiation. Based on the results of the RT-PCR (reverse transcriptase-polymerase chain reaction) method, over a 2-fold increase in the LNGFR mRNA level was found in NGF-treated cultures compared with control cultures at one day after the addition of 100 ng/ml NGF. This increase was maintained for up to 3 days after the addition of NGF. The increase in LNGFR mRNA was found even at 1 ng/ml NGF (=40 pM), indicating that the upregulation of the LNGFR mRNA level in cultured cholinergic neurons occurred at an NGF concentration near the Kd value for the high-affinity NGF receptor. In addtion, immunohistochemical staining showed stronger staining with a monoclonal anti-LNGFR antibody of the cholinergic neurons in NGF-treated cultures than those in control cultures. Our results suggest that NGF can up-regulate LNGFR expression at the mRNA and protein levels in cultured P3 basal forebrain cholinergic neurons and that this mechanism may play an important role in potentiating the effect of NGF on these neurons.