Behar T N, Schaffner A E, Tran H T, Barker J L
Laboratory of Neurophysiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892.
Brain Res. 1994 Nov 21;664(1-2):155-66. doi: 10.1016/0006-8993(94)91966-6.
During rat embryogenesis, fibers containing nerve growth factor (NGF) are present near the target destinations of migratory spinal neuroblasts, suggesting that diffusible gradients of NGF provide signals to newly generated neurons in the developing cord. In vitro, pM concentrations of NGF induce neuroblast chemotaxis (directed migration along a chemical gradient), indicating evoked motility is mediated by high-affinity receptors. Binding of 125I-labelled NGF to fetal cord cells provides additional evidence that rat spinal neuroblasts express the high-affinity receptors; however, their presence has not been directly demonstrated. In the present study, we used immunocytochemistry to show that the high-affinity NGF receptor protein, gp140trk (trk) is detectable in embryonic spinal tissue sections and in cord dissociates. Correlation of trk expression with NGF-induced chemotaxis revealed that both the receptor protein expression and functional responses to NGF develop along a ventro-dorsal gradient that parallels the in vivo pattern of neurogenesis and migration. Analysis of the temporal changes in trk immunoreactivity demonstrated that expression of gp140trk is bimodal, possibly reflecting multiple effects of NGF during development. Chemotaxis to NGF was blocked by nM concentrations of the kinase inhibitor, K252a, suggesting that NGF stimulates motility via high-affinity receptors coupled to kinase activity. Elevated 3',5'-cyclic adenosine monophosphate (cAMP) also attenuated NGF-induced chemotaxis, presenting preliminary evidence that protein kinase A (PKA) may regulate motility responses to NGF.
在大鼠胚胎发育过程中，含有神经生长因子（NGF）的纤维出现在迁移的脊髓神经母细胞的目标目的地附近，这表明NGF的可扩散梯度为发育中的脊髓中新生神经元提供信号。在体外，皮摩尔浓度的NGF可诱导神经母细胞趋化性（沿化学梯度的定向迁移），表明诱发的运动性是由高亲和力受体介导的。125I标记的NGF与胎儿脊髓细胞的结合提供了额外证据，证明大鼠脊髓神经母细胞表达高亲和力受体；然而，它们的存在尚未得到直接证实。在本研究中，我们使用免疫细胞化学方法显示，在胚胎脊髓组织切片和脊髓解离物中可检测到高亲和力NGF受体蛋白gp140trk（trk）。trk表达与NGF诱导的趋化性之间的相关性表明，受体蛋白表达和对NGF的功能反应均沿腹背梯度发展，这与体内神经发生和迁移模式平行。对trk免疫反应性的时间变化分析表明，gp140trk的表达是双峰的，这可能反映了NGF在发育过程中的多种作用。纳摩尔浓度的激酶抑制剂K252a可阻断对NGF的趋化性，这表明NGF通过与激酶活性偶联的高亲和力受体刺激运动性。升高的3',5'-环磷酸腺苷（cAMP）也减弱了NGF诱导的趋化性，这提供了初步证据，表明蛋白激酶A（PKA）可能调节对NGF的运动反应。
