Yao L, Zhang D, Bernd P
Department of Anatomy and Cell Biology, SUNY Health Science Center at Brooklyn, NY 11203, USA.
Neuroscience. 1997 Aug;79(4):1197-206. doi: 10.1016/s0306-4522(96)00698-7.
This study examined the effects of nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3 and neurotrophin-4/5 on substance P levels in dorsal root ganglia of the quail shortly after ganglia formation (stage 26, embryonic day 4.5), during the middle of development (stage 33, embryonic day 7.5) and during late development (stage 44, embryonic day 14). It has already been shown that nerve growth factor increases levels of substance P during the middle and late stages of development, and that messenger RNA for the neurotrophin receptors, trkA, trkB and trkC is present at all of these stages. Dorsal root ganglia were isolated, rinsed with defined medium to dilute endogenous neurotrophins and exposed to one of the neurotrophins for either 4 or 20 h. Substance P levels were quantitated using enzyme immunoassay. None of the neurotrophins had any effect on substance P levels in dorsal root ganglia obtained at stage 26 after either a 4 or 20 h exposure time. Nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3 and neurotrophin-4/5 all significantly increased levels of substance P after either a 4 h or 20 h incubation in ganglia obtained at stages 33 and 44. The effects of nerve growth factor and neurotrophin-3 were specific: increases in substance P were completely blocked by simultaneous exposure to antibodies against either nerve growth factor or neurotrophin-3. The absence of any effect of neurotrophins on substance P expression during early development was unexpected, since dorsal root ganglia exhibit substantial levels of substance P and receptors for the neurotrophins are present and are apparently functional. It was also surprising that brain-derived neurotrophic factor, neurotrophin-3 and neurotrophin-4/5 induced increases in substance P levels during the middle and late stages of development, since substance P was thought to be exclusively localized to small TrkA neurons in dorsal root ganglia. However, immunocytochemical examination of dorsal root ganglia at stages 33 and 44 revealed substance P-like immunoreactivity in larger neurons as well as in small neurons. The results of this study have shown that different cellular responses to neurotrophins, such as effects on survival and/or peptide expression, may be acquired with differing temporal patterns not strictly related to expression of their receptors. Further, the regulation of neuropeptide synthesis in dorsal root ganglia is not due to any one neurotrophic factor. and the factors that regulate expression during early development are still unknown.
本研究检测了神经生长因子、脑源性神经营养因子、神经营养素-3和神经营养素-4/5对鹌鹑背根神经节中P物质水平的影响，检测时间分别为神经节形成后不久（第26阶段，胚胎第4.5天）、发育中期（第33阶段，胚胎第7.5天）和发育后期（第44阶段，胚胎第14天）。此前已有研究表明，神经生长因子在发育中期和后期会增加P物质的水平，并且在所有这些阶段都存在神经营养素受体trkA、trkB和trkC的信使核糖核酸。分离出背根神经节，用限定培养基冲洗以稀释内源性神经营养素，然后将其暴露于其中一种神经营养素中4小时或20小时。使用酶免疫测定法定量P物质水平。在暴露4小时或20小时后，对于在第26阶段获得的背根神经节，没有一种神经营养素对P物质水平有任何影响。在第33和44阶段获得的神经节中，经4小时或20小时孵育后，神经生长因子、脑源性神经营养因子、神经营养素-3和神经营养素-4/5均显著增加了P物质的水平。神经生长因子和神经营养素-3的作用具有特异性：同时暴露于抗神经生长因子或抗神经营养素-3的抗体可完全阻断P物质的增加。神经营养素在早期发育过程中对P物质表达没有任何影响，这一结果出人意料，因为背根神经节中P物质水平很高，且神经营养素受体存在且显然具有功能。同样令人惊讶的是，脑源性神经营养因子、神经营养素-3和神经营养素-4/5在发育中期和后期诱导了P物质水平的增加，因为P物质被认为仅定位于背根神经节中的小TrkA神经元。然而，对第33和44阶段背根神经节进行免疫细胞化学检查发现，大神经元和小神经元中均存在P物质样免疫反应性。本研究结果表明，对神经营养素的不同细胞反应，如对存活和/或肽表达的影响，可能以与它们受体的表达没有严格关系的不同时间模式获得。此外，背根神经节中神经肽合成的调节并非归因于任何一种神经营养因子，并且在早期发育过程中调节表达的因子仍然未知。
