Zheng J Q, Zheng Z, Poo M
Department of Biological Sciences, Columbia University, New York 10027.
J Cell Biol. 1994 Dec;127(6 Pt 1):1693-701. doi: 10.1083/jcb.127.6.1693.
Cyclic AMP-dependent activity at the growth cone or the soma of cultured Xenopus spinal neurons was elevated by local extracellular perfusion of the neuron with culture medium containing 8-bromoadenosine 3',5'-cyclic monophosphate (8-br-cAMP) or forskolin. During local perfusion of one of the growth cones of multipolar neurons with these drugs, the perfused growth cone showed further extension, while the distant, unperfused growth cones were inhibited in their growth. Local perfusion of the growth cone with culture medium or local perfusion with 8-br-cAMP at a cell-free region 100 microns away from the growth cone did not produce any effect on the extension of the growth cone. Reduced extension of all growth cones was observed when the perfusion with 8-br-cAMP was restricted to the soma. The distant inhibitory effect does not depend on the growth of the perfused growth cone since local coperfusion of the growth cone with 8-br-cAMP and colchicine inhibited growth on both perfused and unperfused growth cones, while local perfusion with colchicine alone inhibited only the perfused growth cone. The distant inhibitory effect was abolished when the perfusion of 8-br-cAMP was carried out together with kinase inhibitor H-8, suggesting the involvement of cAMP-dependent protein kinase and/or its downstream factors in the long-range inhibitory signaling. Uniform exposure of the entire neuron to bath-applied 8-br-cAMP, however, led to enhanced growth activity at all growth cones. Thus, local elevation of cAMP-dependent activity produces long-range and opposite effects on distant parts of the neuron, and a cytosolic gradient of second messengers may produce effects distinctly different from those following uniform global elevation of the messenger, leading to differential growth regulation at different regions of the same neuron.
通过用含有8-溴腺苷3',5'-环磷酸（8-br-cAMP）或福斯可林的培养基对培养的非洲爪蟾脊髓神经元的生长锥或胞体进行局部细胞外灌注，可提高环磷酸腺苷（cAMP）依赖性活性。在用这些药物对多极神经元的一个生长锥进行局部灌注期间，被灌注的生长锥进一步伸展，而远处未被灌注的生长锥的生长受到抑制。用培养基对生长锥进行局部灌注或在距生长锥100微米的无细胞区域用8-br-cAMP进行局部灌注，对生长锥的伸展没有任何影响。当将8-br-cAMP的灌注限制在胞体时，观察到所有生长锥的伸展均减少。远处的抑制作用不依赖于被灌注生长锥的生长，因为将8-br-cAMP与秋水仙碱共同局部灌注到生长锥上会抑制被灌注和未被灌注的生长锥的生长，而单独用秋水仙碱进行局部灌注仅抑制被灌注的生长锥。当8-br-cAMP与激酶抑制剂H-8一起进行灌注时，远处的抑制作用消失，这表明cAMP依赖性蛋白激酶和/或其下游因子参与了远程抑制信号传导。然而，将整个神经元统一暴露于浴加的8-br-cAMP下，会导致所有生长锥的生长活性增强。因此，cAMP依赖性活性的局部升高会对神经元的远处部分产生远程且相反的影响，并且第二信使的胞质梯度可能产生与信使均匀整体升高后不同的影响，从而导致同一神经元不同区域的生长调节存在差异。
