Soeda H, Tatsumi H, Katayama Y
Department of Autonomic Physiology, Tokyo Medical and Dental University, Chiyoda-ku, Japan.
Neuroscience. 1997 Apr;77(4):1187-99. doi: 10.1016/s0306-4522(96)00465-4.
Growing neurites of rat dorsal root ganglion neurons in culture formed growth cones at the tips. Possible release of glutamate from these growth cones was investigated by using a whole-cell patch-clamp recording from an acutely dissociated hippocampal neuron containing glutamate receptors. The hippocampal neuron was placed in contact to various regions of the dorsal root ganglion neurons. Inward currents were recorded from the hippocampal neuron positioned on the growth cones of the dorsal root ganglion neurons (diameter, 12-16 microm) in response to the dorsal root ganglion cell body stimulation. The inward currents were associated with an increase in membrane conductance, and the reversal potential was estimated at -6.5 mV (n=8). The inward currents were blocked by 6-cyano-7-nitroquinoxaline (10 microM), but not blocked by 2-amino-5-phosphonovaleric acid (50 microM) and bicuculline (10 microM). The inward currents were abolished by tetrodotoxin (1 microM), EGTA-buffered Ca2+-free external solution or omega-agatoxin IVA (300 nM), and were inhibited by omega-conotoxin GVIA (3 microM), but were not affected by nicardipine (10 microM). Intracellular calcium ion concentration ([Ca2+]i) in growth cones of the dorsal root ganglion neurons increased in response to dorsal root ganglion cell body stimulation, whereas the elevation of [Ca2+]i was not observed either in the presence of tetrodotoxin (1 microM) or in a Ca2+-free external solution. These results indicate that the inward currents were evoked by glutamate released from the growth cones via a Ca2+-dependent process, and suggest that the growth cones are already endowed with much of the machinery for neurotransmitter release, even before making a structure for synaptic transmission.
培养的大鼠背根神经节神经元生长的神经突在其尖端形成生长锥。通过对含有谷氨酸受体的急性解离海马神经元进行全细胞膜片钳记录，研究了这些生长锥是否可能释放谷氨酸。将海马神经元与背根神经节神经元的不同区域接触。当刺激背根神经节细胞体时，记录到位于背根神经节神经元（直径12 - 16微米）生长锥上的海马神经元出现内向电流。这些内向电流与膜电导增加相关，反转电位估计为 - 6.5 mV（n = 8）。内向电流被6 - 氰基 - 7 - 硝基喹喔啉（10微摩尔）阻断，但不被2 - 氨基 - 5 - 磷酸戊酸（50微摩尔）和荷包牡丹碱（10微摩尔）阻断。内向电流被河豚毒素（1微摩尔）、EGTA缓冲的无钙细胞外溶液或ω - 芋螺毒素IVA（300纳摩尔）消除，并被ω - 芋螺毒素GVIA（3微摩尔）抑制，但不受尼卡地平（10微摩尔）影响。背根神经节神经元生长锥中的细胞内钙离子浓度（[Ca2 + ]i）在刺激背根神经节细胞体时升高，而在存在河豚毒素（1微摩尔）或无钙细胞外溶液时未观察到[Ca2 + ]i升高。这些结果表明，内向电流是由生长锥通过钙依赖过程释放的谷氨酸诱发的，提示生长锥甚至在形成突触传递结构之前就已经具备了许多神经递质释放机制。
