Wilson M T, Keith C H
Department of Cellular Biology, University of Georgia, Athens 30602, USA.
J Neurosci Res. 1998 Jun 1;52(5):599-611. doi: 10.1002/(SICI)1097-4547(19980601)52:5<599::AID-JNR12>3.0.CO;2-Y.
Glutamate can both facilitate and inhibit dendrite outgrowth in vitro. The major effects of low levels of glutamate occur only on the dendrites (not the axon) of pyramidal neurons and may be important for modulating dendrite outgrowth during neuronal development in vivo. Cytoskeletal changes resulting from glutamate exposure must underlie these changes in dendrite outgrowth. In the present study, hippocampal neuron cultures were used to measure the outgrowth of both axons and immature dendrites in the presence or absence of 50 microM glutamate. Subsequently, neurons were extracted and fixed for immunofluorescent labeling of microtubules and rhodamine phalloidin labeling of microfilaments. Additionally, neurons were prepared for electron microscopy to examine dendritic microtubules at the ultrastructural level. Glutamate led to increased dendrite outgrowth in the short term (4 hr) and dendrite retraction in the long term (8 hr). After short-term glutamate exposures, no obvious morphological changes occur in either the microtubules or microfilaments. However, longer glutamate exposure causes a decrease in the number of microtubules in the distal region of retracting dendrites, and causes an increase in microtubule number in the dendritic shaft of both retracting and growing dendrites. Thus, the microtubule cytoskeleton may be involved in producing the changes in dendrite outgrowth caused by glutamate exposure.
谷氨酸在体外既能促进也能抑制树突生长。低水平谷氨酸的主要作用仅发生在锥体神经元的树突（而非轴突）上，可能对体内神经元发育过程中树突生长的调节很重要。谷氨酸暴露引起的细胞骨架变化必定是这些树突生长变化的基础。在本研究中，使用海马神经元培养物来测量在存在或不存在50微摩尔谷氨酸的情况下轴突和未成熟树突的生长。随后，提取神经元并固定，用于微管的免疫荧光标记和微丝的罗丹明鬼笔环肽标记。此外，制备神经元用于电子显微镜检查，以在超微结构水平检查树突微管。谷氨酸在短期内（4小时）导致树突生长增加，而在长期内（8小时）导致树突回缩。短期暴露于谷氨酸后，微管或微丝均未出现明显的形态变化。然而，更长时间的谷氨酸暴露会导致回缩树突远端区域的微管数量减少，并导致回缩和生长树突的树突轴中的微管数量增加。因此，微管细胞骨架可能参与产生由谷氨酸暴露引起的松突生长变化。
