Funch P G, Wood M R, Faber D S
J Neurosci. 1984 Sep;4(9):2397-409. doi: 10.1523/JNEUROSCI.04-09-02397.1984.
Injections of Lucifer Yellow (LY) and horseradish peroxidase (HRP) were made within the myelin sheath of the goldfish Mauthner axon to determine the domains of individual oligodendrocytes. Long segments of the myelin sheath were stained with both markers. The lengths and locations of these sheath segments were analyzed in whole mount preparations (LY) or in reconstructions of serial vibratome sections (HRP). The termination sites of individual myelin sheaths, relative to gross anatomical landmarks of the brain, were consistent within and between all fish studied. In particular, the average locations of the termination sites were separated by 2.2 to 2.6 mm and corresponded to the brain regions where active site foci have been previously localized electrophysiologically. Individual sheath segments generally spanned the entire distance between adjacent active sites. The node-internode-node structure of the Mauthner axon that is suggested by these findings was further tested by ejecting tetrodotoxin (TTX) at various discrete rostral-caudal locations just outside the fiber. Large all-or-nothing components of the antidromic action potential were rapidly blocked (within seconds) only when the TTX ejections were made within a few hundred micrometers of the active site foci. The amplitudes of these blocked components are also consistent with predictions based upon previous electrophysiological analyses which demonstrated an active site spacing of 2.2 to 2.6 mm, a space constant of 5.0 mm, and a safety factor of 6 for impulse propagation. It is concluded from these morphological, pharmacological, and electrophysiological observations that the Mauthner axon possesses nodes separated by 2.2 to 2.6 mm and that a single oligodendrocyte spans an internodal region. Although nodal ultrastructure remains to be described, these results rule out the possibility that each of the short (approximately 50 micron), closely spaced (average separation = 155 micron) axon collaterals is a site of action current production.
将路西法黄（LY）和辣根过氧化物酶（HRP）注射到金鱼莫特纳尔轴突的髓鞘内，以确定单个少突胶质细胞的区域。长段髓鞘被两种标记物染色。在整装标本（LY）或连续振动切片重建（HRP）中分析这些髓鞘段的长度和位置。相对于大脑的大体解剖标志，单个髓鞘的终止位点在所有研究的鱼类内部和之间都是一致的。特别是，终止位点的平均位置相隔2.2至2.6毫米，并且对应于先前通过电生理学定位了活性位点焦点的脑区。单个髓鞘段通常跨越相邻活性位点之间的整个距离。这些发现所提示的莫特纳尔轴突的结-节间-结结构，通过在纤维外不同的离散头-尾位置喷射河豚毒素（TTX）进行了进一步测试。仅当在活性位点焦点几百微米内进行TTX喷射时，逆行动作电位的大的全或无成分才会迅速被阻断（在数秒内）。这些被阻断成分的幅度也与基于先前电生理学分析的预测一致，先前的电生理学分析表明活性位点间距为2.2至2.6毫米，空间常数为5.0毫米，冲动传播的安全系数为6。从这些形态学、药理学和电生理学观察结果得出结论，莫特纳尔轴突具有相隔2.2至2.6毫米的结，并且单个少突胶质细胞跨越一个结间区域。尽管结的超微结构仍有待描述，但这些结果排除了每个短的（约50微米）、紧密间隔（平均间距 = 155微米）的轴突侧支是动作电流产生部位的可能性。
