Localization of active sites along the myelinated goldfish Mauthner axon: morphological and pharmacological evidence for saltatory conduction

摘要: njections of Lucifer Yellow (LY) and horseradish peroxidase (HRP) were made within the myelin sheath goldfish Mauthner axon to determine domains individual oligodendrocytes. Long segments stained with both markers. The lengths locations these analyzed in whole mount preparations or reconstructions serial vibratome sections (HRP). termination sites sheaths, relative gross anatomical landmarks brain, consistent between all fish studied. In particular, average separated by 2.2 2.6 mm corresponded brain regions where active site foci have been previously localized electrophysiologically. Individual generally spanned entire distance adjacent sites. node-internode- node structure that is suggested findings was further tested ejecting tetrodotoxin (TTX) at various discrete rostral-caudal just outside fiber. Large all-or-nothing components antidromic action potential rapidly blocked (within seconds) only when TTX ejections a few hundred micrometers foci. amplitudes are also predictions based upon previous electrophysiological analyses which demonstrated an spacing mm, space constant 5.0 safety factor 6 for impulse propagation. It concluded from morphological, pharmacological, observations possesses nodes single oligodendrocyte spans internodal region. Although nodal ultrastructure remains be described, results rule out possibility each short (approximately 50 micron), closely spaced (average separation = 155 micron) collaterals current production.