Postnatal differentiation of rat optic nerve fibers: Electron microscopic observations on the development of nodes of Ranvier and axoglial relations

Abstract

The postnatal differentiation of rat optic nerve fibres was examined by transmission electron microscopy. The results show that many early developing axons contain clusters of vesiculotubular profiles prior to myelination. At places vesicular elements appear to fuse with the axolemma, and, in addition, some axons exhibit deep axolemmal invaginations and axoplasmic lamellated bodies. It is suggested that these features might reflect axolemmal remodelling, possibly involving axoglial signalling and/or functional differentiation of the axolemma. The size distribution of unmyelinated optic nerve axons changes little during development. Ensheathment of larger axons commences 6 days postnatally. The subsequent formation of compact myelin sheaths is accompanied by an increase in axonal diameter. The early sheaths are a few microns long and separated by long bare axon segments. In optic nerves from 10-12-day-old rat pups, a few sheaths consisting of about five layers border primitive asymmetric nodes with a patchy axolemmal undercoating. Extensions from one of the terminating sheaths are often associated with undercoated patches of axolemma. Relatively differentiated nodes of Ranvier first appear 14-16 days after birth. The continued nodal maturation involves establishment of a regular nodal geometry, increasing distinctness of the axolemmal undercoating, and formation of perinodal astrocytic processes embedded in an extracellular node gap substance. The results are compared with available data on the conduction properties of rat optic nerve fibres during development.

Hypoxia—Ischemia Preferentially Triggers Glutamate Depletion from Oligodendroglia and Axons in Perinatal Cerebral White Matter

“…The oligodendroglial population of P7 periventricular white matter is less mature than that of the P10 optic nerve, which initiates myelination at BP6 (Hildebrand and Waxman, 1984). Indeed, the cells studied using immuno-EM by Wilke et al (2004) were identified as oligodendrocytes partly on the basis of having compact myelin profiles within their processes, a phenomenon not seen in the P7 cortical oligodendrocytes studied here.…”

Reticular astrocytes in the fish optic nerve: macroglia with epithelial characteristics form an axially repeated lacework pattern, to which nodes of Ranvier are apposed

“…Nodes and perinodal processes appear together during development, which has raised the question whether their interaction are a factor determining the spacing of nodes (see Hildebrand and Waxman, 1984; reviewed by Black and Waxman, 1988). In this case, however, we found that partition spacing is only a fraction (18%) of the estimated average internode length in mature fish optic nerve fibers.…”

Binocular Input Coincidence Mediates Critical Period Plasticity in the Mouse Primary Visual Cortex

“…The neural signals of spikes were amplified and filtered with a Cerebus 32-channel system (BlackRock Microsystems). Single units were sorted based on Klustakwik clustering analysis of waveforms (Harris et al, 2001) using a custom-written software for supervision.…”