Myelination of the Postnatal Mouse Cochlear Nerve at the Peripheral-Central Nervous System Transitional Zone

Abstract

In the nerve roots of vertebrates, the peripheral nervous system (PNS) and central nervous system (CNS) interface at the PNS-CNS transitional zone (PCTZ), which consists of cell boundaries with various myelin components. We have recently shown that the mouse cochlear nerve presents an exceptionally long segment of the CNS tissue extending into the PNS using light microscopy. However, it is unclear how oligodendrocytes and Schwann cells contribute to the formation of myelin components of the PCTZ. It is undetermined how myelination is initiated along the cochlear nerve, and when it adopts a mature pattern. In this study, immunofluorescence using antibodies specific to oligodendrocyte marker myelin oligodendrocyte glycoprotein (MOG) and Schwann cell marker myelin protein zero (MPZ) were used to detail the expression of myelin components along the postnatal mouse cochlear nerve. We found that the expression of MPZ was initially observed in the soma of bipolar spiral ganglion neurons at postnatal day 0 (P0) and progressed to the central and peripheral processes after P8–P10. Myelination of the CNS tissue was initiated in close proximity to the PCTZ from P7 to P8 and then extended centrally. Myelination of the PCTZ reached a mature style at P14, when the interface of the expression of MOG and MPZ was clearly identified along the cochlear nerve. This knowledge of PCTZ formation of the cochlear nerve will be essential to future myelination research, and it will also gain clinical interest because of its relevance to the degeneration and regeneration of the auditory pathway in hearing impairment.

A role of oligodendrocytes in information processing independent of conduction velocity

“…This, together with the findings that also response thresholds were not different from controls (Figures S2A and S2B), confirms that cochlear function and peripheral conduction is normal in Mbp shi/shi mice. This was expected because the outer region of the auditory nerve is myelinated by Schwann cells that do not require MBP for myelination (Figure 1A iii) 40 . However, the amplitudes of waves II and III were reduced, and those of waves IV and V were increased (Figures 1B and 1F).…”

“…In wild type mice, all auditory projections, including the auditory nerve, are well myelinated 39,40 . Before studying the effect of dysmyelination on information processing, we determined latencies and amplitudes of sound-evoked responses at different auditory stations using auditory brainstem responses (ABR), recorded in vivo through electrodes located on the scalp (Figure 1A i).…”

Extension of the clinical and molecular phenotype of DIAPH1‐associated autosomal dominant hearing loss (DFNA1)

“…The DIAPH1 expression, together with the expression of myelin PLP, the major myelin protein of the central nervous system (CNS), outlines the transition zone at the border between Schwann cells (myelinating glia of the peripheral nervous system (PNS)) and oligodendrocytes that myelinate the auditory central auditory nerve (45,46). The DIAPH1 expression, together with the expression of myelin PLP, the major myelin protein of the central nervous system (CNS), outlines the transition zone at the border between Schwann cells (myelinating glia of the peripheral nervous system (PNS)) and oligodendrocytes that myelinate the auditory central auditory nerve (45,46).…”

Ca2+-Permeable AMPARs Mediate Glutamatergic Transmission and Excitotoxic Damage at the Hair Cell Ribbon Synapse

“…Three AMPA receptor subunits were labeled simultaneously with primary antibodies against GluA2 (mouse IgG2a, catalog #MAB397, Millipore; Vissavajjhala et al, 1996), GluA3 (goat, sc-7612, Santa Cruz Biotechnology), or GluA4 (rabbit, catalog #AB1508, Millipore; Wenthold et al, 1992). Specificity of the GluA2 and GluA4 antibodies (Medvedev et al, 2008;Sagata et al, 2010) were verified in GluA2 and GluA4 knock-out mice (Jia et al, 1996;Sagata et al, 2010), respectively.…”

“…The response to waterjet stimulation was quantified by measuring the mean peak fluorescence and duration of the response across two waterjet stimulation trials. AMPARs desensitize at a faster time course relative to NMDA and kainate receptors (Geiger et al, 1995), a process that can be studied using the drug CTZ, which blocks AMPAR desensitization (Trussell et al, 1993). Bath application of 200 M CTZ had no detectable effect on GCaMP fluorescence under resting conditions, as shown in maximum projections of a z-stack of a terminal before and after CTZ application (Fig.…”