Formation of the peripheral-central transitional zone in the postnatal mouse cochlear nerve.

OBJECTIVES Determine the formation of peripheral and central nervous system (CNS and PNS) transitional zone (PCTZ) along the postnatal mouse cochlear nerve. STUDY DESIGN Prospective, basic science. SETTING Research laboratory. SUBJECTS AND METHODS A novel cryosection model of cochlea-cochlear nerve-brainstem was used in this study. The sections were harvested from a total of 45 mice in 9 groups of postnatal-day-0 to postnatal-day-60 mice (n = 5). Differential interference contrast microscopy and immunofluorescence were used to study the formation of PCTZ along the cochlear nerve of the postnatal mouse. RESULTS The CNS tissue extended peripherally along the cochlear nerve from postnatal-day-0 to postnatal-day-7 and then stably located at the level of the spiral lamina of the basal cochlear turn. The PCTZ reached a mature pattern along the cochlear nerve after postnatal-day-7. A long segment of the CNS tissue extended along the cochlear nerve in the postnatal mouse. CONCLUSION In the early postnatal days, the PCTZ extended peripherally toward the cochlea and obtains a mature pattern along the neonatal mouse cochlear nerve.