title: An electron microscopic analysis of the optic nerve of the eastern chipmunk (Tamias sibiricus asiaticus): total fiber count and retinotopic organisation.
abstract: On the basis of light and electron microscopic observations of the cross-section, the total count of optic nerve fibers in the eastern chipmunk (Tamias sibiricus asiaticus) was estimated to be 5.65 x 10(5). Almost all the fibers were myelinated and only 0.9% were unmyelinated. Axon diameters of myelinated fibers showed a skewed unimodal distribution ranging from 0.2 to 3.6 microns (mean, 0.83) with the peak at 0.6-0.7 microns. Myelin sheath thickness positively correlated with the axon diameter. In the cross-section fiber density was highest in the naso-dorsal to the central part and lowest in the temporo-ventral part. Large axons are concentrated in the temporo-ventral part of the optic nerve, corresponding to the localisation of large ganglion cells in temporal crescent of the retina. A gross retinotopic organisation was verified among the optic nerve fibers in the cross-section after localised lesions by laser beam in the nasal and temporal periphery. However, when the retinal lesion was made in or around the central high density area, a non-retinotopic arrangement of the optic nerve fibers was suggested.
authors.affiliation: Department of Neurophysiology, Osaka University Medical School, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Wakakuwa
authors.forename: M
authors.initials: M
authors.lastname: Watanabe
authors.forename: T
authors.initials: T
authors.lastname: Sugimoto
authors.forename: A
authors.initials: A
authors.lastname: Washida
authors.forename: Y
authors.initials: Y
authors.lastname: Fukuda
mesh_terms: D000818:Animals; D001369:Axons / Q000648:ultrastructure; D002452:Cell Count; D008854:Microscopy, Electron; D009186:Myelin Sheath / Q000648:ultrastructure; D009410:Nerve Degeneration; D009413:Nerve Fibers, Myelinated / Q000648:ultrastructure; D009900:Optic Nerve / Q000648:ultrastructure*; D012589:Sciuridae / Q000033:anatomy & histology*