Biomaterial Database

Numbers of axons in the optic nerve and of retinal ganglion cells during development in the marsupial Setonix brachyurus. 1986

C R Braekevelt, and L D Beazley, and S A Dunlop, and J E Darby

Numbers of axons during postnatal development in the optic nerve of the marsupial Setonix brachyurus were estimated from electron micrographs. Between 14 and 45 days axon totals rose 10-fold from 95,000 to 961,000. Thereafter, counts decreased gradually by almost 5-fold stabilising at the adult level of 180,000-224,000 between 130-150 days. Myelinated axons were first seen at 85 days and constituted 76% of all axons by 150 days, compared to almost 100% in the adult. At comparable stages of development, estimates of cell number in the ganglion cell layer were made from sectioned and whole-mounted retinae. Ganglion cells, labelled with horseradish peroxidase (HRP) injected into the optic tract and visual brain centres, reached a maximum of 304,000 by 50 days. This value was only one-third higher than the adult ganglion cell estimate of 202,000, to which counts fell by 70 days. Such a fall of ca. 100,000 ganglion cells was matched by a reduction from 443,000 to 361,000 in the total number of cells in the retinal ganglion cell layer, that is, cells labelled by HRP plus those which remained unlabelled. Thus, during development axon counts exceeded adult values 4-fold whereas ganglion cell totals were only one-third higher than the mature value. The shortfall of ganglion cells to optic axons indicates that during development the transiently high axon number cannot be explained by a correspondingly raised count of ganglion cells. It is therefore necessary to hypothesise a substantial fibre population which temporarily projects into the nerve from either the brain or the opposite eye. Alternatively, optic axons may branch extensively during development with subsequent loss of collaterals.

UI	MeSH Term	Description	Entries
D007614	Macropodidae	A family of herbivorous leaping MAMMALS of Australia, New Guinea, and adjacent islands. Members include kangaroos, wallabies, quokkas, and wallaroos.	Kangaroos,Macropus,Petrogale,Quokkas,Setonix,Wallabies,Wallabies, Rock,Wallaroo,Macropus robustus,Kangaroo,Petrogales,Quokka,Rock Wallabies,Rock Wallaby,Wallaby,Wallaby, Rock,Wallaroos
D008394	Marsupialia	An infraclass of MAMMALS, also called Metatheria, where the young are born at an early stage of development and continue to develop in a pouch (marsupium). In contrast to Eutheria (placentals), marsupials have an incomplete PLACENTA.	Metatheria,Marsupials,Marsupial
D009413	Nerve Fibers, Myelinated	A class of nerve fibers as defined by their structure, specifically the nerve sheath arrangement. The AXONS of the myelinated nerve fibers are completely encased in a MYELIN SHEATH. They are fibers of relatively large and varied diameters. Their NEURAL CONDUCTION rates are faster than those of the unmyelinated nerve fibers (NERVE FIBERS, UNMYELINATED). Myelinated nerve fibers are present in somatic and autonomic nerves.	A Fibers,B Fibers,Fiber, Myelinated Nerve,Fibers, Myelinated Nerve,Myelinated Nerve Fiber,Myelinated Nerve Fibers,Nerve Fiber, Myelinated
D009900	Optic Nerve	The 2nd cranial nerve which conveys visual information from the RETINA to the brain. The nerve carries the axons of the RETINAL GANGLION CELLS which sort at the OPTIC CHIASM and continue via the OPTIC TRACTS to the brain. The largest projection is to the lateral geniculate nuclei; other targets include the SUPERIOR COLLICULI and the SUPRACHIASMATIC NUCLEI. Though known as the second cranial nerve, it is considered part of the CENTRAL NERVOUS SYSTEM.	Cranial Nerve II,Second Cranial Nerve,Nervus Opticus,Cranial Nerve, Second,Cranial Nerves, Second,Nerve, Optic,Nerve, Second Cranial,Nerves, Optic,Nerves, Second Cranial,Optic Nerves,Second Cranial Nerves
D012160	Retina	The ten-layered nervous tissue membrane of the eye. It is continuous with the OPTIC NERVE and receives images of external objects and transmits visual impulses to the brain. Its outer surface is in contact with the CHOROID and the inner surface with the VITREOUS BODY. The outer-most layer is pigmented, whereas the inner nine layers are transparent.	Ora Serrata
D002452	Cell Count	The number of CELLS of a specific kind, usually measured per unit volume or area of sample.	Cell Density,Cell Number,Cell Counts,Cell Densities,Cell Numbers,Count, Cell,Counts, Cell,Densities, Cell,Density, Cell,Number, Cell,Numbers, Cell
D000367	Age Factors	Age as a constituent element or influence contributing to the production of a result. It may be applicable to the cause or the effect of a circumstance. It is used with human or animal concepts but should be differentiated from AGING, a physiological process, and TIME FACTORS which refers only to the passage of time.	Age Reporting,Age Factor,Factor, Age,Factors, Age
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D001369	Axons	Nerve fibers that are capable of rapidly conducting impulses away from the neuron cell body.	Axon
D012165	Retinal Ganglion Cells	Neurons of the innermost layer of the retina, the internal plexiform layer. They are of variable sizes and shapes, and their axons project via the OPTIC NERVE to the brain. A small subset of these cells act as photoreceptors with projections to the SUPRACHIASMATIC NUCLEUS, the center for regulating CIRCADIAN RHYTHM.	Cell, Retinal Ganglion,Cells, Retinal Ganglion,Ganglion Cell, Retinal,Ganglion Cells, Retinal,Retinal Ganglion Cell