Prenatal development of central optic pathways in albino rats

Lund, Raymond D.; Bunt, Ann H.

doi:10.1002/cne.901650209

Cited by 205 publications

(57 citation statements)

References 30 publications

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“…1). The axons are termed premyelinated because, by adulthood, virtually all rat optic nerve axons will acquire myelin sheaths (13 (27). Relatively few glial cells are present at this age, and the processes from these cells are generally oriented perpendicular to the axons.…”

Section: Resultsmentioning

confidence: 99%

Low density of sodium channels supports action potential conduction in axons of neonatal rat optic nerve.

Waxman

Black²,

Kocsis³

et al. 1989

Proc. Natl. Acad. Sci. U.S.A.

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The density of sodium channels in premyelinated axons was estimated from measurements of the binding of [3H]saxitoxin to neonatal rat optic nerve. The maximum saturable binding capacity of the nerve was 16.2 ± 1.2 fmol/mg of wet weight, with an equilibrium dissociation constant of 0.88 ± 0.18 nM (mean ± SEM). These values correspond to a high-affinity saxitoxin-binding site density of -2/,um2 within premyelinated axon membrane. Action potential propagation in neonatal rat optic nerve is completely blocked by 5 nM saxitoxin, indicating that action potential electrogenesis is mediated by channels that correspond to high-affinity saxitoxin-binding sites. These results demonstrate that action potential conduction is supported by a low density of sodium channels in this system. Since the internodal axon membrane of myelinated fibers may contain a low density of sodium channels, it is possible that restoration of conduction in some demyelinated fibers may not require additional sodium channel incorporation into the demyelinated axon membrane.It is now well established that voltage-gated sodium channels mediate the inward current that underlies the action potential in most axons (1-3). Mammalian myelinated axons display a nonuniform distribution of sodium channels, which are clustered in high density in the axon membrane at the node of Ranvier but are present in very much lower density in the internodal axon membrane beneath the myelin sheath (4, 5). Inexcitability of the internodal axon contributes to the conduction failure that is seen in demyelinated fibers (4, 6). However, there is evidence that, after demyelination, continuous conduction does develop along some axons (7,8). Indeed, morphological studies suggest that the (formerly) internodal axon membrane may reorganize after demyelination so as to develop electrical excitability (9-11).As part of an effort to understand the mechanisms that underlie action potential conduction both in myelinated fibers and in axons that lack myelin, we have examined the development of conduction as axons develop from premyelinated axons (which lack myelin sheaths) into mature myelinated fibers. The rat optic nerve provides an especially tractable system in which to study axon membrane development of premyelinated fibers, since in the neonatal optic nerve none of the axons have yet acquired myelin sheaths, whereas in the adult virtually all the fibers are myelinated (12,13). Previous studies have examined the morphology of the developing optic nerve (14-16) and have demonstrated action potential electrogenesis, mediated by sodium channels, in axons of the neonatal optic nerve prior to ensheathment by myelin-forming oligodendrocytes (13). However, although the sodium channel density in adult optic nerve has been estimated in saxitoxin (STX)-binding studies (17), the sodium channel density in developing optic nerve prior to myelination has not been studied. Moreover, the possibility of STX-insensitive sodium channels (which have been observed in some developing systems; ref. ...

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Section: Resultsmentioning

confidence: 99%

Low density of sodium channels supports action potential conduction in axons of neonatal rat optic nerve.

Waxman

Black²,

Kocsis³

et al. 1989

Proc. Natl. Acad. Sci. U.S.A.

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“…The first axons to enter the optic stalk do so on about E14. By E15, the first axons are identified at the optic chiasm [Lund and Bunt, 1975]. Most of these are directed into the contralateral optic tract, but a small group, which ori ginates predominantly from the nasal retina, enters the opposite optic nerve and retina [Bunt and Lund, 1981].…”

Section: Normal Developmentmentioning

confidence: 99%

Conditions for Optic Axon Outgrowth

et al. 1988

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“…In the rat, for example, ganglion cell axons may reach the LGNd as soon as 24 h after the ganglion cells leave the mitotic cycle [Karlsson. 1967;Raedler and Sievers, 1975;Lund and Bunt, 1976;Rakic, 1977b]. Fur thermore, this differentiation first occurs at or near the posterior pole of the eye [Braekevelt and Hollenberg, 1970;Morest.…”

Section: Development O F Siamese Area Centralismentioning

confidence: 99%

“…Fur thermore, this differentiation first occurs at or near the posterior pole of the eye [Braekevelt and Hollenberg, 1970;Morest. 1970;Kuwabara and Weidman, 1974;Kahn, 1974;Grun, 1975;Fujisawa et al, 1976;Lund and Bunt, 1976;Sharma and Ungar, 1980], at a site which has been sug gested to be the eventual location of the area centralis, at least in cats [Rapaport and Stone, 1981]. Thus, ganglion cell ax ons arising from central retina should be the first to arrive at the LGNd, with axons from increasingly peripheral locations ar riving at successively later times.…”

Section: Development O F Siamese Area Centralismentioning

confidence: 99%

“…Conse quently, early arriving axons may be bet ter able to spread out and establish pro spective synaptic territories than the later arriving axons, which are then com pressed into increasingly smaller areas within the LGNd. The onset of synapto genesis in the LGNd is usually delayed un til well after the ganglion cell axons have arrived [Cragg, 1975;Raedler and Sievers, 1975;Lund and Bunt, 1976;Anker, 1977;Hendrickson and Rakic. 1977;Rakic, 1977b;Shatz and DiBerardino, 1980;Ma son, 1981] and occurs in association with a period of substantial ganglion cell death [Hughes and LaVelle, 1975;Rager and Rager, 1976;McLoon and Hughes, 1978;Lam el al., 1982;Ng and Slone, 1981;Polls et al, 1982;Sengelaub and Finlay, 1981;Jeffery and Perry.…”

Section: Development O F Siamese Area Centralismentioning

confidence: 99%

See 1 more Smart Citation

Characteristics of Nasal and Temporal Retina in Siamese and Normally Pigmented Cats; pp. 103–113

Murakami¹,

Sesma²,

Rowe³

1982

Brain Behav Evol

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Properties of ganglion cells in nasal and temporal retina of Siamese and normally-pigmented cats are described. In agreement with earlier reports on normal cats, the somas of both X and Y cells are larger in temporal than in nasal retina, although these differences are not entirely independent of ganglion cell density. Furthermore, the axons of X cells in temporal retina were distinctly faster and larger than those of X cells in nasal retina. Since, in normal cats, almost all nasal X cells project contralaterally and almost all temporal X cells project ipsilaterally, it is difficult to assess independently the effects of retinal location and laterality of projection on either soma size or axon size of nasal and temporal X cells. However, taking advantage of the abnormal pattern of decussation seen in Siamese cats, in which a substantial number of temporal X cells project contralaterally, it is possible to demonstrate that the difference in soma size is independent of laterality of projection and appears to be a function of retinal location, whereas the difference in axon size is a function of laterality of projection and is independent of retinal location. Thus, soma size and axon diameter are at least partially independent. We were unable to obtain clear support for the suggestion that Siamese cats suffer a selective loss of X-type retinal ganglion cells, and an alternative mechanism for the reduced prominence of the area centralis in Siamese cats is proposed. The distinction between developmental mechanisms influencing the prominence of the area centralis and those influencing laterality of projection, as well as the relationship between retinal specializations associated with acuity and specializations associated with binocularity are also considered. The trajectory of axons arising from temporal retina and travelling above or below the area centralis towards the optic disc is described. In normal cats, the general features of this trajectory are the same for ipsilaterally and contralaterally projecting axons, and for axons of all ganglion cell groups. This also appears to be the case in Siamese cats. However, axons from temporal retina show a greater tendency to pass directly over the area centralis in Siamese than in normal cats, and the boundary between the region of temporal retina from which axons pass superior to the area centralis and the region from which they pass inferior to the area centralis may be closer to the vertical meridian in Siamese than in normal cats. These differences in trajectory could lead to a rearrangement of ipsilaterally projecting axons within the optic nerve. In both Siamese and normal cats, a small number of ganglion cells, scattered throughout nasal retina, project ipsilaterally. On the basis of soma size and dendritic morphology, all cells observed in our material can be identified as either alpha or gamma cells. In Siamese cats, such cells are consistently more numerous than in normal cats. In Siamese cats, however, this group of ipsilaterally projecting cells contains a hig...

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Prenatal development of central optic pathways in albino rats

Cited by 205 publications

References 30 publications

Low density of sodium channels supports action potential conduction in axons of neonatal rat optic nerve.

Low density of sodium channels supports action potential conduction in axons of neonatal rat optic nerve.

Conditions for Optic Axon Outgrowth

Characteristics of Nasal and Temporal Retina in Siamese and Normally Pigmented Cats; pp. 103–113

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