Dev Biol 1986 Jan 01;3891-2:169-77.

The time course of the changes in axon number of both oculomotor nerves in normal and unilaterally enucleated Xenopus laevis.

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In this paper we analyze long-term changes, extending into adulthood, of the number of axons in the oculomotor nerve of Xenopus laevis. We counted the number of axons in that nerve in normal control (nor) animals, and on the operated (ipsilateral, ip) and contralateral (co) sides of enucleated animals at premetamorphosis, metamorphic climax, juvenile (3 and 7 months) and adult (16.5 months) stages. The experimental animals had had one of their ocular primordia removed at hatching. In the nor-nerves there is a loss of 23% of the axons between premetamorphosis and climax, then a further drop of 35% by the 3-month stage, followed by a gain of 39% on reaching adulthood. At premetamorphosis the ip-nerves already contain less than the normal number of axons, which is reduced a further 73% by 3 months; there is no subsequent increase in adulthood. The co-nerves lose no axons from premetamorphosis to climax; they therefore have 30% more axons than normals; this excess is kept until 7 months; from then to sexual maturity the increase is only 11%. (1) unilateral target removal affects also the nerve innervating the contralateral target: the increased loss of axons on the operated side is accompanied by reduced loss on the other; (2) the contralateral side displays for some time an excess of axons compared to normal, but this is finally cancelled out by the addition of many axons in the adult nor animals; (3) adjustment of axon number is not restrained to embryonic stages but continues at least until sexual maturation.(ABSTRACT TRUNCATED AT 250 WORDS)

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