Schwann cell proliferation in the sciatic nerve of hypothyroid chick embryos studied by autoradiography and image analysis

Abstract

SummaryThe proliferation of Schwann cells in the sciatic nerve of chick was studied from day 11 to day 27 of development in control and thyroid-deficient embryos. Hypothyroidism was induced by tetramethylthiourea injection on days 8 and 19 of incubation. The parameters of the cell cycle were determined using autoradiographs (tritiated thymidine) and by image analysis of Feulgen-stained nuclear smears. The duration of the cell cycle was lengthened and the growth fraction was reduced in hypothyroid animals, at 11 and 15 days of incubation. At later stages (days 21 and 27), these parameters were not significantly different from the controls as if the sensitivity of Schwann cells to thyroid hormones was scheduled to occur during a limited period of development. The total number of axons was the same in control and hypothyroid animals suggesting that the slowing down of Schwann cell proliferation is not a consequence of neuronal cell death. The consequence of that slowing down is a delay in the isolation of promyelin axons and a reduction in the proportion of myelinated axons at all the stages studied.

Schwann Cells Proliferate at Rat Neuromuscular Junctions during Development and Regeneration

“…However, 12 of the 40 endplates in soleus and 16 of the 43 in edl had two labeled nuclei in close apposition, suggesting that these were daughter cells that had completed mitosis. The small number of nuclear pairs is not surprising considering that only 9 hr had elapsed since the first BrdU injection and because estimates of the length of G2 ϩ M (the time between the end of synthesis and the end of mitosis) for SCs in the peripheral nerves of mice is ϳ4 -8 hr (Asbury, 1967;Usson and Saxod, 1988). Thus, only those cells that were in the late phase of DNA synthesis at the time of the BrdU injection would have completed mitosis.…”

Development of the human fetal cochlear nerve: a morphometric study

“…administration of ototoxic drugs to expectant mothers). Similarly, endocrinopathies involving the fetus or the mother are known to have deleterious effect on the developing nervous system (Usson and Saxod, 1988;Paternostro and Meisami, 1996). However, there is no data available on the morphology of the fetal CN to determine the changes that occur during the prenatal period.…”

Si⋅⋅⋅H Interligand Interactions in Cobalt(V) and Iridium(V) Bis(silyl)bis(hydride) Complexes

“…First, T3 may have a role in Schwann cell proliferation. Indeed, T3 increases the incorporation of [ 3 H]thymidine in cultured rat Schwann cells, and the proliferation of Schwann cells is reduced in the sciatic nerve of hypothyroid chick embryos (Usson and Saxod, 1988; Barakat‐Walter, 1999). Second, T3 may stimulate the production of neurotrophic factors by Schwann cells, resulting in accelerated axonal growth.…”