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Low thyroid hormone levels impair the perinatal development of the rat retina
Enrique Sevilla-Romero1, Alberto Muñoz, M Dolores Pinazo-Durán
1Department of Cellular Biology and Pathology, Research Centre University Hospital La Fe, Valencia, Spain.
Abstract:
Eye development is regulated by multiple agents including hormones and growth factors. Thyroid hormone (triiodothyronine, or T(3), and the prohormone thyroxine, or T(4)) plays a crucial role in the development of the central nervous system. Here we have examined the effects of low T(3)/T(4) levels (hypothyroid status) on the developing rat retina during the perinatal stage. Eyes from control (CG) and T(3)/T(4)-deficient (HG) fetuses (E19 and E21) and newborn (P0, P3, P5 and P7) rats were obtained by administering a chemical antithyroid solution (0.02% methyl-mercaptoimidazole +1% ClOK(4)) in the tap water to the dams and their offspring, from E9 and throughout gestation until they were killed. Perinatal eyes were processed for light and electron transmission microscopy and subjected to morphological and morphometric analyses. Low T(3)/T(4) levels led to decreased retinal growth during the perinatal stage. In addition, the retinas from the HG presented fewer neuroblasts than those of their euthyroid counterparts (at E21: 705 +/- 83 cells per constant area of 4 x 10(4) microm(2) vs. 440 +/- 60 cells per constant area of 4 x 10(4) microm(2); p = 0.010). During development the index of mitosis in the retina peaked at E21, falling at the end of the 1st postnatal week. Significantly lower values were observed in the HG (at P5: 0.803 +/- 0.374 mitoses/cells % vs. 0.349 +/- 0.180 mitoses/cells %; p = 0.004). Furthermore, we have found that low T(3)/T(4) levels delayed and/or altered a series of developmental processes occurring in the retina during the perinatal stage such as layering and differentiation of several cell types. Our results demonstrate that thyroid hormone regulates rat neuroretinogenesis.
Insights
Thyroid hormone deficiency (low triiodothyronine/T(3) and thyroxine/T(4)) significantly impairs developing rat retina growth and neurogenesis. This hormonal imbalance affects cell development and layering, highlighting thyroid hormone
Area of Science:
- Developmental biology
- Neuroscience
- Endocrinology
Background:
- Thyroid hormones (triiodothyronine/T(3) and thyroxine/T(4)) are essential for central nervous system development.
- Disruptions in thyroid hormone levels can impact various physiological processes, including neural development.
Purpose of the Study:
- To investigate the effects of perinatal hypothyroidism on rat retinal development.
- To analyze the impact of low thyroid hormone levels on neurogenesis and retinal morphology.
Main Methods:
- Induction of hypothyroid status in rat dams and offspring using antithyroid agents from embryonic day 9.
- Morphological and morphometric analyses of retinas from control and hypothyroid groups at various perinatal stages (E19-P7) using light and electron microscopy.
Main Results:
- Hypothyroidism led to decreased retinal growth and fewer neuroblasts in developing rats.
- A significant reduction in the index of mitosis was observed in hypothyroid retinas.
- Low thyroid hormone levels delayed and altered retinal layering and cell differentiation.
Conclusions:
- Thyroid hormones play a critical regulatory role in rat neuroretinogenesis.
- Perinatal thyroid hormone deficiency adversely affects key developmental processes in the retina.
- These findings underscore the importance of adequate thyroid hormone levels for normal visual system development.