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Abstract
 Background: Retinoic acid (RA), one of the vitamin A derivatives, is used for the treatment of acne, psoriasis and some forms of cancer. It plays an important role in the growth and differentiation during development of vertebrates. In this research the effects of exogenous retinoic acid was investigated on forelimb and hind limb bud culture in vitro.
 Material and methods: In this experiment, female mice mated with males and observation of vaginal plug was considered as day 0 of gestation. The embryos were removed from uterus at day 12, their limb bud were excised and cultured in Eagle’s minimum essential media with 20% human embryo cord serum for two days. Experimental limb bud received RA in three concentrations of 10 -6,10 -5 and 10-4 M. Sham limb bud, received only alcohol (the solvent) and control did not receive anything. Samples were fixed in the Bouin’s solution and stained with Alcian blue for morphological features. Histological studies were morphologically examined.
 Results: The toxic effects of RA exogenous on the development of limb buds were observed. This toxic effect was greater on fore limb bud.
 Conclusion: Our results showed that exogenous RA affects the growth and development of limb buds through reducing both the length of proximal–distal axis and the growth of digits in a dose-dependent manner. Microscopic studies revealed that RA hinders chondrogenesis in a dose-dependent manner with higher concentrations significantly reducing the number of limb bud chondrocytes