16. - S. Koussoulakos*, V. 1. Mitashov**, and H. J. Anton***      (back)
Comparison of the Effects of Retinoic Acid on the Regeneration of External and Intra coelomic Limbs of Ambystoma mexicanum
(* Division of Cell Biology and Biophysics, University of Athens, Panepistimiopolis 15784, Greece;**Koltsov Institute of Developmental Biology, Russian Academy of Sciences, ul. Vavilova 26, Moscow, 11 7808 Russia;*** Institute of Zoology, University of Cologne, Weyertal 118, Cologne, Germany )
The investigation was carried out to analyze the effect of retinoic acid on regeneration after bilateral limb amputation, simultaneously at different exposure conditions of each one regenerating limb in the same animal. the experiments were motivated by the observation that identical modes of retinoid administration to several and/or the same animal species resulted to variable responses, a fact with misleading consequences in the interpretation of the results and in the planning of further experiments.
In order to gain more insight into this problem, young axolotls had both their forelimbs amputated through the carpals. The left stump end was then inserted into the abdominal cavity through a small slit made on the body wall. Whereas the right stump remained outside. Several animal groups were exposed to a retinoic acid solution for various time intervals (test animals). The control animals were kept in tap water. After determined time lengths, the left limbs were exteriorized. It was found that (1) both, the test and control intracoelomic limbs regenerated. Some of the test animals displayed proximalization. The degree of proximalization of the intracoelomic (left) regenerate was always lower than that of the externally regenerated (right) counterpart. (2) The intracoelomic regenerates developed smoother epithelial cell layers, in relation, to the external ones. (3) External limbs exhibited more dedifferentiated mesenchymal cells with respect to intracoelomic ones. (4) Wound epithelium and stump epidermis of the intracoelomic limbs had always intact design.   (See paper 78) 
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