Increase in developmental potencies of blastema of rgenerating limbs in toad tadpoles exposed to vitamin A excess

Abstract

During our investigations on the effects of viamin A excess on limb regeneration in anuran tadpoles certain very interesting results have been obtained which contradict the old view that the blastema differentiates only into the structures distal to the level of its origin. --- In experiments, spatula stage hind limbs of the toad Bufo melanostictus tadpoles were amputated through presumptive shank region. The control tadpoles were maintained in ordinary water and the experimental group of such operated tadpoles was immersed in 15 I.U./ml solution of vitamin A palmitate for first 3 days after amputation and then were transferred to ordinary water for the remaining 12 days of the experiment.--- In the control group regeneration of the amputated limbs occurred in 100% cases and all regenerates were completely normal. The regenerated part in each case consisted of only the structures which had been removed distal to the level of amputation. In the experimental group also regeneration occurred in 100% cases and the regenerates were normal in morphology but they differed from the controls in two respects: (i) in 37.5% cases more than one limb regenerated from the same stump; (ii) in all cases regenerates consisted of not only the structures distal to the level of amputation but also the structures proximal to this level including thigh region and the stump portion of the shank. In a number of cases even girdle-like structures had been formed at the level of amputation.--- It is suggested that the exposure of the regenerating limbs in the preblastemic period to vitamin A led to formation of blastemas with greater potency than usual. This resulted in formation of the entire limb from these blastemas and not only the structures actually removed by amputation. This treatment probably also neutralized the so called restrictive or distalizing influence of the stump on the blastema.