Improved hind limb regeneration in tadpoles of Bufo andersonii made hypothyroid with potassium perchlorate

Abstract

It has been suggested that increasing levels of thyroid hormone with the onset and progress of metamorphic changes might be involved in regressive decline and final loss of regenerative capacity of the larvae of anuran amphibians. The present study was aimed at investigating the effects of chemical suppression of thyroid activity on limb regeneration in tadpoles of Bufo andersonii (Boulenger) by treating them with potassium perchlorate which makes them hypothyroid and delays or suppresses metamorphosis. In young to older tadpoles of a series of developmental stages the hind limbs were amputated through thigh or shank. Following this operation the experimental groups of tadpoles were reared in 0.2% solution of potassium perchlorate and thecontrol groups in ordinary water. In another experiment tadpoes were reared in perchlorate solution from some time prior to limb amputation. By the stage when the limbs possessed distinct rudiments of all five toes the regenerative ability in the controls was found to be nearly absent at thigh and very low at shank levels, and in the tadpoles approaching metamorphic climax it had disappeared completely throughout the two levels. Gradual decline of this capacity was manifested in lesser number of cases regenerating at all and the regenerates becoming more and more oligodactylous. In perchlorate treated hypothyroid tadpoles of all developmental stages employed limb regeneration at both thigh and shank levels markedly improved. The improvement was expressed by increasing number regenerating, reduction in the degree of oligodactyly of regenerated feet and greater number of regenerates attaining the normal morphology with five toes in each foot. Treatment with perchlorate from prior to amputation produced even better results and a few of even advanced larvae regenerated to some extent at both levels. Histological analysis showed that perchlorate improved wound healing pattern, intensified dedifferentiation and accelerated blastema formation. However, post-blastemic processes of redifferentiation and growth were retarded. It is suggested that hypothyroid condition is beneficial for upto the stage of blastema formation but for postblastemic events even normal thyroid activity may be required in anuran larvae.