41. THYROIDECTOMY AND 

 EARLY AMPHIBIAN DEVELOPMENT 



PURPOSE: By means of surgical extirpation to determine the functional relationship of 

 the thyroid anlage in the early larva to metamorphic changes in the later tadpole. 



MATERIALS: 



Biological: Anura (stage #17) or Urodele (stage #31) larvae. 



Technical: Standard Equipment. 



METHOD: 



Precautions : 



1. Avoid injury or removal of heart anlage which is just posterior to the thyroid 

 anlage'. 



2. Avoid post-operative bacterial infection. If necessary, use 0. 1% sodium 

 sulfadiazine in operating and in culture media. 



Control: The control consists of embryos of similar age and stage in which similar 

 surgical incisions are made but without the removal of any tissue. Such animals 

 should be given identical treatment as the experimentals. 



Procedure: 



1. Remove the embryos from their jelly capsules and fertilization membranes. 

 If there is any muscular activity, anesthetize them in 1/3,000 MS 222 

 (freshly made up). Ciliary movement cannot be reduced by narcosis. 



2. Make a shallow depression in the Permoplast (or paraffin) of the operating 

 dish. Use Urodele Operating Medium for Urodeles and 2X Standard Solution 

 for Anura, adding 1% sodium sulfadiazine if there is difficulty with infection. 

 Place the embryo on its left side, head away from the operator. 



3. Insert the point of a double-edged lancet (or operating glass needle) between 

 the position of the thyroid and the heart anlage', (see diagrams) and make an 

 outward cut through the throat ectoderm. Remove a wedge of tissue, the 

 apex of which reaches the floor of the pharynx just at the point of the slightly 

 pigmented thyroid evagination. Carefully excavate the cells with the hair 

 loop, avoiding particularly the heart mesoderm. Part of the pharyngael 

 floor will, of necessity, be removed with the thyroid. (If the student finds 

 this operation difficult, refresh his memory of the position of the thyroid 

 anlage' by studying both transverse and sagittal sections of tail-bud stages. 



A complete dissection study of the living tail-bud stage prior to thyroid ex- 

 tirpation is definitely recommended, for this is a delicate operation.) 



4. Transfer the operated embryo to an agar-base in a #2 Stender filled with 

 operating medium for about 30 minutes during which the wound will heal. 

 Then transfer the embryo to Urodele Growing Medium or Standard Solution 

 (depending upon the genus) for further development, preferably at a temper- 

 ature slightly below that of the laboratory. Begin feeding at appropriate 

 stage of development. 



OBSERVATION AND TABULATION OF DATA: 



Operated and control embryos must be giyen identical treatment with respect to volume, 

 medium, light, food, etc. 



1. Make sketches at 1 5 minute intervals of the wound healing of the operated animals. 



2. At weekly intervals following the operation, make drawings (or photographs) of 

 thyroidectomized and control embryos. 



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