HEART FIELD OPERATION 



PURPOSE : By excising, transplanting, and 'blocking the fusion of the bilateral prlmordia, 

 to determine the mode of heart formation. 



MATES IMS : 



Biological : Anura stages #15-#17: Urodela stages #22 -#25, and #5^-#58. 



Technical : Standard Ecjuipment 



METHOD: 



Precautions : 



a. Carry out several exploratory dissections of emhryos to determine the color and 



the extent of heart mesenchyme concerned in the later operations, 

 h. Alcohol sterilization of operating instruments will lessen mortality which is 

 generally high in heart field operations. 



c. Operations on Anura should he in full strength Standard Solution and on Urodela 

 in Operating Medium. Following recovery from the operation, return the emhryos 

 to appropriate culture media. 



d. The post-operated emhryos should be kept at constant and low temperatures, Anura 

 from 15°C. to l80C., and Urodela from 10°C. to 15°C. 



Control : 



a. For the excision experiments, excision of mesoderm from any other region. 



b. For production of double hearts by heart block, the same operation should be per- 

 formed but no mesenchyme is removed and no block is introduced. 



c. For heteroplastic transplantations, similar transplantations of somite mesoderm 

 constitute the control condition. 



d. For isolation culture, the isolation of somite mesoderm would constitute the con- 

 trol. 



Procedure : 



EXCISION OF PART OF THE HEART FIELD 



At Anuran stage #l6 and Urodele stage #25 the lateral mesoderm is converging from the 

 two sides around the pharynx to form the single ventral heart (see diagrams). If the ma- 

 terial of one of the lateral plates la excised, the formation of a normal, single tubular 

 heart by the bilateral rudiments is prevented. 



Outline and peel back the ectoderm over the heart field derived from the right side 

 after placing the embryo in a shallow depression in Permoplast, in Operating Medium 

 (Urodele) or in full strength Standard Solution (Anura). Leave a hinge of ectoderm for 

 attachment so that It can be replaced over the wound. With a hair loop and micro-pipette 

 scoop out all visible mesoderm from the one side. The mesoderm is clear white and granu- 

 lar. Replace the ectodermal flap. If the ectoderm is Insufficient, graft some Indiffer- 

 ent ectoderm from the lateral body wall and from a posterior position of another embiyo. 

 Lay a piece of moist lens paper over the wound for 20 to 50 minutes and, after complete 

 healing, return the' embryo to the normal culture medium either in a #2 Stender or a finger 

 bowl. If the excavated space is extensive, it may be partially filled with yolk from an- 

 other embryo of the same species and stage although this should be avoided if possible. 



THE PRODUCTION OF DOUBLE HEARTS 



This operation may be performed on the Anura (stage #l6) or on the Urodela (stages 

 #22 -#25) although the latter are preferred because the development of the heart can be 

 followed through the transparent skin of the ventral side without exploratory incisions. 



* The author acknowledges, with appreciation, the help of Dr. W. M. Copenhaver in organiz- 

 ing this exercise. 



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