38. HEART FIELD OPERATIONS 



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

 to determine the mode of heart formation. 



MATERIALS: 



Biological: Anura stages # 1 5-# 1 7: Urodela stages #22-#25, and #34-#38. 



Technical: Standard Equipment 



METHOD: 



Precautions: 



1. Carry out several exploratory dissections of embryos to determine the color 

 and the extent of heart mesenchyme concerned in the later operations. 



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

 generally high in heart field operations. 



3. Operations on Anura should be in full strength Standard Solution and on 

 Urodela in Operating Medium. Following recovery from the operation, re- 

 turn the embryos to appropriate culture media. 



4. The post-operated embryos should be kept at constant and low temperatures, 

 Anura from 1 5°C. to 18°C. , and Urodela from 10°C. to 1 5°C. 



Control: 



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



2. For production of double hearts by heart block, the same operation should 

 be performed but no mesenchyme is removed and no block is introduced. 



3. For heteroplastic transplantations, similar transplantations of somite meso- 

 derm constitute the control condition. 



4. For isolation culture, the isolation of somite mesoderm would constitute the 

 control. 



Procedure : 



EXCISION OF PART OF THE HEART FIELD 



At Anuran stage #16 and Urodele stage #23 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 is 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 granular. 

 Replace the ectodermal flap. If the ectoderm is insufficient, graft some indifferent ecto- 

 derm from the lateral body wall and from a posterior position of another embryo. Lay a 

 piece of moist lens paper over the wound for 20 to 30 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 another em- 

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



* The author acknowledges, with appreciation, the help of Dr. W. M. Copenhaver in organizing this exercise. 



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