Decapitation

DECAPITATION (decapitation) as a physiological experiment is used in physiology in two modifications: 1. D. of the animal in the proper sense of the word, where the object of physiological research is the decapitated torso of the animal. This method, introduced into experimental physiology by Sherrington (Charles Sherrington), was used by him mainly for studying spinal reflexes in warm-blooded animals. D. as a method can be successfully used not only for the purposes mentioned, but also in all cases of physiological experiment when it is necessary to eliminate the influence of the brain on peripheral functions. The comparative ease of the experiment and a number of advantages in the above sense have led to the widespread use of the method in both physiology and pharmacology. The most suitable animal is the cat, as the decapitated torso of the latter, under proper experimental conditions, continues to maintain reactivity for many hours. Less hardy are dogs and then rabbits. The technique of D. according to Sherrington. To an immobilized animal, a tracheal cannula is inserted into the trachea, and the carotid arteries are ligated. Immediately below the transverse processes of the atlas, after appropriate preparation, the muscles are cut as deeply as possible. Behind the transverse processes of the atlas, the first strong ligature is applied, which compresses the vertebral arteries at the place where they lie between the transverse processes of the atlas and the second vertebra. The second strong ligature is applied at the level of the thyroid cartilage so as to ligature the neck muscles under the remaining free trachea. Separation of the head is performed with an amputation knife between the base of the skull and the atlas (deep anesthesia is required). The decapitated animal is transferred to artificial respiration before decapitation or immediately after it. It is necessary to maintain normal body temperature using hot water bottles or by placing the torso on a heated table. Artificial ventilation of the lungs is also carried out with heated air. Under these conditions, the work of the heart is not significantly disrupted despite the drop in blood pressure sometimes to relatively low figures (30-40 mm Hg). -Area of application in physiology: study of spinal reflexes, circulation; in pharmacology: for studying the pharmacodynamics of the spinal cord and the cardiovascular apparatus. -Instruments and apparatus: standard physiological set of instruments, apparatus for artificial respiration. 2. D. in the second modification of the experiment is used for studying the function of the brain of a warm-blooded animal independently of peripheral nervous and humoral influences (in the form of the so-called "isolated head"). The idea of the experiment was first expressed by Legal lois (1812), but the experiment on a warm-blooded animal (dog) was actually carried out only in 1858 by Brown-Sequard. In 1887, Hayem and Barrier (G. Hayem, G. Barrier) continued these experiments, introducing a number of improvements into the technique of the experiment. In 1912, Heymans and de Somer (J. F. Heymans, de Somer) published their method of isolating the head of a warm-blooded animal, applying an anastomosis of the vessels of the "isolated head" with carotid-jugular circulation of a "feeding" animal (a larger dog). In 1925-1927, this method was further improved by J. and C. Heymans, who pointed to its exceptional suitability for studying the physiology and pharmacodynamics of the bulbar centers of the heart and respiratory apparatus. (The technique of the experiment by the above-mentioned authors is not described; see original works.) However, the necessity of using in these methods for feeding the isolated head the natural circulation of another (feeding) animal does not eliminate humoral influences on the functions of the brain, and therefore Chechulin and Bryukhonenko in 1928 published a new method that eliminates not only peripheral nervous influences but also humoral ones. In their experiments, a truly complete isolation of the head of a warm-blooded animal was achieved, which was accomplished by using artificial circulation with natural blood with the help of a special apparatus ("artificial heart"). The latter method can be successfully used for studying the physiology and pharmacodynamics of natural reflexes of the brain, as well as for studying the metabolic processes occurring in the brain under the influence of various conditions. The latter circumstance makes the method particularly valuable for studying the conditions of restoration of excitability of brain centers after prolonged oxygen starvation, which is one of the cardinal questions for reviving a deceased organism. (For the technique of the experiment, see the original work.)