Motor Unit Recruitment Pattern in a Respiratory Muscle of Unanesthetized Chickens

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THE amplitude of electrical activity of respiratory muscles of the chicken, as recorded with a needle electrode, seems to be related to the level of anesthesia. Fedde et al. (1964) have shown that motor unit potentials of large amplitude are absent when chickens are deeply anesthetized. Since many investigations of the pattern of motor unit recruitment have used anesthetized animals (Sears, 1964; Fedde et al., 1969), we attempted to determine the motor unit recruitment pattern in unanesthetized chickens.METHODSA biopolar, electromyographic electrode (Fig. 1) was implanted in the transversus abdominis muscle (TA) in six, lightly anesthetized (20 mg./kg. of body weight of sodium pentobarbital administered intravenously) Single Comb White Leghorn males, 12 to 16 weeks old. The skin was incised along the ventro-lateral surface of the abdominal wall; then the fibers of the external abdominal oblique and rectus abdominis muscles were separated by blunt dissection to expose the lateral…