Hypoxia, temperature, and pH/CO2 effects on respiratory discharge from a turtle brain stem preparation

Stephen M. Johnson, Rebecca A. Johnson, Gordon S. Mitchell


Johnson, Stephen M., Rebecca A. Johnson, and Gordon S. Mitchell. Hypoxia, temperature, and pH/CO2 effects on respiratory discharge from a turtle brain stem preparation. J. Appl. Physiol. 84(2): 649–660, 1998.—An in vitro brain stem preparation from adult turtles (Chrysemys picta) was used to examine the effects of anoxia and increased temperature and pH/CO2on respiration-related motor output. At pH ∼7.45, hypoglossal (XII) nerve roots produced patterns of rhythmic bursts (peaks) of discharge (0.74 ± 0.07 peaks/min, 10.0 ± 0.6 s duration) that were quantitatively similar to literature reports of respiratory activity in conscious, vagotomized turtles. Respiratory discharge was stable for 6 h at 22°C; at 32°C, peak amplitude and frequency progressively and reversibly decreased with time. Two hours of hypoxia had no effect on respiratory discharge. Acutely increasing bath temperature from 22 to 32°C decreased episode and peak duration and increased peak frequency. Changes in pH/CO2increased peak frequency from zero at pH 8.00–8.10 to maxima of 0.81 ± 0.01 and 1.44 ± 0.02 peaks/min at 22°C (pH 7.32) and 32°C (pH 7.46), respectively; pH/CO2 sensitivity was similar at both temperatures. We conclude that1) insensitivity to hypoxia indicates that rhythmic discharge does not reflect gasping behavior,2) increased temperature alters respiratory discharge, and 3) central pH/CO2 sensitivity is unaffected by temperature in this preparation (i.e., Q10 ∼1.0).

  • chelonia
  • medulla
  • breathing
  • reptile
  • chemosensitivity


  • Address for reprint requests: S. M. Johnson, Dept. of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, 2015 Linden Dr. West, Madison, WI 53706.

  • This work was supported by National Heart, Lung, and Blood Institute Grants HL-53319 and HL-36780. S. M. Johnson is a Parker B. Francis Fellow in Pulmonary Research.

  • Preliminary reports of this work have appeared in abstract form (22).

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