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

An in vitro brain stem preparation from adult turtles (Chrysemys picta) was used to examine the effects of anoxia and increased temperature and pH/CO2 on respiration-related motor output. At pH approximately 7.45, hypoglossal (XII) nerve roots produced patterns of rhythmic bursts (peaks) of discharge (O.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 degrees C; at 32 degrees 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 degrees C decreased episode and peak duration and increased peak frequency. Changes in pH/CO2 increased 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 degrees C (pH 7.32) and 32 degrees C (pH 7.46), respectively; pH/CO2 sensitivity was similar at both temperatures. We conclude that 1) 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 approximately 1.0).