Brain ECF pH and central chemical control of ventilation during anoxia in turtles

The role of changes in brain extracellular fluid [H+] in the control of breathing during anoxia was studied in unanesthetized turtles, Chrysemys scripta. Ventilation, [minute ventilation (VE), tidal volume (VT), and breathing frequency (f)], cerebral extracellular fluid (ECF) pH, and arterial blood gases were measured at 25 degrees C during a 30-min control period (room air), 30 min of anoxia (100% N2 breathing), and 60 min of recovery (room air). ECF pH was measured in the cerebral cortex with a glass microelectrode (1-2 micron tip diam). Large changes in ventilation, ECF [H+], and arterial blood gases were observed. The predominant ventilatory response was an increase in f with a slight increase in VT. A correlation was observed between ECF [H+] and f, which suggested that central chemoreceptor stimulation was involved in the ventilatory response.