Temperature-induced changes in turtle CSF pH and central control of ventilation

Area of Science:

• Comparative Physiology
• Respiratory Regulation
• Acid-Base Balance

Background:

• Understanding central chemical control of ventilation is crucial for respiratory physiology.
• The alphastat hypothesis proposes a model for ventilatory control independent of temperature-induced pH changes.

Purpose of the Study:

• To investigate the relationship between body temperature, cerebrospinal fluid (CSF) pH, and respiratory minute volume (RMV) in unanesthetized turtles.
• To compare ventilatory control mechanisms between turtles and goats.

Main Methods:

• Measurements of CSF and arterial blood acid-base variables and RMV at varying body temperatures in turtles.
• Perfusion of the turtle brain ventricular system with mock CSF to alter ion-dependent pH.
• Comparison of findings with data from goats.

Main Results:

• RMV remained constant as body temperature increased, while CSF pH decreased.
• Ventilation increased significantly when CSF pH was altered independently of temperature.
• Ventilatory responses in turtles and goats align with the alphastat model.

Conclusions:

• Ventilation in turtles does not track CSF pH when body temperature is the independent variable.
• Central chemical control of ventilation appears conserved across air-breathing vertebrates.
• The fractional dissociation of imidazole is likely maintained constant in central receptive structures, supporting the alphastat model.