EFFECT OF TEMPERATURE ON CENTRAL CHEMICAL CONTROL OF VENTILATION IN THE ALLIGATOR ALLIGATOR-MISSISSIPPIENSIS

Central chemoreceptor function was assessed in unanesthetized alligato rs, Alligator mississippiensis, at body temperatures of 15, 25 and 35- degrees-C. Two experiments were performed. In the first experiment, th e fourth ventricle was perfused with mock cerebrospinal fluid (CSF) so lutions of different pH values (7.1-7.9). Changes in pulmonary ventila tion were evaluated with a pneumotachograph and arterial pH (pHa) was measured. Perfusion with low-pH solutions increased ventilation and ar terial pH. Perfusion with high-pH solutions decreased ventilation and arterial pH. Mock CSF pH had a greater effect at higher temperatures. In the second experiment, the relative contributions of central and pe ripheral chemoreceptor drive to breathing were evaluated using hyperca pnic gas mixtures to stimulate both central and peripheral chemorecept ors. Hypercapnia caused an increase in ventilation which was larger at higher temperatures. To stimulate only the peripheral chemoreceptors, the same hypercapnic gas mixtures were applied while the CSF pH of th e fourth ventricle was kept constant by perfusion with a mock CSF solu tion. This reduced significantly the ventilatory response induced by h ypercapnia. These data indicate that, regardless of the temperature, c entral chemoreceptors play a major role in the ventilatory regulation of the alligator. The change in pHa with temperature is compatible wit h the alphastat hypothesis.