Savannah monitor lizards (Varanus exanthematicus) are unusual among ectothermic vertebrates by maintaining arterial pH nearly constant during changes in body temperature in contrast to the typical α-stat regulating strategy of most other ectotherms. Given the importance of pH in the control of ventilation, we examined the CO2/H+ sensitivity of neurons from the locus coeruleus (LC) region of monitor lizard brainstems. Whole-cell patch clamp electrophysiology was used to record membrane voltage in LC neurons in brainstem slices. Artificial cerebral spinal fluid (aCSF) equilibrated with 80% O2, 0.0–10.0% CO2, balance N2 was superfused across brainstem slices. Changes in firing rate (FR) of LC neurons were calculated from action potential recordings to quantify the chemosensitive response to hypercapnic acidosis. Our results demonstrate that the LC brainstem region contains neurons that can be excited by, inhibited by, and/or not sensitive to CO2 in V. exanthematicus. While few LC neurons were activated by HA (15%), a higher proportion of the LC neurons responded by decreasing their FR during exposure to high CO2 at 20°C (37%); this chemosensitive response was no longer exhibited when increasing temperature to 30°C. Further, the proportion of chemosensitive LC neurons changed at 35°C with a reduction in CO2-inhibited (11%) neurons and an increase in CO2-activated (35%) neurons. Expressing a high proportion of inhibited neurons at low temperature may provide insights into mechanisms underlying the temperature-dependent pH-stat regulatory strategy of Savannah monitor lizards.
- Received February 8, 2016.
- Accepted June 29, 2016.
- © 2016. Published by The Company of Biologists Ltd