Chemosensitive locus coeruleus neurons in the Savannah monitor lizard, Varanus exanthematicus (879.13)

Savannah monitor lizards, Varanus exanthematicus , are unusual among air‐breathing, ectothermic vertebrates by maintaining arterial pH nearly constant during changes in body temperature (‐0.003 U °C ‐1 ) in contrast to the typical α‐stat regulating strategy (‐0.015 to ‐0.017 U °C ‐1 ) of most other ectotherms. Given the importance of pH in the control of ventilation, we examined the CO 2 /H + sensitivity of neurons from the locus coeruleus (LC) region of Savannah monitor lizard brainstems. Whole‐cell patch clamp electrophysiology was used to record membrane voltage (V m ) in neurons within the LC region in brainstem slices; changes in firing rate of LC neurons were calculated from action potential recordings. Upon exposure to hypercapnic acidosis (HA) at 20°C, 60% of neurons significantly decreased firing rate (1.8±0.3 vs. 0.6±0.1 Hz; P <0.05). The percentage of LC neurons inhibited by HA is high at 20°C compared with published percentages from bullfrogs and rats. Increasing temperature to 30°C abolished the inhibited response to HA (2.4±0.9 Hz vs. 2.6±1.0 Hz; P =1.0). The large proportion of neurons inhibited by HA at 20°C may provide a mechanism whereby retention of whole body CO 2 stores with cooling enables the pH‐stat regulation strategy of Varanus exanthematicus . Grant Funding Source : Supported by NSF IOS 1257338