title: Effect of temperature on chemosensitive locus coeruleus neurons of savannah monitor lizards, Varanus exanthematicus.
abstract: Savannah monitor lizards (Varanus exanthematicus) are unusual among ectothermic vertebrates in 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 equilibrated with 80% O2, 0.0-10.0% CO2, balance N2, was superfused across brainstem slices. Changes in firing rate 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 or inhibited by, and/or are not sensitive to CO2in V. exanthematicus While few LC neurons were activated by hypercapnic acidosis (15%), a higher proportion of the LC neurons responded by decreasing their firing rate during exposure to high CO2at 20°C (37%); this chemosensitive response was no longer exhibited when the temperature was increased 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.
authors.affiliation: Department of Animal Morphology and Physiology, College of Agricultural and Veterinary Sciences, São Paulo State University, Jaboticabal, São Paulo 14884-900, Brazil Department of Biological Sciences, Wright State University, Dayton, OH, USA National Institute of Science and Technology in Comparative Physiology (INCT Fisiologia Comparada), Brazil.
authors.forename: Lucas A
authors.initials: LA
authors.lastname: Zena
authors.affiliation: Department of Animal Morphology and Physiology, College of Agricultural and Veterinary Sciences, São Paulo State University, Jaboticabal, São Paulo 14884-900, Brazil Department of Biological Sciences, Wright State University, Dayton, OH, USA National Institute of Science and Technology in Comparative Physiology (INCT Fisiologia Comparada), Brazil.
authors.forename: Elisa M
authors.initials: EM
authors.lastname: Fonseca
authors.affiliation: Department of Biological Sciences, Wright State University, Dayton, OH, USA.
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Santin
authors.affiliation: Department of Animal Morphology and Physiology, College of Agricultural and Veterinary Sciences, São Paulo State University, Jaboticabal, São Paulo 14884-900, Brazil Department of Biological Sciences, Wright State University, Dayton, OH, USA National Institute of Science and Technology in Comparative Physiology (INCT Fisiologia Comparada), Brazil.
authors.forename: Lays
authors.initials: L
authors.lastname: Porto
authors.affiliation: Department of Animal Morphology and Physiology, College of Agricultural and Veterinary Sciences, São Paulo State University, Jaboticabal, São Paulo 14884-900, Brazil National Institute of Science and Technology in Comparative Physiology (INCT Fisiologia Comparada), Brazil.
authors.forename: Luciane H
authors.initials: LH
authors.lastname: Gargaglioni
authors.affiliation: Department of Animal Morphology and Physiology, College of Agricultural and Veterinary Sciences, São Paulo State University, Jaboticabal, São Paulo 14884-900, Brazil National Institute of Science and Technology in Comparative Physiology (INCT Fisiologia Comparada), Brazil.
authors.forename: Kênia C
authors.initials: KC
authors.lastname: Bícego
authors.affiliation: Department of Biological Sciences, Wright State University, Dayton, OH, USA lynn.hartzler@wright.edu.
authors.forename: Lynn K
authors.identifier: http://orcid.org/0000-0002-2355-0174
authors.initials: LK
authors.lastname: Hartzler
keywords: Brainstem; CO2 inhibition; Chemosensitivity; Ectothermic vertebrates; Ventilation; pH regulation