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First published online August 28, 2009
Journal of Experimental Biology 212, 2885-2891 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.024430

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Commentary

Responses to temperature variation: integration of thermoregulation and metabolism in vertebrates

Frank Seebacher

Integrative Physiology, School of Biological Sciences A08, University of Sydney, NSW 2006, Australia

fseebach{at}bio.usyd.edu.au

Accepted 15 June 2009

Many vertebrates regulate their body temperature in response to thermal variability of the environment. Endotherms maintain relatively stable body temperatures by adjusting metabolic heat production in response to varying environmental heat loads. Although most ectotherms do not display adaptive thermogenesis, they do acclimate cellular metabolism to compensate for environmental temperature variation. The components of the thermoregulatory systems in endotherms and ectotherms are evolutionarily conserved, and I suggest that metabolic acclimation in ectotherms relies on the same regulatory pathways as adaptive thermogenesis in endotherms. Both groups rely on transient receptor potential ion channels to sense environmental temperatures. Thermosensory (afferent) information is relayed to the hypothalamus, which initiates a sympathetic efferent response. Cardiovascular responses to heat are similar in ectothermic crocodiles and in mammals, and are mediated by the autonomic nervous system in both cases. The sympathetic nervous system also modulates cellular metabolism by inducing expression of the transcriptional regulator peroxisome proliferator activated receptor coactivator 1 (PGC-1), which interacts with a range of transcription factors that control glycolysis, fatty acid oxidation, gluconeogenesis, mitochondrial biogenesis and bioenergetics, and metabolic rate. PGC-1 is best known from mammalian model species but there is increasing evidence that it is also instrumental in non-mammalian vertebrates. Hence, endothermic adaptive thermogenesis may result from the same regulatory pathways as ectothermic metabolic acclimation, and both could be considered as adaptive metabolic responses to temperature variation.

Key words: body temperature, transient receptor potential ion channels, hypothalamus, sympathetic nervous system, cutaneous blood flow, PGC-1

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