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The Journal of Neuroscience, January 4, 2006, 26(1):241-245; doi:10.1523/JNEUROSCI.3721-05.2006

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BRIEF COMMUNICATION
The Full Expression of Fasting-Induced Torpor Requires 3-Adrenergic Receptor Signaling

Steven J. Swoap,¹ Margaret J. Gutilla,¹ L. Cameron Liles,² Ross O. Smith,¹ and David Weinshenker²

¹Department of Biology, Williams College, Williamstown, Massachusetts 01267 and ²Department of Human Genetics, Emory University School of Medicine, Atlanta, Georgia 30322

Torpor, a controlled rapid drop in metabolic rate and body temperature (T_b), is a hypometabolic adaptation to stressful environmental conditions, which occurs in many small mammals, marsupials, and birds. To date, signaling pathways required for torpor have not been identified. We examined the role of the sympathetic nervous system (SNS) in mediating the torpor adaptation to fasting by telemetrically monitoring the T_b of dopamine -hydroxylase knock-out (Dbh–/–) mice, which lack the ability to produce the SNS transmitters, norepinephrine (NE), and epinephrine. Control (Dbh+/–) mice readily reduced serum leptin levels and entered torpor after a fast in a cool environment. In contrast, Dbh–/– mice failed to reduce serum leptin and enter torpor under fasting conditions, whereas restoration of peripheral but not central NE lowered serum leptin levels and rescued the torpor response. Torpor was expressed in fasted Dbh–/– mice immediately after administration of either the nonselective -adrenergic receptor agonist isoproterenol or the 3-adrenergic receptor (AR)-specific agonist CL 316243 [disodium (RR)-5-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]-amino]propyl]-1,3-benzodioxazole-2,2-dicarboxylate], but not after administration of 1, 2, or 1 agonists. Importantly, the 3-specific antagonist SR 59230A [3-(2-ethylphenoxy)-1-[(1,S)-1,2,3,4-tetrahydronapth-1-ylamino]-2S-2-propanol oxalate] severely blunted fasting-induced torpor in control mice, whereas other AR antagonists were ineffective. These results define a critical role of peripheral SNS activity at 3-AR-containing tissues in the torpor adaptation to limited energy availability and cool ambient temperature.

Key words: adipose; -adrenergic receptor; norepinephrine; knock-out mice; leptin; sympathetic nervous system; fasting

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Received Sep 2, 2005; revised November 3, 2005; accepted November 4, 2005.

This article has been cited by other articles:

				R. Gutman, R. Hacmon-Keren, I. Choshniak, and N. Kronfeld-Schor Effect of food availability and leptin on the physiology and hypothalamic gene expression of the golden spiny mouse: a desert rodent that does not hoard food Am J Physiol Regulatory Integrative Comp Physiol, December 1, 2008; 295(6): R2015 - R2023. [Abstract] [Full Text] [PDF]

				S. J. Swoap, M. Rathvon, and M. Gutilla AMP does not induce torpor Am J Physiol Regulatory Integrative Comp Physiol, July 1, 2007; 293(1): R468 - R473. [Abstract] [Full Text] [PDF]

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