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Am J Physiol Regul Integr Comp Physiol 297: R1028-R1036, 2009. First published August 12, 2009; doi:10.1152/ajpregu.00239.2009
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Articles

Hibernation induces pentobarbital insensitivity in medulla but not cortex

Keith B. Hengen,1 Mary Behan,1,2 Hannah V. Carey,2 Mathew V. Jones,1,3 and Stephen M. Johnson1,2

1Neuroscience Training Program, 2Department of Comparative Biosciences, School of Veterinary Medicine, and 3Department of Physiology, School of Medicine, University of Wisconsin, Madison, Madison, Wisconsin

Submitted May 1, 2009 ; accepted in final form July 28, 2009

The 13-lined ground squirrel (Ictidomys tridecemlineatus), a hibernating species, is a natural model of physiological adaption to an extreme environment. During torpor, body temperature drops to 0–4°C, and the cortex is electrically silent, yet the brain stem continues to regulate cardiorespiratory function. The mechanisms underlying selective inhibition in the brain during torpor are not known. To test whether altered GABAergic function is involved in regional and seasonal differences in neuronal activity, cortical and medullary slices from summer-active (SA) and interbout aroused (IBA) squirrels were placed in a standard in vitro recording chamber. Silicon multichannel electrodes were placed in cortex, ventral respiratory column (VRC), and nucleus tractus solitarius (NTS) to record spontaneous neuronal activity. In slices from IBA squirrels, bath-applied pentobarbital sodium (300 µM) nearly abolished cortical neuronal activity, but VRC and NTS neuronal activity was unaltered. In contrast, pentobarbital sodium (300 µM) nearly abolished all spontaneous cortical, VRC, and NTS neuronal activity in slices from SA squirrels. Muscimol (20 µM; GABAA receptor agonist) abolished all neuronal activity in cortical and medullary slices from both IBA and SA squirrels, thereby demonstrating the presence of functional GABAA receptors. Pretreatment of cortical slices from IBA squirrels with bicuculline (100 µM; GABAA receptor antagonist) blocked pentobarbital-dependent inhibition of spontaneous neuronal activity. We hypothesize that GABAA receptors undergo a seasonal modification in subunit composition, such that cardiorespiratory neurons are uniquely unaffected by surges of an endogenous positive allosteric modulator.

{gamma}-aminobutyric acid receptors; ventral respiratory groups; nucleus tractus solitarius; respiratory control


Address for reprint requests and other correspondence: S. M. Johnson, Assistant Professor, Dept. of Comparative Biosciences, School of Veterinary Medicine, Univ. of Wisconsin, Madison, WI 53706 (e-mail: johnsons{at}svm.vetmed.wisc.edu).






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