Changes in ventral respiratory column GABAaR ε- and δ-subunits during hibernation mediate resistance to depression by EtOH and pentobarbital

Hengen KB, Gomez TM, Stang KM, Johnson SM, Behan M. Changes in ventral respiratory column GABA(a)R epsilon- and delta-subunits during hibernation mediate resistance to depression by EtOH and pentobarbital. Am J Physiol Regul Integr Comp Physiol 300: R272-R283, 2011. First published November 17, 2010; doi: 10.1152/ajpregu.00607.2010.-During hibernation in the 13-lined ground squirrel, Ictidomys tridecemlineatus, the cerebral cortex is electrically silent, yet the brainstem continues to regulate cardiorespiratory function. Previous work showed that neurons in slices through the medullary ventral respiratory column (VRC) but not the cortex are insensitive to high doses of pentobarbital during hibernation, leading to the hypothesis that GABA(A) receptors (GABAAR) in the VRC undergo a seasonal modification in subunit composition. To test whether alteration of GABAAR subunits are responsible for hibernation-associated pentobarbital insensitivity, we examined an array of subunits using RT-PCR and Western blots and identified changes in epsilon- and delta-subunits in the medulla but not the cortex. Using immunohistochemistry, we confirmed that during hibernation, the expression of epsilon-subunit-containing GABA(A)Rs nearly doubles in the VRC. We also identified a population of delta-subunit-containing GABAARs adjacent to the VRC that were differentially expressed during hibernation. As delta-subunit-containing GABAARs are particularly sensitive to ethanol (EtOH), multichannel electrodes were inserted in slices of medulla and cortex from hibernating squirrels and EtOH was applied. EtOH, which normally inhibits neuronal activity, excited VRC but not cortical neurons during hibernation. This excitation was prevented by bicuculline pretreatment, indicating the involvement of GABA(A)Rs. We propose that neuronal activity in the VRC during hibernation is unaffected by pentobarbital due to upregulation of epsilon-subunit-containing GABA(A)Rs on VRC neurons. Synaptic input from adjacent inhibitory interneurons that express delta-subunit-containing GABA(A)Rs is responsible for the excitatory effects of EtOH on VRC neurons during hibernation.