Poster Session 2 - B20
1Arsène Pinguelo, 1Sean C. Haffey, 1Irene Lecker, 1Yu-Feng Xie, 1Dian-Shi Wang, 1,2,3Beverley A. Orser
1 Dept. of Physiology, University of Toronto; 2 Dept. of Anesthesia, University of Toronto; 3 Department of Anesthesia, Sunnybrook Health Sciences Centre
Many patients develop delirium and cognitive deficits in the postoperative period after undergoing general anesthesia. These deficits are associated with poor outcomes including loss of independence and increased mortality (Monk et al 2008). Preclinical studies have shown that most general anesthetic drugs trigger a persistent increase in tonic inhibitory GABAergic current in neurons which impairs memory performance after anesthesia, and this impairment persists following the elimination of the anesthetic drugs from the body (Zurek et al 2014). Interestingly, anesthetic drugs stimulate astrocytes to release soluble factors that trigger a sustained increase in tonic inhibitory current in neurons. The mechanisms underlying such crosstalk between astrocytes and neurons are unknown. Given that GABAA receptors are important targets for general anesthetics, we hypothesized that anesthetic activation of GABAA receptors in astrocytes triggers a persistent increase in GABAA receptor-mediated tonic current in neurons.
Astrocyte cultures were treated with etomidate or a GABAA receptor antagonist bicuculline plus etomidate for 1 hour, then washed out and incubated for further 2 hours. The conditioned medium was then transferred to neuron cultures, and 24 hours later the tonic current was recorded in the neurons. Whole cell voltage clamp recordings were performed from astrocytes in the stratum radiatum of the slices to examine their responses to bath perfusion of GABA. Western blotting was used to study the expression of various GABAA receptor subtypes in our culture system.
Medium from etomidate-treated astrocytes increased the amplitude of the tonic current in neurons. However, when the astrocytes were cotreated with the GABAA receptor antagonist bicuculline and etomidate, the tonic current in neurons did not increase. All astrocytes that were studied in hippocampal slices responded to GABA with a current amplitude of 185 ± 39 pA. Western blotting showed that astrocytes express α2 and β2/3, but not α5 subunits of GABAA receptors. Thus astrocytes express functional GABAA receptors that are likely composed of α2 and β2 or β3 subunits, and activation of these GABAA receptors in astrocytes is necessary for general anesthetics to trigger the persistent increase in tonic current in neurons. These studies provide the first evidence that astrocytic GABAA receptors drive the sustained inhibitory current in neurons and thus may be therapeutic targets for the prevention and treatment of postoperative delirium and cognitive deficits.