Our previous studies revealed that the inhalation anesthetic, sevoflurane, had the suppressive effect on the clock gene Per2 expression in the rat Suprachiasmatic nucleus (SCN). The suppression of Per2 was also observed in SCN slice cultures isolated from peripheral inputs and other brain regions, suggesting a direct action of sevoflurane in the SCN itself.
In this study, we examined intra-SCN spatial susceptibility to sevoflurane and the involvement of GABAergic signal transduction for suppressive effect of sevoflurane on Per2 expression.
Sevoflurane was applied to SCN slice cultures from Per2-dLuc transgenic rats, and luciferase bioluminescence was monitored using a microscope equipped with a high-sensitivity cooled CCD camera. To investigate a detailed spatial property of sevoflurane effect on bioluminescence, acquired time lapse images of the SCN were divided into small regions of interest (ROIs). The bioluminescence in the most of ROIs showed a clear circadian pattern, and the bioluminescence was repressed by sevoflurane application. In each ROIs, no spatial difference within the SCN (mediolateral nor dorsoventral) was observed in the susceptibility to sevoflurane.
We also examined a possibility that sevoflurane suppresses Per2 expression through the modulation of GABA receptor activities, since the SCN neurons express GABAA receptors, and sevoflurane is indicated as a modulator of the GABA receptor activity. To investigate the role of GABA receptors in suppression of Per2 expression by sevoflurane, we applied GABAA blocker bicuculline GABAB 2-hydroxy-saclofen to the SCN cultures prior to sevoflurane application. The suppressive effect of sevoflurane on bioluminescence was totally diminished in the presence of both GABA receptor blockers.
These results suggest that GABAergic mechanism is indispensable for sevoflurane to suppress Per2 expression in the SCN, indicating that sevoflurane may act via GABA receptor systems in individual SCN cells.