Anesthetic Effects of Sevoflurane on the Mouse Somatosensory Cortex: A Flavoprotein Fluorescence Imaging Study

Abstract

Objective: Sevoflurane, a volatile inhaled anesthetic, is used clinically for general anesthesia in humans. However, the mechanism of action of sevoflurane is not fully understood. We used transcranial flavoprotein fluorescence imaging to visualize somatic sensory cortex responses to noxious stimuli in mice without and with sevoflurane inhalation anesthesia at different concentrations to investigate sevoflurane effects in mice. Methods: A bipolar stimulating electrode was inserted into the left buccal region of the mouse, and changes in flavoprotein fluorescence intensity in the right somatic sensory cortex were recorded before and after electrical stimulation. Measurements were taken while the mouse was awake, at four levels of sevoflurane concentration (0.5%, 1.0%, 1.5%, and 2.0%; 5 min each), and at 10, 20, and 30 min after the end of sevoflurane inhalation. Results: During the awake period, flavoprotein fluorescence intensities in the right sensory cortex decreased after the onset of electrical stimulation, but after 0.9 s, the fluorescence intensity began to increase, reaching a peak value at 2.1 s. This biphasic response significantly decreased at 0.5% sevoflurane and completely disappeared at sevoflurane concentrations above 1.5%, and restored 10 min after cessation of the sevoflurane inhalation. Furthermore, low concentrations of sevoflurane had little effect on the reduction of receptive fields or the conduction of excitation. Conclusion: We conclude that low concentrations of sevoflurane have little effect on the reduction of receptive fields or the conduction of excitation, and that sevoflurane concentrations above 1.5% completely abolish the sensory cortex response elicited by noxious stimulation.