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

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. 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. During awake period, flavoprotein fluorescence intensities in the right sensory cortex were 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 was significantly decreased at 0.5% sevoflurane and completely disappeared at sevoflurane concentrations above 1.5%, and was restored 10 min after cessation of the sevoflurane inhalation. Furthermore, low concentrations of sevoflurane have little effect on the reduction of receptive fields or on the conduction of excitation. We conclude that low concentrations of sevoflurane have little effect on the reduction of receptive fields or on the conduction of excitation, and that sevoflurane concentrations above1.5% completely abolishes the sensory cortex response elicited by noxious stimulation.