Abstract
Flavoprotein autofluorescence is intimately coupled with neural activities and applicable for functional brain imaging. Autofluorescence imaging is especially useful for observing mouse cortical activities, because the skull of mice is transparent enough to visualize cortical autofluorescence via the intact skull. In the present study, we investigated neural activities in the auditory cortex of anesthetized mice with this technique. C57BL/6 mice were anesthetized with urethane (1.6 g/kg, i.p.). The skin covering the skull was incised, and the temporal muscle over the right auditory cortex was removed. The exposed surface of the skull was covered with liquid paraffin to prevent drying and to keep the skull transparent. Autofluorescence responses in the auditory cortex were elicited by various sound stimuli at 5-20 kHz for 500 ms. Sound stimuli were applied as pure tones or amplitude-modulated (AM) tones with a sawtooth wave at 20 Hz. Cortical responses were recorded with a cooled CCD camera attached to an epifluorescence binocular microscope. Neural activities elicited by sound stimuli at 5-20 kHz exhibited a tonotopic map in the auditory cortex. Although AM sounds modulated by a fast-rise sawtooth wave and a slow-rise sawtooth wave have the same spectral patterns, the neural activities elicited by the former were larger than those elicited by the latter, indicating neural activities in the auditory cortex are strongly influenced by the temporal profile of sound stimuli. [Jpn J Physiol 55 Suppl:S166 (2005)]
