Physiological functions and underlying cellular/molecular mechanisms of retrograde inputs from higher cortical areas toe sensory cortices

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Using transcranial flavoprotein fluorescence imaging in mice, the following results have been obtained.1. We investigated auditory cortical plasticity regulated by acoustic environments. Mice were reared in various acoustic environments for at least 4 weeks after birth. Cortical responses elicited by tonal stimuli (5, 10 and 20 kHz) exhibited tonotopic maps in the primary auditory cortex (AI). Depression of auditory cortical responses was observed in sound-deprived mice compared with naive mice reared in a normal acoustic environment. When mice were exposed to an environmental tonal stimulus at 10 kHz for more than 4 weeks after birth, the cortical responses were potentiated in a frequency-specific manner. These results suggest that acoustic environments regulate the development of intracortical circuits in the mouse auditory cortex.2. We visualized cortical responses to missing fundamentals in mice. The activity patterns in AI elicited by 5 kHz were different from those elicited by 20 … More kHz or 25 kHz. However, the areas activated by 5 kHz were also activated by the mixture of 20 kHz plus 25 kHz but not by that of 19 kHz plus 26 kHz, suggesting that cortical responses to missing fundamentals in AI were visualized using flavoprotein fluorescence imaging3. Experience-dependent plasticity in the visual cortex was investigated. After monocular deprivation (MD) of 4 days starting from P28, deprived eye responses were suppressed compared to non-deprived eye responses in the binocular zone, but not in the monocular zone. Imaging faithfully recapitulated a critical period for plasticity with maximal effects of MD observed around P28 and not in adulthood even under urethane anesthesia. These results indicate that transcranial flavoprotein fluorescence imaging is a powerful tool for investigating experience-dependent plasticity in the mouse visual cortex.4. We designed a hemilateral prism goggle for mice. This goggle was attached on the skull of mice during the critical period. The visual cortical responses elicited via the eye with a prism were significantly suppressed compared with those elicited via the contralateral normal eye. However, this suppression was not observed in mice, in which whiskers were trimmed. It was suggested that the visual responses might be suppressed by multimodal sensory mismatching between somatosensory inputs and visual inputs regarding spatial recognition. Less