The rodent whisker-barrel cortical system has been a model to reveal somatosensory representation in the brain. Optogenetics would facilitate this with high spatiotemporal resolutions. Recently, we have identified the expression of ChR2 in the mechanoreceptive neurons in the trigeminal ganglion (TG) in one of thy1.2-channelrhodopsin 2 (ChR2)-Venus transgenic rat lines, W-TChR2V4 (Honjoh et al., 2014). Each whisker follicles were also richly innervated by the ChR2-positive nerve endings.
The whiskers were all trimmed and 16 follicles were attached with plastic optic fibers in array of 4x4. Each endings of optic fiber was connected to blue LED, which turned on and off independently by a pulse generated by a computer. Therefore, the whiskers could be stimulated with various spatiotemporal patterns (optogenetic tactile pattern, OTP). The functional magnetic resonance imaging (fMRI) responses of barrel cortex were investigated using OTP under 7T-MRI system.
The whisker photostimulation induced a change of blood oxygenation level-dependent (BOLD) responses in the barrel field of contralateral somatosensory cortex in a manner dependent on time. The response to a single whisker phostimulation was more regional than the simultaneous 16-whisker photostimulation.
It is suggested that the OTP was accompanied with specific spatiotemporal changes of fMRI response. Our OTP, in combination with fMRI, would facilitate to study how the spatiotemporal pattern of the whisker mechanoreception would be represented in the cortex.
All animal procedures were conducted in accordance with the guiding principles of Physiological Society of Japan and NIH.