Fixed tissues were kept in 0.1 M PB with 1% ProClin 200 in 4 °C until sectioned by vibrating microtome. Soft agar-embedded mouse brains were cut into 30 μm sections and subjected to H & E staining. In brief, brain slices were stained with hematoxylin solution for 15 min and then rinsed in running tap water for 10 min before staining with eosin solution for 5 min. After rinsing with running tap water for 10 min, stained slices were mounted on adhesion microscope slides with resin-based mounting medium. Phase contrasted images were taken by a Zeiss Observer A1 inverted microscope under bright field with transmitted-light.