For immunohistochemistry, mice (5-6 mice/genotype/age-group/treatment) were anesthetized and transcardially perfused with 0.9% NaCl, followed by 4 % paraformaldehyde in phosphate buffer (pH 7.2 at 4°C), the brains and peripheral tissues carefully removed and post-fixed for 2-4 hrs, in 4% paraformaldehyde in phosphate buffer (pH 7.2) and placed in 15% sucrose in the solution of phosphate buffer overnight at 4°C.