Hi, Xilu Jiao: you may need rather low amounts, if you may use the method of J.R. Wisniewski (2009) published in Methods in Molecular Biology (eds M.J. Peirce & R. Wait) Springer Protocols.

Best regards, Toni

Surely it works fine if you have quickly transferred the tissue to appropriate thermal conditions (< -20C at least). I always transfer the fresh tissue immediately to centrifuge tubes onto liquid N2 during brain dissection and then to -80C. Virtually, any piece of brain is enough for running a blot with 25 ug of protein. Particularly, I haven't tried the mPFC though I got good immunodetections (total, Thr34 and Thr75) using only 1/3 of total PFC. Just make sure you are gonna use an appropriated lysis buffer with protease and phosphatase inhibitors if you want to keep the phosphorylation sites intact. Good luck!