How does stress cause depression and anxiety ?

a href="http://books.google.com/books?id=lZu56g5-IigC&pg=PA111&lpg=PA111&dq=nmda+receptor+and++pfc&source=web&ots=RDpZpTTvQC&sig=GeAJAN6V6T9ccr9HcmKAYmlIDzY&hl=en&sa=X&oi=book_result&resnum=10&ct=result#PPA121,M1" rel="nofollow"http://books.google.com/books?id=lZu56g5…/a