Price, R.B., Shungu, D.C., Mao, X., Nestadt, P., Kelly, C., Collins, K.A., Murrough, J.W., Charney, D.S. and Mathew, S.J. (2009) Amino acid neurotransmitters assessed by proton magnetic resonance spectroscopy: Relationship to treatment resistance in major depressive disorder. Biological Psychiatry, 65, 792-800.