1. Solomon H. Snyder Department of Neuroscience, Kavli Neuroscience Discovery Institute, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
2. Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
3. National Institute on Drug Abuse + National Institutes of Health/Johns Hopkins University Graduate Partnership Program, Baltimore, MD 21224, USA.
4. Intramural Research Program, Neuronal Circuits and Behavior Unit, National Institute on Drug Abuse, Baltimore, MD 21224, USA.