- Cocaine reward models: conditioned place preference can be established in dopamine- and in serotonin-transporter knockout mice. Sora, I., Wichems, C., Takahashi, N., Li, X.F., Zeng, Z., Revay, R., Lesch, K.P., Murphy, D.L., Uhl, G.R. Proc. Natl. Acad. Sci. U.S.A. (1998)