This study will be a Proof of Mechanism (POM) study to establish evidence of central pharmacodynamic activity for PF 04455242, and will be a parallel group, randomized, double blind, sponsor open study conducted in healthy male subjects. Once subjects achieve steady state of PF 04455242, they will undergo PF 00345768 (spiradoline) challenge. Data will be analyzed to determine whether PF-04455242 blocks spiradoline induced prolactin release.