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.

Inclusion Criteria:

• Healthy male subjects between the ages of 21 and 55 years, inclusive (Healthy is defined as no clinically relevant abnormalities identified by a detailed medical history, full physical examination, including blood pressure and pulse rate measurement, 12 lead ECG and clinical laboratory tests.

Exclusion Criteria:

• Evidence or history of clinically significant hematological, renal, endocrine, pulmonary, gastrointestinal, cardiovascular, hepatic, psychiatric, neurologic, or allergic disease (including drug allergies, but excluding untreated, asymptomatic, seasonal allergies at time of dosing).