GPR158 and Parkinson disease: Although this possibility could not be excluded, it is unlikely based on the following reasons: (1) previous mouse studies have confirmed that OCN’s antianxiety and learning and memory-favoring effects were independent of its metabolic functions (Oury et al., 2013); (2) the OCN concentration in the CSF was much lower in the PD rat model, while its level in the peripheral blood was comparable with that in the control rats, suggesting the involvement of central OCN in PD development is more obvious; and (3) the OCN receptor GPR158 was indeed present in rat brain as revealed in this study.