Evidence suggests that mGLUR5 availability may play a key role in the biology of mood disorders. This study aimed to investigate the changes in metabotropic glutamate receptor 5 (mGLUR5) availability and clinical symptoms in patients with MDD and bipolar disorder(BD) after two months of vortioxetine treatment. The investigators hypothesized that patients with MDD and BP have abnormal mGluR5 availability in certain brain regions, and baseline mGLUR5 availability can predict prognosis the prognosis of MDD and BD. fMRI and NODDI are also used to evaluate the function or neurite condition at baseline and 8 week

Inclusion Criteria:

• Meet DSM-V criteria for a current depressive episode.
• Being first-episode patients who were medication-naïve;
• Score >17 on 17-item Hamilton Depression Rating Scale (HDRS), score >22 on Montgomery-Asberg Depression Rating Scale (MADRS), and score <6 on Young Mania Rating Scale (YMRS).
• Age 18 to 35.
• Able to give written informed consent.

Exclusion Criteria:

• Have a current or past significant medical, neurological or metabolic disorder or head injury
• Have active, significant suicidal ideation or past suicide attempts
• Have implanted metallic devices or any MR contraindications
• Are women who are pregnant or breastfeeding
• Met DSM-5 criteria for substance use disorder
• Met DSM-5 criteria for any current Axis I diagnosis (except Generalized Anxiety Disorder)
• Are MDD patients present with delusions and/or hallucinations

15 healthy controls, 22 MDD patients, 22 BD patients