Neuromelanin-MRI and tobacco smoking in first episode psychosis patients and controls

Tobacco smoking is highly prevalent among patients with psychosis and is associated with worse clinical outcomes. Dopamine functioning is implicated in both psychosis and tobacco use. Neuromelanin-sensitive magnetic resonance imaging (NM-MRI) of the substantia nigra is an emerging imaging technique that provides an indirect marker of dopamine function. Previous studies have shown higher NM-MRI signal in patients with psychosis. However, to date, no NM-MRI studies have examined the effects of tobacco smoking. This pre-registered study investigates the association between tobacco smoking and NM-MRI signal in the substantia nigra-ventral tegmental area (SN-VTA) in first-episode psychosis (FEP) patients and controls. NM-MRI scans from 55 FEP patients and 32 controls were analyzed. Mean contrast ratio (CR) within the SN-VTA was compared using linear regression with smoking status, group, and their interaction, adjusting for age and sex. Voxel-wise analyses within the SN-VTA were performed separately in patients and controls, controlling for age and sex. Exploratorily, analyses were repeated with cigarettes per day as dependent variable. No significant interaction or main effects of smoking status or cigarettes per day were found on mean CR. A group effect showed significantly higher CR in patients versus controls (p = 0.037). Voxel-wise analyses revealed no significant clusters associated with smoking in either group. This study found no evidence that tobacco smoking is associated with altered NM-MRI signal in the SN-VTA in FEP patients or controls. The effects of tobacco do not appear to result in measurable changes in NM accumulation within early-phase or moderately exposed samples.