Major depressive disorder (MDD) is a debilitating illness characterized by low mood and loss of interest in activities. In MDD, the neurotransmitter norepinephrine is believed to be dysregulated, contributing to the depressive symptoms. The goal of this study was to test norepinephrine transporter availability in patients with MDD in attempt to identify potential associations with clinical symptoms. Previous studies have looked at the norepinephrine transporter in MDD, but not at the correlation between norepinephrine and MDD symptoms. Dr. Sho Moriguchi and his team of researchers recruited participants from two psychiatric hospitals and two clinics in the Chiba, Japan area.
19 participants, with an average age of 40.1 years, meeting the criteria for MDD were recruited to undergo a positron emission tomography scan and a magnetic resonance imaging scan to determine potential differences in norepinephrine transporter availability. Patients had no other history of major medical illness and were free of other psychiatric disorders. A control group of age- and sex-matched participants was used which was free of drug use and somatic, psychological, or neurological disorders. Researchers used the Hamilton Depression Rating Scale and the Beck Depression Inventory-II to determine the severity of patients’ MDD. Participants completed the Trail Making Test and Symbol Digit Modalities Test to give data on visual attention and working memory.
Individuals with MDD showed significantly higher levels of norepinephrine transporter availability in the thalamus (p=0.007) and a sub-region of the prefrontal cortex (p=0.002). Furthermore, the neurotransmitter binding potential values in the thalamus and locus coeruleus were negatively correlated with scores on Trail Making Tests part A for working memory and attention. (p<0.003 and p<0.023 respectively)
Future studies could group participants by the different symptoms of depression they experience and test norepinephrine transporter levels accordingly. This study included participants experiencing melancholic depression, so the results of the study cannot be applied to all individuals affected by MDD. Additionally, future studies could recruit more participants for a longitudinal study that can provide a more widespread, comprehensive understanding of the relation between norepinephrine transporter availability and MDD.
- S. Moriguchi et al., Norepinephrine transporter in major depressive disorder: a PET study. The American Journal of Psychiatry 174, 36-41 (2016). doi: 10.1176/appi.ajp.2016.15101334.
- Image retrieved from: https://commons.wikimedia.org/wiki/File:Dr._Nora_Volkow_with_patient_in_PET_scan.jpg