Plasma oxytocin levels in depression and their correlation with the temperament dimension of reward dependence
Caroline J. Bell1*, Helen Nicholson2, Roger T. Mulder1, Sue E. Luty1, Peter R Joyce1

1 Department of Psychological Medicine, Christchurch School of Medicine and Health Sciences, Christchurch, New Zealand
2 Anatomy and Structural Biology, Health Sciences, Otago School of Medical Sciences, Dunedin, New Zealand

Evidence suggests that the neuropeptide oxytocin plays a role in social affiliation. This behaviour may be related more to personality dimensions than specific psychiatric diagnoses. This study investigated the relationship between plasma oxytocin levels and personality dimensions using the Temperament and Character Inventory (TCI) in 60 outpatients with major depression. The strongest correlation was between plasma oxytocin levels and the temperament dimension of Reward Dependence (0.425 Pearson correlation). This suggested that 17% of the variance in plasma oxytocin levels was explained by the Reward Dependence scores. There was a significant positive correlation between plasma oxytocin levels and the Reward Dependence personality dimension.

Nicknamed the "cuddle chemical" because it renders a warm and fuzzy feeling inside, oxytocin, (a naturally produced hormone) has been shown via brain scan to lower activity in the amygdala - a region which is overactive in social phobics. "We now know for the first time what exactly is going on in the brain when oxytocin increases trust," lead researcher Dr Thomas Baumgartner said, "We found that oxytocin has a very specific effect in social situations. It seems to diminish our fears. Based on our results, we can now conclude that a lack of oxytocin is at least one of the causes for the fear experienced by social phobics."