Are Plasma Oxytocin and Vasopressin Levels Reflective of Amygdala Activation during the Processing of Negative Emotions? A Preliminary Study.

Yuka Kotozaki,Ryoichi Yokoyama,Kosuke Motoki,Ryuta Kawashima,Motoaki Sugiura,Hikaru Takeuchi,Seishu Nakagawa

doi:10.3389/fpsyg.2016.00480

Abstract

Plasma oxytocin (OT) and arginine vasopressin (AVP) are associated with individual differences in emotional responses and behaviors. The amygdala is considered to be an important brain region for regulating emotion-based behavior, with OT and AVP modulating activity in the amygdala during the processing of negative emotions. In particular, increased OT levels may diminish amygdala activation (anxiolytic effects) and enhanced AVP levels may augment amygdala activation (anxiogenic effects) when negative emotions are processed. A growing body of research has shown that the effects of OT and AVP are modulated by sex: the aforementioned anxiolytic effects of OT and the anxiogenic effects of AVP occur in men, but not in women. However, we have little knowledge regarding the biological mechanisms underlying OT and AVP plasma levels or their respective anxiogenic and anxiolytic effects; similarly, little is known about the causes and nature of sex differences related to these neuropeptides and their effects on emotional processing. In the current study, we focused on the neural functions associated with the biological mechanisms underlying such effects. We hypothesized that amygdala activation would correlate with trait plasma OT (anxiolytic effects) and AVP (anxiogenic effects) levels because the amygdala is thought to affect the coordinated release of these neuropeptides following affective experiences. We further hypothesized that the effects would be modulated by sex. We assessed 51 participants (male and female) using a paradigm involving negative emotion in conjunction with functional magnetic resonance imaging and measurements of plasma OT and AVP levels. We determined that increased plasma AVP levels were positively associated with amygdala activation (anxiogenic effects) in men, but not in women. These findings highlight the potential underlying neural mechanisms of plasma AVP levels in men.

Highlights

Emotions are basic human biological features; to survive in everyday life requires the ability to monitor, evaluate, and modify our emotional states, and to adaptively express our emotions
The present study investigated the neural mechanisms of the anxiolytic effects of OT and the anxiogenic effects of arginine vasopressin (AVP) in plasma as well as the sex-based modulation of such effects, focusing on the amygdala
The present study provides the first clear evidence that plasma AVP levels are associated with anxiogenic effects in men, but not in women

Summary

Introduction

Emotions are basic human biological features; to survive in everyday life requires the ability to monitor, evaluate, and modify our emotional states, and to adaptively express our emotions. While OT is involved in sexual reproduction, and AVP affects water retention and vasoconstriction, individual differences in plasma OT and AVP are implicated in emotional behaviors and affective disorders, though there is considerable controversy regarding the relationship between peripheral levels of these neuropeptides and their central availability (MeyerLindenberg et al, 2011). Their concentrations in cerebrospinal fluid (CSF), a global measure of the central release of neuropeptides, are positively correlated with plasma levels in some studies (Bartrons et al, 1992), but not in others (Wu and Keysar, 2007)

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