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Nitrous oxide speeds the reduction of distressing intrusive memories in an experimental model of psychological trauma

Published online by Cambridge University Press:  04 March 2016

R. K. Das*
Affiliation:
Clinical Psychopharmacology Unit, UCL, London, UK
A. Tamman
Affiliation:
Clinical Psychopharmacology Unit, UCL, London, UK
V. Nikolova
Affiliation:
Clinical Psychopharmacology Unit, UCL, London, UK
T. P. Freeman
Affiliation:
Clinical Psychopharmacology Unit, UCL, London, UK
J. A. Bisby
Affiliation:
Institute of Cognitive Neuroscience, UCL, London, UK
A. I. Lazzarino
Affiliation:
London School of Hygiene & Tropical Medicine, London, UK Department of Epidemiology and Public Health, UCL, London, UK
S. K. Kamboj*
Affiliation:
Clinical Psychopharmacology Unit, UCL, London, UK
*
*Address for correspondence: Dr R. K. Das, Clinical Psychopharmacology Unit, UCL, 1–19 Torrington Place, London WC1E 7HB, UK. (Email: ravi.das@ucl.ac.uk)
*Address for correspondence: Dr R. K. Das, Clinical Psychopharmacology Unit, UCL, 1–19 Torrington Place, London WC1E 7HB, UK. (Email: ravi.das@ucl.ac.uk)

Abstract

Background

Post-traumatic stress disorder (PTSD) involves maladaptive long-term memory formation which underlies involuntary intrusive thoughts about the trauma. Preventing the development of such maladaptive memory is a key aim in preventing the development of PTSD. We examined whether the N-methyl d-aspartate receptor (NMDAR) antagonist gas nitrous oxide (N2O) could reduce the frequency of intrusive memories by inhibiting NMDAR-dependent memory consolidation in a laboratory analogue of psychological trauma.

Method

Participants were randomized to inhale N2O (N = 25) or medical air (N = 25) after viewing a negatively valenced emotional film clip (‘trauma film’). Participants subsequently completed a daily diary assessing frequency of intrusive thoughts relating to the film clip. A week later, participants completed an explicit memory recall task related to the film.

Results

Post-encoding N2O sped the reduction in intrusive memory frequency, with a significant reduction by the next day in the N2O group compared to 4 days later in the air group. N2O also interacted with post-film dissociation, producing increased intrusion frequency in those who were highly dissociated at baseline. Sleep length and quality the night after viewing the film did not differ between the groups.

Conclusion

N2O speeds the reduction of intrusive analogue trauma memory in a time-dependent manner, consistent with sleep-dependent long-term consolidation disruption. Further research with this drug is warranted to determine its potential to inoculate against enduring effects of psychological trauma; however, caution is also urged in dissociated individuals where N2O may aggravate PTSD-like symptomatology.

Type
Original Articles
Copyright
Copyright © Cambridge University Press 2016 

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