J Psychiatry Neurosci 2012;37(4):224-30
Lourens J.P. Nonkes, MSc; Maaike de Pooter, BSc; Judith R. Homberg, PhD
Nonkes, de Pooter, Homberg — Donders Institute for Brain, Cognition and Behaviour, Centre for Neuroscience, Department of Cognitive Neuroscience, Radboud University Nijmegen Medical Centre, Nijmegen, the Netherlands
Background: The “biological susceptibility” model posits that some individuals, by genetic predisposition, are highly sensitive to environmental stimuli. Exposure to adverse stimuli leads to negative outcomes, and better outcomes follow favourable stimuli. Recent studies indicate that individuals carrying the low-activity (short; s) variant of the serotonin transporter (5-HTT)-linked polymorphic region (5-HTTLPR) show an enhanced vulnerability to posttraumatic stress disorder (PTSD). Simultaneously, they respond poorly to exposure therapy, the first-line treatment to enhance fear extinction in individuals with PTSD. Given that s-allele carriers also show improved adaptive responding when exposed to positive stimuli, we hypothesized that this trait could be used to offset impaired fear extinction.
Methods: We explored this hypothesis preclinically using wild-type and 5-HTT knockout (5-HTT–/– ) male rats (n = 36) that share behavioural similarities with 5-HTTLPR s-allele carriers. Subsequent to cued fear conditioning, animals were tested for short- (1 and 2 days postconditioning) and long-term (6 days postconditioning) fear extinction in the absence or presence of a secondary “distracting” stimulus predicting the delivery of sucrose pellets.
Results: Introducing a secondary stimulus predicting sucrose pellets that distracts attention away from the fear-predicting stimulus led to a long-lasting improvement of impaired fear extinction in 5-HTT–/– male rats.
Limitations: The contextdependency of the efficacy of the “distraction therapy” was not tested. In addition, it remains to be clarified whether the positive valence of the distracting stimulus is critical for the distraction of attention or whether a neutral and/or novel stimulus can induce similar effects. Finally, although of lesser importance from a therapeutic perspective, underlying mechanisms remain to be elucidated.
Conclusion: These data indicate that positive environmental stimuli can be used to offset heightened responses to negative stimuli, particularly in individuals characterized by inherited 5-HTT downregulation and high sensitivity to environmental stimuli.
Submitted Aug. 29, 2011; Revised Sept. 1, Nov. 23, 29, 2011; Accepted Nov. 30, 2011.
Acknowledgements: We thank Dick Heeren for his technical assistance. This work was funded by The Netherlands Organization for Scientific Research (NWO), grant #86410003, awarded to J.R. Homberg. The NWO had no further role in the design of the study, in the collection, analysis and interpretation of data, in the writing of the report, and in the decision to submit the paper for publication.
Competing interests: None declared for L.J.P. Nonkes and M. de Pooter. As above for J.R. Homberg.
Contributors: L.J.P. Nonkes and J.R. Homberg designed the study. L.J.P. Nonkes and M. de Pooter acquired and analyzed the data. L.J.P. Nonkes wrote the article, which M. de Pooter and J.R. Homberg reviewed. All authors approved its publication.
Correspondence to: J.R. Homberg, Radboud University Nijmegen Medical Centre, Geert Grooteplein 21 (route 126), 6525 EZ Nijmegen, the Netherlands; firstname.lastname@example.org