Unraveling the Neurobiology of Fear Extinction

1. Unraveling the Neurobiology of Fear Extinction Victoria B. Risbrough, Ph.D. Technology and Innovation for the Prevention & Treatment of PTSD October 31, 2012

2. Outline • Review of Fear Extinction Circuits and Mechanisms • Translational Models of Fear Extinction: • Individual differences in fear extinction in mice to identify biomarkers of Risk • Ongoing prospective study of extinction learning as predictor of risk in Active Duty Marines • Human Model to test potential adjunctive PTSD treatments • Oxytocin Effects on Fear Extinction

3. Mechanisms of PTSD risk and recovery: focus on fear extinction • Although most individuals experience trauma in their lifetime, individuals differ dramatically in how they recover from traumatic events. • One extant hypothesis with some empirical support is that extinction mechanisms are disrupted in PTSD (Milad et al. 2008, Orr et al.2000, Norrholm et al. 2011) PTSD Symptoms Rothbaum and Davis, 2003

4. PTSD patients exhibit reduced vmPFC (“IL”) and increased dACC (“PL”) activation Milad et al. 2009

5. Rodent fear extinction is predictive for extinction treatment efficacy and neural substrates of extinction in humans Milad and Quirk 2002 Walker et al. 2002

6. Animal Fear extinction is predictive for extinction treatment efficacy and neural substrates of extinction in humans Biological Psychiatry 2012 Biological Psychiatry 2008

7. 1. Using Individual Differences in Extinction to Identify Mechanisms of PTSD Risk • PTSD has moderate heritability ~30-50% (True et al. 1993, Stein et al. 2002, Sartor et al. 2012). • Genes identified thus far have relatively small effect sizes: e.g. COMT, DAR2, 5-HTT, FKBP5, CRF-R1 (see Yehuda et al. 2011). • Environmental predictors of risk have larger effect sizes (e.g. past trauma exposure, early life stress/childhood trauma, Mehta and Binder, 2012). • Can we develop a model for non-genomic risk in animals to test hypotheses of epigenetic and other non-genomic risk factors?

8. Mouse Fear Conditioning and extinction Day 1 Day 2 Day 3 Freezing Freezing Freezing

9. Variation in fear extinction in inbred mouse strain: Slow and Fast Recovery Groups Slow Recovery Group=“SR” Fast Recovery Group=“FR” Recall %Extinction Training Acquisition Block (10 CS+)

10. Slow Extinction Learners exhibit other PTSD-like behaviors: ↑avoidance, ↑ startle and ↓ sociality No differences in: Locomotor activity Nociception Sensorimotor gating Perez et al. under submission

11. Neural Substrate for FR/SR phenotype: Cortical Spine Measurement of Prefrontal cortex Sierra-Mercado et al. 2011, Knapska et al. 2012

12. SR mice exhibit reduced IL and increased PL spine density Infralimbic Prelimbic Perez et al. under submission

13. SR extinction deficits reversed by HDAC inhibition: role for epigenetic modification Valproate (100 mg/kg IP) 24 hrs Extinction Training Extinction Recall Block (10 CS+ exposures) Perez et al. under submission

14. Markers of Spine “Maturity” Altered in PrL after Valproate Treatment * * Perez et al. under submission

15. Future Directions • This model has utility to identify epigenetic (and potentially modifiable) factors associated with PTSD-like risk to develop prevention treatments. • Identify the specific HDAC mechanisms (e.g H3, H4) underlying the SR neural and behavioral phenotype and how can they be reversed? • Are there translational blood-based markers we can use to predict SR/FR phenotype before fear conditioning? • Does early-life stress (e.g. maternal care) influence SR/FR phenotype in adulthood? If so we can use this model to develop prevention treatments related to ELS (Wilson et al. 2012, Green et al. 2011). • Can we use a similar strategy to predict mechanisms of PTSD-risk in humans?

16. Ongoing: Marine Resiliency Study - II Neurocognition • Prospective assessment of neurocognitive factors that may predict PTSD risk • 1195 Marines were assessed pre-deployment, post-deployment assessment begins Jan 2013 • Neurocognition using the Penn Battery (Gur et al. 2011) and Fear Learning and Extinction paradigm (Norrholm et al. 2011) • Collecting blood, saliva and urine, and genotyping analysis is ongoing • Testing the hypothesis that extinction performance may contribute to risk/resilience to PTSD Extinction to fear conditioned cues Pooled SEM N=216 CS+ previously paired with aversive air puff to the throat

17. 2. Using the extinction model in healthy human subjects to develop novel treatments: Oxytocin OT/VP receptor expression OT has shown some efficacy to facilitate fear extinction in rodents and reduce amygdala activation and promote social cognition in humans OT/VP receptor expression MacDonald et al. 2010

18. Fear Conditioning and Extinction Methods Acquisition Phase Extinction Phase Recall Phase 8 Trials of Each Cue - CS+, CS-, NA 8 Trials of Each Cue - CS+, CS-, NA 18 Trials of Each Cue - CS+, CS-, NA 0.5 sec 0-5 mA 6 sec 40 ms, 105 dB

19. OT Treatment Time Line (N=20-21/treatment group) Intra Nasal Oxytocin (0 or 24 IU OT) 45 min 24 hrs Recall Phase Acquisition Phase Extinction Phase Split into 2 groups (Drug “A” and Drug “B”) counterbalanced for fear acquisition

20. Pre-Treatment Fear Conditioning * * *

21. OT Inhibits Initial Fear Extinction During Training (Day 1) IN Treatment * # Tx *p<0.05 vs. Placebo #p<0.01 vs. Late Acq

22. OT Increases 24 hr Extinction Recall * Extinction Recall (Day 2) %Extinction Recall=100-(Day 2 CS+/Max Acquisition CS+ on Day 1)*100 Formula per Milad et al. 2009 Acheson et al. under submission

23. Summary and Discussion of OT Treatment Effects • OT inhibited early extinction but facilitated long term (24 hr) extinction recall. • Possible mechanism may be via enhanced coupling of FCX and AMYG (Sripada et al. 2012) or enhanced pFCX LTP (Ninan et al. 2012). • But – In social phobia OT treatment during exposure enhanced only exposure-specific effects on self evaluation, this effect did not generalize to overall social phobia symptoms (Guastella et al. 2008) . • Supports further research of OT as an adjunctive treatment for exposure therapy.

24. Summary • Selecting for high and low extinction performance learning in mice models multiple domains of PTSD-like phenotype: poor extinction, increased anxiety and reduced sociality. • This model shows predictive validity for neural substrate abnormalities linked to PTSD (spine density ratios across PrL/IL), and can be used for future studies of epigenetic and treatment mechanisms of PTSD risk and prevention. • This mouse model can be used to validate/explore biomarkers associated with fear learning and extinction traits in humans, and how those markers relate to PTSD risk (Prospective Study of Fear Learning/Extinction in Active Duty Marines). • Preliminary data in healthy subjects suggests that Oxytocin may facilitate fear extinction recall, this data supports further research of OT treatment as an adjunctive therapy for extinction based therapies in anxiety disorders such as PTSD..

25. Acknowledgements • Individual Differences in Extinction: • Javier Perez, Chelsea Wallace, Jeff Sanders, Susan Powell, Mark Geyer, Chris ReistFunding: NIMHR01074697 • Oxytocin Effects on Fear Extinction: • Dean Acheson, Sofieke de Wilde, Rebecca McKinney, David Feifel Funding: VA CESAMH, DOD • Prospective Study of PTSD in Active Duty Military: Neurocognition: • The MRS-II Team, Dewleen Baker, Mark Geyer, Dean Acheson, Dan O’Connor, Ruben Gur, Jennifer Vasterling, Andrew De La Rosa, Caroline Nievergelt, Elin Olsson, Tina Patel. Funding: Navy BUMED, Marine HQ