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. 2016 Dec 6;6(12):e974.
doi: 10.1038/tp.2016.231.

Enhancing Dopaminergic Signaling and Histone Acetylation Promotes Long-Term Rescue of Deficient Fear Extinction

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Free PMC article

Enhancing Dopaminergic Signaling and Histone Acetylation Promotes Long-Term Rescue of Deficient Fear Extinction

N Whittle et al. Transl Psychiatry. .
Free PMC article

Abstract

Extinction-based exposure therapy is used to treat anxiety- and trauma-related disorders; however, there is the need to improve its limited efficacy in individuals with impaired fear extinction learning and to promote greater protection against return-of-fear phenomena. Here, using 129S1/SvImJ mice, which display impaired fear extinction acquisition and extinction consolidation, we revealed that persistent and context-independent rescue of deficient fear extinction in these mice was associated with enhanced expression of dopamine-related genes, such as dopamine D1 (Drd1a) and -D2 (Drd2) receptor genes in the medial prefrontal cortex (mPFC) and amygdala, but not hippocampus. Moreover, enhanced histone acetylation was observed in the promoter of the extinction-regulated Drd2 gene in the mPFC, revealing a potential gene-regulatory mechanism. Although enhancing histone acetylation, via administering the histone deacetylase (HDAC) inhibitor MS-275, does not induce fear reduction during extinction training, it promoted enduring and context-independent rescue of deficient fear extinction consolidation/retrieval once extinction learning was initiated as shown following a mild conditioning protocol. This was associated with enhanced histone acetylation in neurons of the mPFC and amygdala. Finally, as a proof-of-principle, mimicking enhanced dopaminergic signaling by L-dopa treatment rescued deficient fear extinction and co-administration of MS-275 rendered this effect enduring and context-independent. In summary, current data reveal that combining dopaminergic and epigenetic mechanisms is a promising strategy to improve exposure-based behavior therapy in extinction-impaired individuals by initiating the formation of an enduring and context-independent fear-inhibitory memory.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Dietary Zn restriction rescues impaired fear extinction in an enduring and context-independent manner. (a) Scheme illustrating experimental paradigm. Cond., ‘normal' 0.6 mA fear conditioning in context A; Ext., extinction training in context B; ER, extinction retrieval in context B; SR, spontaneous recovery in context B; RN, fear renewal in context C; Ctl, Control diet; ZnR, zinc-restricted diet. (b) Freezing during Cond., Ext., ER, SR and RN in Ctl, ZnR-Ext and ZnR-Exp groups. 0, pre-tone freezing. During fear extinction training (trial blocks), ER, SR and RN individual freezing data are presented as the average freezing during two conditioned stimulus (CS) presentations. n=10 per group. *P<0.05 post hoc testing Ctl-Ext versus ZnR-Ext, #P<0.05 ZnR-Exp versus ZnR-Ext.
Figure 2
Figure 2
Rescue of impaired fear extinction induces a select transcriptional response in the medial prefrontal cortex (mPFC) and amygdala. (a) Scheme illustrating experimental paradigm. Mice were subjected to ‘normal' 0.6 mA fear conditioning (Cond.) in context A and fear extinction (Ext training in context B). All groups were conditioned on control diet (Ctl) before mice were subjected to dietary zinc restriction (ZnR) for 14 days till Ext. (b) Heatmap depicting differentially expressed genes in the mPFC (491) and amygdala (52) determined using microarray analysis between non-extinguishing Ctl diet-fed mice and extinguishing ZnR-fed mice. Each line depicts a differentially regulated gene; each row depicts the gene expression in each animal. Blue and red indicate low and high levels of expression, respectively. (c) Histogram showing the biological process to which the differentially regulated genes belong (orange, number of differentially regulated genes per biological process; green, significance of enrichment).
Figure 3
Figure 3
Rescue of impaired fear extinction enhances expression of genes coding for dopamine D1 (Drd1a) and D2 (Drd2) receptors. (a) Scheme illustrating experimental paradigm for b, c. Cond, ‘normal' 0.6 mA fear conditioning; Ext, extinction training; Exp, fear expression; Ctl, control diet; ZnR, dietary zinc restriction. Expression of dopaminergic genes in the medial prefrontal cortex (mPFC) and amygdala following successful rescue of impaired fear extinction (b) and following fear expression (c). *P<0.05 Ctl versus ZnR, **P<0.01 Ctl versus ZnR. n=3–8 per group. (d) Scheme illustrating experimental paradigm for e. Cond., ‘normal' (0.6 mA) conditioning; ER, extinction retrieval; SR, spontaneous recovery; RN, fear renewal. (e) Lower freezing was observed in L-dopa-treated mice when compared with VEH-treated during Ext. trial blocks 7–8 through to 15–16 and also during ER. n=10 per group. *P<0.05 post hoc testing L-dopa versus VEH. (f) Scheme illustrating experimental paradigm for g. Cond., ‘weak' (0.3 mA) conditioning. (g) Lower freezing was observed in L-dopa-treated mice when compared with VEH-treated mice during ER. n=7–8 per group. *P<0.05 post hoc testing L-dopa versus VEH.
Figure 4
Figure 4
Enhancing histone acetylation promotes enduring and context-independent rescue of newly formed extinction memories. (a) Scheme illustrating experimental paradigm for b, c. Cond., ‘normal' fear conditioning; Exp, fear extinction; Exp, fear expression; Ctl, control diet; ZnR, zinc-restricted diet. n=3–8 per group. (b) Enhanced abundance of acH4 was observed in the promoter region of Drd2 following fear extinction in the medial prefrontal cortex (mPFC). (c) No changes in any group were observed following fear expression. (d) Scheme illustrating experimental paradigm for ep. ER, extinction retrieval; SR, spontaneous recovery; RN, renewal. (e) Freezing was lower in MS-275 administered mice during ER, SR and RN. n=9–10 per group. *P<0.05 post hoc testing MS-275 versus VEH. (f) Representative epifluorescent photomicrograph of a coronal section (Bregma +1.78 mm) stained for acH4 immunoreactivity. IL, infralimbic cortex; PL, prelimbic cortex. Scale bar=500 μm. (g) Representative epifluorescent photomicrographs delineating the cortical layers within the IL. Scale bar=100 μm. (h, i) Enhanced acH4 epifluorescence was observed in NeuN-positive (NeuN+) cell populations following MS-275 administration and following successful fear extinction (CS+) in layer II and in layer III, but not layer V/VI, compared with vehicle-treated counterparts (VEH). **P<0.01 post hoc testing MS-275 versus VEH in conditioned (CS+) groups. n=4–6/group. Scale bar=20 μm. (j) Representative epifluorescent photomicrograph of a coronal section (Bregma −1.56 mm) delineating the basal amygdala region quantified. BA, basal amygdala; Ce, central amygdala; LA, lateral amygdala. Scale bar=250 μm. (k, l) Enhanced acH4 epifluorescence was observed in NeuN-positive nuclei (NeuN+) only successful fear extinction acquisition and MS-275 administration. Scale bar=20 μm. **P<0.01 post hoc testing MS-275 versus VEH in conditioned (CS+) groups. n=4–6/group. (m) Representative epifluorescent photomicrograph of a coronal section (Bregma +1.78 mm) stained for acH4 immunoreactivity. IL, infralimbic cortex; PL, prelimbic cortex. Scale bar=500 μm. (n) Representative epifluorescent photomicrographs delineating the cortical layers within the PL. Scale bar=100 μm. (o,p) Enhanced acH4 epifluorescence was observed in NeuN-positive (NeuN+) cell populations following successful fear extinction (CS+) in mice administered VEH and MS-275 to a similar level in layer II, but not layers II or V/VI, compared to vehicle-treated counterparts (VEH). Scale bar=20 μm. *P<0.05, **P<0.01 post hoc testing MS-275 versus VEH in conditioned (CS+) groups. n=4–6 per group.
Figure 5
Figure 5
Combined treatments that enhance dopaminergic signaling and histone deacetylase inhibition are necessary to rescue impaired fear extinction in an enduring and context-independent manner. (a) Scheme illustrating experimental paradigm. Cond., ‘normal' fear conditioning; Ext., fear extinction; ER, extinction retrieval, SR, spontaneous recovery; RN, fear renewal. (b) During extinction training and compared with VEH/VEH control group, reduced freezing was observed in L-dopa/VEH-treated mice during extinction trial blocks 9–10, 11–12 and 15–16 and in L-dopa/MS-275 during extinction trial blocks 9–10 through to 15–16. During ER reduced freezing was observed in L-dopa/VEH and L-dopa/MS-275 compared with VEH/VEH. L-dopa/MS-275-treated mice exhibited lower freezing compared with VEH/VEH during SR and VEH/VEH and L-dopa/VEH during RN. * VEH/VEH versus L-dopa/VEH, # VEH/VEH versus L-dopa/MS-275, §P<0.05 post hoc testing L-dopa/VEH versus L-dopa/MS-275. n=8–10 per group.

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References

    1. Kessler RC, Berglund P, Demler O, Jin R, Merikangas KR, Walters EE. Lifetime prevalence and age-of-onset distributions of DSM-IV disorders in the National Comorbidity Survey Replication. Arch Gen Psychiatry 2005; 62: 593–602. - PubMed
    1. Kessler RC, Avenevoli S, McLaughlin KA, Green JG, Lakoma MD, Petukhova M et al. Lifetime co-morbidity of DSM-IV disorders in the US National Comorbidity Survey Replication Adolescent Supplement (NCS-A). Psychol Med 2012; 42: 1997–2010. - PMC - PubMed
    1. Wittchen HU, Jacobi F, Rehm J, Gustavsson A, Svensson M, Jonsson B et al. The size and burden of mental disorders and other disorders of the brain in Europe 2010. Eur Neuropsychopharmacol 2011; 21: 655–679. - PubMed
    1. Cuijpers P. Effective therapies or effective mechanisms in treatment guidelines for depression? Depress Anxiety 2013; 30: 1055–1057. - PubMed
    1. Bandelow B, Reitt M, Rover C, Michaelis S, Gorlich Y, Wedekind D. Efficacy of treatments for anxiety disorders: a meta-analysis. Int Clin Psychopharmacol 2015; 30: 183–192. - PubMed

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