Exploring the impact of trauma type and extent of exposure on posttraumatic alterations in 5-HT1A expression

Predicting Fear Extinction in Posttraumatic Stress Disorder

Fear extinction is the basis of exposure therapies for posttraumatic stress disorder (PTSD), but half of patients do not improve. Predicting fear extinction in individuals with PTSD may inform personalized exposure therapy development. The participants were 125 trauma-exposed adults (96 female) with a range of PTSD symptoms. Electromyography, electrocardiogram, and skin conductance were recorded at baseline, during dark-enhanced startle, and during fear conditioning and extinction. Using a cross-validated, hold-out sample prediction approach, three penalized regressions and conventional ordinary least squares were trained to predict fear-potentiated startle during extinction using 50 predictor variables (5 clinical, 24 self-reported, and 21 physiological). The predictors, selected by penalized regression algorithms, were included in multivariable regression analyses, while univariate regressions assessed individual predictors. All the penalized regressions outperformed OLS in prediction accuracy and generalizability, as indexed by the lower mean squared error in the training and holdout subsamples. During early extinction, the consistent predictors across all the modeling approaches included dark-enhanced startle, the depersonalization and derealization subscale of the dissociative experiences scale, and the PTSD hyperarousal symptom score. These findings offer novel insights into the modeling approaches and patient characteristics that may reliably predict fear extinction in PTSD. Penalized regression shows promise for identifying symptom-related variables to enhance the predictive modeling accuracy in clinical research.

Impact of Trauma Type on Startle Reactivity to Predictable and Unpredictable Threats

ABSTRACT

Trauma exposure has been repeatedly linked to psychophysiological threat reactivity, although the directionality of this association has been inconsistent. Several factors likely contribute to inconsistent findings including type of trauma and threat paradigm. The present study therefore examined the impact of trauma type on psychophysiological reactivity to predictable (P-) and unpredictable (U-) threat in young adults (N = 112). Participants were classified into three groups: history of interpersonal or noninterpersonal trauma, or no history of trauma. Startle eyeblink potentiation was recorded during a well-validated threat-of-shock paradigm. Results indicated individuals with interpersonal trauma exposure displayed exaggerated startle reactivity to U-threat (only) compared with both other groups. In contrast, individuals with noninterpersonal trauma exhibited blunted startle reactivity to U-threat (only) compared with both other groups. Findings reveal that trauma and threat type influence threat reactivity and that those with a history of interpersonal trauma may uniquely display exaggerated sensitivity to stressors that are uncertain.

Cannabidiol and the corticoraphe circuit in post-traumatic stress disorder

Post-Traumatic Stress Disorder (PTSD), characterized by re-experiencing, avoidance, negative affect, and impaired memory processing, may develop after traumatic events. PTSD is complicated by impaired plasticity and medial prefrontal cortex (mPFC) activity, hyperactivity of the amygdala, and impaired fear extinction. Cannabidiol (CBD) is a promising candidate for treatment due to its multimodal action that enhances plasticity and calms hyperexcitability. CBD’s mechanism in the mPFC of PTSD patients has been explored extensively, but literature on the mechanism in the dorsal raphe nucleus (DRN) is lacking. Following the PRISMA guidelines, we examined current literature regarding CBD in PTSD and overlapping symptomologies to propose a mechanism by which CBD treats PTSD via corticoraphe circuit. Acute CBD inhibits excess 5-HT release from DRN to amygdala and releases anandamide (AEA) onto amygdala inputs. By first reducing amygdala and DRN hyperactivity, CBD begins to ameliorate activity disparity between mPFC and amygdala. Chronic CBD recruits the mPFC, creating harmonious corticoraphe signaling. DRN releases enough 5-HT to ameliorate mPFC hypoactivity, while the mPFC continuously excites DRN 5-HT neurons via glutamate. Meanwhile, AEA regulates corticoraphe activity to stabilize signaling. AEA prevents DRN GABAergic interneurons from inhibiting 5-HT release so the DRN can assist the mPFC in overcoming its hypoactivity. DRN-mediated restoration of mPFC activity underlies CBD’s mechanism on fear extinction and learning of stress coping.

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CBD reduces PTSD symptoms via the DRN and corticoraphe circuit.

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Acute effects of CBD reduce DRN-amygdala excitatory signaling to lessen the activity disparity between amygdala and mPFC.

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Chronic CBD officially resolves mPFC hypoactivity by facilitating 5-HT release from DRN to mPFC.

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CBD-facilitated endocannabinoid signaling stabilizes DRN activity and restores mPFC inhibitory control.

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Chronically administered CBD acts via the corticoraphe circuit to favor fear extinction over fear memory reconsolidation.

Hippocampal and Septal 5-HT1A Receptor Expression in Two Rat Models of Temporal Lobe Epilepsy

Experimental and clinical data suggest an impact of serotonergic signaling on seizure susceptibility and epilepsy-associated psychiatric comorbidities. Previous µPET studies revealed increased binding of the 5-HT_1A receptor ligand [¹⁸F]MPPF in two rat models with spontaneous recurrent seizures. These findings raised the question whether these alterations are due to altered 5-HT_1A receptor expression or a modification of extracellular serotonin concentrations. 5-HT_1A receptor expression rates were quantitatively analyzed in rat brain tissue from an electrical and a chemical post-status epilepticus model. Based on the µPET findings, stereological analysis was focused on hippocampal subregions and the septum. Evaluation of 5-HT_1A receptor expression in the electrical post-status epilepticus model revealed a decreased optical density in hippocampal CA3 region. In all other brain regions of interest, the analysis demonstrated comparable 5-HT_1A receptor expression rates among all experimental groups in the brain regions evaluated. Moreover, 5-HT_1A total receptor volume did not differ between groups. A model-specific correlation was demonstrated between 5-HT_1A receptor expression and selected seizure and behavioral parameters. In conclusion, analysis in post-status epilepticus models in rats argued against widespread and pronounced alterations in 5-HT_1A receptor expression. In view of previous µPET findings, the present data indicate that alterations in in-vivo receptor binding are due to a reduction in extracellular serotonin concentrations rather than changes in receptor density. Correlation analysis points to a possible link between 5-HT_1A receptor expression and ictogenesis, seizure termination and behavioral patterns. However, as these findings proved to be model specific, the relevance needs to be further assessed in future studies focusing on other models and species.

Associations and interactions of the serotonin receptor genes 5-HT1A, 5-HT2A, and childhood trauma with alexithymia in two independent general-population samples

Previous studies suggested that childhood trauma and a disturbed serotonergic neurotransmission are involved in the pathogenesis of alexithymia. Specifically, genetic polymorphisms of the serotonin receptors 5-HT1A and 5-HT2A were found to be associated with alexithymia. However, it is unclear whether these factors show main or interaction effects with childhood trauma on alexithymia. Data from two independent general-population cohorts of the Study of Health in Pomerania (SHIP-Trend: N=3,706, Age: range=20-83, 51.6% female, SHIP-LEGEND: N=2,162, Age: range=20-80, 52.5% female) were used. The Toronto Alexithymia Scale-20 (TAS-20) and the Childhood Trauma Questionnaire (CTQ) were applied. Genotypes of rs6295 of 5-HT1A and rs6311 of 5-HT2A were determined. Ordinary least-squared regression models with robust standard errors were applied to investigate associations of the main and interaction effects of childhood maltreatment and the polymorphisms with alexithymia. Childhood trauma, but none of the investigated polymorphisms showed main effects on alexithymia. However, childhood trauma showed significant CTQ sum score x rs6295 interactions in male subjects in both samples such that the presence of the G-allele diminished the CTQ associated increase in the TAS-20 sum scores. Our results support a strong role of early life stress and interactions with rs6295 on alexithymic personality features at least in male subjects.