How serotonin transporter gene variance affects defensive behaviours along the threat imminence continuum

Rethinking minority stress: A social safety perspective on the health effects of stigma in sexually-diverse and gender-diverse populations

For over two decades, the minority stress model has guided research on the health of sexually-diverse individuals (those who are not exclusively heterosexual) and gender-diverse individuals (those whose gender identity/expression differs from their birth-assigned sex/gender). According to this model, the cumulative stress caused by stigma and social marginalization fosters stress-related health problems. Yet studies linking minority stress to physical health outcomes have yielded mixed results, suggesting that something is missing from our understanding of stigma and health. Social safety may be the missing piece. Social safety refers to reliable social connection, inclusion, and protection, which are core human needs that are imperiled by stigma. The absence of social safety is just as health-consequential for stigmatized individuals as the presence of minority stress, because the chronic threat-vigilance fostered by insufficient safety has negative long-term effects on cognitive, emotional, and immunological functioning, even when exposure to minority stress is low. We argue that insufficient social safety is a primary cause of stigma-related health disparities and a key target for intervention.

Exploring the utility of RDoC in differentiating effectiveness amongst antidepressants: A systematic review using proposed psychometrics as the unit of analysis for the Negative Valence Systems domain

Background

RDoC conceptualises psychopathology as neurobiologically-rooted behavioural psychological “constructs” that span dimensionally from normality to pathology, but its clinical utility remains controversial.

Aim

To explore RDoC’s potential clinical utility by examining antidepressant effectiveness through Negative Valence Systems (NVS) domain constructs.

Method

A systematic review was conducted on Web of Science, MEDLINE, EMBASE and PsycINFO for antidepressant trials that included psychometric instruments assessed by Watson, Stanton & Clark (2017) to represent NVS constructs of Acute Threat, Potential Threat and Loss.

Results

221 citations were identified; 13 were included in qualitative synthesis, none for quantitative analysis. All suffered from significant bias risks. 9 antidepressants were investigated, most within 1 construct, and most were found to be effective. Paroxetine, citalopram and fluvoxamine were found to be effective for Acute Threat, fluoxetine, desvenlafaxine and sertraline for Potential Threat, and sertraline, fluvoxamine, fluoxetine and desvenlafaxine effective for Loss. Nefazodone was found to be ineffective for acute fear.

Conclusion

Preliminary evidence supports RDoC NVS constructs’ clinical utility in assessing antidepressant effectiveness, but lack of discriminant validity between Potential Threat and Loss supports their recombination into a single Distress construct. Finding of effectiveness within “normal” construct levels support the utility of a dimensional approach. Testable hypotheses were generated that can further test RDoC’s clinical utility.

The association between serotonin transporter availability and the neural correlates of fear bradycardia

Reduced expression of the serotonin transporter (5-HTT) is associated with susceptibility to stress-related psychopathology, but the underlying mechanisms remain elusive. We investigated whether an aberrant physiological and neural response to threat underlies this increased vulnerability. In a cross-species approach, we investigated the association between genetically encoded differences in 5-HTT expression and the neural correlates of fear bradycardia, a defensive response linked to vigilance. In both humans and rats, reduced 5-HTT expression was associated with exaggerated bradycardia or bradycardia-associated freezing, reduced activity of the medial prefrontal cortex, and increased threat-induced amygdala-periaqueductal grey connectivity and central amygdala somatostatin neuron activity. We have delineated a previously unknown neurogenetic mechanism underlying individual differences in the expression of anticipatory threat responses, contributing to stress sensitivity.

Susceptibility to stress-related psychopathology is associated with reduced expression of the serotonin transporter (5-HTT), particularly in combination with stress exposure. Aberrant physiological and neuronal responses to threat may underlie this increased vulnerability. Here, implementing a cross-species approach, we investigated the association between 5-HTT expression and the neural correlates of fear bradycardia, a defensive response linked to vigilance and action preparation. We tested this during threat anticipation induced by a well-established fear conditioning paradigm applied in both humans and rodents. In humans, we studied the effect of the common 5-HTT-linked polymorphic region (5-HTTLPR) on bradycardia and neural responses to anticipatory threat during functional magnetic resonance imaging scanning in healthy volunteers (n = 104). Compared with homozygous long-allele carriers, the 5-HTTLPR short-allele carriers displayed an exaggerated bradycardic response to threat, overall reduced activation of the medial prefrontal cortex (mPFC), and increased threat-induced connectivity between the amygdala and periaqueductal gray (PAG), which statistically mediated the effect of the 5-HTTLPR genotype on bradycardia. In parallel, 5-HTT knockout (KO) rats also showed exaggerated threat-related bradycardia and behavioral freezing. Immunohistochemistry indicated overall reduced activity of glutamatergic neurons in the mPFC of KO rats and increased activity of central amygdala somatostatin-positive neurons, putatively projecting to the PAG, which—similarly to the human population—mediated the 5-HTT genotype’s effect on freezing. Moreover, the ventrolateral PAG of KO rats displayed elevated overall activity and increased relative activation of CaMKII-expressing projection neurons. Our results provide a mechanistic explanation for previously reported associations between 5-HTT gene variance and a stress-sensitive phenotype.