Background: The neuroendocrine control of ovulation is orchestrated by neuronal circuits that ultimately drive the release of gonadotropin-releasing hormone (GnRH) from the hypothalamus to trigger the preovulatory surge in luteinizing hormone (LH) secretion. While estrogen feedback signals are determinant in triggering activation of GnRH neurons, through stimulation of afferent kisspeptin neurons in the rostral periventricular area of the third ventricle (RP3V^KISS1 neurons), many neuropeptidergic and classical neurotransmitter systems have been shown to regulate the LH surge. Among these, several lines of evidence indicate that the monoamine neurotransmitter serotonin (5-HT) has an excitatory, permissive, influence over the generation of the surge, via activation of type 2 5-HT (5-HT₂) receptors. The mechanisms through which this occurs, however, are not well understood. We hypothesized that 5-HT exerts its influence on the surge by stimulating RP3V^KISS1 neurons in a 5-HT₂ receptor-dependent manner.

Methods: We tested this using kisspeptin neuron-specific calcium imaging and electrophysiology in brain slices obtained from male and female mice.

Results: We show that exogenous 5-HT reversibly increases the activity of the majority of RP3V^KISS1 neurons. This effect is more prominent in females than in males, is likely mediated directly at RP3V^KISS1 neurons and requires activation of 5-HT₂ receptors. The functional impact of 5-HT on RP3V^KISS1 neurons, however, does not significantly vary during the estrous cycle.

Conclusion: Taken together, these data suggest that 5-HT₂ receptor-mediated stimulation of RP3V^KISS1 neuron activity might be involved in mediating the influence of 5-HT on the preovulatory LH surge.

Introduction: Innate immune response to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection activates multiple interferon stimulated genes (ISGs), including ADAR1 p150 isoform, which edits adenosine (A) residues within double stranded RNAs in both the virus and the host. In addition to its immune role, ADAR editing also serves as a mechanism of dynamic regulation of transcriptome and proteome diversity. While evidence points to changes in ADAR editing during infection, we do not know whether editing targets change over the course of the infection.

Methods: Here, we explored temporal changes in ADAR expression and editing patterns, across three distinct stages of SARS-CoV-2 infection. Furthermore, we examined whether infection-triggered dysregulation in ADAR editing persists or returns to pre-infection states post-viral clearance using publicly available whole blood RNA sequencing samples from forty-five, age-matched individuals. The individuals selected had no documented comorbidities, developed mild COVID-19, and were sampled across three distinct stages of SARS-CoV-2 infection: pre-, mid-, and post-infection.

Results and discussion: Our results demonstrate dynamic changes in ADAR expression and editing across the three stages. We further identified editing sites that were edited only in one of the three stages of infection within genes involved in immune response pathways, specifically, within neutrophil degranulation pathway genes. Our results demonstrate a consistent trend of elevated ADAR expression and reduced overall ADAR editing within each individual mid-infection. Subsequently, post-infection, though ADAR expression returns to pre-infection levels, ADAR editing remains dysregulated in some individuals. Given that dysregulated ADAR editing could be a mechanistic link between viral infections and sequalae, it is possible that persistent dysregulation of ADAR editing in a subset of recovered individuals contributes to the heterogeneity in disease outcomes seen in individuals post-SARS-CoV-2 infection.

The conversion of Adenosine (A) to Inosine (I), by Adenosine Deaminases Acting on RNA or ADARs, is an essential post-transcriptional modification that contributes to proteome diversity and regulation in metazoans including humans. In addition to its transcriptome-regulating role, ADARs also play a major part in immune response to viral infection, where an interferon response activates interferon-stimulated genes, such as ADARp150, in turn dynamically regulating host-virus interactions. A previous report has shown that infection from reoviruses, despite strong activation of ADARp150, does not influence the editing of some of the major known editing targets, while likely editing others, suggesting a potentially nuanced editing pattern that may depend on different factors. However, the results were based on a handful of selected editing sites and did not cover the entire transcriptome. Thus, to determine whether and how reovirus infection specifically affects host ADAR editing patterns, we analyzed a publicly available deep-sequenced RNA-seq dataset, from murine fibroblasts infected with wild-type and mutant reovirus strains that allowed us to examine changes in editing patterns on a transcriptome-wide scale. To the best of our knowledge, this is the first transcriptome-wide report on host editing changes after reovirus infection. Our results demonstrate that reovirus infection induces unique nuanced editing changes in the host, including introducing sites uniquely edited in infected samples. Genes with edited sites are overrepresented in pathways related to immune regulation, cellular signaling, metabolism, and growth. Moreover, a shift in editing targets has also been observed, where the same genes are edited in infection and control conditions but at different sites, or where the editing rate is increased for some and decreased for other differential targets, supporting the hypothesis of dynamic and condition-specific editing by ADARs.

Enhanced signaling of dopamine and/or serotonin during highly arousing situations can be reduced in part by monoamine transporters, such as plasma membrane monoamine transporter (PMAT, Slc29a4). An absence of selective pharmacological inhibitors means genetically modified mice constitutively deficient in PMAT remain the best tool for studying PMAT’s organism-level functional effects. Fear conditioning is a high arousal process. Generalization of fear is evolutionarily advantageous, whereby information learned from one experience is applied to other new but similar encounters. Pathological fear generalization, in contrast, is a core feature of most anxiety disorders. Given our previous findings indicating PMAT function reduces male mice’s context fear and enhances extinction of female mice’s cued fear, we hypothesized PMAT would similarly reduce generalization (i.e., enhance discrimination) of context and cued fear in male and female mice, respectively. Our context and cued fear conditioning experiments in adult PMAT wildtype (+/+) and heterozygous (+/−) male and female mice partially supported our hypotheses. We discovered PMAT facilitates extinction of contextually generalized fear, plus subsequent extinction of context-specific fear, selectively in females. Moreover, when specific fear cues or contexts were temporally presented before cues or contexts that were similar enough to make generalization possible, PMAT enhanced biological sex differences. Growing evidence reports common PMAT polymorphisms elicit measurable effects when PMAT function is reduced. Thus, we suspect future experiments may reveal positive associations between PMAT polymorphisms and risk for anxiety disorder symptoms, particularly in people assigned female at birth. Inclusion of these genetic variations in pharmacogenomic analyses may prove therapeutically beneficial.