Premotor projections from the locus coeruleus and periaqueductal grey are altered in two rat models with inborn differences in emotional behavior.

Emotionally motivated behaviors rely on the coordinated activity of descending neural circuits involved in motor and autonomic functions. Using a pseudorabies (PRV) tract-tracing approach in typically behaving rats, our group previously identified descending premotor, presympathetic, and dual-labeled premotor-presympathetic populations throughout the central rostral-caudal axis. The premotor-presympathetic populations are thought to integrate somatomotor and sympathetic activity. To determine whether these circuits are dysregulated in subjects with altered emotional regulation, subsequent neuroanatomical analyses were performed in male subjects of two distinct genetic models relevant to clinical depression and anxiety: the Wistar Kyoto (WKY) rat and selectively bred Low Novelty Responder (bLR) rat. The present study explored alterations in premotor efferents from locus coeruleus (LC) and subdivisions of the periaqueductal grey (PAG), two areas involved in emotionally motivated behaviors. Compared to Sprague Dawley rats, WKY rats had significantly fewer premotor projections to hindlimb skeletal muscle from the LC and from the dorsomedial (DMPAG), lateral (LPAG), and ventrolateral (VLPAG) subdivisions of PAG. Relative to selectively bred High Novelty Responder (bHR) rats, bLR rats had significantly fewer premotor efferents from LC and dorsolateral PAG (DLPAG). Cumulatively, these results demonstrate that somatomotor circuitry in several brain areas involved in responses to stress and emotional stimuli are altered in rat models with depression-relevant phenotypes. These somatomotor circuit differences could be implicated in motor-related impairments in clinically depressed patients.

Disrupted serotonin system development via early life antidepressant exposure impairs maternal care and increases serotonin receptor expression in adult female offspring.

Manipulating serotonin (5-HT) levels in the developing brain elicits a range of effects on brain function and behavior. For example, early-life exposure to selective 5-HT reuptake inhibitor (SSRI) antidepressants disrupts dorsal raphe function and triggers aberrant adult behaviors such as increased passive stress coping and anhedonia. However, much less is understood about how alterations in 5-HT signaling in early life impact outcomes in female offspring, including critical social functions such as maternal care. The present study shows that early-life SSRI exposure disrupts adult female offspring's maternal behavior. Pregnant/postpartum female Sprague-Dawley rats were treated with the SSRI citalopram in drinking water or provided regular tap water as control. Female offspring were raised to adulthood and mated with treatment-naïve males. Following parturition, we observed maternal behavior during portions of the light and dark phases of postnatal days (P)1-14. Relative to controls, dams with a history of early-life SSRI exposure exhibited decreased maternal care, including diminished arched-back nursing, reduced licking and grooming of pups, and increased behavioral inconsistency. Brains were collected from dams with and without a history of early-life SSRI exposure to measure relative mRNA expression of select 5-HT receptor transcripts (5HTR1A, -1B, -2A, -2C) in regions involved in maternal care. Early-life SSRI exposure augmented expression of 5-HTR1A in the medial preoptic area and 5-HTR1B, 5-HTR2A, and 5-HTR2C in the prefrontal cortex. These results demonstrate that early alterations to 5-HT signaling through SSRI exposure may disrupt nurturing parental behaviors and 5-HT receptor expression in affected female rat offspring.

Resilience to Stress: Lessons from Rodents about Nature versus Nurture.

Individual differences in human temperament influence how we respond to stress and can confer vulnerability (or resilience) to emotional disorders. For example, high levels of behavioral inhibition in children predict increased risk of mood and anxiety disorders in later life. The biological underpinnings of temperament are unknown, although improved understanding can offer insight into the pathogenesis of emotional disorders. Our laboratory has used a rat model of temperamental differences to study neurodevelopmental factors that lead to a highly inhibited, stress vulnerable phenotype. Selective breeding for high versus low behavioral response to novelty created two rat strains that exhibit dramatic behavior differences over multiple domains relevant to emotional disorders. Low novelty responder (bLR) rats exhibit high levels of behavioral inhibition, passive stress coping, anhedonia, decreased sociability and vulnerability to chronic stress compared to high novelty responders (bHRs). On the other hand, bHRs exhibit high levels of behavioral dis-inhibition, active coping, and aggression. This review article summarizes our work with the bHR/bLR model showing the developmental emergence of the bHR/bLR phenotypes, the role the environment plays in shaping it, and the involvement of epigenetic processes such as DNA methylation that mediate differences in emotionality and stress reactivity.

Modeling heritability of temperamental differences, stress reactivity, and risk for anxiety and depression: Relevance to research domain criteria (RDoC).

Animal models provide important tools to study biological and environmental factors that shape brain function and behavior. These models can be effectively leveraged by drawing on concepts from the National Institute of Mental Health Research Domain Criteria (RDoC) Initiative, which aims to delineate molecular pathways and neural circuits that underpin behavioral anomalies that transcend psychiatric conditions. To study factors that contribute to individual differences in emotionality and stress reactivity, our laboratory utilized Sprague-Dawley rats that were selectively bred for differences in novelty exploration. Selective breeding for low versus high locomotor response to novelty produced rat lines that differ in behavioral domains relevant to anxiety and depression, particularly the RDoC Negative Valence domains, including acute threat, potential threat, and loss. Bred Low Novelty Responder (LR) rats, relative to their High Responder (HR) counterparts, display high levels of behavioral inhibition, conditioned and unconditioned fear, avoidance, passive stress coping, anhedonia, and psychomotor retardation. The HR/LR traits are heritable, emerge in the first weeks of life, and appear to be driven by alterations in the developing amygdala and hippocampus. Epigenomic and transcriptomic profiling in the developing and adult HR/LR brain suggest that DNA methylation and microRNAs, as well as differences in monoaminergic transmission (dopamine and serotonin in particular), contribute to their distinct behavioral phenotypes. This work exemplifies ways that animal models such as the HR/LR rats can be effectively used to study neural and molecular factors driving emotional behavior, which may pave the way toward improved understanding the neurobiological mechanisms involved in emotional disorders.

Perinatal SSRI Exposure Disrupts G Protein-coupled Receptor BAI3 in Developing Dentate Gyrus and Adult Emotional Behavior: Relevance to Psychiatric Disorders.

Selective serotonin reuptake inhibitor (SSRI) antidepressants are widely prescribed to pregnant women suffering with depression, although the long-term impact of these medications on exposed offspring are poorly understood. Perinatal SSRI exposure alters human offspring's neurodevelopment and increases risk for psychiatric illness in later life. Rodent studies suggest that perinatal SSRI-induced behavioral abnormalities are driven by changes in the serotonin system as well as epigenetic and transcriptomic changes in the developing hippocampus. A major gene altered by perinatal SSRI exposure is the G-protein coupled receptor Brain Angiogenesis Inhibitor 3 (BAI3). Our present study shows that perinatal exposure to the SSRI citalopram increases mRNA expression of Bai3 and related molecules (including its C1ql ligands) in the early postnatal dentate gyrus of male and female offspring. Transient Bai3 mRNA knockdown in perinatal SSRI-exposed dentate gyrus lessened behavioral consequences of perinatal SSRI exposure, leading to increased active stress coping. To determine translational implications of this work, we examined expression of BAI3 and related molecules in hippocampus and prefrontal cortex from patients that suffered with depression or schizophrenia relative to healthy control subjects. We found sex- and region-specific changes in mRNA expression of BAI3 and its ligands C1QL2 and C1QL3 in men and women with a history of psychiatric disorders compared to healthy controls. Together these results suggest that abnormal BAI3 signaling may contribute to molecular mechanisms that drive adverse effects of perinatal SSRI exposure, and show evidence for alterations of BAI3 signaling in the hippocampus of patients that suffer depression and schizophrenia.

Neonatal resource scarcity alters maternal care and impacts offspring core temperature and growth in rats.

Stressful experiences during childhood, including poverty and inconsistent parental care, can enhance vulnerability for worsened physical and mental health outcomes in adulthood. Using Sprague Dawley rats, the present study explored the impact of limited resource availability on maternal behavior and physiological and emotional behavior outcomes in the offspring. Early life adversity was induced by incorporating aspects of the limited bedding and nesting and scarcity models, wherein limited resource availability has previously been shown to provoke unpredictable or adverse maternal care respectively. In our hands, neonatal limited bedding (NLB) stress during postnatal days (P)2-9 altered maternal care, augmenting pup-directed behaviors and reducing self-directed behaviors, and modestly increased the frequency of transitions between discrete behaviors across consecutive timed observations. NLB-exposed pups had lower core body temperatures immediately following the stressful manipulation and exhibited decreased body weight gain across development. However, NLB exposure did not impact adult offspring's social or emotional behavior outcomes in the three-chamber social interaction, novelty-suppressed feeding, splash, or forced swim tests. These findings add to the literature demonstrating that early life adversity impacts maternal care in rodents and can disrupt certain metabolic and thermoregulatory outcomes in the offspring.

Inborn differences in emotional behavior coincide with alterations in hypothalamic paraventricular motor projections.

Integrated behavioral responses to emotionally salient stimuli require the concomitant activation of descending neural circuits that integrate physiological, affective, and motor responses to stress. Our previous work interrogated descending circuits in the brainstem and spinal cord that project to motor and sympathetic targets. The hypothalamic paraventricular nucleus (PVN), a key node of this circuitry, integrates multiple motor and sympathetic responses activated by stress. The present study sought to determine whether descending projections from the PVN to targets in muscle and adrenal gland are differentially organized in rats with inborn differences in emotionality and stress responsivity. We utilized retrograde transsynaptic tract-tracing with unique pseudorabies virus (PRV) recombinants that were injected into sympathectomized gastrocnemius muscle and adrenal gland in two rat models featuring inborn differences in emotional behavior. Our tract-tracing results revealed a significant decrease in the number of PVN neurons with poly-synaptic projections to the gastrocnemius in male Wistar Kyoto [WKY] rats (versus Sprague Dawley rats) and selectively bred Low Novelty Responder [bLR] rats (versus selectively bred High Novelty Responder [bHR] rats). These neuroanatomical differences mirrored behavioral observations showing that both WKY and bLR rats display marked inhibition of emotional motor responses in a variety of settings relative to their respective controls. Our findings suggest that, in male rodents, PVN poly-synaptic projections to skeletal muscle may regulate emotional motor and coping responses to stress. More broadly, perturbations in PVN motor circuitry may play a role in mediating psychomotor disturbances observed in depression or anxiety-related disorders.

Sex differences in the hypothalamic-pituitary-adrenal axis response following a single or multiple days of sleep restriction.

One in three adults reports experiencing inadequate or disrupted sleep throughout the night, with the incidence being higher in women than in men. Disturbances in nightly sleep result in physiological alterations that contribute to a number of disorders. Poor sleep quality is believed to contribute to the pathogenesis of these disorders through interactions with the hypothalamic-pituitary-adrenal (HPA) axis. The present study investigated the effect of one and three days of restricted sleep on HPA axis reactivity. Male and female C57BL/6J (n = 8/group) mice were sleep-deprived for a 20 h period for one day or three consecutive days using the modified multiple platform method, and then subjected to acute restraint stress. In response to sleep restriction, males showed blunted restraint-induced rises in CORT relative to controls. After three days of restricted sleep, females showed a similar attenuation in restraint-induced CORT. However, this effect was ablated after a single day of sleep restriction. Analyses of gene expression revealed significant elevations in the expression of pituitary HPA axis regulatory genes proopiomelanocortin and corticotropin releasing factor receptor 1 in both sexes following sleep restriction. In males, but not females, adrenal mRNA expression of 11ß-hydroxylase and melanocortin receptor 2 were also increased. Altogether, these data suggest several possible mechanisms are involved in the HPA axis dysregulation following sleep restriction, and that there are sex differences in how the HPA axis responds to sleep loss.Lay summarySleep restriction alters the stress response differently in males and females following varying nights of sleep restriction. These alterations are accompanied by changes in gene expression in the pituitary and adrenal glands.

Sleep Deprivation Alters the Pituitary Stress Transcriptome in Male and Female Mice.

Poor sleep hygiene is a growing problem, with detrimental effects on many biological systems. The pituitary gland plays a crucial role in the regulation of sleep and the stress response, and its dysfunction leads to sleep-related disorders. However, the interaction between these critical functions remains unclear. Thus, we performed a comparative, whole-transcriptome, analysis to identify stress-induced genes and relevant pathways that may be affected by sleep deprivation. One day following 12 h of Paradoxical Sleep Deprivation (PSD), mice were restrained for 20 min. Gene expression changes in the pituitary were assessed via RNA-Seq and Gene Ontology in PSD and/or restrained groups compared to controls. We show that restraint triggers transcriptional responses involved in hormone secretion, the glucocorticoid response, and apoptosis in both sexes, with 285 differentially expressed genes in females and 93 in males. When PSD preceded restraint stress, the numbers of differentially expressed genes increased to 613 in females and 580 in males. The pituitary transcriptome of restraint+PSD animals was enriched for microglia and macrophage proliferation, cellular response to corticosteroids, and apoptosis, among others. Finally, we identify sex-specific differences in restraint-induced genes following PSD. These findings provide genetic targets to consider when studying sleep and the response to stress.

Perinatal exposure to the SSRI paroxetine alters the methylome landscape of the developing dentate gyrus.

Evidence in humans and rodents suggests that perinatal exposure to selective serotonin reuptake inhibitor (SSRI) antidepressants can have serious long-term consequences in offspring exposed in utero or infancy via breast milk. In spite of this, there is limited knowledge of how perinatal SSRI exposure impacts brain development and adult behaviour. Children exposed to SSRIs in utero exhibit increased internalizing behaviour and abnormal social behaviour between the ages of 3 and 6, and increased risk of depression in adolescence; however, the neurobiological changes underlying this behaviour are poorly understood. In rodents, perinatal SSRI exposure perturbs hippocampal gene expression and alters adult emotional behaviour (including increased depression-like behaviour). The present study demonstrates that perinatal exposure to the SSRI paroxetine leads to DNA hypomethylation and reduces DNA methyltransferase 3a (Dnmt3a) mRNA expression in the hippocampus during the second and third weeks of life. Next-generation sequencing identified numerous differentially methylated genomic regions, including altered methylation and transcription of several dendritogenesis-related genes. We then tested the hypothesis that transiently decreasing Dnmt3a expression in the early postnatal hippocampus would mimic the behavioural effects of perinatal SSRI exposure. We found that siRNA-mediated knockdown of Dnmt3a in the dentate gyrus during the second to third week of life produced greater depression-like behaviour in adult female (but not male) offspring, akin to the behavioural consequences of perinatal SSRI exposure. Overall, these data suggest that perinatal SSRI exposure may increase depression-like behaviours, at least in part, through reduced Dnmt3a expression in the developing hippocampus.