Stress-induced intracellular trafficking of corticotropin-releasing factor receptors in rat locus coeruleus neurons

Sex and stress interactions in fear synchrony of mouse dyads

Socially coordinated threat responses support the survival of animal groups. Given their distinct social roles, males and females must differ in such coordination. Here, we report such differences during the synchronization of auditory-conditioned freezing in mouse dyads. To study the interaction of emotional states with social cues underlying synchronization, we modulated emotional states with prior stress or modified the social cues by pairing unfamiliar or opposite-sex mice. In same-sex dyads, males exhibited more robust synchrony than females. Stress disrupted male synchrony in a prefrontal cortex-dependent manner but enhanced it in females. Unfamiliarity moderately reduced synchrony in males but not in females. In dyads with opposite-sex partners, fear synchrony was resilient to both stress and unfamiliarity. Decomposing the synchronization process in the same-sex dyads revealed sex-specific behavioral strategies correlated with synchrony magnitude: following partners' state transitions in males and retroacting synchrony-breaking actions in females. Those were altered by stress and unfamiliarity. The opposite-sex dyads exhibited no synchrony-correlated strategy. These findings reveal sex-specific adaptations of socio-emotional integration defining coordinated behavior and suggest that sex-recognition circuits confer resilience to stress and unfamiliarity in opposite-sex dyads.

Hindbrain Adrenergic/Noradrenergic Control of Integrated Endocrine and Autonomic Stress Responses

Hindbrain adrenergic/noradrenergic nuclei facilitate endocrine and autonomic responses to physical and psychological challenges. Neurons that synthesize adrenaline and noradrenaline target hypothalamic structures to modulate endocrine responses while descending spinal projections regulate sympathetic function. Furthermore, these neurons respond to diverse stress-related metabolic, autonomic, and psychosocial challenges. Accordingly, adrenergic and noradrenergic nuclei are integrative hubs that promote physiological adaptation to maintain homeostasis. However, the precise mechanisms through which adrenaline- and noradrenaline-synthesizing neurons sense interoceptive and exteroceptive cues to coordinate physiological responses have yet to be fully elucidated. Additionally, the regulatory role of these cells in the context of chronic stress has received limited attention. This mini-review consolidates reports from preclinical rodent studies on the organization and function of brainstem adrenaline and noradrenaline cells to provide a framework for how these nuclei coordinate endocrine and autonomic physiology. This includes identification of hindbrain adrenaline- and noradrenaline-producing cell groups and their role in stress responding through neurosecretory and autonomic engagement. Although temporally and mechanistically distinct, the endocrine and autonomic stress axes are complementary and interconnected. Therefore, the interplay between brainstem adrenergic/noradrenergic nuclei and peripheral physiological systems is necessary for integrated stress responses and organismal survival.

Hypothalamus and Post-Traumatic Stress Disorder: A Review

Humans have lived in a dynamic environment fraught with potential dangers for thousands of years. While fear and stress were crucial for the survival of our ancestors, today, they are mostly considered harmful factors, threatening both our physical and mental health. Trauma is a highly stressful, often life-threatening event or a series of events, such as sexual assault, war, natural disasters, burns, and car accidents. Trauma can cause pathological metaplasticity, leading to long-lasting behavioral changes and impairing an individual's ability to cope with future challenges. If an individual is vulnerable, a tremendously traumatic event may result in post-traumatic stress disorder (PTSD). The hypothalamus is critical in initiating hormonal responses to stressful stimuli via the hypothalamic-pituitary-adrenal (HPA) axis. Linked to the prefrontal cortex and limbic structures, especially the amygdala and hippocampus, the hypothalamus acts as a central hub, integrating physiological aspects of the stress response. Consequently, the hypothalamic functions have been attributed to the pathophysiology of PTSD. However, apart from the well-known role of the HPA axis, the hypothalamus may also play different roles in the development of PTSD through other pathways, including the hypothalamic-pituitary-thyroid (HPT) and hypothalamic-pituitary-gonadal (HPG) axes, as well as by secreting growth hormone, prolactin, dopamine, and oxytocin. This review aims to summarize the current evidence regarding the neuroendocrine functions of the hypothalamus, which are correlated with the development of PTSD. A better understanding of the role of the hypothalamus in PTSD could help develop better treatments for this debilitating condition.

A review of neuroendocrine immune system abnormalities in IBS based on the brain–gut axis and research progress of acupuncture intervention

Irritable bowel syndrome (IBS) is a common digestive disorder observed in clinics. Current studies suggest that the pathogenesis of the disease is closely related to abnormal brain–gut interactions, hypokinesia, visceral sensory hypersensitivity in the gastrointestinal tract, and alterations in the intestinal microenvironment. However, it is difficult for a single factor to explain the heterogeneity of symptoms. The Rome IV criteria emphasized the holistic biologic-psycho-social model of IBS, suggesting that symptoms of the disease are closely related to neurogastroenterology and various abnormalities in brain–gut interaction. This study comprehensively reviewed the relationship between the brain–gut axis and IBS, the structure of the brain–gut axis, and the relationship between the brain–gut axis and intestinal microenvironment, and discussed the relationship between the abnormal regulation of the nervous system, endocrine system, and immune system and the incidence of IBS on the basis of brain–gut axis. In terms of treatment, acupuncture therapy can regulate the neuroendocrine-immune system of the body and improve the intestinal microenvironment, and it has the advantages of safety, economy, and effectiveness. We study the pathogenesis of IBS from local to global and micro to macro, and review the use of acupuncture to treat the disease as a whole so as to provide new ideas for the treatment of the disease.

Properties and modulation of excitatory inputs to the locus coeruleus

Excitatory inputs drive burst firing of locus coeruleus (LC) noradrenaline (NA) neurons in response to a variety of stimuli. Though a small number of glutamatergic LC afferents have been investigated, the overall landscape of these excitatory inputs is largely unknown. The current study used an optogenetic approach to isolate three glutamatergic afferents: the prefrontal cortex (PFC), lateral hypothalamus (LH) and periaqueductal grey (PAG). AAV5-DIO-ChR2 was injected into each region in male and female CaMKII-Cre mice and the properties of excitatory inputs on LC-NA cells were measured. Notably we found differences among these inputs. First, the pattern of axonal innervation differed between inputs such that LH afferents were concentrated in the posterior portion of the LC-NA somatic region while PFC afferents were denser in the medial dendritic region. Second, basal intrinsic properties varied for afferents, with LH inputs having the highest connectivity and the largest amplitude excitatory postsynaptic currents while PAG inputs had the lowest initial release probability. Third, while orexin and oxytocin had minimal effects on any input, dynorphin strongly inhibited excitatory inputs originating from the LH and PAG, and corticotrophin releasing factor (CRF) selectively inhibited inputs from the PAG. Overall, these results demonstrate that individual afferents to the LC have differing properties, which may contribute to the modularity of the LC and its ability to mediate various behavioural outcomes. KEY POINTS: Excitatory inputs to the locus coeruleus (LC) are important for driving noradrenaline neuron activity and downstream behaviours in response to salient stimuli, but little is known about the functional properties of different glutamate inputs that innervate these neurons We used a virus-mediated optogenetic approach to compare glutamate afferents from the prefrontal cortex (PFC), the lateral hypothalamus (LH) and the periaqueductal grey (PAG). While PFC was predicted to make synaptic inputs, we found that the LH and PAG also drove robust excitatory events in LC noradrenaline neurons. The strength, kinetics, and short-term plasticity of each input differed as did the extent of neuromodulation by both dynorphin and corticotrophin releasing factor. Thus each input displayed a unique set of basal properties and modulation by peptides. This characterization is an important step in deciphering the heterogeneity of the LC.

Targeting the cannabinoid system to counteract the deleterious effects of stress in Alzheimer’s disease

Alzheimer’s disease is a progressive neurodegenerative disorder characterized histologically in postmortem human brains by the presence of dense protein accumulations known as amyloid plaques and tau tangles. Plaques and tangles develop over decades of aberrant protein processing, post-translational modification, and misfolding throughout an individual’s lifetime. We present a foundation of evidence from the literature that suggests chronic stress is associated with increased disease severity in Alzheimer’s patient populations. Taken together with preclinical evidence that chronic stress signaling can precipitate cellular distress, we argue that chronic psychological stress renders select circuits more vulnerable to amyloid- and tau- related abnormalities. We discuss the ongoing investigation of systemic and cellular processes that maintain the integrity of protein homeostasis in health and in degenerative conditions such as Alzheimer’s disease that have revealed multiple potential therapeutic avenues. For example, the endogenous cannabinoid system traverses the central and peripheral neural systems while simultaneously exerting anti-inflammatory influence over the immune response in the brain and throughout the body. Moreover, the cannabinoid system converges on several stress-integrative neuronal circuits and critical regions of the hypothalamic-pituitary-adrenal axis, with the capacity to dampen responses to psychological and cellular stress. Targeting the cannabinoid system by influencing endogenous processes or exogenously stimulating cannabinoid receptors with natural or synthetic cannabis compounds has been identified as a promising route for Alzheimer’s Disease intervention. We build on our foundational framework focusing on the significance of chronic psychological and cellular stress on the development of Alzheimer’s neuropathology by integrating literature on cannabinoid function and dysfunction within Alzheimer’s Disease and conclude with remarks on optimal strategies for treatment potential.

Neuroinflammation as an etiological trigger for depression comorbid with inflammatory bowel disease

Patients with inflammatory bowel disease (IBD) suffer from depression at higher rates than the general population. An etiological trigger of depressive symptoms is theorised to be inflammation within the central nervous system. It is believed that heightened intestinal inflammation and dysfunction of the enteric nervous system (ENS) contribute to impaired intestinal permeability, which facilitates the translocation of intestinal enterotoxins into the blood circulation. Consequently, these may compromise the immunological and physiological functioning of distant non-intestinal tissues such as the brain. In vivo models of colitis provide evidence of increased blood–brain barrier permeability and enhanced central nervous system (CNS) immune activity triggered by intestinal enterotoxins and blood-borne inflammatory mediators. Understanding the immunological, physiological, and structural changes associated with IBD and neuroinflammation may aid in the development of more tailored and suitable pharmaceutical treatment for IBD-associated depression.

The role of the corticotropin-releasing hormone and its receptors in the regulation of stress response

Stress is an essential part of everyday life. The neuropeptide corticotropin-releasing hormone (CRH, also called CRF and corticoliberin) plays a key role in the integration of neuroendocrine, autonomic and behavioral responses to stress. The activation of the hypothalamic-pituitary-adrenal axis (HPA axis) by neurons of the paraventricular hypothalamic nucleus (PVN), the primary site of synthesis CRH, triggers stress reactions. In addition to the hypothalamus, CRH is widespread in extrahypothalamic brain structures, where it functions as a neuromodulator for coordination and interaction between the humoral and behavioral aspects of a stress response. The axons of neurons expressing CRH are directed to various structures of the brain, where the neuropeptide interacts with specific receptors (CRHR1, CRHR2) and can affect various mediator systems that work together to transmit signals to different brain regions to cause many reactions to stress. Moreover, the effect of stress on brain functions varies from behavioral adaptation to increased survival and increased risk of developing mental disorders. Disturbances of the CRH system regulation are directly related to such disorders: mental pathologies (depression, anxiety, addictions), deviations of neuroendocrinological functions, inflammation, as well as the onset and development of neurodegenerative diseases such as Alzheimer’s disease. In addition, the role of CRH as a regulator of the neurons structure in the areas of the developing and mature brain has been established. To date, studies have been conducted in which CRHR1 is a target for antidepressants, which are, in fact, antagonists of this receptor. In this regard, the study of the participation of the CRH system and its receptors in negative effects on hormone-dependent systems, as well as the possibility of preventing them, is a promising task of modern physiological genetics. In this review, attention will be paid to the role of CRH in the regulation of response to stress, as well as to the involvement of extrahypothalamic CRH in pathophysiology and the correction of mental disorders.

Sex differences in anxiety and depression: circuits and mechanisms

Epidemiological sex differences in anxiety disorders and major depression are well characterized. Yet the circuits and mechanisms that contribute to these differences are understudied, because preclinical studies have historically excluded female rodents. This oversight is beginning to be addressed, and recent studies that include male and female rodents are identifying sex differences in neurobiological processes that underlie features of these disorders, including conflict anxiety, fear processing, arousal, social avoidance, learned helplessness and anhedonia. These findings allow us to conceptualize various types of sex differences in the brain, which in turn have broader implications for considering sex as a biological variable. Importantly, comparing the sexes could aid in the discovery of novel therapeutics.

Acute Corticotropin-Releasing Factor Receptor Type 2 Agonism Results in Sustained Symptom Improvement in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Background

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex multi-symptom disease with widespread evidence of disrupted systems. The authors hypothesize that it is caused by the upregulation of the corticotropin-releasing factor receptor type 2 (CRFR2) in the raphé nuclei and limbic system, which impairs the ability to maintain homeostasis. The authors propose utilizing agonist-mediated receptor endocytosis to downregulate CRFR2.

Materials and Methods

This open-label trial tested the safety, tolerability and efficacy of an acute dose of CT38s (a short-lived, CRFR2-selective agonist, with no known off-target activity) in 14 ME/CFS patients. CT38s was subcutaneously-infused at one of four dose-levels (i.e., infusion rates of 0.01, 0.03, 0.06, and 0.20 μg/kg/h), for a maximum of 10.5 h. Effect was measured as the pre-/post-treatment change in the mean 28-day total daily symptom score (TDSS), which aggregated 13 individual patient-reported symptoms.

Results

ME/CFS patients were significantly more sensitive to the transient hemodynamic effects of CRFR2 stimulation than healthy subjects in a prior trial, supporting the hypothesized CRFR2 upregulation. Adverse events were generally mild, resolved without intervention, and difficult to distinguish from ME/CFS symptoms, supporting a CRFR2 role in the disease. The acute dose of CT38s was associated with an improvement in mean TDSS that was sustained (over at least 28 days post-treatment) and correlated with both total exposure and pre-treatment symptom severity. At an infusion rate of 0.03 μg/kg/h, mean TDSS improved by -7.5 ± 1.9 (or -25.7%, p = 0.009), with all monitored symptoms improving.

Conclusion

The trial supports the hypothesis that CRFR2 is upregulated in ME/CFS, and that acute CRFR2 agonism may be a viable treatment approach warranting further study.

Clinical Trial Registration

ClinicalTrials.gov, identifier NCT03613129.

Sex and the noradrenergic system

The central noradrenergic system comprises multiple brainstem nuclei whose cells synthesize and release the catecholamine transmitter norepinephrine (NE). The largest of these nuclei is the pontine locus coeruleus (LC), which innervates the vast majority of the forebrain. NE interacts with a number of pre- and postsynaptically expressed G protein-coupled receptors to affect a wide array of functions, including sensory signal processing, waking and arousal, stress responsiveness, mood, attention, and memory. Given the myriad functions ascribed to the locus coeruleus-noradrenergic (LC-NE) system, it is unsurprising that it is implicated in many disease states, including various mood, cognitive, neuropsychiatric, and neurodegenerative diseases. The LC-NE system is also notably sexually dimorphic with regard to its morphologic and anatomical features as well as how it responds to the peptide transmitter corticotropin releasing hormone (CRH), a major mediator of the central stress response. The sex-biased morphology and signaling that is observed in the LC could then be considered a potential contributor to the differential prevalence of various diseases between men and women. This chapter summarizes the primary differences between the male and female LC, based primarily on preclinical observations and how these disparities may relate to differential diagnoses of several diseases between men and women.

Noradrenergic tone mediates marble burying behavior after chronic stress and ethanol

RATIONALE

Stress plays a major role in the development of alcohol use disorder (AUD)-a history of chronic stress contributes to alcohol misuse, and withdrawal from alcohol elevates stress, perpetuating cycles of problematic drinking. Recent studies have shown that, in male mice, repeated chronic intermittent ethanol (CIE) and stress elevates alcohol use above either manipulation alone and impacts cognitive functions such as behavioral flexibility.

OBJECTIVE

Here, we investigated the impact of CIE and stress on anxiety in both sexes, and whether the norepinephrine (NE) system via locus coeruleus, which is implicated in both stress and alcohol motivation, is involved.

RESULTS

Male and female mice received multiple cycles of CIE and/or repeated forced swim stress (FSS), producing elevated drinking in both sexes. CIE/FSS treatment increased anxiety, which was blocked by treatment with the α1-AR inverse agonist prazosin. In contrast, administration of the corticotropin releasing factor receptor antagonist CP376395 into locus coeruleus did not reduce CIE/FSS-elevated anxiety. We also observed sex differences in behavioral responses to a history of CIE or FSS alone as well as differential behavioral consequences of prazosin treatment.

CONCLUSIONS

These data indicate that NE contributes to the development of anxiety following a history of alcohol and/or stress, and that the influence of both treatment history and NE signaling is sex dependent. These results argue for further investigation of the NE system in relation to disrupted behavior following chronic alcohol and stress, and support the assertion that treatments may differ across sex based on differential neural system engagement.

Corticotropin releasing factor modulates excitatory synaptic transmission

The mammalian brain contains many regions which synthesize and release the hormone and transmitter corticotropin releasing factor. This peptide is a key player in the function of the hypothalamic-pituitary-adrenal axis and has major role in mediating the endocrine limb of the stress response. However, there are several regions outside of the paraventricular nucleus of the hypothalamus which synthesize this peptide in which it has a role more akin to a classical neurotransmitter. A significant body of literature exists in which its role as a transmitter and its cellular effects in many brain regions, as well as how it affects various forms of behavior, is described. However, the receptors which corticotropin releasing factor interacts with in the brain are G-protein coupled receptors, and therefore their activation promotes a multitude of cellular effects. Despite this, comparatively little research has been done to investigate how this peptide affects excitatory synaptic transmission in the brain. This is important because both excitatory and inhibitory regulation of physiology are important extrinsic factors in the operation of neurons which occur in conjunction with their intrinsic properties. By not taking into account how corticotropin releasing factor affects these processes, a complete picture of this peptide's role in brain function is not available. In this chapter, the limited body of research which has explicitly investigated how corticotropin releasing factor affects excitatory synaptic transmission in various brain regions will be explored.

The role of catecholamines in modulating responses to stress: Sex-specific patterns, implications, and therapeutic potential for post-traumatic stress disorder and opiate withdrawal

Emotional arousal is one of several factors that determine the strength of a memory and how efficiently it may be retrieved. The systems at play are multifaceted; on one hand, the dopaminergic mesocorticolimbic system evaluates the rewarding or reinforcing potential of a stimulus, while on the other, the noradrenergic stress response system evaluates the risk of threat, commanding attention, and engaging emotional and physical behavioral responses. Sex-specific patterns in the anatomy and function of the arousal system suggest that sexually divergent therapeutic approaches may be advantageous for neurological disorders involving arousal, learning, and memory. From the lens of the triple network model of psychopathology, we argue that post-traumatic stress disorder and opiate substance use disorder arise from maladaptive learning responses that are perpetuated by hyperarousal of the salience network. We present evidence that catecholamine-modulated learning and stress-responsive circuitry exerts substantial influence over the salience network and its dysfunction in stress-related psychiatric disorders, and between the sexes. We discuss the therapeutic potential of targeting the endogenous cannabinoid system; a ubiquitous neuromodulator that influences learning, memory, and responsivity to stress by influencing catecholamine, excitatory, and inhibitory synaptic transmission. Relevant preclinical data in male and female rodents are integrated with clinical data in men and women in an effort to understand how ideal treatment modalities between the sexes may be different.

Corticotropin-Releasing Factor Receptors in the Locus Coeruleus Modulate the Enhancement of Active Coping Behaviors Induced by Chronic Predator Odor Inoculation in Mice

Stress inoculation has been proved to induce active coping behaviors to subsequent stress. However, the specific neural mechanisms underlying this effect remain unclear. In this study, a chronic and mild predator odor exposure model was established to investigate the effect of predator odor stress inoculation on behaviors in novel predator odor exposure, open field test and forced swimming test (FST), and on the expression of CRF receptors in locus coeruleus (LC) and dorsal raphe nuclei (DRN). The results showed that predator odor stress inoculation increased the active coping of mice under the severe stress environment without changing the stress response to a new predator odor. Meanwhile, in LC, the CRFR1 expression was increased by predator odor stress inoculation. These results suggested that predator odor stress inoculation can be used as an effective training method to improve active response to later severe stress and the function of CRFR1 in LC might be a potential underlying biological mechanism.

Mechanisms of Shared Vulnerability to Post-traumatic Stress Disorder and Substance Use Disorders

Psychoactive substance use is a nearly universal human behavior, but a significant minority of people who use addictive substances will go on to develop an addictive disorder. Similarly, though ~90% of people experience traumatic events in their lifetime, only ~10% ever develop post-traumatic stress disorder (PTSD). Substance use disorders (SUD) and PTSD are highly comorbid, occurring in the same individual far more often than would be predicted by chance given the respective prevalence of each disorder. Some possible reasons that have been proposed for the relationship between PTSD and SUD are self-medication of anxiety with drugs or alcohol, increased exposure to traumatic events due to activities involved in acquiring illegal substances, or addictive substances altering the brain's stress response systems to make users more vulnerable to PTSD. Yet another possibility is that some people have an intrinsic vulnerability that predisposes them to both PTSD and SUD. In this review, we integrate clinical and animal data to explore these possible etiological links between SUD and PTSD, with an emphasis on interactions between dopaminergic, adrenocorticotropic, GABAergic, and glutamatergic neurobehavioral mechanisms that underlie different emotional learning styles.

Regulation of CRF mRNA in the Rat Extended Amygdala Following Chronic Cocaine: Sex Differences and Effect of Delta Opioid Receptor Agonism

BACKGROUND

Cocaine withdrawal activates stress systems. Females are more vulnerable to relapse to cocaine use and more sensitive to withdrawal-induced negative affect. Delta opioid receptors modulate anxiety-like behavior during cocaine withdrawal in rats. This study measured the time course of gene regulation of one of the main stress peptides, corticotropin-releasing factor (CRF), and its type 1 receptor in male and female rats as well as the ability of the delta opioid receptor agonist SNC80 to normalize cocaine withdrawal-induced changes in CRF mRNA.

METHODS

Rats were injected with cocaine or saline 3 times daily for 14 days. Brains were collected 30 minutes, 24 hours, 48 hours, 7 days, and 14 days following the last injection. The paraventricular nucleus of the hypothalamus, central amygdala, and bed nucleus of the stria terminalis were processed for quantitative reverse transcriptase PCR measurement of CRF and CRFR1 mRNA. Additional rats received SNC80 during early cocaine withdrawal, and CRF mRNA was measured in the central amygdala.

RESULTS

CRF mRNA was elevated in the central amygdala at 24 hours and the paraventricular nucleus at 48 hours of cocaine withdrawal in males and females. Significant sex differences in cocaine-induced CRF upregulation were found in the bed nucleus of the stria terminalis at 30 minutes and 24 hours. SNC80 administration attenuated the increase in CRF mRNA in the central amygdala of female rats only.

CONCLUSIONS

CRF mRNA regulation during cocaine withdrawal is sex, time, and brain region dependent. Administration of a delta opioid receptor agonist during early withdrawal may ameliorate stress-related negative affect in females by abrogating the induction of CRF mRNA.

Constitutive Serotonin Transporter Reduction Resembles Maternal Separation with Regard to Stress-Related Gene Expression

Interactive effects between allelic variants of the serotonin transporter (5-HTT) promoter-linked polymorphic region (5-HTTLPR) and stressors on depression symptoms have been documented, as well as questioned, by meta-analyses. Translational models of constitutive 5-htt reduction and experimentally controlled stressors often led to inconsistent behavioral and molecular findings and often did not include females. The present study sought to investigate the effect of 5-htt genotype, maternal separation, and sex on the expression of stress-related candidate genes in the rat hippocampus and frontal cortex. The mRNA expression levels of Avp, Pomc, Crh, Crhbp, Crhr1, Bdnf, Ntrk2, Maoa, Maob, and Comt were assessed in the hippocampus and frontal cortex of 5-htt ^± and 5-htt ^+/+ male and female adult rats exposed, or not, to daily maternal separation for 180 min during the first 2 postnatal weeks. Gene- and brain region-dependent, but sex-independent, interactions between 5-htt genotype and maternal separation were found. Gene expression levels were higher in 5-htt ^+/+ rats not exposed to maternal separation compared with the other experimental groups. Maternal separation and 5-htt ^+/- genotype did not yield additive effects on gene expression. Correlative relationships, mainly positive, were observed within, but not across, brain regions in all groups except in non-maternally separated 5-htt ^+/+ rats. Gene expression patterns in the hippocampus and frontal cortex of rats exposed to maternal separation resembled the ones observed in rats with reduced 5-htt expression regardless of sex. These results suggest that floor effects of 5-htt reduction and maternal separation might explain inconsistent findings in humans and rodents.

Noradrenergic depletion causes sex specific alterations in the endocannabinoid system in the Murine prefrontal cortex

Brain endocannabinoids (eCB), acting primarily via the cannabinoid type 1 receptor (CB1r), are involved in the regulation of many physiological processes, including behavioral responses to stress. A significant neural target of eCB action is the stress-responsive norepinephrine (NE) system, whose dysregulation is implicated in myriad psychiatric and neurodegenerative disorders. Using Western blot analysis, the protein expression levels of a key enzyme in the biosynthesis of the eCB 2-arachidonoylglycerol (2-AG), diacylglycerol lipase-α (DGL-α), and two eCB degrading enzymes monoacylglycerol lipase (MGL) and fatty acid amide hydrolase (FAAH) were examined in a mouse model that lacks the NE-synthesizing enzyme, dopamine β-hydroxylase (DβH-knockout, KO) and in rats treated with N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP-4). In the prefrontal cortex (PFC), DGL-α protein expression was significantly increased in male and female DβH-KO mice (P < 0.05) compared to wild-type (WT) mice. DβH-KO male mice showed significant decreases in FAAH protein expression compared to WT male mice. Consistent with the DβH-KO results, DGL-α protein expression was significantly increased in male DSP-4-treated rats (P < 0.05) when compared to saline-treated controls. MGL and FAAH protein expression levels were significantly increased in male DSP-4 treated rats compared to male saline controls. Finally, we investigated the anatomical distribution of MGL and FAAH in the NE containing axon terminals of the PFC using immunoelectron microscopy. MGL was predominantly within presynaptic terminals while FAAH was localized to postsynaptic sites. These results suggest that the eCB system may be more responsive in males than females under conditions of NE perturbation, thus having potential implications for sex-specific treatment strategies of stress-related psychiatric disorders.

Endocannabinoids, stress signaling, and the locus coeruleus-norepinephrine system

The endocannabinoid (eCB) system has been implicated in a variety of physiological functions due to abundant expression of its receptors and endogenous ligands in the central nervous system. Substantial progress has been made in understanding how the eCB system influences the brain norepinephrine (NE) system, an important neurochemical target in the continued development of new therapies for stress-induced psychiatric disorders. We, and others, have characterized the neuroanatomical, biochemical and pharmacological effects of cannabinoid receptor modulation on brain noradrenergic circuitry and defined how molecular elements of the eCB system are positioned to directly impact the locus coeruleus (LC)-prefrontal cortex pathway, a neural circuit well recognized for contributing to symptoms of hyperarousal, a key pathophysiological feature of stress-related disorders. We also described molecular and electrophysiological properties of LC noradrenergic neurons and NE release in the medial prefrontal cortex under conditions of cannabinoid type 1 receptor deletion. Finally, we identified how stress influences cannabinoid modulation of the coeruleo-cortical pathway. A number of significant findings emerged from these studies that will be summarized in the present review and have important implications for clinical studies targeting the eCB system in the treatment of stress-induced psychiatric disorders.

Neurochemically distinct circuitry regulates locus coeruleus activity during female social stress depending on coping style

Stress-related psychiatric diseases are nearly twice as prevalent in women compared to men. We recently showed in male rats that the resident-intruder model of social stress differentially engages stress-related circuitry that regulates norepinephrine-containing neurons of the locus coeruleus (LC) depending on coping strategy as determined by the latency to assume a defeat posture. Here, we determined whether this social stress had similar effects in female rats. LC afferents were retrogradely labeled with Fluorogold (FG) and rats had one or five daily exposures to an aggressive resident. Sections through the nucleus paragigantocellularis (PGi), a source of enkephalin (ENK) afferents to the LC, and central nucleus of the amygdala (CeA), a source of corticotropin-releasing factor (CRF) afferents to the LC, were processed for immunocytochemical detection of c-fos, a marker of neuronal activity, FG and ENK or CRF. Like male rats, female rats defeated with a relatively short latency (SL) in response to a single resident-intruder exposure and showed significant c-fos activation of LC neurons, PGi-ENK LC afferents, and CeA-CRF-LC afferents. With repeated exposure, some rats exhibited a long latency to defeat (LL). LC neurons and CeA-CRF-LC afferents were activated in SL rats compared to control and LL, whereas PGi-ENK LC afferents were not. Conversely, in LL rats, PGi-ENK LC and CeA-CRF-LC afferents were activated compared to controls but not LC neurons. CRF type 1 receptor (CRF1) and µ-opioid receptor (MOR) expression levels in LC were decreased in LL rats. Finally, electron microscopy showed a relative increase in MOR on the plasma membrane of LL rats and a relative increase in CRF1 on the plasma membrane of SL rats. Together, these results suggest that as is the case for males, social stress engages divergent circuitry to regulate the LC in female rats depending on coping strategy, with a bias towards CRF influence in more subordinate rats and opioid influence in less subordinate rats.

Sex differences in stress reactivity in arousal and attention systems

Women are more likely than men to suffer from psychiatric disorders with hyperarousal symptoms, including posttraumatic stress disorder (PTSD) and major depression. In contrast, women are less likely than men to be diagnosed with schizophrenia and attention deficit hyperactivity disorder (ADHD), which share attentional impairments as a feature. Stressful events exacerbate symptoms of the aforementioned disorders. Thus, researchers are examining whether sex differences in stress responses bias women and men towards different psychopathology. Here we review the preclinical literature suggesting that, compared to males, females are more vulnerable to stress-induced hyperarousal, while they are more resilient to stress-induced attention deficits. Specifically described are sex differences in receptors for the stress neuropeptide, corticotropin-releasing factor (CRF), that render the locus coeruleus arousal system of females more vulnerable to stress and less adaptable to CRF hypersecretion, a condition found in patients with PTSD and depression. Studies on the protective effects of ovarian hormones against CRF-induced deficits in sustained attention are also detailed. Importantly, we highlight how comparing males and females in preclinical studies can lead to the development of novel therapeutics to improve treatments for psychiatric disorders in both women and men.

Sex differences in morphine-induced trafficking of mu-opioid and corticotropin-releasing factor receptors in locus coeruleus neurons

The locus coeruleus (LC)-norepinephrine (NE) system is a key nucleus in which endogenous opioid and stress systems intersect to regulate the stress response. LC neurons of male rats become sensitized to stress following chronic morphine administration. Whether sex dictates this pattern of opioid-induced plasticity has not been demonstrated. Delineating the neurobiological adaptations produced by chronic opioids will enhance our understanding of stress vulnerability in opioid-dependent individuals, and may reveal how stress negatively impacts addiction recovery. In the present study, the effect of chronic morphine on the subcellular distribution of mu-opioid (MOR) and CRF receptors (CRFR) was investigated in the LC of male and female rats using immunoelectron microscopy. Results showed that placebo-treated females exhibited higher MOR and CRFR cytoplasmic distribution ratio when compared to placebo-treated males. Chronic morphine exposure induced a shift in the distribution of MOR immunogold-silver particles from the plasma membrane to the cytoplasm selectively in male LC neurons. Interestingly, chronic morphine exposure induced CRFR recruitment to the plasma membrane of both male and female LC neurons. These findings provide a potential mechanism by which chronic opioid administration increases stress vulnerability in males and females via an increase in surface availability of CRFR in LC neurons. However, our results also support the notion that cellular adaptations to chronic opioids differ across the sexes as redistribution of MOR following morphine exposure was only observed in male LC neurons.

CRF modulation of central monoaminergic function: Implications for sex differences in alcohol drinking and anxiety

Decades of research have described the importance of corticotropin-releasing factor (CRF) signaling in alcohol addiction, as well as in commonly co-expressed neuropsychiatric diseases, including anxiety and mood disorders. However, CRF signaling can also acutely regulate binge alcohol consumption, anxiety, and affect in non-dependent animals, possibly via modulation of central monoaminergic signaling. We hypothesize that basal CRF tone is particularly high in animals and humans with an inherent propensity for high anxiety and alcohol consumption, and thus these individuals are at increased risk for the development of alcohol use disorder and comorbid neuropsychiatric diseases. The current review focuses on extrahypothalamic CRF circuits, particularly those stemming from the bed nucleus of the stria terminalis (BNST), found to play a role in basal phenotypes, and examines whether the intrinsic hyperactivity of these circuits is sufficient to escalate the expression of these behaviors and steepen the trajectory of development of disease states. We focus our efforts on describing CRF modulation of biogenic amine neuron populations that have widespread projections to the forebrain to modulate behaviors, including alcohol and drug intake, stress reactivity, and anxiety. Further, we review the known sex differences and estradiol modulation of these neuron populations and CRF signaling at their synapses to address the question of whether females are more susceptible to the development of comorbid addiction and stress-related neuropsychiatric diseases because of hyperactive extrahypothalamic CRF circuits compared to males.

The Corticotropin-Releasing Factor Family: Physiology of the Stress Response

The physiological stress response is responsible for the maintenance of homeostasis in the presence of real or perceived challenges. In this function, the brain activates adaptive responses that involve numerous neural circuits and effector molecules to adapt to the current and future demands. A maladaptive stress response has been linked to the etiology of a variety of disorders, such as anxiety and mood disorders, eating disorders, and the metabolic syndrome. The neuropeptide corticotropin-releasing factor (CRF) and its relatives, the urocortins 1–3, in concert with their receptors (CRFR1, CRFR2), have emerged as central components of the physiological stress response. This central peptidergic system impinges on a broad spectrum of physiological processes that are the basis for successful adaptation and concomitantly integrate autonomic, neuroendocrine, and behavioral stress responses. This review focuses on the physiology of CRF-related peptides and their cognate receptors with the aim of providing a comprehensive up-to-date overview of the field. We describe the major molecular features covering aspects of gene expression and regulation, structural properties, and molecular interactions, as well as mechanisms of signal transduction and their surveillance. In addition, we discuss the large body of published experimental studies focusing on state-of-the-art genetic approaches with high temporal and spatial precision, which collectively aimed to dissect the contribution of CRF-related ligands and receptors to different levels of the stress response. We discuss the controversies in the field and unravel knowledge gaps that might pave the way for future research directions and open up novel opportunities for therapeutic intervention.

Sex Differences in the Subcellular Distribution of Corticotropin-Releasing Factor Receptor 1 in the Rat Hippocampus following Chronic Immobilization Stress

Corticotropin-releasing factor receptors (CRFR1) contribute to stress-induced adaptations in hippocampal structure and function that can affect learning and memory processes. Our prior studies showed that female rats with elevated estrogens compared to males have more plasmalemmal CRFR1 in CA1 pyramidal cells, suggesting a greater sensitivity to stress. Here, we examined the distribution of hippocampal CRFR1 following chronic immobilization stress (CIS) in female and male rats using immuno-electron microscopy. Without stress, total CRFR1 dendritic levels were higher in females in CA1 and in males in the hilus; moreover, plasmalemmal CRFR1 was elevated in pyramidal cell dendrites in CA1 in females and in CA3 in males. Following CIS, near-plasmalemmal CRFR1 increased in CA1 pyramidal cell dendrites in males but not to levels of control or CIS females. In CA3 and the hilus, CIS decreased cytoplasmic and total CRFR1 in dendrites in males only. These results suggest that in naive rats, CRF could induce a greater activation of CA1 pyramidal cells in females than males. Moreover, after CIS, which leads to even greater sex differences in CRFR1 by trafficking it to different subcellular compartments, CRF could enhance activation of CA1 pyramidal cells in males but to a lesser extent than either unstressed or CIS females. Additionally, CA3 pyramidal cells and inhibitory interneurons in males have heightened sensitivity to CRF, regardless of stress state. These sex differences in CRFR1 distribution and trafficking in the hippocampus may contribute to reported sex differences in hippocampus-dependent learning processes in baseline conditions and following chronic stress.

Stress induced neural reorganization: A conceptual framework linking depression and Alzheimer's disease

Chronic stress is a risk factor for a number of physiological disorders including cardiovascular disease, obesity and gastrointestinal disorders, as well as psychiatric and neurodegenerative disorders. There are a number of underlying molecular and cellular mechanisms altered in the course of chronic stress, which may increase the vulnerability of individuals to develop psychiatric disorders such as depression, and neurodegenerative disorders such as Alzheimer's Disease (AD). This is evident in the influence of stress on large-scale brain networks, including the resting state Default Mode Network (DMN), the effects of stress on neuronal circuitry and architecture, and the cellular and molecular adaptations to stress, which may render individuals with stress related psychiatric disorders more vulnerable to neurodegenerative disease later in life. These alterations include decreased negative feedback inhibition of the hypothalamic pituitary axis (HPA) axis, decreased dendritic arborization and spine density in the prefrontal cortex (PFC) and hippocampus, and the release of proinflammatory cytokines, which may suppress neurogenesis and promote neuronal cell death. Each of these factors are thought to play a role in stress-related psychiatric disease as well as AD, and have been observed in clinical and post-mortem studies of individuals with depression and AD. The goal of the current review is to summarize clinical and preclinical evidence supporting a role for chronic stress as a putative link between neuropsychiatric and neurodegenerative disease. Moreover, we provide a rationale for the importance of taking a medical history of stress-related psychiatric diseases into consideration during clinical trial design, as they may play an important role in the etiology of AD in stratified patient populations.

Persistent Stress-Induced Neuroplastic Changes in the Locus Coeruleus/Norepinephrine System

Neural plasticity plays a critical role in mediating short- and long-term brain responses to environmental stimuli. A major effector of plasticity throughout many regions of the brain is stress. Activation of the locus coeruleus (LC) is a critical step in mediating the neuroendocrine and behavioral limbs of the stress response. During stressor exposure, activation of the hypothalamic-pituitary-adrenal axis promotes release of corticotropin-releasing factor in LC, where its signaling promotes a number of physiological and cellular changes. While the acute effects of stress on LC physiology have been described, its long-term effects are less clear. This review will describe how stress changes LC neuronal physiology, function, and morphology from a genetic, cellular, and neuronal circuitry/transmission perspective. Specifically, we describe morphological changes of LC neurons in response to stressful stimuli and signal transduction pathways underlying them. Also, we will review changes in excitatory glutamatergic synaptic transmission in LC neurons and possible stress-induced modifications of AMPA receptors. This review will also address stress-related behavioral adaptations and specific noradrenergic receptors responsible for them. Finally, we summarize the results of several human studies which suggest a link between stress, altered LC function, and pathogenesis of posttraumatic stress disorder.

Sex differences in stress responses: a critical role for corticotropin-releasing factor

Rates of post-traumatic stress disorder, panic disorder, and major depression are higher in women than in men. Another shared feature of these disorders is that dysregulation of the stress neuropeptide, corticotropin-releasing factor (CRF), is thought to contribute to their pathophysiology. Therefore, sex differences in responses to CRF could contribute to this sex bias in disease prevalence. Here, we review emerging data from non-human animal models that reveal extensive sex differences in CRF functions ranging from its presynaptic regulation to its postsynaptic efficacy. Specifically, detailed are sex differences in the regulation of CRF-containing neurons and the amount of CRF that they produce. We also describe sex differences in CRF receptor expression, distribution, trafficking, and signaling. Finally, we highlight sex differences in the processes that mitigate the effects of CRF. In most cases, the identified sex differences can lead to increased stress sensitivity in females. Thus, the relevance of these differences for the increased risk of depression and anxiety disorders in women compared to men is also discussed.

Female psychopharmacology matters! Towards a sex-specific psychopharmacology

There is increasing recognition that women have a higher prevalence of certain psychiatric illnesses, and a differential treatment response and course of illness compared to men. Additionally, clinicians deal with a number of disorders like premenstrual syndrome, premenstrual dysphoric disorder, and postpartum depression, which affect women specifically and for which treatment and biological pathways are still unclear. In this article we highlight recent research which suggests that different biological mechanisms may underlie sex differences in responsiveness to stress. Sex differences are evident at the receptor level; where the corticotropin-releasing factor receptor shows differential coupling to adaptor proteins in males and females. The neuropeptide oxytocin also shows sex-specific effects in a range of social behaviors. It may act as a biomarker in post-traumatic stress disorder where sex differences are evident. Studies in women using hormonal contraception show that some of these oxytocin-mediated effects are likely influenced by sex hormones. In female rats rapid changes in circulating progesterone levels are associated with exaggerated behavioral responses to mild stress and blunted responses to benzodiazepines that could be prevented by acute treatment with low-dose fluoxetine. Perceived barriers in research on women have hindered progress. The development of a sex-specific psychopharmacology as a basis for translating this type of research into clinical practice is vital to improve treatment outcomes for women.

The Influence of Early Life Experience on Visceral Pain

Pain is the most reported and troublesome symptom of nearly all functional disorders affecting the genitourinary and gastrointestinal organs. Patients with irritable bowel syndrome (IBS), interstitial cystitis/painful bladder syndrome (IC/PBS), vulvodynia, and/or chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS; collectively termed chronic pelvic pain syndromes) report pain severe enough to impact quality of life and often suffer from symptoms of or are diagnosed with more than one of these syndromes. This increased comorbidity between chronic pelvic pain syndromes, and with pain disorders of disparate body regions, as well as with mood disorders, can be influenced by disruptions in the hypothalamic-pituitary-adrenal (HPA) axis, which regulates the response to stress and influences the perception of pain. Experiencing trauma, neglect, or abuse in early life can permanently affect the functioning of the HPA axis. As such, a significant proportion of patients suffering from comorbid chronic pelvic pain syndromes report a history of early life stress or trauma. Here we will report on how these early life experiences influence chronic pelvic pain in patients. We will also discuss various rodent models that have been developed to study this phenomenon to understand the mechanisms underlying HPA axis dysfunction, as well as potential underlying mechanisms connecting these syndromes to one another.

Effect of Deep Brain Stimulation of the ventromedial prefrontal cortex on the noradrenergic system in rats

BACKGROUND

Deep Brain Stimulation (DBS) of the subgenual cingulate cortex (SCC) is a promising therapeutic alternative to treat resistant major depressive disorder. In preclinical studies, DBS of the ventromedial prefrontal cortex (vmPFC, the rodent SCC correlate) provokes an antidepressant-like effect, along with changes in noradrenaline levels at the site of stimulation. Hence, DBS appears to activate the noradrenergic-locus coeruleus (LC) system.

OBJECTIVE/HYPOTHESIS

The aim of this study was to evaluate the effect of vmPFC DBS on the electrical activity of noradrenergic LC neurons, cortical oscillations and coherence between both brain areas in male rats.

METHODS

The antidepressant-like effect of vmPFC DBS was evaluated through the forced swimming test. Tonic and evoked activity of LC neurons, LC activity of alpha2-adrenoceptors, local field potentials from LC and electrocorticogram signals were studied after DBS by electrophysiological recordings in anaesthetized rats. The effect of DBS on tyrosine hydroxylase (TH), noradrenaline transporters (NAT), phosphorylation of the extracellular signal-regulated kinase (ERK) and corticotropin releasing factor (CRF) expression in the LC were measured by western blot assays.

RESULTS

DBS induced an antidepressant-like effect increasing climbing behaviour in the FST that was accompanied by a robust increase of TH expression in the rat LC. The tonic and evoked activity of LC neurons was enhanced by DBS, which impaired alpha2-adrenoceptors activity. DBS also promoted an increase in slow LC oscillations, as well as a shift in LC-cortical coherence.

CONCLUSION

DBS of the vmPFC appears to affect the LC, producing changes that may underlie its antidepressant-like effects.

Sex differences in stress regulation of arousal and cognition

There are sex differences in the prevalence and presentation of many psychiatric disorders. For example, posttraumatic stress disorder (PTSD) and major depression are more common in women than men, and women with these disorders present with more hyperarousal symptoms than men. In contrast, attention deficit hyperactivity disorder (ADHD) and schizophrenia are more common in men than women, and men with these disorders have increased cognitive deficits compared to women. A shared feature of the aforementioned psychiatric disorders is the contribution of stressful events to their onset and/or severity. Here we propose that sex differences in stress responses bias females towards hyperarousal and males towards cognitive deficits. Evidence from clinical and preclinical studies is detailed. We also describe underlying neurobiological mechanisms. For example, sex differences in stress receptor signaling and trafficking in the locus coeruleus-arousal center are detailed. In learning circuits, evidence for sex differences in dendritic morphology is provided. Finally, we describe how evaluating sex-specific mechanisms for responding to stress in female and male rodents can lead to better treatments for stress-related psychiatric disorders.

Sex-biased cellular signaling: molecular basis for sex differences in neuropsychiatric diseases

The recognition that there are fundamental biological sex differences that extend beyond those that define sexual behavior and reproductive function has inspired the drive toward inclusion of both sexes in research design. This is supported by an underlying clinical rationale that studying both sexes is necessary to elucidate pathophysiology and develop treatments for the entire population. However, at a more basic level, sex differences, like genetic differences, can be exploited to better understand biology. Here, we discuss how sex differences at the molecular level of cell signaling and protein trafficking are amplified to create a state of vulnerability that under the right conditions can result in symptoms of neuropsychiatry disease. Although this dialogue focuses on the specific example of corticotropin-releasing factor, the potential for analogous sex differences in signaling and/or trafficking of receptors for other neuromodulators has broad biological and therapeutic implications.

Co-localization of the cannabinoid type 1 receptor with corticotropin-releasing factor-containing afferents in the noradrenergic nucleus locus coeruleus: implications for the cognitive limb of the stress response

The noradrenergic system has been shown to play a key role in the regulation of stress responses, arousal, mood, and emotional states. Corticotropin-releasing factor (CRF) is a primary mediator of stress-induced activation of noradrenergic neurons in the nucleus locus coeruleus (LC). The endocannabinoid (eCB) system also plays a key role in modulating stress responses, acting as an "anti-stress" neuro-mediator. In the present study, we investigated the cellular sites for interactions between the cannabinoid receptor type 1 (CB1r) and CRF in the LC. Immunofluorescence and high-resolution immunoelectron microscopy showed co-localization of CB1r and CRF in both the core and peri-LC areas. Semi-quantitative analysis revealed that 44% (208/468) of CRF-containing axon terminals in the core and 35% (104/294) in the peri-LC expressed CB1r, while 18% (85/468) of CRF-containing axon terminals in the core and 6.5% (19/294) in the peri-LC were presynaptic to CB1r-containing dendrites. In the LC core, CB1r + CRF axon terminals were more frequently of the symmetric (inhibitory) type; while in the peri-LC, a majority were of the asymmetric (excitatory) type. Triple label immunofluorescence results supported the ultrastructural analysis indicating that CB1r + CRF axon terminals contained either gamma amino butyric acid or glutamate. Finally, anterograde transport from the central nucleus of the amygdala revealed that CRF-amygdalar afferents projecting to the LC contain CB1r. Taken together, these results indicate that the eCB system is poised to directly modulate stress-integrative heterogeneous CRF afferents in the LC, some of which arise from limbic sources.

Converging, Synergistic Actions of Multiple Stress Hormones Mediate Enduring Memory Impairments after Acute Simultaneous Stresses

Stress influences memory, an adaptive process crucial for survival. During stress, hippocampal synapses are bathed in a mixture of stress-released molecules, yet it is unknown whether or how these interact to mediate the effects of stress on memory. Here, we demonstrate novel synergistic actions of corticosterone and corticotropin-releasing hormone (CRH) on synaptic physiology and dendritic spine structure that mediate the profound effects of acute concurrent stresses on memory. Spatial memory in mice was impaired enduringly after acute concurrent stresses resulting from loss of synaptic potentiation associated with disrupted structure of synapse-bearing dendritic spines. Combined application of the stress hormones corticosterone and CRH recapitulated the physiological and structural defects provoked by acute stresses. Mechanistically, corticosterone and CRH, via their cognate receptors, acted synergistically on the spine-actin regulator RhoA, promoting its deactivation and degradation, respectively, and destabilizing spines. Accordingly, blocking the receptors of both hormones, but not each alone, rescued memory. Therefore, the synergistic actions of corticosterone and CRH at hippocampal synapses underlie memory impairments after concurrent and perhaps also single, severe acute stresses, with potential implications to spatial memory dysfunction in, for example, posttraumatic stress disorder.

SIGNIFICANCE STATEMENT

Stress influences memory, an adaptive process crucial for survival. During stress, adrenal corticosterone and hippocampal corticotropin-releasing hormone (CRH) permeate memory-forming hippocampal synapses, yet it is unknown whether (and how) these hormones interact to mediate effects of stress. Here, we demonstrate novel synergistic actions of corticosterone and CRH on hippocampal synaptic plasticity and spine structure that mediate the memory-disrupting effects of stress. Combined application of both hormones provoked synaptic function collapse and spine disruption. Mechanistically, corticosterone and CRH synergized at the spine-actin regulator RhoA, promoting its deactivation and degradation, respectively, and destabilizing spines. Notably, blocking both hormones, but not each alone, prevented the enduring memory problems after acute concurrent stresses. Therefore, synergistic actions of corticosterone and CRH underlie enduring memory impairments after concurrent acute stresses, which might be relevant to spatial memory deficits described in posttraumatic stress disorder.

Extended Amygdala to Ventral Tegmental Area Corticotropin-Releasing Factor Circuit Controls Binge Ethanol Intake

BACKGROUND

Corticotropin-releasing factor (CRF) signaling at the CRF₁ receptor (CRF₁R) in the ventral tegmental area (VTA) can modulate ethanol consumption in rodents. However, the effects of binge-like ethanol drinking on this system have not been thoroughly characterized, and little is known about the role of CRF₂R or the CRF neurocircuitry involved.

METHODS

The effects of binge-like ethanol consumption on the VTA CRF system were assessed following drinking-in-the-dark procedures. Intra-VTA infusions of selective CRF₁R and/or CRF₂R compounds were employed to assess the contributions of these receptors in modulating binge-like ethanol consumption (n = 89). To determine the potential role of CRF projections from the bed nucleus of the stria terminalis (BNST) to the VTA, CRF neurons in this circuit were chemogenetically inhibited (n = 32). Binge-induced changes in VTA CRF system protein and messenger RNA were also assessed (n = 58).

RESULTS

Intra-VTA antagonism of CRF₁R and activation of CRF₂R resulted in decreased ethanol intake, which was eliminated by simultaneous blockade of both receptors. Chemogenetic inhibition of local CRF neurons in the VTA did not alter binge-like ethanol drinking, but inhibition of VTA-projecting CRF neurons from the BNST significantly reduced intake.

CONCLUSIONS

We provide novel evidence that 1) blunted binge-like ethanol consumption stemming from CRF₁R blockade requires intact CRF₂R signaling, and CRF₂R activation reduces binge-like drinking; 2) inhibiting VTA-projecting BNST CRF neurons attenuates binge-like drinking; and 3) binge-like ethanol drinking alters protein and messenger RNA associated with the VTA-CRF system. These data suggest that ethanol-induced activation of BNST-to-VTA CRF projections is critical in driving binge-like ethanol intake.

Altered functionality of the corticotrophin-releasing hormone receptor-2 in the hypothalamic paraventricular nucleus of hyperphagic maternally separated rats

Early-life stress induces endocrine and metabolic alterations that increase food intake and overweight in adulthood. The stress response activates the corticotropin-releasing hormone (CRH) and urocortins' (Ucns) system in the hypothalamic paraventricular nucleus (PVN). These peptides induce anorexic effects through CRH-R2 receptor activation; however, chronic stressed animals develop hyperphagia despite of high PVN CRH expression. We analyzed this paradoxical behavior in adult rats subjected to maternal separation (MS) for 180min/daily during post-natal days 2-14, evaluating their body weight gain, food intake, serum corticosterone and vasopressin concentrations, PVN mRNA expression of CRH-R1, CRH-R2, CRH, Ucn2, Ucn3, vasopressin and CRH-R2 protein levels. MS adults increased their feeding, weight gain as well as circulating corticosterone and vasopressin levels, evincing chronic hyperactivity of the stress system. MS induced higher PVN CRH, Ucn2 and CRH-R2 mRNA expression and protein levels of CRH-R2 showed a tendency to decrease in the cellular membrane fraction. An intra-PVN injection of the CRH-R2 antagonist antisauvagine-30 in control adults increased receptor's mRNA expression, mimicking the observed PVN receptor's up-regulation of early-life MS adults. An injection of Ucn-2 directly into the PVN reduced food intake and increased PVN pCREB/CREB ratio in control animals; in contrast, Ucn-2 was unable to reduce food intake and enhance phosphorylated-CREB levels in PVN of MS rats. In conclusion, the chronic hyperactivity of the stress axis and PVN CRH-R2 resistance to Ucn2 effects, supported impaired receptor functionality in MS animals, probably due to its chronic stimulation by CRH or Ucn2, induced by early-life stress.

Corticotropin releasing factor dose-dependently modulates excitatory synaptic transmission in the noradrenergic nucleus locus coeruleus

The noradrenergic nucleus locus coeruleus (LC) is critically involved in the stress response and receives afferent input from a number of corticotropin releasing factor (CRF) containing structures. Several in vivo and in vitro studies in rat have shown that CRF robustly increases the firing rate of LC neurons in a dose-dependent manner. While it is known that these increases are dependent on CRF receptor subtype 1 and mediated by effects of cAMP intracellular signaling cascades on potassium conductance, the impact of CRF on synaptic transmission within LC has not been clarified. In the present study, we used whole-cell patch clamp electrophysiology to assess how varying concentrations of bath-applied CRF affect AMPA-receptor dependent spontaneous excitatory post-synaptic currents (sEPSCs). Compared to vehicle, 10, 25, and 100 nm CRF had no significant effects on any sEPSC parameters. Fifty nanomolar CRF, however, significantly increased sEPSC amplitude, half-width, and charge transfer, while these measures were significantly decreased by 200 nm CRF. These observations suggest that stress may differentially affect ongoing excitatory synaptic transmission in LC depending on how much CRF is released from presynaptic terminals. Combined with the well-documented effects of CRF on membrane properties and spontaneous LC discharge, these observations may help explain how stress and CRF release are able to modulate the signal to noise ratio of LC neurons. These findings have implications for how stress affects the fidelity of signal transmission and information flow through LC and how it might impact norepinephrine release in the CNS.

Distribution of Corticotrophin-Releasing Factor Type 1 Receptor-Like Immunoreactivity in the Rat Pituitary

Corticotrophin-releasing factor (CRF) regulates the hypothalamic-pituitary-adrenal axis response to stress through its type 1 receptor (CRF₁ ) in the corticotrophs of the anterior pituitary. Although CRF₁ mRNA expression has been confirmed in the rat pituitary, the distribution pattern of CRF₁ protein in the pituitary has not been reported. Therefore, we generated an antiserum against the amino acid fragment corresponding to the 177-188 sequence of the first extracellular loop of the rat CRF₁ . Using the antiserum, CRF₁ -like immunoreactivity (CRF₁ -LI) was detected in the anterior lobe cells of the rat pituitary where some of them expressed intense signals. CRF₁ -LI also appeared in the intermediate lobe cells and on the fibre-like elements of the posterior lobe of the pituitary. Dual immunofluorescence labelling showed that corticotrophs exhibited the highest percentage of CRF₁ (male: 27.1 ± 3.0%, female: 18.0 ± 3.0%), followed by lactotrophs (male: 6.7 ± 3.0%, female: 12.1 ± 1.3%), gonadotrophs (male: 2.6 ± 1.0%, female: 7.5 ± 0.5%), thyrotrophs (male: 2.9 ± 0.1%, female: 5.3 ± 1.2%) and somatotrophs (male: 1.1 ± 0.3%, female: 1.2 ± 0.5%). The percentage of CRF₁ -LI-positive cells that were corticotrophs was significantly higher in male rats than in female rats, whereas CRF₁ -LI-positive lactotrophs and gonadotrophs were significantly higher in female rats than in male rats. Almost all of the melanotrophs were positive for CRF₁ in the intermediate lobe (98.9 ± 0.2%). CRF₁ -LI and the percentage of CRF₁ -LI in corticotrophs were decreased in the anterior pituitary, and the distribution patterns were altered from a diffuse to punctate one by adrenalectomy; the changes were restored by treatment with dexamethasone (100 μg/kg bw). These results suggest that CRF₁ is involved in the modulation of the functions of the pituitary; moreover, protein expression and the distribution patterns of CRF₁ are regulated by glucocorticoids in the rat anterior pituitary.

Sex-biased cellular signaling: molecular basis for sex differences in neuropsychiatric diseases

The recognition that there are fundamental biological sex differences that extend beyond those that define sexual behavior and reproductive function has inspired the drive toward inclusion of both sexes in research design. This is supported by an underlying clinical rationale that studying both sexes is necessary to elucidate pathophysiology and develop treatments for the entire population. However, at a more basic level, sex differences, like genetic differences, can be exploited to better understand biology. Here, we discuss how sex differences at the molecular level of cell signaling and protein trafficking are amplified to create a state of vulnerability that under the right conditions can result in symptoms of neuropsychiatry disease. Although this dialogue focuses on the specific example of corticotropin-releasing factor, the potential for analogous sex differences in signaling and/or trafficking of receptors for other neuromodulators has broad biological and therapeutic implications.

Region-specific roles of the corticotropin-releasing factor-urocortin system in stress

Dysregulation of the corticotropin-releasing factor (CRF)-urocortin (UCN) system has been implicated in stress-related psychopathologies such as depression and anxiety. It has been proposed that CRF-CRF receptor type 1 (CRFR1) signalling promotes the stress response and anxiety-like behaviour, whereas UCNs and CRFR2 activation mediate stress recovery and the restoration of homeostasis. Recent findings, however, provide clear evidence that this view is overly simplistic. Instead, a more complex picture has emerged that suggests that there are brain region- and cell type-specific effects of CRFR signalling that are influenced by the individual's prior experience and that shape molecular, cellular and ultimately behavioural responses to stressful challenges.

Episodic Social Stress-Escalated Cocaine Self-Administration: Role of Phasic and Tonic Corticotropin Releasing Factor in the Anterior and Posterior Ventral Tegmental Area

Intermittent social defeat stress escalates later cocaine self-administration. Reward and stress both activate ventral tegmental area (VTA) dopamine neurons, increasing downstream extracellular dopamine concentration in the medial prefrontal cortex and nucleus accumbens. The stress neuropeptide corticotropin releasing factor (CRF) and its receptors (CRF-R1, CRF-R2) are located in the VTA and influence dopaminergic activity. These experiments explore how CRF release and the activation of its receptors within the VTA both during and after stress influence later cocaine self-administration in rats.In vivo microdialysis of CRF in the VTA demonstrated that CRF is phasically released in the posterior VTA (pVTA) during acute defeat, but, with repeated defeat, CRF is recruited into the anterior VTA (aVTA) and CRF tone is increased in both subregions. Intra-VTA antagonism of CRF-R1 in the pVTA and CRF-R2 in the aVTA during each social defeat prevented escalated cocaine self-administration in a 24 h "binge." VTA CRF continues to influence cocaine seeking in stressed animals long after social defeat exposure. Unlike nonstressed controls, previously stressed rats show significant cocaine seeking after 15 d of forced abstinence. Previously stressed rats continue to express elevated CRF tone within the VTA and antagonism of pVTA CRF-R1 or aVTA CRF-R2 reverses cocaine seeking. In conclusion, these experiments demonstrate neuroadaptive changes in tonic and phasic CRF with repeated stress, that CRF release during stress may contribute to later escalated cocaine taking, and that persistently elevated CRF tone in the VTA may drive later cocaine seeking through increased activation of pVTA CRF-R1 and aVTA CRF-R2.

SIGNIFICANCE STATEMENT

Corticotropin releasing factor (CRF) within the ventral tegmental area (VTA) has emerged as a likely candidate molecule underlying the fundamental link between stress history and escalated drug self-administration. However, the nature of CRF release in the VTA during acute and repeated stress, as well as its role in enduring neuroadaptations driving later drug taking and seeking, are poorly understood. These experiments explore how CRF is released and interacts with its receptors in specific regions of the VTA both during and after stress to fuel later escalated cocaine taking and seeking behavior. Understanding these acute and persistent changes to the VTA CRF system may lead to better therapeutic interventions for addiction.

Etiological theories of addiction: A comprehensive update on neurobiological, genetic and behavioural vulnerability

Currently, about 246 million people around the world have used an illicit drug. The reasons for this use are multiple: e.g. to augment the sensation of pleasure or to reduce the withdrawal and other aversive effects of a given substance. This raises the problem of addiction, which remains a disease of modern society. This review offers a comprehensive update of the different theories about the etiology of addictive behaviors with emphasis on the neurobiological, environmental, psychopathological, behavioural and genetic aspects of addictions, discussed from an evolutionary perspective. The main conclusion of this review is that vulnerability to drug addiction suggests an interaction between many brain systems (including the reward, decision-making, serotonergic, oxytocin, interoceptive insula, CRF, norepinephrine, dynorphin/KOR, orexin and vasopressin systems), genetic predisposition, sociocultural context, impulsivity and drugs types. Further advances in biological and psychological science are needed to address the problems of addiction at its roots.

Ascending mechanisms of stress integration: Implications for brainstem regulation of neuroendocrine and behavioral stress responses

In response to stress, defined as a real or perceived threat to homeostasis or well-being, brain systems initiate divergent physiological and behavioral processes that mobilize energy and promote adaptation. The brainstem contains multiple nuclei that engage in autonomic control and reflexive responses to systemic stressors. However, brainstem nuclei also play an important role in neuroendocrine responses to psychogenic stressors mediated by the hypothalamic-pituitary-adrenocortical axis. Further, these nuclei integrate neuroendocrine responses with stress-related behaviors, significantly impacting mood and anxiety. The current review focuses on the prominent brainstem monosynaptic inputs to the endocrine paraventricular hypothalamic nucleus (PVN), including the periaqueductal gray, raphe nuclei, parabrachial nuclei, locus coeruleus, and nucleus of the solitary tract (NTS). The NTS is a particularly intriguing area, as the region contains multiple cell groups that provide neurochemically-distinct inputs to the PVN. Furthermore, the NTS, under regulatory control by glucocorticoid-mediated feedback, integrates affective processes with physiological status to regulate stress responding. Collectively, these brainstem circuits represent an important avenue for delineating interactions between stress and health.