Mineralocorticoid receptors in the medial prefrontal cortex and hippocampus mediate rats' unconditioned fear behaviour

The Interaction of Vasopressin with Hormones of the Hypothalamo-Pituitary-Adrenal Axis: The Significance for Therapeutic Strategies in Cardiovascular and Metabolic Diseases

A large body of evidence indicates that vasopressin (AVP) and steroid hormones are frequently secreted together and closely cooperate in the regulation of blood pressure, metabolism, water-electrolyte balance, and behavior, thereby securing survival and the comfort of life. Vasopressin cooperates with hormones of the hypothalamo-pituitary-adrenal axis (HPA) at several levels through regulation of the release of corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH), and multiple steroid hormones, as well as through interactions with steroids in the target organs. These interactions are facilitated by positive and negative feedback between specific components of the HPA. Altogether, AVP and the HPA cooperate closely as a coordinated functional AVP-HPA system. It has been shown that cooperation between AVP and steroid hormones may be affected by cellular stress combined with hypoxia, and by metabolic, cardiovascular, and respiratory disorders; neurogenic stress; and inflammation. Growing evidence indicates that central and peripheral interactions between AVP and steroid hormones are reprogrammed in cardiovascular and metabolic diseases and that these rearrangements exert either beneficial or harmful effects. The present review highlights specific mechanisms of the interactions between AVP and steroids at cellular and systemic levels and analyses the consequences of the inappropriate cooperation of various components of the AVP-HPA system for the pathogenesis of cardiovascular and metabolic diseases.

In vivo synaptic potency, short-term and long-term plasticity at the hippocampal Schaffer collateral-CA1 synapses: Role of different light-dark cycles in male rats

The changes in the light-dark(L/D) cycle could modify cellular mechanisms in some brain regions. The present study compared the effects of various L/D cycles on invivo synaptic potency, short-term and long-term plasticity in the hippocampal CA1 area, adrenal glands weight(AGWs), corticosterone (CORT) levels, and body weight differences(BWD) in male rats. Male rats were assigned into different L/D cycle groups: L4/D20, L8/D16, L12/D12(control), L16/D8, and L20/D4. The slope, amplitude, and the area under curve(AUC) related to the field excitatory postsynaptic potentials(fEPSPs) were assessed, using the input-output(I/O) functions, paired-pulse(PP) responses at different interpulse intervals, and after the induction of long-term potentiation(LTP) in the hippocampal CA1 area. Also, the CORT levels, AGWs, and BWDs were measured in all groups. The slope, amplitude, and AUC of fEPSP in the I/O functions, all three phases of PP, before and after the LTP induction, were significantly decreased in all experimental groups, especially in the L20/D4 and L4/D20 groups. As such, the CORT levels and AGWs were significantly increased in all experimental groups, especially in the L20/D4 group. Overall, the uncommon L/D cycles (minimum and particularly maximum durations of light) significantly reduced the cellular mechanism of learning and memory. Also, downtrends were observed in synaptic potency, as well as short-term and long-term plasticity. The changes in PP with high interpulse intervals, or activity of GABAB receptors, were more significant than the changes in other PP phases with different L/D durations. Additionally, the CORT levels, adrenal glands, and body weight gain occurred time-independently concerning different L/D lengths.

From Ligands to Behavioral Outcomes: Understanding the Role of Mineralocorticoid Receptors in Brain Function

Stress is a normal response to situational pressures or demands. Exposure to stress activates the hypothalamic-pituitary-adrenal (HPA) axis and leads to the release of corticosteroids, which act in the brain via two distinct receptors: mineralocorticoid receptors (MR) and glucocorticoid receptors (GR). Persistent HPA axis overactivation or dysregulation can disrupt an individual's homeostasis, thereby contributing to an increased risk for mental illness. On the other hand, successful coping with stressful events involves adaptive and cognitive processes in the brain that render individuals more resilient to similar stressors in the future. Here we review the role of the MR in these processes, starting with an overview of the physiological structure, ligand binding, and expression of MR, and further summarizing its role in the brain, its relevance to psychiatric disorders, and related rodent studies. Given the central role of MR in cognitive and emotional functioning, and its importance as a target for promoting resilience, future research should investigate how MR modulation can be used to alleviate disturbances in emotion and behavior, as well as cognitive impairment, in patients with stress-related psychiatric disorders.

The infralimbic mineralocorticoid blockage prevents the stress-induced impairment of aversive memory extinction in rats

Individuals deal with adversity and return to a normal lifestyle when adversity ends. Nevertheless, in specific cases, traumas may be preceded by memory distortions in stress-related malaises, and memory extinction impairment is strictly associated with the symptoms of post-traumatic stress disorder. Glucocorticoids (GCs), the central stress mediator, target mineralocorticoid (MR) and glucocorticoid (GR) receptors and coordinate stress responses. Despite MRs being present in brain regions essential to cognition, emotions, and initial stress processing, such as the medial prefrontal cortex (mPFC), most studies attempt to elucidate the stress-induced deleterious actions of GCs via GR. Therefore, it is necessary to understand the relationship between stress, infralimbic mPFC (IL), and memory and how MR-mediated intracellular signaling influences this relationship and modulates memory extinction. We observed that acutely restraint-stressed male Wistar rats showed high corticosterone (CORT) levels, and previous intra-IL-spironolactone administration (a selective MR antagonist) decreased it 60 min after the stress started. Intra-IL-CORT118335, a novel mixed MR/GR selective modulator, increased CORT throughout stress exposure. Ten days after stress, all rats increased freezing in the memory retrieval test and acquired the aversive contextual memory. During the extinction test, intra-IL injection of spironolactone, but not CORT118335, prevented the stress-impaired memory extinction, suggesting that the IL-MR activity controls CORT concentration, and it is crucial to the establishment of late extinction impairment. Also, the concomitant GR full activation overrode MR blockage. It increased CORT levels leading to the stress-induced extinction memory impairment, reinforcing that the MR/GR balance is crucial to predicting stress-induced behavioral outcomes.

Blockade of the mineralocorticoid receptors in the medial prefrontal cortex prevents the acquisition of one-trial tolerance in mice

One-trial tolerance (OTT) is characterized by the lack of anxiolytic-like effects of benzodiazepines in animals submitted to a trial 2 in the elevated plus-maze (EPM) and is described to be influenced by learning mechanisms. Mineralocorticoid receptors (MR) in the infralimbic subregion (IL) of the medial prefrontal cortex (mPFC) are important modulators of emotional learning, but the MR involvement in the establishment of OTT remains unclear. We investigated the effects of intra-IL infusions of RU 28318 (an MR antagonist) on the OTT to the anxiolytic effects of midazolam (MDZ, GABA_A-benzodiazepine agonist) in mice exposed to a two-trial protocol in the EPM. First, mice were treated with saline or MDZ (2mgkg^-1, i.p.) 30minutes before trial 1 or 2 in the EPM, to characterize the OTT. To investigate the role of MR in the OTT, independent groups of mice received intra-IL infusions of vehicle or RU 28318 (5 or 10ng 0.1µL^-1) immediately before or after first trial in the EPM. Twenty-four hours later, the same mice received injections of saline or MDZ and were re-tested in the EPM. The MDZ decreased anxiety-like behaviors in trial 1, but the same anxiolytic-like effect was not observed in MDZ-mice prior to the second EPM test, confirming the OTT. Blockade of MR in the IL before, but not after, trial 1 restored the anxiolytic effects if MDZ administered in trial 2. These findings indicate that the MR in the IL-mPFC contributing to the OTT by mediating the acquisition, but not the consolidation of emotional learning.

Antibiotic cocktail-induced gut microbiota depletion in different stages could cause host cognitive impairment and emotional disorders in adulthood in different manners

Gut microbiota depletion may result in cognitive impairment and emotional disorder. This study aimed to determine the possible association between host gut microbiota, cognitive function, and emotion in various life stages and its related underlying mechanisms. Seventy-five neonatal mice were randomly divided into five groups (n = 15 per group). Mice in the vehicle group were administered distilled water from birth to death, and those in the last four groups were administered antibiotic cocktail from birth to death, from birth to postnatal day (PND) 21 (infancy), from PND 21 to 56 (adolescence), and from PND 57 to 84 (adulthood), respectively. Antibiotic exposure consistently altered the gut microbiota composition and decreased the diversity of gut microbiota. Proteobacteria were the predominant bacteria instead of Firmicutes and Bacteroidetes after antibiotic exposure in different life stages. Long-term and infant gut microbiota depletion resulted in anxiety- and depression-like behaviors, memory impairments, and increased expression of γ-aminobutyric acid type A receptor α1 of adult mice. Long-term antibiotic exposure also significantly decreased serum interleukin (IL)-1β, IL-10, and corticosterone of adult mice. Gut microbiota depletion in adolescence resulted in anxiety-like behaviors, short-term memory decline, decreased serum interferon-γ (IFN-γ), mRNA expression of 5-hydroxytryptamine receptor 1A, and neuropeptide Y receptor Y2 in the prefrontal cortex of adult mice. Antibiotic exposure in adulthood damaged short-term memory and decreased serum IL-10, IFN-γ, and increased γ-aminobutyric acid type B receptor 1 mRNA expression of adult mice. These results suggest that antibiotic-induced gut microbiota depletion in the long term and infancy resulted in the most severe cognitive and emotional disorders followed by depletion in adolescence and adulthood. These results also suggest that gut microbes could influence host cognitive function and emotion in a life stage-dependent manner by affecting the function of the immune system, hypothalamic-pituitary-adrenal axis, and the expression of neurochemicals in the brain.

Chronic cerebral hypoperfusion in male rats results in sustained HPA activation and hyperinsulinemia

Vascular contributions to cognitive impairment and dementia (VCID) is a spectrum of cognitive deficits caused by cerebrovascular disease, for which insulin resistance is a major risk factor. A major cause of VCID is chronic cerebral hypoperfusion (CCH). Under stress, sustained hypothalamic-pituitary-adrenal axis (HPA) activation can result in insulin resistance. Little is known about the effects of CCH on the HPA axis. We hypothesized that CCH causes sustained HPA activation and insulin resistance. Male rats were subjected to bilateral carotid artery stenosis (BCAS) for 12 wk to induce CCH and VCID. BCAS reduced cerebral blood flow and caused memory impairment. Plasma adrenocorticotropic hormone was increased in the BCAS rats (117.2 ± 9.6 vs. 88.29 ± 9.1 pg/mL, BCAS vs. sham, P = 0.0236), as was corticosterone (220 ± 21 vs. 146 ± 18 ng/g feces, BCAS vs. sham, P = 0.0083). BCAS rats were hypoglycemic (68.1 ± 6.1 vs. 76.5 ± 5.9 mg/dL, BCAS vs. sham, P = 0.0072), with increased fasting insulin (481.6 ± 242.6 vs. 97.94 ± 40.02 pmol/L, BCAS vs. sham, P = 0.0003) indicating that BCAS rats were insulin resistant [homeostasis model assessment of β-cell function-insulin resistance (HOMA-IR): 11.71 ± 6.47 vs. 2.62 ± 0.93; BCAS vs. control, P = 0.0008]. Glucose tolerance tests revealed that BCAS rats had lower blood glucose areas under the curve (AUCs) than controls (250 ± 12 vs. 326 ± 20 mg/dL/h, BCAS vs. sham, P = 0.0075). These studies indicate that CCH causes sustained activation of the HPA and results in insulin resistance, a condition that is expected to worsen VCID.NEW & NOTEWORTHY Cerebrovascular disease and insulin resistance are two major risk factors for the development of dementia. Here, we demonstrate that chronic cerebral hypoperfusion results in glucocorticoid excess and hyperinsulinemia. This study indicates that chronic cerebral hypoperfusion, glucocorticoid excess, and insulin resistance participate in a detrimental cycle that could exacerbate cerebral vascular disease and dementia.

Anxiety and Alzheimer's disease: Behavioral analysis and neural basis in rodent models of Alzheimer's-related neuropathology

Alzheimer's disease (AD) pathology is commonly associated with cognitive decline but is also composed of neuropsychiatric symptoms including psychological distress and alterations in mood, including anxiety and depression. Emotional dysfunction in AD is frequently modeled using tests of anxiety-like behavior in transgenic rodents. These tests often include the elevated plus-maze, light/dark test and open field test. In this review, we describe prototypical behavioral paradigms used to examine emotional dysfunction in transgenic models of AD, specifically anxiety-like behavior. Next, we summarize the results of studies examining anxiety-like behavior in transgenic rodents, noting that the behavioral outcomes using these paradigms have produced inconsistent results. We suggest that future research will benefit from using a battery of tests to examine emotional behavior in transgenic AD models. We conclude by discussing putative, overlapping neurobiological mechanisms underlying AD-related neuropathology, stress and anxiety-like behavior reported in AD models.

Circadian Modulation of Neurons and Astrocytes Controls Synaptic Plasticity in Hippocampal Area CA1

Most animal species operate according to a 24-h period set by the suprachiasmatic nucleus (SCN) of the hypothalamus. The rhythmic activity of the SCN modulates hippocampal-dependent memory, but the molecular and cellular mechanisms that account for this effect remain largely unknown. Here, we identify cell-type-specific structural and functional changes that occur with circadian rhythmicity in neurons and astrocytes in hippocampal area CA1. Pyramidal neurons change the surface expression of NMDA receptors. Astrocytes change their proximity to synapses. Together, these phenomena alter glutamate clearance, receptor activation, and integration of temporally clustered excitatory synaptic inputs, ultimately shaping hippocampal-dependent learning in vivo. We identify corticosterone as a key contributor to changes in synaptic strength. These findings highlight important mechanisms through which neurons and astrocytes modify the molecular composition and structure of the synaptic environment, contribute to the local storage of information in the hippocampus, and alter the temporal dynamics of cognitive processing.

Effects of early life social experience on fear extinction and related glucocorticoid profiles - behavioral and neurochemical approaches in a rat model of PTSD

People may agonize over an intrusive fear-inducing memory even when the traumatic event has passed, which is the principle manifestation of posttraumatic stress disorder (PTSD). However, many traumatized people do not present symptoms of PTSD, implying that certain hidden factors help those individuals to cope with the traumatic stress. Increasing evidence suggests that early life experience may serve as a predisposing factor in the development of PTSD. For example, early life social deprivation disrupts the glucocorticoid system, one of the biological abnormalities of PTSD. By employing isolation rearing (IR) with a subsequent single prolonged stress (SPS) paradigm, we examined the hypothesis that early-life social experience may change the outcome of traumatic stress in both behavioral and neurochemical profiles. Behaviorally, the performance of rats on a Pavlovian fear conditioning test was measured to evaluate their retrieval ability of fear memory extinction. Neurochemically, plasma corticosterone levels and glucocorticoid receptor (GR), FK506-binding proteins 4 and 5 (FKBP4 and FKBP5) and early growth response-1 (Egr-1) expression were measured in GR-abundant brain areas, including the hypothalamus, medial prefrontal cortex, and hippocampus. Our results demonstrated an area-dependent IR effect on the SPS outcomes. IR prevented the SPS-impaired fear extinction retrieval ability and averted the SPS-elevated expression of GR, FKBP4, and Egr-1 in the hippocampus, whereas it did not change the SPS-reduced plasma corticosterone levels and SPS-enhanced GR activity in the mPFC and hypothalamus. The present study provides some new insights to support the hypothesis that early-life experience may play a role in the occurrence of PTSD.

Corticosteroid Receptors in the Brain: Transcriptional Mechanisms for Specificity and Context-Dependent Effects

Corticosteroid hormones act in the brain to support adaptation to stress via binding to mineralocorticoid and glucocorticoid receptors (MR and GR). These receptors act in large measure as transcription factors. Corticosteroid effects can be highly divergent, depending on the receptor type, but also on brain region, cell type, and physiological context. These differences ultimately depend on differential interactions of MR and GR with other proteins, which determine ligand binding, nuclear translocation, and transcriptional activities. In this review, we discuss established and potential mechanisms that confer receptor and cell type-specific effects of the MR and GR-mediated transcriptional effects in the brain.

Influence of allelic variations in relation to norepinephrine and mineralocorticoid receptors on psychopathic traits: a pilot study

Background

Past findings support a relationship between abnormalities in the amygdala and the presence of psychopathic traits. Among other genes and biomarkers relevant to the amygdala, norepinephrine and mineralocorticoid receptors might both play a role in psychopathy due to their association with traits peripheral to psychopathy. The purpose is to examine if allelic variations in single nucleotide polymorphisms related to norepinephrine and mineralocorticoid receptors play a role in the display of psychopathic traits and executive functions.

Methods

Fifty-seven healthy participants from the community provided a saliva sample for SNP sampling of rs5522 and rs5569. Participants then completed the Psychopathic Personality Inventory–Short Form (PPI-SF) and the Tower of Hanoi.

Results

Allelic variations of both rs5522 and rs5569 were significant when compared to PPI-SF total score and the fearless dominance component of the PPI-SF. A significant result was also obtained between rs5522 and the number of moves needed to complete the 5-disk Tower of Hanoi.

Conclusion

This pilot study offers preliminary results regarding the effect of allelic variations in SNPs related to norepinephrine and mineralocorticoid receptors on the presence of psychopathic traits. Suggestions are provided to enhance the reliability and validity of a larger-scale study.

Neuroanatomical pathways underlying the effects of hypothalamo-hypophysial-adrenal hormones on exploratory activity

When injected via the intracerebroventricular route, corticosterone-releasing hormone (CRH) reduced exploration in the elevated plus-maze, the center region of the open-field, and the large chamber in the defensive withdrawal test. The anxiogenic action of CRH in the elevated plus-maze also occurred when infused in the basolateral amygdala, ventral hippocampus, lateral septum, bed nucleus of the stria terminalis, nucleus accumbens, periaqueductal grey, and medial frontal cortex. The anxiogenic action of CRH in the defensive withdrawal test was reproduced when injected in the locus coeruleus, while the amygdala, hippocampus, lateral septum, nucleus accumbens, and lateral globus pallidus contribute to center zone exploration in the open-field. In addition to elevated plus-maze and open-field tests, the amygdala appears as a target region for CRH-mediated anxiety in the elevated T-maze. Thus, the amygdala is the principal brain region identified with these three tests, and further research must identify the neural circuits underlying this form of anxiety.

60 YEARS OF NEUROENDOCRINOLOGY: Redefining neuroendocrinology: stress, sex and cognitive and emotional regulation

The discovery of steroid hormone receptors in brain regions that mediate every aspect of brain function has broadened the definition of 'neuroendocrinology' to include the reciprocal communication between the brain and the body via hormonal and neural pathways. The brain is the central organ of stress and adaptation to stress because it perceives and determines what is threatening, as well as the behavioral and physiological responses to the stressor. The adult and developing brain possess remarkable structural and functional plasticity in response to stress, including neuronal replacement, dendritic remodeling, and synapse turnover. Stress causes an imbalance of neural circuitry subserving cognition, decision-making, anxiety and mood that can alter expression of those behaviors and behavioral states. This imbalance, in turn, affects systemic physiology via neuroendocrine, autonomic, immune and metabolic mediators. In the short term, as for increased fearful vigilance and anxiety in a threatening environment, these changes may be adaptive. But, if the danger passes and the behavioral state persists along with the changes in neural circuitry, such maladaptation may need intervention with a combination of pharmacological and behavioral therapies, as is the case for chronic anxiety and depression. There are important sex differences in the brain responses to stressors that are in urgent need of further exploration. Moreover, adverse early-life experience, interacting with alleles of certain genes, produce lasting effects on brain and body over the life-course via epigenetic mechanisms. While prevention is most important, the plasticity of the brain gives hope for therapies that take into consideration brain-body interactions.

Gap junctions in the ventral hippocampal-medial prefrontal pathway are involved in anxiety regulation

Anxiety disorders are highly prevalent but little is known about their underlying mechanisms. Gap junctions exist in brain regions important for anxiety regulation, such as the ventral hippocampus (vHIP) and mPFC, but their functions in these areas have not been investigated. Using pharmacological blockade of neuronal gap junctions combined with electrophysiological recordings, we found that gap junctions play a role in theta rhythm in the vHIP and mPFC of adult mice. Bilateral infusion of neuronal gap junction blockers into the vHIP decreased anxiety-like behavior on the elevated plus maze and open field. Similar anxiolytic effects were observed with unilateral infusion of these drugs into the vHIP combined with contralateral infusion into the mPFC. No change in anxious behavior was observed with gap junction blockade in the unilateral vHIP alone or in the bilateral dorsal HIP. Since physical exercise is known to reduce anxiety, we examined the effects of long-term running on the expression of the neuronal gap junction protein connexin-36 among inhibitory interneurons and found a reduction in the vHIP. Despite this change, we observed no alteration in theta frequency or power in long-term runners. Collectively, these findings suggest that neuronal gap junctions in the vHIP-mPFC pathway are important for theta rhythm and anxiety regulation under sedentary conditions but that additional mechanisms are likely involved in running-induced reduction in anxiety.

Mesocortical dopamine depletion and anxiety-related behavior in the rat: sex and hemisphere differences

The mesocortical dopamine (DA) system of the rat plays an important role in prefrontal cortex (PFC) regulation of stress and emotion and exhibits functional hemispheric asymmetry for such processing. Since few studies examine sex differences in this context, we compared the effects of left vs. right unilateral PFC DA depletion in males and females in several behavioral situations associated with anxiety or aversion. Adult rats received unilateral injections of 6-hydroxydopamine (6-OHDA) or vehicle in the ventromedial (vm) PFC. Behavioral tests included a predator odor burying test, elevated plus maze and sucrose consumption with simple taste aversion. Tissue analysis confirmed that vmPFCs injected with 6-OHDA were depleted of DA (75-85%) compared to controls. Burying behavior and sucrose consumption were affected only by left lesions, similarly in both sexes. However, risk assessment behaviors were affected by right lesions in opposite directions in males and females. Behaviors modified preferentially by the left cortex thus showed less evidence of sex differences than those modulated by the right. While mesocortical DA depletion effects are lateralized, the nature of these effects can vary with sex and specific behavior. Such findings may be clinically significant, given the large gender differences in the incidence of mood and anxiety disorders, which also show many lateralized prefrontal abnormalities.

Exposure to variable prenatal stress in rats: effects on anxiety-related behaviors, innate and contextual fear, and fear extinction

Rats repeatedly exposed to variable prenatal stress (PNS) exhibit behavioral features often observed in neuropsychiatric disorders including elevated sensitivity to stimulants and impairments of attention, inhibitory control and memory-related task performance. However, to date there have been relatively few studies designed to assess the effects of PNS on anxiety, stress and fear responses, or the function of the hypothalamic-pituitary-adrenal (HPA) axis (a system clearly linked to stress and fear-related responses as well as neuropsychiatric disorders). In the current study, rats exposed to variable PNS were evaluated for anxiety-related behaviors in open field, elevated plus maze, and light/dark preference tasks. Innate fear responses were assessed using a predatory odor task and learned fear and extinction were assessed with a contextual fear conditioning task. As an indicator of HPA axis function, serum corticosterone levels were determined by enzyme immunoassay at various time points. The results indicated that PNS resulted in several behavioral anomalies including decreased innate fear responses to predator odor, impaired fear extinction, increased locomotor activity and stereotypic-like behaviors. Baseline levels of corticosterone in PNS subjects were similar to non-stressed controls; however, when exposed to acute stress, they exhibited an increase in corticosterone that was greater in magnitude. PNS was not associated with increased anxiety-like behaviors or deficits in learning or retention during contextual fear conditioning. Collectivity, these data support the argument that variable PNS in rats is a valid model system for studying some behavioral components of neuropsychiatric disorders as well as the influence of stress hormones.