Serotonin, stress and corticoids

The serotonin gene 5-HTTLPR and brain food-reward responses during sadness: a mood-induction neuroimaging study

BACKGROUND

High-calorie foods become particularly rewarding and difficult to resist under affective stressful circumstances. Individuals carrying the short allele variant of the serotonin transporter gene (s-allele 5-HTTLPR) often exhibit enhanced emotional and neuroendocrine stress responsiveness, which increases their risk to gain weight or to develop obesity.

OBJECTIVE

To explore whether homozygous S-allele 5-HTTLPR carriers are more sensitive to the rewarding effects of high- compared to low-calorie foods during sad mood.

METHODS

From a large (n = 827) DNA 5-HTTLPR database, a selected subgroup of homozygous S-allele and L-allele carriers were monitored for affective-motivational (mood, wanting-liking) and neural (fMRI) food-reward responsiveness during a food exposure task, before and after sad mood induction. Brain responsiveness was measured for high versus low calorie food pictures in a set of appetitive- and cognitive control ROIs, respectively.

RESULTS

Mood induction significantly increased sad mood in the majority of participants. Analyses revealed a genotype x mood induction interaction in cognitive control but not in affective ROIs. LL- compared to SS-carriers exhibited greater contrast value in the inferior frontal sulcus, dorsolateral PFC and superior parietal lob when viewing high- compared to low-calorie food pictures, which only in LL-genotypes significantly declined after sad mood induction.

CONCLUSION

LL- compared to SS-genotypes may have stronger high-calorie food responses in cognitive control brain areas in the absence of stress indicating better capacity to resist the rewarding effects of palatable foods.

Connectome modeling of discrimination exposure: Impact on your social brain and psychological symptoms

Discrimination is a social stressor that is associated with adverse health outcomes, but the underlying neural mechanisms remain unclear. The fusiform, including the fusiform face area (FFA) plays a critical role in face perception especially regarding hostile faces during discrimination exposure; and are key regions involved in social cognition. We compared resting-state spontaneous activity and connectivity of the fusiform and FFA, between 153 individuals (110 women) with high (N = 73) and low (N = 80) levels of discrimination (measured by the Everyday Discrimination Scale) and evaluated the relationships of these brain signatures with psychological outcomes and stress-related neurotransmitters. Discrimination-related group differences showed altered fusiform signal fluctuation dynamics (Hurst exponent) and connectivity. These alterations predicted discrimination experiences and correlated with anxiety, depression, and cognitive difficulties. A molecular architecture analysis using cross-modal spatial correlation of brain signatures and nuclear imaging derived estimates of stress-related neurotransmitters demonstrated overlap between discrimination-related connectivity and dopamine, serotonin, gamma-aminobutyric acid (GABA), and acetylcholine. Discrimination exposure associated with alterations in the fusiform and face processing area may reflect enhanced baseline preparedness and vigilance towards facial stimuli and decreased top-down regulation of potential threats. These brain alterations may contribute to increased vulnerability for the development of mental health symptoms, demonstrating clinical relevance of social cognition in stressful interpersonal relationships.

The stress-immune system axis: Exploring the interplay between stress and immunity

The chapter talks about how our body and mind respond to stress and how it affects our immune system. Stress reactions, especially the fight-or-flight reaction, are helpful at first but can be harmful if they last too long. Long-term stress, caused by hormones like cortisol and adrenaline, weakens the immune system and makes people more likely to get sick. Important brain chemicals like serotonin and norepinephrine help control how our immune system works. Also, the connection between our gut and brain is an important way that mental health affects how our immune system functions. Getting older and experiencing stress early in life can affect how our immune system works. Inflammation caused by stress is connected to health issues like heart disease, depression, and autoimmune diseases. There are ways to manage stress, like being mindful and having support from friends, are important for keeping your immune system healthy and lessening harm caused by stress.

What matters to a mouse? Effects of internal and external context on male vocal response to female squeaks

House mice adjust their signaling behavior depending on the social context of an interaction, but which aspects of context elicit the strongest responses from these individuals is often difficult to determine. To explore how internal and external contextual factors influence how house mice produce and respond to social signals, we assessed how dominant and subordinate male mice differed in their ultrasonic vocalization (USV) production in response to playback of broadband vocalizations (BBVs, or squeaks) when given limited access to a stimulus female. We used a repeated measures design in which each male was exposed to two types of trials with different odor conditions: either just female odors (Fem condition) or female odors in addition to the odors of potential competitors, other males (Fem+Male condition). The presence of odors from other males in this assay served as a proxy for an "audience" as the male interacted with the stimulus female. These conditions were replicated for two distinct cohorts of individuals: males exposed to the odor of familiar competitors in the Fem+Male condition (Familiar odor cohort), and males exposed to the odor of unfamiliar competitors in the Fem+Male condition (Unfamiliar odor cohort). By assessing dominance status of the focal individual and familiarity of the "audience", we are able to explore how these factors may affect one another as males respond to BBVs. Dominants and subordinates did not differ in their baseline vocal production (vocalizations produced prior to squeak playback) or response to squeaks. However, all groups, regardless of dominance status or odor condition, reduced their vocal production in response to BBV playback. The presence of unfamiliar male odor prompted mice to decrease their baseline level of calling and decrease the complexity of their vocal repertoire compared to trials that only included female odor, and this effect also did not differ across dominance status. Importantly, the presence of male odor did not affect vocal behavior when the male odor was familiar to the focal individual. These findings suggest that mice alter their vocal behavior during courtship interactions in response to cues that indicate the presence of potential competitors, and this response is modulated by the familiarity of these competitor cues.

Addiction and stress: Exploring the reward pathways in brain affected by different drugs

This chapter delves into the complex interplay among addiction, stress, and the reward pathways in the brain, emphasizing the ways in which various drugs affect these systems and exacerbate SUD. Drugs have physiological effects that can be both pleasurable and unpleasant. These effects change behavior through both positive and negative reinforcement. A person's genetic predisposition to addiction is mostly determined by factors such as biological sex, age of first usage, and dopamine receptor density. Drug use behaviors are also greatly influenced by environmental stressors, media exposure, and substance accessibility; nevertheless, protective variables including social support, participation in healthy activities, and preventative programs serve to reduce the dangers associated with drug use. The reinforcement of addictive behaviors is mostly dependent on the brain's reward circuits, which include the nucleus accumbens, ventral tegmental region, and prefrontal cortex, in addition to neurotransmitters such as dopamine, serotonin, and endorphins. Stress makes addiction worse by intensifying cravings and raising the possibility of relapsing. Examined are the impacts of several drug types, such as opioids, stimulants, depressants, and hallucinogens, emphasizing the long-term consequences on brain function and susceptibility to addiction. In order to create individualized interventions that target the environmental and neurological components of addiction and eventually improve treatment results, a thorough understanding of these elements is important.

Regulation of Stress-Induced Immunosuppression in the Context of Neuroendocrine, Cytokine, and Cellular Processes

Understanding the regulatory mechanisms of stress-induced immunosuppression and developing reliable diagnostic methods are important tasks in clinical medicine. This will allow for the development of effective strategies for the prevention and treatment of conditions associated with immune system dysfunction induced by chronic stress. The purpose of this review is to conduct a comprehensive analysis and synthesis of existing data on the regulatory mechanisms of stress-induced immunosuppression. The review is aimed at identifying key neuroendocrine, cytokine, and cellular processes underlying the suppression of the immune response under stress. This study involved a search of scientific literature covering the neuroendocrine, cellular, and molecular mechanisms of stress-induced immunosuppression regulation, as well as modern methods for its diagnosis. Major international bibliographic databases covering publications in biomedicine, psychophysiology, and immunology were selected for the search. The results of the analysis identified key mechanisms regulating stress-induced immunosuppression. The reviewed publications provided detailed descriptions of the neuroendocrine and cytokine processes underlying immune response suppression under stress. A significant portion of the data confirms that the activation of the hypothalamic-pituitary-adrenal (HPA) axis and subsequent elevation of cortisol levels exert substantial immunosuppressive effects on immune cells, particularly macrophages and lymphocytes, leading to the suppression of innate and adaptive immune responses. The data also highlight the crucial role of cortisol and catecholamines (adrenaline and noradrenaline) in initiating immunosuppressive mechanisms under chronic stress.

The Role of Intestinal Microbiota and Probiotics Supplementation in Multiple Sclerosis Management

Multiple sclerosis (MS) is a neurological autoimmune disorder predominantly afflicting young adults. The etiology of MS is intricate, involving a variety of environmental and genetic factors. Current research increasingly focuses on the substantial contribution of gut microbiota in MS pathogenesis. The commensal microbiota resident within the intestinal milieu assumes a central role within the intricate network recognized as the gut-brain axis (GBA), wielding beneficial impact in neurological and psychological facets. As a result, the modulation of gut microbiota is considered a pivotal aspect in the management of neural disorders, including MS. Recent investigations have unveiled the possibility of using probiotic supplements as a promising strategy for exerting a positive impact on the course of MS. This therapeutic approach operates through several mechanisms, including the reinforcement of gut epithelial integrity, augmentation of the host's resistance against pathogenic microorganisms, and facilitation of mucosal immunomodulatory processes. The present study comprehensively explains the gut microbiome's profound influence on the central nervous system (CNS). It underscores the pivotal role played by probiotics in forming the immune system and modulating neurotransmitter function. Furthermore, the investigation elucidates various instances of probiotic utilization in MS patients, shedding light on the potential therapeutic advantages afforded by this intervention.

Unveiling a novel memory center in human brain: neurochemical identification of the nucleus incertus, a key pontine locus implicated in stress and neuropathology

BACKGROUND

The nucleus incertus (NI) was originally described by Streeter in 1903, as a midline region in the floor of the fourth ventricle of the human brain with an 'unknown' function. More than a century later, the neuroanatomy of the NI has been described in lower vertebrates, but not in humans. Therefore, we examined the neurochemical anatomy of the human NI using markers, including the neuropeptide, relaxin-3 (RLN3), and began to explore the distribution of the NI-related RLN3 innervation of the hippocampus.

METHODS

Histochemical staining of serial, coronal sections of control human postmortem pons was conducted to reveal the presence of the NI by detection of immunoreactivity (IR) for the neuronal markers, microtubule-associated protein-2 (MAP2), glutamic acid dehydrogenase (GAD)-65/67 and corticotrophin-releasing hormone receptor 1 (CRHR1), and RLN3, which is highly expressed in NI neurons in diverse species. RLN3 and vesicular GABA transporter 1 (vGAT1) mRNA were detected by fluorescent in situ hybridization. Pons sections containing the NI from an AD case were immunostained for phosphorylated-tau, to explore potential relevance to neurodegenerative diseases. Lastly, sections of the human hippocampus were stained to detect RLN3-IR and somatostatin (SST)-IR.

RESULTS

In the dorsal, anterior-medial region of the human pons, neurons containing RLN3- and MAP2-IR, and RLN3/vGAT1 mRNA-positive neurons were observed in an anatomical pattern consistent with that of the NI in other species. GAD65/67- and CRHR1-immunopositive neurons were also detected within this area. Furthermore, RLN3- and AT8-IR were co-localized within NI neurons of an AD subject. Lastly, RLN3-IR was detected in neurons within the CA1, CA2, CA3 and DG areas of the hippocampus, in the absence of RLN3 mRNA. In the DG, RLN3- and SST-IR were co-localized in a small population of neurons.

CONCLUSIONS

Aspects of the anatomy of the human NI are shared across species, including a population of stress-responsive, RLN3-expressing neurons and a RLN3 innervation of the hippocampus. Accumulation of phosphorylated-tau in the NI suggests its possible involvement in AD pathology. Further characterization of the neurochemistry of the human NI will increase our understanding of its functional role in health and disease.

Embryonic Zebrafish as a Model for Investigating the Interaction between Environmental Pollutants and Neurodegenerative Disorders

Environmental pollutants have been linked to neurotoxicity and are proposed to contribute to neurodegenerative disorders. The zebrafish model provides a high-throughput platform for large-scale chemical screening and toxicity assessment and is widely accepted as an important animal model for the investigation of neurodegenerative disorders. Although recent studies explore the roles of environmental pollutants in neurodegenerative disorders in zebrafish models, current knowledge of the mechanisms of environmentally induced neurodegenerative disorders is relatively complex and overlapping. This review primarily discusses utilizing embryonic zebrafish as the model to investigate environmental pollutants-related neurodegenerative disease. We also review current applicable approaches and important biomarkers to unravel the underlying mechanism of environmentally related neurodegenerative disorders. We found embryonic zebrafish to be a powerful tool that provides a platform for evaluating neurotoxicity triggered by environmentally relevant concentrations of neurotoxic compounds. Additionally, using variable approaches to assess neurotoxicity in the embryonic zebrafish allows researchers to have insights into the complex interaction between environmental pollutants and neurodegenerative disorders and, ultimately, an understanding of the underlying mechanisms related to environmental toxicants.

Stress induced exacerbation of Alzheimer's disease brain pathology is thwarted by co-administration of nanowired cerebrolysin and monoclonal amyloid beta peptide antibodies with serotonin 5-HT6 receptor antagonist SB-399885

Alzheimer's disease is one of the devastating neurodegenerative diseases affecting mankind worldwide with advancing age mainly above 65 years and above causing great misery of life. About more than 7 millions are affected with Alzheimer's disease in America in 2023 resulting in huge burden on health care system and care givers and support for the family. However, no suitable therapeutic measures are available at the moment to enhance quality of life to these patients. Development of Alzheimer's disease may reflect the stress burden of whole life inculcating the disease processes of these neurodegenerative disorders of the central nervous system. Thus, new strategies using nanodelivery of suitable drug therapy including antibodies are needed in exploring neuroprotection in Alzheimer's disease brain pathology. In this chapter role of stress in exacerbating Alzheimer's disease brain pathology is explored and treatment strategies are examined using nanotechnology based on our own investigation. Our observations clearly show that restraint stress significantly exacerbate Alzheimer's disease brain pathology and nanodelivery of a multimodal drug cerebrolysin together with monoclonal antibodies (mAb) to amyloid beta peptide (AβP) together with a serotonin 5-HT6 receptor antagonist SB399885 significantly thwarted Alzheimer's disease brain pathology exacerbated by restraint stress, not reported earlier. The possible mechanisms and future clinical significance is discussed.

Restraint Stress and Repeated Corticosterone Administration Differentially Affect Neuronal Excitability, Synaptic Transmission and 5-HT7 Receptor Reactivity in the Dorsal Raphe Nucleus of Young Adult Male Rats

Exogenous corticosterone administration reduces GABAergic transmission and impairs its 5-HT₇ receptor-dependent modulation in the rat dorsal raphe nucleus (DRN), but it is largely unknown how neuronal functions of the DRN are affected by repeated physical and psychological stress. This study compared the effects of repeated restraint stress and corticosterone injections on DRN neuronal excitability, spontaneous synaptic transmission, and its 5-HT₇ receptor-dependent modulation. Male Wistar rats received corticosterone injections for 7 or 14 days or were restrained for 10 min twice daily for 3 days. Repeated restraint stress and repeated corticosterone administration evoked similar changes in performance in the forced swim test. They increased the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) recorded from DRN neurons. In contrast to the treatment with corticosterone, restraint stress-induced changes in sEPSC kinetics and decreased intrinsic excitability of DRN neurons did not modify inhibitory transmission. Repeated injections of the 5-HT₇ receptor antagonist SB 269970 ameliorated the effects of restraint on excitability and sEPSC frequency but did not restore the altered kinetics of sEPSCs. Thus, repeated restraint stress and repeated corticosterone administration differ in consequences for the intrinsic excitability of DRN projection neurons and their excitatory and inhibitory synaptic inputs. Effects of repeated restraint stress on DRN neurons can be partially abrogated by blocking the 5-HT₇ receptor.

Sex Differences in Serotonin 5-HT 1A Receptor Responses to Repeated Restraint Stress in Adult Male and Female Rats

BACKGROUND

Male and female rats were exposed to repeated restraint to determine how changes in serotonin (5-hydroxytryptamine; 5-HT) 1A receptors associate with stress hypothalamic-pituitary-adrenal (HPA) axis habituation.

METHODS

In response to 2-hour episodes of restraint, repeated daily for 5 consecutive days, males and females displayed reliable declines in HPA output, indicated by diminished adrenocorticotropin and corticosterone secretory responses. Using the 5-HT 1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) as a pharmacological challenge for inducing hypothermia and elevations in plasma corticosterone, males displayed sensitized hypothermal responses after repeated restraint, whereas corticosterone responses to 8-OH-DPAT were enhanced in both sexes following single or repeated exposure.

RESULTS

Only males showed elevations in 5-HT 1A receptor G-protein coupling responses in the dorsal raphe after repeated restraint, whereas only females showed an increase in 5-HT 1A receptor responses in the hippocampus following single or repeated exposure. G-protein coupling responses within both regions correlated positively with 5-HT 1A receptor binding capacity. Thus, despite expressing similar capacities for stress HPA axis habituation, males and females emerged from repeated restraint to show region-specific changes in 5-HT 1A receptor function that may be explained, at least in part, by changes in receptor availability.

CONCLUSIONS

Based on the hypothermal and corticosteroid responses to 8-OH-DPAT, the present data suggest that stress habituation is met by an increase in the sensitivity of presynaptic 5-HT 1A receptors in males and by an increase in the sensitivity of a population of postsynaptic receptors in both sexes.

5-HT2A receptor dysregulation in a schizophrenia relevant mouse model of NMDA receptor hypofunction

Blockade of N-methyl-D-aspartate receptors (NMDAR) is known to augment cortical serotonin 2A receptors (5-HT2ARs), which is implicated in psychosis. However, the pathways from NMDAR hypofunction to 5-HT2AR up-regulation are unclear. Here we addressed in mice whether genetic deletion of the indispensable NMDAR-subunit Grin1 principally in corticolimbic parvalbumin-positive fast-spiking interneurons, could up-regulate 5-HT2ARs leading to cortical hyper-excitability. First, in vivo local-field potential recording revealed that auditory cortex in Grin1 mutant mice became hyper-excitable upon exposure to acoustic click-train stimuli that release 5-HT in the cortex. This excitability increase was reproduced ex vivo where it consisted of an increased frequency of action potential (AP) firing in layer 2/3 pyramidal neurons of mutant auditory cortex. Application of the 5-HT2AR agonist TCB-2 produced similar results. The effect of click-trains was reversed by the 5-HT2AR antagonist M100907 both in vivo and ex vivo. Increase in AP frequency of pyramidal neurons was also reversed by application of Gαq protein inhibitor BIM-46187 and G protein-gated inwardly-rectifying K⁺ (GIRK) channel activator ML297. In fast-spiking interneurons, 5-HT2AR activation normally promotes GABA release, contributing to decreased excitability of postsynaptic pyramidal neurons, which was missing in the mutants. Moreover, unlike the controls, the GABA_A receptor antagonist (+)-bicuculline had little effect on AP frequency of mutant pyramidal neurons, indicating a disinhibition state. These results suggest that the auditory-induced hyper-excitable state is conferred via GABA release deficits from Grin1-lacking interneurons leading to 5-HT2AR dysregulation and GIRK channel suppression in cortical pyramidal neurons, which could be involved in auditory psychosis.

Cellular and serotonergic correlates of habituated neuroendocrine responses in male and female rats

Male and females appear equally capable of showing habituated hypothalamic-pituitary-adrenal (HPA) axis output responses to repeated exposures of the same challenge. Whether this reflects, within males and females, common mechanisms of decreased neuronal activity within stress responding, afferents to the paraventricular hypothalamic nucleus (PVH), the final common pathway to the HPA axis, has not been examined. Here we compared in adult male and female rats the extent to which declines in HPA axis responses to repeated restraint are met by habituated cellular (Fos) responses, in addition to changes in serotonin (5-hydroxytryptamine; 5-HT) expression and signaling, which normally stimulates the HPA axis. Thus, alterations in this component of HPA axis drive could provide an underlying basis for sex differences in adaptive responses. Males and females showed reliable declines in ACTH and corticosterone responses after 10 daily episodes of repeated restraint, recapitulated, in largest part, by similar regional patterns of Fos habituation, including within the PVH, several stress sensitive cell groups of the limbic forebrain, as well as within the raphe nucleus. Serotonin staining in the dorsal raphe and terminal profiles in the forebrain continued to reflect a higher pre-synaptic capacity for the 5-HT system in females. The sexual dimorphism encountered within the lateral septum and medial preoptic area of control animals was less distinguished in the repeat condition, however, whereas 5-HT varicosities in the PVH increased after repeated restraint only in females. Relative to their singly restrained counterparts, males displayed an increase in 5-HT 1 A receptor expression in the raphe nucleus after repeated restraint, whereas females showed a decrease in 5-HT 1 A mRNA levels in the hippocampus and in the zona incerta, representing the most proximal of cell groups expressing the 5-HT 1 A receptor in the vicinity of the PVH. In conclusion, similar regional profiles of cellular habituation in males and females suggest common CNS substrates of neuroendocrine adaptation. However, this process may be met by underlying sex differences in serotonergic control, given the respective roles for pre- and postsynaptic 5-HT 1 A receptors in mediating serotonin availability and signal transfer.

The role of the vagus nerve in fibromyalgia syndrome

Fibromyalgia (FM) syndrome is a common illness characterized by chronic widespread pain, sleep problems, fatigue, and cognitive difficulties. Dysfunctional neurotransmitter systems that influence the body's endogenous stress response systems are thought to underlie many of the major FM-related symptoms. A model of FM pathogenesis suggests biological and psychosocial variables interact to influence the genetic predisposition, but the precise mechanisms remain unclear. The Polyvagal Theory provides a theoretical framework from which to investigate potential biological mechanisms. The vagus nerve (VN) has anti-inflammatory properties via its afferent and efferent fibers. A low vagal tone (as assessed by low heart rate variability), has been observed in painful and inflammatory diseases, including FM, while the ventral branch of the VN is linked to emotional expression and social engagement. These anti-inflammatory and psychological (limbic system) properties of the VN may possess therapeutic potential in treating FM. This review paper summarizes the scientific literature regarding the potential role of the VN in transducing and/or therapeutically managing FM signs and symptoms.

Kinetics and 28-day test-retest repeatability and reproducibility of [11C]UCB-J PET brain imaging

[11C]UCB-J is a novel radioligand that binds to synaptic vesicle glycoprotein 2A (SV2A). The main objective of this study was to determine the 28-day test-retest repeatability (TRT) of quantitative [11C]UCB-J brain positron emission tomography (PET) imaging in Alzheimer's disease (AD) patients and healthy controls (HCs). Nine HCs and eight AD patients underwent two 60 min dynamic [11C]UCB-J PET scans with arterial sampling with an interval of 28 days. The optimal tracer kinetic model was assessed using the Akaike criteria (AIC). Micro-/macro-parameters such as tracer delivery (K1) and volume of distribution (VT) were estimated using the optimal model. Data were also analysed for simplified reference tissue model (SRTM) with centrum semi-ovale (white matter) as reference region. Based on AIC, both 1T2k_VB and 2T4k_VB described the [11C]UCB-J kinetics equally well. Analysis showed that whole-brain grey matter TRT for VT, DVR and SRTM BPND were -2.2% ± 8.5, 0.4% ± 12.0 and -8.0% ± 10.2, averaged over all subjects. [11C]UCB-J kinetics can be well described by a 1T2k_VB model, and a 60 min scan duration was sufficient to obtain reliable estimates for both plasma input and reference tissue models. TRT for VT, DVR and BPND was <15% (1SD) averaged over all subjects and indicates adequate quantitative repeatability of [11C]UCB-J PET.

Antidepressants on Multiple Sclerosis: A Review of In Vitro and In Vivo Models

Background

Increased prevalence of depression has been observed among patients with multiple sclerosis (MS) and correlated with the elevated levels of proinflammatory cytokines and the overall deregulation of monoaminergic neurotransmitters that these patients exhibit. Antidepressants have proved effective not only in treating depression comorbid to MS, but also in alleviating numerous MS symptoms and even minimizing stress-related relapses. Therefore, these agents could prospectively prove beneficial as a complementary MS therapy.

Objective

This review aims at illustrating the underlying mechanisms involved in the beneficial clinical effects of antidepressants observed in MS patients.

Methods

Through a literature search we screened and comparatively assessed papers on the effects of antidepressant use both in vitro and in vivo MS models, taking into account a number of inclusion and exclusion criteria.

Results

In vitro studies indicated that antidepressants promote neural and glial cell viability and differentiation, reduce proinflammatory cytokines and exert neuroprotective activity by eliminating axonal loss. In vivo studies confirmed that antidepressants delayed disease onset and alleviated symptoms in Experimental Autoimmune Encephalomyelitis (EAE), the most prevalent animal model of MS. Further, antidepressant agents suppressed inflammation and restrained demyelination by decreasing immune cell infiltration of the CNS.

Conclusion

Antidepressants were efficient in tackling numerous aspects of disease pathophysiology both in vitro and in vivo models. Given that several antidepressants have already proved effective in clinical trials on MS patients, the inclusion of such agents in the therapeutic arsenal of MS should be seriously considered, following an individualized approach to minimize the adverse events of antidepressants in MS patients.

Role of Hippocampal 5-HT6 Receptors in Glucocorticoid-Induced Enhancement of Memory Consolidation in Rats

Introduction:

of the study: Post-training administration of glucocorticoids enhance memory consolidation of inhibitory avoidance learning. Given the involvement of 5-HT6 receptors in memory processing and the interaction of glucocorticoids with the brain serotonergic system in modulating memory processing, we investigated whether the effect of glucocorticoids on the consolidation of emotionally arousing training depends on hippocampal 5-HT6 receptors.

Methods:

Rats were trained in an inhibitory avoidance task and immediately received the systemic injections of corticosterone (CORT) as well as the intra-hippocampal injections of 5-HT receptors agonist or antagonist. The memory retention test was done 48 hours after training and immediately after the behavioral test, the animals were sacrificed and the hippocampi (left and right) rapidly dissected out for molecular studies.

Results:

Post-training injections of different doses of CORT (1.25, 2.5, 5, and 10 mg/kg) enhanced memory retention in a dose-dependent manner. The CORT-induced enhancement of memory consolidation was blocked by bilateral intra-hippocampal injections of 5-HT6 receptor antagonist SB271046 (5 or 10 ng/per side), but not agonist EMD386088 (5 or 10 ng/per side). Furthermore, systemic CORT reduced 5-HT6 receptor mRNA and protein expression in the hippocampus. Both doses of 5-HT6 receptor agonist and antagonist significantly enhanced and reduced the expression of the 5-HT6 receptor, respectively, and both ligands at the higher dose (10 ng) enhanced memory consolidation. Moreover, CORT injection attenuated and enhanced, respectively, the effects of agonist and antagonist on 5-HT6 receptor expression.

Conclusion:

These behavioral and molecular findings indicated an interaction between glucocorticoids and hippocampal 5-HT6 receptors in the consolidation of emotionally arousing experiences.

Long term effects of early life stress on HPA circuit in rodent models

Adaptation to environmental challenges represents a critical process for survival, requiring the complex integration of information derived from both external cues and internal signals regarding current conditions and previous experiences. The Hypothalamic-pituitary-adrenal axis plays a central role in this process inducing the activation of a neuroendocrine signaling cascade that affects the delicate balance of activity and cross-talk between areas that are involved in sensorial, emotional, and cognitive processing such as the hippocampus, amygdala, Prefrontal Cortex, Ventral Tegmental Area, and dorsal raphe. Early life stress, especially early critical experiences with caregivers, influences the functional and structural organization of these areas, affects these processes in a long-lasting manner and may result in long-term maladaptive and psychopathological outcomes, depending on the complex interaction between genetic and environmental factors. This review summarizes the results of studies that have modeled this early postnatal stress in rodents during the first 2 postnatal weeks, focusing on the long-term effects on molecular and structural alteration in brain areas involved in Hypothalamic-pituitary-adrenal axis function. Moreover, a brief investigation of epigenetic mechanisms and specific genetic targets mediating the long-term effects of these early environmental manipulations and at the basis of differential neurobiological and behavioral effects during adulthood is provided.

Alleviation of cognitive deficits and high copper levels by an NMDA receptor antagonist in a rat depression model

BACKGROUND

Major depressive disorder (MDD) is frequently associated with cognitive deficits and high copper levels. Dysfunction of N-methyl-d-aspartate (NMDA) receptors has been postulated to underlie MDD pathogenesis. This study sought to investigate the curative effect of the NMDA receptor antagonist memantine on cognitive deficits in depression and the underlying mechanisms.

METHODS

Adult male Sprague-Dawley rats received corticosterone (CORT) (20 mg/kg) bi-weekly via subcutaneous injection and/or copper gluconate (7 mg/kg) via daily intragastric administration. After 3 weeks, sucrose preference tests and open field tests showed anhedonia and high anxiety in both the CORT and CORT+Cu groups. Memantine intervention (20 mg/kg daily via intragastric administration for 14 days) led to recovery of anhedonia and anxiety behaviors. Memantine also remarkably suppressed serum copper ion levels. Moreover, memantine treatment effectively rescued depression-related spatial memory deficits as shown by the Morris water maze task.

RESULTS

Compared to the pre-memantine treatment results, the results of behavioral tests and cognitive function after memantine treatment were significantly normalized, and the copper concentration was decreased in all groups.

CONCLUSIONS

Collectively, our findings suggest that the NMDA receptor antagonist memantine may improve symptoms of anhedonia and anxiety and the cognitive deficits associated with depression, likely be related to suppress serum copper ion levels.

Temperature and predator-mediated regulation of plasma cortisol and brain gene expression in juvenile brown trout (Salmo trutta)

Background

Temperature affects many aspects of performance in poikilotherms, including how prey respond when encountering predators. Studies of anti-predator responses in fish mainly have focused on behaviour, whereas physiological responses regulated through the hypothalamic-pituitary-interrenal axis have received little attention. We examined plasma cortisol and mRNA levels of stress-related genes in juvenile brown trout (Salmo trutta) at 3 and 8 °C in the presence and absence of a piscivorous fish (burbot, Lota lota).

Results

A redundancy analysis revealed that both water temperature and the presence of the predator explained a significant amount of the observed variation in cortisol and mRNA levels (11.4 and 2.8%, respectively). Trout had higher cortisol levels in the presence than in the absence of the predator. Analyses of individual gene expressions revealed that trout had significantly higher mRNA levels for 11 of the 16 examined genes at 3 than at 8 °C, and for one gene (retinol-binding protein 1), mRNA levels were higher in the presence than in the absence of the predator. Moreover, we found interaction effects between temperature and predator presence for two genes that code for serotonin and glucocorticoid receptors.

Conclusions

Our results suggest that piscivorous fish elicit primary stress responses in juvenile salmonids and that some of these responses may be temperature dependent. In addition, this study emphasizes the strong temperature dependence of primary stress responses in poikilotherms, with possible implications for a warming climate.

Dopamine and serotonin mediate the impact of stress on cleaner fish cooperative behavior

Stress is known to modulate behavioral responses and rapid decision-making processes, especially under challenging contexts which often occur in social and cooperative interactions. Here, we evaluated the effects of acute stress on cooperative behavior of the Indo-Pacific cleaner wrasse (Labroides dimidiatus) and the implications of pre-treatment with monoaminergic compounds: the selective serotonin reuptake inhibitor - fluoxetine, the 5-HT_1A receptor antagonist - WAY-100,635, the D₁ receptor agonist - SKF-38393, and the D₁ receptor antagonist - SCH-23390. We demonstrated that stress decreased the predisposal to interact and increased cortisol levels in cleaners, which are alleviated by fluoxetine and the dopaminergic D₁ antagonist. Overall, our findings highlight the crucial influence of stress on cooperative behavior.

Effect of 5-HT2C receptor agonist and antagonist on chronic unpredictable stress (CUS) - Mediated anxiety and depression in adolescent Wistar albino rat: Implicating serotonin and mitochondrial ETC-I function in serotonergic neurotransmission

Anxiety and depression are among the major neuropsychiatric disorders worldwide, and yet the etiologies of these disorders remain unclear to date. Chronic unpredictable stress (CUS) procedure mimics several behavioral characteristics such as anxiety and depression in rodents. Using this animal model, we have attempted to understand the serotonergic system in the hippocampus and prefrontal cortex, while using the 5-HT_2CR agonist and antagonist in evaluating 5-HT_2C receptor neurotransmission. A decrease in serotonin (5-HT) level, tryptophan hydroxylase-2 activity and, 5-HT_2CR receptor protein down-regulation in the CUS exposed group, explains the involvement of 5-HT and 5-HT_2CR neurotransmission in the genesis of anxiety and depression. Besides, the oxidative stress - attenuated electrolyte imbalance via decrease ATPase pump activity, and compromised oxidative phosphorylation via decrease ETC-I activity are some of the underlying factors affecting neuronal cell survival and serotonergic neurotransmission. To complement our finding, altered behavioral performance scored in the open field test, elevated plus maze test, and the forced swim test, when exposed to CUS is indicative or consistent with anxiety, depression, emotional and locomotor status of the animals. Keeping these findings in mind, treatment with 5-HT_2CR agonist (1-Methylpsilocin at 0.7 mg/kg), and 5-HT_2CR antagonist (RS-102221 hydrochloride at 1 mg/kg) displayed varying results. One prominent finding was the anxiolytic ability of the 5-HT_2CR agonist and the anti-depressive ability of the 5-HT_2CR antagonist on the 7th-day treatment. Though the exact mechanism of action is not clear, their ability to equilibrate brain redox status, restoring Ca²⁺ level via Ca²⁺ATPase pump activity, and sustaining the mitochondrial bioenergetics can all be accounted for facilitating neurogenesis and the serotonergic system.

Hormonal Regulation of Mammalian Adult Neurogenesis: A Multifaceted Mechanism

Adult neurogenesis—resulting in adult-generated functioning, integrated neurons—is still one of the most captivating research areas of neuroplasticity. The addition of new neurons in adulthood follows a seemingly consistent multi-step process. These neurogenic stages include proliferation, differentiation, migration, maturation/survival, and integration of new neurons into the existing neuronal network. Most studies assessing the impact of exogenous (e.g., restraint stress) or endogenous (e.g., neurotrophins) factors on adult neurogenesis have focused on proliferation, survival, and neuronal differentiation. This review will discuss the multifaceted impact of hormones on these various stages of adult neurogenesis. Specifically, we will review the evidence for hormonal facilitation (via gonadal hormones), inhibition (via glucocorticoids), and neuroprotection (via recruitment of other neurochemicals such as neurotrophin and neuromodulators) on newly adult-generated neurons in the mammalian brain.

Serotonergic system may be involved in alterations of sleep homeostasis in spontaneously hypertensive rats

Hypertension is associated with sleep disorders. Spontaneously hypertensive rats are derived from Wistar-Kyoto rats and widely used in research on hypertension. The present study investigated the propensity to sleep and electroencephalographic spectrum changes over 24 hr in spontaneously hypertensive rats, and proposed the involvement of the serotonergic system in these alterations. Time-course analysis showed that spontaneously hypertensive rats exhibit hyperarousal during the light phase but hypersomnia during the dark phase. Spontaneously hypertensive rats also exhibited less slight fluctuation in electroencephalographic delta power density over 24 hr as compared with Wistar-Kyoto rats, suggesting that the accumulation or elimination of sleep pressure was disrupted. Sleep deprivation disrupted the regulation of sleep homeostasis in spontaneously hypertensive rats, reflected by less sleep time and poor sleep quality during the recovery period. The density and activity of serotonergic neurons in the dorsal raphe nucleus were higher in spontaneously hypertensive rats compared with Wistar-Kyoto rats. Interestingly, we observed the absence of fluctuations in 5-hydroxytryptamine and 5-hydroxyindoleacetic acid across the sleep, wake, sleep deprivation and sleep recovery stages in spontaneously hypertensive rats, which were dramatically different from Wistar-Kyoto rats. These results indicate that the disruption of sleep-wake pattern and sleep homeostasis in spontaneously hypertensive rats might be related to abnormalities of the serotonergic system.

Therapeutic and Medicinal Uses of Terpenes

Terpenes, also known as terpenoids are the largest and most diverse group of naturally occurring compounds. Based on the number of isoprene units they have, they are classified as mono, di, tri, tetra, and sesquiterpenes. They are mostly found in plants and form the major constituent of essential oils from plants. Among the natural products that provide medical benefits for an organism, terpenes play a major and variety of roles. The common plant sources of terpenes are tea, thyme, cannabis, Spanish sage, and citrus fruits (e.g., lemon, orange, mandarin). Terpenes have a wide range of medicinal uses among which antiplasmodial activity is notable as its mechanism of action is similar to the popular antimalarial drug in use—chloroquine. Monoterpenes specifically are widely studied for their antiviral property. With growing incidents of cancer and diabetes in modern world, terpenes also have the potential to serve as anticancer and antidiabetic reagents. Along with these properties, terpenes also allow for flexibility in route of administration and suppression of side effects. Certain terpenes were widely used in natural folk medicine. One such terpene is curcumin which holds anti-inflammatory, antioxidant, anticancer, antiseptic, antiplasmodial, astringent, digestive, diuretic, and many other properties. Curcumin has also become a recent trend in healthy foods and open doors for several medical researches. This chapter summarizes the various terpenes, their sources, medicinal properties, mechanism of action, and the recent studies that are underway for designing terpenes as a lead molecule in the modern medicine.

Stressor during Early Adolescence in Hyperreactive Female Wistar Kyoto Rats Induces a 'Double Hit' Manifested by Variation in Neurobehaviors and Brain Monoamines

Stress is an additive factor in the development of depressive-like profiles that mainly onsets during adolescence. However, effects of early post-weaning stress on developing brain neurochemical pathways in inducing anxiety- and depressive-like profiles in vulnerable females have not been extensively studied. The Wistar Kyoto (WKY) rat, a putative model of adolescent depression and stress-sensitivity could elucidate the pathophysiology of stress-related depression in vulnerability. Through such an approach, links between inherent risk for predisposition to depression and homotypic stress, as in a 'double hit' would unravel endocrine regulation, interference in developing neural pathways and neurobehaviors. Here, early adolescent WKY female rats were subjected to 1-h physical restraint over 7 days followed by neurobehavioral testing in the elevated plus maze (EPM) and forced swim test (FST). The stressor's effectiveness was assayed by plasma corticosterone (CORT) and altered functioning in depression-implicated brain areas by assaying monoamines/metabolites. Homotypic stress induced an anxiolytic-like response in the EPM with learned helplessness and reduced struggling behavior in FST. Significant elevation in CORT levels (p < 0.05) indicated an upregulated HPA axis. Medial prefrontal cortex, a still maturing brain area, exhibited increased serotonin (5-HT) metabolite (p < 0.01) and turnover rates (p < 0.01) indicative of altered/maladaptive serotonergic functioning. Nucleus accumbens (p < 0.05) and dorsal striatum (p < 0.01) also depicted increased 5-HT metabolite, with the latter also demonstrating reduced Dopamine turnover (p < 0.01) as a result of homotypic stress. Hence, female WKY rats could constitute a diathesis-stress model to study underlying mechanisms of stress-related depression.

Circadian regulation of depression: A role for serotonin

Synchronizing circadian (24 h) rhythms in physiology and behavior with the environmental light-dark cycle is critical for maintaining optimal health. Dysregulation of the circadian system increases susceptibility to numerous pathological conditions including major depressive disorder. Stress is a common etiological factor in the development of depression and the circadian system is highly interconnected to stress-sensitive neurotransmitter systems such as the serotonin (5-hydroxytryptamine, 5-HT) system. Thus, here we propose that stress-induced perturbation of the 5-HT system disrupts circadian processes and increases susceptibility to depression. In this review, we first provide an overview of the basic components of the circadian system. Next, we discuss evidence that circadian dysfunction is associated with changes in mood in humans and rodent models. Finally, we provide evidence that 5-HT is a critical factor linking dysregulation of the circadian system and mood. Determining how these two systems interact may provide novel therapeutic targets for depression.

Differences Between the Prenatal Effects of Fluoxetine or Buspirone Alone or in Combination on Pain and Affective Behaviors in Prenatally Stressed Male and Female Rats

The selective serotonin reuptake inhibitor fluoxetine and the 5-HT1A receptor agonist buspirone are used to treat depression and anxiety. Previously we demonstrated that chronic stress during pregnancy (prenatal stress) in rats, used as a model of maternal depression risk, increased inflammatory pain and depressive-like behavior in the offspring; buspirone injected to pregnant dams was protective. Clinically, the addition of buspirone to fluoxetine increases the latter’s efficacy in treating depression in patients. Here, we investigated the influence of repeated prenatal injections of fluoxetine, buspirone or their combination on pain- and depressive-like behaviors in prenatally stressed young male and female rats. Prenatal stress augmented depressive-like behavior and both thermal and inflammatory pain (formalin test), replicating our prior findings, and increased basal levels of corticosterone in the blood plasma. Both drugs and their combination reduced the effects of prenatal stress on thermal pain and depressive-like behavior independently of sex. The combination of fluoxetine and buspirone, compared with fluoxetine, was more antinociceptive in the hot plate test in both sexes, and when compared with buspirone, was more antinociceptive only in males. A detailed study of the time-course of formalin-induced pain showed a nuanced effect of these drugs that was sex-dependent. The combination of the two drugs was less effective in females than males during the initial acute phase of nociceptive behavior in flexing + shaking behaviors, whereas that combination was more effective than fluoxetine alone in the first acute phase of licking behavior in females. The antinociceptive effect of buspirone dominated that of the drug combination and of fluoxetine alone, especially during the interphase of the formalin test in both sexes for both flexing + shaking and licking, suggesting a more effective prenatal action of buspirone on the development of a descending serotonergic inhibitory system modulating pain in the spinal cord dorsal horn neurons. Our results indicate that inflammatory pain-like responses integrated at the spinal level in males were more vulnerable to prenatal stress than females. In licking, the antinociceptive effect of fluoxetine and drug combination in the interphase was more in males than females. The data underscore the importance of considering sexual dimorphism when using drug therapy.

Label-Free Optical Detection of Multiple Biomarkers in Sweat, Plasma, Urine, and Saliva

We report a novel label-free quantitative detection of human performance "stress" biomarkers in different body fluids based on optical absorbance of the biomarkers in the ultraviolet (UV) region. Stress biomarker (hormones and neurotransmitters) concentrations in bodily fluids (blood, sweat, urine, saliva) predict the physical and mental state of the individual. The stress biomarkers primarily focused on in this manuscript are cortisol, serotonin, dopamine, norepinephrine, and neuropeptide Y. UV spectroscopy of stress biomarkers performed in the 190-400 nm range has revealed primary and secondary absorption peaks at near-UV wavelengths depending on their molecular structure. UV characterization of individual and multiple biomarkers is reported in various biofluids. A microfluidic/optoelectronic platform for biomarker detection is reported, with a prime focus toward cortisol evaluation. The current limit of detection of cortisol in sweat is ∼200 ng/mL (∼0.5 μM), which is in the normal (healthy) range. Plasma samples containing both serotonin and cortisol resulted in readily detectable absorption peaks at 203 (serotonin) and 247 (cortisol) nm, confirming feasibility of simultaneous detection of multiple biomarkers in biofluid samples. UV spectroscopy performed on various stress biomarkers shows a similar increasing absorption trend with concentration. The detection mechanism is label free, applicable to a variety of biomarker types, and able to detect multiple biomarkers simultaneously in various biofluids. A microfluidic flow cell has been fabricated on a polymer substrate to enable point-of-use/care UV measurement of target biomarkers. The overall sensor combines sample dispensing and fluid transport to the detection location with optical absorption measurements with a UV light emitting diode (LED) and photodiode. The biomarker concentration is indicated as a function of photocurrent generated at the target wavelength.

A Memory Circuit for Coping with Impending Adversity

Organisms’ capacity to anticipate future conditions is key for survival. Associative memories are instrumental for learning from past experiences, yet little is known about the processes that follow memory retrieval and their potential advantage in preparing for impending developments. Here, using C. elegans nematodes, we demonstrate that odor-evoked retrieval of aversive memories induces rapid and protective stress responses, which increase animal survival prospects when facing imminent adversities. The underlying mechanism relies on two sensory neurons: one is necessary during the learning period, and the other is necessary and sufficient for memory retrieval. Downstream of memory reactivation, serotonin secreted from two head neurons mediates the systemic stress response. Thus, evoking stressful memories, stored within individual sensory neurons, allows animals to anticipate upcoming dire conditions and provides a head start to initiate rapid and protective responses that ultimately increase animal fitness.

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Reactivation of an aversive memory induces a fast protective stress response

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The fast response provides the animals with a fitness advantage

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One neuron is necessary for memory formation

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Another neuron is necessary and sufficient for memory reactivation

Inhibition of LPS induced neurochemical imbalance and oxidative stress by pigmented and non-pigmented rice bran extracts

This study evaluated the neuroprotective efficacy of the pigmented and non-pigmented rice bran extract, against LPS induced neurotransmitter imbalance and oxidative stress markers. Male wistar rats were orally supplemented with 2% ethanolic rice bran extracts daily for two weeks. On the last day of experiment, rats were challenged intraperitoneally (i.p) with LPS for 4 hr. LPS exposure resulted in the elevation of malondialdehyde and nitrite levels, decreased GSH, increased antioxidant enzymes activity and led to imbalance in neurotransmitters, norepinephrine, dopamine and serotonin and their metabolites 3,4-dihydroxyphenylacetic acid, homovanillic levels and acetylcholinesterase activity. Pre-treatment with rice bran extracts significantly attenuated LPS induced oxidative stress by improving the antioxidant systems, acetylcholinesterase activity and neurotransmitters imbalance with the higher potency for pigmented bran extracts. The findings suggest the possibility of utilization of pigmented bran extract for the prevention of neurodegenerative diseases and promote the overall good health of the brain. PRACTICAL APPLICATION: Present study provides the current evidence for the neuroprotective efficacy of bran extracts from pigmented and non-pigmented rice. These findings indicate the beneficial effects of pre-treatment of rice bran extracts on LPS induced oxidative stress and neurochemical imbalance by improvement in the antioxidant machinery and neurotransmitters level. This study emphasizes the possibility of utilization of pigmented bran extract as a food ingredient to improve the overall brain health.

The Interaction of TPH1 A779C Polymorphism and Maternal Authoritarianism on Creative Potential

Exploring the possible mechanisms through which gene may interact with environment to influence creativity has been one of the leading issues in creativity research. In a sample of four hundred and twenty-one Chinese undergraduate students, the present study investigated for the first time the interaction of TPH1 A779C polymorphism and maternal parenting styles on creative potential. The results showed that there was a significant interaction of TPH1 A779C polymorphism and maternal authoritarianism on creative potential. Moreover, the analysis of regions of significance (Ros) provided supporting evidences for both the diathesis-stress model (flexibility) and the differential susceptibility model (originality). These findings extend our understanding concerning the mechanisms by which gene and environment may act in coordination to contribute to creativity.

Stress Biomarkers in Biological Fluids and Their Point-of-Use Detection

Hormones produced by glands in the endocrine system and neurotransmitters produced by the nervous system control many bodily functions. The concentrations of these molecules in the body are an indication of its state, hence the use of the term biomarker. Excess concentrations of biomarkers, such as cortisol, serotonin, epinephrine, and dopamine, are released by the body in response to a variety of conditions, for example, emotional state (euphoria, stress) and disease. The development of simple, low-cost modalities for point-of-use (PoU) measurements of biomarkers levels in various bodily fluids (blood, urine, sweat, saliva) as opposed to conventional hospital or lab settings is receiving increasing attention. This paper starts with a review of the basic properties of 12 primary stress-induced biomarkers: origin in the body (i.e., if they are produced as hormones, neurotransmitters, or both), chemical composition, molecular weight (small/medium size molecules and polymers, ranging from ∼100 Da to ∼100 kDa), and hydro- or lipophilic nature. Next is presented a detailed review of the published literature regarding the concentration of these biomarkers found in several bodily fluids that can serve as the medium for determination of the condition of the subject: blood, urine, saliva, sweat, and, to a lesser degree, interstitial tissue fluid. The concentration of various biomarkers in most fluids covers a range of 5-6 orders of magnitude, from hundreds of nanograms per milliliter (∼1 μM) down to a few picograms per milliliter (sub-1 pM). Mechanisms and materials for point-of-use biomarker sensors are summarized, and key properties are reviewed. Next, selected methods for detecting these biomarkers are reviewed, including antibody- and aptamer-based colorimetric assays and electrochemical and optical detection. Illustrative examples from the literature are discussed for each key sensor approach. Finally, the review outlines key challenges of the field and provides a look ahead to future prospects.

Akebia quinata Decaisne aqueous extract acts as a novel anti-fatigue agent in mice exposed to chronic restraint stress

ETHNOPHARMACOLOGICAL RELEVANCE

Akebia quinata Decaisne extract (AQE; Lardizabalaceae) is used in traditional herbal medicine for stress- and fatigue-related depression, improvement of fatigue, and mental relaxation.

AIM OF THE STUDY

To clarify the effects of AQE on stress-induced fatigue, we investigated the neuroprotective pharmacological effects of A. quinata Decaisne in mice exposed to chronic restraint stress.

MATERIALS AND METHODS

Seven-week old C57BL/6 mice chronically stressed by immobilization for 3 h daily for 15 d and non-stressed control mice underwent daily oral administration of AQE or distilled water. The open field, sucrose preference, and forced swimming behavioral tests were carried out once weekly, and immunohistochemical analyses of NeuN, brain-derived neurotrophic factor (BDNF), phosphorylated cAMP response element-binding (CREB) protein, and BDNF receptor tropomyosin receptor kinase B (TrkB) in striatum and hippocampus were performed at the end of the experimental period. Brain levels of serotonin, adrenaline, and noradrenaline as well as serum levels of corticosterone were measured.

RESULTS

Behavioral tests showed that treatment with AQE improved all lethargic behaviors examined. AQE significantly attenuated the elevated levels of adrenaline, noradrenaline, and serotonin in the brain and corticosterone, alanine transaminase, and aspartate transaminase levels in the serum. Histopathological analysis showed that AQE reduced liver injury and lateral ventricle size in restraint-stress mice via inhibition of neuronal cell death. Immunohistochemical analysis showed increased phosphorylation of CREB and expression of BDNF and its receptor TrkB in striatum and hippocampus. Chlorogenic acid, isochlorogenic acid A, and isochlorogenic acid C were identified as the primary components of AQE. All three agents increased expression of BDNF in SH-SY5Y cells and PC12 cells with H₂O₂-induced neuronal cell damage.

CONCLUSIONS

AQE may have a neuroprotective effect and ameliorate the effects of stress and fatigue-associated brain damage through mechanisms involving regulation of BDNF-TrkB signaling.

Neurobiology of depression: A neurodevelopmental approach

OBJECTIVES

The main aims of this paper are to review and evaluate the neurobiology of the depressive syndrome from a neurodevelopmental perspective.

METHODS

An English language literature search was performed using PubMed.

RESULTS

Depression is a complex syndrome that involves anatomical and functional changes that have an early origin in brain development. In subjects with genetic risk for depression, early stress factors are able to mediate not only the genetic risk but also gene expression. There is evidence that endocrine and immune interactions have an important impact on monoamine function and that the altered monoamine signalling observed in the depressive syndrome has a neuro-endocrino-immunological origin early in the development.

CONCLUSIONS

Neurodevelopment is a key aspect to understand the whole neurobiology of depression.

The Roles of Serotonin in Decision-making under Social Group Conditions

People in a social group often have to make decisions under conflict, for instance, to conform to the group or obey authority (subjects at higher social rank in the group). The neural mechanisms underlying how social group setting affects decision-making have largely remained unclear. In this study, we designed novel behavioral tests using food access priority and fear conditioning paradigms that captured decision-making under conflict associated with social group environments in mice and examined the roles of serotonin (5-HT) on these processes. Using these behavioral tests, administration of the selective 5-HT reuptake inhibitor, which increased 5-HT transmission, was found to attenuate conflicts in decision-making that may be associated with human cases of social obedience and conformity in mice under group housing. The results suggest that 5-HT plays important roles in the regulation of individual behaviors that organize social group dynamics.

The 5-HTTLPR genotype, early life adversity and cortisol responsivity to psychosocial stress in women

BACKGROUND

The serotonin transporter gene-linked polymorphic region (5-HTTLPR) has previously been associated with hypothalamus-pituitary-adrenal axis function. Moreover, it has been suggested that this association is moderated by an interaction with stressful life experiences.

AIMS

To investigate the moderation of cortisol response to psychosocial stress by 5-HTTLPR genotype, either directly or through an interaction with early life stress.

METHOD

A total of 151 women, 85 of which had personality psychopathology, performed the Trier Social Stress Test while cortisol responsivity was assessed.

RESULTS

The results demonstrate a main effect of genotype on cortisol responsivity. Women carrying two copies of the long version of 5-HTTLPR exhibited stronger cortisol responses to psychosocial stress than women with at least one copy of the short allele (P = 0.03). However, the proportion of the variance of stress-induced cortisol responsivity explained by 5-HTTLPR genotype was not further strengthened by including early life adversity as a moderating factor (P = 0.52).

CONCLUSIONS

Our results highlight the need to clarify gender-specific biological factors influencing the serotonergic system. Furthermore, our results suggest that childhood maltreatment, specifically during the first 15 years of life, is unlikely to exert a moderating influence of large effect on the relationship between the 5-HTTLPR genotype and cortisol responsivity to psychosocial stress.

DECLARATION OF INTEREST

None.

Testosterone, Cortisol and Financial Risk-Taking

Both testosterone and cortisol have major actions on financial decision-making closely related to their primary biological functions, reproductive success and response to stress, respectively. Financial risk-taking represents a particular example of strategic decisions made in the context of choice under conditions of uncertainty. Such decisions have multiple components, and this article considers how much we know of how either hormone affects risk-appetite, reward value, information processing and estimation of the costs and benefits of potential success or failure, both personal and social. It also considers how far we can map these actions on neural mechanisms underlying risk appetite and decision-making, with particular reference to areas of the brain concerned in either cognitive or emotional functions.

Corticosterone and serotonin similarly influence GABAergic and purinergic pathways to affect cortical inhibitory networks

Both serotonin (5-HT) and stress exert changes in cortical inhibitory tone to shape the activity of cortical networks. Because astrocytes are also known to affect inhibition through established purinergic pathways, we assessed the role of GABA and purinergic pathways with respect to the effects of rapid corticosterone (CORT) and 5-HT on cortical inhibition. We used a paired-pulse paradigm (P1 and P2) in acutely isolated mouse brain slices to evaluate changes in cortical evoked inhibition. Normally, 5-HT decreases the amplitude of the first pulse P1, whereas it increases the amplitude of P2 (increasing frequency transmission). Interestingly, it was observed that CORT application decreased P1 and increased P2 similar to that of 5-HT application. Given that CORT and 5-HT are known to modulate inhibition, we applied the GABA_A antagonist bicuculline in the presence of both and found that the increase in P2 and the P2/P1 was lost, providing evidence for a common mechanism involving GABA_A receptor signalling. Additional occlusion experiments (ie, 5-HT in presence of CORT and CORT in presence of 5-HT) provide further support for a common mechanism. Because both 5-HT and CORT blocked the increase in P2 and P2/P1 with respect to the other, we suggest 5-HT/CORT already utilise the shared mechanism to affect cortical inhibition. Using low concentrations of the GAPDH inhibitor iodoacetate, as commonly used to selectively disrupt astrocyte metabolism, we found that the increase in P2 and P2/P1 was similarly blocked in response to both CORT and 5-HT. Because astrocyte signalling depends in large part on purinergic pathways, the purinergic contribution was assessed using Ab129 (P2Y antagonist) and SCH 58261 (A2A antagonist). Once again, P2Y and A2A receptor blockade similarly disrupted 5-HT- or CORT-mediated increases in P2 and P2/P1. Taken together, these results support the common involvement of GABAergic and purinergic pathways in the effects of CORT and 5-HT that may also involve astrocytes.

The brain-gut axis of fish: Rainbow trout with low and high cortisol response show innate differences in intestinal integrity and brain gene expression

In fish, the stress hormone cortisol is released through the action of the hypothalamic pituitary interrenal axis (HPI-axis). The reactivity of this axis differs between individuals and previous studies have linked this to different behavioural characteristics and stress coping styles. In the current study, low and high responding (LR and HR) rainbow trout in terms of cortisol release during stress were identified, using a repeated confinements stress test. The expression of stress related genes in the forebrain and the integrity of the stress sensitive primary barrier of the intestine was examined. The HR trout displayed higher expression levels of mineralocorticoid and serotonergic receptors and serotonergic re-uptake pumps in the telencephalon during both basal and stressed conditions. This confirms that HPI-axis reactivity is linked also to other neuronal behavioural modulators, as both the serotonergic and the corticoid system in the telencephalon are involved in behavioural reactivity and cognitive processes. Involvement of the HPI-axis in the brain-gut-axis was also found. LR trout displayed a lower integrity in the primary barrier of the intestine during basal conditions compared to the HR trout. However, following stress exposure, LR trout showed an unexpected increase in intestinal integrity whereas the HR trout instead suffered a reduction. This could make the LR individuals more susceptible to pathogens during basal conditions where instead HR individuals would be more vulnerable during stressed conditions. We hypothesize that these barrier differences are caused by regulation/effects on tight junction proteins possibly controlled by secondary effects of cortisol on the intestinal immune barrier or differences in parasympathetic reactivity.

The 5-HT7 receptor antagonist SB 269970 ameliorates corticosterone-induced alterations in 5-HT7 receptor-mediated modulation of GABAergic transmission in the rat dorsal raphe nucleus

RATIONALE

Chronic stress and corticosterone have been shown to affect serotonin (5-HT) neurotransmission; however, the influence of stress on the activity of the dorsal raphe nucleus (DRN), the main source of 5-HT in the forebrain, is not well understood. In particular, it is unknown if and how stress modifies DRN 5-HT₇ receptors, which are involved in the modulation of the firing of local inhibitory interneurons responsible for regulating the activity of DRN projection cells.

OBJECTIVES

Our study aimed to investigate the effect of repeated corticosterone injections on the modulation of the inhibitory transmission within the DRN by 5-HT₇ receptors and whether it could be reversed by treatment with a 5-HT₇ receptor antagonist.

METHODS

Male Wistar rats received corticosterone injections repeated twice daily for 14 days. Spontaneous inhibitory postsynaptic currents (sIPSCs) were then recorded from DRN projection cells in ex vivo slice preparations obtained 24 h after the last injection.

RESULTS

Repeated corticosterone administration resulted in decreased frequency, but not amplitude, of sIPSCs in DRN projection cells. There were no changes in the excitability of these cells; however, corticosterone treatment suppressed the 5-HT₇ receptor-mediated increase in sIPSC frequency. Administration of the 5-HT₇ receptor antagonist SB 269970 for 7 days beginning on the eighth day of corticosterone treatment reversed the detrimental effects of corticosterone on 5-HT₇ receptor reactivity and GABAergic transmission in the DRN.

CONCLUSIONS

Elevated corticosterone level reduces DRN 5HT₇ receptor reactivity and decreases GABAergic transmission within the DRN, which can be reversed by the 5-HT₇ receptor antagonist SB 269970.

HPA-axis genes as potential risk variants for neurocognitive decline in trauma-exposed, HIV-positive females

PURPOSE

Previous studies have independently provided evidence for the effects of HIV infection, hypothalamic-pituitary-adrenal (HPA) axis dysfunction and early life trauma on neurocognitive impairment (NCI). This study examined the interaction between single-nucleotide polymorphisms (SNPs) of two HPA axis genes, corticotrophin-releasing hormone receptor 1 (CRHR1; rs110402, rs242924, rs7209436, and rs4792888) and corticotrophin-releasing hormone-binding protein (CRHBP; rs32897, rs10062367, and rs1053989), childhood trauma, and HIV-associated NCI.

PATIENTS AND METHODS

The sample comprised 128 HIV-positive Xhosa females of whom 88 (69%) had a history of childhood trauma. NCI was assessed using a battery of 17 measures sensitive to the effects of HIV, and the history of childhood trauma was assessed using the validated retrospective Childhood Trauma Questionnaire-Short Form. Generalized linear regression models were used to compare allelic distribution by trauma status and global NCI. The association between genotype, childhood trauma, and cognitive scores was also evaluated using generalized linear regression models, assuming additive models for the SNPs, and ANOVA.

RESULTS

Of the seven polymorphisms assessed, only the rs10062367 variant of CRHBP was significantly associated with global NCI (P=0.034), independent of childhood trauma. This polymorphism was not significantly associated with z-scores on any specific cognitive domain. The interaction of childhood trauma and variants of CRHR1 was associated with poorer learning (rs110402) and/or recall (rs110402 and rs4792888).

CONCLUSION

These findings suggest that CRHBP rs10062367 A allele is a possible risk variant for NCI in HIV, independent of childhood trauma. Furthermore, results show that the interaction of childhood trauma with variants of CRHR1, rs110402 and rs4792888, confer added vulnerability to NCI in HIV-infected individuals in cognitive domains that are known to be impacted by HIV. While these findings need independent replication in larger samples, it adds CRHBP and CRHR1 to the list of known genes linked to HIV- and childhood trauma-associated neurocognitive phenotypes.

An Elongin-Cullin-SOCS Box Complex Regulates Stress-Induced Serotonergic Neuromodulation

Neuromodulatory cells transduce environmental information into long-lasting behavioral responses. However, the mechanisms governing how neuronal cells influence behavioral plasticity are difficult to characterize. Here, we adapted the translating ribosome affinity purification (TRAP) approach in C. elegans to profile ribosome-associated mRNAs from three major tissues and the neuromodulatory dopaminergic and serotonergic cells. We identified elc-2, an Elongin C ortholog, specifically expressed in stress-sensing amphid neuron dual ciliated sensory ending (ADF) serotonergic sensory neurons, and we found that it plays a role in mediating a long-lasting change in serotonin-dependent feeding behavior induced by heat stress. We demonstrate that ELC-2 and the von Hippel-Lindau protein VHL-1, components of an Elongin-Cullin-SOCS box (ECS) E3 ubiquitin ligase, modulate this behavior after experiencing stress. Also, heat stress induces a transient redistribution of ELC-2, becoming more nuclearly enriched. Together, our results demonstrate dynamic regulation of an E3 ligase and a role for an ECS complex in neuromodulation and control of lasting behavioral states.