Restraint stress-induced brain activation patterns in two strains of mice differing in their anxiety behaviour

Functional Differentiation along the Rostro-Caudal Axis of the Avian Hippocampal Formation

INTRODUCTION

Different functional domains can be identified along the longitudinal axis of the mammalian hippocampus. We have recently hypothesized that a similar functional gradient may exist along the longitudinal axis of the avian hippocampal formation (HF) as well. If the 2 gradients are homologous, we would expect the caudal HF to be more responsive to acute stress than the rostral HF.

METHODS

We restrained 8 adult Dekalb White hens in a bag for 30 min under red-light conditions and compared FOS-immunoreactive (FOS-ir) cell densities in different hippocampal subdivisions to control hens.

RESULTS

Although we could find no evidence of an activated stress response in the hypothalamic-pituitary-adrenal axis of the restrained birds, we did find a significant increase in FOS-ir cell densities in the rostral HF of the restrained birds compared to controls.

CONCLUSION

We speculate that the HF response is not due to an acute stress response, but instead, it is related to the change in spatial context that was part of taking the birds and restraining them in a different room. We see no activation in the caudal HF. This would be consistent with our hypothesis that the longitudinal axis of the avian HF is homologous to the long axis of the mammalian hippocampus.

D2-like dopamine receptors blockade within the dentate gyrus shows a greater effect on stress-induced analgesia in the tail-flick test compared to D1-like dopamine receptors

INTRODUCTION

Acute stress, as a protective mechanism to respond to an aversive stimulus, can often be accompanied by suppressing pain perception via promoting consistent burst firing of dopamine neurons. Besides, sensitive and advanced research techniques led to the recognition of the mesohippocampal dopaminergic terminals, particularly in the hippocampal dentate gyrus (DG). Moreover, previous studies have shown that dopamine receptors within the hippocampal DG play a critical role in induced antinociceptive responses by forced swim stress (FSS) in the presence of inflammatory pain. Since different pain states can trigger various mechanisms and transmitter systems, the present experiments aimed to investigate whether dopaminergic receptors within the DG have the same role in the presence of acute thermal pain.

METHODS

Ninety-seven adult male albino Wistar rats underwent stereotaxic surgery, and a stainless steel guide cannula was unilaterally implanted 1 mm above the DG. Different doses of SCH23390 or sulpiride as D1- and D2-like dopamine receptor antagonists were microinjected into the DG 5-10 min before exposure to FSS, and 5 min after FSS exposure, the tail-flick test evaluated the effect of stress on the nociceptive response at the time-set intervals.

RESULTS

The results demonstrated that exposure to FSS could significantly increase the acute pain perception threshold, while intra-DG administration of SCH23390 and sulpiride reduced the antinociceptive effect of FSS in the tail-flick test.

DISCUSSION

Additionally, it seems the D2-like dopamine receptor within the DG plays a more prominent role in FSS-induced analgesia in the acute pain model.

Locomotion changes in methamphetamine and amphetamine withdrawal: a systematic review

Despite extensive preclinical research over the years, a significant gap remains in our understanding of the specific effects of methamphetamine (METH) and amphetamine (AMPH) withdrawal. Understanding these differences could be pivotal to unveiling the unique pathophysiology underlying each stimulant. This may facilitate the development of targeted and effective treatment strategies tailored to the specific characteristics of each substance. Following PRISMA guidelines, this systematic review was conducted to examine alterations in spontaneous locomotor activity, specifically horizontal activity, in animals experiencing withdrawal from extended and repeated administration of AMPH or METH. Original articles were retrieved from four electronic databases, supplemented by a review of the references cited in the published papers. A total of thirty-one full-length articles (n = 31) were incorporated in the analysis. The results indicated that six studies documented a significant increase in horizontal activity among animals, seven studies reported decreased locomotion, and eighteen studies (8 AMPH; 10 METH) reported no significant alterations in the animals' locomotor activity. Studies reporting heightened locomotion mainly employed mice undergoing withdrawal from METH, studies reporting diminished locomotion predominantly involved rats undergoing withdrawal from AMPH, and studies reporting no significant changes in horizontal activity employed both rats and mice (12 rats; 6 mice). Drug characteristics, routes of administration, animal models, dosage regimens, duration, and assessment timing seem to influence the observed outcomes. Despite more than 50% of papers enlisted in this review indicate no significant changes in the locomotion during the stimulant withdrawal, the unique reactions of animals to withdrawal from METH and AMPH reported by some underscore the need for a more nuanced understanding of stimulant withdrawal.

Inhibition of FKBP51 induces stress resilience and alters hippocampal neurogenesis

Stress-related psychiatric disorders such as depression are among the leading causes of morbidity and mortality. Considering that many individuals fail to respond to currently available antidepressant drugs, there is a need for antidepressants with novel mechanisms. Polymorphisms in the gene encoding FK506-binding protein 51 (FKBP51), a co-chaperone of the glucocorticoid receptor, have been linked to susceptibility to stress-related psychiatric disorders. Whether this protein can be targeted for their treatment remains largely unexplored. The aim of this work was to investigate whether inhibition of FKBP51 with SAFit2, a novel selective inhibitor, promotes hippocampal neuron outgrowth and neurogenesis in vitro and stress resilience in vivo in a mouse model of chronic psychosocial stress. Primary hippocampal neuronal cultures or hippocampal neural progenitor cells (NPCs) were treated with SAFit2 and neuronal differentiation and cell proliferation were analyzed. Male C57BL/6 mice were administered SAFit2 while concurrently undergoing a chronic stress paradigm comprising of intermittent social defeat and overcrowding, and anxiety and depressive -related behaviors were evaluated. SAFit2 increased neurite outgrowth and number of branch points to a greater extent than brain derived neurotrophic factor (BDNF) in primary hippocampal neuronal cultures. SAFit2 increased hippocampal NPC neurogenesis and increased neurite complexity and length of these differentiated neurons. In vivo, chronic SAFit2 administration prevented stress-induced social avoidance, decreased anxiety in the novelty-induced hypophagia test, and prevented stress-induced anxiety in the open field but did not alter adult hippocampal neurogenesis in stressed animals. These data warrant further exploration of inhibition of FKBP51 as a strategy to treat stress-related disorders.

Brain Adaptation to Acute Stress: Effect of Time, Social Buffering, and Nicotinic Cholinergic System

Both social behavior and stress responses rely on the activity of the prefrontal cortex (PFC) and basolateral nucleus of the amygdala (BLA) and on cholinergic transmission. We previously showed in adult C57BL/6J (B6) mice that social interaction has a buffering effect on stress-related prefrontal activity, depending on the β2-/- cholinergic nicotinic receptors (nAChRs, β2-/- mice). The latency for this buffer to emerge being short, we question here whether the associated brain plasticity, as reflected by regional c-fos protein quantification and PFC-BLA functional connectivity, is modulated by time. Overall, we show that time normalized the stress-induced PFC hyperactivation in B6 mice and PFC hypo-activation in β2-/- mice, with no effect on BLA. It also triggered a multitude of functional links between PFC subareas, and between PFC and BLA in B6 mice but not β2-/- mice, showing a central role of nAChRs in this plasticity. Coupled with social interaction and time, stress led to novel and drastic diminution of functional connectivity within the PFC in both genotypes. Thus, time, emotional state, and social behavior induced dissociated effects on PFC and BLA activity and important cortico-cortical reorganizations. Both activity and plasticity were under the control of the β2-nAChRs.

Reproducible induction of depressive-like behavior in C57BL/6J mice exposed to chronic social defeat stress with a modified sensory contact protocol

AIMS

C57BL/6J mice are well-known to exhibit resilience to chronic social defeat stress (CSDS) for induction of depressive-like behavior. Establishment of protocols for reproducible induction of depressive-like behavior in C57BL/6J mice would be useful to elucidate the underlying molecular mechanisms using target gene-knock-in and -out mice whose background is generally C57BL/6J. Here, we developed a modified CSDS protocol for reproducible induction of depressive-like behavior in C57BL/6J mice, and compared the profile of their gut microbiota with that with the standard CSDS protocol.

MAIN METHODS

To prevent acclimation of defeated C57BL/6J mice to aggressive ICR mice, the sensory contact following a daily 10 min-defeat episode was performed by housing an individual defeated mouse in a cage set next to a cage for the aggressor one.

KEY FINDINGS

The number of attacks by ICR mice on C57BL/6J ones was significantly increased with the modified CSDS protocol, and the susceptible mice exhibited greater hippocampal inflammation and an increased immobility time in the forced swim test, compared in the case of the standard CSDS protocol, and the reproducibility was confirmed in another set of experiments. Both the standard and modified CSDS protocols changed the diversity and relative composition of gut microbiota in the susceptible mice, but there was no apparent difference in them between the standard and modified CSDS-susceptible mice.

SIGNIFICANCE

We established a CSDS protocol for reproducible induction of depressive-like behavior in C57BL/6J mice, and the features of the gut microbiota were similar in the susceptible mice with and without the depressive-like behavior.

Testosterone works through androgen receptors to modulate neuronal response to anxiogenic stimuli

Testosterone (T) exerts anxiolytic effects through functional androgen receptors (ARs) in rodents. T treatment of castrated mice reduces anxiety-like behavior in wild-type (WT) males, but not males with a spontaneous mutation that renders AR dysfunctional (testicular feminization mutation, Tfm). Using Cre-LoxP technology we created males carrying induced dysfunctional AR allele (induced TFM; iTfm) to determine the brain regions responsible for T-induced anxiolysis. Adult WT and iTfm mice were castrated and T treated. Castrated WTs given a blank capsule (WT + B) served as additional controls. Mice were later exposed to the anxiogenic light/dark box, sacrificed and their brains processed for immediate early gene cFos immunoreactivity. Analyses revealed that T treatment increased cFos-expressing neurons in the basolateral amygdala (blAMY) of WT males, but not in iTfm males, which did not differ from WT + B mice. In contrast, WT + T males displayed fewer cFos + cells than iTfm + T or WT + B groups in the suprachiasmatic nucleus of the hypothalamus (SCN). No effects of genotype or hormone were seen in cFos expression in the hippocampus, medial prefrontal cortex, paraventricular nucleus of the hypothalamus, oval and anterodorsal bed nucleus of the stria terminalis, or dorsal periaqueductal grey. AR immunohistochemistry indicated that ∼65 % of cells in the blAMY and SCN were AR + in WT males, so AR could act directly within neurons in these regions to modulate the animals' response to anxiogenic stimuli. Because absence of a functional AR did not affect cFos response to mild stress in the other brain regions, they are unlikely to mediate androgen's anxiolytic effects.

Sexual dimorphic effects of restraint stress on prefrontal cortical function are mediated by glucocorticoid receptor activation

Stress, a major regulator and precipitating factor of cognitive and emotional disorders, differentially manifests between males and females. Our aim was to investigate the mechanisms underlying the sexual dimorphic effects of acute restraint stress (RS) on males and females on the function of the prefrontal cortex (PFC). Adult male and female mice were subjected to RS or left in their home-cage (NR), and then tested in the light-dark test followed by the temporal order object recognition (TOR) task. Female mice exhibited increased anxiety-like levels, whereas male mice only showed deficits in the TOR task. When the behavioural tests were conducted 24 hr following restraint stress (RS24), only the reduced performance in the TOR task in male mice persisted. In a different cohort, evoked field excitatory postsynaptic potentials (fEPSPs) were recorded in layer II of acute PFC slices, immediately or 24 hr after RS. Long-term potentiation (LTP) was significantly reduced in RS and RS24 male, but not female, compared with their respective NR group. LTP in PFC slices incubated with corticosterone showed significantly reduced LTP only in males. To determine whether glucocorticoid signalling is implicated in the RS-induced behavioural effects, a different cohort of mice was administered mifepristone, a corticosterone receptor antagonist. Mifepristone administration 1 hr before RS prevented the effects of RS on the TOR task in males, but not anxiety. In conclusion, RS has differential effects on recency memory and anxiety, in males and females, which are partly mediated by the effects of corticosterone signalling on synaptic plasticity.

Influences of Stress and Sex on the Paraventricular Thalamus: Implications for Motivated Behavior

The paraventricular nucleus of the thalamus (PVT) is a critical neural hub for the regulation of a variety of motivated behaviors, integrating stress and reward information from environmental stimuli to guide discrete behaviors via several limbic projections. Neurons in the PVT are activated by acute and chronic stressors, however several roles of the PVT in behavior modulation emerge only following repeated stress exposure, pointing to a role for hypothalamic pituitary adrenal (HPA) axis modulation of PVT function. Further, there may be a reciprocal relationship between the PVT and HPA axis in which chronic stress-induced recruitment of the PVT elicits an additional role for the PVT to regulate motivated behavior by modulating HPA physiology and thus the neuroendocrine response to stress itself. This complex interaction may make the PVT and its role in influencing motivated behavior particularly susceptible to chronic stress-induced plasticity in the PVT, especially in females who display increased susceptibility to stress-induced maladaptive behaviors associated with neuropsychiatric diseases. Though literature is describing the sex-specific effects of acute and chronic stress exposure on HPA axis activation and motivated behaviors, the impact of sex on the role of the PVT in modulating the behavioral and neuroendocrine response to stress is less well established. Here, we review what is currently known regarding the acute and chronic stress-induced activation and behavioral role of the PVT in male and female rodents. We further explore stress hormone and neuropeptide signaling mechanisms by which the HPA axis and PVT interact and discuss the implications for sex-dependent effects of chronic stress on the PVT's role in motivated behaviors.

Effect of Aging on Daily Rhythms of Lactate Metabolism in the Medial Prefrontal Cortex of Male Mice

Aging is associated with reduced amplitude and earlier timing of circadian (daily) rhythms in sleep, brain function, and behavior. We examined whether age-related circadian dysfunction extends to the metabolic function of the brain, particularly in the prefrontal cortex (PFC). Using enzymatic amperometric biosensors, we recorded lactate concentration changes in the PFC in Young (7 mos) and Aged (19 mos) freely-behaving C57BL/6N male mice. Both Young and Aged mice displayed diurnal and circadian rhythms of lactate, with the Aged rhythm slightly phase advanced. Under constant conditions, the Aged rhythm showed a reduced amplitude not seen in the Young mice. We simultaneously observed a relationship between arousal state and PFC lactate rhythm via electroencephalography, which was modified by aging. Finally, using RT-qPCR, we found that aging affects the daily expression pattern of Glucose Transporter 1 (GLUT-1).

Weissella paramesenteroides WpK4 plays an immunobiotic role in gut-brain axis, reducing gut permeability, anxiety-like and depressive-like behaviors in murine models of colitis and chronic stress

The relationship between inflammatory bowel disease (IBD) and mood disorders is complex and involves overlapping metabolic pathways, which may determine comorbidity. Several studies have been shown that this comorbidity could worsen IBD clinical course. The treatment of ulcerative colitis is complex, and involves traditional therapy to promote the function of epithelial barrier, reducing exacerbated inflammatory responses. Recently, it has been shown that some probiotic strains could modulate gut-brain axis, reducing depressive and anxiety scores in humans, including IBD patients. Accordingly, this study aimed to evaluate the role of Weissella paramesenteroides WpK4 in murine models of ulcerative colitis and chronic stress. It was observed that bacterium ingestion improved health of colitis mice, reducing intestinal permeability, besides improving colon histopathological appearance. In stressed mice, bacterial consumption was associated with a reduced anxiety-like and depressive-like behaviors. In both assays, the beneficial role of W. paramesenteroides WpK4 was related to its immunomodulatory feature. It is possible to state that W. paramesenteroides WpK4 exerted their beneficial roles in gut-brain axis through their immunomodulatory effects with consequences in several metabolic pathways related to intestinal permeability and hippocampal physiology.

Concurrent environmental enrichment and chronic restraint stress: Effects on innate anxiety and depressive-like behavior in male adolescent mice

Adolescence is a period that exhibits both vulnerability and adaptation to environmental stimulus. This study explored the co-existence effect of environmental enrichment (EE) and restraint stress (RS) on innate anxiety and depressive-like behavior in adolescent mice. Male ICR mice were treated with daily EE and RS (4 h/d or 8 h/d) for 2 or 4 weeks from early adolescence (postnatal day 30) and emotional behaviors were evaluated 24 h after the end of treatment. 4 weeks of 8 h RS treatment decreased immobility time in forced swimming test, demonstrating an antidepressant-like effect. For 2 weeks of treatment, 8 h RS significantly reduced the time spent in the lighted compartment of the light-dark box, indicating an increased anxiety level. These results show that under the present experimental design, RS treatment with different duration could have different effect on mice emotion-related behavior, but there was no interaction between EE and RS.

Comparative Expression Analysis of Stress-Inducible Genes in Murine Immune Cells

Background: Psychological stress affects the immune system. Upon stress occurrence, glucocorticoid is released that binds to the glucocorticoid receptor and regulates gene expression. Thus, we aimed to examine the stress-induced immunomodulatory mechanisms by investigating the expression patterns of stress-inducible genes in murine immune cells. Methods: BALB/c, C57BL/6, glucocorticoid-receptor congenic mice, and corticotropin-releasing hormone (CRH)-deficient mice were exposed to synthetic glucocorticoid, dexamethasone, or placed under a restraint condition. The expression level of stress-related genes, such as Rtp801, Gilz, Mkp-1, Bnip3, and Trp53inp1 was measured in the immune cells in these mice. Results: Short restraint stress induced Rtp801 and Gilz expressions that were higher in the spleen of BALB/c mice than those in C57BL/6 mice. Mkp-1 expression increased equally in these two strains, despite the difference in the glucocorticoid level. These three genes induced by short restraint stress were not induced in the CRH-deficient mice. In contrast, Bnip3 and Trp53inp1 were only upregulated upon longer restraint events. In the thymus, Trp53inp1 expression was induced upon short restraint stress, whereas Gilz expression constantly increased upon short and repetitive restraint stresses. Conclusion: These results suggest that singular and repetitive bouts of stress lead to differential gene expression in mice and stress-induced gene expression in thymocytes is distinct from that observed in splenocytes. Gilz, Rtp801, and Mkp-1 genes induced by short restraint stress are dependent on CRH in the spleen.

High-refined carbohydrate diet consumption induces neuroinflammation and anxiety-like behavior in mice

Consumption of poor nutrients diets is associated with fat tissue expansion and with a central and peripheral low-grade inflammation. In this sense, the microglial cells in the central nervous system are activated and release pro-inflammatory cytokines that up-regulate the inducible nitric oxide synthase (iNOS), promoting Nitric Oxide (NO) production. The excess of NO has been proposed to facilitate anxious states in humans and rodents. We evaluated whether consumption of a high-refined carbohydrate-containing diet (HC) in mice induced anxiety-like behavior in the Novelty Suppressed Feeding Test (NFST) trough facilitation of NO, in the prefrontal cortex (PFC) and hippocampus (HIP). We also verified if HC diet induces activation of microglial cells, alterations in cytokine and leptin levels in such regions. Male BALB/c mice received a standard diet or a HC diet for 3 days or 12 weeks. The chronic consumption of HC diet, but not acute, induced an anxiogenic-like effect in the NSF test and an increase in the nitrite levels in the PFC and HIP. The preferential iNOS inhibitor, aminoguanidine (50 mg/kg, i.p.), attenuated such effects. Moreover, microglial cells in the HIP and PFC were activated after chronic consumption of HC diet. Finally, the expression of iNOS in the PFC and TNF, IL6 and leptin levels in HIP were higher in chronically HC fed mice. Taken together, our data reinforce the notion that diets containing high-refined carbohydrate facilitate anxiety-like behavior, mainly after a long period of consumption. The mechanisms involve, at least in part, the augmentation of neuroinflammatory processes in brain areas responsible for anxiety control.

Ten-Eleven Translocation Proteins Modulate the Response to Environmental Stress in Mice

5-hydroxymethylcytosine (5hmC) is enriched in brain and has been recognized as an important DNA modification. However, the roles of 5hmC and its writers, ten-eleven translocation (Tet) proteins, in stress-induced response have yet to be elucidated. Here, we show that chronic restraint stress (CRS) induced depression-like behavior in mice and resulted in a 5hmC reduction in prefrontal cortex (PFC). We found that loss of Tet1 (Tet1 KO) led to resistance to CRS, whereas loss of Tet2 (Tet2 KO) increased the susceptibility of mice to CRS. Genome-wide 5hmC profiling identified the phenotype-associated stress-induced dynamically hydroxymethylated loci (PA-SI-DhMLs), which are strongly enriched with hypoxia-induced factor (HIF) binding motifs. We demonstrated the physical interaction between TET1 and HIF1α induced by CRS and revealed that the increased HIF1α binding under CRS is associated with SI-DhMLs. These results suggest that TET1 could regulate stress-induced response by interacting with HIFIα.

The roles of 5-hydroxymethylcytosine (5hmC) and its writers, Tet proteins, in stress-induced response remain unclear. Cheng et al. show that Tet1 knockout mice exhibit resistance, whereas Tet2 knockout mice have increased susceptibility to stress. Biochemical and genome-wide analyses suggest that Tet1 could regulate stress-induced response by interacting with Hif1α.

Is chronodisruption a vulnerability factor to stress?

Since the circadian system seems to modulate stress responses, this study aimed to evaluate if the combination of circadian strain and stress amplifies changes expected from each factor alone. Control Balb/c mice (12:12-NS) kept in standard 12:12 light:dark cycles (LD) and submitted to no stress procedures (NS) were compared to groups submitted to shortened LD (10:10-NS), chronic mild stress (CMS) but no circadian strain (12:12-CMS), or shortened LD followed by CMS (10:10-CMS). Rest-activity/temperature rhythms and body weight were assessed throughout the experiments. In Experiment 1 mice were submitted to 3 weeks of CMS; in Experiment 2 sucrose preference and light-dark tests were performed. Also, blood samples were collected at the end of Experiment 2 to assess metabolic parameters. Relative amplitude of temperature after CMS was increased only in the 10:10-CMS group, while body weight change was reduced during CMS regardless of LD intervention. During the CMS, the relative amplitude of temperature was negatively correlated with body weight gain. No differences in behavior and metabolic parameters were seen among groups. Identifying suitable research designs to investigate our hypothesis that circadian disturbances may increase vulnerability to stress-induced depression and anxiety is warranted.

Involvement of the central hypothalamic-pituitary-adrenal axis in hair growth and melanogenesis among different mouse strains

Stress has been demonstrated to play an important role in hair follicle function and the pathogenesis of some hair disorders. The central hypothalamic-pituitary-adrenal (HPA) axis is activated by stress stimuli, synthesizes and releases various components and eventually induces the pathogenesis and recurrence of peripheral diseases. Our aim is to compare the different responses under exposure of stress in hair follicle function among different mouse strains, and to detect the involvement of the central HPA axis after stress in hair follicle growth and melanogenesis. In this study, we exposed different mouse strains (C57BL/6, CBA/J, C3H/HeN, BALB/c and ICR) to a 21-day chronic restraint stress protocol and selected C57BL/6, CBA/J and BALB/c mice for further study because of their significant behavioral alterations. Then, we evaluated and compared the different responses and sensitivity to chronic restraint stress in hair follicle function and central HPA axis among the selected strains. The results showed that expression of POMC, CRF and GR mRNA and protein and serum levels of corticosterone were inhibited in response to stress. These findings suggested that chronic restraint stress may inhibit hair follicle growth and melanogenesis via regulating the key elements of the central HPA axis. In addition, the results revealed different mouse strains exhibit different responses in the central HPA axis and hair follicle after stress exposure. C57BL/6 might be the most sensitive strain among the three strains tested as well as an appropriate strain to study possible pathophysiological mechanisms by which the nervous system influences skin function and screen dermatological drugs suitable for psychotherapy. We believe the current study will provide some useful information for researchers who are interested in the bidirectional communication between the nervous and skin systems and the management of stress-induced cutaneous diseases.

Social defeat-induced Cingulate gyrus immediate-early gene expression and anxiolytic-like effect depend upon social rank

Social hierarchy is considered to impart an adaptive advantage to the species by reducing long-term conflict between conspecifics. While social stratification is frequently established via stress-inducing stimuli, the subsequent integration of individuals into the hierarchy may attenuate anxiety. Presently, we hypothesized that repeated reinforcement of murine social hierarchy in the dominant-submissive relationship (DSR) food-competition test would engender divergent neuroplastic changes mediating both social and anxiety-like behavior among selectively-bred Dominant (Dom) and Submissive (Sub) mice. Two weeks of repeated respective social victory or defeat reduced serum corticosterone levels of both Dom and Sub mice, whereas socially-defeated Sub mice demonstrated markedly greater exploration of the open arms of the elevated plus maze (EPM). At the same time, social victory led to markedly greater expression of the immediate-early genes (IEGs) c-Jun and EGR-1 in the lateral septal nucleus (LSN) among Dom mice, in contrast with defeated Sub counterparts which demonstrated four-fold greater IEG expression in the cingulate gyrus (Cg). These findings point towards involvement of the Cg in the anxiety-like effect among Sub mice after repeated social defeat, and suggest stabilization of the social hierarchy to attenuate the stress-inducing nature of social interaction, particularly for subordinates. Further study of the potentially anxiolytic-like effects of Cg activity should shed light upon the functional significance of the Cg in social interaction, social hierarchical sorting and anxiety.

Impaired neural stem cell expansion and hypersensitivity to epileptic seizures in mice lacking the EGFR in the brain

Mice lacking the epidermal growth factor receptor (EGFR) develop an early postnatal degeneration of the frontal cortex and olfactory bulbs and show increased cortical astrocyte apoptosis. The poor health and early lethality of EGFR^−/− mice prevented the analysis of mechanisms responsible for the neurodegeneration and function of the EGFR in the adult brain. Here, we show that postnatal EGFR‐deficient neural stem cells are impaired in their self‐renewal potential and lack clonal expansion capacity in vitro. Mice lacking the EGFR in the brain (EGFR^Δbrain) show low penetrance of cortical degeneration compared to EGFR^−/− mice despite genetic recombination of the conditional allele. Adult EGFR^Δ mice establish a proper blood–brain barrier and perform reactive astrogliosis in response to mechanical and infectious brain injury, but are more sensitive to Kainic acid‐induced epileptic seizures. EGFR‐deficient cortical astrocytes, but not midbrain astrocytes, have reduced expression of glutamate transporters Glt1 and Glast, and show reduced glutamate uptake in vitro, illustrating an excitotoxic mechanism to explain the hypersensitivity to Kainic acid and region‐specific neurodegeneration observed in EGFR‐deficient brains.

Functional disruption of stress modulatory circuits in a model of temporal lobe epilepsy

Clinical data suggest that the neuroendocrine stress response is chronically dysregulated in a subset of patients with temporal lobe epilepsy (TLE), potentially contributing to both disease progression and the development of psychiatric comorbidities such as anxiety and depression. Whether neuroendocrine dysregulation and psychiatric comorbidities reflect direct effects of epilepsy-related pathologies, or secondary effects of disease burden particular to humans with epilepsy (i.e. social estrangement, employment changes) is not clear. Animal models provide an opportunity to dissociate these factors. Therefore, we queried whether epileptic mice would reproduce neuroendocrine and behavioral changes associated with human epilepsy. Male FVB mice were exposed to pilocarpine to induce status epilepticus (SE) and the subsequent development of spontaneous recurrent seizures. Morning baseline corticosterone levels were elevated in pilocarpine treated mice at 1, 7 and 10 weeks post-SE relative to controls. Similarly, epileptic mice had increased adrenal weight when compared to control mice. Exposure to acute restraint stress resulted in hypersecretion of corticosterone 30 min after the onset of the challenge. Anatomical analyses revealed reduced Fos expression in infralimbic and prelimbic prefrontal cortex, ventral subiculum and basal amygdala following restraint. No differences in Fos immunoreactivity were found in the paraventricular nucleus of the hypothalamus, hippocampal subfields or central amygdala. In order to assess emotional behavior, a second cohort of mice underwent a battery of behavioral tests, including sucrose preference, open field, elevated plus maze, 24h home-cage monitoring and forced swim. Epileptic mice showed increased anhedonic behavior, hyperactivity and anxiety-like behaviors. Together these data demonstrate that epileptic mice develop HPA axis hyperactivity and exhibit behavioral dysfunction. Endocrine and behavioral changes are associated with impaired recruitment of forebrain circuits regulating stress inhibition and emotional reactivity. Loss of forebrain control may underlie pronounced endocrine dysfunction and comorbid psychopathologies seen in temporal lobe epilepsy.

Mouse Strain Affects Behavioral and Neuroendocrine Stress Responses Following Administration of Probiotic Lactobacillus rhamnosus JB-1 or Traditional Antidepressant Fluoxetine

Currently, there is keen interest in the development of alternative therapies in the treatment of depression. Given the explosion of research focused on the microbiota-gut-brain axis, consideration has turned to the potential of certain probiotics to improve patient outcomes for those suffering from mood disorders. Here we examine the abilities of a known antidepressant, fluoxetine, and the probiotic Lactobacillus rhamnosus JB-1™, to attenuate responses to two established criteria for depressive-like behavior in animal models, the tail suspension test (TST) and the corticosterone response to an acute restraint stressor. We examine two different strains of mice known to differ in the extent to which they express both anxiety-like behavior and measures of despair—BALB/c and Swiss Webster—with respectively high and normal behavioral phenotypes for each. While adult male BALB/c mice responded with increased antidepressive-like behavior to both fluoxetine and L. rhamnosus JB-1 in both the TST and the corticosterone stress response, SW mice did not respond to either treatment as compared to controls. These findings highlight the importance of investigating putative antidepressants in mouse strains known to express face validity for some markers of depression. Clinical studies examining the activity of L. rhamnosus JB-1 in patients suffering from mood disorders are warranted, as well as further pre-clinical work examining how interactions between host genotype and intestinal microbial alterations may impact behavioral responses. This study adds to the literature supporting the possibility that modifying the intestinal microbiota via probiotics represents a promising potential therapeutic breakthrough in the treatment of psychiatric disease.

Vortioxetine Improves Context Discrimination in Mice Through a Neurogenesis Independent Mechanism

Major Depressive Disorders (MDD) patients may exhibit cognitive deficits and it is currently unclear to which degree treatment with antidepressants may affect cognitive function. Preclinical and clinical observations showed that vortioxetine (VORT, an antidepressant with multimodal activity), presents beneficial effects on aspects of cognitive function. In addition, VORT treatment increases adult hippocampal neurogenesis (AHN) in rodents, a candidate mechanism for antidepressant activity. Pattern separation (PS) is the ability to discriminate between two similar contexts/events generating two distinct and non-overlapping representations. Impaired PS may lead to overgeneralization and anxiety disorders. If PS impairments were described in depressed patients, the consequences of antidepressant treatment on context discrimination (CD) are still in its infancy. We hypothesized that VORT-increased AHN may improve CD. Thus, in an attempt to elucidate the molecular mechanism underpinning VORT treatment effects on CD, a rodent model of PS, the role of AHN and stress-induced c-Fos activation was evaluated in the adult mouse hippocampus. Chronic treatment with VORT (1.8 g/kg of food weight; corresponding to a daily dose of 10 mg/kg, 3 weeks) improved CD in mice. Interestingly, chronic treatment with VORT reversed ablation of AHN-induced delay in CD and freezing behavior. VORT treatment decreased stress-induced c-Fos activation in the dorsal but not ventral dentate gyrus. VORT treatment did not affect c-Fos activity in the hippocampus of mice with ablated neurogenesis. This study highlights a role of VORT in CD, which may be independent from AHN and hippocampal c-Fos activation. Further studies elucidating the mechanisms underlying VORT’s effects in CD could contribute to future strategies for alleviating the disease burden for individuals suffering from depression and/or anxiety disorders.

DNA N6-methyladenine is dynamically regulated in the mouse brain following environmental stress

Chemical modifications on DNA molecules, such as 5-methylcytosine and 5-hydroxymethylcytosine, play important roles in the mammalian brain. A novel DNA adenine modification, N(6)-methyladenine (6mA), has recently been found in mammalian cells. However, the presence and function(s) of 6mA in the mammalian brain remain unclear. Here we demonstrate 6mA dynamics in the mouse brain in response to environmental stress. We find that overall 6mA levels are significantly elevated upon stress. Genome-wide 6mA and transcriptome profiling reveal an inverse association between 6mA dynamic changes and a set of upregulated neuronal genes or downregulated LINE transposon expression. Genes bearing stress-induced 6mA changes significantly overlap with loci associated with neuropsychiatric disorders. These results suggest an epigenetic role for 6mA in the mammalian brain as well as its potential involvement in neuropsychiatric disorders.

N6-methyladenine is a covalent epigenetic modification of the genome. Here, Yao and colleagues show that N6-methyladenine level in the mouse brain is dynamic following environmental stress, and the subsequent differential gene expression is correlated with LINE transposon expression.

Elucidation of the neural circuits activated by a GABAB receptor positive modulator: Relevance to anxiety

Although there is much evidence for a role of GABA_B receptors in the pathophysiology of anxiety, the underlying neuronal mechanisms are largely unclear. The GABA_B receptor allosteric positive modulator, GS39783, exerts anxiolytic effects without interfering with GABA_B-mediated modulation of body temperature, cognitive performance and locomotor activity thus offering advantages over GABA_B receptor agonists. However, the precise neural circuits underlying the anxiolytic effects of GS39783 are unknown. The aim of the present study was to identify brain structures and associated neuronal circuits that are modulated by GS39783 under either basal or mild stress conditions. To this end, the expression pattern of c-Fos, a marker of neuronal activation, was examined in mice acutely treated with GS39783 under basal conditions or following a mild anxiogenic challenge induced by exposure to the Open Arm (OA) of an Elevated Plus Maze. OA exposure enhanced c-Fos expression in vehicle-treated animals in several brain regions, including the medial prefrontal cortex, lateral septum, amygdala, hippocampus, paraventricular nucleus of the hypothalamus and the periaqueductal gray (PAG). Under basal conditions, GS39783 increased c-Fos in a restricted panel of areas notably amygdala nuclei, cortical areas and PAG subregions, while it inhibited c-Fos expression in the dorsal raphe nucleus (DRN). Under stress conditions, GS39783 reversed OA-induced c-Fos expression in the granular cell layer of the dentate gyrus, no longer increased c-Fos expression in the amygdala nor reduced c-Fos expression in the DRN. These specific patterns of neural activation by GS39783 might explain the neurobiological correlates implicated in GABA_B-mediated anti-anxiety effects. This article is part of the "Special Issue Dedicated to Norman G. Bowery".

Lost in translation? The potential psychobiotic Lactobacillus rhamnosus (JB-1) fails to modulate stress or cognitive performance in healthy male subjects

BACKGROUND

Preclinical studies have identified certain probiotics as psychobiotics - live microorganisms with a potential mental health benefit. Lactobacillus rhamnosus (JB-1) has been shown to reduce stress-related behaviour, corticosterone release and alter central expression of GABA receptors in an anxious mouse strain. However, it is unclear if this single putative psychobiotic strain has psychotropic activity in humans. Consequently, we aimed to examine if these promising preclinical findings could be translated to healthy human volunteers.

OBJECTIVES

To determine the impact of L. rhamnosus on stress-related behaviours, physiology, inflammatory response, cognitive performance and brain activity patterns in healthy male participants.

METHODS

An 8week, randomized, placebo-controlled, cross-over design was employed. Twenty-nine healthy male volunteers participated. Participants completed self-report stress measures, cognitive assessments and resting electroencephalography (EEG). Plasma IL10, IL1β, IL6, IL8 and TNFα levels and whole blood Toll-like 4 (TLR-4) agonist-induced cytokine release were determined by multiplex ELISA. Salivary cortisol was determined by ELISA and subjective stress measures were assessed before, during and after a socially evaluated cold pressor test (SECPT).

RESULTS

There was no overall effect of probiotic treatment on measures of mood, anxiety, stress or sleep quality and no significant effect of probiotic over placebo on subjective stress measures, or the HPA response to the SECPT. Visuospatial memory performance, attention switching, rapid visual information processing, emotion recognition and associated EEG measures did not show improvement over placebo. No significant anti-inflammatory effects were seen as assessed by basal and stimulated cytokine levels.

CONCLUSIONS

L. rhamnosus was not superior to placebo in modifying stress-related measures, HPA response, inflammation or cognitive performance in healthy male participants. These findings highlight the challenges associated with moving promising preclinical studies, conducted in an anxious mouse strain, to healthy human participants. Future interventional studies investigating the effect of this psychobiotic in populations with stress-related disorders are required.

Retrieving fear memories, as time goes by…

Research in fear conditioning has provided a comprehensive picture of the neuronal circuit underlying the formation of fear memories. In contrast, our understanding of the retrieval of fear memories is much more limited. This disparity may stem from the fact that fear memories are not rigid, but reorganize over time. To bring some clarity and raise awareness about the time-dependent dynamics of retrieval circuits, we review current evidence on the neuronal circuitry participating in fear memory retrieval at both early and late time points following auditory fear conditioning. We focus on the temporal recruitment of the paraventricular nucleus of the thalamus (PVT) for the retrieval and maintenance of fear memories. Finally, we speculate as to why retrieval circuits change with time, and consider the functional strategy of recruiting structures not previously considered as part of the retrieval circuit.

Growing up in a Bubble: Using Germ-Free Animals to Assess the Influence of the Gut Microbiota on Brain and Behavior

There is a growing recognition of the importance of the commensal intestinal microbiota in the development and later function of the central nervous system. Research using germ-free mice (mice raised without any exposure to microorganisms) has provided some of the most persuasive evidence for a role of these bacteria in gut-brain signalling. Key findings show that the microbiota is necessary for normal stress responsivity, anxiety-like behaviors, sociability, and cognition. Furthermore, the microbiota maintains central nervous system homeostasis by regulating immune function and blood brain barrier integrity. Studies have also found that the gut microbiota influences neurotransmitter, synaptic, and neurotrophic signalling systems and neurogenesis. The principle advantage of the germ-free mouse model is in proof-of-principle studies and that a complete microbiota or defined consortiums of bacteria can be introduced at various developmental time points. However, a germ-free upbringing can induce permanent neurodevelopmental deficits that may deem the model unsuitable for specific scientific queries that do not involve early-life microbial deficiency. As such, alternatives and complementary strategies to the germ-free model are warranted and include antibiotic treatment to create microbiota-deficient animals at distinct time points across the lifespan. Increasing our understanding of the impact of the gut microbiota on brain and behavior has the potential to inform novel management strategies for stress-related gastrointestinal and neuropsychiatric disorders.

Carbohydrate-enriched diet predispose to anxiety and depression-like behavior after stress in mice

OBJECTIVES

Obesity is a chronic disease frequently associated with serious co-morbidities, such as diabetes type II, metabolic syndrome, and psychiatric disorders. Little is known, however, regarding the behavioral consequences of modified diet constituents and the propensity to development of stress related disorders. Thus, the aim of this study was to verify whether chronic exposure to a normocaloric/high-carbohydrate diet will modify the animal's behavior after different stressful stimuli.

METHODS

BALB/c mice were fed for 12 weeks with a standard chow diet or high refined carbohydrate-containing diet (HC). Following this period, independent groups of animals were exposed to different stress paradigms: 1 - two hours of restraint stress followed by exposure to the Elevated Plus Maze test (EPM) 24 hours later; 2 - The contextual fear conditioning (CFC) test and 3 - the tail suspension test (TST).

RESULTS

Despite no change on total body weight, animals fed with HC diet showed increase in serum leptin levels and higher adiposity compared to diet control group. In behavioral tests, animals from HC diet group displayed reduction in the percentage of entries into the open arms of the EPM, evaluated 24 hours after restraint stress, suggesting an anxiogenic-like effect. It is also observed increase in aversive memory in the CFC test and depressive-like behavior in TST.

DISCUSSION

Our results suggest that a moderate obesity, induced by high refined carbohydrate diet, may facilitate the development of anxiety and depressive-like behaviors after the stress. The mechanisms responsible for such effects remain to be elucidated.

Bifidobacteria modulate cognitive processes in an anxious mouse strain

Increasing evidence suggests that a brain-gut-microbiome axis exists, which has the potential to play a major role in modulating behaviour. However, the role of this axis in cognition remains relatively unexplored. Probiotics, which are commensal bacteria offering potential health benefit, have been shown to decrease anxiety, depression and visceral pain-related behaviours. In this study, we investigate the potential of two Bifidobacteria strains to modulate cognitive processes and visceral pain sensitivity. Adult male BALB/c mice were fed daily for 11 weeks with B. longum 1714, B. breve 1205 or vehicle treatment. Starting at week 4, animals were behaviourally assessed in a battery of tests relevant to different aspects of cognition, as well as locomotor activity and visceral pain. In the object recognition test, B. longum 1714-fed mice discriminated between the two objects faster than all other groups and B. breve 1205-fed mice discriminated faster than vehicle animals. In the Barnes maze, B. longum 1714-treated mice made fewer errors than other groups, suggesting a better learning. In the fear conditioning, B. longum 1714-treated group also showed better learning and memory, yet presenting the same extinction learning profile as controls. None of the treatments affected visceral sensitivity. Altogether, these data suggest that B. longum 1714 had a positive impact on cognition and also that the effects of individual Bifidobacteria strains do not generalise across the species. Clinical validation of the effects of probiotics on cognition is now warranted.

Inverse effects of lipopolysaccharides on anxiety in pregnant mice and their offspring

This study aimed to evaluate the effects of the bacterial lipopolysaccharide (LPS) exposure during early pregnancy on anxiety-related behaviour of both pregnant female mice and their male offspring. Pregnant NMRI mice were treated with subcutaneous injections of LPS (30, 60, 120, 240 and 480 μg/kg) on the tenth gestational day of pregnancy. Pro-inflammatory cytokines, such as TNF-α, IL-1β, IL-6 and corticosterone levels, were measured in maternal serum 1.5h following the LPS injections. Baseline anxiety levels of pregnant mice (1.5h after LPS administration) and their male offspring (at postnatal days 60-70) were investigated with the elevated plus maze (EPM) test. In addition, anxiety levels in the offspring were measured after 2h restraint stress or TNF-α (10 μg/kg) administration. Our results demonstrate that LPS administration induces anxiety-like behaviour and a significant increase in cytokines and corticosterone levels in maternal serum. However, in male offspring, prenatal LPS administration has no significant effects on serum cytokines and corticosterone secretion with an exception of the lowest LPS dose that slightly reduced corticosterone levels. Interestingly, prenatal LPS treatment seemed to decrease the baseline anxiety levels, while pretreatment with restraint stress or TNF-α abolished this anxiolytic effects. In summary, our results suggest that prenatal exposure to LPS during early pregnancy may result in reduced baseline anxiety in adult male offspring.

GABAB(1) receptor subunit isoforms differentially regulate stress resilience

Stressful life events increase the susceptibility to developing psychiatric disorders such as depression; however, many individuals are resilient to such negative effects of stress. Determining the neurobiology underlying this resilience is instrumental to the development of novel and more effective treatments for stress-related psychiatric disorders. GABAB receptors are emerging therapeutic targets for the treatment of stress-related disorders such as depression. These receptors are predominantly expressed as heterodimers of a GABAB(2) subunit with either a GABAB(1a) or a GABAB(1b) subunit. Here we show that mice lacking the GABAB(1b) receptor isoform are more resilient to both early-life stress and chronic psychosocial stress in adulthood, whereas mice lacking GABAB(1a) receptors are more susceptible to stress-induced anhedonia and social avoidance compared with wild-type mice. In addition, increased hippocampal expression of the GABAB(1b) receptor subunit is associated with a depression-like phenotype in the helpless H/Rouen genetic mouse model of depression. Stress resilience in GABAB(1b)(-/-) mice is coupled with increased proliferation and survival of newly born cells in the adult ventral hippocampus and increased stress-induced c-Fos activation in the hippocampus following early-life stress. Taken together, the data suggest that GABAB(1) receptor subunit isoforms differentially regulate the deleterious effects of stress and, thus, may be important therapeutic targets for the treatment of depression.

Characterization of excitatory and inhibitory neuron activation in the mouse medial prefrontal cortex following palatable food ingestion and food driven exploratory behavior

The medial prefrontal cortex (mPFC) is implicated in aspects of executive function, that include the modulation of attentional and memory processes involved in goal selection. Food-seeking behavior has been shown to involve activation of the mPFC, both during the execution of strategies designed to obtain food and during the consumption of food itself. As these behaviors likely require differential engagement of the prefrontal cortex, we hypothesized that the pattern of neuronal activation would also be behavior dependent. In this study we describe, for the first time, the expression of Fos in different layers and cell types of the infralimbic/dorsal peduncular and prelimbic/anterior cingulate subdivisions of mouse mPFC following both the consumption of palatable food and following exploratory activity of the animal directed at obtaining food reward. While both manipulations led to increases of Fos expression in principal excitatory neurons relative to control, food-directed exploratory activity produced a significantly greater increase in Fos expression than observed in the food intake condition. Consequently, we hypothesized that mPFC interneuron activation would also be differentially engaged by these manipulations. Interestingly, Fos expression patterns differed substantially between treatments and interneuron subtype, illustrating how the differential engagement of subsets of mPFC interneurons depends on the behavioral state. In our experiments, both vasoactive intestinal peptide- and parvalbumin-expressing neurons showed enhanced Fos expression only during the food-dependent exploratory task and not during food intake. Conversely, elevations in arcuate and paraventricular hypothalamic fos expression were only observed following food intake and not following food driven exploration. Our data suggest that select activation of these cell types may be required to support high cognitive demand states such as observed during exploration while being dispensable during the ingestion of freely available food.

LSN2424100: a novel, potent orexin-2 receptor antagonist with selectivity over orexin-1 receptors and activity in an animal model predictive of antidepressant-like efficacy

We describe a novel, potent and selective orexin-2 (OX2)/hypocretin-2 receptor antagonist with in vivo activity in an animal model predictive of antidepressant-like efficacy. N-biphenyl-2-yl-4-fluoro-N-(1H-imidazol-2-ylmethyl) benzenesulfonamide HCl (LSN2424100) binds with high affinity to recombinant human OX2 receptors (Ki = 4.5 nM), and selectivity over OX1 receptors (Ki = 393 nM). LSN2424100 inhibited OXA-stimulated intracellular calcium release in HEK293 cells expressing human and rat OX2 receptors (Kb = 0.44 and 0.83 nM, respectively) preferentially over cells expressing human and rat OX1 (Kb = 90 and 175 nM, respectively). LSN2424100 exhibits good exposure in Sprague–Dawley rats after IP, but not PO, administration of a 30 mg/kg dose (AUC_{0–6 h} = 1300 and 269 ng^*h/mL, respectively). After IP administration in rats and mice, LSN2424100 produces dose-dependent antidepressant-like activity in the delayed-reinforcement of low-rate (DRL) assay, a model predictive of antidepressant-like efficacy. Efficacy in the DRL model was lost in mice lacking OX2, but not OX1 receptors, confirming OX2-specific activity. Importantly, antidepressant-like efficacy of the tricyclic antidepressant, imipramine, was maintained in both OX1 and OX2 receptor knock-out mice. In conclusion, the novel OX2 receptor antagonist, LSN2424100, is a valuable tool compound that can be used to explore the role of OX2 receptor-mediated signaling in mood disorders.

The microbiome-gut-brain axis during early life regulates the hippocampal serotonergic system in a sex-dependent manner

Bacterial colonisation of the intestine has a major role in the post-natal development and maturation of the immune and endocrine systems. These processes are key factors underpinning central nervous system (CNS) signalling. Regulation of the microbiome-gut-brain axis is essential for maintaining homeostasis, including that of the CNS. However, there is a paucity of data pertaining to the influence of microbiome on the serotonergic system. Germ-free (GF) animals represent an effective preclinical tool to investigate such phenomena. Here we show that male GF animals have a significant elevation in the hippocampal concentration of 5-hydroxytryptamine and 5-hydroxyindoleacetic acid, its main metabolite, compared with conventionally colonised control animals. Moreover, this alteration is sex specific in contrast with the immunological and neuroendocrine effects which are evident in both sexes. Concentrations of tryptophan, the precursor of serotonin, are increased in the plasma of male GF animals, suggesting a humoral route through which the microbiota can influence CNS serotonergic neurotransmission. Interestingly, colonisation of the GF animals post weaning is insufficient to reverse the CNS neurochemical consequences in adulthood of an absent microbiota in early life despite the peripheral availability of tryptophan being restored to baseline values. In addition, reduced anxiety in GF animals is also normalised following restoration of the intestinal microbiota. These results demonstrate that CNS neurotransmission can be profoundly disturbed by the absence of a normal gut microbiota and that this aberrant neurochemical, but not behavioural, profile is resistant to restoration of a normal gut flora in later life.

Environmental enrichment and gut inflammation modify stress-induced c-Fos expression in the mouse corticolimbic system

Environmental enrichment (EE) has a beneficial effect on rodent behaviour, neuronal plasticity and brain function. Although it may also improve stress coping, it is not known whether EE influences the brain response to an external (psychological) stressor such as water avoidance stress (WAS) or an internal (systemic) stressor such as gastrointestinal inflammation. This study hence explored whether EE modifies WAS-induced activation of the mouse corticolimbic system and whether this stress response is altered by gastritis or colitis. Male C67BL/6N mice were housed under standard or enriched environment for 9 weeks, after which they were subjected to a 1-week treatment with oral iodoacetamide to induce gastritis or oral dextran sulfate sodium to induce colitis. Following exposure to WAS the expression of c-Fos, a marker of neuronal activation, was measured by immunocytochemistry. EE aggravated experimentally induced colitis, but not gastritis, as shown by an increase in the disease activity score and the colonic myeloperoxidase content. In the brain, EE enhanced the WAS-induced activation of the dentate gyrus and unmasked an inhibitory effect of gastritis and colitis on WAS-evoked c-Fos expression within this part of the hippocampus. Conversely, EE inhibited the WAS-evoked activation of the central amygdala and prevented the inhibitory effect of gastritis and colitis on WAS-evoked c-Fos expression in this region. EE, in addition, blunted the WAS-induced activation of the infralimbic cortex and attenuated the inhibitory effect of gastritis and colitis on WAS-evoked c-Fos expression in this area. These data reveal that EE has a region-specific effect on stress-induced c-Fos expression in the corticolimbic system, which is likely to improve stress resilience. The response of the prefrontal cortex – amygdala – hippocampus circuitry to psychological stress is also modified by the systemic stress of gut inflammation, and this interaction between external and internal stressors is modulated by the housing environment.

Treadmill exercise during pregnancy ameliorates post‑traumatic stress disorder‑induced anxiety‑like responses in maternal rats

Post‑traumatic stress disorder (PTSD) is an anxiety disorder triggered by life‑threatening events that cause intense fear. Exercise is known to have protective effects on neuropsychiatric diseases. The present study investigated whether treadmill exercise during pregnancy reduced or alleviated symptoms of PTSD in maternal rats. To induce predator stress in pregnant rats, rats were exposed to a hunting dog in an enclosed room. Exposure time was three 10‑min daily sessions separated by 1 h, starting at week 1 of pregnancy until delivery. Pregnant rats in the exercise group were forced to run on a treadmill for 30 min once a day, starting one week following pregnancy until delivery. Rats receiving predator stress during pregnancy exhibited PTSD anxiety‑like behaviors following delivery. Expression of 5‑hydroxytryptamine (5‑HT) and its synthesizing enzyme tryptophan hydroxylase (TPH) in the dorsal raphe was increased compared with unstressed rats. Expression of c‑Fos and neuronal nitric oxide synthases (nNOS) in the hypothalamus and locus coeruleus were higher in the rats receiving stress during pregnancy compared with unstressed rats. By contrast, treadmill exercise during pregnancy ameliorated anxiety‑like behaviors and reduced the expression of 5‑HT, TPH, c‑Fos and nNOS in the PTSD maternal rats. The results of the present study indicate that exercise during pregnancy is suitable for use as a therapeutic strategy to reduce anxiety‑related disorders, including PTSD.

Mind-altering microorganisms: the impact of the gut microbiota on brain and behaviour

Recent years have witnessed the rise of the gut microbiota as a major topic of research interest in biology. Studies are revealing how variations and changes in the composition of the gut microbiota influence normal physiology and contribute to diseases ranging from inflammation to obesity. Accumulating data now indicate that the gut microbiota also communicates with the CNS--possibly through neural, endocrine and immune pathways--and thereby influences brain function and behaviour. Studies in germ-free animals and in animals exposed to pathogenic bacterial infections, probiotic bacteria or antibiotic drugs suggest a role for the gut microbiota in the regulation of anxiety, mood, cognition and pain. Thus, the emerging concept of a microbiota-gut-brain axis suggests that modulation of the gut microbiota may be a tractable strategy for developing novel therapeutics for complex CNS disorders.

Differential lipopolysaccharide-induced immune alterations in the hippocampus of two mouse strains: effects of stress

Immunological activation may result in the development of depressive-like symptoms in a large percentage of patients treated with cytokine-based therapies. The mechanisms underlying susceptibility to cytokine-induced depression are currently unknown; however activation of the tryptophan catabolising enzyme indoleamine 2,3-dioxygenase (IDO) is associated with the induction of cytokine-induced depression. Peripheral administration of lipopolysaccharide (LPS) is one of the most commonly used immunological challenges in animal models of cytokine-induced depression. Inbred mouse strains are useful tools in the investigation of the neurobiology of psychiatric illnesses. In this study we hypothesised that two strains which differ in stress susceptibility, namely the BALB/c and C57BL/6J mice, would respond differentially to LPS and swim-stress in cytokine profile, corticosterone concentrations and mRNA expression of genes coding for the tryptophan metabolising enzymes, IDO1, IDO2, Tph1 and Tph2. The stress-sensitive BALB/c strain exhibited increased depressive-like behaviour and enhanced corticosterone concentrations in response to LPS. Furthermore, swim-stress attenuated the LPS-induced corticosterone response in BALB/c mice only. LPS significantly increased plasma interleukin (IL)-1β and tumour necrosis factor α (TNFα) concentrations to a greater extent in BALB/c mice. The LPS-induced increase in IL-1β mRNA expression was significantly attenuated by swim-stress in the hippocampus of C57BL/6J but not in BALB/c mice. TNFα mRNA expression was significantly increased in BALB/c mice only; this increase was attenuated by swim-stress. Tph1 mRNA expression was upregulated in the brainstem of C57BL/6J mice post-LPS and following the combination of swim-stress and LPS in BALB/c mice. In the hippocampus Tph1 and Tph2 mRNA expression was increased in C57BL/6J but not BALB/c mice in response to LPS challenge and swim-stress. Conversely, IDO2 but not IDO1 mRNA expression was significantly altered following swim-stress and LPS, particularly in the hippocampus of BALB/c mice. These data indicate altered central mRNA expression of tryptophan metabolising enzymes and immune activation in BALB/c mice compared to the normo-sensitive C57BL/6J strain.

Enhanced anxiety observed in cocaine withdrawn rats is associated with altered reactivity of the dorsomedial prefrontal cortex

Discontinuation of drug intake in cocaine abusers commonly produces a variety of adverse withdrawal symptoms among which anxiety and depression-related behavior are prevailing during the initial period of abstinence. The aim of this study was to provide further insight into the neurobiological dysregulations that might contribute to these pathological states. Rats were treated with cocaine or saline for 14 days (20 mg/kg; i.p) and anxiety-related behavior was assessed in different paradigms (elevated plus-maze (EPM), confinement to an open arm of the EPM and shock-probe burying tests) for up to 4 weeks after withdrawal. Depression-like behavior was assessed by the forced swim test and sucrose preference test. Altogether our results demonstrated that cocaine withdrawal induced persistent heightened levels of anxiety that last for at least 28 days but did not affect depression-like behavior. We then used Fos immunohistochemistry to map neuronal activation patterns in withdrawn rats confined to one open arm of an EPM, and a double labeling procedure using Fos immunohistochemistry and in situ hybridization of glutamic acid decarboxylase or vesicular glutamate transporter mRNAs to identify the phenotype of the activated neurons. Our data showed that the exacerbated anxiety observed in cocaine withdrawn rats exposed to an elevated open arm was accompanied by an altered reactivity of the dorsal part of the medial prefrontal cortex (anterior cingulate and dorsal prelimbic cortices), the paraventricular thalamic nucleus and the lateral and anterior areas of the hypothalamus. In the medial prefrontal cortex, we evidenced a negative correlation between Fos expression in its dorsal part and open arm-induced freezing in NaCl-treated rats but not in cocaine withdrawn rats. We also found that more than 65% of activated neurons were glutamatergic projection neurons. The present study provides new insights into the neuroanatomical regions and neuronal cell types that may underlie pathological anxiety during cocaine withdrawal.

Social context induces two unique patterns of c-Fos expression in adolescent and adult rats

The study assessed possible age differences in brain activation patterns to low dose ethanol (.5 g/kg intraperitoneally) and the influence of social context on this activation. Early adolescent or young adult male Sprague-Dawley rats were placed either alone or with an unfamiliar partner of the same age and sex following saline or ethanol administration. c-Fos protein immunoreactivity was used to index neuronal activation in 15 regions of interest. Ethanol had little effect on c-Fos activation. In adolescents, social context activated an "autonomic" network including the basolateral and central amygdala, bed nucleus of the stria terminalis, lateral hypothalamus, and lateral septum. In contrast, when adult rats were alone, activation was evident in a "reward" network that included the substantia nigra, nucleus accumbens, anterior cingulate and orbitofrontal cortices, lateral parabrachial nucleus, and locus coeruleus.

Imaging trait anxiety in high anxiety F344 rats: Focus on the dorsomedial prefrontal cortex

Functional magnetic resonance imaging (fMRI) has become an important method in clinical psychiatry research whereas there are still only few comparable preclinical investigations. Herein, we report that fMRI in rats can provide key information regarding brain areas underlying anxiety behavior. Perfusion as surrogate for neuronal activity was measured by means of arterial spin labeling-based fMRI in various brain areas of high anxiety F344 rats and control Sprague-Dawley rats. In one of these areas, the dorsomedial prefrontal cortex (dmPFC), c-Fos labeling was compared between these two strains with immunolabeling. The effects of a neurotoxic ibotenic acid lesion of the dmPFC in F344 rats were examined in a social approach-avoidance anxiety procedure and fMRI. Regional brain activity of high anxiety F344 rats was different in selective cortical and subcortical areas as compared to that of low anxiety Sprague-Dawley rats; the largest difference (i.e. hyperactivity) was measured in the dmPFC. Independently, c-Fos labeling confirmed that F344 rats show increased dmPFC activity. The functional role was confirmed by neurotoxic lesion of the dmPFC that reversed the high anxiety-like behavior and partially normalized the brain activity pattern of F344 rats. The current findings may have translational value as increased activity is reported in an equivalent cortical area in patients with social anxiety, suggesting that pharmacological or functional inhibition of activity in this brain area should be explored to alleviate social anxiety in patients.

Chronic stress-induced alterations in mouse colonic 5-HT and defecation responses are strain dependent

Mood disorders and chronic stress are frequently associated with gastrointestinal (GI) symptoms including diarrhoea or constipation. Locally produced serotonin [5-hydroxytryptamine (5-HT)] regulates GI motility and is a key factor in the pathophysiology of stress-associated GI disorders. We aimed to establish whether chronic stress can differentially affect faecal output and colon 5-HT concentration in two inbred mouse strains: BALB/c and C57BL/6 which differ in their ability to cope with stress. Adult male BALB/c and C57BL/6 mice were restrained for 2 h daily for 10 days. Defecation was monitored during each stress session. Twenty-four hours after the last session of stress, plasma corticosterone concentration was higher than control in both strains, indicative of a physiological effect of chronic stress; however, stress-induced diarrhoea was more persistent in C57BL/6 mice. Basal concentration of colon 5-HT was higher in C57BL/6 mice, and stress elicited an increase in colon 5-HT only in this strain. Finally, naïve BALB/c mice had a higher sensitivity (incidence of diarrhoea) to 5-HT (0.33 mg/kg, i.p.) than C57BL/6 mice. Our results suggest that differential defecation responses to stress may be associated with colon 5-HT concentration, which may in turn reflect the individual sensitivity to 5-HT. In addition, C57BL/6 mice emerge as a relevant model for studying GI alterations induced by chronic stress.

Increased expression of the Vesicular Glutamate Transporter-1 (VGLUT1) in the prefrontal cortex correlates with differential vulnerability to chronic stress in various mouse strains: effects of fluoxetine and MK-801

Major depression is a chronic psychiatric illness that is highly prevalent and disabling. The available medications are ineffective for many patients suggesting that differents molecular pathways could be specifically altered in the unresponsive patients. Recently, the glutamatergic system has emerged as a target in the research on depression and acute NMDA receptor blockade has been shown to produce strong antidepressant effects. We have studied the adaptations of four mice strains (C57BL/6, DBA/2, C3H and BALB/c) to a chronic unpredictable stress protocol, a widely used model of depression in rodents. BALB/c mice displayed strikingly different behavioral and neurochemical adaptations compared to the other strains tested, suggesting that different molecular pathways are involved in their specific vulnerability. They became hyperactive during the dark period, anhedonic-like and displayed no alterations in the tail suspension test (TST). After chronic stress, only the BALB/c displayed an increased frontocortical VGLUT1 expression which is suggestive of a dysregulation of their prefrontal glutamatergic system, and no BDNF mRNA alteration, although the acute stress modulation of this mRNA is similar to the other strains. Chronic administration of an antagonist of NMDA receptors, MK-801, induced antidepressant-like effects in the TST for stressed BALB/c, but was ineffective for the hyperactivity and anhedonia-like behavior, in contrast to fluoxetine. Chronic MK-801 was totally inactive on the behavior of stressed C57BL/6 mice. MK-801, but not fluoxetine, inhibited the VGLUT1 prefrontal increase in BALB/c. Fluoxetine increased VGLUT1 and BDNF mRNA expression in the hippocampus of the C57BL/6 but not in the BALB/c strain, suggesting a different reactivity in-between strain to both stress and antidepressant. Interestingly enough, the BDNF or VGLUT1 increase is not necessary to reverse the stress induced behavioral alterations in our experimental settings. This observation supports the conclusion that BDNF and VGLUT1 are depressive state markers, but not involved in its etiology. Finally, there is a substantial similarity between the phenotypes that are observed in the BALB/c mice and endogenous depression in humans, as well as between C57BL/6 mice and atypical depression. To have a better understanding of the variability of depression etiologies in human, and the implication of the glutamatergic system, it may be suggested that future animal studies in the mouse would systematically compare the two strains BALB/c and C57BL/6 for the identification of relevant biological mechanisms. This article is part of a special Issue entitled 'Anxiety and Depression'.