Differences in prefrontal cortex GABA/glutamate ratio after acute restraint stress in rats are associated with specific behavioral and neurobiological patterns

Effects of maternal depression and antidepressant treatment on neurotransmitters, brain regions, and mitochondrial function in rat dams

Increasing evidence suggests that mothers experience stress before or during pregnancy, which can significantly impact their GABAergic system and lead to amygdala hyperactivity. While animal models are expected to reflect the above findings in humans, the current knowledge on the effects of chronic unpredictable mild stress (CUMS) in rat dams remains insufficient. Therefore, the objective of this study was to investigate the structural and neurochemical alterations in the dorsal hippocampus, specifically gamma-aminobutyric acid (GABA) and glutamate (Glu) relative to total creatine (tCr), induced by the CUMS and the effects of antidepressant mirtazapine (MIR) treatment. Magnetic resonance imaging and proton localized magnetic resonance spectroscopy were used in rat dams at two time points to assess the reversibility of these alterations. Eight weeks post-CUMS, chronic stress induced significant alterations in hippocampal metabolism and structural changes, including lower GABA/tCr concentrations and an increased amygdala volume compared to controls. In stressed dams treated with MIR, no changes in GABA levels or amygdala volume were observed. Fourteen weeks post-CUMS, no significant changes in hippocampal neurochemistry were confirmed, while amygdala changes persisted in stressed dams. Moreover, significant time-dependent changes were observed in the amygdala and hypothalamus in the control group with MIR. Interestingly, high-resolution respirometry was performed to assess brain mitochondrial function, revealing only changes in this group. Based on these findings, we confirmed the reversibility of metabolite. Furthermore, MIR has demonstrated potential in regulating neurotransmitter levels and protecting amygdala volume after stress; however, further research is needed to fully understand its therapeutic effects.

Both acute glyphosate and the aminomethylphosphonic acid intoxication decreased the acetylcholinesterase activity in rat hippocampus, prefrontal cortex and gastrocnemius muscle

It has been reported that glyphosate, one of the most common herbicides used in agriculture, impairs locomotion and cognition. Glyphosate has a variable half-life in soil up to biotic and/or abiotic factors transform the molecule in metabolites such as the aminomethylphosphonic acid (AMPA) that has a longer half-life. In this study, female Sprague Dawley rats were acutely exposed to different doses of glyphosate or AMPA (i.e. 10, 56 or 100 mg/kg) and, subsequently, the acetylcholinesterase (AChE) activity was measured in the hippocampus, prefrontal cortex (PFC) and the gastrocnemius muscle. Both glyphosate and AMPA produced a similar decrease in the AChE activity in all the tissues tested. These results suggest that interference with normal cholinergic neurotransmission may be one of the mechanisms involved in glyphosate-induced motor alterations in rats. Moreover, our results highlight the biological importance of AMPA as a molecule with anticholinesterase action in brain and skeletal muscle. To our knowledge, this is the first report showing in vivo that AMPA, the major metabolite of glyphosate, behaves as an organophosphate.

Pre- and Post-Synaptic protein in the major depressive Disorder: From neurobiology to therapeutic targets

Major depressive disorder (MDD) has demonstrated its negative impact on various aspects of the lives of those affected. Although several therapies have been developed over the years, it remains a challenge for mental health professionals. Thus, understanding the pathophysiology of MDD is necessary to improve existing treatment options or seek new therapeutic alternatives. Clinical and preclinical studies in animal models of depression have shown the involvement of synaptic plasticity in both the development of MDD and the response to available drugs. However, synaptic plasticity involves a cascade of events, including the action of presynaptic proteins such as synaptophysin and synapsins and postsynaptic proteins such as postsynaptic density-95 (PSD-95). Additionally, several factors can negatively impact the process of spinogenesis/neurogenesis, which are related to many outcomes, including MDD. Thus, this narrative review aims to deepen the understanding of the involvement of synaptic formations and their components in the pathophysiology and treatment of MDD.

Generalized fear after acute stress is caused by change in neuronal cotransmitter identity

Overgeneralization of fear to harmless situations is a core feature of anxiety disorders resulting from acute stress, yet the mechanisms by which fear becomes generalized are poorly understood. In this study, we show that generalized fear in mice results from a transmitter switch from glutamate to γ-aminobutyric acid (GABA) in serotonergic neurons of the lateral wings of the dorsal raphe. Similar change in transmitter identity was found in the postmortem brains of individuals with posttraumatic stress disorder (PTSD). Overriding the transmitter switch in mice prevented the acquisition of generalized fear. Corticosterone release and activation of glucocorticoid receptors mediated the switch, and prompt antidepressant treatment blocked the cotransmitter switch and generalized fear. Our results provide important insight into the mechanisms involved in fear generalization.

Brain metabolic derangements examined using 1H MRS and their (in)consistency among different rodent models of depression

Major depressive disorder (MDD) is underlined by neurochemical changes in the brain. Proton magnetic resonance spectroscopy (1H MRS) is a useful tool for their examination as it provides information about the levels of metabolites. This review summarises the current knowledge of 1H MRS findings from rodent models of MDD, assesses the results from both a biological and a technical perspective, and identifies the main sources of bias. From a technical point of view, bias-introducing factors are the diversity of the measured volumes and their positioning in the brain, the data processing, and the metabolite concentration expression. The biological variables are strain, sex, and species, as well as the model itself, and in vivo vs. ex vivo exploration. This review identified some consistency in the 1H MRS findings in the models of MDD: lower levels of glutamine, glutamate + glutamine, and higher levels of myo-inositol and taurine in most of the brain regions of MDD models. This may suggest changes in regional metabolism, neuronal dysregulation, inflammation, and a compensatory effect reaction in the MDD rodent models.

Impact of stress on excitatory and inhibitory markers of adolescent cognitive critical period plasticity

Adolescence is a time of significant neurocognitive development. Prolonged maturation of prefrontal cortex (PFC) through adolescence has been found to support improvements in executive function. Changes in excitatory and inhibitory mechanisms of critical period plasticity have been found to be present in the PFC through adolescence, suggesting that environment may have a greater effect on development during this time. Stress is one factor known to affect neurodevelopment increasing risk for psychopathology. However, less is known about how stress experienced during adolescence could affect adolescent-specific critical period plasticity mechanisms and cognitive outcomes. In this review, we synthesize findings from human and animal literatures looking at the experience of stress during adolescence on cognition and frontal excitatory and inhibitory neural activity. Studies indicate enhancing effects of acute stress on cognition and excitation within specific contexts, while chronic stress generally dampens excitatory and inhibitory processes and impairs cognition. We propose a model of how stress could affect frontal critical period plasticity, thus potentially altering neurodevelopmental trajectories that could lead to risk for psychopathology.

Laterality in functional and metabolic state of the bulbectomised rat brain detected by ASL and 1H MRS: A pilot study

OBJECTIVES

Pilot study validating the animal model of depression - the bilateral olfactory bulbectomy in rats - by two nuclear magnetic resonance methods, indirectly detecting the metabolic state of the brain. Furthermore, the study focussed on potential differences in brain laterality.

METHODS

Arterial spin labelling assessed cerebral brain flow in prefrontal, sensorimotor, and piriform cortices, nucleus accumbens, hippocampus, thalamus, circle of Willis, and whole brain. Proton magnetic resonance spectroscopy provided information about relative metabolite concentrations in the cortex and hippocampus.

RESULTS

Arterial spin labelling found no differences in cerebral perfusion in the group comparison but revealed lateralisation in the thalamus of the control group and the sensorimotor cortex of the bulbectomized rats. Lower Cho/tCr and Cho/NAA levels were found in the right hippocampus in bulbectomized rats. The differences in lateralisation were shown in the hippocampus: mI/tCr in the control group, Cho/NAA, NAA/tCr, Tau/tCr in the model group, and in the cortex: NAA/tCr, mI/tCr in the control group.

CONCLUSION

Olfactory bulbectomy affects the neuronal and biochemical profile of the rat brain laterally and, as a model of depression, was validated by two nuclear magnetic resonance methods.

Continuous Ingestion of Lacticaseibacillus rhamnosus JB-1 during Chronic Stress Ensures Neurometabolic and Behavioural Stability in Rats

The intestinal microbiome composition and dietary supplementation with psychobiotics can result in neurochemical alterations in the brain, which are possible due to the presence of the brain–gut–microbiome axis. In the present study, magnetic resonance spectroscopy (MRS) and behavioural testing were used to evaluate whether treatment with Lacticaseibacillus rhamnosus JB-1 (JB-1) bacteria alters brain metabolites’ levels and behaviour during continuous exposure to chronic stress. Twenty Wistar rats were subjected to eight weeks of a chronic unpredictable mild stress protocol. Simultaneously, half of them were fed with JB-1 bacteria, and the second half was given a daily placebo. Animals were examined at three-time points: before starting the stress protocol and after five and eight weeks of stress onset. In the elevated plus maze behavioural test the placebo group displayed increased anxiety expressed by almost complete avoidance of exploration, while the JB-1 dietary supplementation mitigated anxiety which resulted in a longer exploration time. Hippocampal MRS measurements demonstrated a significant decrease in glutamine + glutathione concentration in the placebo group compared to the JB-1 bacteria-supplemented group after five weeks of stress. With the progression of stress, the decrease of glutamate, glutathione, taurine, and macromolecular concentrations were observed in the placebo group as compared to baseline. The level of brain metabolites in the JB-1-supplemented rats were stable throughout the experiment, with only the taurine level decreasing between weeks five and eight of stress. These data indicated that the JB-1 bacteria diet might stabilize levels of stress-related neurometabolites in rat brain and could prevent the development of anxiety/depressive-like behaviour.

The neurogenic niche in Alzheimer's disease

Adult hippocampal neurogenesis is the process of generation and functional incorporation of new neurons, formed by adult neural stem cells in the dentate gyrus. Adult hippocampal neurogenesis is highly dependent upon the integration of dynamic external stimuli and is instrumental in the formation of new spatial memories. Adult hippocampal neurogenesis is therefore uniquely sensitive to the summation of neuronal circuit and neuroimmune environments that comprise the neurogenic niche, and has powerful implications in diseases of aging and neurological disorders. This sensitivity underlies the neurogenic niche alterations commonly observed in Alzheimer's disease, the most common form of dementia. This review summarizes Alzheimer's disease associated changes in neuronal network activity, neuroinflammatory processes, and adult neural stem cell fate choice that ultimately result in neurogenic niche dysfunction and impaired adult hippocampal neurogenesis. A more comprehensive understanding of the complex changes mediating neurogenic niche disturbances in Alzheimer's disease will aid development of future therapies targeting adult neurogenesis.

MicroRNA Let-7e in the Mouse Prefrontal Cortex Differentiates Restraint-Stress-Resilient Genotypes from Susceptible Genotype

Three strains of mice with various susceptibilities to restraint stress (RS), i.e., mice with a knocked out norepinephrine transporter gene (NET-KO), SWR/J and C57BL/6J (WT) mice were shown to serve as a good model to study the molecular mechanisms underlying different stress-coping strategies. We identified 14 miRNAs that were altered by RS in the PFC of these mice in a genotype-dependent manner, where the most interesting was let-7e. Further in silico analysis of its potential targets allowed us to identify five mRNAs (Bcl2l11, Foxo1, Pik3r1, Gab1 and Map2k4), and their level alterations were experimentally confirmed. A next-generation sequencing (NGS) approach, which was employed to find transcripts differentially expressed in the PFC of NET-KO and WT mice, showed that, among others, two additional mRNAs were regulated by mmu-let-7e, i.e., mRNAs that encode Kmt2d and Inf2. Since an increase in Bcl2l11 and Pik3r1 mRNAs upon RS in the PFC of WT mice resulted from the decrease in mmu-let-7e and mmu-miR-484 regulations, we postulated that MAPK, FoxO and PI3K-Akt signaling pathways were associated with stress resilience, although via different, genotype-dependent regulation of various mRNAs by let-7e and miR-484. However, a higher level of Kmt2d mRNA (regulated by let-7e) that was found with NGS analysis in the PFC of NET-KO mice indicated that histone methylation was also important for stress resilience.

Mating and parenting experiences sculpture mood-modulating effects of oxytocin-MCH signaling

The two hypothalamic neuropeptides oxytocin and melanin concentrating hormone (MCH) share several physiological actions such as the control of maternal care, sexual behavior, and emotions. In this study, we uncover the role for the oxytocin-MCH signaling pathway in mood regulation. We identify discrete effects of oxytocin-MCH signaling on depressive behavior and demonstrate that parenting and mating experiences shape these effects. We show that the selective deletion of OXT receptors from MCH neurons increases and decreases depressive behavior in sexually naïve and late postpartum female mice respectively, with no effect on sexually naïve male mice. We demonstrate that both parenting experience and mood-regulating effects of oxytocin-MCH are associated with synaptic plasticity in the reward and fear circuits revealed by the alterations of Arc expressions, which are associated with the depressive behavior. Finally, we uncover the sex-dependent effects of mating on depressive behavior; while the sexual activity reduces the basal levels of depressive behavior in male mice, it reduces in female mice evoked-depression only. We demonstrate that the oxytocin-MCH pathway mediates the effects of sexual activity on depressive behavior. Our data suggest that the oxytocin-MCH pathway can serve as a potential therapeutic target for the treatment of major depression and postpartum mood disorders.

5-Fluorouracil induced dysregulation of the microbiome-gut-brain axis manifesting as depressive like behaviors in rats

Disturbances of the gut microbiome have been widely suggested to be associated with 5-fluorouracil (5-Fu) induced digestive pathologies. Furthermore, it has been elucidated that the gut microbiome may play a key role in the pathogenesis of depressive disorders via the microbiota-gut-brain axis. Despite the speculation, there exists no direct evidence proving the causality between disturbances in the gut microbiome induced by 5-Fu and depressive mood dysregulation. Herein, behavioral testing was used to evaluate depressive-like behaviors in 5-Fu treated rats. Subsequently, the gut microbiota and prefrontal cortex (PFC) metabolic were analyzed by 16S rRNA sequencing and ¹H nuclear magnetic resonance (¹H NMR). To clarify the association between the gut microbiota and their role on depressive-like behaviors caused by 5-Fu, a fecal microbiota transplantation (FMT) experiment was carried out. The results suggested that 5-Fu could significantly alter the diversity and abundance of the gut microbiome, and induce PFC metabolic disorders, as well as depressive behaviors in rats. Transplantation of fecal microbiota from healthy control into 5-Fu treated rats significantly alleviated the PFC metabolic disorder and depressive-like behaviors. In conclusion, this study demonstrated that the gut microbiome was actively involved in the occurrence of 5-Fu induced depressive-like behaviors, and manipulation of specific gut microbiome parameters may serve as a promising novel target for side effects of 5-Fu treatment.

Ketamine administration induces early and persistent neurochemical imbalance and altered NADPH oxidase in mice

Administration in adulthood of subanaesthetic doses of ketamine, an NMDA receptor (NMDA-R) antagonist, is commonly used to induce psychotic-like alterations in rodents. The NADPH oxidase (NOX) derived-oxidative stress has been shown to be implicated in ketamine-induced neurochemical dysfunctions and in the loss of parvalbumin (PV)-positive interneurons associated to the administration of this NMDA receptor antagonist in adult mice. However, very few data are available on the effects of early ketamine administration and its contribution to the development of long-term dysfunctions leading to psychosis. Here, by administering a subanaesthetic dose of ketamine (30 mg/kg i.p.) to mice at postnatal days (PNDs) 7, 9 and 11, we aimed at investigating early neurochemical and oxidative stress-related alterations induced by this NMDA-R antagonist in specific brain regions of mice pups, i.e. prefrontal cortex (PFC) and nucleus accumbens (NAcc) and to assess whether these alterations lasted until the adult period. To this purpose, we evaluated glutamatergic, glutamine and GABAergic tissue levels, as well as PV amount in the PFC, both two hours after the last ketamine injection (PND 11) and at 10  weeks of age. Dopamine (DA) tissue levels and DA turnover were also evaluated in the NAcc at the same time points. Levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a reliable biomarker of oxidative stress, as well as of the free radical producers NOX1 and NOX2 enzymes, were also assessed in both PFC and NAcc of ketamine-treated pups and adult mice. Ketamine-treated pups showed increased cortical levels of glutamate (GLU) and glutamine, as well as similar GABA amount compared to controls, together with an early reduction of cortical PV levels. In the adult period, the same was observed for GLU and PV, whereas GABA levels were increased and no changes in glutamine amount were detected. Ketamine administration in early life induced a decrease in DA tissue levels and an increase of DA turnover which were also detectable at 10 weeks of age. These alterations were accompanied by 8-OHdG elevations in both PFC and NAcc at the two considered life stages. The expression of NOX1 was significantly reduced in these brain regions following ketamine administration at early life stages, while, in the adult period, significant elevation of this enzyme was observed. Levels of NOX2 were found increased at both time points. Our results suggest that an early increase of NOX2-derived oxidative stress may contribute to the development of neurochemical imbalance in PFC and NAcc, induced by ketamine administration. Modifications of NOX1 expression might represent, instead, an early response of the developing brain to a neurotoxic insult, followed by a later attempt to counterbalance ketamine-related detrimental effects.

Changes in saliva proteins in two conditions of compromised welfare in pigs: An experimental induced stress by nose snaring and lameness

The aim of this study was to identify biological pathways and proteins differentially expressed in saliva of pigs in two conditions of compromised welfare: an acute stress consisting of restraint with a nose snare and in pigs with lameness which is a highly frequent problem in the swine industry. For this purpose, high-resolution quantitative proteomics based on Tandem Mass Tags labelling was used. Four proteins showed significant differences in the conditions of compromised welfare, namely cornulin, the heat shock protein 27 and lactate dehydrogenase (LDH), that showed significant increases, whereas immunoglobulin J chain showed a significant decrease. LDH, which was the protein that showed the highest differences, was selected for validation and clinical evaluation as a diagnostic biomarker. Significant changes in this protein were observed between pigs restrained with a nose snare and pigs with lameness compared with healthy pigs when measured with available commercial assays in a larger population of pigs. In conclusion, this study reports that in situations of compromised welfare on farm, such as acute stress and lameness in pigs, there are changes in proteins and metabolic pathways in saliva, and describes a series of proteins that could potentially be used as biomarkers for both short term acute stress and longer term chronic stress of lameness. These biomarkers would have the advantage of being measured in saliva by a noninvasive and not stressful collection sampling procedure.

Investigation of anterior cingulate cortex gamma-aminobutyric acid and glutamate-glutamine levels in obsessive-compulsive disorder using magnetic resonance spectroscopy

BACKGROUND

Obsessive-compulsive disorder (OCD) is a relatively common and disabling psychiatric disorder whose pathophysiology is incompletely understood. In this study, we utilized magnetic resonance spectroscopy (MRS) in an effort to provide a better understanding of the role of brain gamma-aminobutyric acid (GABA) and glutamate in the pathophysiology of OCD. We hypothesized that beyond the separate effects of these neurotransmitter systems, a disruption in the balance between GABA and glutamate could be particularly relevant to OCD.

METHODS

We obtained MRS measures of GABA and glutamate concentrations in the anterior cingulate cortex from 23 adult patients with OCD and 20 sex- and age-matched healthy community volunteers. Established clinical rating scales were used to assess the severities of OCD, anxiety, and depression symptoms. Statistical analysis involved the assessment of patient-control group differences in the individual measures of GABA and glutamate, as well as in the ratio of the GABA to glutamate measures. Additionally, we explored whether differences in the MRS measures existed between two subgroups of patients formed according to the severity of their OCD symptoms. Finally, we assessed the relations of demographic and clinical variables to the MRS measures.

RESULTS

Patients with OCD displayed a higher estimated GABA level and a higher GABA to glutamate ratio than healthy participants, but no significant group differences were observed in the measure of glutamate. The MRS measures did not vary by subgroup and showed no correlations with demographic and clinical variables.

CONCLUSIONS

These results indicate that GABA abnormalities within the anterior cingulate cortex contribute to the pathophysiology of OCD. The results fail to provide evidence that glutamate abnormalities alone are involved in adult OCD. Yet, it seems that a disruption in the balance between glutamate and GABA neurotransmission may have a particularly important role to play in OCD pathophysiology.

Mechanisms of ketamine on mice hippocampi shown by gas chromatography-mass spectrometry-based metabolomic analysis

In the present study, we used a gas chromatography-mass spectrometry-based metabolomics method to evaluate the effects of ketamine on mice hippocampi. Multivariate statistical analysis and ingenuity pathway analysis were then used to identify and explore the potential mechanisms and biofunction of ketamine. Compared with the control (CON) group, 14 differential metabolites that involved amino acid metabolism, energy metabolism, and oxidative stress metabolism were identified. After combination with 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline-2,3-dione (NBQX) administration, six of the 14 metabolites remained significantly differentially expressed between the ketamine (KET) and KET+NBQX groups, including glycine, alanine, glutamine, aspartic acid, myoinositol, and ascorbate, whereas no difference was found in the levels of the other eight metabolites between the KET and KET+NBQX groups, including phosphate, 4-aminobutyric acid, urea, creatine, L-malic acid, galactinol, inosine, and aminomalonic. Our findings indicate that ketamine exerts antidepressant effects through an α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid inhibition-dependent mechanism and a mechanism not affected by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid inhibition. Which provides further insight into the therapeutic mechanisms of ketamine in the hippocampus.

The possible beneficial effects of creatine for the management of depression

Depression, a highly prevalent neuropsychiatric disorder worldwide, causes a heavy burden for the society and is associated with suicide risk. The treatment of this disorder remains a challenge, since currently available antidepressants provide a slow and, often, incomplete response and cause several side effects that contribute to diminish the adhesion of patients to treatment. In this context, several nutraceuticals have been investigated regarding their possible beneficial effects for the management of this neuropsychiatric disorder. Creatine stands out as a supplement frequently used for ergogenic purpose, but it also is a neuroprotective compound with potential to treat or mitigate a broad range of central nervous systems diseases, including depression. This review presents preclinical and clinical evidence that creatine may exhibit antidepressant properties. The focus is given on the possible molecular mechanisms underlying its effects based on the results obtained with different animal models of depression. Finally, evidence obtained in animal models of depression addressing the possibility that creatine may produce rapid antidepressant effect, similar to ketamine, are also presented and discussed.

UPLC-Q-TOF-MS profiling of the hippocampus reveals metabolite biomarkers for the impact of Dl-3-n-butylphthalide on the lipopolysaccharide-induced rat model of depression

PURPOSE

An increasing body of evidence reveals that inflammation is involved in the pathological mechanisms of depression. Our previous basic research confirmed that Dl-3-n-butylphthalide (NBP) possess anti-inflammatory properties. However, studies investigating metabolite biomarkers for the involvement of NBP in hippocampus tissue in the lipopolysaccharide (LPS)-induced rat model of depression are currently limited. Thus, the aim of this study was to identify metabolite biomarkers in the hippocampus for the impact of NBP in this model of depression.

MATERIAL AND METHODS

Male Sprague-Dawley rats were randomly allocated to one of the following three groups (n=6): Control, LPS-induced rat model of depression (LPS), and NBP involvement in the LPS-induced rat model of depression (LPS+NBP). Ultra-high-performance liquid chromatography-mass spectroscopy was used to determine the hippocampal metabolites. Multivariate statistical analysis was performed to identify differentially expressed hippocampal metabolites in the three groups.

RESULTS

Most of the identified differentially expressed metabolites were related to amino acid, lipid, energy, and oxidative stress metabolism. Additionally, metabolites were eventually connected to different pathways and metabolic networks, which may partly account for the pathophysiological process of depression.

CONCLUSION

The present findings provide insight into the anti-inflammatory effects of NBP, and further elucidate the pathophysiological mechanisms underlying inflammation-induced depression.

Neuro-metabolite profiles of rodent models of psychiatric dysfunctions characterised by MR spectroscopy

Neuroimaging endophenotypes in animal models provide an objective and translationally-relevant alternative to cognitive/behavioral traits in human psychopathologies. Metabolic alterations, such as those involved in the glutamate-cycle, have been proposed to play a preponderant role in both depression and schizophrenia. Chronic Mild Unpredictable Stress (CMUS) and sub-chronic administration of NMDA receptor antagonist generate animal models of depression and schizophrenia, respectively. The models are based on etiologically-relevant factors related to the induction and support of these psychopathologies. To test metabolic alterations within the glutamate-cycle and in other major neurochemicals, single-voxel Magnetic Resonance Spectroscopy was recorded within the hippocampus in both rat models and control animals. Surprisingly, altered glutamate-related metabolites were observed in the CMUS model, but not NMDA-based model, as indicated by decreased glutamine and increased GABA levels. However, both models presented elevated total visible choline and inositol levels relative to controls. These results indicate the presence cell membrane metabolic alterations and inflammatory processes shared in both models, comparable to evidence presented in schizophrenia and depression and other comparable animal models. These translationally-relevant biomarkers may thus form the basis for drug-development targets in both psychopathologies.

State-Dependent Memory: Neurobiological Advances and Prospects for Translation to Dissociative Amnesia

In susceptible individuals, overwhelming traumatic stress often results in severe abnormalities of memory processing, manifested either as the uncontrollable emergence of memories (flashbacks) or as an inability to remember events (dissociative amnesia, DA) that are usually, but not necessarily, related to the stressful experience. These memory abnormalities are often the source of debilitating psychopathologies such as anxiety, depression and social dysfunction. The question of why memory for some traumatic experiences is compromised while other comparably traumatic experiences are remembered perfectly well, both within and across individuals, has puzzled clinicians for decades. In this article, we present clinical, cognitive, and neurobiological perspectives on memory research relevant to DA. In particular, we examine the role of state dependent memory (wherein memories are difficult to recall unless the conditions at encoding and recall are similar), and discuss how advances in the neurobiology of state-dependent memory (SDM) gleaned from animal studies might be translated to humans.

Stress exposure alters brain mRNA expression of the genes involved in insulin signalling, an effect modified by a high fat/high fructose diet and cinnamon supplement

In occidental societies, high fat and high sugar diets often coincide with episodes of stress. The association is likely to modify brain energy control. Brain insulin signalling is rarely studied in stressed individuals consuming high fat diets. Furthermore the effects of cinnamon supplement are not known in these conditions. Therefore, we exposed rats, over a 12-week period, to a control (C) or a high fat/high fructose (HF/HFr) diet that induces peripheral insulin resistance. A cinnamon supplement (C+CN and HF/HFr +CN) was added or not. After diet exposure, one group of rats was exposed to a 30-min restraint followed by a 10-min open-field test, their combination featuring a moderate stressor, the other rats staying unstressed in their home cages. The insulin signalling in hippocampus and frontal cortex was studied through the mRNA expression of the following genes: insulin receptor (Ir), insulin receptor substrate (Irs1), glucose transporters (Glut1 and Glut3), glycogen synthase (Gys1) and their modulators, Akt1 and Pten. In C rats, stress enhanced the expression of Ir, Irs1, Glut1, Gys1 and Akt1 mRNA. In C+CN rats, stress induced an increase in Pten but a decrease in Gys1 mRNA expression. In HF/HFr rats, stress was associated with an increase in Pten mRNA expression. In HF/HFr+CN rats, stress increased Pten mRNA expression but also decreased Gys1 mRNA expression. This suggests that a single moderate stress favours energy refilling mechanisms, an effect blunted by a previous HF/HFr diet and cinnamon supplement.

Arc/Arg3.1 protein expression in dorsal hippocampal CA1, a candidate event as a biomarker for the effects of exercise on chronic stress-evoked behavioral abnormalities

[Purpose]

Chronic stress is a risk factor for behavioral deficits, including impaired memory processing and depression. Exercise is well known to have beneficial impacts on brain health.

[Methods]

Mice were forced to treadmill running (4-week) during chronic restraint stress (6h/21d), and then behavioral tests were conducted by Novel object recognition, forced swimming test: FST, sociality test: SI. Dissected brain was stained with anti-calbindin-d28k and anti-Arc antibodies. Also, mice were treated with CX546 intraperitoneally during chronic restraint stress, and behavioral tests were assessed using Morris water maze, FST, and SI. Dissected brain was stained with anti-Arc antibody.

[Results]

The current study demonstrated that chronic stress-induced impairment of memory consolidation and depression-like behaviors, along with the changes in calbindin-d28k and Arc protein levels in the hippocampal CA1 area, were attenuated by regular treadmill running. Further, prolonged ampakine treatment prevented chronic stress-evoked behavioral abnormalities and nuclear Arc levels in hippocampal CA1 neurons. Nuclear localization of Arc protein in hippocampal CA1 neurons, but not total levels, was correlated with behavioral outcome in chronically stressed mice in response to a regular exercise regimen.

[Conclusion]

These results suggest that nuclear levels of Arc are strongly associated with behavioral changes, and highlight the role of exercise acting through an α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor (AMPAR)-mediated mechanisms in a chronic stress-induced maladaptive condition.

High-fat diet-induced hyperglutamatergic activation of the hippocampus in mice: A proton magnetic resonance spectroscopy study at 9.4T

The aim of this study was to investigate the long-term neurochemical alterations in the hippocampus of mice fed a high-fat diet (HFD) while plasma leptin and corticosterone levels were monitored. Although metabolic disturbances induced by the excess intake of fat are assumed to cause depression, the relationship underlying dysfunctional adipose tissue, stress hormone release, and excitatory metabolism has not been fully understood yet. Four-week-old male C57BL/6 mice were separated into a HFD-fed group (n = 8) and low-fat diet-fed group (n = 8). Proton magnetic resonance spectroscopy was used to measure the long-term changes in neurochemicals in the hippocampus at 0, 5, and 10 weeks and blood samples were taken at the same time to assess plasma hormones levels. At the end of the experiment, magnetic resonance imaging was performed to quantify abdominal fat accumulation. At 10 weeks, corticosterone and leptin levels were significantly increased in the HFD group compared with the low-fat diet group. In addition, aspartate, glutamate, total choline, and N-acetylaspartic acid levels were significantly increased, but glutamine/glutamate ratios were substantially decreased at 10 weeks in the HFD group. These results were compatible with HFD-induced acute stress responses and changes in N-methyl-d-aspartate receptor-induced plasticity. These findings demonstrated that the long-term ingestion of a HFD induced hyperglutamatergic metabolism and altered glutamine-glutamate cycling. Therfore, it is suggested that hypothalamic-pituitary-adrenal dysfunction and hyperglutamatergic activation in the hippocampus resulting from the HFD.

Recent Advances in Translational Magnetic Resonance Imaging in Animal Models of Stress and Depression

Magnetic resonance imaging (MRI) is a valuable translational tool that can be used to investigate alterations in brain structure and function in both patients and animal models of disease. Regional changes in brain structure, functional connectivity, and metabolite concentrations have been reported in depressed patients, giving insight into the networks and brain regions involved, however preclinical models are less well characterized. The development of more effective treatments depends upon animal models that best translate to the human condition and animal models may be exploited to assess the molecular and cellular alterations that accompany neuroimaging changes. Recent advances in preclinical imaging have facilitated significant developments within the field, particularly relating to high resolution structural imaging and resting-state functional imaging which are emerging techniques in clinical research. This review aims to bring together the current literature on preclinical neuroimaging in animal models of stress and depression, highlighting promising avenues of research toward understanding the pathological basis of this hugely prevalent disorder.

Decreased Glutamatergic Activity in the Frontal Cortex of Single Prolonged Stress Model: In vivo and Ex Vivo Proton MR Spectroscopy

Single prolonged stress (SPS) is one of the preclinical models of posttraumatic stress disorder (PTSD) in humans. Not every traumatized person develops PTSD and the onset of the disease varies from months to many years after exposure to life-threatening events. The pathogenetic neurometabolites in PTSD have not been investigated to date, and could provide a means for therapeutic interventions. Therefore the present study aimed to evaluate neurochemical changes in the frontal cortex in the SPS model during time-dependent sensitization using in vivo and ex vivo proton magnetic spectroscopy (¹H-MRS). Twenty-one male Sprague-Dawley rats (200-220 g) were randomly assigned into two groups (Control, n = 10; SPS, n = 11). SPS consists of three consecutive stressors (restraint, forced swimming, and ether exposure) followed by 7 days without disturbance. In vivo ¹H-MRS scans were conducted at baseline, immediately after SPS, and 3 and 7 days after SPS to quantify time-dependent alterations in the frontal cortex. On day 7, all animals were sacrificed and ex vivo ¹H-MRS was performed. After SPS exposure, the SPS group showed signs of excitatory activities (glutamate) and cellular membrane turnover (choline and total choline) for 7 days. After the time-sensitization period, the SPS group showed lower glutamate and creatine levels and higher choline and lactate levels than the control group. These results indicate that SPS induces sustained adaptation of glutamatergic neuronal activity in the frontal cortex. Therefore, we conclude that SPS-induced stress reduces glutamatergic metabolism in the frontal cortex.

Utilizing a unique animal model to better understand human temperament

Individual differences in temperament are associated with psychopathology in humans. Moreover, the relationship between temperament and anxiety-, depression-, PTSD- and addiction-related behaviors can be modeled in animals. This review will highlight these relationships with a focus on individual differences in the response to stressors, fear conditioning and drugs of abuse using animals that differ in their response to a novel environment. We will discuss behavioral and neurobiological commonalities amongst these behaviors with a focus on the hippocampus and, in particular, growth factors as promising novel targets for therapeutic intervention.

Cognitive Deficits and Inflammatory Response Resulting from Mild-to-Moderate Traumatic Brain Injury in Rats Are Exacerbated by Repeated Pre-Exposure to an Innate Stress Stimulus

Traumatic brain injury (TBI) is common in both military and civilian populations, and often results in neurobehavioral sequelae that impair quality of life in both patients and their families. Although individuals who are chronically exposed to stress are more likely to experience TBI, it is still unknown whether pre-injury stress influences the outcome after TBI. The present study tested whether behavioral and cognitive long-term outcome after TBI in rats is affected by prior exposure to an innate stress stimulus. Young adult male Sprague-Dawley rats were exposed to the predator odor 2,5-dihydro-2,4,5-trimethylthiazoline (TMT) or to water (WAT); exposure was repeated eight times at irregular intervals over a 2-week period. Rats were subsequently subjected to either mild-to-moderate bilateral brain injury (lateral fluid percussion [LFP]) or sham surgery (Sham). Four experimental groups were studied: Sham-WAT, Sham-TMT, LFP-WAT and LFP-TMT. Compared with Sham-WAT rats, LFP-WAT rats exhibited transient locomotor hyperactivity without signs of anxiety, minor spatial learning acquisition and hippocampal long-term potentiation deficits, and lower baseline activity of the hypothalamic-pituitary-adrenal axis with slightly stronger reactivity to restraint stress. Exposure to TMT had only negligible effects on Sham rats, whereas it exacerbated all deficits in LFP rats except for locomotor hyperactivity. Early brain inflammatory response (8 h post-trauma) was aggravated in rats pre-exposed to TMT, suggesting that increased brain inflammation may sustain functional deficits in these rats. Hence, these data suggest that pre-exposure to stressful conditions can aggravate long-term deficits induced by TBI, leading to severe stress response deficits, possibly due to dysregulated inflammatory response.

Acute stress effects on GABA and glutamate levels in the prefrontal cortex: A 7T 1H magnetic resonance spectroscopy study

There is ample evidence that the inhibitory GABA and the excitatory glutamate system are essential for an adequate response to stress. Both GABAergic and glutamatergic brain circuits modulate hypothalamus-pituitary-adrenal (HPA)-axis activity, and stress in turn affects glutamate and GABA levels in the rodent brain. However, studies examining stress-induced GABA and glutamate levels in the human brain are scarce. Therefore, we investigated the influence of acute psychosocial stress (using the Trier Social Stress Test) on glutamate and GABA levels in the medial prefrontal cortex of 29 healthy male individuals using 7 Tesla proton magnetic resonance spectroscopy. In vivo GABA and glutamate levels were measured before and 30 min after exposure to either the stress or the control condition. We found no associations between psychosocial stress or cortisol stress reactivity and changes over time in medial prefrontal glutamate and GABA levels. GABA and glutamate levels over time were significantly correlated in the control condition but not in the stress condition, suggesting that very subtle differential effects of stress on GABA and glutamate across individuals may occur. However, overall, acute psychosocial stress does not appear to affect in vivo medial prefrontal GABA and glutamate levels, at least this is not detectable with current practice ¹H-MRS.

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Psychosocial stress did not alter glutamate and GABA levels in the medial prefrontal cortex in healthy male individuals.

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Moreover, cortisol stress reactivity was not associated with medial prefrontal glutamate and GABA level change over time.

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Together, acute stress does not seem to affect in vivo medial prefrontal 7T MRI GABA and glutamate levels in humans.

Preclinical Magnetic Resonance Imaging and Spectroscopy Studies of Memory, Aging, and Cognitive Decline

Neuroimaging provides for non-invasive evaluation of brain structure and activity and has been employed to suggest possible mechanisms for cognitive aging in humans. However, these imaging procedures have limits in terms of defining cellular and molecular mechanisms. In contrast, investigations of cognitive aging in animal models have mostly utilized techniques that have offered insight on synaptic, cellular, genetic, and epigenetic mechanisms affecting memory. Studies employing magnetic resonance imaging and spectroscopy (MRI and MRS, respectively) in animal models have emerged as an integrative set of techniques bridging localized cellular/molecular phenomenon and broader in vivo neural network alterations. MRI methods are remarkably suited to longitudinal tracking of cognitive function over extended periods permitting examination of the trajectory of structural or activity related changes. Combined with molecular and electrophysiological tools to selectively drive activity within specific brain regions, recent studies have begun to unlock the meaning of fMRI signals in terms of the role of neural plasticity and types of neural activity that generate the signals. The techniques provide a unique opportunity to causally determine how memory-relevant synaptic activity is processed and how memories may be distributed or reconsolidated over time. The present review summarizes research employing animal MRI and MRS in the study of brain function, structure, and biochemistry, with a particular focus on age-related cognitive decline.

Behavioral effects and CRF expression in brain structures of high- and low-anxiety rats after chronic restraint stress

The aim of our study was to investigate the influence of chronic restraint stress (5 weeks, 3h/day) on behavior and central corticotropin-releasing factor (CRF) expression in rats selected for high (HR) and low anxiety (LR). The conditioned freezing response was used as a discriminating variable. Moreover, we assessed the influence of acute restraint on CRF expression in the brain in HR and LR rats. We found that chronic restraint induced symptoms of anhedonia (decreased consumption of 1% sucrose solution) in HR rats. In addition, HR restraint rats showed an increased learned helplessness behavior (immobility time in the Porsolt test) as well as neophobia in the open field test vs. LR restraint and HR control rats. These behavioral changes were accompanied by a decreased expression of CRF in the paraventricular nucleus of the hypothalamus (pPVN) and the dentate gyrus of the hippocampus (DG) compared to the HR control and LR restraint rat groups, respectively. The acute restraint condition increased the expression of CRF in the pPVN of HR rats compared to the HR control group, and enhanced the expression of CRF in the CA1 area and DG of LR restraint animals compared to the HR restraint and LR control rats, respectively. The present results indicate that chronic restraint stress in high anxiety rats attenuated CRF expression in the pPVN and DG, which was probably due to detrimental actions on the hippocampus-hypothalamus-pituitary-adrenal gland feedback mechanism, thus modulating the stress response and inducing anhedonia and depressive-like symptoms.

Metabolomic analysis reveals metabolic disturbances in the prefrontal cortex of the lipopolysaccharide-induced mouse model of depression

Major depressive disorder (MDD) is a debilitating illness. However, the underlying molecular mechanisms of depression remain largely unknown. Increasing evidence supports that inflammatory cytokine disturbances may be associated with the pathophysiology of depression in humans. Systemic administration of lipopolysaccharide (LPS) has been used to study inflammation-associated neurobehavioral changes in rodents, but no metabonomic study has been conducted to assess differential metabolites in the prefrontal cortex (PFC) of a LPS-induced mouse model of depression. Here, we employed a gas chromatography-mass spectrometry-based metabonomic approach in the LPS-induced mouse model of depression to investigate any significant metabolic changes in the PFC. Multivariate statistical analysis, including principal component analysis (PCA), partial least squares-discriminate analysis (PLS-DA), and pair-wise orthogonal projections to latent structures discriminant analysis (OPLS-DA), was implemented to identify differential PFC metabolites between LPS-induced depressed mice and healthy controls. A total of 20 differential metabolites were identified. Compared with control mice, LPS-treated mice were characterized by six lower level metabolites and 14 higher level metabolites. These molecular changes were closely related to perturbations in neurotransmitter metabolism, energy metabolism, oxidative stress, and lipid metabolism, which might be evolved in the pathogenesis of MDD. These findings provide insight into the pathophysiological mechanisms underlying MDD and could be of valuable assistance in the clinical diagnosis of MDD.

Urinary Metabolomics Identifies a Molecular Correlate of Interstitial Cystitis/Bladder Pain Syndrome in a Multidisciplinary Approach to the Study of Chronic Pelvic Pain (MAPP) Research Network Cohort

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a poorly understood syndrome affecting up to 6.5% of adult women in the U.S. The lack of broadly accepted objective laboratory markers for this condition hampers efforts to diagnose and treat this condition. To identify biochemical markers for IC/BPS, we applied mass spectrometry-based global metabolite profiling to urine specimens from a cohort of female IC/BPS subjects from the Multidisciplinary Approach to the Study of Chronic Pelvic Pain (MAPP) Research Network. These analyses identified multiple metabolites capable of discriminating IC/BPS and control subjects. Of these candidate markers, etiocholan-3α-ol-17-one sulfate (Etio-S), a sulfoconjugated 5-β reduced isomer of testosterone, distinguished female IC/BPS and control subjects with a sensitivity and specificity > 90%. Among IC/BPS subjects, urinary Etio-S levels are correlated with elevated symptom scores (symptoms, pelvic pain, and number of painful body sites) and could resolve high- from low-symptom IC/BPS subgroups. Etio-S-associated biochemical changes persisted through 3–6 months of longitudinal follow up. These results raise the possibility that an underlying biochemical abnormality contributes to symptoms in patients with severe IC/BPS.

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Unbiased small molecule profiling identified an interstitial cystitis/bladder pain syndrome associated metabolite.

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This urinary metabolite independently identified patients with severe symptoms scores.

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Associated biochemical changes persisted over 3–6 months and hint at broader metabolic dysfunction in patients.

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a poorly understood syndrome associated with chronic bladder or pelvic pain, often accompanied by frequent urination. Identifying biochemical pathways associated with IC/BPS is necessary to understand the disease processes and suggest new therapeutic targets. Here we applied a biochemical approach to compare all detectable urinary metabolites from human subjects with and without IC/BPS. This analysis identified a steroid hormone metabolite that corresponds to patients that report the most severe symptoms. This result offers insight into IC/BPS pathophysiology, and provides a new biochemical clue to guide future investigation into this mysterious condition.

Expression of Npas4 mRNA in Telencephalic Areas of Adult and Postnatal Mouse Brain

The transcription factor neuronal PAS domain-containing protein 4 (Npas4) is an inducible immediate early gene which regulates the formation of inhibitory synapses, and could have a significant regulatory role during cortical circuit formation. However, little is known about basal Npas4 mRNA expression during postnatal development. Here, postnatal and adult mouse brain sections were processed for isotopic in situ hybridization using an Npas4 specific cRNA antisense probe. In adults, Npas4 mRNA was found in the telencephalon with very restricted or no expression in diencephalon or mesencephalon. In most telencephalic areas, including the anterior olfactory nucleus (AON), piriform cortex, neocortex, hippocampus, dorsal caudate putamen (CPu), septum and basolateral amygdala nucleus (BLA), basal Npas4 expression was detected in scattered cells which exhibited strong hybridization signal. In embryonic and neonatal brain sections, Npas4 mRNA expression signals were very low. Starting at postnatal day 5 (P5), transcripts for Npas4 were detected in the AON, CPu and piriform cortex. At P8, additional Npas4 hybridization was found in CA1 and CA3 pyramidal layer, and in primary motor cortex. By P13, robust mRNA expression was located in layers IV and VI of all sensory cortices, frontal cortex and cingulate cortex. After onset of expression, postnatal spatial mRNA distribution was similar to that in adults, with the exception of the CPu, where Npas4 transcripts became gradually restricted to the most dorsal part. In conclusion, the spatial distribution of Npas4 mRNA is mostly restricted to telencephalic areas, and the temporal expression increases with developmental age during postnatal development, which seem to correlate with the onset of activity-driven excitatory transmission.

A critical evaluation of the activity-regulated cytoskeleton-associated protein (Arc/Arg3.1)'s putative role in regulating dendritic plasticity, cognitive processes, and mood in animal models of depression

Major depressive disorder (MDD) is primarily conceptualized as a mood disorder but cognitive dysfunction is also prevalent, and may limit the daily function of MDD patients. Current theories on MDD highlight disturbances in dendritic plasticity in its pathophysiology, which could conceivably play a role in the production of both MDD-related mood and cognitive symptoms. This paper attempts to review the accumulated knowledge on the basic biology of the activity-regulated cytoskeleton-associated protein (Arc or Arg3.1), its effects on neural plasticity, and how these may be related to mood or cognitive dysfunction in animal models of MDD. On a cellular level, Arc plays an important role in modulating dendritic spine density and remodeling. Arc also has a close, bidirectional relationship with postsynaptic glutamate neurotransmission, since it is stimulated by multiple glutamatergic receptor mechanisms but also modulates α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor internalization. The effects on AMPA receptor trafficking are likely related to Arc's ability to modulate phenomena such as long-term potentiation, long-term depression, and synaptic scaling, each of which are important for maintaining proper cognitive function. Chronic stress models of MDD in animals show suppressed Arc expression in the frontal cortex but elevation in the amygdala. Interestingly, cognitive tasks depending on the frontal cortex are generally impaired by chronic stress, while those depending on the amygdala are enhanced, and antidepressant treatments stimulate cortical Arc expression with a timeline that is reminiscent of the treatment efficacy lag observed in the clinic or in preclinical models. However, pharmacological treatments that stimulate regional Arc expression do not universally improve relevant cognitive functions, and this highlights a need to further refine our understanding of Arc on a subcellular and network level.