Strain Differences in Responsiveness to Repeated Restraint Stress Affect Remote Contextual Fear Memory and Blood Transcriptomics.

The role of stress in altering fear memory is not well understood. Since individual variations in stress reactivity exist, and stress alters fear memory, exposing individuals with differing stress-reactivity to repeated stress would affect their fear memory to various degrees. We explored this question using the average stress-reactive Fisher 344 (F344) rat strain and the Wistar-Kyoto (WKY) strain with its heightened stress-reactivity. Male F344 and WKY rats were exposed to the contextual fear conditioning (CFC) paradigm and then chronic restraint stress (CRS) or no stress (NS) was administered for two weeks before a second CFC. Both recent and reinstated fear memory were greater in F344s than WKYs, regardless of the stress status. In contrast, remote memory was attenuated only in F344s after CRS. In determining whether this strain-specific response to CRS was mirrored by transcriptomic changes in the blood, RNA sequencing was carried out. Overlapping differentially expressed genes (DEGs) between NS and CRS in the blood of F344 and WKY suggest a convergence of stress-related molecular mechanisms, independent of stress-reactivity. In contrast, DEGs unique to the F344 and the WKY stress responses are divergent in their functionality and networks, beyond that of strain differences in their non-stressed state. These results suggest that in some individuals chronic or repeated stress, different from the original fear memory-provoking stress, can attenuate prior fear memory. Furthermore, the novel blood DEGs can report on the general state of stress of the individual, or can be associated with individual variation in stress-responsiveness.

Polarity and subfield specific effects of transcranial direct current stimulation on hippocampal plasticity.

An increasing number of studies using human subjects substantiate the use of transcranial direct current stimulation (tDCS) as a noninvasive approach to treat various neurological symptoms. tDCS has been tested in conditions from motor to cognition dysfunctions. Performance enhancement of healthy subjects using tDCS has also been explored. The underlying physiological mechanism for tDCS effects is hypothesized to be through changes in neuroplasticity and we have previously demonstrated that in vivo anodal tDCS can enhance neuroplasticity of hippocampal CA1 neurons. The purpose of this study was to determine whether the underlying electrophysiological changes that occur following in vivo tDCS are polarity specific. We also examined both the CA1 and CA3 regions of the hippocampus to determine whether the tDCS effects were subfield specific. We conducted in vivo tests of cathodal tDCS versus anodal tDCS on synaptic plasticity of CA1 and CA3 neurons of male rats. In each region we assessed long term potentiation (LTP), paired pulse facilitation (PPF) and long term depression (LTD). In the CA1 region, we found anodal tDCS significantly enhanced not only LTP and PPF, but also LTD. There was no statistical difference in LTP, PPF or LTD of hippocampal CA1 neurons resulting from cathodal tDCS. Neither anodal nor cathodal tDCS induced significant changes in neuroplasticity of hippocampal CA3 neurons. Results indicate that the effects of tDCS are subfield specific and polarity dependent with anodal tDCS having greater impact on synaptic activity in the rat hippocampus than cathodal tDCS.

Noninvasive Brain Stimulation Enhances Memory Acquisition and Is Associated with Synaptoneurosome Modification in the Rat Hippocampus.

Transcranial direct-current stimulation (tDCS) is a non-invasive brain stimulation approach previously shown to enhance memory acquisition, but more studies are needed to elucidate the underlying mechanisms. Here, we examined the effects of anodal tDCS (0.25 mA for 30 min) on the memory performance of male Sprague Dawley rats in the passive avoidance test (PAT) and the associated modifications to the hippocampal proteomes. Results indicate anodal tDCS applied before the acquisition period significantly enhanced memory performance in the PAT. Following PAT, synaptoneurosomes were biochemically purified from the hippocampi of tDCS-treated or sham-treated rats and individual protein abundances were determined by bottom-up liquid chromatography mass spectrometry analysis. Proteomic analysis identified 184 differentially expressed hippocampal proteins when comparing the sham to the tDCS before memory acquisition treatment group. Ingenuity pathway analysis (IPA) showed anodal tDCS before memory acquisition significantly enhanced pathways associated with memory, cognition, learning, transmission, neuritogenesis, and long-term potentiation (LTP). IPA identified significant upstream regulators including bdnf, shank3, and gsk3b Protein-protein interaction (PPI) and protein sequence similarity (PSS) networks show that glutamate receptor pathways, ion channel activity, memory, learning, cognition, and long-term memory were significantly associated with anodal tDCS. Centrality measures from both networks identified key proteins including dlg, shank, grin, and gria that were significantly modified by tDCS applied before the acquisition period. Together, our results provide descriptive molecular evidence that anodal tDCS enhances memory performance in the PAT by modifying hippocampal synaptic plasticity related proteins.

A functional promoter variant of the human formimidoyltransferase cyclodeaminase (FTCD) gene is associated with working memory performance in young but not older adults.

OBJECTIVE: The central role of working memory in IQ and the high heritability of working memory performance motivated interest in identifying the specific genes underlying this heritability. The FTCD (formimidoyltransferase cyclodeaminase) gene was identified as a candidate gene for allelic association with working memory in part from genetic mapping studies of mouse Morris water maze performance. METHOD: The present study tested variants of this gene for effects on a delayed match-to-sample task of a large sample of younger and older participants. RESULTS: The rs914246 variant, but not the rs914245 variant, of the FTCD gene modulated accuracy in the task for younger, but not older, people under high working memory load. The interaction of haplotype × distance × load had a partial eta squared effect size of 0.015. Analysis of simple main effects had partial eta squared effect sizes ranging from 0.012 to 0.040. A reporter gene assay revealed that the C allele of the rs914246 genotype is functional and a main factor regulating FTCD gene expression. CONCLUSION: This study extends previous work on the genetics of working memory by revealing that a gene in the glutamatergic pathway modulates working memory in young people but not in older people. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Brain region-specific expression of genes mapped within quantitative trait loci for behavioral responsiveness to acute stress in Fisher 344 and Wistar Kyoto male rats.

Acute stress responsiveness is a quantitative trait that varies in severity from one individual to another; however, the genetic component underlying the individual variation is largely unknown. Fischer 344 (F344) and Wistar Kyoto (WKY) rat strains show large differences in behavioral responsiveness to acute stress, such as freezing behavior in response to footshock during the conditioning phase of contextual fear conditioning (CFC). Quantitative trait loci (QTL) have been identified for behavioral responsiveness to acute stress in the defensive burying (DB) and open field test (OFT) from a reciprocal F2 cross of F344 and WKY rat strains. These included a significant QTL on chromosome 6 (Stresp10). Here, we hypothesized that the Stresp10 region harbors genes with sequence variation(s) that contribute to differences in multiple behavioral response phenotypes between the F344 and WKY rat strains. To test this hypothesis, first we identified differentially expressed genes within the Stresp10 QTL in the hippocampus, amygdala, and frontal cortex of F344 and WKY male rats using genome-wide microarray analyses. Genes with both expression differences and non-synonymous sequence variations in their coding regions were considered candidate quantitative trait genes (QTGs). As a proof-of-concept, the F344.WKY-Stresp10 congenic strain was generated with the Stresp10 WKY donor region into the F344 recipient strain. This congenic strain showed behavioral phenotypes similar to those of WKYs. Expression patterns of Gpatch11 (G-patch domain containing 11), Cdkl4 (Cyclin dependent kinase like 4), and Drc1 (Dynein regulatory complex subunit 1) paralleled that of WKY in the F344.WKY-Stresp10 strain matching the behavioral profiles of WKY as opposed to F344 parental strains. We propose that these genes are candidate QTGs for behavioral responsiveness to acute stress.

AMPA receptor translocation and phosphorylation are induced by transcranial direct current stimulation in rats.

Over the last decade, the interest in transcranial direct current stimulation (tDCS) has continued to increase, along with consideration of how it affects neuroplasticity mechanisms in the brain. Both human and animal studies have demonstrated numerous benefits and, although its application has increased, the neurophysiological mechanisms underlying tDCS' beneficial effects remain largely unknown. Recent studies have shown that long-term potentiation (LTP) increases following tDCS. In this work, we utilized a rodent model of tDCS to directly assess changes in the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor, a critical protein for enhancing synaptic transmission. Animals were subjected to 250 µA of direct current (DC) stimulation for 30 min with immediate tissue collection. Translocation and phosphorylation of AMPA receptors were examined using protein immunoblot analysis following a subcellular fractionation method. Our findings show that a single application of in vivo tDCS can affect both the translocation and phosphorylation of AMPA receptors in the hippocampus while increasing AMPA receptor phosphorylation in the hypothalamus. In the hippocampus, tDCS increased AMPA translocation to the synapse and increased the phosphorylation of the S831 site on GluA1. In the hypothalamus, no statistically significant changes were observed in AMPA translocation while an increase in the phosphorylation of the S831 site was observed. No changes in the phosphorylation of GluA1 at the S845 site were detected in either brain region. In sum, our findings identify specific AMPA receptor changes induced by tDCS, thereby providing further details on the mechanisms by which tDCS could affect the establishment of LTP and modulate neuroplasticity.

Divergence in Morris Water Maze-Based Cognitive Performance under Chronic Stress Is Associated with the Hippocampal Whole Transcriptomic Modification in Mice.

Individual susceptibility determines the magnitude of stress effects on cognitive function. The hippocampus, a brain region of memory consolidation, is vulnerable to stressful environments, and the impact of stress on hippocampus may determine individual variability in cognitive performance. Therefore, the purpose of this study was to define the relationship between the divergence in spatial memory performance under chronically unpredictable stress and an associated transcriptomic alternation in hippocampus, the brain region of spatial memory consolidation. Multiple strains of BXD (B6 × D2) recombinant inbred mice went through a 4-week chronic variable stress (CVS) paradigm, and the Morris water maze (MWM) test was conducted during the last week of CVS to assess hippocampal-dependent spatial memory performance and grouped animals into low and high performing groups based on the cognitive performance. Using hippocampal whole transcriptome RNA-sequencing data, differential expression, PANTHER analysis, WGCNA, Ingenuity's upstream regulator analysis in the Ingenuity Pathway Analysis® and phenotype association analysis were conducted. Our data identified multiple genes and pathways that were significantly associated with chronic stress-associated cognitive modification and the divergence in hippocampal dependent memory performance under chronic stress. Biological pathways associated with memory performance following chronic stress included metabolism, neurotransmitter and receptor regulation, immune response and cellular process. The Ingenuity's upstream regulator analysis identified 247 upstream transcriptional regulators from 16 different molecule types. Transcripts predictive of cognitive performance under high stress included genes that are associated with a high occurrence of Alzheimer's and cognitive impairments (e.g., Ncl, Eno1, Scn9a, Slc19a3, Ncstn, Fos, Eif4h, Copa, etc.). Our results show that the variable effects of chronic stress on the hippocampal transcriptome are related to the ability to complete the MWM task and that the modulations of specific pathways are indicative of hippocampal dependent memory performance. Thus, the divergence in spatial memory performance following chronic stress is related to the unique pattern of gene expression within the hippocampus.

Nutritional Ketosis Affects Metabolism and Behavior in Sprague-Dawley Rats in Both Control and Chronic Stress Environments.

Nutritional ketosis may enhance cerebral energy metabolism and has received increased interest as a way to improve or preserve performance and resilience. Most studies to date have focused on metabolic or neurological disorders while anecdotal evidence suggests that ketosis may enhance performance in the absence of underlying dysfunction. Moreover, decreased availability of glucose in the brain following stressful events is associated with impaired cognition, suggesting the need for more efficient energy sources. We tested the hypotheses that ketosis induced by endogenous or exogenous ketones could: (a) augment cognitive outcomes in healthy subjects; and (b) prevent stress-induced detriments in cognitive parameters. Adult, male, Sprague Dawley rats were used to investigate metabolic and behavioral outcomes in 3 dietary conditions: ketogenic (KD), ketone supplemented (KS), or NIH-31 control diet in both control or chronic stress conditions. Acute administration of exogenous ketones resulted in reduction in blood glucose and sustained ketosis. Chronic experiments showed that in control conditions, only KD resulted in pronounced metabolic alterations and improved performance in the novel object recognition test. The hypothalamic-pituitary-adrenal (HPA) axis response revealed that KD-fed rats maintained peripheral ketosis despite increases in glucose whereas no diet effects were observed in ACTH or CORT levels. Both KD and KS-fed rats decreased escape latencies on the third day of water maze, whereas only KD prevented stress-induced deficits on the last testing day and improved probe test performance. Stress-induced decrease in hippocampal levels of ß-hydroxybutyrate was attenuated in KD group while both KD and KS prevented stress effects on BDNF levels. Mitochondrial enzymes associated with ketogenesis were increased in both KD and KS hippocampal samples and both endothelial and neuronal glucose transporters were affected by stress but only in the control diet group. Our results highlight the complex relationship between peripheral metabolism, behavioral performance and biochemical changes in the hippocampus. Endogenous ketosis improved behavioral and metabolic parameters associated with energy metabolism and cognition while ketone supplementation replicated the biochemical effects within the hippocampus but only showed modest effects on behavioral improvements.

Safety parameter considerations of anodal transcranial Direct Current Stimulation in rats.

A commonly referenced transcranial Direct Current Stimulation (tDCS) safety threshold derives from tDCS lesion studies in the rat and relies on electrode current density (and related electrode charge density) to support clinical guidelines. Concerns about the role of polarity (e.g. anodal tDCS), sub-lesion threshold injury (e.g. neuroinflammatory processes), and role of electrode montage across rodent and human studies support further investigation into animal models of tDCS safety. Thirty-two anesthetized rats received anodal tDCS between 0 and 5mA for 60min through one of three epicranial electrode montages. Tissue damage was evaluated using hemotoxylin and eosin (H&E) staining, Iba-1 immunohistochemistry, and computational brain current density modeling. Brain lesion occurred after anodal tDCS at and above 0.5mA using a 25.0mm2 electrode (electrode current density: 20.0A/m2). Lesion initially occurred using smaller 10.6mm2 or 5.3mm2 electrodes at 0.25mA (23.5A/m2) and 0.5mA (94.2A/m2), respectively. Histological damage was correlated with computational brain current density predictions. Changes in microglial phenotype occurred in higher stimulation groups. Lesions were observed using anodal tDCS at an electrode current density of 20.0A/m2, which is below the previously reported safety threshold of 142.9A/m2 using cathodal tDCS. The lesion area is not simply predicted by electrode current density (and so not by charge density as duration was fixed); rather computational modeling suggests average brain current density as a better predictor for anodal tDCS. Nonetheless, under the assumption that rodent epicranial stimulation is a hypersensitive model, an electrode current density of 20.0A/m2 represents a conservative threshold for clinical tDCS, which typically uses an electrode current density of 2A/m2 when electrodes are placed on the skin (resulting in a lower brain current density).

Mechanisms and Effects of Transcranial Direct Current Stimulation.

The US Air Force Office of Scientific Research convened a meeting of researchers in the fields of neuroscience, psychology, engineering, and medicine to discuss most pressing issues facing ongoing research in the field of transcranial direct current stimulation (tDCS) and related techniques. In this study, we present opinions prepared by participants of the meeting, focusing on the most promising areas of research, immediate and future goals for the field, and the potential for hormesis theory to inform tDCS research. Scientific, medical, and ethical considerations support the ongoing testing of tDCS in healthy and clinical populations, provided best protocols are used to maximize safety. Notwithstanding the need for ongoing research, promising applications include enhancing vigilance/attention in healthy volunteers, which can accelerate training and support learning. Commonly, tDCS is used as an adjunct to training/rehabilitation tasks with the goal of leftward shift in the learning/treatment effect curves. Although trials are encouraging, elucidating the basic mechanisms of tDCS will accelerate validation and adoption. To this end, biomarkers (eg, clinical neuroimaging and findings from animal models) can support hypotheses linking neurobiological mechanisms and behavioral effects. Dosage can be optimized using computational models of current flow and understanding dose-response. Both biomarkers and dosimetry should guide individualized interventions with the goal of reducing variability. Insights from other applied energy domains, including ionizing radiation, transcranial magnetic stimulation, and low-level laser (light) therapy, can be prudently leveraged.

Safety of Transcranial Direct Current Stimulation: Evidence Based Update 2016.

This review updates and consolidates evidence on the safety of transcranial Direct Current Stimulation (tDCS). Safety is here operationally defined by, and limited to, the absence of evidence for a Serious Adverse Effect, the criteria for which are rigorously defined. This review adopts an evidence-based approach, based on an aggregation of experience from human trials, taking care not to confuse speculation on potential hazards or lack of data to refute such speculation with evidence for risk. Safety data from animal tests for tissue damage are reviewed with systematic consideration of translation to humans. Arbitrary safety considerations are avoided. Computational models are used to relate dose to brain exposure in humans and animals. We review relevant dose-response curves and dose metrics (e.g. current, duration, current density, charge, charge density) for meaningful safety standards. Special consideration is given to theoretically vulnerable populations including children and the elderly, subjects with mood disorders, epilepsy, stroke, implants, and home users. Evidence from relevant animal models indicates that brain injury by Direct Current Stimulation (DCS) occurs at predicted brain current densities (6.3-13 A/m(2)) that are over an order of magnitude above those produced by conventional tDCS. To date, the use of conventional tDCS protocols in human trials (≤40 min, ≤4 milliamperes, ≤7.2 Coulombs) has not produced any reports of a Serious Adverse Effect or irreversible injury across over 33,200 sessions and 1000 subjects with repeated sessions. This includes a wide variety of subjects, including persons from potentially vulnerable populations.

Transcriptomic Modification in the Cerebral Cortex following Noninvasive Brain Stimulation: RNA-Sequencing Approach.

Transcranial direct current stimulation (tDCS) has been shown to modulate neuroplasticity. Beneficial effects are observed in patients with psychiatric disorders and enhancement of brain performance in healthy individuals has been observed following tDCS. However, few studies have attempted to elucidate the underlying molecular mechanisms of tDCS in the brain. This study was conducted to assess the impact of tDCS on gene expression within the rat cerebral cortex. Anodal tDCS was applied at 3 different intensities followed by RNA-sequencing and analysis. In each current intensity, approximately 1,000 genes demonstrated statistically significant differences compared to the sham group. A variety of functional pathways, biological processes, and molecular categories were found to be modified by tDCS. The impact of tDCS on gene expression was dependent on current intensity. Results show that inflammatory pathways, antidepressant-related pathways (GTP signaling, calcium ion binding, and transmembrane/signal peptide pathways), and receptor signaling pathways (serotonergic, adrenergic, GABAergic, dopaminergic, and glutamate) were most affected. Of the gene expression profiles induced by tDCS, some changes were observed across multiple current intensities while other changes were unique to a single stimulation intensity. This study demonstrates that tDCS can modify the expression profile of various genes in the cerebral cortex and that these tDCS-induced alterations are dependent on the current intensity applied.

Modulating Hippocampal Plasticity with In Vivo Brain Stimulation.

Investigations into the use of transcranial direct current stimulation (tDCS) in relieving symptoms of neurological disorders and enhancing cognitive or motor performance have exhibited promising results. However, the mechanisms by which tDCS effects brain function remain under scrutiny. We have demonstrated that in vivo tDCS in rats produced a lasting effect on hippocampal synaptic plasticity, as measured using extracellular recordings. Ex vivo preparations of hippocampal slices from rats that have been subjected to tDCS of 0.10 or 0.25 mA for 30 min followed by 30 min of recovery time displayed a robust twofold enhancement in long-term potentiation (LTP) induction accompanied by a 30% increase in paired-pulse facilitation (PPF). The magnitude of the LTP effect was greater with 0.25 mA compared with 0.10 mA stimulations, suggesting a dose-dependent relationship between tDCS intensity and its effect on synaptic plasticity. To test the persistence of these observed effects, animals were stimulated in vivo for 30 min at 0.25 mA and then allowed to return to their home cage for 24 h. Observation of the enhanced LTP induction, but not the enhanced PPF, continued 24 h after completion of 0.25 mA of tDCS. Addition of the NMDA blocker AP-5 abolished LTP in both control and stimulated rats but maintained the PPF enhancement in stimulated rats. The observation of enhanced LTP and PPF after tDCS demonstrates that non-invasive electrical stimulation is capable of modifying synaptic plasticity. SIGNIFICANCE STATEMENT: Researchers have used brain stimulation such as transcranial direct current stimulation on human subjects to alleviate symptoms of neurological disorders and enhance their performance. Here, using rats, we have investigated the potential mechanisms of how in vivo brain stimulation can produce such effect. We recorded directly on viable brain slices from rats after brain stimulation to detect lasting changes in pattern of neuronal activity. Our results showed that 30 min of brain stimulation in rats induced a robust enhancement in synaptic plasticity, a neuronal process critical for learning and memory. Understanding such molecular effects will lead to a better understanding of the mechanisms by which brain stimulation produces its effects on cognition and performance.

Neuroendocrine Function After Hypothalamic Depletion of Glucocorticoid Receptors in Male and Female Mice.

Glucocorticoids act rapidly at the paraventricular nucleus (PVN) to inhibit stress-excitatory neurons and limit excessive glucocorticoid secretion. The signaling mechanism underlying rapid feedback inhibition remains to be determined. The present study was designed to test the hypothesis that the canonical glucocorticoid receptors (GRs) is required for appropriate hypothalamic-pituitary-adrenal (HPA) axis regulation. Local PVN GR knockdown (KD) was achieved by breeding homozygous floxed GR mice with Sim1-cre recombinase transgenic mice. This genetic approach created mice with a KD of GR primarily confined to hypothalamic cell groups, including the PVN, sparing GR expression in other HPA axis limbic regulatory regions, and the pituitary. There were no differences in circadian nadir and peak corticosterone concentrations between male PVN GR KD mice and male littermate controls. However, reduction of PVN GR increased ACTH and corticosterone responses to acute, but not chronic stress, indicating that PVN GR is critical for limiting neuroendocrine responses to acute stress in males. Loss of PVN GR induced an opposite neuroendocrine phenotype in females, characterized by increased circadian nadir corticosterone levels and suppressed ACTH responses to acute restraint stress, without a concomitant change in corticosterone responses under acute or chronic stress conditions. PVN GR deletion had no effect on depression-like behavior in either sex in the forced swim test. Overall, these findings reveal pronounced sex differences in the PVN GR dependence of acute stress feedback regulation of HPA axis function. In addition, these data further indicate that glucocorticoid control of HPA axis responses after chronic stress operates via a PVN-independent mechanism.

Variable impact of chronic stress on spatial learning and memory in BXD mice.

The effects of chronic stress on learning are highly variable across individuals. This variability stems from gene-environment interactions. However, the mechanisms by which stress affects genetic predictors of learning are unclear. Thus, we aim to determine whether the genetic pathways that predict spatial memory performance are altered by previous exposure to chronic stress. Sixty-two BXD recombinant inbred strains of mice, as well as parent strains C57BL/6J and DBA/2J, were randomly assigned as behavioral control or to a chronic variable stress paradigm and then underwent behavioral testing to assess spatial memory and learning performance using the Morris water maze. Quantitative trait loci (QTL) mapping was completed for average escape latency times for both control and stress animals. Loci on chromosomes 5 and 10 were found in both control and stress environmental populations; eight additional loci were found to be unique to either the control or stress environment. In sum, results indicate that certain genetic loci predict spatial memory performance regardless of prior stress exposure, while exposure to stress also reveals unique genetic predictors of training during the memory task. Thus, we find that genetic predictors contributing to spatial learning and memory are susceptible to the presence of chronic stress.

Unique genetic loci identified for emotional behavior in control and chronic stress conditions.

An individual's genetic background affects their emotional behavior and response to stress. Although studies have been conducted to identify genetic predictors for emotional behavior or stress response, it remains unknown how prior stress history alters the interaction between an individual's genome and their emotional behavior. Therefore, the purpose of this study is to identify chromosomal regions that affect emotional behavior and are sensitive to stress exposure. We utilized the BXD behavioral genetics mouse model to identify chromosomal regions that predict fear learning and emotional behavior following exposure to a control or chronic stress environment. 62 BXD recombinant inbred strains and C57BL/6 and DBA/2 parental strains underwent behavioral testing including a classical fear conditioning paradigm and the elevated plus maze. Distinct quantitative trait loci (QTLs) were identified for emotional learning, anxiety and locomotion in control and chronic stress populations. Candidate genes, including those with already known functions in learning and stress were found to reside within the identified QTLs. Our data suggest that chronic stress history reveals novel genetic predictors of emotional behavior.

Interactive effects of the COMT gene and training on individual differences in supervisory control of unmanned vehicles.

OBJECTIVE: We examined whether a gene known to influence dopamine availability in the prefrontal cortex is associated with individual differences in learning a supervisory control task. BACKGROUND: Methods are needed for selection and training of human operators who can effectively supervise multiple unmanned vehicles (UVs). Compared to the valine (Val) allele, the methionine (Met) allele of the COMT gene has been linked to superior executive function, but it is not known whether it is associated with training-related effects in multi-UV supervisory control performance. METHOD: Ninety-nine healthy adults were genotyped for the COMT Val158Met single nucleotide polymorphism (rs4680) and divided into Met/Met, Val/Met, and Val/Val groups. Participants supervised six UVs in an air defense mission requiring them to attack incoming enemy aircraft and protect a no-fly zone from intruders in conditions of low and high task load (numbers of enemy aircraft). Training effects were examined across four blocks of trials in each task load condition. RESULTS: Compared to the Val/Met and Val/Val groups, Met/Met individuals exhibited a greater increase in enemy targets destroyed and greater reduction in enemy red zone incursions across training blocks. CONCLUSION: Individuals with the COMT Met/Met genotype can acquire skill in executive function tasks, such as multi-UV supervisory control, to a higher level and/or faster than other genotype groups. APPLICATION: Potential applications of this research include the development of individualized training methods for operators of multi-UV systems and selecting personnel for complex supervisory control tasks.

Identification of chronic stress-activated regions reveals a potential recruited circuit in rat brain.

Chronic stress induces presynaptic and postsynaptic modifications in the paraventricular nucleus of the hypothalamus that are consistent with enhanced excitatory hypothalamo-pituitary-adrenocortical (HPA) axis drive. The brain regions mediating these molecular modifications are not known. We hypothesized that chronic variable stress (CVS) tonically activates stress-excitatory regions that interact with the paraventricular nucleus of the hypothalamus, culminating in stress facilitation. In order to identify chronically activated brain regions, ΔFosB, a documented marker of tonic neuronal activation, was assessed in known stress regulatory limbic and brainstem sites. Four experimental groups were included: CVS, repeated restraint (RR) (control for HPA habituation), animals weight-matched (WM) to CVS animals (control for changes in circulating metabolic factors due to reduced weight gain), and non-handled controls. CVS, (but not RR or WM) induced adrenal hypertrophy, indicating that sustained HPA axis drive only occurred in the CVS group. CVS (but not RR or WM) selectively increased the number of FosB/ΔFosB nuclei in the nucleus of the solitary tract, posterior hypothalamic nucleus, and both the infralimbic and prelimbic divisions of the medial prefrontal cortex, indicating an involvement of these regions in chronic drive of the HPA axis. Increases in FosB/ΔFosB-immunoreactive cells were observed following both RR and CVS in the other regions (e.g. the dorsomedial hypothalamus), suggesting activation by both habituating and non-habituating stress conditions. The data suggest that unpredictable stress uniquely activates interconnected cortical, hypothalamic, and brainstem nuclei, potentially revealing the existence of a recruited circuitry mediating chronic drive of brain stress effector systems.

Opposing effects of chronic stress and weight restriction on cardiovascular, neuroendocrine and metabolic function.

Chronic stress is associated with dysregulation of energy homeostasis, but the link between the two is largely unknown. For most rodents, periods of chronic stress reduce weight gain. We hypothesized that these reductions in weight are an additional homeostatic challenge, contributing to the chronic stress syndrome. Experiment #1 examined cardiovascular responsivity following exposure to prolonged intermittent stress. We used radio-telemetry to monitor mean arterial pressure and heart rate in freely moving, conscious rats. Three groups of animals were tested: chronic variable stress (CVS), weight-matched (WM), and controls. Using this design, we can distinguish between effects due to stress and effects due to the changing body weight. WM, but not CVS, markedly reduced basal heart rate. Although an acute stress challenge elicited similar peak heart rate, WM expedited the recovery to baseline heart rate. The data suggest that CVS prevents the weight-induced attenuation of cardiovascular stress reactivity. Experiment #2 investigated hypothalamic-pituitary-adrenal axis and metabolic hormone reactivity to novel psychogenic stress. WM increased corticosterone area under the curve. CVS blunted plasma glucose, leptin, and insulin levels in response to restraint. Experiment #3 tested the effects of WM and CVS on PVN oxytocin and corticotrophin-releasing hormone mRNA expression. CVS increased, while WM reduced PVN CRH mRNA expression, whereas both CVS and WM reduced dorsal parvocellular PVN oxytocin mRNA. Overall, the data suggest that weight loss is unlikely to account for the deleterious effects of chronic stress on the organism, but in fact produces beneficial effects that are effectively absent or indeed, reversed in the face of chronic stress exposure.

Lack of vasopressin does not prevent the behavioural and endocrine changes induced by chronic unpredictable stress.

Vasopressin (VP) plays an important role in hypothalamo-pituitary-adrenal (HPA) axis regulation and in stress-related disorders. Our previous studies confirmed the role of VP in acute situations, where VP-deficient Brattleboro rats had less depression-like behaviour compared to animals that express VP. In this study, we test the hypothesis that VP-deficient rats are more resistant to the development of chronic HPA axis hyperactivity and depression-like symptoms after chronic unpredictable stress (CUS). Male VP-deficient Brattleboro rats were compared to their heterozygous littermates (controls). CUS consisted of different mild stimuli for 5 weeks. Elevated plus maze and forced swim test were used for behavioural characterization, while organs and blood for HPA axis parameters were collected at the end of the experiment. In controls, CUS resulted in the development of chronic stress state characterized by typical somatic (body weight reduction, thymus involution) and endocrine changes (resting plasma ACTH and corticosterone elevation and POMC mRNA elevation in anterior lobe of the pituitary). Floating time in the forced swim test was enhanced together with reduced open arm entries on elevated plus maze and a reduction in daily food intake. Unexpectedly, the lack of VP did not alter the effect of CUS on the somatic and behavioural measures, but only prevented CUS-induced corticosterone changes. In conclusion, lifelong VP-deficiency has a positive effect on corticosterone elevation following CUS but does not affect the behavioural consequences of CUS. It is likely that the interplay of several related factors, rather than an alteration in a single neuropeptide, modulates behaviour and disease pathogenesis.