Chronic psychosocial stress-induced impairment of hippocampal LTP: possible role of BDNF

URB597 modulates neuroplasticity, neuroinflammatory, and Nrf2/HO-1 signaling pathways in the hippocampus and prefrontal cortex of male and female rats in a stress-induced model of depression

Major depressive disorder is often associated with cognitive impairments, and neuroinflammation is considered a key contributor to the onset of depression. Pharmacological inhibition of fatty acid amide hydrolase (FAAH), which augments endocannabinoid signaling, has emerged as a promising approach to treating depression. The main purpose of this study is to asses the influence of FAAH inhibitor URB597 on inflammatory response and oxidative stress in chronic unpredictable stress (CUS)-induced depressive female and male rats and to explore the underlying molecular mechanisms. Chronically stressed animals showed long-term memory deficits, while URB597 improved memory only in stressed males. URB597 treatment enhanced levels of brain-derived neurotrophic factor (BDNF) in the hippocampus and mPFC of stressed female and male rats and increased phosphorylated calcium/calmodulin-dependent protein kinase II (pCaMKII) levels in the hippocampus and mPFC of CUS males. Additionally, increased phosphorylation of JAK2 and STAT3 in the hippocampus and mPFC of CUS male and female rats, was reduced following URB597 treatment. URB597 decreased the CUS-enhanced iNOS protein expression in the hippocampus and mPFC of both sexes. Furthermore, URB597 normalized CUS-induced reductions in Nrf2 and HO-1 levels in the mPFC of both sexes, with no changes in the hippocampus. Our findings suggest that URB597 may inhibit the CUS-induced neuroinflammatory response by suppressing the pro-inflammatory mediators and the activation of the JAK2/STAT3 signaling in the hippocampus and mPFC of both sexes. URB597 treatment contributed to synaptic plasticity in a sex-specific manner by upregulating brain CaMKII signaling in males. URB597 also exerts neuroprotective effects through region-specific antioxidant properties. These results have implications for sex-specific treatment strategies in stress-related neuropsychiatric disorders.

Heterogenous effect of early adulthood stress on cognitive aging and synaptic function in the dentate gyrus

Cognitive aging widely varies among individuals due to different stress experiences throughout the lifespan and vulnerability of neurocognitive mechanisms. To understand the heterogeneity of cognitive aging, we investigated the effect of early adulthood stress (EAS) on three different hippocampus-dependent memory tasks: the novel object recognition test (assessing recognition memory: RM), the paired association test (assessing episodic-like memory: EM), and trace fear conditioning (assessing trace memory: TM). Two-month-old rats were exposed to chronic mild stress for 6 weeks and underwent behavioral testing either 2 weeks or 20 months later. The results show that stress and aging impaired different types of memory tasks to varying degrees. RM is affected by combined effect of stress and aging. EM became less precise in EAS animals. TM, especially the contextual memory, showed impairment in aging although EAS attenuated the aging effect, perhaps due to its engagement in emotional memory systems. To further explore the neural underpinnings of these multi-faceted effects, we measured long-term potentiation (LTP), neural density, and synaptic density in the dentate gyrus (DG). Both stress and aging reduced LTP. Additionally, the synaptic density per neuron showed a further reduction in the stress aged group. In summary, EAS modulates different forms of memory functions perhaps due to their substantial or partial dependence on the functional integrity of the hippocampus. The current results suggest that lasting alterations in hippocampal circuits following EAS could potentially generate remote effects on individual variability in cognitive aging, as demonstrated by performance in multiple types of memory.

Dopamine, Psychosis, and Symptom Fluctuation: A Narrative Review

It has been hypothesized since the 1960s that the etiology of schizophrenia is linked to dopamine. In the intervening 60 years, sophisticated brain imaging techniques, genetic/epigenetic advances, and new experimental animal models of schizophrenia have transformed schizophrenia research. The disease is now conceptualized as a heterogeneous neurodevelopmental disorder expressed phenotypically in four symptom domains: positive, negative, cognitive, and affective. The aim of this paper is threefold: (a) to review recent research into schizophrenia etiology, (b) to review papers that elicited subjective evidence from patients as to triggers and repressors of symptoms such as auditory hallucinations or paranoid thoughts, and (c) to address the potential role of dopamine in schizophrenia in general and, in particular, in the fluctuations in schizophrenia symptoms. The review also includes new discoveries in schizophrenia research, pointing to the involvement of both striatal neurons and glia, signaling pathway convergence, and the role of stress. It also addresses potential therapeutic implications. We conclude with the hope that this paper opens up novel avenues of research and new possibilities for treatment.

Sleep fragmentation engages stress-responsive circuitry, enhances inflammation and compromises hippocampal function following traumatic brain injury

Traumatic brain injury (TBI) impairs the ability to restore homeostasis in response to stress, indicating hypothalamic-pituitary-adrenal (HPA)-axis dysfunction. Many stressors result in sleep disturbances, thus mechanical sleep fragmentation (SF) provides a physiologically relevant approach to study the effects of stress after injury. We hypothesize SF stress engages the dysregulated HPA-axis after TBI to exacerbate post-injury neuroinflammation and compromise recovery. To test this, male and female mice were given moderate lateral fluid percussion TBI or sham-injury and left undisturbed or exposed to daily, transient SF for 7- or 30-days post-injury (DPI). Post-TBI SF increases cortical expression of interferon- and stress-associated genes characterized by inhibition of the upstream regulator NR3C1 that encodes glucocorticoid receptor (GR). Moreover, post-TBI SF increases neuronal activity in the hippocampus, a key intersection of the stress-immune axes. By 30 DPI, TBI SF enhances cortical microgliosis and increases expression of pro-inflammatory glial signaling genes characterized by persistent inhibition of the NR3C1 upstream regulator. Within the hippocampus, post-TBI SF exaggerates microgliosis and decreases CA1 neuronal activity. Downstream of the hippocampus, post-injury SF suppresses neuronal activity in the hypothalamic paraventricular nucleus indicating decreased HPA-axis reactivity. Direct application of GR agonist, dexamethasone, to the CA1 at 30 DPI increases GR activity in TBI animals, but not sham animals, indicating differential GR-mediated hippocampal action. Electrophysiological assessment revealed TBI and SF induces deficits in Schaffer collateral long-term potentiation associated with impaired acquisition of trace fear conditioning, reflecting dorsal hippocampal-dependent cognitive deficits. Together these data demonstrate that post-injury SF engages the dysfunctional post-injury HPA-axis, enhances inflammation, and compromises hippocampal function. Therefore, external stressors that disrupt sleep have an integral role in mediating outcome after brain injury.

Molecular insights into the benefits of nicotine on memory and cognition (Review)

The health risks of nicotine are well known, but there is some evidence of its beneficial effects on cognitive function. The present review focused on the reported benefits of nicotine in the brain and summarizes the associated underlying mechanisms. Nicotine administration can improve cognitive impairment in Alzheimer's disease (AD), and dyskinesia and memory impairment in Parkinson's disease (PD). In terms of its mechanism of action, nicotine slows the progression of PD by inhibiting Sirtuin 6, a stress‑responsive protein deacetylase, thereby decreasing neuronal apoptosis and improving neuronal survival. In AD, nicotine improves cognitive impairment by enhancing protein kinase B (also referred to as Akt) activity and stimulating phosphoinositide 3‑kinase/Akt signaling, which regulates learning and memory processes. Nicotine may also activate thyroid receptor signaling pathways to improve memory impairment caused by hypothyroidism. In healthy individuals, nicotine improves memory impairment caused by sleep deprivation by enhancing the phosphorylation of calmodulin‑dependent protein kinase II, an essential regulator of cell proliferation and synaptic plasticity. Furthermore, nicotine may improve memory function through its effect on chromatin modification via the inhibition of histone deacetylases, which causes transcriptional changes in memory‑related genes. Finally, nicotine administration has been demonstrated to rescue long‑term potentiation in individuals with sleep deprivation, AD, chronic stress and hypothyroidism, primarily by desensitizing α7 nicotinic acetylcholine receptors. To conclude, nicotine has several cognitive benefits in healthy individuals, as well as in those with cognitive dysfunction associated with various diseases. However, further research is required to shed light on the effect of acute and chronic nicotine treatment on memory function.

Understanding stress: Insights from rodent models

Through incorporating both physical and psychological forms of stressors, a variety of rodent models have provided important insights into the understanding of stress physiology. Rodent models also have provided significant information with regards to the mechanistic basis of the pathophysiology of stress-related disorders such as anxiety disorders, depressive illnesses, cognitive impairment and post-traumatic stress disorder. Additionally, rodent models of stress have served as valuable tools in the area of drug screening and drug development for treatment of stress-induced conditions. Although rodent models do not accurately reproduce the biochemical or physiological parameters of stress response and cannot fully mimic the natural progression of human disorders, yet, animal research has provided answers to many important scientific questions. In this review article, important studies utilizing a variety of stress models are described in terms of their design and apparatus, with specific focus on their capabilities to generate reliable behavioral and biochemical read-out. The review focusses on the utility of rodent models by discussing examples in the literature that offer important mechanistic insights into physiologically relevant questions. The review highlights the utility of rodent models of stress as important tools for advancing the mission of scientific research and inquiry.

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Stressful life events may lead to the onset of severe psychopathologies in humans.

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Rodents may model many features of stress exposure in human populations.

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Induction of stress via pharmacological and psychological manipulations alter rodent behavior.

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Mechanistic rodent studies reveal key molecular targets critical for new therapeutic targets.

Evaluation of the Effect of Hypericum triquetrifolium Turra on Memory Impairment Induced by Chronic Psychosocial Stress in Rats: Role of BDNF

BACKGROUND

Chronic psychosocial stress impairs memory function and leads to a depression-like phenotype induced by a persistent status of oxidative stress. Hypericum perforatum L. (St. John's wort) is widely used to relieve symptoms of anxiety and depression; however, its long-term use is associated with adverse effects. Hypericum triquetrifolium Turra is closely related to H. perforatum. Both plants belong to Hypericaceae family and share many biologically active compounds. Previous work by our group showed that methanolic extracts of H. triquetrifolium have potent antioxidant activity as well as high hypericin content, a component that proved to have stress-relieving and antidepressant effects by other studies. Therefore, we hypothesized that H. triquetrifolium would reduce stress-induced cognitive impairment in a rat model of chronic stress.

OBJECTIVE

To determine whether chronic treatment with H. triquetrifolium protects against stress-associated memory deficits and to investigate a possible mechanism.

METHODS

The radial arm water maze (RAWM) was used to test learning and memory in rats exposed to daily stress using the resident-intruder paradigm. Stressed and unstressed rats received chronic H. triquetrifolium or vehicle. We also measured levels of brain-derived neurotrophic factor (BDNF) in the hippocampus, cortex and cerebellum.

RESULTS

Neither chronic stress nor chronic H. triquetrifolium administration affected performance during acquisition. However, memory tests in the RAWM showed that chronic stress impaired different post-encoding memory stages. H. triquetrifolium prevented this impairment. Furthermore, hippocampal BDNF levels were markedly lower in stressed animals than in unstressed animals, and chronic administration of H triquetrifolium chronic administration protected against this reduction. No significant difference was observed in the effects of chronic stress and/or H. triquetrifolium treatment on BDNF levels in the cerebellum and cortex.

CONCLUSION

H. triquetrifolium extract can oppose stress-associated hippocampus-dependent memory deficits in a mechanism that may involve BDNF in the hippocampus.

The role of CREB and BDNF in neurobiology and treatment of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia worldwide. β-amyloid peptide (Aβ) is currently assumed to be the main cause of synaptic dysfunction and cognitive impairments in AD, but the molecular signaling pathways underlying its neurotoxic consequences have not yet been completely explored. Additional investigations regarding these pathways will contribute to development of new therapeutic targets. In context, developing evidence suggest that Aβ decreases brain-derived neurotrophic factor (BDNF) mostly by lowering phosphorylated cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) protein. In fact, it has been observed that brain or serum levels of BDNF appear to be beneficial markers for cognitive condition. In addition, the participation of transcription mediated by CREB has been widely analyzed in the memory process and AD development. Designing pharmacologic or genetic therapeutic approaches based on the targeting of CREB-BDNF signaling could be a promising treatment potential for AD. In this review, we summarize data demonstrating the role of CREB-BDNF signaling pathway in cognitive status and mediation of Aβ toxicity in AD. Finally, we also focus on the developing intervention methods for improvement of cognitive decline in AD based on targeting of CREB-BDNF pathway.

Farnesoid X Receptor-Mediated Cytoplasmic Translocation of CRTC2 Disrupts CREB-BDNF Signaling in Hippocampal CA1 and Leads to the Development of Depression-Like Behaviors in Mice

BACKGROUND

We recently identified neuronal expression of farnesoid X receptor (FXR), a bile acid receptor known to impair autophagy by inhibiting cyclic adenosine monophosphate response element-binding protein (CREB), a protein whose underfunctioning is linked to neuroplasticity and depression. In this study, we hypothesize that FXR may mediate depression via a CREB-dependent mechanism.

METHODS

Depression was induced in male C57BL6/J mice via chronic unpredictable stress (CUS). Subjects underwent behavioral testing to identify depression-like behaviors. A variety of molecular biology techniques, including viral-mediated gene transfer, Western blot, co-immunoprecipitation, and immunofluorescence, were used to correlate depression-like behaviors with underlying molecular and physiological events.

RESULTS

Overexpression of FXR, whose levels were upregulated by CUS in hippocampal CA1, induced or aggravated depression-like behaviors in stress-naïve and CUS-exposed mice, while FXR short hairpin RNA (shRNA) ameliorated such symptoms in CUS-exposed mice. The behavioral effects of FXR were found to be associated with changes in CREB-brain-derived neurotrophic factor (BDNF) signaling, as FXR overexpression aggravated CUS-induced reduction in BDNF levels while the use of FXR shRNA or disruption of FXR-CREB signaling reversed the CUS-induced reduction in the phosphorylated CREB and BDNF levels. Molecular analysis revealed that FXR shRNA prevented CUS-induced cytoplasmic translocation of CREB-regulated transcription coactivator 2 (CRTC2); CRTC2 overexpression and CRTC2 shRNA abrogated the regulatory effect of FXR overexpression or FXR shRNA on CUS-induced depression-like behaviors.

CONCLUSIONS

In stress conditions, increased FXR in the CA1 inhibits CREB by targeting CREB and driving the cytoplasmic translocation of CRTC2. Uncoupling of the FXR-CREB complex may be a novel strategy for depression treatment.

Memory Impairment Induced by Chronic Psychosocial Stress Is Prevented by L-Carnitine

Introduction

Psychosocial stress (STS) negatively influences memory. This might be associated to oxidative stress-induced progressive destruction of numerous brain structures and functions. L-carnitine (L-CAR) is a widely used antioxidant compound that is endogenously made in mammalian species. The current study investigated the effect of L-CAR on STS-induced memory impairment in the rat hippocampus.

Methods

The STS was induced using intruder model, where two rats were randomly switched from each one cage to another, once/day for 6 weeks. Concurrently, L-CAR (300mg/kg/day) was intraperitoneally administered for 6 weeks. After that, radial arm water maze (RAWM) was used to assess spatial learning memory in rats. Hippocampal biomarkers of oxidative stress, including thiobarbituric acid reactive substance (TBARs), oxidized glutathione (GSSG), reduced glutathione (GSH), glutathione peroxidase (GPx), catalase, and superoxide dismutase (SOD), and Brain-derived neurotrophic factor (BDNF) were examined.

Results

The results showed impairment of short-term memory (P < 0.05) during STS, whereas L-CAR treatment protected against this effect. Furthermore, while no change was observed in GSH, GSSG, GPx, catalase, and SOD, L-carnitine normalized STS-induced reduction in the hippocampal BDNF levels and increase in TBARS levels.

Discussion

Chronic psychosocial stress-induced memory impairment was prevented via L-CAR administration, which could have been achieved via normalizing changes in lipid peroxidation (TBARs) and BDNF levels in the hippocampus.

Obese mice exposed to psychosocial stress display cardiac and hippocampal dysfunction associated with local brain-derived neurotrophic factor depletion

INTRODUCTION

Obesity and psychosocial stress (PS) co-exist in individuals of Western society. Nevertheless, how PS impacts cardiac and hippocampal phenotype in obese subjects is still unknown. Nor is it clear whether changes in local brain-derived neurotrophic factor (BDNF) account, at least in part, for myocardial and behavioral abnormalities in obese experiencing PS.

METHODS

In adult male WT mice, obesity was induced via a high-fat diet (HFD). The resident-intruder paradigm was superimposed to trigger PS. In vivo left ventricular (LV) performance was evaluated by echocardiography and pressure-volume loops. Behaviour was indagated by elevated plus maze (EPM) and Y-maze. LV myocardium was assayed for apoptosis, fibrosis, vessel density and oxidative stress. Hippocampus was analyzed for volume, neurogenesis, GABAergic markers and astrogliosis. Cardiac and hippocampal BDNF and TrkB levels were measured by ELISA and WB. We investigated the pathogenetic role played by BDNF signaling in additional cardiac-selective TrkB (cTrkB) KO mice.

FINDINGS

When combined, obesity and PS jeopardized LV performance, causing prominent apoptosis, fibrosis, oxidative stress and remodeling of the larger coronary branches, along with lower BDNF and TrkB levels. HFD/PS weakened LV function similarly in WT and cTrkB KO mice. The latter exhibited elevated LV ROS emission already at baseline. Obesity/PS augmented anxiety-like behaviour and impaired spatial memory. These changes were coupled to reduced hippocampal volume, neurogenesis, local BDNF and TrkB content and augmented astrogliosis.

INTERPRETATION

PS and obesity synergistically deteriorate myocardial structure and function by depleting cardiac BDNF/TrkB content, leading to augmented oxidative stress. This comorbidity triggers behavioral deficits and induces hippocampal remodeling, potentially via lower BDNF and TrkB levels. FUND: J.A. was in part supported by Rotary Foundation Global Study Scholarship. G.K. was supported by T32 National Institute of Health (NIH) training grant under award number 1T32AG058527. S.C. was funded by American Heart Association Career Development Award (19CDA34760185). G.A.R.C. was funded by NIH (K01HL133368-01). APB was funded by a Grant from the Friuli Venezia Giulia Region entitled: "Heart failure as the Alzheimer disease of the heart; therapeutic and diagnostic opportunities". M.C. was supported by PRONAT project (CNR). N.P. was funded by NIH (R01 HL136918) and by the Magic-That-Matters fund (JHU). V.L. was in part supported by institutional funds from Scuola Superiore Sant'Anna (Pisa, Italy), by the TIM-Telecom Italia (WHITE Lab, Pisa, Italy), by a research grant from Pastificio Attilio Mastromauro Granoro s.r.l. (Corato, Italy) and in part by ETHERNA project (Prog. n. 161/16, Fondazione Pisa, Italy). Funding source had no such involvement in study design, in the collection, analysis, interpretation of data, in the writing of the report; and in the decision to submit the paper for publication.

The effects of repetitive stress on tat protein-induced pro-inflammatory cytokine release and steroid receptor expression in the hippocampus of rats

Human immunodeficiency virus type 1 (HIV-1) affects the central nervous system (CNS) that may lead to the development of HIV-associated neuropathologies. Tat protein is one of the viral proteins that have been linked to the neurotoxic effects of HIV. Since many individuals living with HIV often experience significant adverse circumstances, the present study investigated whether exposure to stressful conditions would exacerbate harmful effects of tat protein on brain function. Tat protein (10 μg/10 μl) was injected bilaterally into the dorsal hippocampus of the animal using stereotaxic techniques. The control group received an injection of saline (10 μl). Some control and tat protein-treated animals were subjected to restrain stress for 6 h per day for 28 days and compared to a non-stress group. All animals underwent two behavioural tests, the open field test (OFT) and the novel object recognition test (NORT) to assess their mood state and cognitive function respectively. The release of pro-inflammatory cytokines (TNF-α and IL-1β) and the expression of mineralocorticoid (MR) and glucocorticoid (GR) receptors were also measured to see whether the impact of the repetitive stress on Tat protein-induced behavioural effects was mediated by elements of the immune system and the HPA axis. Rats treated with tat protein showed the following behavioural changes when compared to control animals: there was a significant decrease in time spent in the center of the open field during the OFT, a significant reduction in time spent with the novel object during the NORT, but no change in locomotor activity. Real-time PCR data showed that the expression levels of GR and MR mRNA were significantly reduced, while Western blot analysis showed that the protein expression levels of TNF-α and IL-1β were significantly increased. The present findings indicated that injection of tat protein into the hippocampus of rats not subjected to stress may lead to anxiety-like behaviour and deficits in learning and memory. Tat-treated animals subjected to stress evoked only a modest effect on their behaviour and neurochemistry, while stress alone led to behavioural and neurochemical changes similar to tat protein.

Neuroprotective Effects of Nicotine on Hippocampal Long-Term Potentiation in Brain Disorders

Long-term potentiation (LTP) is commonly considered the cellular correlate of learning and memory. In learning and memory impairments, LTP is invariably diminished in the hippocampus, the brain region responsible for memory formation. LTP is measured electrophysiologically in various areas of the hippocampus. Two mechanistically distinct phases of LTP have been identified: early phase LTP, related to short-term memory; and late-phase LTP, related to long-term memory. These two forms can be severely reduced in a variety of conditions but can be rescued by treatment with nicotine. This report reviews the literature on the beneficial effect of nicotine on LTP in conditions that compromise learning and memory.

Delayed effects of combined stress and Aβ infusion on L-LTP of the dentate gyrus: Prevention by nicotine

Alzheimer's Disease (AD) is a progressive dementia hallmarked by the presence in the brain of extracellular beta-amyloid (Aβ) plaques and intraneuronal fibrillary tangles. Chronic stress is associated with heightened Aβ buildup and acceleration of development of AD, however, stress alone has no significant effect on synaptic plasticity in the dentate gyrus (DG) area. Previously, we have reported that the combination of stress and AD causes more severe inhibition of synaptic plasticity of hippocampal area CA1 than chronic stress or AD alone, and that chronic nicotine treatment prevents this impairment. To investigate the effect of stress and nicotine on synaptic plasticity in the relatively injury-resistant DG area, the present experiments analyzed the effect of chronic stress and the neuroprotective effect of nicotine on LTP in the DG area of a rat model of AD. Wistar rats were chronically stressed and treated with nicotine (1 mg/kg/twice daily; s.c.) for six weeks. Then, at weeks 5-6, AD model was generated by 14-day i.c.v osmotic pump infusion of Aβ peptides (300 pmol/day) into the brains of these rats. Field potential recordings from the DG area of anesthetized rats, revealed that while chronic stress did not accentuate Aβ-induced impairments of E-LTP, it markedly augmented Aβ effect on L-LTP that was only seen 100 min after multiple high frequency stimulation. This delayed action is likely to be due to impairment of process of de novo protein synthesis required for maintenance phase of L-LTP. Chronic nicotine treatment prevented stress-enhanced suppression of synaptic plasticity.

The Role of Musk in Relieving the Neurodegenerative Changes Induced After Exposure to Chronic Stress

OBJECTIVE

This study aimed to evaluate the effect induced by musk on Alzheimer's disease-such as neurodegenerative changes in mice exposed to chronic unpredictable mild stress (CUMS).

MATERIAL AND METHODS

Forty male Swiss albino mice were divided into 4 groups (n = 10); control, CUMS, CUMS + fluoxetine, CUMS + musk. At the end of the experiment, behavior of the mice was assessed. Serum corticosterone level, hippocampal protein level of the glucocorticoid receptors, and brain-derived neurotropic factor were also assessed. Hippocampus was histopathologically examined.

RESULTS

Musk improved depressive status induced after exposure to CUMS as evidenced by the forced swimming and open field tests and improved the short-term memory as evidenced by the elevated plus maze test. Musk reduced both corticosterone levels and the hippocampal neurodegenerative changes observed after exposure to CUMS. These improvements were comparable to those induced by fluoxetine.

CONCLUSION

Musk alleviated the memory impairment and neurodegenerative changes induced after exposure to the chronic stress.

Ocimum basilicum improve chronic stress-induced neurodegenerative changes in mice hippocampus

Alzheimer's disease (AD), one of the progressive neurodegenerative diseases might be associated with exposure to stress and altered living conditions. This study aimed to evaluate the effectiveness of Ocimum basilicum (OB) essential oils in improving the neurodegenerative-like changes induced in mice after exposed to chronic unpredictable mild stress (CUMS). Forty male Swiss albino mice divided into four groups (n = 10); the control, CUMS, CUMS + Fluoxetine, CUMS + OB were used. Behavioral tests, serum corticosterone level, hippocampus protein level of the glucocorticoid receptors (GRs) and brain-dreived neurotropic factor (BDNF) were determined after exposure to CUMS. Hippocampus was histopathologically examined. Data were analyzed using statistical package for the social sciences (SPSS) and P value of less than 0.05 was considered significant. OB diminished the depression manifestation as well as impaired short term memory observed in the mice after exposure to the CUMS as evidenced by the forced swimming and elevated plus maze test. OB also up-regulated the serum corticosterone level, hippocampal protein level of the glucocorticoid receptor and the brain-derived neurotropic factor and reduced the neurodegenerative and atrophic changes induced in the hippocampus after exposure to CUMS. Essential oils of OB alleviated the memory impairment and hippocampal neurodegenerative changes induced by exposure to the chronic unpredictable stress indicating that it is the time to test its effectiveness on patients suffering from Alzheimer disease.

Exercise as a Positive Modulator of Brain Function

Various forms of exercise have been shown to prevent, restore, or ameliorate a variety of brain disorders including dementias, Parkinson's disease, chronic stress, thyroid disorders, and sleep deprivation, some of which are discussed here. In this review, the effects on brain function of various forms of exercise and exercise mimetics in humans and animal experiments are compared and discussed. Possible mechanisms of the beneficial effects of exercise including the role of neurotrophic factors and others are also discussed.

Interactions between stress and physical activity on Alzheimer's disease pathology

Physical activity and stress are both environmental modifiers of Alzheimer's disease (AD) risk. Animal studies of physical activity in AD models have largely reported positive results, however benefits are not always observed in either cognitive or pathological outcomes and inconsistencies among findings remain. Studies using forced exercise may increase stress and mitigate some of the benefit of physical activity in AD models, while voluntary exercise regimens may not achieve optimal intensity to provide robust benefit. We evaluated the findings of studies of voluntary and forced exercise regimens in AD mouse models to determine the influence of stress, or the intensity of exercise needed to outweigh the negative effects of stress on AD measures. In addition, we show that chronic physical activity in a mouse model of AD can prevent the effects of acute restraint stress on Aβ levels in the hippocampus. Stress and physical activity have many overlapping and divergent effects on the body and some of the possible mechanisms through which physical activity may protect against stress-induced risk factors for AD are discussed. While the physiological effects of acute stress and acute exercise overlap, chronic effects of physical activity appear to directly oppose the effects of chronic stress on risk factors for AD. Further study is needed to identify optimal parameters for intensity, duration and frequency of physical activity to counterbalance effects of stress on the development and progression of AD.

Effects of Crocin on Learning and Memory in Rats Under Chronic Restraint Stress with Special Focus on the Hippocampal and Frontal Cortex Corticosterone Levels

Background:

Chronic stress adversely influences brain functions while crocin, as an effective component of saffron, exhibits positive effects on memory processes. This study investigated the effects of different doses of crocin on the improvement of learning and memory as well as corticosterone (CORT) levels in the hippocampus and frontal cortex of rats subjected to chronic stress.

Materials and Methods:

Forty male rats were randomly allocated to five different groups (n = 8): Control, sham; stress (6 h/day for 21 days) groups, and two groups receiving daily intraperitoneal injections of one of two doses (30 and 60 mg/kg) of crocin accompanied by 21 days of restraint stress. Latency was evaluated as a brain function using the passive avoidance test before and one-day after a foot shock. CORT levels were measured in the homogenized hippocampus and frontal cortex.

Results:

Results revealed that chronic stress had a significantly (P < 0.01) negative effect on memory. Crocin (30 and 60 mg/kg), however, gave increase to significantly (P < 0.01 and P < 0.05; respectively) improved memory functions in the stressed rats. Furthermore, the CORT levels in the hippocampus and frontal cortex declined significantly (P < 0.05) in the stress group compared to the control. Only a crocin dose of 30 mg/kg was observed modulate significantly (P < 0.05) the CORT levels in the hippocampus and frontal cortex in the stressed group.

Conclusions:

It was found that the lower crocin dose (30 mg/kg) had more beneficial effects than its higher (60 mg/kg) dose on learning and memory under chronic stress conditions. Moreover, it was speculated that different doses of crocin act on different neurotransmitters and biochemical factors in the brain.

Nicotine-prevented learning and memory impairment in REM sleep-deprived rat is modulated by DREAM protein in the hippocampus

INTRODUCTION

REM sleep deprivation is associated with impairment in learning and memory, and nicotine treatment has been shown to attenuate this effect. Recent studies have demonstrated the importance of DREAM protein in learning and memory processes. This study investigates the association of DREAM protein in REM sleep-deprived rats hippocampus upon nicotine treatment.

METHODS

Male Sprague Dawley rats were subjected to normal condition, REM sleep deprivation and control wide platform condition for 72 hr. During this procedure, saline or nicotine (1 mg/kg) was given subcutaneously twice a day. Then, Morris water maze (MWM) test was used to assess learning and memory performance of the rats. The rats were sacrificed and the brain was harvested for immunohistochemistry and Western blot analysis.

RESULTS

MWM test found that REM sleep deprivation significantly impaired learning and memory performance without defect in locomotor function associated with a significant increase in hippocampus DREAM protein expression in CA1, CA2, CA3, and DG regions and the mean relative level of DREAM protein compared to other experimental groups. Treatment with acute nicotine significantly prevented these effects and decreased expression of DREAM protein in all the hippocampus regions but only slightly reduce the mean relative level of DREAM protein.

CONCLUSION

This study suggests that changes in DREAM protein expression in CA1, CA2, CA3, and DG regions of rat's hippocampus and mean relative level of DREAM protein may involve in the mechanism of nicotine treatment-prevented REM sleep deprivation-induced learning and memory impairment in rats.

Danggui-Jakyak-San enhances hippocampal long-term potentiation through the ERK/CREB/BDNF cascade

ETHNOPHARMACOLOGICAL RELEVANCE

Danggui-Jakyak-San (DJS), a traditional herbal prescription, has long been used to treat gerontological disorders due to insufficient blood supply.

AIM OF THE STUDY

Previously, we reported that DJS increased hippocampal neurogenesis and enhanced learning and memory. However, the precise mechanism of DJS and its effects on learning and memory are still not well understood. In this study, we investigated the effect of DJS on hippocampal long-term potentiation (LTP), a cellular mechanism thought to underlie learning and memory.

MATERIALS AND METHODS

To understand the effect of DJS on LTP, we used acute mouse hippocampal slices and delivered one train of high frequency stimulation (100 Hz, 100 pulses). Western blots were used to analyze the changes in protein levels induced by DJS. Morris water maze test was used to evaluate the effect of DJS on spatial long-term memory.

RESULTS

DJS enhanced LTP in the Schaffer-collateral pathway of the hippocampus in a concentration-dependent manner. Extracellular signal-regulated kinase 1/2 (ERK1/2) and cAMP response element-binding protein (CREB) were activated by DJS. Moreover, brain-derived neurotropic factor (BDNF) was also increased by DJS. Blockade of ERK1/2 activation with PD198306 blocked the DJS-induced activation of the ERK1/2/CREB/BDNF cascade and LTP enhancement. In vivo, DJS improved spatial long-term memory and upregulated the hippocampal CREB/BDNF cascade.

CONCLUSION

These results suggest that DJS enhances hippocampal LTP and spatial memory through the ERK/CREB/BDNF cascade.

The adaptive and maladaptive continuum of stress responses – a hippocampal perspective

Exposure to stressors elicits a spectrum of responses that span from potentially adaptive to maladaptive consequences at the structural, cellular and physiological level. These responses are particularly pronounced in the hippocampus where they also appear to influence hippocampal-dependent cognitive function and emotionality. The factors that influence the nature of stress-evoked consequences include the chronicity, severity, predictability and controllability of the stressors. In addition to adult-onset stress, early life stress also elicits a wide range of structural and functional responses, which often exhibit life-long persistence. However, the outcome of early stress exposure is often contingent on the environment experienced in adulthood, and could either aid in stress coping or could serve to enhance susceptibility to the negative consequences of adult stress. This review comprehensively examines the consequences of adult and early life stressors on the hippocampus, with a focus on their effects on neurogenesis, neuronal survival, structural and synaptic plasticity and hippocampal-dependent behaviors. Further, we discuss potential factors that may tip stress-evoked consequences from being potentially adaptive to largely maladaptive.

Early life inflammatory pain induces long-lasting deficits in hippocampal-dependent spatial memory in male and female rats

The present experiment tested the hypothesis that neonatal injury disrupts adult hippocampal functioning and that normal aging or chronic stress during adulthood, which are known to have a negative impact on hippocampal function, exacerbate these effects. Male and female Sprague-Dawley rats were given an intraplantar injection of the inflammatory agent carrageenan (1%) on the day of birth and their memory was tested in the hippocampal-dependent spatial water maze in adulthood and again in middle age. We found that neonatal injury impaired hippocampal-dependent memory in adulthood, that the effects of injury on memory were more pronounced in middle-aged male rats, and that chronic stress accelerated the onset of these memory deficits. Neonatal injury also decreased glucocorticoid receptor mRNA in the dorsal CA1 area of middle-aged rats, a brain region critical for spatial memory. Morphine administration at the time of injury completely reversed injury-induced memory deficits, but neonatal morphine treatments in the absence of injury produced significant memory impairments in adulthood. Collectively, these findings are consistent with our hypothesis that neonatal injury produces long-lasting disruption in adult hippocampal functioning.

Resveratrol prevents impaired cognition induced by chronic unpredictable mild stress in rats

Depression is one of the most common neuropsychiatric disorders and has been associated with impaired cognition, as well as causing neuroendocrine systems and brain proteins alterations. Resveratrol is a natural polyphenol enriched in polygonum cuspidatum and has diverse biological activities, including potent antidepressant-like effects. The aim of this study was to determine whether resveratrol administration influences chronic unpredictable mild stress (CUMS)-induced cognitive deficits and explores underlying mechanisms. The results showed that CUMS (5weeks) was effective in producing cognitive deficits in rats as indicated by Morris water maze and novel object recognition task. Additionally, CUMS exposure significantly elevated serum corticosterone levels and decreased BDNF levels in the prefrontal cortex (PFC) and hippocampus, accompanied by decreased phosphorylation of extracellular signal-regulated kinase (pERK) and cAMP response element-binding protein (pCREB). Chronic administration of resveratrol (80mg/kg, i.p., 5weeks) significantly prevented all these CUMS-induced behavioral and biochemical alterations. In conclusion, our study shows that resveratrol may be an effective therapeutic agent for cognitive disturbances as was seen within the stress model and its neuroprotective effect was mediated in part by normalizing serum corticosterone levels, up-regulating of the BDNF, pCREB and pERK levels.

Treadmill exercise prevents learning and memory impairment in Alzheimer's disease-like pathology

Alzheimer's disease (AD) is a neurodegenerative disorder that is characterized by progressive memory loss. In contrast, accumulating evidence suggests a neuroprotective role of regular exercise in aging associated memory impairment. In this study, we investigated the ability of regular exercise to prevent impairments of short-term memory (STM) and early long-term potentiation (E-LTP) in area CA1 of the hippocampus in a rat model of AD (i.c.v. infusion of 250 pmol/day Aβ1-42 peptides). We utilized behavioral assessment, in vivo electrophysiological recording, and immunoblotting in 4 groups of adult Wistar rats: control, treadmill exercise (Ex), β-amyloid-infused (Aβ), and amyloid-infused/treadmill exercised (Ex/Aβ). Our findings indicated that Aβ rats made significantly more errors in the radial arm water maze (RAWM) compared to all other groups and exhibited suppressed E-LTP in area CA1, which correlated with deleterious alterations in the levels of memory and E-LTP-related signaling molecules including calcineurin (PP2B), brain derivedneurotrophic factor (BDNF) and phosphorylated CaMKII (p-CaMKII). Compared to controls, Ex and Ex/Aβ rats showed a similar behavioral performance and a normal E-LTP with no detrimental changes in the levels of PP2B, BDNF, and p- CaMKII. We conclude that treadmill exercise maybe able to prevent cognitive impairment associated with AD pathology.

Levothyroxin replacement therapy restores hypothyroidism induced impairment of L-LTP induction: critical role of CREB

Cyclic-AMP response element binding protein (CREB) is a transcription factor crucial for late phase long-term potentiation (L-LTP) induction and maintenance. Upon multiple high frequency stimulation (MHFS), large Ca(2+) influx activates adenylyl cyclase. This, in turn, activates PKA, which by itself or through MAPK p42/p44 can activate (phosphorylate) CREB. Upon phosphorylation, P-CREB activates multiple genes essential for L-LTP generation. Calcium calmodulin kinase IV (CaMKIV) is also activated by calcium and can directly activate CREB. We have shown previously that hypothyroidism impairs L-LTP and reduces the basal protein levels of CREB, MAPK p42/p44, and CaMKIV in area CA1 of the hippocampus. In the present study, levels of these signaling molecules were determined in area CA1 during the induction and maintenance phases of L-LTP. Standard MHFS was used to evoke L-LTP in the CA1 area of hypothyroid, levothyroxin treated hypothyroid and sham control anesthetized adult rats. Chronic levothyroxin treatment reversed hypothyroidism-induced L-LTP impairment. Five minutes after MHFS, western blotting showed an increase in the levels of P-CREB, and P-MAPK p42/p44 in sham-operated control, and levothyroxin treated hypothyroid animals, but not in hypothyroid animals. The protein levels of total CREB, total MAPK p42/p44, BDNF and CaMKIV were not altered in all groups five minutes after MHFS. Four hours after MHFS, the levels of P-CREB, and P-MAPK p42/p44 remained unchanged in hypothyroid animals, while they were elevated in sham-operated control, and levothyroxin treated hypothyroid animals. We conclude that respective normalized phosphorylation of essential kinases such as P-CREB and P-MAPK p42/p44 is correlated with restoration of normal L-LTP induction and maintenance in the CA1 area of levothyroxin-treated hypothyroid animals.

Chronic nicotine treatment reverses hypothyroidism-induced impairment of L-LTP induction phase: critical role of CREB

We have previously shown that adult onset hypothyroidism impairs late-phase long-term potentiation (L-LTP) and reduces basal protein levels of cyclic-AMP response element binding protein (CREB), mutagen-activated protein kinase (MAPKp42/44), and calcium calmodulin kinase IV (CaMKIV) in area Cornu Ammonis 1 (CA1) of the hippocampus. These changes were reversed by chronic nicotine treatment. In the present study, levels of signaling molecules important for L-LTP were determined in CA1 area of the hippocampus during the induction phase. Standard multiple high-frequency stimulation (MHFS) was used to evoke L-LTP in the CA1 area of the hippocampus of hypothyroid, nicotine-treated hypothyroid, nicotine, and sham control anaesthetized adult rats. Chronic nicotine treatment reversed hypothyroidism-induced impairment of L-LTP at the induction phase. Five minutes after MHFS, Western blotting showed an increase in the levels of P-CREB, and P-MAPKp42/44 in sham-operated control, nicotine, and nicotine-treated hypothyroid animals, but not in hypothyroid animals. The protein levels of total CREB, total MAPK p42/44, BDNF, and CaMKIV were not altered in all groups 5 min after MHFS. Therefore, normalized phosphorylation of essential kinases such as P-CREB and P-MAPK p42/44 in the CA1 area of nicotine-treated hypothyroid animals plays a crucial role in nicotine-induced rescue of L-LTP induction during hypothyroidism.

Cytoskeletal protein translation and expression in the rat brain are stressor-dependent and region-specific

Stress is an integral component of life that can sometimes cause a critical overload, depending on the qualitative and quantitative natures of the stressors. The involvement of actin, the predominant component of dendritic integrity, is a plausible candidate factor in stress-induced neuronal cytoskeletal changes. The major aim of this study was to compare the effects of three different stress conditions on the transcription and translation of actin-related cytoskeletal genes in the rat brain. Male Wistar rats were exposed to one or other of the frequently used models of physical stress, i.e. electric foot shock stress (EFSS), forced swimming stress (FSS), or psychosocial stress (PSS) for periods of 3, 7, 14, or 21 days. The relative mRNA and protein expressions of β-actin, cofilin and mitogen-activated protein kinase 1 (MAPK-1) were determined by qRT- PCR and western blotting from hippocampus and frontal cortex samples. Stressor-specific alterations in both β-actin and cofilin expression levels were seen after stress. These alterations were most pronounced in response to EFSS, and exhibited a U-shaped time course. FSS led to a significant β-actin mRNA expression elevation in the hippocampus and the frontal cortex after 3 and 7 days, respectively, without any subsequent change. PSS did not cause any change in β-actin or cofilin mRNA or protein expression in the examined brain regions. EFSS, FSS and PSS had no effect on the expression of MAPK-1 mRNA at any tested time point. These findings indicate a very delicate, stress type-dependent regulation of neuronal cytoskeletal components in the rat hippocampus and frontal cortex.

Regular treadmill exercise prevents sleep deprivation-induced disruption of synaptic plasticity and associated signaling cascade in the dentate gyrus

STUDY OBJECTIVES

Evidence suggests that regular exercise can protect against learning and memory impairment in the presence of insults such as sleep deprivation. The dentate gyrus (DG) area of the hippocampus is a key staging area for learning and memory processes and is particularly sensitive to sleep deprivation. The purpose of this study was to determine the effect of regular exercise on early-phase long-term potentiation (E-LTP) and its signaling cascade in the presence of sleep deprivation.

EXPERIMENTAL DESIGN

Rats were exposed to 4 weeks of regular treadmill exercise then subsequently sleep-deprived for 24h using the modified multiple platform model before experimentation. We tested the effects of exercise and/or sleep deprivation using electrophysiological recording in the DG to measure synaptic plasticity; and Western blot analysis to quantify the levels of key signaling proteins related to E-LTP.

MEASUREMENTS AND RESULTS

Regular exercise prevented the sleep deprivation-induced impairment of E-LTP in the DG area as well as the sleep deprivation-associated decrease in basal protein levels of phosphorylated and total α calcium/calmodulin-dependent protein kinase II (P/total-CaMKII) and brain-derived neurotrophic factor (BDNF). High frequency stimulation (HFS) to the DG area was used to model learning stimuli and increased the P-CaMKII and BDNF levels in normal animals: yet failed to change these levels in sleep-deprived rats. However, HFS in control and sleep-deprived rats increased the levels of the phosphatase calcineurin. In contrast, exercise increased BDNF and P-CaMKII levels in exercised/sleep-deprived rats.

CONCLUSIONS

Regular exercise appears to exert a protective effect against sleep deprivation-induced spatial memory impairment by inducing hippocampal signaling cascades that positively modulate basal and stimulated levels of key effectors such as P-CaMKII and BDNF, while attenuating increases in the protein phosphatase calcineurin.

Brain Physiology and Pathophysiology in Mental Stress

Exposure to various forms of stress is a common daily occurrence in the lives of most individuals, with both positive and negative effects on brain function. The impact of stress is strongly influenced by the type and duration of the stressor. In its acute form, stress may be a necessary adaptive mechanism for survival and with only transient changes within the brain. However, severe and/or prolonged stress causes overactivation and dysregulation of the hypothalamic pituitary adrenal (HPA) axis thus inflicting detrimental changes in the brain structure and function. Therefore, chronic stress is often considered a negative modulator of the cognitive functions including the learning and memory processes. Exposure to long-lasting stress diminishes health and increases vulnerability to mental disorders. In addition, stress exacerbates functional changes associated with various brain disorders including Alzheimer’s disease and Parkinson’s disease. The primary purpose of this paper is to provide an overview for neuroscientists who are seeking a concise account of the effects of stress on learning and memory and associated signal transduction mechanisms. This review discusses chronic mental stress and its detrimental effects on various aspects of brain functions including learning and memory, synaptic plasticity, and cognition-related signaling enabled via key signal transduction molecules.

Role of α7- and α4β2-nAChRs in the neuroprotective effect of nicotine in stress-induced impairment of hippocampus-dependent memory

We have previously shown that nicotine prevents stress-induced memory impairment. In this study, we have investigated the role of α7- and α4β2-nicotinic acetylcholine receptors (nAChRs) in the protective effect of nicotine during chronic stress conditions. Chronic psychosocial stress was induced using a form of rat intruder model. During stress, specific antagonist for either α7-nAChRs [methyllycaconitine (MLA)] or α4β2-nAChRs [dihydro-β-erythroidine (DHβE)] was infused into the hippocampus using a 4-wk osmotic pump at a rate of 82 μg/side.d and 41 μg/side.d, respectively. Three weeks after the start of infusion, all rats were subjected to a series of cognitive tests in the radial arm water maze (RAWM) for six consecutive days or until the animal reached days to criterion (DTC) in the fourth acquisition trial and in all memory tests. DTC is defined as the number of days the animal takes to make no more than one error in three consecutive days. In the short-term memory test, MLA-infused stressed/nicotine-treated rats made similar errors to those of stress and significantly more errors compared to those of stress/nicotine, nicotine or control groups. This finding was supported by the DTC values for the short memory tests. Thus, MLA treatment blocked the neuroprotective effect of nicotine during chronic stress. In contrast, DHβE infusion did not affect the RAWM performance of stress/nicotine animals. These results strongly suggest the involvement of α7-nAChRs, but not α4β2-nAChRs, in the neuroprotective effect of chronic nicotine treatment during chronic stress conditions.

Neurobiological consequences of sleep deprivation

Although the physiological function of sleep is not completely understood, it is well documented that it contributes significantly to the process of learning and memory. Ample evidence suggests that adequate sleep is essential for fostering connections among neuronal networks for memory consolidation in the hippocampus. Sleep deprivation studies are extremely valuable in understanding why we sleep and what are the consequences of sleep loss. Experimental sleep deprivation in animals allows us to gain insight into the mechanism of sleep at levels not possible to study in human subjects. Many useful approaches have been utilized to evaluate the effect of sleep loss on cognitive function, each with relative advantages and disadvantages. In this review we discuss sleep and the detrimental effects of sleep deprivation mostly in experimental animals. The negative effects of sleep deprivation on various aspects of brain function including learning and memory, synaptic plasticity and the state of cognition-related signaling molecules are discussed.

Unraveling the time domains of corticosteroid hormone influences on brain activity: rapid, slow, and chronic modes

Brain cells are continuously exposed to corticosteroid hormones, although the levels vary (e.g., after stress). Corticosteroids alter neural activity via two receptor types, mineralocorticoid (MR) and glucocorticoid receptors (GR). These receptors regulate gene transcription but also, as we now know, act nongenomically. Via nongenomic pathways, MRs enhance and GRs suppress neural activity. In the hypothalamus, inhibitory GR effects contribute to negative feedback regulation of the stress axis. Nongenomic MR actions are also important extrahypothalamically and help organisms to immediately select an appropriate response strategy. Via genomic mechanisms, corticosteroid actions in the basolateral amygdala and ventral-most part of the cornu ammonis 1 hippocampal area are generally excitatory, providing an extended window for encoding of emotional aspects of a stressful event. GRs in hippocampal and prefrontal pyramidal cells increase surface expression of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors and strengthen glutamatergic signaling through pathways partly overlapping with those involved in long-term potentiation. This raises the threshold for subsequent induction of synaptic potentiation and promotes long-term depression. Synapses activated during stress are thus presumably strengthened but protected against excitatory inputs reaching the cells later. This restores higher cognitive control and promotes, for example, consolidation of stress-related contextual information. When an organism experiences stress early in life or repeatedly in adulthood, the ability to induce synaptic potentiation is strongly reduced and the likelihood to induce depression enhanced, even under rest. Treatment with antiglucocorticoids can ameliorate cellular effects after chronic stress and thus provide an interesting lead for treatment of stress-related disorders.

The impact of sleep deprivation on neuronal and glial signaling pathways important for memory and synaptic plasticity

Sleep deprivation is a common feature in modern society, and one of the consequences of sleep loss is the impairment of cognitive function. Although it has been widely accepted that sleep deprivation affects learning and memory, only recently has research begun to address which molecular signaling pathways are altered by sleep loss and, more importantly, which pathways can be targeted to reverse the memory impairments resulting from sleep deprivation. In this review, we discuss the different methods used to sleep deprive animals and the effects of different durations of sleep deprivation on learning and memory with an emphasis on hippocampus-dependent memory. We then review the molecular signaling pathways that are sensitive to sleep loss, with a focus on those thought to play a critical role in the memory and synaptic plasticity deficits observed after sleep deprivation. Finally, we highlight several recent attempts to reverse the effects of sleep deprivation on memory and synaptic plasticity. Future research building on these studies promises to contribute to the development of novel strategies to ameliorate the effects of sleep loss on cognition.

Elevation of BACE in an Aβ rat model of Alzheimer's disease: exacerbation by chronic stress and prevention by nicotine

In Alzheimer's disease (AD), progressive accumulation of β-amyloid (Aβ) peptides impairs nicotinic acetylcholine receptor (nAChR) function by a mechanism that may involve α7 and α4β2-nAChR subtypes. Additionally, the beta-site amyloid precursor protein (APP)-cleaving enzyme (BACE), the rate-limiting enzyme in the pathogenic Aβ production pathway, is expressed at high levels in hippocampal and cortical regions of AD brains. We measured hippocampal area CA1 protein levels of BACE and α7- and α4β2-nAChR subunits using an Aβ rat model of AD (14-d osmotic pump i.c.v. infusion of 300 pmol/d Aβ peptides) in the presence and absence of chronic stress and/or chronic nicotine treatment. There was a significant increase in the levels of BACE in Aβ-infused rats, which were markedly intensified by chronic (4-6 wk) stress, but were normalized in Aβ rats chronically treated with nicotine (1 mg/kg b.i.d.). The levels of the three subunits α7, α4 and β2 were significantly decreased in Aβ rats, but these were also normalized in Aβ rats chronically treated with nicotine. Chronic stress did not further aggravate the reduction of nAChRs in Aβ-infused rats. The increased BACE levels and decreased nAChR levels, which are established hallmarks of AD, provide additional support for the validity of the Aβ i.c.v.-infused rat as a model of AD.

The beneficial effects of regular exercise on cognition in REM sleep deprivation: behavioral, electrophysiological and molecular evidence

Inadequate sleep is prevalent in modern societies and is known to profoundly impair cognitive function. We examined the impact of 4 weeks of regular treadmill exercise on sleep deprivation induced spatial learning and memory, synaptic plasticity and related signaling molecules in area CA1 of the rat hippocampus. Rats were exercised on a treadmill and subsequently sleep-deprived for 24h using the modified multiple platform technique. Testing of learning and short-term memory performance in the radial arm water maze showed that although sedentary sleep deprived rats were severely impaired, exercised sleep deprived rats' performance was normal. Extracellular recording from area CA1 of anesthetized rats revealed that early phase LTP (E-LTP) was markedly impaired in the sedentary sleep deprived animals, but was normal in the exercised sleep deprived group. Additionally, immunoblot analysis of CA1 area before (basal) and after expression of E-LTP indicated that the significant down-regulation of the brain derived neurotrophic factor (BDNF) and phosphorylated calcium-calmodulin dependent protein kinase II (P-CaMKII) levels in sleep deprived animals was prevented by the regular exercise regimen. The results suggest that the regular exercise protocol prevents the sleep deprivation induced impairments in short-term memory and E-LTP by preventing deleterious changes in the basal and post-stimulation levels of P-CaMKII and BDNF associated with sleep deprivation.

Chronic stress and Alzheimer's disease-like pathogenesis in a rat model: prevention by nicotine

Environmental factors including chronic stress may play a critical role in the manifestation of Alzheimer's disease (AD).This review summarizes our studies of the aggravation of the impaired cognitive ability and its cellular and molecular correlates by chronic psychosocial stress and prevention by nicotine in an Aβ rat model of AD. We utilized three approaches: learning and memory tests in the radial arm water maze, electrophysiological recordings of the cellular correlates of memory, long-term potentiation (LTP) and long-term depression (LTD), in anesthetized rats, and immunoblot analysis of synaptic plasticity- and cognition-related signaling molecules. The Aβ rat model, representing the sporadic form of established AD, was induced by continuous i.c.v. infusion of a pathogenic dose of Aβ peptides via a 14- day osmotic pump. In this AD model, chronic stress intensified cognitive deficits, accentuated the disruption of signaling molecules levels and produced greater depression of LTP than what was seen with Aβ infusion alone. Chronic treatment with nicotine was highly efficient in preventing the effects of Aβ infusion and the exacerbating impact of chronic stress. Possible mechanisms for the effect of chronic stress are discussed.

Chronic psychosocial stress enhances long-term depression in a subthreshold amyloid-beta rat model of Alzheimer's disease

In addition to genetic aspects, environmental factors such as stress may also play a critical role in the etiology of the late onset, sporadic Alzheimer's disease (AD). The present study examined the effect of chronic psychosocial stress in a sub-threshold Aβ (subAβ) rat model of AD on long-term depression by two techniques: electrophysiological recordings of synaptic plasticity in anesthetized rats, and immunoblot analysis of memory- and AD-related signaling molecules. Chronic psychosocial stress was induced using a rat intruder model. The subAβ rat model of AD, which was intended to represent outwardly normal individuals with a pre-disposition to AD, was induced by continuous infusion of 160 pmol/day Aβ₁₋₄₂ via a 14-day i.c.v. osmotic pump. Results from electrophysiological recordings showed that long-term depression evoked in stress/subAβ animals was significantly enhanced compared with that in animals exposed to stress or subAβ infusion alone. Molecular analysis of various signaling molecules 1 h after induction of long-term depression revealed an increase in the levels of calcineurin and phosphorylated CaMKII in groups exposed to stress compared with other groups. The levels of the brain-derived neurotrophic factor (BDNF) were significantly decreased in stress/subAβ animals but not in stress or subAβ animals. In addition, the levels of beta-site amyloid precursor protein cleaving enzyme were markedly increased in stress/subAβ. These findings suggest that chronic stress may accelerate the impairment of synaptic plasticity and consequently cognition in individuals 'at-risk' for AD.

Post-learning REM sleep deprivation impairs long-term memory: reversal by acute nicotine treatment

Rapid eye movement sleep deprivation (REM-SD) is associated with spatial learning and memory impairment. During REM-SD, an increase in nicotine consumption among habitual smokers and initiation of tobacco use by non-smokers have been reported. We have shown recently that nicotine treatment prevented learning and memory impairments associated with REM-SD. We now report the interactive effects of post-learning REM-SD and/or nicotine. The animals were first trained on the radial arm water maze (RAWM) task, then they were REM-sleep deprived using the modified multiple platform paradigm for 24h. During REM-SD period, the rats were injected with saline or nicotine (1mg/kg s.c. every 12h: a total of 3 injections). The animals were tested for long-term memory in the RAWM at the end of the REM-SD period. The 24h post-learning REM-SD significantly impaired long-term memory. However, nicotine treatment reversed the post-learning REM-SD-induced impairment of long-term memory. On the other hand, post-learning treatment of normal rats with nicotine for 24h enhanced long-term memory. These results indicate that post-learning acute nicotine treatment prevented the deleterious effect of REM-SD on cognitive abilities.

Epidemiology of Alzheimer disease

The global prevalence of dementia is estimated to be as high as 24 million, and is predicted to double every 20 years through to 2040, leading to a costly burden of disease. Alzheimer disease (AD) is the leading cause of dementia and is characterized by a progressive decline in cognitive function, which typically begins with deterioration in memory. Before death, individuals with this disorder have usually become dependent on caregivers. The neuropathological hallmarks of the AD brain are diffuse and neuritic extracellular amyloid plaques-which are frequently surrounded by dystrophic neurites-and intracellular neurofibrillary tangles. These hallmark pathologies are often accompanied by the presence of reactive microgliosis and the loss of neurons, white matter and synapses. The etiological mechanisms underlying the neuropathological changes in AD remain unclear, but are probably affected by both environmental and genetic factors. Here, we provide an overview of the criteria used in the diagnosis of AD, highlighting how this disease is related to, but distinct from, normal aging. We also summarize current information relating to AD prevalence, incidence and risk factors, and review the biomarkers that may be used for risk assessment and in diagnosis.

Depression: a repair response to stress-induced neuronal microdamage that can grade into a chronic neuroinflammatory condition?

Depression is a major contributor to the global burden of disease and disability, yet it is poorly understood. Here we review data supporting a novel theoretical model for the biology of depression. In this model, a stressful life event leads to microdamage in the brain. This damage triggers an injury repair response consisting of a neuroinflammatory phase to clear cellular debris and a spontaneous tissue regeneration phase involving neurotrophins and neurogenesis. During healing, released inflammatory mediators trigger sickness behavior and psychological pain via mechanisms similar to those that produce physical pain during wound healing. The depression remits if the neuronal injury repair process resolves successfully. Importantly, however, the acute psychological pain and neuroinflammation often transition to chronicity and develop into pathological depressive states. This hypothesis for depression explains substantially more data than alternative models, including why emerging data show that analgesic, anti-inflammatory, pro-neurogenic and pro-neurotrophic treatments have antidepressant effects. Thus, an acute depressive episode can be conceptualized as a normally self-limiting but highly error-prone process of recuperation from stress-triggered neuronal microdamage.