Effects of chronic variable stress on cognition and Bace1 expression among wild-type mice.

Stressful life events, activation of the hypothalamic-pituitary-adrenal (HPA) axis and glucocorticoids are now thought to have a role in the development of several neurodegenerative and psychiatric disorders including Alzheimer's disease (AD) through mechanisms that may include exacerbation of cognitive impairment, neuronal loss, and beta-amyloid (Aß) and tau neuropathology. In the current study, we use a wild-type mouse model to demonstrate that chronic variable stress impairs cognitive function and that aged mice are particularly susceptible. We also find that stress exposure is associated with a 1.5- to 2-fold increase in the expression of Bace1 in the hippocampus of young adult mice and the hippocampus, prefrontal cortex and amygdala of aged mice. Further, the increased expression of Bace1 was associated with decreased methylation of several CpGs in the Bace1 promoter region. In a second series of experiments, exposure to environmental enrichment (EE) prevented the stress-related changes in cognition, gene expression and DNA methylation. Together, these findings re-affirm the adverse effects of stress on cognition and further suggest that aged individuals are especially susceptible. In addition, demonstrating that chronic stress results in decreased DNA methylation and increased expression of Bace1 in the brain may provide a novel link between stress, Aß pathology and AD. Finally, understanding the mechanisms by which EE prevented the effects of stress on cognition and Bace1 expression will be an important area of future study that may provide insights into novel approaches to the treatment of AD.

Search for common targets of lithium and valproic acid identifies novel epigenetic effects of lithium on the rat leptin receptor gene.

Epigenetics may have an important role in mood stabilizer action. Valproic acid (VPA) is a histone deacetylase inhibitor, and lithium (Li) may have downstream epigenetic actions. To identify genes commonly affected by both mood stabilizers and to assess potential epigenetic mechanisms that may be involved in their mechanism of action, we administered Li (N = 12), VPA (N = 12), and normal chow (N = 12) to Brown Norway rats for 30 days. Genomic DNA and mRNA were extracted from the hippocampus. We used the mRNA to perform gene expression analysis on Affymetrix microarray chips, and for genes commonly regulated by both Li and VPA, we validated expression levels using quantitative real-time PCR. To identify potential mechanisms underlying expression changes, genomic DNA was bisulfite treated for pyrosequencing of key CpG island 'shores' and promoter regions, and chromatin was prepared from both hippocampal tissue and a hippocampal-derived cell line to assess modifications of histones. For most genes, we found little evidence of DNA methylation changes in response to the medications. However, we detected histone H3 methylation and acetylation in the leptin receptor gene, Lepr, following treatment with both drugs. VPA-mediated effects on histones are well established, whereas the Li effects constitute a novel mechanism of transcriptional derepression for this drug. These data support several shared transcriptional targets of Li and VPA, and provide evidence suggesting leptin signaling as an epigenetic target of two mood stabilizers. Additional work could help clarify whether leptin signaling in the brain has a role in the therapeutic action of Li and VPA in bipolar disorder.

Long-term impact of early life events on physiology and behaviour.

This review discusses the effects of stress and nutrition throughout development and summarises studies investigating how exposure to stress or alterations in nutrition during the pre-conception, prenatal and early postnatal periods can affect the long-term health of an individual. In general, the data presented here suggest that that anything signalling potential adverse conditions later in life, such as high levels of stress or low levels of food availability, will lead to alterations in the offspring, possibly of an epigenetic nature, preparing the offspring for these conditions later in life. However, when similar environmental conditions are not met in adulthood, these alterations may have maladaptive consequences, resulting in obesity and heightened stress sensitivity. The data also suggest that the mechanism underlying these adult phenotypes might be dependent on the type and the timing of exposure.

A novel obesity model: synphilin-1-induced hyperphagia and obesity in mice.

AIMS: The pathogenesis of obesity remains incompletely understood and the exploration of the role of novel proteins in obesity may provide important insights into its causes and treatments. Here, we report a previously unidentified role for synphilin-1 in the control of food intake and body weight. Synphilin-1, a cytoplasmic protein, was initially identified as an interaction partner of alpha-synuclein, and has implications in Parkinson's disease pathogenesis related to protein aggregation. SUBJECTS AND METHODS: To study the in vivo role of synphilin-1, we characterized a human synphilin-1 transgenic mouse (SP1) by assessing synphilin-1 expression, plasma parameters, food intake and spontaneous activity to determine the major behavioral changes and their consequences in the development of the obesity phenotype. RESULTS: Expression of human synphilin-1 in brain neurons in SP1 mice resulted in increased food intake, body weight and body fat. SP1 mice also displayed hyperinsulinemia, hyperleptinemia and impaired glucose tolerance. Pair-feeding SP1 mice to amounts consumed by non-transgenic mice prevented the increased body weight, adiposity, hyperinsulinemia and hyperleptinemia demonstrating that these were all the consequences of increased food intake. Transgenic expression of synphilin-1 was enriched in hypothalamic nuclei involved in feeding control, and fasting-induced elevated endogenous synphilin-1 levels at these sites, suggesting that synphilin-1 is an important player in the hypothalamic energy balance regulatory system. CONCLUSION: These studies identify a novel function of synphilin-1 in controlling food intake and body weight, and may provide a unique obesity model for future studies of obesity pathogenesis and therapeutics.

Chronic stress, metabolism, and metabolic syndrome.

The prevalence of obesity has rapidly escalated and now represents a major public health concern. Although genetic associations with obesity and related metabolic disorders such as diabetes and cardiovascular disease have been identified, together they account for a small proportion of the incidence of disease. Environmental influences such as chronic stress, behavioral and metabolic disturbances, dietary deficiency, and infection have now emerged as contributors to the development of metabolic disease. Although epidemiological data suggest strong associations between chronic stress exposure and metabolic disease, the etiological mechanisms responsible remain unclear. Mechanistic studies of the influence of chronic social stress are now being conducted in both rodent and nonhuman primate models, and phenotypic results are consistent with those in humans. The advantage of these models is that potential neural mechanisms may be examined and interventions to treat or prevent disease may be developed and tested. Further, circadian disruption and metabolic conditions such as diabetes mellitus could increase susceptibility to other stressors or serve as a stressor itself. Here, we review data from leading investigators discussing the interrelationship between chronic stress and development of metabolic disorders.

Lentivirus-mediated downregulation of hypothalamic insulin receptor expression.

Regulation of feeding behavior and energy balance are among the central effects of insulin. For example, intracerebroventricular administration of insulin decreases food intake and body weight, whereas antisense oligodeoxynucleotide downregulation of insulin receptors (IRs) produces hyperphagia. To further examine the role of IRs in the central actions of insulin, we designed an IR antisense lentiviral vector (LV-IRAS) and injected this vector into the third ventricle to selectively decrease IR expression in the rat hypothalamus. Three weeks after LV-IRAS administration, the expression of IRs in the hypothalamus was significantly decreased, whereas no changes were observed in hippocampal IR levels. LV-IRAS administration decreased insulin-stimulated phosphorylation of hypothalamic IRs and translocation of the insulin-sensitive glucose transporter GLUT4 in the hypothalamus; no changes in IR signaling were observed in the hippocampus of LV-IRAS-treated rats. Lentivirus-mediated downregulation of IR expression and signaling produced significant increases in body weight, as well as increases in fat mass that were selective for the subcutaneous compartment. Conversely, lean muscle mass and water mass were not affected in LV-IRAS-treated rats compared to rats treated with control virus. Changes in peripheral adiposity were associated with increases in basal hypothalamic leptin signaling in the absence of changes in leptin receptor expression in LV-IRAS rats. Collectively, these data illustrate the important functional relationships between hypothalamic insulin and leptin signaling in the regulation of body composition and provide insight into the mechanisms through which decreases in IR expression and signaling dysregulates leptin activity, thereby promoting increases in peripheral adiposity.

Repeated exposure to social stress has long-term effects on indirect markers of dopaminergic activity in brain regions associated with motivated behavior.

The visible burrow system (VBS) is a chronic social stress paradigm in which a dominance hierarchy forms among male rats housed with females. Males in the VBS undergo behavioral and physiological changes thought to be manifestations of chronic social stress. Since it is unclear whether chronic social stress affects motivation and reward behavior, brain areas related to these regions were examined. Long-term effects of a single or repeated VBS exposure on mesolimbic subregions were investigated by exposing rats to the VBS either once (one cycle of VBS housing and recovery) or repeatedly (three cycles). Behavior in the VBS was observed and rats were classified as dominants or subordinates. Subordinates were further sub-classified on the basis of stress hormone (corticosterone) response to an acute stressor (i.e. restraint stress). Normal responders were categorized as stress-responsive subordinates (SRS) and animals with a blunted hypothalamic-pituitary-adrenal axis response were designated as non-responsive subordinates (NRS). Controls males were pair-housed with a single female during VBS periods and alone during recovery. Lowered enkephalin-mRNA levels were observed in the nucleus accumbens (Acb) after single VBS exposure in SRS and repeated VBS exposure both subordinate groups (i.e. SRS + NRS) compared with controls. Decreased dopamine transporter density was detected after single VBS exposure in the dorsolateral caudate putamen (DLCPu) of NRS and after repeated VBS exposure in the Acb of NRS compared with controls. Dopamine D2 receptor density was elevated after single VBS exposure in the Acb of both subordinate groups (SRS + NRS) and after repeated VBS exposure in the DLCPu, dorsomedial CPu, and Acb of NRS compared with controls. No changes in dopamine D1 receptor binding were observed in any group. These results suggest that long-term changes in dopamine activity in mesolimbic structures persist after repeated exposures to chronic social stress and may provide insight into the neurochemical basis of depressive illness and subsequent comorbidity with drug abuse vulnerability.

Postnatal growth and behavioral development of mice cloned from adult cumulus cells.

Since the first successful cloning of mammals from adult somatic cells, there has been no examination of the learning or behavior of cloned offspring. The possibility of adverse effects on animals produced through adult somatic cell cloning is high because many natural biological processes are bypassed and DNA from adult cells, which presumably contain mutations, are used. In this study, we compared cloned mice produced by microinjection transfer of cumulus cell nuclei into enucleated oocytes, to control mice that were specifically generated to eliminate confounding factors that are unique to our cloning procedure. Postnatal weight gain of clones was significantly greater than that of controls. Preweaning development observations revealed that first appearance or performance of 3 out of 10 measures was delayed in cloned mice; however, results of subsequent tests of learning and memory, activity level, and motor skills were comparable for both groups. Together, these data suggest that nuclear transfer of adult somatic cell nuclei to produce cloned mice may delay the appearance of a few developmental milestones but it does not adversely affect the overall postnatal behavior of mice. In addition, this procedure may cause late onset of significantly increased body weight in cloned offspring, the cause or causes of which are being further examined.

Bypassing spermiogenesis for several generations does not have detrimental consequences on the fertility and neurobehavior of offspring: a study using the mouse.

PURPOSE: This study was conducted to determine whether the omission of spermiogenesis and all prefertilization events for five generations in mice affects the fertility or behavior of offspring. METHODS: Fifth-generation hybrid (C57BL/6 x DBA/2) mice were produced using round spermatid injection (ROSI). Control groups consisted of mice born after natural mating with and without sham operation. The growth, fertility, and behavior of offspring were compared. Behavior tests conducted assessed elementary reasoning (Krushinsky test), emotionality (Mouse Defense Test Battery), and spatial learning and memory (Morris water maze). RESULTS: There were no significant differences in the growth and fertility of fifth-generation ROSI mice compared to natural fertilization mice. We also found no evidence of significant learning or behavioral deficits of the fifth-generation ROSI mice. CONCLUSIONS: In this study, we found no evidence that bypassing the natural biological processes involved in spermiogenesis produces adverse effects on the growth, fertility, or behavior of mouse offspring.