Nyctohemeral differences in response to restraint stress in CD-1 and C57BL/6 mice

Wheel Running During Pregnancy Alleviates Anxiety-and Depression-Like Behaviors During the Postpartum Period in Mice: The Roles of NLRP3 Neuroinflammasome Activation, Prolactin, and the Prolactin Receptor in the Hippocampus

Despite the increase in the prevalence of postpartum depression among maternal disorder, its treatment outcomes remain suboptimal. Studies have shown that exercise can reduce postpartum depressive episodes in the mother, but the effects of exercise during pregnancy on maternal behavior and the potential mechanisms involved remain poorly understood. From the second day of pregnancy to the day of birth, dams exercised for 1 h a day by running on a controlled wheel. The maternal behaviors of the dams were assessed on postpartum day 2 to postpartum day 8. Chronic restraint stress was applied from postpartum day 2 to day 12. Blood was collected on postpartum days 3 and 8, then subjected to ELISA to determine the serum concentration of prolactin. The weight of each dam and the food intake were recorded. Anxiety- and depression-like behavioral tests were conducted, and hippocampal neuroinflammation and prolactin receptor levels were measured. The dams exhibited elevated levels of anxiety and depression, decreased serum prolactin levels, decreased prolactin receptor expression, and activation of NLRP3-mediated neuroinflammation in the hippocampus following the induction of postpartum chronic restraint stress, which were reversed with controlled wheel running during pregnancy. Overall, the findings of this study revealed that the preventive effects of exercise during pregnancy on postpartum anxiety-and depression-like behaviors were accompanied by increased serum prolactin levels, hippocampal prolactin receptor expression and hippocampal NLRP3-mediated neuroinflammation.

Light and Cognition: Roles for Circadian Rhythms, Sleep, and Arousal

Light exerts a wide range of effects on mammalian physiology and behavior. As well as synchronizing circadian rhythms to the external environment, light has been shown to modulate autonomic and neuroendocrine responses as well as regulating sleep and influencing cognitive processes such as attention, arousal, and performance. The last two decades have seen major advances in our understanding of the retinal photoreceptors that mediate these non-image forming responses to light, as well as the neural pathways and molecular mechanisms by which circadian rhythms are generated and entrained to the external light/dark (LD) cycle. By contrast, our understanding of the mechanisms by which lighting influences cognitive processes is more equivocal. The effects of light on different cognitive processes are complex. As well as the direct effects of light on alertness, indirect effects may also occur due to disrupted circadian entrainment. Despite the widespread use of disrupted LD cycles to study the role circadian rhythms on cognition, the different experimental protocols used have subtly different effects on circadian function which are not always comparable. Moreover, these protocols will also disrupt sleep and alter physiological arousal, both of which are known to modulate cognition. Studies have used different assays that are dependent on different cognitive and sensory processes, which may also contribute to their variable findings. Here, we propose that studies addressing the effects of different lighting conditions on cognitive processes must also account for their effects on circadian rhythms, sleep, and arousal if we are to fully understand the physiological basis of these responses.

Effects of chronic stress on the onset and progression of Huntington's disease in transgenic mice

Huntington's disease (HD) is a neurodegenerative disease caused by a tandem repeat mutation encoding an expanded polyglutamine tract. Our previous work showed that memory deficits in HD transgenic mice could be accelerated by increased levels of stress hormone, while memory in WT mice remained unaffected. HD patients experience higher levels of stress compared to the general population and symptoms of HD also include motor, cognitive, psychiatric, sexual and olfactory abnormalities, and an associated decline in activities of daily living. Therefore we investigated the impact of a robust stressor (i.e. restraint) on the onset and progression of a range of behavioral phenotypes in R6/1 transgenic HD mice. Restraint was administered for 1h daily from 6weeks of age and continued until R6/1 mice were clearly motor symptomatic at 14weeks of age. Serum corticosterone levels in both R6/1 and WT littermates were elevated immediately after the last restraint session and weight gain was suppressed in restrained animals throughout the treatment period. Motor coordination and locomotor activity were enhanced by chronic restraint in males, regardless of genotype. However, there was no effect of restraint on motor performances in female animals. At 8weeks of age, olfactory sensitivity was impaired by restraint in R6/1 HD female mice, but not in WT mice. In male R6/1 mice, the olfactory deficit was exacerbated by restraint and olfaction was also impaired in male WT mice. The development of deficits in saccharin preference, Y-maze memory, nest-building and sexually-motivated vocalizations was unaffected by chronic restraint in R6/1 and had little impact on such behavioral performances in WT animals. We provide evidence that chronic stress can negatively modulate specific endophenotypes in HD mice, while the same functions were affected to a lesser extent in WT mice. This vulnerability in HD animals seems to be sex-specific depending on the stress paradigm used. It is hoped that our work will stimulate clinical investigations into the effects of stress on both pre-symptomatic and symptomatic gene-positive members of HD families, and inform the development of new therapeutic approaches.

Contrasting mechanisms by which social isolation and restraint impair healing in male mice

Stress modulates vital aspects of immune functioning in both human and non-human animals, including tissue repair. For example, dermal wounds heal more slowly and are associated with prolonged inflammation and increased bacterial load in mice that experience chronic physical restraint. Social stressors also negatively affect healing; however, previous studies suggest that the affected healing mechanisms may be stress model-specific. Here, the effects of either social isolation or physical restraint on dermal wound healing (3.5 mm wounds on the dorsum) were compared in hairless male mice. Social isolation beginning 3 weeks prior to wounding delayed healing comparably to physical restraint (12 h/day for eight days), in spite of marked differences in metabolic and hormonal consequences (i.e. body mass) between the two stress models. Additionally, isolated mice exhibited reductions in wound bacterial load and inflammatory gene expression (interleukin-1beta [IL-1β], monocyte chemoattractant protein [MCP]), whereas restraint significantly increased both of these parameters relative to controls. Experimentally augmenting bacterial concentrations in wounds of isolated mice did not ameliorate healing, whereas this treatment accelerated healing in controls. This work indicates that social isolation and restraint stressors comparably impair healing, but do so through disparate mechanisms and at different phases of healing.

Immediate Effects of Maternal Deprivation on the (Re)Activity of the HPA-Axis Differ in CD1 and C57Bl/6J Mouse Pups

The postnatal development of the mouse is characterized by a period of hypo-responsiveness of the hypothalamic-pituitary-adrenal (HPA) axis to mild stressors. Maternal deprivation (MD) during this period can disrupt the quiescence of the HPA-axis. The present study examined the influence of strain (outbred CD1 vs. inbred C57BL/6J mice) on some central and peripheral components of the HPA-axis in neonatal mice (5-day-old) in the presence of their mother or after 24 h MD (on postnatal day 4) under basal or mild stressful conditions. In the presence of the dam, adrenal corticosterone (CORT) secretion was low in both mouse strains. Compared to CD1 mice, C57BL/6J had lower CORT levels associated with higher ACTH levels and ACTH/CORT ratio (i.e., lower adrenal sensitivity to ACTH), and higher glucocorticoid receptor (GR) mRNA expression in the paraventricular nucleus. Although MD disinhibited the HPA-axis in both strains as reflected by increased basal CORT and ACTH, we found a strain-dependent pattern. MD increased CORT more in C57BL/6J compared to CD1 mice together with a lower ACTH/CORT ratio (i.e., higher adrenal sensitivity to ACTH), while GR mRNA was no longer different in the two strains. However, this increased adrenal sensitivity in maternally deprived C57BL/6J mice was not reflected in their CORT response to a subsequent novelty stressor, possibly due to an MD-induced ceiling effect in their steroidogenic capacity. In conclusion, the immediate outcome of MD depends on the genetic background of the mother-infant dyad, suggesting that maybe also the outcome in later-life cannot be generalized.

Individual variation in glucocorticoid stress responses in animals

When stimuli from the environment are perceived to be a threat or potential threat then animals initiate stress responses, with activation of the hypothalamo-pituitary-adrenal axis and secretion of glucocorticoid hormones (cortisol and corticosterone). Whilst standard deviation or standard error values are always reported, it is only when graphs of individual responses are shown that the extensive variation between animals is apparent. Some animals have little or no response to a stressor that evokes a relatively large response in others. Glucocorticoid responses of fish, amphibian, reptiles, birds, and mammals are considered in this review. Comparisons of responses between animals and groups of animals focused on responses to restraint or confinement as relatively standard stressors. Individual graphs could not be found in the literature for glucocorticoid responses to capture or restraint in fish or reptiles, with just one graph in mammals with the first sample was collected when animals were initially restrained. Coefficients of variation (CVs) calculated for parameters of glucocorticoid stress responses showed that the relative magnitudes of variation were similar in different vertebrate groups. The overall mean CV for glucocorticoid concentrations in initial (0 min) samples was 74.5%, and CVs for samples collected over various times up to 4 h were consistently between 50% and 60%. The factors that lead to the observed individual variation and the extent to which this variation is adaptive or non-adaptive are little known in most animals, and future studies of glucocorticoid responses in animals can focus on individual responses and their origins and significance.

GSK-3β: a signaling pathway node modulating neural stem cell and endothelial cell interactions

The neurogenic areas of the brain are highly organized structures in which there is dynamic reciprocal modulation of neural stem cells (NSC) and microvascular endothelial cells (BEC) resulting in control of neural stem cell and vascular proliferation, survival and differentiation throughout the life of the individual. Select molecules such as GSK-3β, functioning as signaling nodes, and their downstream signaling components including HIF-1α, HIF-2α and β-catenin participate in regulating and orchestrating the diverse responses involved in this complex process. In this report we demonstrate GSK-3β's role as a signaling node in two mouse strains (C57BL/6, which have been found to respond to and recover from a hypoxic insult from P3 to P11 poorly and CD-1, which have been found to respond to and recover from a hypoxic insult from P3 to P11 well both in vivo and in vitro) which mimic the wide range of responsiveness to hypoxic insult observed in the very low birth weight premature infant population. Differences in levels of neural stem cell and microvascular endothelial cell GSK-3β activation, β-catenin serine phosphorylation, HIF-1α and 2α, BDNF, SDF-1 and VEGF, β-III-tubulin and cleaved notch-1 expression in C57BL/6 and CD-1 subventricular zone tissues, and cultured NSC and BEC were noted. Specifically, CD1 pups, SVZ tissues and isolated NSC and BEC exhibit less GSK-3β and β-catenin serine phoslphorylation and greater HIF-1α and 2α, BDNF, SDF-1 and VEGF, β-III-tubulin and cleaved notch-1 expression compared to C57BL/6. Correlating with these changes were differences of several neural stem cell and microvascular endothelial cell behaviors including proliferation, apoptosis, migration and differentiation with CD1 NSC exhibiting greater proliferation and migration and decreased apoptosis and differentiation and CD1 BEC exhibiting greater angiogenesis. Further, upon treatment with nanomolar concentrations of a GSK-3β inhibitor (SB412682), C57 NSC and BEC behaviors could be brought to CD1 levels, consistent with the concept of GSK-3β functioning as a multifunctional signaling pathway node, modulating several behaviors in these cells. Lastly, the therapeutic potential of targeting GSK-3β is discussed.

Antidepressive behaviors induced byenriched environment might be modulated by glucocorticoid levels

Exposure to enriched environment (EE) can influence expression of depression symptoms, however, the underlying mechanism has not been established, although neurogenesis was probably involved. It has been reported that EE stimulates glucocorticoids release. However, the role of corticosterone (CORT) in effects of EE is still unknown. To address these issues, we examined depression-like behaviors of the animals exposed to EE with low dose CORT supplement following bilateral adrenalectomy (ADX+CORT). Two months after housing, tail suspension test and forced swim test were used to assess depression-related behavior of mice. Serum CORT levels were measured by radio-immunoassay. Signals of DNA synthesis marker bromodeoxyuridine and immature neuronal marker doublecortin were measured by immunohistochemistry. Results showed that EE significantly decreased immobility time of the mice in both the tail suspension test and forced swim test, showing distinctive antidepressive behaviors. Exposure to EE also increased serum CORT level, and prevention of this increase with ADX+CORT eliminated the decrease of immobility time of the animals. Both the mice exposed to EE and those receiving ADX+CORT treatment showed enhanced newly born cells and immature granule neurons in the hippocampus. Taken together, our data suggest that glucocorticoids elevation is required for antidepressive behaviors of EE.

Enduring influences of peripubertal/adolescent stressors on behavioral response to estradiol and progesterone in adult female mice

Exposure to stressors during particular stages of development leads to acute and long-term physiological and behavioral changes. We have reported that shipping mice during the peripubertal/adolescent period results in decreased induction of feminine sexual behavior by estradiol and progesterone in adult female mice. To study further the factors involved in this decreased behavioral response, female mice were exposed to a variety of experimental stressors when 6 wk old. Effects of peripubertal/adolescent exposure to these stressors on acute plasma corticosterone levels and changes in body weight and adult behavioral response to estradiol and progesterone were assessed. Although restraint for three daily 3-h periods, 36-h food deprivation, or a multiple stressor regimen acutely increased plasma corticosterone levels and reduced body weight, only exposure to particular doses of the bacterial endotoxin lipopolysaccharide (LPS; 1-1.5 mg/kg body weight, doses that induced moderate levels of sickness behavior in these studies) resulted in reduced behavioral response to estradiol and progesterone in adulthood. Like the effects of shipping, the effects of LPS on adult feminine sexual behavior appear most robust when injected at 6 wk old and are limited to exposure during a vulnerable period at approximately 4-6 wk of age. Therefore, an immune stressor during the peripubertal/adolescent period, but not restraint, food restriction, or a combined stressor, has an enduring influence on behavioral response to estradiol and progesterone. This demonstrates that the decreased response to estradiol and progesterone is not a general response to all stressors during this developmental stage.

Stress and hypothermia in mice in a nose-only cigarette smoke exposure system

In nose-only exposure systems, animals need to be restrained inside a tube, which leads to stress. Stress is known to cause hyperthermia in rodents. Chronically repeated episodes of hyperthermia could be detrimental to animal health and influence results of nose-only exposure studies. Therefore we investigated whether hyperthermia occurred in male C57BL/6J mice that were restrained for increasing lengths of time, using nosepieces held at room temperature, preheated at 37 degrees C, or thermostat controlled at different temperatures, with and without exposure to different concentrations of cigarette smoke. Body temperature, body weight, plasma corticosterone levels, and adrenal weights were recorded. Restraint using nosepieces at room temperature caused a time-dependent decrease in body temperature, which could be reversed by preheating the nosepieces to 37 degrees C. Cigarette smoke dose-dependently caused an additional decrease, which was counteracted by controlling nosepiece temperature at 38 degrees C. During 3 mo of exposure using heated nosepieces, Delta body temperature remained constant. Body weight gain did not differ between smoke-exposed and room air-breathing animals exposed using either heated or room-temperature nosepieces, but both groups gained significantly less weight, while adrenal weights were significantly and similarly increased, when compared to unrestrained littermates. Plasma corticosterone levels did not differ between the three groups. In conclusion, during restraint in nose-only exposure tubes with room temperature metal nosepieces, mice suffer a pronounced hypothermia. Preventing this by heating the nosepieces does not reduce the stress experienced by the animals.

Prior activation of kappa opioid receptors by U50,488 mimics repeated forced swim stress to potentiate cocaine place preference conditioning

Repeated forced-swim stress (FSS) produced analgesia, immobility and potentiation of cocaine-conditioned place preference (CPP) in wild-type C57Bl/6 mice, but not in littermates lacking the kappa opioid receptor (KOR) gene. These results were surprising because kappa agonists are known to produce conditioned place aversion and to suppress cocaine-CPP when coadministered with cocaine. The possibility that disruption of the kappa system blocked the stress response by adversely affecting the hypothalamic-pituitary axis was examined by measuring plasma corticosterone levels. However, disruption of the dynorphin/kappa system by gene deletion or receptor antagonism did not reduce the FSS-induced elevation of plasma corticosterone levels. A second explanation for the difference is that kappa receptor activation caused by FSS occurred prior to cocaine conditioning rather than contemporaneously. To test this hypothesis, we measured the effects of the kappa agonist (trans)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]benzeneacetamide (U50,488) administered to mice at various intervals preceding cocaine conditioning. The results showed that the interaction between the kappa system and cocaine reinforcement depended on the timing of the drug pairing. Mice given U50,488 60 min prior to cocaine showed a robust, nor-BNI-sensitive potentiation of cocaine-CPP, whereas administration 15 min before cocaine significantly suppressed cocaine-CPP. In the absence of cocaine, U50,488 given 60 min prior to saline conditioning produced no place preference, whereas administration 15 min before saline conditioning produced significant place aversion. The results of this study suggest that kappa receptor activation induced by FSS prior to the cocaine-conditioning session may be both necessary and sufficient for potentiation of the reinforcing actions of cocaine.

Exposure to alcohol on E9 raises poststress corticosterone in mature but not old mice

Prenatal exposure to alcohol alters postnatal function of the hypothalamic-pituitary-adrenal axis. Hyperresponsiveness to stress, or increased secretion of corticosterone, is a commonly studied effect in offspring of rats exposed to alcohol during a substantial period of gestation. No studies have reported on stress hormone secretion following alcohol exposure on a single day during embryonic development even though exposure at this time may damage the hypothalamus and pituitary. To explore the effect of an acute exposure, we used the offspring of C57BL/6J mice exposed to alcohol or saline on embryonic day (E) 9 (2.9 g/kg administered twice, 4h apart). At 7.5 or 22 months of age these mice were subjected to a 12-h restraint stress, or merely kept in the same environment without restraint. After the 12-h period, a blood sample was obtained from the retro-orbital plexus, and analyzed for the amount of corticosterone. The 7.5-month old group of alcohol-treated offspring were indeed hyperresponsive to restraint stress, but the 22-month old mice were not. Whether the normal-appearing corticosterone response of the old alcohol-exposed mice indicated adaptation to restraint, an aging-associated ceiling effect in corticosterone secretion, or an expression of pathology, cannot be decided on the basis of present data.