REM sleep's unique associations with corticosterone regulation, apoptotic pathways, and behavior in chronic stress in mice

Lycopene ameliorates chronic stress-induced hippocampal injury and subsequent learning and memory dysfunction through inhibiting ROS/JNK signaling pathway in rats

The natural carotenoid lycopene (LYC) has strong antioxidant and neuroprotective capacities. This study investigated the effects and mechanisms of LYC on chronic stress-induced hippocampal lesions and learning and memory dysfunction. Rats were administered LYC and/or chronic restraint stress (CRS) for 21 days. Morris water maze results demonstrated that LYC prevented CRS-induced learning and memory dysfunction. Histopathological staining and transmission electron microscopy observation revealed that LYC ameliorated CRS-induced hippocampal microstructural and ultrastructural damage. Furthermore, LYC alleviated CRS-induced oxidative stress by reducing reactive oxygen species (ROS) production and enhancing antioxidant enzyme activities. LYC also improved CRS-induced hippocampal mitochondrial dysfunction by recovering mitochondrial membrane potential, and complex I (NADH dehydrogenase) and II (succinate dehydrogenase) activities. Moreover, LYC reduced CRS-induced apoptosis via the mitochondrial apoptotic pathway, and decreased the number of terminal deoxynucleotidyl transferase dUTP nick-end-labeled positive cells. Additionally, western blot analysis demonstrated that LYC inhibited CRS-induced activation of the c-Jun N-terminal kinase (JNK) signaling pathway. Correlation analysis indicated that ROS levels, JNK activation, and the mitochondrial apoptotic pathway were positively correlated. Further investigation of the underlying mechanisms revealed that the ROS scavenger N-acetyl-l-cysteine inhibited CRS-induced JNK activation. Furthermore, the JNK inhibitor SP600125 relieved CRS-induced hippocampal mitochondrial dysfunction, apoptosis via the mitochondrial apoptotic pathway, and learning and memory dysfunction. Together, these results suggest that LYC alleviates hippocampal oxidative stress, mitochondrial dysfunction, and apoptosis by inhibiting the ROS/JNK signaling pathway, thereby improving CRS-induced hippocampal injury and learning and memory dysfunction. This study provides a theoretical basis and new therapeutic strategies for the application of LYC to relieve chronic stress encephalopathy.

Loss of Arc attenuates the behavioral and molecular responses for sleep homeostasis in mice

The activity-regulated cytoskeleton-associated protein (Arc) gene is a neural immediate early gene that is involved in synaptic downscaling and is robustly induced by prolonged wakefulness in rodent brains. Converging evidence has led to the hypothesis that wakefulness potentiates, and sleep reduces, synaptic strengthening. This suggests a potential role for Arc in these and other sleep-related processes. However, the role of Arc in sleep remains unknown. Here, we demonstrated that Arc is important for the induction of multiple behavioral and molecular responses associated with sleep homeostasis. Arc knockout (KO) mice displayed increased time spent in rapid eye movement (REM) sleep under baseline conditions and marked attenuation of sleep rebound to both 4 h of total sleep deprivation (SD) and selective REM deprivation. At the molecular level, the following homeostatic sleep responses to 4-h SD were all blunted in Arc KO mice: increase of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor GluA1 and its phosphorylation in synaptoneurosomes; induction of a subset of SD-response genes; and suppression of the GluA1 messenger RNA in the cortex. In wild-type brains, SD increased Arc protein expression in multiple subcellular locations, including the nucleus, cytoplasm, and synapse, which is reversed in part by recovery sleep. Arc is critical for these behavioral and multiple molecular responses to SD, thus providing a multifunctional role for Arc in the maintenance of sleep homeostasis, which may be attributed by the sleep/wake-associated changes in subcellular location of Arc.

How Early Life Adversity Influences Defensive Circuitry

Childhood maltreatment increases the likelihood of developing anxiety disorders in humans. Early life adversity (ELA) paradigms in rodents produce lasting increases in avoidant and inhibitory responses to both immediate and nonspecific threats, collectively referred to as defensive behaviors. This approach provides an opportunity to thoroughly investigate the underlying mechanisms, an effort that is currently under way. In this review, we consider the growing literature indicating that ELA alters the rhythmic firing of neurons in brain regions associated with defensive behavior, as well as potential neuronal, glial, and extracellular matrix contributions to functional changes in this circuitry. We also consider how ELA studies in rodents may inform us about both susceptible and resilient outcomes in humans.

Emerging roles of the unfolded protein response (UPR) in the nervous system: A link with adaptive behavior to environmental stress?

Stressors elicit a neuroendocrine response leading to increased levels of glucocorticoids, allowing the organism to adapt to environmental changes and maintain homeostasis. Glucocorticoids have a broad effect in the body, modifying the activity of the immune system, metabolism, and behavior through the activation of receptors in the limbic system. Chronic exposition to stressors operates as a risk factor for psychiatric diseases such as depression and posttraumatic stress disorder. Among the cellular alterations observed as a consequence of environmental stress, alterations to organelle function at the level of mitochondria and endoplasmic reticulum (ER) are emerging as possible factors contributing to neuronal dysfunction. ER proteostasis alterations elicit the unfolded protein response (UPR), a conserved signaling network that re-establish protein homeostasis. In addition, in the context of brain function, the UPR has been associated to neurodevelopment, synaptic plasticity and neuronal connectivity. Recent studies suggest a role of the UPR in the adaptive behavior to stress, suggesting a mechanistic link between environmental and cellular stress. Here, we revise recent evidence supporting an evolutionary connection between the neuroendocrine system and the UPR to modulate behavioral adaptive responses.

Effects of 3 Weeks of Water Immersion and Restraint Stress on Sleep in Mice

Repeated stress is a risk factor for mental disorders and can also lead to sleep disturbances. Although the effects of stress on sleep architecture have been investigated in rodents, the length of the stress exposure period in most studies has been limited to about 10 days, and few studies have analyzed the effects of chronic stress over a longer period. Here we investigated how sleep is affected in a mouse model of depression induced by 3 weeks of daily water immersion and restraint stress (WIRS). Sleep was recorded after 1, 2, and 3 weeks of stress exposure. Some stress-induced changes in several sleep measures were maintained across the 3 weeks, whereas other changes were most prominent during the 1st week. The total amount of non-rapid eye movement sleep (NREMS) was increased and the total amount of time spent awake was decreased across all 3 weeks. On the other hand, the amount of REMS during the dark phase was significantly increased in the 1st week compared with that at baseline or the 2nd and 3rd weeks. Electroencephalogram (EEG) power in the delta range was decreased during NREMS, although the total amount of NREMS was increased. These findings indicate that repeated WIRS, which eventually leads to a depression-like phenotype, differentially affects sleep between the early and subsequent periods. The increase in the amount of REMS during the dark phase in the 1st week significantly correlated with changes in body weight. Our results show how sleep changes throughout a long period of chronic stress in a mouse model of depression.

Acute Social Defeat Stress Increases Sleep in Mice

Social conflict is a major source of stress in humans. Animals also experience social conflicts and cope with them by stress responses that facilitate arousal and activate sympathetic and neuroendocrine systems. The effect of acute social defeat (SoD) stress on the sleep/wake behavior of mice has been reported in several models based on a resident-intruder paradigm. However, the post-SoD stress sleep/wake effects vary between the studies and the contribution of specific effects in response to SoD or non-specific effects of the SoD procedure (e.g., sleep deprivation) is not well established. In this study, we established a mouse model of acute SoD stress based on strong aggressive mouse behavior toward unfamiliar intruders. In our model, we prevented severe attacks of resident mice on submissive intruder mice to minimize behavioral variations during SoD. In response to SoD, slow-wave sleep (SWS) strongly increased during 9 h. Although some sleep changes after SoD stress can be attributed to non-specific effects of the SoD procedure, most of the SWS increase is likely a specific response to SoD. Slow-wave activity was only enhanced for a short period after SoD and dissipated long before the SWS returned to baseline. Moreover, SoD evoked a strong corticosterone response that may indicate a high stress level in the intruder mice after SoD. Our SoD model may be useful for studying the mechanisms and functions of sleep in response to social stress.