The Nucleus Accumbens CRH–CRHR1 System Mediates Early-Life Stress-Induced Sleep Disturbance and Dendritic Atrophy in the Adult Mouse

Adverse experiences in early life have long-lasting negative impacts on behavior and the brain in adulthood,one of which is sleep disturbance.As the corticotropin-releasing hormone(CRH)–corticotropin-releasing hormone receptor 1(CRHR1)system and nucleus accumbens(NAc)play important roles in both stress responses and sleep-wake regulation,in this study we investigated whether the NAc CRH–CRHR1 system mediates early-life stress-induced abnormalities in sleep-wake behavior in adult mice.Using the limited nesting and bedding material paradigm from postnatal days 2 to 9,we found that early-life stress disrupted sleep-wake behaviors during adulthood,including increased wakefulness and decreased non-rapid eye movement(NREM)sleep time during the dark period and increased rapid eye movement(REM)sleep time during the light period.The stress-induced sleep disturbances were accompanied by dendritic atrophy in the NAc and both were largely reversed by daily systemic administration of the CRHR1 antagonist antalarmin during stress exposure.Importantly,Crh overexpression in the NAc reproduced the effects of early-life stress on sleep-wake behavior and NAc morphology,whereas NAc Crhr1 knockdown reversed these effects(including increased wakefulness and reduced NREM sleep in the dark period and NAc dendritic atrophy).Together,our findings demonstrate the negative influence of early-life stress on sleep architecture and the structural plasticity of the NAc,and highlight the critical role of the NAc CRH–CRHR1 system in modulating these negative outcomes evoked by early-life stress.

Masing Behavior and Microstructural Change of Quenched and Tempered High-Strength Steel Under Low Cycle Fatigue

Low cycle fatigue behavior of a quenched and tempered high-strength steel(Q960 E) was studied in the strain amplitude ranging from ± 0.5% to ± 1.2% at room temperature. As a result of fatigue loading, the dislocation structural evolution and fracture mechanism were examined and studied by transmission electron microscopy and scanning electron microscopy(SEM). The results showed that this Q960 E steel showed cyclic softening at different strain amplitudes, and the softening tendency was more apparent at strain amplitude of ±(0.6–1.2)% than that at ± 0.5%. The reduction in dislocation density with increasing strain amplitude is responsible for the softening tendency of cyclic stress with the strain amplitude. The material illustrates near-Masing behavior at strain amplitude ranging from ± 0.6% to ± 1.2%. The near-Masing behavior of Q960 E high-strength steel can be the result of stability of martensite lath at different strain amplitudes. Partial transformation from martensite laths to dislocation cells is responsible for the derivation from ideal Masing behavior. In the SEM examination of fracture surfaces, transgranular cracks initiate on the sample surface. Striations can be found during the crack propagation stage.

Prefrontal Nectin3 Reduction Mediates Adolescent Stress-Induced Deficits of Social Memory,Spatial Working Memory,and Dendritic Structure in Mice

Chronic stress may disrupt the normal neurodevelopmental trajectory of the adolescent brain(especially the prefrontal cortex) and contribute to the pathophysiology of stress-related mental illnesses,but the underlying molecular mechanisms remain unclear.Here,we investigated how synaptic cell adhesion molecules(e.g.,nectin3)are involved in the effects of adolescent chronic stress on mouse medial prefrontal cortex(mPFC).Male C57BL/6N mice were subjected to chronic social instability stress from postnatal days 29 to 77.One week later,the mice exposed to chronic stress exhibited impaired social recognition and spatial working memory,simplified dendritic structure,and reduced spine density in the mPFC.Membrane localization of nectin3 was also altered,and was significantly correlated with behavioral performance.Furthermore,knocking down mPFC nectin3 expression by adeno-associated virus in adolescent mice reproduced the stress-induced changes in behavior and mPFC morphology.These results support the hypothesis that nectin3 is a potential mediator of the effects of adolescent chronic stress on prefrontal structural and functional abnormalities.

Adolescent stress increases depression-like behaviors and alters the excitatory-inhibitory balance in aged mice

Background:Depression affects approximately 5% of elderly people and its etiology might be related to chronic stress exposure during neurodevelopmental periods.In this study,we examined the effects of adolescent chronic social stress in aged mice on depressive behaviors and the excitatory-inhibitory (E/I) balance in stress-sensitive regions of the brain.Methods:Sixty-four adolescent,male C57BL/6 mice were randomly assigned to either the 7-week (from post-natal days 29 to 77) social instability stress (stress group,n =32) or normal housing conditions (control group,n =32).At 15 months of age,16 mice were randomly selected from each group for a series of behavioral tests,including two depression-related tasks (the sucrose preference test and the tail suspension test).Three days following the last behavioral test,eight mice were randomly selected from each group for immunohistochemical analyses to measure the cell density of parvalbumin (PV+)-and calretinin (CR+)-positive gamma-aminobutyric-acid (GABA)ergic inhibitory inter-neurons,and the expression levels of vesicular transporters of glutamate-1 (VGIuT1) and vesicular GABA transporter (VGAT) in three stress-sensitive regions of the brain (the medial pre-frontal cortex [mPFC],hippocampus,and amygdala).Results:Behaviorally,compared with the control group,adolescent chronic stress increased depression-like behaviors as shown in decreased sucrose preference (54.96 ± 1.97% vs.43.11 ± 2.85%,t(22)=3.417,P =0.003) and reduced latency to immobility in the tail suspension test (92.77 ± 25.08 s vs.33.14 ± 5.95 s,t(25)=2.394,P =0.025),but did not affect anxiety-like behaviors and pre-pulse inhibition.At the neurobiologic level,adolescent stress down-regulated PV+,not CR+,inter-neuron density in the mPFC (F(1,39)=19.30,P < 0.001),and hippocampus (F(1,42)=5.823,P =0.020) and altered the CR+,not PV+,inter-neuron density in the amygdala (F(1,28)=23.16,P < 0.001).The VGluT1/VGAT ratio was decreased in all three regions (all F > 10.09,all P < 0.004),which suggests stress-induced hypoexcitability in these regions.Conclusions:Chronic stress during adolescence increased depression-like behaviors in aged mice,which may be associated with the F/I imbalance in stress-sensitive brain regions.

Early-life stress alters sleep structure and the excitatory-inhibitory balance in the nucleus accumbens in aged mice

Background:Exposure to adverse experiences in early life may profoundly reshape the neurodevelopmental trajectories of the brain and lead to long-lasting behavioral and neural alterations.One deleterious effect of early-life stress that manifests in later life is sleep disturbance,but this has not been examined in aged mice and the underlying neural mechanisms remain unknown.Considering the important role of the nucleus accumbens (NAc) in the sleep-wake regulation,this study aimed to assess the effects of early-life stress on the sleep behaviors in aged mice and the potential involvement of the NAc in stress-induced sleep abnormalities.Methods:Twenty aged male C57BL/6 mice (>16 months,n =10 per group) were used in this study.During post-natal days 2 to 9,dams were provided with either sufficient (control) or a limited nesting and bedding materials (stressed).When the mice were 16 to 17 months old,their sleep-wake behaviors were recorded over 24 h using electroencephalogram and electromyelogram.The amount of each sleep-wake stage,mean duration,and stage transition was analyzed.Then,five animals were randomly chosen from each group and were used to measure the expression levels of vesicular glutamate transporter-1 (VGluT1) and vesicular transporters of γ-aminobutyric acid (VGAT) in the NAc using immunohistochemistry.Group comparisons were carried out using Student t test or analysis of variances when appropriate.Results:Compared with the control mice,the early-life stressed aged mice spent less time awake over 24 h (697.97 ± 77.47 min vs.631.33 ± 34.73 min,t17 =2.376,P =0.030),accordingly,non-rapid eye movement sleep time was increased (667.37 ± 62.07 min vs.723.54 ± 39.21 min,t17 =2.326,P =0.033) and mean duration of rapid eye movement sleep was prolonged (73.00 ± 8.98 min vs.89.39 ± 12.69 min,t17 =3.277,P =0.004).Meanwhile,we observed decreased VGluT1/VGAT ratios in the NAc in the stressed group (F(1,16) =81.04,P < 0.001).Conclusion:Early adverse experiences disrupt sleep behaviors in aged mice,which might be associated with the excitatory-inhibitory imbalance in the NAc.