Long term effects of stress on hippocampal function: Emphasis on early life stress paradigms and potential involvement of neuropeptide Y

Dexmedetomidine Alleviates Acute Stress-Induced Acute Kidney Injury by Attenuating Inflammation and Oxidative Stress via Inhibiting the P2X7R/NF-κB/NLRP3 Pathway in Rats

This study aimed to investigate the potential protective effects of Dexmedetomidine (DEX) against acute kidney injury (AKI) induced by acute stress (AS). Wistar rats were divided into five groups: Control, DEX, AS, AS + DEX, and AS + A438079. The results showed that AS led to AKI by increasing inflammatory biomarkers and oxidative stress-related indicators. The acute stress model in rats was successfully established. Renal function, histopathology, oxidative stress, and inflammation were assessed. Localization of P2X7 receptor (P2X7R) was determined by immunofluorescence. Additionally, the key inflammatory proteins of the P2X7R/NF-κB/NLRP3 signaling pathway were measured by Western blotting. DEX significantly improved kidney function, alleviated kidney injury, and reduced oxidative stress and inflammation. DEX inhibited the activation of the P2X7R, decreased the expression of NF-κB, NLRP3 inflammasome, and Caspase-1, and inhibited the expression of interleukin-1β (IL-1β) and tumor necrosis factor α (TNFα). Furthermore, DEX also alleviated AS-induced AKI by inhibiting the excessive production of reactive oxygen species (ROS) and reducing oxidative stress. In conclusion, DEX attenuates AS-induced AKI by mitigating inflammation and oxidative stress through the inhibition of the P2X7R/NF-κB/NLRP3 pathway in rats.

Prenatal ethanol and cannabis exposure have sex- and region-specific effects on somatostatin and neuropeptide Y interneurons in the rat hippocampus

BACKGROUND

Cannabis is increasingly being legalized and socially accepted around the world and is often used with alcohol in social settings. We recently showed that in utero exposure to both substances can alter the density of parvalbumin-expressing interneurons in the hippocampus. Here we investigate the effects of in utero alcohol and cannabis exposure, alone or in combination, on somatostatin- and neuropeptide Y-positive (NPY) interneurons. These are separate classes of interneurons important for network synchrony and inhibition in the hippocampus.

METHODS

A 2 (Ethanol, Air) × 2 (tetrahydrocannabinol [THC], Vehicle) design was used to expose pregnant Sprague-Dawley rats to either ethanol or air, in addition to either THC or the inhalant vehicle solution, during gestational days 5-20. Immunohistochemistry for somatostatin- and NPY-positive interneurons was performed in 50 μm tissue sections obtained at postnatal day 70.

RESULTS

Exposure to THC in utero had region-specific and sex-specific effects on the density of somatostatin-positive interneurons in the adult rat hippocampus. A female-specific decrease in NPY interneuron cell density was observed in the CA1 region following THC exposure. Combined exposure to alcohol and THC reduced NPY neurons selectively in the ventral dentate gyrus hippocampal subfield. However, overall, co-exposure to alcohol and cannabis had neither additive nor synergistic effects on interneuron populations in other areas of the hippocampus.

CONCLUSIONS

These results illustrate how alcohol and cannabis exposure in utero may affect hippocampal function by altering inhibitory processes in a sex-specific manner.

Early life stress modulates the genetic influence on brain structure and cognitive function in children

The enduring influence of early life stress (ELS) on brain and cognitive development has been widely acknowledged, yet the precise mechanisms underlying this association remain elusive. We hypothesize that ELS might disrupt the genome-wide influence on brain morphology and connectivity development, consequently exerting a detrimental impact on children's cognitive ability. We analyzed the multimodal data of DNA genotypes, brain imaging (structural and diffusion MRI), and neurocognitive battery (NIH Toolbox) of 4276 children (ages 9-10 years, European ancestry) from the Adolescent Brain Cognitive Development (ABCD) study. The genome-wide influence on cognitive function was estimated using the polygenic score (GPS). By using brain morphometry and tractography, we identified the brain correlates of the cognition GPSs. Statistical analyses revealed relationships for the gene-brain-cognition pathway. The brain structural variance significantly mediated the genetic influence on cognition (indirect effect = 0.016, PFDR < 0.001). Of note, this gene-brain relationship was significantly modulated by abuse, resulting in diminished cognitive capacity (Index of Moderated Mediation = -0.007; 95 % CI = -0.012 ∼ -0.002). Our results support a novel gene-brain-cognition model likely elucidating the long-lasting negative impact of ELS on children's cognitive development.

Gestational environmental enrichment prevents chronic social stress induced anxiety- and ethanol-related behaviors in offspring

Epidemiological surveys have shown a strong relationship between maternal stress and offspring's mood disorders. Growing evidence suggested that environmental enrichment (EE) improves cognitive function in models of psychiatric and neurological disorders. However, the potential protective effects of gestational EE on social stress-elicited mood disorders in offspring have not been studied. Knowing that the undeveloped brain is more sensitive to gestational environmental stimuli, we hypothesized that initiating cognitive stimulation, during gestation, would protect against social stress-induced behavioral alterations in adulthood. Therefore, the present study aimed to investigate the effects of gestational EE on social stress-elicited anxiety- and ethanol-related behaviors in adult offspring. EE consisted of free access, of dams, to tubular devices of different shapes, colors, and sizes that were changed regularly. After birth and weaning, young adult offspring were exposed to 19 days of social stress and anxiety-like behavior was evaluated by elevated plus maze, open field, and marbles burying tests. The two-bottle choice (TBC) drinking paradigm was used to assess stress-induced ethanol intake. Results showed that gestational EE prevented social stress-elicited anxiogenic-like effects with no differences in spontaneous locomotor activity. Moreover, in the TBC paradigm, mice pre-exposed to EE consistently showed a significantly decreased consumption and preference for ethanol with no effects on tastants' intakes. Interestingly, gestational EE increased serum BDNF levels, which showed a correlation with measures of anxiety- and ethanol-related behaviors. These findings indicate that some neurodevelopmental changes associated with prenatal EE may counteract adult social stress-induced behavioral alterations through a BDNF mechanism. Therefore, we propose that gestational EE has significant protective and beneficial effects on social stress-induced cognitive impairment. It can also alleviate anxiety-like behavior and subsequent excessive alcohol consumption.

Subchronic Arsenic Exposure Induces Behavioral Impairments and Hippocampal Damage in Rats

This study investigated the effects of subchronic arsenic exposure on behavior, neurological function, and hippocampal damage in rats. Thirty-two male Wistar rats were divided into four groups and exposed to different concentrations of arsenic in their drinking water for 12 weeks, while weekly water intake and body weight were recorded. Various neurobehavioral tests were conducted, evaluating overall activity levels, exploratory behavior, short-term memory, spatial learning and memory, anxiety-like behavior, and depressive-like states. Arsenic levels in urine, serum, and brain tissue were measured, and histopathological analysis assessed hippocampal damage using hematoxylin and eosin staining. The results demonstrated that arsenic exposure did not significantly affect overall activity or exploratory behavior. However, it impaired short-term memory and spatial learning and memory functions. Arsenic-exposed rats exhibited increased anxiety-like behavior and a depressive-like state. Arsenic levels increased dose-dependently in urine, serum, and brain tissue. The histopathological examinations revealed significant hippocampal damage, including neuronal shrinkage, cell proliferation, irregular structure, disordered arrangement, and vacuolation. These findings emphasize the importance of understanding the impact of arsenic exposure on behavior and brain health, highlighting its potential neurological consequences.

Hippocampus: Molecular, Cellular, and Circuit Features in Anxiety

Anxiety disorders are currently a major psychiatric and social problem, the mechanisms of which have been only partially elucidated. The hippocampus serves as a major target of stress mediators and is closely related to anxiety modulation. Yet so far, its complex anatomy has been a challenge for research on the mechanisms of anxiety regulation. Recent advances in imaging, virus tracking, and optogenetics/chemogenetics have permitted elucidation of the activity, connectivity, and function of specific cell types within the hippocampus and its connected brain regions, providing mechanistic insights into the elaborate organization of the hippocampal circuitry underlying anxiety. Studies of hippocampal neurotransmitter systems, including glutamatergic, GABAergic, cholinergic, dopaminergic, and serotonergic systems, have contributed to the interpretation of the underlying neural mechanisms of anxiety. Neuropeptides and neuroinflammatory factors are also involved in anxiety modulation. This review comprehensively summarizes the hippocampal mechanisms associated with anxiety modulation, based on molecular, cellular, and circuit properties, to provide tailored targets for future anxiety treatment.

The liver X receptors agonist GW3965 attenuates depressive-like behaviors and suppresses microglial activation and neuroinflammation in hippocampal subregions in a mouse depression model

Liver X receptors (LXRs) have recently been reported to be novel and potential targets for the reversal of depressive-like behaviors, but the mechanism remains unclear. Hippocampal neuroinflammation and impairment of the normal structure and function of microglia are closely associated with depression. To investigate the effects of LXRs agonist (GW3965) on neuroinflammation and microglia in the hippocampal formation of mice with chronic unpredictable stress (CUS)-induced depression, depressive-like behaviors were evaluated by behavioral tests, hippocampal LXRs gene expression were evaluated by qRT-PCR, the protein expression levels of interleukin-1β, tumor necrosis factor-α, inducible nitric oxide synthase, nuclear factor kappa B, and cluster of differentiation 206 were estimated by western blotting, modern stereological methods were used to precisely quantify the total number of microglia in each hippocampal subregion, and immunofluorescence was used to detect the density of activated microglia and the morphology of microglia. We found that GW3965 alleviated the depressive-like behavior induced by CUS, reversed the decrease in hippocampal LXRα and LXRβ induced by CUS, increased the protein expression of pro-inflammatory factors, and decreased the protein expression of antiinflammatory factors induced by CUS. Moreover, CUS intervention significantly increased the number of microglia in the CA1 region, CA2/3 region, and dentate gyrus and the density of activated microglia in the CA2/3 region and dentate gyrus and significantly decreased the endpoints of microglial branches and process length of microglia in the dentate gyrus, while 4 weeks of injections with GW3965 reversed these changes. These findings suggest that regulating the number, activated state, and morphology of microglia in hippocampal subregions might be an important basis for the antidepressant effects of LXRs.

Escitalopram alters the hypothalamic OX system but does not affect its up-regulation induced by early-life stress in adult rats

We hypothesized that there is a relationship between the orexinergic system (OX) alterations and changes elicited by escitalopram or venlafaxine in adult rats subjected to maternal separation (MS). This animal model of childhood adversity induces long-lasting consequences in adult physiology and behavior. Male Wistar rats from the control and MS groups were injected with escitalopram or venlafaxine (10 mg/kg) IP from postnatal day (PND) 69-89. Adult rats were subjected to behavioral assessment, estimation of hypothalamic-pituitary-adrenal (HPA) axis activity and analysis of the OX system (quantitative PCR and immunohistochemistry) in the hypothalamus and amygdala. MS caused anxiety- and depressive-like behavior, endocrine stress-related response, and up-regulation of the OX system in the hypothalamus. Escitalopram, but not venlafaxine, increased the activity of hypothalamic OX system in the control rats and both drugs had no effect on OXs in the MS group. The disturbed signaling of the OX pathway may be significant for harmful long-term consequences of early-life stress. Our data show that the normal brain and brain altered by MS respond differently to escitalopram. Presumably, anti-anxiety and antidepressant effects of this drug do not depend on the activity of hypothalamic OX system.

Sex Differences in Depression Caused by Early Life Stress and Related Mechanisms

Depression is a common psychiatric disease caused by various factors, manifesting with continuous low spirits, with its precise mechanism being unclear. Early life stress (ELS) is receiving more attention as a possible cause of depression. Many studies focused on the mechanisms underlying how ELS leads to changes in sex hormones, neurotransmitters, hypothalamic pituitary adrenocortical (HPA) axis function, and epigenetics. The adverse effects of ELS on adulthood are mainly dependent on the time window when stress occurs, sex and the developmental stage when evaluating the impacts. Therefore, with regard to the exact sex differences of adult depression, we found that ELS could lead to sex-differentiated depression through multiple mechanisms, including 5-HT, sex hormone, HPA axis, and epigenetics.

Hydrangea macrophylla and Thunberginol C Attenuate Stress-Induced Anxiety in Mice

Stress is an important neurological input for successful life. However, chronic stress and stress hormones could be a cause of various neurological disorders including anxiety disorders. Therefore, there have been many efforts to find effective materials for curing stress-induced neurological disorders. In this study, we examined the effect of Hydrangea macrophylla (HM) on corticosterone-induced neurotoxicity, stress-induced anxiety in mice and suggested a possible active ingredient of HM. HM protected cortical neurons against neurotoxicity of corticosterone (CORT), a stress hormone. HM also blocked CORT-induced hippocampal synaptic deficit via regulating Akt signaling. Oral administration of HM improved chronic restraint stress-induced anxiety in Elevated Plus maze test along with reduction of plasma corticosterone and TNF-α levels. Moreover, HM reduced stress-induced neuroinflammation and oxidative stress. Thunberginol C, an active ingredient of HM, also prevented CORT-induced neuronal cell death and restraint stress-induced anxiety. Moreover, thunberginol C reduced plasma TNF-α level and neuroinflammation and oxidative stress. Collectively, HM could be a good candidate for preventing stress-induced neurological disorders and thunberginol C may be an active ingredient of HM for this purpose.

Resilience to the effects of social stress on vulnerability to developing drug addiction

We review the still scarce but growing literature on resilience to the effects of social stress on the rewarding properties of drugs of abuse. We define the concept of resilience and how it is applied to the field of drug addiction research. We also describe the internal and external protective factors associated with resilience, such as individual behavioral traits and social support. We then explain the physiological response to stress and how it is modulated by resilience factors. In the subsequent section, we describe the animal models commonly used in the study of resilience to social stress, and we focus on the effects of chronic social defeat (SD), a kind of stress induced by repeated experience of defeat in an agonistic encounter, on different animal behaviors (depression- and anxiety-like behavior, cognitive impairment and addiction-like symptoms). We then summarize the current knowledge on the neurobiological substrates of resilience derived from studies of resilience to the effects of chronic SD stress on depression- and anxiety-related behaviors in rodents. Finally, we focus on the limited studies carried out to explore resilience to the effects of SD stress on the rewarding properties of drugs of abuse, describing the current state of knowledge and suggesting future research directions.

Effect of depression and suicidal behavior on neuropeptide Y (NPY) and its receptors in the adult human brain: A postmortem study

Neuropeptides are small proteinaceous molecules (3-100 amino acids) that are secreted by neurons and act on both neuronal and non-neuronal cells. Neuropeptide Y (NPY), a highly conserved and expressed neuropeptide in the central nervous system of mammals, plays a major role in stress response and resilience. Increasing evidence suggests that NPY and its receptors are altered in depression and suicide, pointing to their antidepressant-like nature. The objective of this study was to examine the role of NPY system in depression and suicidal behavior. Expression of NPY and its four receptors, NPY1R, NPY2R, NPY4R, and NPY5R was studied at the transcriptional and translational levels in the prefrontal cortex (PFC) and hippocampus regions of the postmortem brain of normal control (NC) (n = 24) and depressed suicide (DS) (n = 24) subjects. We observed a significant decrease in NPY mRNA and upregulation in NPY1R and NPY2R mRNA in both brain regions of DS subjects compared with NC subjects. We also observed a significant decrease in NPY protein expression in the PFC of subjects with DS. This study provides the first detailed evidence of alterations in the NPY system and the associated stress response in depression and suicidal behavior in humans. The outcomes of this study could be applied in the development of novel NPY system-targeted approaches for the treatment of depression.

Diverse identities and sites of action of cochlear neurotransmitters

Accurate encoding of acoustic stimuli requires temporally precise responses to sound integrated with cellular mechanisms that encode the complexity of stimuli over varying timescales and orders of magnitude of intensity. Sound in mammals is initially encoded in the cochlea, the peripheral hearing organ, which contains functionally specialized cells (including hair cells, afferent and efferent neurons, and a multitude of supporting cells) to allow faithful acoustic perception. To accomplish the demanding physiological requirements of hearing, the cochlea has developed synaptic arrangements that operate over different timescales, with varied strengths, and with the ability to adjust function in dynamic hearing conditions. Multiple neurotransmitters interact to support the precision and complexity of hearing. Here, we review the location of release, action, and function of neurotransmitters in the mammalian cochlea with an emphasis on recent work describing the complexity of signaling.

Long-term behavioral effects observed in mice chronically exposed to static ultra-high magnetic fields

PURPOSE

The primary goal of this study was to investigate whether chronic exposures to ultra-high B₀ fields can induce long-term cognitive, behavioral, or biological changes in C57BL/6 mice.

METHODS

C57BL/6 mice were chronically exposed to 10.5-T or 16.4-T magnetic fields (3-h exposures, two exposure sessions per week, 4 or 8 weeks of exposure). In vivo single-voxel ¹ H magnetic resonance spectroscopy was used to investigate possible neurochemical changes in the hippocampus. In addition, a battery of behavioral tests, including the Morris water-maze, balance-beam, rotarod, and fear-conditioning tests, were used to examine long-term changes induced by B₀ exposures.

RESULTS

Hippocampal neurochemical profile, cognitive, and basic motor functions were not impaired by chronic magnetic field exposures. However, the balance-beam-walking test and the Morris water-maze testing revealed B₀ -induced changes in motor coordination and balance. The tight-circling locomotor behavior during Morris water-maze tests was found as the most sensitive factor indexing B₀ -induced changes. Long-term behavioral changes were observed days or even weeks subsequent to the last B₀ exposure at 16.4 T but not at 10.5 T. Fast motion of mice in and out of the 16.4-T magnet was not sufficient to induce such changes.

CONCLUSION

Observed results suggest that the chronic exposure to a magnetic field as high as 16.4 T may result in long-term impairment of the vestibular system in mice. Although observation of mice may not directly translate to humans, nevertheless, they indicate that studies focused on human safety at very high magnetic fields are necessary.

Anesthesia, sex and miscarriage history may influence the association between cesarean delivery and autism spectrum disorder

BACKGROUND

To explore the association between cesarean section (CS) and risk of autism spectrum disorder (ASD), and evaluate the possible factors influencing this association.

METHODS

In total, 950 patients diagnosed with ASD and 764 healthy controls were recruited in this study. Socio-demographic characteristics and prenatal, perinatal, and neonatal characteristics were compared between the two groups. Univariate and multivariable conditional logistic regression analyses were applied to adjust for confounders. Further stratified analyses based on sex and miscarriage history were similarly performed to explore the factors influencing the association between CS and ASD.

RESULTS

CS was evidently associated with an elevated risk of ASD (adjusted odds ratio [aOR] = 1.606, 95% confidence interval (CI) = 1.311-1.969). Unlike regional anesthesia (RA), only CS performed under general anesthesia (GA) consistently elevated the risk of ASD (aOR = 1.887, 95% CI = 1.273-2.798) in females and males in further stratified analysis. The risk of children suffering from ASD following emergency CS was apparently increased in males (aOR = 2.390, 95% CI = 1.392-5.207), whereas a higher risk of ASD was observed among voluntary CS and indicated CS subgroups (aOR = 2.167, 95% CI = 1.094-4.291; aOR = 2.919, 95% CI = 1.789-4.765, respectively) in females. Moreover, the interaction term of CS and past miscarriage history (β = - 0.68, Wald χ2 = 7.5, df = 1, p = 0.006)) was similarly defined as influencing ASD.

CONCLUSIONS

The exposure of children to GA during CS may explain the possible/emerging association between CS and ASD. In addition, sex and miscarriage history could equally be factors influencing the association between CS and ASD.