Effect of chronic handling and social isolation on emotion and cognition in adolescent rats

Relationship of Physical Well-Being, Emotional Well-Being, and Social Engagement to Cognition in a Multiethnic Older Population

PURPOSE

To investigate the association between cognition, social engagement, physical well-being, and emotional well-being in a diverse older population.

METHOD

A secondary data analysis was conducted using a factor score structural equation model in a multiethnic sample of African American, Afro-Caribbean, Hispanic American, and European American participants.

RESULTS

Statistically significant (direct effects) between the latent constructs of physical well-being, emotional well-being, and social engagement were found. Model invariance testing suggests a partial invariance model with differences in life space, depression, and anxiety across racial/ethnic groups. As a mediator, social engagement significantly diminished the effects of emotional well-being (i.e., anxiety and depression) and increased the effects of physical well-being (Life Space Assessment and SF-36 Physical Component Summary: β = -0.07, standard error [SE] = 0.14, p = 0.045, and β = -0.15, SE = 0.14, p = 0.040, respectively) on cognition.

CONCLUSION

Results suggest good model fit and a critical role for social engagement in its impact on cognition. [Research in Gerontological Nursing, 18(3), 124-136.].

Integrating the COM-B model into behavioral neuroscience: A framework for understanding animal behavior

In light of the intricate nature of animal behavior regulation, a theoretical model is proposed, grounded in the COM-B (Capability, Opportunity, Motivation - Behavior) framework, which has gained considerable traction in the domain of human behavioral intervention. When extending the COM-B model to behavioral neuroscience, we first discuss the utility of the model in animal research, particularly its capacity to integrate environmental and social factors, and enhance cross-species comparisons, including animal-to-human translations and evolutionary considerations. The subsequent discussion then summarizes the advantages of utilizing the COM-B model in neuroscience are summarized, including the facilitation of a systems-level understanding of behavior and the establishment of a link between neural mechanisms and specific behavioral components. The experimental design for the application of the COM-B model in neuroscience is proposed to elucidate the brain regulatory processes that govern behavior. Finally, three specific examples are provided to illustrate the theoretical considerations, namely feeding and social behavior, and the role of neuromodulators in the control of behavior.

Exploring the effects of adolescent social isolation stress on the serotonin system and ethanol-motivated behaviors

RATIONALE

Alcohol is one of the most frequently used drugs of abuse and has a major impact on human health worldwide. People assigned female at birth and those with adverse childhood experiences are stress-vulnerable and more likely to report drinking as a means of "self-medication." Prior studies in our laboratory showed that adolescent social isolation stress (SIS) increases vulnerability to ethanol (EtOH) intake and consumption despite negative consequences in female rats.

OBJECTIVES

Here, we explored modulation of the dorsal raphe nucleus (DRN)-serotonin (5-HT) system, a sexually dimorphic neurotransmitter system involved in stress-reward interactions, to determine its contribution to EtOH-motivated behaviors in rats that have undergone SIS.

RESULTS

We employed electrophysiological and functional neuroanatomy strategies to show that both SIS and EtOH exposure induce persistent hypofunction of the DRN 5-HT system, particularly in females. Chemogenetic activation of DRN 5-HT neurons attenuated reward value for both EtOH and sucrose and elevated punished responding for EtOH in a stress-dependent manner.

CONCLUSIONS

Our results highlight an inverse relationship between EtOH consumption and the 5-HT system, the sex- and stress-dependent nature of this relationship, and a connection between DRN 5-HT signaling and acute responding to rewards and punishment. These data support the DRN 5-HT system as a potential target to treat aberrant alcohol consumption and drinking despite negative consequences in stress-vulnerable populations.

Social isolation increases impulsive choice with minor changes on metabolic function in middle-aged rats

The effects of social isolation (SI) during middle age remain unclear, so we tested the hypothesis that SI would lead to an increase in impulsive choice (IC), anxiety-like behavior, and metabolic dysfunction in middle-aged rats. Male and female rats were housed individually or in groups of four with same-sex housing mates at 11 months of age. Two months later, IC behavior was assessed using a delay-discounting task and anxiety-like behavior through a novelty-suppressed feeding (NSF) task. Lastly, glucose tolerance and insulin sensitivity following exposure to a high-fat diet were assessed using an oral glucose tolerance test (OGTT) and an insulin tolerance test (ITT). The results showed that socially isolated rats displayed more IC behavior than did group-housed rats of both sexes. However, no significant effect of housing was evident in the NSF task, OGTT, or ITT. Male rats had a higher plasma insulin concentration and insulin resistance index compared to females. Our findings demonstrate that SI in middle age is sufficient to increase IC behavior and highlight inherent sex-specific differences in metabolic profiles. These findings underscore the importance of investigating mechanisms that underlie the effects of social isolation during different stages of life.

Third-party punishment-like behavior in a rat model

Third-party punishment (TPP) is an altruistic behavior or sense willing to punish transgressors as a third party not directly involved in the transgression. TPP is observed worldwide, regardless of tradition and culture, and is essential for morality in human society. Moreover, even preverbal infants display TPP-like judgement, suggesting that TPP is evolutionarily conserved and innate. Thus, it is possible that non-human animals display TPP-like behavior, although TPP has been said to be human-specific. We investigated whether or not male mature Wistar rats displayed TPP-like behaviors when they witnessed deadly aggression by an unknown aggressive mouse toward another unknown victim mouse. Normally reared rats did not display TPP-like behaviors, but rats reared with extensive affectionate handling by human caretakers as beloved pets contacted the unknown aggressive mice in a gentle manner leading to reduced aggression toward the unknown victim mice, even when the aggressive mice fought back. Furthermore, the handled rats touched unknown rat pups that were drowning in water and anesthesia-induced comatose rats more frequently than control rats. These findings suggest a possibility that TPP is not in fact human-specific and innate but rather an acquired behavior that flourishes in affectionate circumstances.

Social Isolation Induces Changes in the Monoaminergic Signalling in the Rat Medial Prefrontal Cortex

(1) Background: The effects of short-term social isolation during adulthood have not yet been fully established in rats behaviourally, and not at all transcriptomically in the medial prefrontal cortex (mPFC). (2) Methods: We measured the behavioural effects of housing adult male rats in pairs or alone for 10 days. We also used RNA sequencing to measure the accompanying gene expression alterations in the mPFC of male rats. (3) Results: The isolated animals exhibited reduced sociability and social novelty preference, but increased social interaction. There was no change in their aggression, anxiety, or depression-like activity. Transcriptomic analysis revealed a differential expression of 46 genes between the groups. The KEGG pathway analysis showed that differentially expressed genes are involved in neuroactive ligand-receptor interactions, particularly in the dopaminergic and peptidergic systems, and addiction. Subsequent validation confirmed the decreased level of three altered genes: regulator of G protein signalling 9 (Rgs9), serotonin receptor 2c (Htr2c), and Prodynorphin (Pdyn), which are involved in dopaminergic, serotonergic, and peptidergic function, respectively. Antagonizing Htr2c confirmed its role in social novelty discrimination. (4) Conclusions: Social homeostatic regulations include monoaminergic and peptidergic systems of the mPFC.

Relationships between trace elements and cognitive and depressive behaviors in sprague dawley and wistar albino rats

Introduction: This study investigates the effects of social isolation on mental health and cognitive functions in Sprague Dawley (SD) and Wistar Albino (WIS) rat strains, prompted by the heightened awareness of such impacts amid the COVID-19 pandemic. This study aims to explore the impact of social isolation on memory, learning, and behavioral changes in middle-aged SD and WIS rat strains and to investigate cortical trace element levels, seeking potential correlations between these levels and the observed behavioral responses to social isolation. Methods: Four groups of 14-month-old male rats were established: control and isolated SDs and WIS rats (CONT-SD, ISO-SD, CONT-WIS, ISO-WIS). Morris Water Maze and Porsolt Forced Swimming tests were conducted for behavioral assessment. Following behavioral tests, rats were sacrificed under general anesthesia, and cortices were isolated for analysis of macro and trace element levels (ICP/MS). Results: In behavioral tests, CONT-SD rats exhibited superior performance in the Morris Water Maze test compared to CONT-WIS rats, but displayed increased depressive behaviors following social isolation, as evident in the Porsolt Forced Swimming test (p < 0.05). ISO-SD rats showed elevated levels of Co and Cu, along with reduced levels of Cs and As, compared to ISO-WIS rats. Moreover, isolation resulted in decreased Cu and Mo levels but increased Rb levels in WIS rats. Comparison of trace element levels in naïve groups from different strains revealed lower Zn levels in the WIS group compared to SD rats. Discussion: The findings suggest that the SD strain learns faster, but is more susceptible to depression after isolation compared to the WIS strain. Increased Co and Cu levels in ISO-SD align with previous findings, indicating potential trace element involvement in stress responses. Understanding these mechanisms could pave the way for preventive treatment strategies or therapeutic targets against the consequences of stressors, contributing to research and measures promoting a balanced diet to mitigate neurobehavioral abnormalities associated with social isolation in the future.

Preparation and Evaluation of Curcumin Derivatives Nanoemulsion Based on Turmeric Extract and Its Antidepressant Effect

Purpose

The early stage of this study verified that a turmeric extract (TUR) including 59% curcumin (CU), 22% demethoxycurcumin (DMC), and 18% bisdemethoxycurcumin (BDMC), could enhance the stability of CU and had greater antidepressant potential in vitro. The objective of the study was to develop a nano-delivery system containing TUR (TUR-NE) to improve the pharmacokinetic behavior of TUR and enhance its antidepressant effect.

Methods

The antidepressant potential of TUR was explored using ABTS, oxidative stress-induced cell injury, and a high-throughput screening model. TUR-NE was fabricated, optimized and characterized. The pharmacokinetic behaviors of TUR-NE were evaluated following oral administration to normal rats. The antidepressant effect of TUR-NE was assessed within chronic unpredictable mild stress model (CUMS) mice. The behavioral and biochemical indexes of mice were conducted.

Results

The results depicted that TUR had 3.18 and 1.62 times higher antioxidant capacity than ascorbic acid and CU, respectively. The inhibition effect of TUR on ASP+ transport was significantly enhanced compared with fluoxetine and CU. TUR-NE displayed a particle size of 116.0 ± 0.31 nm, polydispersity index value of 0.121 ± 0.007, an encapsulation rate of 98.45%, and good release and stability in cold storage. The results of pharmacokinetics indicated the AUC(0-t) of TUR-NE was 8.436 and 4.495 times higher than that of CU and TUR, while the Cmax was 9.012 and 5.452 times higher than that of CU and TUR, respectively. The pharmacodynamic study confirmed that the superior antidepressant effect of TUR-NE by significantly improving the depressant-like behaviors and elevating the content of 5-hydroxytryptamine in plasma and brain in CUMS mice. TUR-NE showed good safety with repeated administration.

Conclusion

TUR-NE, which had small and uniform particle size, enhanced the bioavailability and antidepressant effect of TUR. It could be a promising novel oral preparation against depression.

In silico and in vivo analysis of the relationship between ADHD and social isolation in pups rat model: Implication of redox mechanisms, and the neuroprotective impact of Punicalagin

Attention deficit hyperactivity disorder (ADHD) has high incidence rate among children which may be due to excessive monosodium glutamate (MSG) consumption and social isolation (SI).

AIM

We aimed to explore the relationships between MSG, SI, and ADHD development and to evaluate the neuroprotective potential of Punicalagin (PUN).

METHODS

Eighty male rat pups randomly distributed into eight groups. Group I is the control, and Group II is socially engaged rats treated with PUN. Groups III to VII were exposed to ADHD-inducing factors: Group III to SI, Group IV to MSG, and Group V to both SI and MSG. Furthermore, Groups VI to VIII were the same Groups III to V but additionally received PUN treatment.

KEY FINDINGS

Exposure to MSG and/or SI led to pronounced behavioral anomalies, histological changes and indicative of ADHD-like symptoms in rat pups which is accompanied by inhibition of the nuclear factor erythroid 2-related factor 2 (Nrf2)/Heme-oxygenase 1 (HO-1)/Glutathione (GSH) pathway, decline of the brain-derived neurotrophic factor (BDNF) expression and activation of the Toll-like receptor 4 (TLR4)/Nuclear factor kappa B (NF-kB)/NLR Family Pyrin Domain Containing 3 (NLRP3) pathway. This resulted in elevated inflammatory biomarker levels, neuronal apoptosis, and disrupted neurotransmitter equilibrium. Meanwhile, pretreatment with PUN protected against all the previous alterations.

SIGNIFICANCE

We established compelling associations between MSG consumption, SI, and ADHD progression. Moreover, we proved that PUN is a promising neuroprotective agent against all risk factors of ADHD.

Sex differences in ethanol consumption and drinking despite negative consequences following adolescent social isolation stress in male and female rats

Alcohol use disorder (AUD) is a debilitating psychiatric disorder characterized by drinking despite negative social and biological consequences. AUDs make up 71% of substance use disorders, with relapse rates as high as 80%. Current treatments stem from data conducted largely in males and fail to target the psychological distress motivating drinking in stress-vulnerable and at-risk populations. Here we employed a rat model and hypothesized that early life stress would reveal sex differences in ethanol intake and drinking despite negative consequences in adulthood. Rats were group housed or isolated postweaning to evaluate sex and stress effects on ethanol consumption in homecage drinking, self-administration (SA), and punished SA (drinking despite negative consequences) in adulthood. Stressed rats showed elevated homecage ethanol intake, an effect more pronounced in females. During SA, males were more sensitive to stress-induced elevations of drinking over time, but females drank more overall. Stressed rats, regardless of sex, responded more for ethanol than their non-stressed counterparts. Stressed females showed greater resistance to punishment-suppressed SA than stressed males, indicating a more stress-resistant drinking phenotype. Results support our hypothesis that adolescent social isolation stress enhances adult ethanol intake in a sex- and model-dependent manner with females being especially sensitive to early life stress-induced elevations in ethanol intake and punished SA in adulthood. Our findings echo the clinical literature which indicates that stress-vulnerable populations are more likely to 'self-medicate' with substances. Elucidating a potential mechanism that underlies why vulnerable populations 'self-medicate' with alcohol can lead towards developing catered pharmacotherapeutics that could reduce punishment-resistant drinking and relapse.

Cognitive Performance during the Development of Diabetes in the Zucker Diabetic Fatty Rat

Increased insulin levels may support the development of neural circuits involved in cognition, while chronic mild inflammation may also result in cognitive impairment. This study aimed to gain more insight into whether cognition is already impacted during adolescence in a genetic rat model for obesity and type 2 diabetes. Visual discrimination learning throughout adolescence and the level of motivation during early adulthood were investigated in Zucker Diabetic Fatty (ZDF) obese and ZDF lean rats using operant touchscreens. Blood glucose, insulin, and lipids were longitudinally analyzed. Histological analyses were performed in the liver, white adipose tissues, and the prefrontal cortex. Prior to the experiments with the genetic ZDF research model, all experimental assays were performed in two groups of outbred Long Evans rats to investigate the effect of different feeding circumstances. Adolescent ZDF obese rats outperformed ZDF lean rats on visual discrimination performance. During the longitudinal cognitive testing period, insulin levels sharply increased over weeks in ZDF obese rats and were significantly enhanced from 6 weeks of age onwards. Early signs of liver steatosis and enlarged adipocytes in white adipose tissue were observed in early adult ZDF obese rats. Histological analyses in early adulthood showed no group differences in the number of prefrontal cortex neurons and microglia, nor PSD95 and SIRT1 mRNA expression levels. Together, our data show that adolescent ZDF obese rats even display enhanced cognition despite their early diabetic profile.

Feasibility of pair-housing of rats after cranial implant surgery

Rat models employing cranial implants are increasingly employed to facilitate neural stimulation and recording in freely moving animals. Due to possible damage to wound, implant or attached devices, rats with cranial implants are traditionally housed singly, and little information is available on group- or pair-housing. Here we describe a protocol for pair-housing rats following cranial implant surgery and describe our experience with pair-housing during post-surgical recovery and up to 16 weeks following surgery.Thirty-six adult Wistar rats of both sexes were implanted with deep brain stimulation electrodes. Ten rats were equipped with an additional wireless headstage. Rats were housed in stable pairs before surgery and re-introduced 0-18 h post-surgery. Rat grimace scores did not indicate pain after conclusion of the analgesia protocol, physiological parameters were in the normal range three days post-surgery and weight loss did not exceed 10%. Rats with a cement cap only were pair-housed continuously without damage to the headcap. Rats carrying an additional fragile headstage had to be separated during lights-off periods to prevent headstage damage but could be pair-housed during lights-on periods.Pair-housing is a feasible and effective method to facilitate the rats' need for social companionship following cranial implant surgery.

Restricted cafeteria feeding and treadmill exercise improved body composition, metabolic profile and exploratory behavior in obese male rats

The aim of this study was to evaluate, in male Long-Evans rats, whether a restricted-cafeteria diet (CAFR), based on a 30% calorie restriction vs continuous ad libitum cafeteria (CAF) fed animals, administered alone or in combination with moderate treadmill exercise (12 m/min, 35 min, 5 days/week for 8 weeks), was able to ameliorate obesity and the associated risk factors induced by CAF feeding for 18 weeks and to examine the changes in circadian locomotor activity, hypothalamic-pituitary-adrenal (HPA) axis functionality, and stress response elicited by this dietary pattern. In addition to the expected increase in body weight and adiposity, and the development of metabolic dysregulations compatible with Metabolic Syndrome, CAF intake resulted in a sedentary profile assessed by the home-cage activity test, reduced baseline HPA axis activity through decreased corticosterone levels, and boosted exploratory behavior. Both CAFR alone and in combination with exercise reduced abdominal adiposity and hypercholesterolemia compared to CAF. Exercise increased baseline locomotor activity in the home-cage in all dietary groups, boosted exploratory behavior in STD and CAF, partially decreased anxiety-like behavior in CAF and CAFR, but did not affect HPA axis-related parameters.

Role of sirtuin1 in impairments of emotion-related behaviors in mice with chronic mild unpredictable stress during adolescence

Long-term exposure to physical and/or psychosocial stress during early life and/or adolescence increases the risk of psychiatric disorders such as major depressive disorder and anxiety disorders. However, the molecular mechanisms underlying early stress-induced brain dysfunction are poorly understood. In the present study, mice at 4 weeks old were subjected to chronic mild unpredictable stress (CMUS) for 4 weeks, and subsequently to assays of emotion-related behaviors. Thereafter, they were sacrificed and their brains were collected for real-time quantitative polymerase chain reaction (RT-qPCR). Mice with CMUS during adolescence showed despair behavior, anxiety-like behavior, social behavior deficits, and anhedonia in forced-swim, marble-burying, social interaction, and sucrose preference tests, respectively. Additionally, RT-qPCR revealed that the expression levels of sirtuin1 (SIRT1), a NAD⁺-dependent deacetylase that mediates stress responses, were down-regulated in the prefrontal cortex and hippocampus of mice with CMUS compared with control mice. Next, to investigate the pathophysiological role of decreased Sirt1 expression levels in stress-induced behavioral deficits, we assessed the effects of resveratrol, a pharmacological activator of SIRT1, in mice exposed to CMUS. Chronic treatment with resveratrol prevented -induced social behavior deficits and depression-like behaviors. These results suggest that CMUS during adolescence decreases Sirt1 expression in the brain, leading to deficits in emotional behavior. Accordingly, SIRT1 activators, such as resveratrol, may be preventive agents against abnormalities in emotional behavior following stress during an immature period.

Depression and anxiety among children and adolescents pre and post COVID-19: A comparative meta-analysis

BACKGROUND

Published studies in comparing pre and post the COVID-19 pandemic depression and anxiety levels among children and adolescents yielded incongruent results. Therefore, there is a necessity to perform a timely meta-analysis to synthesize existing evidence.

METHODS

A total of 10 digital databases (PubMed, Web of Science, PsycINFO, the Cochrane Library, Embase, Scopus, ScienceDirect, CNKI, WanFang, CQVIP) were fully searched for eligible studies published before November 6, 2021. Based on quality assessment results, relevant data were extracted for eligible studies of higher quality. We combined standardized mean difference (SMD) or prevalence ratio (RR) for anxiety and depression pre and post the COVID-19 pandemic by using random-effects models. Sensitivity analysis was further performed to evaluate heterogeneity of included studies.

RESULTS

14,508 articles were preliminarily identified, and after stepwise screening process, 8 articles were included eventually. The results showed that the SMD for post COVID-19 anxiety score measured by GAD-7 was 0.12 (95% CI: 0.08, 0.17), an significant increase compared with pre COVID-19 period; the SMDs and 95% CIs for post COVID-18 depression scores measured by PHQ-9, PHQ-8, and MFQ were 0.17 (95% CI: 0.10, 0.24), 0.23 (95% CI: 0.08, 0.38), and 0.11 (95% CI: 0.06, 0.17), respectively, also significantly increased compared with pre COVID-19 period. The RR for depression was 2.54 (95% CI: 2.48, 2.60) in post COVID-19 period when compared with pre-pandemic.

CONCLUSIONS

Children and adolescents reported deteriorated anxiety and depression levels after the COVID-19 pandemic. More attention should be paid to this vulnerable group. Effective, expedient, and practical intervention measures which are compatible with COVID-19 prevention and control policies should be developed and implemented to maintain mental health wellbeing of the youths.

Environmental enrichment as a strategy: Attenuates the anxiety and memory impairment in social isolation stress

BACKGROUND

Social isolation (SI) early in life produces behavioral and cognitive abnormalities. On the contrary, environmental enrichment (EE) offers beneficial effects on brain plasticity and development. This study was designed to examine how EE affects memory functions, anxiety level, and the expression levels of memory/anxiety-related genes such as NR2A, NR2B, BDNF, and cFos in the hippocampus of socially isolated rats.

MATERIALS AND METHODS

Wistar albino male rats (n = 40) were separated into the five groups: Standard cage (SC), SI, EE, SI + SC, and SI + EE group. For each group, eight rats were housed, either grouped or isolated, in a standard or 3-week EE, respectively. Morris water maze test (MWMT) was used for measuring the learning and memory function. Elevated plus maze (EPM) and open field (OF) were used for the evaluation of anxiety behavior. Blood corticosterone level was evaluated by the ELISA method. The expression levels of genes were measured by the RT-PCR method.

RESULTS

Results showed that EE increased memory performance in the SI group (p < 0.05). SI caused anxiety while EE improved anxiety behavior (p < 0.05). There was no significant difference between the groups in the OF test. Corticosterone levels did not change between groups. BDNF expression level was downregulated in EE and SI + SC compared with the SC group (respectively; p = 0.012; p = 0.011). NR2A, NR2B, and cFos expression levels did not change between groups significantly.

CONCLUSIONS

SI impaired memory performance while EE has beneficial effects on memory in socially isolated rats. EE alone was insufficient to cause alterations in the memory performance. The therapeutic effects of EE became strengthened while applied together with stress protocol. Together with improving the effectiveness of memory function, EE has the potential to decrease anxiety behavior. EE seemed to be the reason for decreasing in BDNF.

Early Life Exposure to a Diet With a Supramolecular Lipid Structure Close to That of Mammalian Milk Improves Early Life Growth, Skeletal Development, and Later Life Neurocognitive Function in Individually and Socially Housed Male C57BL/6J Mice

Breastfeeding (duration) can be positively associated with infant growth outcomes as well as improved cognitive functions during childhood and later life stages. (Prolonged) exposure to optimal lipid quantity and quality, i.e., the supramolecular structure of lipids, in mammalian milk, may contribute to these beneficial effects through nutritional early-life programming. In this pre-clinical study, we exposed male C57BL/6J mice from post-natal Days 16 to 42 (i.e., directly following normal lactation), to a diet with large lipid droplets coated with bovine milk fat globule membrane-derived phospholipids, which mimic more closely the supramolecular structure of lipid droplets in mammalian milk. We investigated whether exposure to this diet could affect growth and brain development-related parameters. As these outcomes are also known to be affected by the post-weaning social environment in mice, we included both individually housed and pair-wise housed animals and studied whether effects of diet were modulated by the social environment. After Day 42, all the animals were fed standard semi-synthetic rodent diet. Growth and body composition were assessed, and the mice were subjected to various behavioral tests. Individual housing attenuated adolescent growth, reduced femur length, and increased body fat mass. Adult social interest was increased due to individual housing, while cognitive and behavioral alterations as a result of different housing conditions were modest. The diet increased adolescent growth and femur length, increased lean body mass, reduced adolescent anxiety, and improved adult cognitive performance. These effects of diet exposure were comparable between individually and socially housed mice. Hence, early life exposure to a diet with lipid droplets that mimic the supramolecular structure of those in mammalian milk may improve adolescent growth and alters brain function in both socially and individually housed mice. These findings suggest that lipid structure in infant milk formula may be a relevant target for nutritional solutions, targeting both healthy infants and infants facing growth challenges.