Social Isolation Of Rats Research Articles

Prefrontal Cortex Cytosolic Proteome and Machine Learning-Based Predictors of Resilience toward Chronic Social Isolation in Rats.

Chronic social isolation (CSIS) generates two stress-related phenotypes: resilience and susceptibility. However, the molecular mechanisms underlying CSIS resilience remain unclear. We identified altered proteome components and biochemical pathways and processes in the prefrontal cortex cytosolic fraction in CSIS-resilient rats compared to CSIS-susceptible and control rats using liquid chromatography coupled with tandem mass spectrometry followed by label-free quantification and STRING bioinformatics. A sucrose preference test was performed to distinguish rat phenotypes. Potential predictive proteins discriminating between the CSIS-resilient and CSIS-susceptible groups were identified using machine learning (ML) algorithms: support vector machine-based sequential feature selection and random forest-based feature importance scores. Predominantly, decreased levels of some glycolytic enzymes, G protein-coupled receptor proteins, the Ras subfamily of GTPases proteins, and antioxidant proteins were found in the CSIS-resilient vs. CSIS-susceptible groups. Altered levels of Gapdh, microtubular, cytoskeletal, and calcium-binding proteins were identified between the two phenotypes. Increased levels of proteins involved in GABA synthesis, the proteasome system, nitrogen metabolism, and chaperone-mediated protein folding were identified. Predictive proteins make CSIS-resilient vs. CSIS-susceptible groups linearly separable, whereby a 100% validation accuracy was achieved by ML models. The overall ratio of significantly up- and downregulated cytosolic proteins suggests adaptive cellular alterations as part of the stress-coping process specific for the CSIS-resilient phenotype.

Prefrontal cortical synaptoproteome profile combined with machine learning predicts resilience towards chronic social isolation in rats

Chronic social isolation (CSIS) of rats serves as an animal model of depression and generates CSIS-resilient and CSIS-susceptible phenotypes. We aimed to investigate the prefrontal cortical synaptoproteome profile of CSIS-resilient, CSIS-susceptible, and control rats to delineate biochemical pathways and predictive biomarker proteins characteristic for the resilient phenotype. A sucrose preference test was performed to distinguish rat phenotypes. Class separation and machine learning (ML) algorithms support vector machine with greedy forward search and random forest were then used for discriminating CSIS-resilient from CSIS-susceptible and control rats. CSIS-resilient compared to CSIS-susceptible rat proteome analysis revealed, among other proteins, downregulated glycolysis intermediate fructose-bisphosphate aldolase C (Aldoc), and upregulated clathrin heavy chain 1 (Cltc), calcium/calmodulin-dependent protein kinase type II (Cam2a), synaptophysin (Syp) and fatty acid synthase (Fasn) that are involved in neuronal transmission, synaptic vesicular trafficking, and fatty acid synthesis. Comparison of CSIS-resilient and control rats identified downregulated mitochondrial proteins ATP synthase subunit beta (Atp5f1b) and citrate synthase (Cs), and upregulated protein kinase C gamma type (Prkcg), vesicular glutamate transporter 1 (Slc17a7), and synaptic vesicle glycoprotein 2 A (Sv2a) involved in signal transduction and synaptic trafficking. The combined protein differences make the rat groups linearly separable, and 100% validation accuracy is achieved by standard ML models. ML algorithms resulted in four panels of discriminative proteins. Proteomics-data-driven class separation and ML algorithms can provide a platform for accessing predictive features and insight into the molecular mechanisms underlying synaptic neurotransmission involved in stress resilience.

Fatty Acid Amide Hydrolase and Cannabinoid Receptor Type 1 Genes Regulation is Modulated by Social Isolation in Rats.

Social isolation is a state of lack of social connections, involving the modulation of different molecular signalling cascades and associated with high risk of mental health issues. To investigate if and how gene expression is modulated by social experience at the central level, we analyzed the effects of 5weeks of social isolation in rats focusing on endocannabinoid system genes transcription in key brain regions involved in emotional control. We observed selective reduction in mRNA levels for fatty acid amide hydrolase (Faah) and cannabinoid receptor type 1 (Cnr1) genes in the amygdala complex and of Cnr1 in the prefrontal cortex of socially isolated rats when compared to controls, and these changes appear to be partially driven by trimethylation of Lysine 27 and acetylation of Lysine 9 at Histone 3. The alterations of Cnr1 transcriptional regulation result also directly correlated with those of oxytocin receptor gene. We here suggest that to counteract the effects of SI, it is of relevance to restore the endocannabinoid system homeostasis via the use of environmental triggers able to revert those epigenetic mechanisms accounting for the alterations observed.

Upregulations of α1 adrenergic receptors and noradrenaline synthases in the medial prefrontal cortex are associated with emotional and cognitive dysregulation induced by post-weaning social isolation in male rats

Early-life social isolation induces emotional and cognitive dysregulation, such as increased aggression and anxiety, and decreases neuron excitability in the medial prefrontal cortex (mPFC). The noradrenergic system in the mPFC regulates emotion and cognitive function via α1 or α2A adrenergic receptors, depending on noradrenaline levels. However, social isolation-induced changes in the mPFC noradrenergic system have not been reported. Here, male Wistar rats received post-weaning social isolation for nine consecutive weeks and were administered behavioral tests (novel object recognition, elevated plus maze, aggression, and forced swimming, sequentially). Protein expression levels in the mPFC noradrenergic system (α1 and α2A adrenergic receptors, tyrosine hydroxylase, and dopamine-β-hydroxylase used as indices of noradrenaline synthesis and release) were examined through western blotting. Social isolation caused cognitive dysfunction, anxiety-like behavior, and aggression, but not behavioral despair. Socially-isolated rats exhibited increased protein levels of the α1 adrenergic receptor, tyrosine hydroxylase, and dopamine-β-hydroxylase in the mPFC; there was no significant difference between the groups in the α2A adrenergic receptor expression levels. Preferential activation of the α1 adrenergic receptor caused by high noradrenaline concentration in the mPFC may be involved in social isolation-induced emotional and cognitive regulation impairments. Targeting the α1 adrenergic receptor signaling pathway is a potential therapeutic strategy for psychiatric disorders with symptomatic features such as emotional and cognitive dysregulation.

Effects of Early Risperidone Treatment on Metabolic Parameters in Socially Isolated Rats-Implication of Antipsychotic Intervention across Developmental Stages of Schizophrenia.

Second-generation antipsychotics (SGAs) is thought responsible for the metabolic abnormalities of schizophrenic patients, however, some untreated schizophrenic patients had already developed problems with glucose metabolism. The present study examined the hypothesis that schizophrenia itself but not risperidone, an extensively employed SGA, is accountable for metabolic abnormalities. A 56-day risperidone regimen (1 mg/kg/day) was employed for rats of social isolation rearing (SIR) beginning at different developmental stage (28 or 56 days after weaning, i.e., adolescent and young adulthood, respectively). Metabolic parameters including body weight, systolic blood pressure (SBP), triglyceride, high-density lipoprotein (HDL), low-density lipoprotein (LDL), total cholesterol, and plasma glucose were measured at baseline, 28, and 56 days of the regimen. Oral glucose tolerance test (OGTT) was performed at the end of the regimen. Insulin function was evaluated by area under the curve (AUC) of OGTT, homeostasis model assessment-insulin resistance (HOMA-ir), and Matsuda index. Our results demonstrated that: (i) SIR rats presented higher body weight, plasma triglyceride, and HOMA-ir than social controls. (ii) Higher insulin resistance was specifically presented in young adult rather than adolescent SIR rats. (iii) Adolescent drugged rats showed a lower level of LDL in day 28 of the regimen than young adult. Risperidone led to a lower LDL level in only young adult IR rats in day 56 than undrugged rats. (iv) SIR-induced dysregulation of insulin can be reversed by chronic risperidone treatment beginning at adolescence but not young adulthood. Our findings support the primary role of schizophrenia in metabolic abnormalities and risperidone appear beneficial when administered earlier.

Changes in Sociability and Preference for Social Novelty in Female Rats in Prolonged Social Isolation.

Chronic stress due to social isolation (SI) can lead to distress with negative consequences for both humans and animals. Numerous disorders caused by SI include disorders in the emotional-motivational domain and cognitive functions, as well as changes in social behavior. There are currently no data identifying the sequelae of SI when its duration is significantly increased. Although female rats have been shown to be highly sensitive to stress, research on them is lacking. The present study assessed sociability and preference for "social novelty" in a three-chamber social test in female Wistar rats in two series of experiments at different time points during prolonged SI, which began at adolescence and continued to ages 5.5 and 9.5 months. At two months of SI, rats showed an increased preference for a social object over a non-social object (increased sociability) simultaneously with the appearance of signs of a decrease in the preference for a new social object over an already familiar social object (signs of a decrease in the preference for social novelty). In a social interaction test, the rats also displayed increases in the durations of social contacts, including aggressive interactions; they showed a decrease in exploratory risk assessments (head dips from the open arms) in the elevated plus maze test and a decrease in exploratory activity. After SI lasting 8.5 months, the rats showed signs of social deficit and a marked decrease in the preference for social novelty. No signs of increased aggressiveness were found. Thus, the impact of SI on social behavior depended on its duration and, we believe, was accompanied by a change in coping strategies.

Differential effects of lipopolysaccharide on cognition, corticosterone and cytokines in socially-housed vs isolated male rats

Social isolation is an established risk factor for mental illness and impaired immune function. Evidence suggests that neuroinflammatory processes contribute to mental illness, possibly via cytokine-induced modulation of neural activity. We examined the effects of lipopolysaccharide (LPS) administration and social home cage environment on cognitive performance in the 5-Choice Serial Reaction Time Task (5CSRTT), and their effects on corticosterone and cytokines in serum and brain tissue. Male Long-Evans rats were reared in pairs or in isolation before training on the 5CSRTT. The effects of saline and LPS (150 µg/kg i.p.) administration on sickness behaviour and task performance were then assessed. LPS-induced sickness behaviour was augmented in socially-isolated rats, translating to increased omissions and slower response times in the 5CSRTT. Both social isolation and LPS administration reduced impulsive responding, while discriminative accuracy remained unaffected. With the exception of reduced impulsivity in isolated rats, these effects were not observed following a second administration of LPS, revealing behavioural tolerance to repeated LPS injections. In a separate cohort of animals, social isolation potentiated the ability of LPS to increase serum corticosterone and IL-6, which corresponded to increased IL-6 in the orbitofrontal and medial prefrontal cortices and the nucleus accumbens. Basal IL-4 levels in the nucleus accumbens were reduced in socially-isolated rats. These findings are consistent with the adaptive response of reduced motivational drive following immune challenge, and identify social isolation as an exacerbating factor. Enhanced IL-6 signalling may play a role in mediating the potentiated behavioural response to LPS administration in isolated animals.

Abstract 12: Social isolation promotes mammary cancer recurrence, increases IL6/JAK/STAT3 signaling and causes mitochondrial dysfunction in tamoxifen treated rats, and a traditional herbal mixture reverses all these changes

Abstract Social isolation is associated with increased risk and mortality from many diseases, such as breast cancer. Socially isolated breast cancer survivors have a 43% higher risk of recurrence and a 64% higher risk of breast cancer-specific mortality than socially integrated survivors. Since Covid-19 has dramatically increased the incidence of social isolation, it is important to determine if social isolation affects the response to endocrine therapy and/or recurrence after the therapy is completed. Since previous studies indicate that social isolation increases circulating inflammatory cytokines, we investigated if an anti-inflammatory herbal mixture Jaeumkanghwa-tang (JGT) prevents the adverse effects of social isolation on breast cancer mortality. Estrogen receptor positive mammary tumors were initiated with 7,12-dimethylbenz[a]anthracene. When a rat developed a palpable mammary tumor, it was either socially isolated (SI) by housing it singly or a rat was allowed to remain group-housed (GH). Tamoxifen (340ppm via diet) or tamoxifen + JGT (500ppm via drinking water) started when the first mammary tumor reached a size of 11 mm in diameter. Tamoxifen administration ended when a complete response to this therapy had lasted for 9 weeks (corresponds to 5 years in women). During tamoxifen therapy, social isolation non-significantly reduced the rate of complete responses to 21%, from 31% in GH group (p>0.05). After the therapy was completed, SI significantly increased local mammary tumor recurrence (p<0.001; 45% GH vs 75% SI). RNAseq analysis was performed in the mammary glands. Gene set enrichment analysis (GSEA) of transcriptome showed that the increased recurrence risk in socially isolated rats was associated with an enrichment of IL6/JAK/STAT3 signaling: this result was confirmed in the tumors. In addition, oxidative phosphorylation (OXPHOS) pathway was suppressed: the suppressed genes included those involved in mitochondrial pyruvate transport and conversion of pyruvate to acetyl CoA as well as genes in the TCA cycle and mediating electron transport in mitochondrial complexes I-IV. Social isolation also increased the expression of inflammatory receptor for advanced glycation end-products (RAGE) (p≤0.05). Consumption of an anti-inflammatory JGT inhibited IL6/JAK/STAT3 signaling, upregulated OXPHOS signaling and prevented the increased risk of mammary cancer recurrence in socially isolated animals. The percentage of recurrences in the SI rats dropped from 75% without JGT to 22% with JGT (p<0.001). Breast cancer mortality among socially isolated survivors may be most effectively prevented by focusing on the period following endocrine therapy using tools that inhibit IL6/JAK/STAT3 inflammatory cytokine signaling and correct disrupted OXPHOS and mitochondrial dysfunction. Citation Format: Fabia de Oliveira Andrade, Lu Jin, Robert Clarke, Imani Wood, MaryAnn Dutton, Chezaray Anjorin, Grace Rubin, Audrey Gao, Surojeet Sengupta, Kevin FitzGerald, Leena Hilakivi-Clarke. Social isolation promotes mammary cancer recurrence, increases IL6/JAK/STAT3 signaling and causes mitochondrial dysfunction in tamoxifen treated rats, and a traditional herbal mixture reverses all these changes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 12.

Regulation of oxytocin receptor gene expression in obsessive\u2013compulsive disorder: a possible role for the microbiota-host epigenetic axis

BackgroundObsessive–compulsive disorder (OCD) is a prevalent and severe clinical condition. Robust evidence suggests a gene-environment interplay in its etiopathogenesis, yet the underlying molecular clues remain only partially understood. In order to further deepen our understanding of OCD, it is essential to ascertain how genes interact with environmental risk factors, a cross-talk that is thought to be mediated by epigenetic mechanisms. The human microbiota may be a key player, because bacterial metabolites can act as epigenetic modulators. We analyzed, in the blood and saliva of OCD subjects and healthy controls, the transcriptional regulation of the oxytocin receptor gene and, in saliva, also the different levels of major phyla. We also investigated the same molecular mechanisms in specific brain regions of socially isolated rats showing stereotyped behaviors reminiscent of OCD as well as short chain fatty acid levels in the feces of rats.ResultsHigher levels of oxytocin receptor gene DNA methylation, inversely correlated with gene expression, were observed in the blood as well as saliva of OCD subjects when compared to controls. Moreover, Actinobacteria also resulted higher in OCD and directly correlated with oxytocin receptor gene epigenetic alterations. The same pattern of changes was present in the prefrontal cortex of socially-isolated rats, where also altered levels of fecal butyrate were observed at the beginning of the isolation procedure.ConclusionsThis is the first demonstration of an interplay between microbiota modulation and epigenetic regulation of gene expression in OCD, opening new avenues for the understanding of disease trajectories and for the development of new therapeutic strategies.

Adult resocialization restores sociability, reduced by adolescent social isolation in rats

We aimed to assess the effect of 6-week adolescent social isolation on sociability and social novelty preference in male Wistar rats. In addition, we examined whether isolation effects would persist after adult resocialization. Our findings demonstrate that social isolation resulted in decreased social interest (the time spent interacting with an unfamiliar rat of the same sex and age decreased from 115.4 ± 13.3 s in group-housed animals to 82.3 ± 11.0 s in isolated, P < 0.05), while social novelty preference was not significantly different between isolated and group-housed rats. We also report that 6-week resocialization was sufficient to restore social interaction levels in isolated rats (time spent with an unfamiliar rat was 117.9 ± 12.6 s in isolated animals and 102.5 ± 10.9 s in group-housed). These findings may be useful for better understanding the impact of social deprivation on human subjects, which has recently become especially relevant due to the restrictions of the COVID-19 pandemic.

The differential effects of brief environmental enrichment following social isolation in rats.

Environmental enrichment (EE) in rodents is associated with a wide range of physiological, affective, and cognitive benefits. A seemingly opposite housing condition, social isolation (SI), is used as a rodent model of stress, negatively affecting several neurobiological mechanisms and hampering cognitive performance. Experimental designs that involve switching between these housing conditions produced mixed results. We evaluated different behavioral and cognitive effects of brief EE following long-term, SI-induced stress. We revealed the influence of enrichment after 30 days of isolation on behavioral despair, anxiety-like behavior, and spatial working memory in adult male Wistar rats and found a substantial anxiolytic effect in the experimental (SI to EE) group. Interestingly, rats exposed to EE also showed increased behavioral despair compared with the control (continuous SI) group. There was no difference in spatial working memory performance at the end of a 5-day water Y-maze (WYM) test. However, the SI to EE animals displayed better memory performance in the first 2 days of the WYM, indicating faster learning. In line with this difference, we recorded significantly more c-Fos-immunopositive (c-Fos+) cells in the retrosplenial and perirhinal cortices of the SI to EE animals. The lateral and basolateral nuclei of the amygdala showed no such difference. These results suggest that brief enrichment following isolation stress leads to differential results in affective and cognitive systems.

Abstract P4-02-13: Social isolation promotes mammary cancer recurrence, increases IL6/JAK/STAT3 signaling and causes mitochondrial dysfunction in tamoxifen treated rats, and a traditional herbal mixture reverses all these changes

Abstract BACKGROUND: Social isolation is associated with increased risk and mortality from many diseases, such as breast cancer. Socially isolated breast cancer survivors have a 43% higher risk of recurrence and a 64% higher risk of breast cancer-specific mortality than socially integrated survivors. Since Covid-19 has dramatically increased the incidence of social isolation, it is important to determine if social isolation affects the response to endocrine therapy and/or recurrence after the therapy is completed. Further, since previous studies indicate that social isolation increases circulating inflammatory cytokines, we investigated if an anti-inflammatory herbal mixture Jaeumkanghwa-tang (JEKHT) prevents the adverse effects of social isolation on breast cancer mortality. METHODS: Estrogen receptor positive mammary tumors were initiated with 7,12-dimethylbenz[a]anthracene. When a rat developed a palpable mammary tumor, it was either socially isolated (SI) by housing it singly or a rat was allowed to remain group-housed (GH). Tamoxifen (340ppm via diet) or tamoxifen + JEKHT (500ppm via drinking water) started when the first mammary tumor was detected. Tamoxifen administration ended when a complete response to this therapy had lasted for 9 weeks (corresponds to 5 years in women). Rats which received JEKHT during tamoxifen therapy continued to take it also after tamoxifen therapy ended. RESULTS: During tamoxifen therapy, social isolation non-significantly reduced the rate of complete responses to 21%, from 31% in GH group (p>0.05). After the therapy was completed, SI significantly increased local mammary tumor recurrence (p<0.001; 45% GH vs 75% SI). RNAseq analysis was performed in the mammary glands, since only tamoxifen resistant or recurring mammary tumors were available for analysis. Gene set enrichment analysis (GSEA) of transcriptome showed that the increased recurrence risk in socially isolated rats was associated with an enrichment of IL6/JAK/STAT3 signaling: this result was confirmed in the tumors. In addition, oxidative phosphorylation (OXPHOS) pathway was suppressed: the suppressed genes included those involved in mitochondrial pyruvate transport and conversion of pyruvate to acetyl CoA as well as genes in the TCA cycle and mediating electron transport in mitochondrial complexes I-IV. Despite the reduction in pyruvate transporting and converting genes, lactate levels or lactate dehydrogenase activity were not increased in socially isolated rats, indicating no changes in Warburg effect. Social isolation also increased the expression of inflammatory receptor for advanced glycation end-products (RAGE) (p≤0.05). Consumption of an anti-inflammatory JEKHT inhibited IL6/JAK/STAT3 signaling, upregulated OXPHOS signaling and prevented the increased risk of mammary cancer recurrence in socially isolated animals. The percentage of recurrences in the SI rats dropped from 75% without JEKHT to 22% with JEKHT (p<0.001). CONCLUSION: Breast cancer mortality among socially isolated survivors may be most effectively prevented by focusing on the period following endocrine therapy using tools that inhibit IL6/JAK/STAT3 inflammatory cytokine signaling and correct disrupted OXPHOS and mitochondrial dysfunction. Citation Format: Fabia Andrade, Lu Jin, Robert Clarke, Imani Wood, MaryAnn Dutton, Chezaray Anjorin, Grace Rubin, Audrey Gao, Surojeet Sengupta, Kevin FitzGerald, Leena Hilakivi-Clarke. Social isolation promotes mammary cancer recurrence, increases IL6/JAK/STAT3 signaling and causes mitochondrial dysfunction in tamoxifen treated rats, and a traditional herbal mixture reverses all these changes [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P4-02-13.

Effect of neuropeptide Y antagonist BMS193885 on overeating and emotional responses induced by social isolation in rats

BACKGROUND: Chronic stress of social isolation is associated with an increased risk of mental illness, such as atypical depression, and is usually accompanied by hyperphagia and weight gain. We have previously shown that the NPY antagonist Y1R BMS193885 reduces the conditioned place preference of ethanol. The involvement of NPY receptors in non-chemical forms of addiction is assumed.
 AIM: Was to analyze the effects of NPY Y1R BMS193885 on emotional responses and elements of bindge eating in rats caused by rearing in social isolation.
 MATERIALS AND METHODS: We used the tests open field, elevated plus maze, Porsolts forced swimming test, resident intruder test and method of conditioned eating test in well-fed rats.
 RESULTS: The level of depression, negative emotionality and locomotor activity increased in rats reared in isolation. After intranasal administration of BMS193885 high locomotor activity was maintained, but investigating activity increased in isolated rats. Isolated animals showed an increase in body weight at the 6th week of life. By to the 9th week, the body weight of the isolated rats was significantly higher than in animals reared in the community (р 0.05). Intranasal administration of 20 g BMS193885 for 1 week caused a decrease in feed intake in both groups of animals (р 0.05). Isolated rats began to consume the same amount of food as animals reared in the community after administration of 0.9% NaCl solution. At the same time, elements of bindge eating were observed in the study of the conditioned food test in satiated isolated rats, which did not appear after 1 week of intranasal administration of 20 g of BMS193885.
 CONCLUSIONS: The data obtained prove that rats reared in isolation can be considered as a potential model for binge eating, the basis for metabolic imbalance caused by individual housing in rodents. These considerations are of particular relevance when evaluating the effectiveness of drugs, diet, or other interventions for metabolic health and depressive disorders.

Social isolation in rats: Effects on animal welfare and molecular markers for neuroplasticity.

Early life stress compromises brain development and can contribute to the development of mental illnesses. A common animal model used to study different facets of psychiatric disorders is social isolation from early life on. In rats, this isolation can induce long-lasting alterations in molecular expression and in behavior. Since social isolation models severe psychiatric symptoms, it is to be expected that it affects the overall wellbeing of the animals. As also promoted by the 3Rs principle, though, it is pivotal to decrease the burden of laboratory animals by limiting the number of subjects (reduce, replace) and by improving the animals’ wellbeing (refine). The aim of this study was therefore to test possible refinement strategies such as resocialization and mere adult social isolation. We examined whether the alternatives still triggered the necessary phenotype while minimizing the stress load on the animals. Interestingly, we did not find reduced wellbeing-associated burrowing performance in isolated rats. The hyperactive phenotype seen in socially isolated animals was observed for rats undergoing the adult-only isolation, but resocializing ameliorated the locomotor abnormality. Isolation strongly affected markers of neuroplasticity in the prefrontal cortex independent of timing: mRNA levels of Arc, Bdnf and the pool of Bdnf transcripts with the 3’ long UTR were reduced in all groups. Bdnf splice variant IV expression was reduced in lifelong-isolated animals. Some of these deficits normalized after resocialization; likewise, exon VI Bdnf mRNA levels were reduced only in animals persistently isolated. Conversely, social deprivation did not affect the expression of Gad67 and Pvb, two GABAergic markers, whereas changes occurred in the expression of dopamine d1 and d2 receptors. As adult isolation was sufficient to trigger the hyperactive phenotype and impaired neuroplasticity in the prefrontal cortex, it could be a candidate for a refinement strategy for certain research questions. To fully grade the severity of post-weaning social isolation and the alternatives, adult isolation and resocialization, a more profound and multimodal assessment approach is necessary.

Effects of swimming exercise on social isolation-induced memory impairment and apoptosis in old rats.

Effect of swimming exercise on serotonin (5-hydroxytryptamine, 5-HT) expression and apoptosis in social isolation rats during old age was investigated. Rats in the old social isolation groups were housed alone per cage for 4 weeks. Rats in the swimming exercise groups were allowed to swim for 30 min once daily for 4 weeks. Morris water maze task determined spatial working memory and elevated plus maze test determined anxiety. Immunohistochemistry for tryptophan hydroxylase (TPH) and 5-HT in the dorsal raphe and for doublecortin (DCX) in the hippocampal dentate gyrus was conducted. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining in the hippocampal dentate gyrus was performed. Western blot analysis for Bax, Bcl-2, and cytochrome c in the hippocampus was conducted. Social isolation in rats of old age reduced spatial working memory and increased anxiety level. Swimming exercise enhanced spatial working memory and suppressed anxiety level. Social isolation in rats of old age inhibited TPH and 5-HT expression in dorsal rape. Swimming exercise increased TPH and 5-HT expression. Social isolation in rats of old age inhibited DCX-positive cells in the hippocampal dente gyrus. Swimming exercise increased DCX-positive cells. Social isolation in rats of old age increased TUNEL-positive cells, Bax and cytochrome c expression, and decreased Bcl-2 expression, which promoted apoptosis. Swimming exercise suppressed TUNEL-positive cells, Bax and cytochrome c expression, and increased Bcl-2 expression, which inhibited apoptosis. Swimming exercise improved 5-HT expression and suppressed apoptosis to alleviate anxiety and memory impairment during old age.

Treadmill exercise ameliorates social isolation-induced memory impairment by enhancing silent information regulator-1 expression in rats.

The effect of treadmill exercise on the social isolation-induced memory impairment in relation with the silent information regulator-1 (SIRT-1) was investigated. The rats in the control groups lived four in the stan-dard cages for 8 weeks. The rats in the social isolation groups lived alone in the small cages for 8 weeks. The rats in the treadmill exercise groups were subjected to run on a treadmill for 30 min once a day for 8 weeks. We used step-through avoidance test for short-term memory and Morris water maze task for spatial working memory. Immunohisto-chemistry for SIRT-1 and western blot analysis for Bax, Bcl-2, cleaved caspase-3, brain-derived neurotrophic factor (BDNF), and tropomyosin receptor kinase B (TrkB) were performed. The rats in the social isolation group showed a decrease in short-term memory and spatial working memory. Treadmill exercise alleviated short-term memory and spatial working memory in the social isolation rats. SIRT-1 expression in the hippocampus was decreased in the rats of social isolation group. Treadmill exercise increased SIRT-1 expression in the social isolation rats. Bax expression was increased, Bcl-2 expression was decreased, and cleaved caspase-3 expression in the hippocampus was increased in the rats of social isolation group. Treadmill exercise decreased Bax expression, increased Bcl-2 expression, and decreased cleaved caspase-3 expression in the social isolation rats. Hippocampal BDNF and TrkB expression was decreased in the rats of social isolation group. Treadmill exercise increased BDNF and TrkB expression in the social isolation rats.

Swimming exercise ameliorates mood disorder and memory impairment by enhancing neurogenesis, serotonin expression, and inhibiting apoptosis in social isolation rats during adolescence.

Social isolation during adolescence is associated with anxiety, depres-sion, and memory impairment. Exercise has been reported as a positive effect on brain function, especially hippocampus. The present study ex-amined the effect of swimming exercise on apoptosis, cell proliferation, and serotonin expression in social isolation rats during adolescence stage. Social isolation started at postnatal day 21 and continued for 6 weeks. The rats in the swimming group were forced to swim for 60 min once daily during 6 days per week for 6 consecutive weeks. The rats in the social isolation during adolescence showed anxiety, depression, short-term memory impairment. Social isolation facilitated apoptosis and inhibited cell proliferation and differentiation. Social isolation sup-pressed expression of serotonin, brain-derived neurotrophic factor, and tyrosine kinase B. Swimming exercise alleviated anxiety, depression, short-term impairment. Swimming exercise suppressed apoptosis, en-hanced neurogenesis, and increased serotonin expression. In our study, swimming exercise ameliorates mood disorder and memory impairment by enhancing neurogenesis and serotonin expression and inhibiting apoptosis in social isolation.

Linkage of Non-receptor Tyrosine Kinase Fyn to mGlu5 Receptors in Striatal Neurons in a Depression Model

The Src family kinase (SFK) is a subfamily of non-receptor tyrosine kinases. The SFK member Fyn is enriched at synaptic sites in the limbic reward circuit and plays a pivotal role in the regulation of glutamate receptors. In this study, we investigated changes in phosphorylation and function of the two key SFK members (Fyn and Src) and SFK interactions with a metabotropic glutamate (mGlu) receptor in the limbic striatum of adult rats in response to chronic passive stress, i.e., prolonged social isolation which is a pre-validated animal paradigm modeling depression in adulthood. In rats that showed typical anhedonic/depression-like behavior after chronic social isolation, phosphorylation of SFKs at a conserved and activation-associated autophosphorylation site (Y416) was not altered in the two subdivisions of the striatum, the nucleus accumbens and caudate putamen. The total level of phosphorylation and kinase activity of individual Fyn and Src immunopurified from the striatum also remained stable after social isolation. Noticeably, Fyn and Src were found to interact with a Gαq-coupled mGlu5 receptor in striatal neurons. The interaction of Fyn with mGlu5 receptors was selectively elevated in socially isolated rats. Moreover, social isolation induced an increase in surface expression of striatal mGlu5 receptors, which was reduced by an SFK inhibitor. These results indicate that Fyn interacts with mGlu5 receptors in striatal neurons. Adulthood social isolation in rats enhances the Fyn-mGlu5 interaction, which appears to be critical for the upregulation of surface mGlu5 receptor expression in striatal neurons.

Neural Mechanisms of Early-Life Social Stress as a Developmental Risk Factor for Severe Psychiatric Disorders

BackgroundTo explore the domain-general risk factor of early-life social stress in mental illness, rearing rodents in persistent postweaning social isolation has been established as a widely used animal model with translational relevance for neurodevelopmental psychiatric disorders such as schizophrenia. Although changes in resting-state brain connectivity are a transdiagnostic key finding in neurodevelopmental diseases, a characterization of imaging correlates elicited by early-life social stress is lacking. MethodsWe performed resting-state functional magnetic resonance imaging of postweaning social isolation rats (N = 23) 9 weeks after isolation. Addressing well-established transdiagnostic connectivity changes of psychiatric disorders, we focused on altered frontal and posterior connectivity using a seed-based approach. Then, we examined changes in regional network architecture and global topology using graph theoretical analysis. ResultsSeed-based analyses demonstrated reduced functional connectivity in frontal brain regions and increased functional connectivity in posterior brain regions of postweaning social isolation rats. Graph analyses revealed a shift of the regional architecture, characterized by loss of dominance of frontal regions and emergence of nonfrontal regions, correlating to our behavioral results, and a reduced modularity in isolation-reared rats. ConclusionsOur result of functional connectivity alterations in the frontal brain supports previous investigations postulating social neural circuits, including prefrontal brain regions, as key pathways for risk for mental disorders arising through social stressors. We extend this knowledge by demonstrating more widespread changes of brain network organization elicited by early-life social stress, namely a shift of hubness and dysmodularity. Our results highly resemble core alterations in neurodevelopmental psychiatric disorders such as schizophrenia, autism, and attention-deficit/hyperactivity disorder in humans.

Chronic Treatment with Fluoxetine or Clozapine of Socially Isolated Rats Prevents Subsector-Specific Reduction of Parvalbumin Immunoreactive Cells in the Hippocampus

The dysfunction of parvalbumin-positive (PV+) interneurons, the most abundant type of hippocampal GABAergic inhibitory interneuron, has been implicated in mood disorders. We recently reported that adult male Wistar rats exposed to three weeks of social isolation show depressive- and anxiety-like behaviors and a reduced number of PV+ interneurons in all hippocampal subregions. As GABA neurotransmission has been proposed as a potential therapeutic target of antidepressant and antipsychotic medications, we examined whether treatment with the antidepressant fluoxetine (Flx) (15 mg/kg/day) or the antipsychotic clozapine (Clz) (20 mg/kg/day) during three weeks of social isolation in rats offered protection from the isolation stress-induced reduction in the number of PV+ interneurons in hippocampal subregions. Using immunofluorescence analysis, we revealed that both chronic Flx and Clz partially prevented the isolation-induced changes. Flx prevented the reduction in the number of PV+ interneurons in the CA2, CA3, without affecting the CA1 and dentate gyrus DG areas, whereas Clz prevented this decrement in the CA2, CA3 and DG regions but not in CA1 areas. Moreover, Flx increased the number of PV+ interneurons in CA1 in control animals. These findings suggest that chronic administration of Flx or Clz may offer partial protection from social isolation stress via modulation of the hippocampal GABAergic system.