Reorganization of Brain Networks as a Substrate of Resilience: An Analysis of Cytochrome c Oxidase Activity in Rats

Pro-resilient effects of environmental enrichment on social isolation: Behavioural and cytochrome c oxidase brain analysis in Wistar adult rats

The COVID-19 pandemic has underscored the impact of social isolation on mental well-being. This study aims to evaluate the emotional and cerebral consequences of social isolation and assess whether prior environmental enrichment can mitigate the adverse effects. For that purpose, four groups were established: Behaviour group (Beh), n=8, subjected to a 4 % sucrose consumption test and the elevated zero maze (EZM) to assess anhedonia and unconditioned anxiety; Social isolation (SI) + Behaviour group, n=8, subjected to 4 consecutive weeks of social isolation followed by the behavioural testing; Environmental enrichment: EE+SI + Behaviour group, n = 8, subjected to EE prior to SI followed by behavioural assessment; and Basal group (BG), n = 8, used to determine the baseline of cytochrome c-oxidase (CCO). After behavioural testing, brain tissue from the prefrontal cortex (PFC), dorsal and ventral hippocampus (vHIP), nucleus accumbens (NAc), and ventral tegmental area (VTA) were analysed for CCO activity. Results show that SI serves as a significant stressor, increasing anxiety and anhedonic responses in the SI group. However, pre-exposure to EE significantly reduced these responses. Regarding CCO activity, the SI group exhibited elevated levels across all brain regions compared to the EE+SI group. Moreover, the EE+SI group maintained CCO activity levels similar to those of the Basal group, suggesting that prior EE exposure mitigates the metabolic impact of social isolation across most brain regions, except for the vHIP. These results indicate that pre-exposure to an EE may buffer the adverse effects of SI, supporting enhanced resilience.

Synergistic impact of early-life stress and prenatal immune activation on spatial memory and oxidative metabolism in rat cortico-limbic networks

Early life exposure to immune activation and stress are critical factors involved in the development of mental and neurodevelopmental disorders in adulthood. This study explored the individual and combined effects of prenatal lipopolysaccharide-induced (LPS)-induced immune activation and postnatal maternal separation on cognitive performance and oxidative metabolism in male Wistar rats. Using a 2 × 2 factorial design, pregnant dams were exposed to LPS or saline on gestational day 15, and offspring underwent maternal separation from postnatal days 2-14. In adulthood, cognitive function was assessed using the Morris Water Maze, and regional brain energy metabolism was evaluated using quantitative histochemistry of cytochrome c oxidase (CCO) quantitative histochemistry in the prefrontal cortex, hippocampus, and retrosplenial cortex. Rats exposed to both stressors demonstrated significant impairments in spatial memory and cognitive flexibility, supporting the "two-hit" hypothesis of early adversity, which posits that early life exposure to an adverse environmental event (first hit) combined with subsequent exposure to stress during critical developmental periods (second hit) can significantly increase the risk of developing behavioral or neurodevelopmental disorders in adulthood. Accordingly, adult animals exposed to prenatal LPS and maternal separation showed prolonged escape latencies and decreased spatial memory retention during the behavioral tasks. Concurrently, CCO activity was markedly increased in all measured regions, reflecting heightened metabolic demands. These changes are consistent with impaired hippocampal-prefrontal-retrosplenial network integration and the underlying key processes involved in cognitive alterations such as memory or attention. This study underscores the synergistic effects of these environmental factors on cognitive and metabolic dysfunction, providing a translational model to better understand the etiology of neurodevelopmental disorders. The findings highlight the importance of addressing multiple interacting environmental factors in the context of early life adversity.

The disappointment centre of the brain gets exciting: a systematic review of habenula dysfunction in depression

BACKGROUND

The habenula is an epithalamic brain structure that acts as a neuroanatomical hub connecting the limbic forebrain to the major monoamine centres. Abnormal habenula activity is increasingly implicated in depression, with a surge in publications on this topic in the last 5 years. Direct activation of the habenula is sufficient to induce a depressive phenotype in rodents, suggesting a causative role in depression. However, the molecular basis of habenula dysfunction in depression remains elusive and it is unclear how the preclinical advancements translate to the clinical field.

METHODS

A systematic literature search was conducted following the PRISMA guidelines. The two search terms depress* and habenula* were applied across Scopus, Web of Science and PubMed databases. Studies eligible for inclusion must have examined the habenula in clinical cases of depression or preclinical models of depression and compared their measures to an appropriate control.

RESULTS

Preclinical studies (n = 63) measured markers of habenula activity (n = 16) and neuronal firing (n = 22), largely implicating habenula hyperactivity in depression. Neurotransmission was briefly explored (n = 15), suggesting imbalances within excitatory and inhibitory habenula signalling. Additional preclinical studies reported neuroconnectivity (n = 1), inflammatory (n = 3), genomic (n = 3) and circadian rhythm (n = 3) abnormalities. Seven preclinical studies (11%) included both males and females. From these, 5 studies (71%) reported a significant difference between the sexes in at least one habenula measure taken. Clinical studies (n = 24) reported abnormalities in habenula connectivity (n = 15), volume (n = 6) and molecular markers (n = 3). Clinical studies generally included male and female subjects (n = 16), however, few of these studies examined sex as a biological variable (n = 6).

CONCLUSIONS

Both preclinical and clinical evidence suggest the habenula is disrupted in depression. However, there are opportunities for sex-specific analyses across both areas. Preclinical evidence consistently suggests habenula hyperactivity as a primary driver for the development of depressive symptoms. Clinical studies support gross habenula abnormalities such as altered activation, connectivity, and volume, with emerging evidence of blood brain barrier dysfunction, however, progress is limited by a lack of detailed molecular analyses and limited imaging resolution.

Experimental Periodontitis Increases Anxious Behavior and Worsens Cognitive Aspects and Systemic Oxidative Stress in Wistar Rats

OBJECTIVES

Periodontitis (PD) has the potential to induce systemic changes that affect both physical and behavioral aspects. These alterations may be associated with changes in both the inflammatory profile and the oxidative stress status of individuals with PD. Therefore, we aimed to evaluate the effects of PD on oxidative stress, as well as on behavioral parameters and cognitive impairment, in a preclinical model.

MATERIAL AND METHODS

Twenty-four male Wistar rats were randomly assigned to PD and sham groups. PD was induced by the ligature protocol for 14 days. Behavioral tests were initiated on the 9th day of the experiment to evaluate anxious behavior and cognition (learning and memory). After euthanasia, oxidative stress was evaluated in the gums, blood, hippocampus, and amygdala. Alveolar bone loss, bone microstructure, and elemental compositions of the mandibular bone were also assessed.

RESULTS

PD increased alveolar bone loss, reduced the calcium and phosphorus content in the mandibular bone, and increased anxiety-like behavior and cognitive decline (p < 0.05). Furthermore, PD significantly affected the redox balance, as evidenced by increased total antioxidant capacity (TAC) in the gingiva and hippocampus (p < 0.05). It also led to increased lipid peroxidation in the gingiva and erythrocytes (p < 0.05), decreased antioxidant defenses in erythrocytes (superoxide dismutase) and the hippocampus (catalase), and increased antioxidant activity (catalase) in the amygdala (p < 0.05).

CONCLUSION

PD resulted in cognitive alterations, including impairments in spatial learning and memory, as well as increased anxious behavior, likely due to redox imbalance in rats.

Physical activity as a promoter of stress resilience: An analysis of behavioral effects and brain connectivity with cytochrome c-oxidase activity in adult male Wistar rats

Physical activity (PA) is very beneficial for physical and mental health. This study aims to examine the resilience-inducting effect of PA in adult male Wistar rats exposed to unpredictable chronic mild stress (UCMS). Furthermore, we analyzed the influence of PA on behavioral tasks and functional brain connectivity with cytochrome c oxidase technique. The cytochrome c oxidase (CCO) is a mitochondrial enzyme involved in oxidative phosphorylation and ATP generation. For this analysis, we included five groups: Basal (n = 10, to determine the basal level of brain activity), Behav (n = 15, subjected exclusively to behavioral tests), PA (n = 10, exposed to physical activity), UCMS (n = 15, subjected to a stress protocol) and PA + UCMS (n = 15, exposed to PA prior to stress). The UCMS protocol consisted of randomly presenting several different stressors over four consecutive weeks. We evaluated several behaviors of the Behav, UCMS, and PA + UCMS groups. This assessment includes the hedonic responses using the sucrose consumption task, unconditioned anxiety with the zero maze, and coping strategies assessed with the cat odor test. The UCMS group showed an anhedonia profile and increased anxiety compared with the other groups. Although in the exposure to cat odor test, the PA + UCMS remained for the same time in the cat odor compartment as the other groups, it did not approach the odor, showing that it detected the risk. This response is more adaptive than the responses of the UCMS and Behav groups. An exploratory analysis of the cerebral connections showed an increase in CCO activity in the UCMS group compared to the other groups. This overactivity was reduced in dorsal Cornu Ammonis 3(dCA3) by prior PA. In this region, PA + UCMS showed similar activity as the groups not subjected to chronic stress. Therefore, PA can prevent the harmful effects of chronic stress on dCA3.

Impact of environmental enrichment on the GABAergic neurons and glucocorticoid receptors in the hippocampus and nucleus accumbens of Wistar rats: pro-resilient effects

The unpredictable chronic mild stress (UCMS) model has been used to induce depressive-like symptoms in animal models. Our work aims to evaluate the impact of environmental enrichment on male Wistar rats in an animal model for depression. For this purpose, we aim to assess changes in GR and GABAergic (PV+) density in cerebral regions related to cognitive-affective processes associated with depressive disorder, such as the dorsal- ventral hippocampus and accumbens nuclei. Three groups of rats were used: UCMs (unpredictable chronic mild stress), EE+ UCMs (enrichment + stress) and CONT (behavioral tests only). Hedonic responses elicited by sucrose solution were examined by licking behavior analysis; the anxiety level was evaluated using the elevated zero maze and the forced swimming (passive coping) tests. The environmental enrichment reduced the effects of chronic stress, promoting greater resilience. Thus, the UCMs group showed an anhedonia response, more anxiety and immobility behavior than either the control or the EE+ UCMs groups. Regarding immunochemistry results, there was a reduction in GABAergic activity coupled with increased activation of GR in UCMs in the dorsal hippocampus, but there were no differences between groups in the ventral hippocampus. These results suggest environmental enrichment could enhance greater resilience, reducing the vulnerability of the subjects to develop disorders such as depression and anxiety.