Impact of chronic lithium treatment on brain oxidative stress and anxiety-like behaviors in rats: Dose-dependent effects.

Lithium (Li) is a mood-stabilizing drug. Although one of the potential mechanisms underlying the neuroprotective effects of lithium is related to its antioxidative effect, its mechanisms of action are not fully understood. Herein we aimed to investigate the impact of varied dosages of long-term lithium therapy on oxidative stress parameters in the brains of healthy rats, and on anxiety-like behaviors, and whether any changes in behavior can be attributed to modifications in oxidative stress levels within the brain. Thirty-two adult Wistar albino male rats were randomly assigned to four treatment groups. While the control (C) group was fed with a standard diet, low Li (1.4 g/kg/diet), moderate Li (1.8 g/kg/diet), and high Li (2.2 g/kg/diet) groups were fed with lithium bicarbonate (Li2CO3) for 30 days. Malondialdehyde increased, while superoxide dismutase and catalase levels decreased in the brains of the high Li group animals. In addition, anxiety-like behaviors of animals increased in the high Li group considering fewer entries to and less time spent in the open arms of the elevated plus maze test. Our findings underscore the potential adverse effects of prolonged lithium treatment, especially at doses approaching the upper therapeutic range. The induction of toxicity, manifested through heightened oxidative stress, appears to be a key mechanism contributing to the observed increase in anxiety-like behaviors. Consequently, caution is warranted when considering extended lithium therapy at higher doses, emphasizing the need for further research to delineate the precise mechanisms underlying these effects and to inform safer therapeutic practices.

Physiological and behavioral contagion/buffering effects of chronic unpredictable stress in a socially enriched environment: A preliminary study.

Rodents are sensitive to the emotional state of conspecifics. While the presence of affiliative social partners mitigates the physiological response to stressors (buffering), the partners of stressed individuals show behavioral and endocrine changes indicating that stress parameters can be transmitted across the group members (contagion). In this study, we investigated the social contagion/buffering phenomena in behavior and neuroendocrine mechanisms after exposure to chronic stress, in groups of rats living in the PhenoWorld (PhW). Three groups were tested (8 stressed rats, 8 unstressed rats, and a mixed group with 4 and 4) and these were analyzed under 4 conditions: stressed (pure stress group, n = 8), unstressed (naive control group, n = 8), stressed from mixed group (stressed companion group, n = 8), unstressed from mixed group (unstressed companion group, n = 8. While naive control animals remained undisturbed, pure stress group animals were all exposed to stress. Half of the animals under the mixed-treatment condition were exposed to stress (stressed companion group) and cohabitated with their unstressed partners (unstressed companion group). We confirmed the well-established chronic unpredictable stress (CUS) effects in physiological, behavioral, and neuroendocrine endpoints; body weight gain, open arm entries and time in EPM, and oxytocin receptor expression levels in the amygdala decreased by stress exposure, whereas adrenal weight was increased by stress. Furthermore, we found that playing, rearing and solitary resting behaviors decreased, whereas huddling behavior increased by CUS. In addition, we detected significant increases (stress-buffering) in body weight gain and huddling behaviors between pure stress and stress companion animals, and significant stress contagion effects in emotional behavior and oxytocin receptor expression levels between naive control and control companion groups. Hence, we demonstrate buffering and contagion effects were evident in physiological parameters, emotional behaviors, and social home-cage behaviors of rats and we suggest a possible mediation of these effects by oxytocin neurotransmission. In conclusion, the results herein suggest that the stress status of animals living in the same housing environment influences the behavior of the group.

Home-cage behavior is impacted by stress exposure in rats.

Being social animals, rats exhibit a range of social behaviors that help them build social bonds and maintain group cohesion. Behavior is influenced by multiple factors, including stress exposure, and the expression of the impact of stress on both social and non-social behaviors may also be affected by the living conditions of rats. In this study, we explored the physiological and behavioral effects of chronic unpredictable stress on group-housed rats in the PhenoWorld (PhW), a socially and physically enriched environment closer to real-life conditions. Two independent experiments were performed: one in the control condition (PhW control, n = 8) and one in the stress condition (PhW stress, n = 8). Control animals remained undisturbed except for cage cleaning and daily handling procedures. Stress group animals were all exposed to chronic unpredictable stress. Data confirm that stress exposure triggers anxiety-like behavior in the PhW. In terms of home-cage behaviors, we found that stress affects social behaviors (by decreased playing and increased huddling behaviors) and non-social behaviors (as shown by the decrease in rearing and walking behaviors). These results are of relevance to expand our knowledge on the influence of stress on social and non-social behaviors, which are of importance to understand better species-typical behaviors.

The effects of environmental enrichment and transport stress on the weights of lymphoid organs, cell-mediated immune response, heterophil functions and antibody production in laying hens.

The effects of environmental enrichment and transport stress on the immune system were investigated in laying hens. A total of 48 1-day-old chickens were used, half of the chickens were reared in conventional cages (RCC) and the rest in enriched cages (REC). Transport stress was applied in the 17th week. Liver weight decreased, spleen and bursa of Fabricius weights, white blood cell count, CD4+ and CD8+ cell proportions increased due to the transport. Environmental enrichment significantly increased antibody production and tended to increase monocyte percentage and CD8+ cell proportion. The effect of transport on, heterophil (H) and lymphocyte (L) percentages was not significant in RCC chickens. While heterophil percentage and H:L ratio increased, lymphocyte percentage decreased in REC chickens subjected to transport. Transport stress increased heterophil functions both in REC and RCC chickens, but the increase was higher in REC hens than in RCC hens. In conclusion, although environmental enrichment did not neutralize the effect of transport on lymphoid organs, it activated the non-specific immune system, cellular and the humoral branches of the specific immune system by increasing heterophil functions, CD8+ cells and antibody production, respectively. Therefore, environmental enrichment suggested for improving animal welfare may also be beneficial to improve the immune system of birds exposed to stress.

The effect of furnished cages on the immune response of laying hens under social stress.

The aim of the study was to examine the effects of cage furnishing and social stress on some lymphoid organ weight and innate, cell-mediated, and humoral immune responses in laying hens. Sixty-four chickens were used. The chickens were divided into 2 groups; one of the groups was reared in furnished cages (RFC) and the other was reared in conventional cages (RCC). In wk 17, social stress was applied. Heterophil and lymphocyte percentages; liver, spleen, thymus, and bursa of Fabricius weights; phagocytic activity; oxidative burst and chemotaxic activity of heterophil; CD4+ and CD8+ cell proportions; and antibody production were measured. The effect of rearing methods was significant on heterophil, lymphocyte percentage, heterophil/lymphocyte (H/L) ratio, and antibody production. Heterophil percentage and H/L ratio were lower (P=0.001, P=0.001, respectively), and antibody production was higher (P=0.003) in RFC hens compared to RCC hens. The main effect of social stress was also significant on heterophil, lymphocyte percentages, and H/L ratio. Heterophil percentage was higher (P=0.049); H/L ratio tended to be higher (P=0.068); and lymphocyte percentage tended to be lower (P=0.072) due to stress. In addition, thymus and bursa of Fabricius weights tended to be lower (P=0.073 and P=0.074, respectively) in stressed hens. There were significant interactions between rearing methods and social stress on oxidative burst, chemotaxic activity, and CD4+ and CD8+ proportion (P=0.001, P=0.004, P=0.054, and P=0.001, respectively). These parameters were significantly higher in RFC hens, when they were exposed to stress. On the other hand, they did not differ in RCC or unstressed RFC hens. These results indicated that cage furnishing positively affected heterophil functions, CD4+ and CD8+ cell proportions, and antibody production. Therefore, we suggest that cage furnishing, which is recommended for improving the welfare of animals, is also beneficial for improving the immune response of hens under the stress condition.

Noise stress changes mRNA expressions of corticotropin-releasing hormone, its receptors in amygdala, and anxiety-related behaviors.

Noise is a psychological, environmental stressor that activates limbic sites in the brain. Limbic sites such as the amygdala and the amygdaloid corticotropin-releasing hormone (CRH) system play an important role in integrating stress response. We investigated the association between noise exposures, CRH-related molecules in the amygdala, and behavioral alterations. In total 54 Sprague-Dawley rats were divided into the following three groups: Control (CON), acute noise exposure (ANE), and chronic noise exposure (CNE). The ANE group was exposed to 100 dB white noise only once in 4 h and the CNE group was exposed to the same for 4 h per day for 30 days. Expression profiles of CRH and its receptors CRH-R1 and CRH-R2 were analyzed by quantitative real-time polymerase chain reaction (qPCR). The same stress procedure was applied to the ANE and CNE groups for behavior testing. The anxiety responses of the animals after acute and chronic stress exposure were measured in the defensive withdrawal test. CNE upregulated CRH and CRH-R1 mRNA levels but downregulated CRH-R2 mRNA levels. ANE led to a decrease in both CRH-R1 and CRH-R2 expression. In the defensive withdrawal test, while the ANE increased, CNE reduced anxiety-like behaviors. The present study shows that the exposure of rats to white noise (100 dB) leads to behavioral alterations and molecule-specific changes in the CRH system. Behavioral alterations can be related to these molecular changes in the amygdala.

Transmission of stress between cagemates: a study in rats.

The neuroendocrine responses triggered by stressors cause significant behavioral changes in animals. Considering the continuous behavioral interaction between social animals, it would be reasonable to suggest that the aforementioned behavioral changes can lead to transmission of stress between individuals. In the present study the aim is to investigate the outcomes of the behavioral interaction between stressed and unstressed animals housed together. A total of 28 adult male Wistar rats were used in the study. The animals were randomly allocated to four groups. Two of the groups were exposed to white noise stress in a period of 15days, while the other two groups remained unstressed. One of the stress exposed groups served as the stress control (SC) group and one of the non-stressed groups served as the reference value (RV) group. The remaining two groups were transmission groups. Every two animals of the non-stressed transmission group (TC) have been housed with two other animals of the stress exposed transmission group (TS) during the experimental period. After the stress exposure period, six animals from each group were subjected to behavioral assessment in an elevated plus maze (EPM), and subsequently, their cortisol levels were determined. White noise exposure of animals in the SC group induced a stress response indicated by an 1.8 fold increase of plasma cortisol level compared to the RV group (2.11±0.43 and 1.16±0,02, respectively). The transmission groups (TS and TC) entered the open arms more frequently and spent more time in open arms compared to the RV group. White noise exposure caused a stress response characterized by an elevation of cortisol level in rats. The gradual decrease of cortisol level from the SC towards the RV group may be interpreted as an evidence supporting the hypothesis of stress-transmission between cagemates. The moderate stress levels of the transmission groups, but not low and high levels of the SC and RV groups, decreased the anxiety-like behavior, which indicates an inverted U-shaped relationship between stress levels and anxiolytic effectiveness.

Long-term aspirin pretreatment in the prevention of cerulein-induced acute pancreatitis in rats.

AIM: To investigate the effects of long term pretreatment with low-, medium- and high-dose aspirin (acetylsalicylic acid, ASA) on a model of acute pancreatitis (AP) induced in rats. METHODS: Forty male Wistar rats were used. Three experimental groups, each consisting of eight animals, received low- (5 mg/kg per day), medium- (150 mg/kg per day) and high-dose (350 mg/kg per day) ASA in supplemented pellet chow for 100 d. Eight animals, serving as the AP-control group, and another eight, serving as reference value (RV) group, were fed with standard pellet chow for the same period. After pretreatment, AP was induced in the experimental animals by intraperitoneal administration of cerulein (2 × 50 µg/kg), while the RV group received saline in the same way. Twelve hours after the second injection, the animals were sacrificed. Pancreatic tissue and plasma samples were collected. One part of the collected pancreatic tissues was used for histopathological evaluation, and the remaining portion was homogenized. Cytokine levels [tumor necrosis factor, interleukin (IL)-1ß, IL-6], hemogram parameters, biochemical parameters (amylase and lipase), nuclear factor-κB, aspirin triggered lipoxins and parameters related to the antioxidant system (malondialdehyde, nitric oxide, hemeoxygenase-1, catalase and superoxide dismutase) were measured. RESULTS: Cerulein administration induced mild pancreatitis, characterized by interstitial edema (total histopathological score of 5.88 ± 0.44 vs 0.25 ± 0.16, P < 0.001). Subsequent pancreatic tissue damage resulted in an increase in amylase (2829.71 ± 772.48 vs 984.57 ± 49.22 U/L, P = 0.001) and lipase (110.14 ± 75.84 U/L vs 4.71 ± 0.78 U/L, P < 0.001) in plasma, and leucocytes (6.89 ± 0.48 vs 4.36 ± 0.23, P = 0.001) in peripheral blood. Cytokines, IL-1ß (18.81 ± 2.55 pg/µg vs 6.65 ± 0.24 pg/µg, P = 0.002) and IL-6 (14.62 ± 1.98 pg/µg vs 9.09 ± 1.36 pg/µg, P = 0.04) in pancreatic tissue also increased. Aspirin pretreatment reduced the increase in the aforementioned parameters to a certain degree and partially improved the histopathological alterations caused by cerulein. No evidence of side effects related to chronic ASA administration (e.g., inflammation or bleeding) was observed in the gastrointestinal tract in macroscopic and histopathological examination. CONCLUSION: Long term ASA pretreatment could prevent and/or ameliorate certain hematological, serological and histological alterations caused by cerulein-induced AP.