Effects of animal care procedures on plasma corticosterone levels in group-housed mice during the nocturnal active phase

Effects of more natural housing conditions on the muscular and skeletal characteristics of female C57BL/6J mice

BACKGROUND

Enrichment of home cages in laboratory experiments offers clear advantages, but has been criticized in some respects. First, there is a lack of definition, which makes methodological uniformity difficult. Second, there is concern that the enrichment of home cages may increase the variance of results in experiments. Here, the influence of more natural housing conditions on physiological parameters of female C57BL/6J mice was investigated from an animal welfare point of view. For this purpose, the animals were kept in three different housing conditions: conventional cage housing, enriched housing and the semi naturalistic environment. The focus was on musculoskeletal changes after long-term environmental enrichment.

RESULTS

The housing conditions had a long-term effect on the body weight of the test animals. The more complex and natural the home cage, the heavier the animals. This was associated with increased adipose deposits in the animals. There were no significant changes in muscle and bone characteristics except for single clues (femur diameter, bone resorption marker CTX-1). Additionally, the animals in the semi naturalistic environment (SNE) were found to have the fewest bone anomalies. Housing in the SNE appears to have the least effect on stress hormone concentrations. The lowest oxygen uptake was observed in enriched cage housing.

CONCLUSIONS

Despite increasing values, observed body weights were in the normal and strain-typical range. Overall, musculoskeletal parameters were slightly improved and age-related effects appear to have been attenuated. The variances in the results were not increased by more natural housing. This confirms the suitability of the applied housing conditions to ensure and increase animal welfare in laboratory experiments.

Light and Cognition: Roles for Circadian Rhythms, Sleep, and Arousal

Light exerts a wide range of effects on mammalian physiology and behavior. As well as synchronizing circadian rhythms to the external environment, light has been shown to modulate autonomic and neuroendocrine responses as well as regulating sleep and influencing cognitive processes such as attention, arousal, and performance. The last two decades have seen major advances in our understanding of the retinal photoreceptors that mediate these non-image forming responses to light, as well as the neural pathways and molecular mechanisms by which circadian rhythms are generated and entrained to the external light/dark (LD) cycle. By contrast, our understanding of the mechanisms by which lighting influences cognitive processes is more equivocal. The effects of light on different cognitive processes are complex. As well as the direct effects of light on alertness, indirect effects may also occur due to disrupted circadian entrainment. Despite the widespread use of disrupted LD cycles to study the role circadian rhythms on cognition, the different experimental protocols used have subtly different effects on circadian function which are not always comparable. Moreover, these protocols will also disrupt sleep and alter physiological arousal, both of which are known to modulate cognition. Studies have used different assays that are dependent on different cognitive and sensory processes, which may also contribute to their variable findings. Here, we propose that studies addressing the effects of different lighting conditions on cognitive processes must also account for their effects on circadian rhythms, sleep, and arousal if we are to fully understand the physiological basis of these responses.

Ethanol Reversal of Tolerance to the Respiratory Depressant Effects of Morphine

Opioids are the most common drugs associated with unintentional drug overdose. Death results from respiratory depression. Prolonged use of opioids results in the development of tolerance but the degree of tolerance is thought to vary between different effects of the drugs. Many opioid addicts regularly consume alcohol (ethanol), and post-mortem analyses of opioid overdose deaths have revealed an inverse correlation between blood morphine and ethanol levels. In the present study, we determined whether ethanol reduced tolerance to the respiratory depressant effects of opioids. Mice were treated with opioids (morphine, methadone, or buprenorphine) for up to 6 days. Respiration was measured in freely moving animals breathing 5% CO2 in air in plethysmograph chambers. Antinociception (analgesia) was measured as the latency to remove the tail from a thermal stimulus. Opioid tolerance was assessed by measuring the response to a challenge dose of morphine (10 mg/kg i.p.). Tolerance developed to the respiratory depressant effect of morphine but at a slower rate than tolerance to its antinociceptive effect. A low dose of ethanol (0.3 mg/kg) alone did not depress respiration but in prolonged morphine-treated animals respiratory depression was observed when ethanol was co-administered with the morphine challenge. Ethanol did not alter the brain levels of morphine. In contrast, in methadone- or buprenorphine-treated animals no respiratory depression was observed when ethanol was co-administered along with the morphine challenge. As heroin is converted to morphine in man, selective reversal of morphine tolerance by ethanol may be a contributory factor in heroin overdose deaths.

Glucocorticoid receptor knockdown decreases the antioxidant protection of B16 melanoma cells: an endocrine system-related mechanism that compromises metastatic cell resistance to vascular endothelium-induced tumor cytotoxicity

We previously reported an interorgan system in which stress-related hormones (corticosterone and noradrenaline), interleukin-6, and glutathione (GSH) coordinately regulate metastatic growth of highly aggressive B16-F10 melanoma cells. Corticosterone, at levels measured in tumor-bearing mice, also induces apoptotic cell death in metastatic cells with low GSH content. In the present study we explored the potential role of glucocorticoids in the regulation of metastatic cell death/survival during the early stages of organ invasion. Glucocorticoid receptor (GCR) knockdown decreased the expression and activity of γ-glutamylcysteine synthetase (γ-GCS), the rate-limiting step in GSH synthesis, in metastatic cells in vivo independent of the tumor location (liver, lung, or subcutaneous). The decrease in γ-GCS activity was associated with lower intracellular GSH levels. Nrf2- and p53-dependent down-regulation of γ-GCS was associated with a decrease in the activities of superoxide dismutase 1 and 2, catalase, glutathione peroxidase, and glutathione reductase, but not of the O₂⁻-generating NADPH oxidase. The GCR knockdown-induced decrease in antioxidant protection caused a drastic decrease in the survival of metastatic cells during their interaction with endothelial cells, both in vitro and in vivo; only 10% of cancer cells attached to the endothelium survived compared to 90% survival observed in the controls. This very low rate of metastatic cell survival was partially increased (up to 52%) in vivo by inoculating B16-F10 cells preloaded with GSH ester, which enters the cell and delivers free GSH. Taken together, our results indicate that glucocorticoid signaling influences the survival of metastatic cells during their interaction with the vascular endothelium.

Age and isolation influence steroids release and chemical signaling in male mice

Social interactions in mice involve olfactory signals, which convey information about the emitter. In turn, the mouse social and physiological status may modify the release of chemical cues. In this study, the influences of age and social isolation on the endocrine response and the release of chemical signals were investigated in male CD1 mice, allocated into four groups: Young Isolated (from weaning till 60days; N=6), Adult Isolated (till 180days; N=6), Young Grouped (6 mice/cage; till 60days; N=18), Adult Grouped (6 mice/cage; till 180days; N=18). Mice were transferred in a clean cage to observe the micturition pattern and then sacrificed. Body and organs weights, serum testosterone, dehydroepiandrosterone, corticosterone and the ratio Major Urinary Protein/creatinine were measured. Urinary volatile molecules potentially involved in pheromonal communication were identified. Androgen secretion was greater in isolated mice (P<0.05), suggesting a greater reactivity of the Hypothalamic-Pituitary-Gonadal axis. Grouped mice presented a higher degree of adrenal activity, and young mice showed a higher serum corticosterone (P<0.05) suggesting a greater stimulation of the Hypothalamic-Pituitary-Adrenal axis. The micturition pattern typical of dominant male, consisting in voiding numerous droplets, was observed in Young Isolated mice only, which showed a higher protein/creatinine ratio (P<0.05). Urinary 2-s-butyl-thiazoline was higher in both Young and Adult Isolated mice (P<0.005). Young Isolated mice showed the most prominent difference in both micturition pattern and potentially active substance emission, while long term isolation resulted in a less extreme phenotype; therefore social isolation had a higher impact on young mice hormone and pheromone release.

Stress hormones promote growth of B16-F10 melanoma metastases: an interleukin 6- and glutathione-dependent mechanism

BACKGROUND

Interleukin (IL)-6 (mainly of tumor origin) activates glutathione (GSH) release from hepatocytes and its interorgan transport to B16-F10 melanoma metastatic foci. We studied if this capacity to overproduce IL-6 is regulated by cancer cell-independent mechanisms.

METHODS

Murine B16-F10 melanoma cells were cultured, transfected with red fluorescent protein, injected i.v. into syngenic C57BL/6J mice to generate lung and liver metastases, and isolated from metastatic foci using high-performance cell sorting. Stress hormones and IL-6 levels were measured by ELISA, and CRH expression in the brain by in situ hybridization. DNA binding activity of NF-κB, CREB, AP-1, and NF-IL-6 was measured using specific transcription factor assay kits. IL-6 expression was measured by RT-PCR, and silencing was achieved by transfection of anti-IL-6 small interfering RNA. GSH was determined by HPLC. Cell death analysis was distinguished using fluorescence microscopy, TUNEL labeling, and flow cytometry techniques. Statistical analyses were performed using Student's t test.

RESULTS

Plasma levels of stress-related hormones (adrenocorticotropin hormone, corticosterone, and noradrenaline) increased, following a circadian pattern and as compared to non-tumor controls, in mice bearing B16-F10 lung or liver metastases. Corticosterone and noradrenaline, at pathophysiological levels, increased expression and secretion of IL-6 in B16-F10 cells in vitro. Corticosterone- and noradrenaline-induced transcriptional up-regulation of IL-6 gene involves changes in the DNA binding activity of nuclear factor-κB, cAMP response element-binding protein, activator protein-1, and nuclear factor for IL-6. In vivo inoculation of B16-F10 cells transfected with anti-IL-6-siRNA, treatment with a glucocorticoid receptor blocker (RU-486) or with a β-adrenoceptor blocker (propranolol), increased hepatic GSH whereas decreased plasma IL-6 levels and metastatic growth. Corticosterone, but not NORA, also induced apoptotic cell death in metastatic cells with low GSH content.

CONCLUSIONS

Our results describe an interorgan system where stress-related hormones, IL-6, and GSH coordinately regulate metastases growth.

Differences in micronucleus induction in peripheral blood reticulocytes of mice exposed to N-ethyl-N-nitrosourea at light and dark dosing times

Mammals, including human beings, have a circadian clock system to regulate behavioral and physiological processes. In this study, we investigated the effect of dosing time on micronucleus induction in the bone marrow by evaluating the frequencies of micronucleated peripheral reticulocytes (MNRETs) in mice exposed to N-ethyl-N-nitrosourea (ENU) to assess any difference in genotoxic sensitivity to chemicals between light and dark periods (inactive phase for rodents and active phase for rodents). Male C3H/He mice were treated intraperitoneally with ENU (12.5 or 25 mg/kg body weight) at zeitgeber time (ZT) 3 in the light period or ZT15 in the dark period, and then the time courses of the frequencies of the MNRETs were determined. The frequencies of the MNRETs induced by ENU increased time-dependently and peaked at 48 hr after treatment for ZT3 and ZT15, and were obviously higher in the ZT15 treatment group than the ZT3 treatment group. The MNRETs were measured at 48 hr after treatment with ENU (25 mg/kg body weight) at various dosing times (ZT0, 3, 6, 12, 15 and 18). The frequencies of the MNRETs in mice treated at ZT0, 15 and 18 were significantly higher than those in mice treated at ZT3, 6 and 12. These results suggest that genotoxic sensitivity to chemicals in mouse bone marrow is different between light and dark periods maybe due to different biological responses (detoxification, cell cycle, DNA repair, etc.) related to circadian rhythms.

The acute glucocorticoid stress response does not differentiate between rewarding and aversive social stimuli in rats

The mere presence of elevated plasma levels of corticosterone is generally regarded as evidence of compromised well-being. However, environmental stimuli do not necessarily need to be of a noxious or adverse nature to elicit activation of the stress response systems. In the present study, the physiological and neuroendocrine responses to repeated social stimuli that can be regarded as emotional opposites, i.e. social defeat and sexual behavior, were compared. Similar corticosterone responses were observed in animals confronted for the first time with either a highly aggressive male intruder or a receptive female, but a decrease was noticed in defeated rats tested during a third interaction. Only if animals are being physically attacked does the corticosterone response remain similar to the one observed during sexual behavior. In addition, the number of activated cells in the parvocellular hypothalamic paraventricular nucleus, as visualized by c-Fos immunocytochemistry, shows no difference between rats 1h after the third exposure to defeat or sex. Finally, biotelemetric recordings of heart rate, body temperature and locomotor activity show a robust response to both social stimuli that is generally, however, higher in animals being confronted with a receptive female. The data clearly indicate that acute plasma corticosterone levels are not reflecting the emotional valence of a salient stimulus. The magnitude of the response seems to be a direct reflection of the behavioral activity and hence of the metabolic requirements of activated tissues. Next to its direct metabolic role, acute increases in plasma corticosterone will have neurobiological and behavioral effects that largely depend on the neural circuitry that is activated by the stimulus that triggered its release.