Coping with stress: The Impact of the Hypothalamus Pituitary Adrenal (HPA) System and Neurotrophic Circuits in the Learned Helplessness Model of Depression

Animal models currently represent a viable route for gaining further insights into the mechanisms involved in the pathogenesis of particular diseases. Depression, in this respect, constitutes a major challenge since the characterization of disease-specific traits is complicated due to the multifactorial nature of the disorder. The understanding of diverse factors, e.g. neurotrophic circuits and the role of the HPA axis, which have to be considered in the pathophysiology of the disease represent a major target of behavioural animal models of depression. Working on a model such as Learned Helplessness, consequently requires careful consideration of modulating aspects to ensure representative results. This work aims at elucidating the role of recently postulated target genes of depression as well as the impact of potential distorting factors, such as housing conditions of the experimental animals. To guarantee a specific readout, which permits concrete statements regarding the role of particular target genes like BDNF, CREB, and GR, we compared both, the effects of different social and as environmental factors with regard to general and Helplessness-specific effects on behaviour. Furthermore, we confirmed the model by a pharmacological validation, simultaneously monitoring effects of the obligatory handling procedure. In studies of depression and emotionality it is important to establish standardized protocols, involving the animal’s environment, to be able to precisely assess potential sources of stress and exclude artefacts. The design and modification of animal models like the Learned Helplessness subsequently bears the advantage of not only detecting potential genetic aspects by investigating mice carrying mutations of particular target genes, e.g. the glucocorticoid receptor, in which significant differences with regard to helpless behaviour and further depressive-like parameters became evident, but also to exploit fundamental causes of depressive-like phenotypes such as stress effects. The detailed evaluation of the Learned Helplessness in mice as a model of depression suggests it as a valuable instrument to investigate mouse models for depression, like GR heterozygous animals, in which the behavioural phenotype was associated with depressive-like characteristics such as a decrease of BDNF protein and relevant physiological parameters which mimick stress, i.e. a depression-typical Dex/CRH Test and elevated corticosterone levels after restraint stress

Marble burying as compulsive behaviors in male and female mice

Marble burying is considered an, albeit controversial, animal model of the compulsive like behaviors of obsessive‑compulsive disorder (OCD). Hallmark features of OCD patients are similarities and, more prominent, differences from anxiety disorders, e.g., the absence of sex differences and resistance to spontaneous remission. We report an experiment on marble burying by male and female C57/BL6/N mice. Animals were administered either the classic anxiolytic drug, diazepam, that targets the GABA receptor or a "pure" inhibitor of the serotonin transporter, escitalopram, that has been reported to be particularly effective in OCD. A burying paradigm that more precisely mimics the human condition was used, e.g., testing in the home environment, chronic drug exposure and acknowledging individual differences by pre‑selecting for high marble burying. Results were that there were no sex differences in groups treated with drugs or in control mice. Both diazepam and escitalopram decreased numbers of marbles buried compared to vehicle‑only controls in the absence of correlated changes in anxiety. Diazepam, however, was more effective than escitalopram in suppressing MB. The conclusion is that along with serotonin, GABA is involved in regulating compulsive behaviors. The marble burying paradigm may prove more useful for pharmacological drugs tests of impulsivity or attention deficit because of the involvement of serotonin and GABA in both disorders

Effect of Population Heterogenization on the Reproducibility of Mouse Behavior : A Multi-Laboratory Study

Peer reviewe

Differences in Mouse Maternal Care Behavior – Is There a Genetic Impact of the Glucocorticoid Receptor?

Depressive episodes are frequently preceded by stressful life events. Evidence from genetic association studies suggests a role for the glucocorticoid receptor (GR), an essential element in the regulation of stress responses, in the pathophysiology of the disorder. Since the stress response system is affected by pregnancy and postpartum-associated changes, it has also been implicated in the pathophysiology of postpartum depression. Using a 2×2 factorial design, we investigated whether a heterozygous deletion of GR would influence maternal care behavior in C57BL/6 and Balb/c mice, two inbred strains known to display qualitative differences in this behavior. Behavioral observation was carried out between postnatal days 1 and 7, followed by a pup retrieval test on postnatal days 7 or 8. While previously noted inter-strain differences were confirmed for different manifestations of caring behavior, self-maintenance and neglecting behaviors as well as the pup retrieval test, no strain-independent effect of the GR mutation was noted. However, an interaction between GR genotype and licking/grooming behavior was observed: it was down-regulated in heterozygous C57BL/6 mice to the level recorded for Balb/c mice. Home cage observation poses minimal disturbance of the dam and her litter as compared to more invasive assessments of dams' emotional behavior. This might be a reason for the absence of any overall effects of the GR mutation, particularly since GR heterozygous animals display a depressive-like phenotype under stressful conditions only. Still, the subtle effect we observed may point towards a role of GR in postpartum affective disorders

Effect of three different forms of handling on the variation of aggression-associated parameters in individually and group-housed male C57BL/6NCrl mice.

Mice are social animals hence group-housing of mice is preferred over individual housing. However, aggression in group-housed male mice under laboratory housing conditions is a well-known problem leading to serious health issues, including injury or death. Therefore, group-housed mice are frequently separated for welfare reasons. In this study, we investigated the effect of 3 different handling methods (tail, forceps, tube) in 2 different housing conditions (single vs. group) on the variance of aggression-associated parameters in male C57BL/6NCrl mice over 8 weeks. Blood glucose concentration, body weight, body temperature, plus number and severity of bite wounds and barbering intensity in group-housed mice were recorded. An assessment of nest complexity was also performed weekly. Feces were collected in week 3 and 7 for analysis of corticosterone metabolites. We also monitored the level of aggression by recording the behavior of group-housed animals after weekly cage cleaning. An open field test followed by a social novel object test, a light/dark box test, a hotplate and a resident-intruder test were performed at the end of the 8-week handling period. Post-mortem, we assessed organ weights. We found that forceps-handled mice, independent of the housing condition, had significantly higher levels of stress-induced-hyperthermia and enhanced aggression after cage cleaning, and they performed worse in the nest complexity test. In addition, handling male mice by the tail seems to be most effective to reduce aggressiveness after transferring animals into new cages, thereby representing an appropriate refinement

Evaluation of Potential Sustainable Bedding Substrates Focusing on Preference, Behavior, and Stress Physiology in Rats—A Pilot Study

Ensuring optimal housing conditions for laboratory animals is a crucial prerequisite for high-quality and ethically justifiable in vivo science. In addition to guaranteeing animal welfare and promoting scientific validity, environmental sustainability is also increasingly gaining attention in laboratory animal facilities. Consequently, comprehensive management of such aspects is one of the core tasks of any research vivarium. Hygienic monitoring and adhering to standardized experimental protocols have been highlighted in the past; nevertheless, various environmental aspects of housing animals still need to be evaluated in greater depth. In this pilot study, we aimed at assessing the suitability of spelt and corncob as economical and ecologically friendly bedding substrates as compared with commonly used aspen wood chips. Therefore, following a descriptive study design, we examined the preferences of male and female Wistar rats for corncob and spelt under specific conditions. In addition, we evaluated potential effects on behavior, metabolism, and stress physiology. The type of bedding did not seem to influence behavior in the observed parameters but did have time- and sex-dependent effects on blood glucose. Furthermore, housing animals on spelt led to a significant reduction in food consumption, probably compensated for by the intake of spelt, and although it did not influence glucose levels, it may have certainly impacted the nutrient supply. Our descriptive pilot study, therefore, highlights the importance of a thorough condition-associated evaluation of even seemingly marginal environmental factors, when balancing potential cost-benefit advances in sustainability and questions of standardization and reproducibility of experimental protocols