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Rodents’ behavioural analysis can be influenced by several factors, including housing. The PhenoWorld (PhW) is an enriched housing and testing paradigm, which proved to be relevant for screening depressive-like behaviours in rats, being remarkably sensitive for hedonic behaviour. Herein, we assessed neuronal plasticity as a consequence of living in the PhW, by comparing the structure of the medial prefrontal cortex (mPFC) and the nucleus accumbens (NAc), two brain areas involved in the circuitry regulating motivation and reward. Our findings indicate that male rats living in the PhW display increased mPFC layer II volumes, as well as increased immature spine densities and total numbers in the mPFC pyramidal neurons. The NAc volumes and NAc medium spiny neurons branching tend also to be higher in animals experiencing the physical enrichment provided in the PhW, but significant differences were not found between animals living in PhW compared to animals living in standard cages (STD6). These results demonstrate that living in a more naturalistic complex environment, closer to real life experience, impacts on the structure of brain regions implicated in complex multidimensional disorders.

Human interaction and physical environmental factors are part of the stimuli presented to laboratory animals everyday, influencing their behaviour and physiology and contributing to their welfare. Certain environmental conditions and routine procedures in the animal facility might induce stress responses and when the animal is unable to maintain its homeostasis in the presence of a particular stressor, the animal's wellbeing is threatened. This review article summarizes several published studies on the impact of environmental factors such as light, noise, cage cleaning and in-house transport on welfare and stress of laboratory rats. The behaviour and physiological responses of laboratory rats to different environmental housing conditions and routine procedures are reviewed. Recommendations on the welfare of laboratory rats and refinements in experimental design are discussed and how these can influence and improve the quality of scientific data.

Modeling depression in animals has inherent complexities that are augmented by intrinsic difficulties to measure the characteristic features of the disorder. Herein, we describe the PhenoWorld (PhW), a new setting in which groups of six rats lived in an ethological enriched environment, and have their feeding, locomotor activity, sleeping and social behavior automatically monitored. A battery of emotional and cognitive tests was used to characterize the behavioral phenotype of animals living in the PhW and in standard conditions (in groups of six and two rats), after exposure to an unpredictable chronic mild stress paradigm (uCMS) and antidepressants. Data reveal that animals living in the PhW displayed similar, but more striking, behavioral differences when exposed to uCMS, such as increased behavioral despair shown in the forced swimming test, resting/sleep behavior disturbances and reduced social interactions. Moreover, several PhW-cage behaviors, such as spontaneous will to go for food or exercise in running wheels, proved to be sensitive indicators of depressive-like behavior. In summary, this new ethological enriched paradigm adds significant discriminative power to screen depressive-like behavior, in particularly rodent's hedonic behavior.

The use of group-housed rodents in many fields of biomedical research imposes a need to identify individuals in a cage. Few studies have been designed to assess possible negative effects of identification methods of newborn mice on their development and wellbeing. In the present study, three different identification methods were applied to newborn C57BL/6J mice on postnatal day (pnd) 5 (toe clipping, toe tattoo ink puncture and subcutaneous implantation of a small transponder). All identification methods used proved to be effective for long-term marking of individual animals. Newborn mice showed the least reaction to toe clipping followed by toe tattoo ink puncture and transponder implantation was the most distressful individual identification procedure in newborn mice. Importantly, clipped toe tissue proved to be enough for genotyping purposes. No overall consistent differences in somatic and neurological reflex development during the postnatal period were shown as a result of the newborn individual identification procedures used. Further, none of the methods interfered significantly with the adult animals' general normal behaviour (e.g. ability to move, grasp, climb) and sensory-motor functions as assessed with a simplified SHIRPA battery of tests, as well as Rotarod and Elevated Plus Maze tests. Postmortem thymus and adrenal gland weights gave no indication of chronic stress as a consequence of the identification method. We conclude that toe clipping might even be advisable in newborn mice at a very young age, when genotyping is needed. Toe tattoo ink puncture is also a good identification method for newborn mice and transponder implantation should only be used in older newborns or applied at weaning., As this study was performed within the framework of the first author’s master thesis, thanks are due to Laboratory Animals Ltd for providing financial support.