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.

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.

In tissue engineering, the evaluation of the host response to the biomaterial implantation must be assessed to determine the extent of the inflammatory reaction. We studied the degradation of poly(butylene succinate) and chitosan in vitro using lipase and lysozyme enzymes, respectively. The subcutaneous implantation of the scaffolds was performed to assess tissue response. The type of inflammatory cells present in the surrounding tissue, as well as within the scaffold, was determined histologically and by immunohistochemistry. In the presence of lipase or lysozyme, the water uptake of the scaffolds increased. Based on the weight loss data and scanning electron microscopy analysis, the lysozyme combined with lipase had a notable effect on the in vitro degradation of the scaffolds. The in vivo implantation showed a normal inflammatory response, with presence of neutrophils, in a first stage, and macrophages, lymphocytes, and giant cells in a later stage. Vascularization in the surrounding tissue and within the implant increased with time. Moreover, the collagen deposition increased with time inside the implant. In vivo, the scaffolds maintained the structural integrity. The degradation in vitro was faster and greater compared to that observed in vivo within the same time periods.

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 animals is essential in biomedical research. The laboratory environment where the animals are housed has a major impact on them throughout their lives and influences the outcome of animal experiments. Therefore, there has been an increased effort in the refinement of laboratory housing conditions which is explicitly reflected in international regulations and recommendations. Since housing conditions affect behaviour and brain function as well as well-being, the validation of an animal model or paradigm to study the brain and central nervous system disorders is not complete without an evaluation of its implication on animal welfare. Here we discuss several aspects of animal welfare, comparing groups of six rats living in the PhenoWorld (PhW), a recently developed and validated paradigm for studying rodent behaviour, with standard-housed animals (in cages of six rats or pair-housed). In this study we present new data on home-cage behaviour showing that PhW animals have a clearer circadian pattern of sleep and social interaction. We conclude that, by promoting good basic health and functioning, together with the performance of natural behaviours, and maintaining animals' control over some of their environment but still keeping some physical and social challenges, the PhW stimulates positive affective states and higher motivation in rats, which might contribute to an increased welfare for animals living in the PhW.

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 evolution of the field of behavioral neuroscience is significantly dependent on innovative disruption triggered by our ability to model and phenotype animal models of neuropsychiatric disorders. The ability to adequately elicit and measure behavioral parameters are the fundaments on which the behavioral neuroscience community establishes the pathophysiological mechanisms of neuropsychiatric disorders as well as contributes to the development of treatment strategies for those conditions. Herein, we review how mood disorders, in particular depression, are currently modeled in rodents, focusing on the limitations of these models and particularly on the analyses of the data obtained with different behavioral tests. Finally, we propose the use of new paradigms to study behavior using multidimensional strategies that better encompasses the complexity of psychiatric conditions, namely depression; these paradigms provide holistic phenotyping that is applicable to other conditions, thus promoting the emergence of novel findings that will leverage this field.

Access to vital needs shapes social orders. In rats, social systems tend to maintain a certain stability, but alterations in the physical environment can change inter-individual relations, which consequently can alter social orders. Principles governing social systems are, however, difficult to study and most analyses have been restricted to dyads of animals over short periods of time, hardly capturing the complexity and temporal dynamics of social interactions. Herein, we studied social interactions in a colony of six rats living in a customized enriched environment (PhenoWorld, PhW), under variable conditions of access/availability to limited resources. Reductions in food accessibility and availability resulted in a marked heterogeneity in sniffing, chasing and fighting/struggling behaviors, and, in the latter condition, an overall increase of these displays. The introduction of the possibility of interaction with a female rat also increased the amount of sniffing and fighting/struggling in a homogeneous manner. Results also showed that individual food retrieval success had no association with fighting/struggling when food pellets are delivered to the animals. However, there was a statistically significant correlation between fighting/struggling and impulsivity as measured by the amount of premature responses in the Variable-to-Signal-Test outside of the PhW providing external validation to our measures. To sum up, through continuous monitoring of a group of rats in the PhW, we demonstrated how variations in access to reinforcers modulate social behavior.