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International audience; Background: One of the fundamental questions in Neuroscience is to understand how we choose one option instead of another one when we are in uncertain or ambiguous situation. Some decisions have short- and long-term consequences. The Iowa Gambling Task (IGT) is classically used to study decision-making in humans because it mimics real life situations. By developing a new mice model, we aimed at studying behavioral traits and brain circuits that impact on inter-individual differences in decision making processes.Methods: 72 male C57Bl/6J mice were used to adapt the IGT. We first attempted to adapt the task in operant chambers from rats’ works using long delays as penalties. Our results were not conclusive so we adapted the task to a maze version. Quinine pellets were used as penalties and food pellets as rewards. We also performed behavioral measures of anxiety, novelty exploration, locomotion and social interaction. Finally, we measured levels of monoamines in different brain tissues sampled from the mice subjected to the behavioral task.Results: We show that transferring directly the protocol of the rat’s gambling task to mice using operant conditioning was not successful presumably because of species particularities, such as lower sensitivity to delay penalties. In the maze version, we found that mice exhibited a clear preference for small but safer rewards that allow the maximization of benefits in the long-term. We observed the progressive emergence of inter-individuals differences and specific behavioral and biochemical traits for each subgroup. Namely, risk-prone mice exhibited lower 5-HT level in the prefrontal cortex compared to the others.Conclusion: We were thus able to validate a mouse gambling task and to determine individual profile close to the human and rat results. This study allows us to characterize within a healthy population, subgroups with different behavioral and biochemical profiles.

International audience; The study of social interactions in mice is used as a model for normal and pathological cognitive and emotional processes. But extracting comprehensive behavioral information from videos of interacting mice is still a challenge. We describe a computerized method and software, MiceProfiler, that uses geometrical primitives to model and track two mice without requiring any specific tagging. The program monitors a comprehensive repertoire of behavioral states and their temporal evolution, allowing the identification of key elements that trigger social contact. Using MiceProfiler we studied the role of neuronal nicotinic receptors in the establishment of social interactions and risk-prone postures. We found that the duration and type of social interactions with a conspecific evolves differently over time in mice lacking neuronal nicotinic receptors (Chrnb2-/-, here called β2(-/-)), compared to C57BL/6J mice, and identified a new type of coordinated posture, called back-to-back posture, that we rarely observed in β2(-/-) mice.

International audience; Beside a critical role in nicotine addiction, the role of nicotinic receptors in cognitive or emotional processes remains difficult to elucidate, mostly because of a lack of specificity of compounds and because they up or down regulate easily. Using knockout mice may be one key to elucidate the role of nicotinic receptors stimulated by their endogenous ligand acetylcholine. We and others have previously explored the behaviour of mice knockout for the beta2-subunit containing nicotinic receptor - β2*nAChRs - β2(-/-) mice. These mice exhibit a particular kind of hyperactive locomotion, with profound deficits in cognitive and social interaction tasks, only when they have to show flexible choices. We wonder here whether the latter is due to a lack of motor control - i.e. motor impulsivity, a lack of estimation of reward value - i.e. cognitive impulsivity, and/or a lack of appropriate ranking or choice between different motivations. We designed behavioural tasks allowing the study of these distinct processes in mice. Our current results highlight the important role of β2*nAChRs in flexible behaviours in conflicting situations, such as social contact, spatial exploration and food consumption. They also show that the cognitive deficits exhibited by β2(-/-) mice cannot be explained by impaired inhibitory behaviours. Although social cognition is considerably enriched in humans as compared to rodents, we provide here novel data for the neurobiology of flexible social behaviours that could ultimately be useful for humans. Indeed, the ability to show flexible behaviours and to display adapted social interactions is profoundly impaired in a myriad of psychiatric disorders.

International audience; Social behavior is a defining mammalian feature that integrates emotional and motivational processes with external rewarding stimuli. It is thus an appropriate readout for complex behaviors, yet its neuronal and molecular bases remain poorly understood. In this study, we investigated the role of the mouse prefrontal area, particularly the involvement of β2-subunit nicotinic receptors (β2*-nAChRs) in a paradigm of social behavior with concurrent motivations. We previously observed that mice lacking β2*-nAChRs (β2(-/-)) display increased time in social contact and exaggerated approach movements toward the novel conspecific. Here, combining behavioral analysis, localized brain lesions, and lentiviral gene rescue, we found that c-Fos expression is specifically activated in the prelimbic (PrL) area of the prefrontal cortex (PFC) of mice exposed to a novel conspecific; lesions of the PrL area in wild-type mice produce the same social pattern as in β2(-/-) mice; and virally mediated reexpression of the β2-subunit in the PrL area of β2(-/-) mice rescues behavioral components in the social interaction task up to normal levels. Together, these data reveal that social interactions particularly mobilize the PrL area of the mouse PFC and that the presence of functional PrL β2*-nAChRs is necessary for this integrated behavior to emerge.

This paper tackles the problem of tracking multiple articulated objects undergoing frequent contacts in a video sequence. Conventional tracking methods usually fail to distinguish objects during contact, implying the use of disambiguation techniques to recover the identity of each object. Moreover, such methods do not provide detailed shape information at the articulation level. We address these limitations by proposing a novel approach to track multiple articulated objects using the mean-shift technique and physics engines. By defining a model of each object using geometrical primitives and physical constraints, we exploit the physics engine force solver as a control layer of the mean-shift process and follow the model and its deformation along the sequence. The method is applied to track mice observed with a webcam and two sporozoites observed in reflection interference contrast microscopy, highlighting the flexibility and genericity of the framework.