Approaches
Active place avoidance
The paradigm consists in a circular grid rotating at 1 revolution per minute. The platform is delimited by a transparent cylinder which allows using distal cues present in the environment to locate a shock zone in which each entry results in a mild aversive stimulus. The protocol consists in a Pretraining phase followed by a training phase during which they actively learn to avoid the aversive zone. Reversal training can be achieved by displacing the shock zone to the opposite end of the arena. APA is measured as the number of times a mouse enters the aversive zone.
The active place avoidance paradigm we use and the results we typically obtain. The heat-map reflects the time a mouse spends on the platform during a conditioning session.
Markerless pose estimation
We measure specific behaviors (freezing, flight, rearing, sniffing) with deep neural networks (DeepLabCut). This efficient and reproductible approach allows us to explore behavioral motifs at subsecond resolution.
Tracking several mouse attributes (nose, ears, sides, hips and tail) with DeepLabCut .
Estrous cycle
We evaluate the relationship between the estrous cycle and performances in the place avoidance paradigm in female mice. We monitor the length and phases of the cycle using vaginal smears/cytology. This information is especially relevant as sex is increasingly treated as a biological variable. Ruling out the involvement of changes in sex hormone levels is as important as demonstrating one.
Major phases of the estrous cycle in mice identified with a combination of three main cell types. The cytology proceeding from vaginal smears reflects changes in steroid sex hormones. Scale bar: 50 um.
Mouse genetics and stereotaxy
We use male and female transgenic mouse lines in order to target specific cell types in the brain. We can selectively inject viral vectors into brain areas to express proteins of interest in genetically defined cell types using the Cre-Lox system.
We targeted dopamine neurons in the ventral tegmental area by injecting a viral vector allowing the conditional expression of a calcium sensor in Dat-Cre mice. The green label identifies dopamine neurons expressing a calcium sensor (GCaMP8m) and the blue label identifies all brain cell nuclei (DAPI). Scale bar: 250 um.
In vivo optogenetics
We use stereotaxy to express optogenetic tools to control the activity of neural circuits with light. We combine this approach with mouse genetics to target genetically defined cell types.
We targeted dopamine neurons in the ventral tegmental area by injecting a viral vector allowing the conditional expression of red-shifted opsins in Dat-Cre mice. The orange label identifies dopamine neurons expressing ChrimsonR (tdTomato) and the blue label identifies all brain cell nuclei (DAPI). Scale bar: 250 um. We used a real-time place preference protocol in which mice preferred the photostimulated side. These results echo previous findings suggesting a role for VTA dopamine neurons in motivation.
Live calcium imaging
We record single cell calcium events using a miniaturized single photon endoscope. This approach allows chronic, longitudinal, live calcium imaging at cellular resolution in male and female mice expressing GCaMP8m. This approach will allow visualizing and monitoring the activity of projection-specific neurons with high spatial and temporal selectivity.
Live calcium imaging in freely moving mice using miniaturized endoscopes (left), we will visualize calcium dynamics across projection-specific neurons (middle) with high spatial and temporal selectivity (right). Scale bar: 25 um.
