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.

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

We use male and female transgenic mouse lines in order to target specific hippocampal subfields. The hippocampus plays an important role in encoding spatial information. These signals are subsequently relayed to downstream cortical and subcortical areas enabling behavioral responses.

Here we used two transgenic mouse lines (Grik4-Cre & Wfs1-CreERT2). These mouse lines were bred with a reporter line to label principal neurons in DG-CA3 (left) and CA1 (right) with a fluorescent protein (tdTomato). The yellow label identifies principal neurons in CA2 (Rgs14) and blue label identifies all brain cell nuclei (DAPI). Scale bar: 250 um.

Stereotaxy

We inject viral vectors into the brain of anesthetized mice allowing the expression of optogenetic tools to monitor and control the activity of neural circuits in live freely moving animals. We combine this approach with mouse genetics to target genetically defined hippocampal cell types.

We targeted distal (left) or proximal (right) parts of CA3 in mice expressing the Cre recombinase in area CA3 (Grik4-Cre mice). The green label identifies principal neurons expressing a calcium sensor (GCaMP7f) and the blue label identifies all brain cell nuclei (DAPI). Scale bar: 250 um.

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 GCaMP7f. 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.