Girls gone wild: Social isolation induces hyperactivity and exploration in aged female mice

D. Gregory Sullens; Kayla Gilley; Kendall Jensen; Melanie J. Sekeres

Behavioral tasks were conducted in a least-to-most aversive order, and each test apparatus was cleaned with 70% ethanol between trials. Only a single behavioral task was conducted on each day. were located in each of the side chambers. One isolation cage contained a novel sex-matched conspecific mouse. The other cage remained empty during the trial. The test mouse was placed in the center chamber and allowed 5 min to habituate to the chamber. The sliding doors were then raised, the mouse was allowed to freely explore all three chambers of the arena for an additional 5 min. The total time spent exploring the chamber containing the conspecific relative to the other two chambers was measured. Increased time spent in the social side chamber relative to the non-social side chamber indicates a preference for social interaction. The copyright holder for this preprint (which was not peer-reviewed) is the . https://doi.org/10.1101/2020.04.15.043877 doi: bioRxiv preprint clear Plexiglas cylinder (5 cm diameter, 25 cm high) was filled halfway with room temperature water. The mouse was placed in the chamber for 6 min. The latency to immobility, and the durations of immobility and high activity during the task was calculated. High activity was defined by the SMART behavioral analysis software as ≥ 15% change in pixels between serial video frames during the task. Lower periods of activity are indicative of a learned helplessness phenotype or depressive-like behavior. Context Fear Conditioning and Testing (CFC): Fear conditioning was conducted in a chamber (19 cm × 20 cm × 128 cm) with shock-grid floors (bars 3.2 mm in diameter spaced 7.9 mm apart), clear acrylic front and back walls, and aluminum side-walls and roof (Coulborn Instruments). Mice were allowed 2 min to explore the chamber, then received 3 foot shocks (0.5 mA, 2 sec duration, 1 min apart). Mice were removed from the chambers 1 min after the last shock. Twenty-four hours later, the mouse was replaced in the conditioning chamber and freezing behavior was recorded for 3 min. Freezing is a species-specific defense reaction that is typically used as a measure of fear in rodents. Behavior in the chamber was recorded by an overhead camera, and activity levels were analyzed using Freezeframe software (Actimetrix, RRID:SCR_014429).