Measuring locomotor strategies of freely moving previsual rat pups

Abstract

Blind walks of previsual rat pups in the open field test were analyzed for random components and/or strategies of locomotion. Wistar infants (n = 51) on their 13th postnatal day was tracked in the open field test for 2 minutes. At this age, immature rats should rely only on non-visual modalities in their navigation. Three distinct patterns were observed. A large portion of the pups (n = 22) performed sub-diffusive localized walks in the center. A smaller cohort (n = 9) undertook almost immediate quasi-linear raids in a random direction, thus succeeded in reaching a shelter (i.e., walls' vicinity). The rest (n = 20) demonstrated a mixed strategy: localized walks interspersed with quasi-linear raids. We applied a method of space potentials for an automated segmentation of the tracks into the localized walks and quasi-linear fragments. We found that the localized walks were random only for the time scale below 2-3 seconds, but essentially non-random (sub-diffusive) for longer scales. The sub-diffusion was caused by the trajectories' re-attraction, as seen from the averaged velocity autocorrelation function. Self-odor traces can be a physical cue ensuring the trajectorial returns. Oppositely, the quasi-linear raids can be considered a primary form of an active escape response.

Keywords: Locomotion; Method of space potentials; Previsual rat pups; Random walk models; Trajectory analysis.