The home-cage automated skilled reaching apparatus (HASRA): individualized training of group-housed mice in a single pellet reaching task

Abstract

The single pellet reaching task is commonly used in rodents to assess the acquisition of fine motor skill and recovery of function following nervous system injury. Although this task is useful for gauging skilled forelimb use in rodents, the process of training animals is labor intensive and variable across studies and labs. To address these limitations, we developed a single pellet reaching paradigm for training and testing group housed mice within their home cage. Mice enter a training compartment attached to the outside of the cage and retrieve millet seeds presented on a motorized pedestal that can be individually positioned to present seeds to either forelimb. To identify optimal training parameters, we compared task participation and success rates between groups of animals that were presented seeds at two different heights (floor vs. mouth height) and at different intervals (fixed-time vs. trial-based). The mouth height/fixed interval presentation style was most effective at promoting reaching behavior as all mice reached for seeds within five days. Using this paradigm, we assessed stroke-induced deficits in home cage reaching. Following 3 weeks of baseline training, reaching success rate was ∼40%, with most trials performed during the dark cycle. A forelimb motor cortex stroke significantly decreased interaction with presented seeds within the first 2 days and impaired reaching success rates for the first 7 days. Our data demonstrate that group-housed mice can be efficiently trained on a single pellet reaching task in the home cage and that this assay is sensitive to stroke induced motor impairments.

Significance Statement We developed an automated apparatus and single pellet reach training paradigm for group housed mice within the home cage. This task allows individualized training progression and handedness of presentation for each mouse, minimizes stress induced by experimenter interaction, and enables experiments and data collection on a massive scale, previously impossible due to the demands of one-on-one behavioral testing. We demonstrate an optimized set of task parameters and the utility of this apparatus for assessing lesion-induced motor impairments. Herein, we provide an open-source, scalable, platform for training and assessing skilled reaching in mice with minimal need for experimenter handling that is equivalent to gold-standard, manual single pellet training paradigms.