Basic neuroscienceAn automated behavioral box to assess forelimb function in rats
Introduction
Rodent forelimb function is widely studied in the context of motor learning, neural plasticity and recovery from injury (Girgis et al., 2007, Hays et al., 2013, Kleim et al., 2007, Montoya et al., 1991, Ramanathan et al., 2006, Ramanathan et al., 2009, Rioult-Pedotti et al., 1998, Slutzky et al., 2010, Weishaupt et al., 2013, Whishaw et al., 2008, Whishaw et al., 1986). More specifically, the Whishaw single-pellet reach-to-grasp task is among the mostly commonly used behavioral assessment of forelimb function (Fu et al., 2012, Kleim et al., 2007, Rioult-Pedotti et al., 1998, Whishaw et al., 2008, Whishaw et al., 1986, Whishaw and Pellis, 1990, Xu et al., 2009). Early variations of this task included the use of trays in the home cage containing multiple pellets simultaneously (Castro, 1972, Whishaw et al., 1986). The single-pellet task is more difficult as it requires reaching, grasping and retrieving a single pellet located at a distance outside of the behavior box (Whishaw and Pellis, 1990); inaccurate reaches typically result in the pellet being knocked away. The original version of this task included an acrylic box that biased reaching movements to a single limb and allowed video based monitoring of movements from multiple perspectives. Numerous studies have now shown that the single-pellet reaching task involves the learning and acquisition of a new motor skill (Conner et al., 2003, Francis and Song, 2011, Kleim et al., 2007, Rioult-Pedotti et al., 2000, Rioult-Pedotti et al., 1998); it has become an important focus for studies of the neural substrates of motor learning in both rats and mice (Fu et al., 2012, Kleim et al., 1998, Xu et al., 2009). The same task is also commonly used to study recovery of forelimb function after stroke or brain injury (Ramanathan et al., 2006, Whishaw et al., 2008, Whishaw et al., 1986). In addition, it may be used to assess motor function in other models of neurological dysfunction (e.g. Parkinson's disease) (Klein and Dunnett, 2012, Vergara-Aragon et al., 2003).
While the single-pellet reaching task is widely recognized as a very sensitive measure of distal forelimb function, it is also known to be very labor and time intensive (Kleim et al., 2007). In a typical reaching session, rats are given the opportunity to obtain 20–25 pellets (i.e. 20–25 trials per day). Traditionally, this requires an experimenter to manually present each pellet and to observe/shape the behavior of the rat by placing a subsequent pellet only when the rat has relocated to the other end of the cage. Such a training paradigm requires ∼2 weeks to achieve adequate plateau performance levels (Francis and Song, 2011, Kleim et al., 2007). This is only compounded by the fact that multiple trials are necessary to assess outcomes after injury (i.e. if also used as a serial measure of functional recovery).
The primary goal of this study was to develop and validate a low-cost, automated high-throughput version of this task. Our specific focus was to minimize the need for user input and supervision during the training and assessment of animals. Importantly, the ability to automate assessments has the added benefit of facilitating blinding of assessments (i.e. done automatically without human intervention). We further demonstrated the potential use of such a box in varying the trial structure during motor learning as well as its compatibility with chronic electrophysiological recording techniques.
Section snippets
Subjects
We used a total of 22 male Long Evans rats weighing approximately 250 g. The rats were housed in a temperature-controlled, 12:12 h light cycle environment in which behavioral testing occurred with lights on during the day. Rats were food scheduled, where they received a part of their food requirements from the reaching task depending on trial structure. Rats following the traditional training paradigm of one 25-trial session per day were given an opportunity to obtain a maximum of 25 pellets in
Traditional and high-throughput training paradigms
We systematically varied the trial structure and exposure to the task in order to test the time-dependent differences in motor skill formation. Traditionally, one training session of 25 trials per day prepared naïve rats to understand the task reward structure and gradually master the reaching technique over two to three weeks (Fig. 3A). The automation of the setup enabled us to train multiple rats simultaneously in closed, soundproof chambers. The independent, self-regulating nature of the
Discussion
The single-pellet reaching task is a validated method to evaluate forelimb function in rats (Francis and Song, 2011, Kleim et al., 2007). However, the necessity for manual placement of pellets and determination of trial outcomes is a significant burden, both with respect to time invested as well as a possible confound during electrophysiological assessments. Our results illustrate the feasibility of fashioning a low-cost automated behavioral setup that permits high-throughput training and
Conclusion
Our automated behavioral setup facilitates high-throughput training and assessment of forelimb function in rats without constant experimenter supervision. The modular apparatus is readily adaptable to customized task structures, allowing for numerous variations to be tested. By expediting the acquisition period for skilled reaching, the temporal evolution of motor learning can be more easily examined, particularly in correlation with electrophysiology recordings. Given its flexibility, the
Acknowledgements
This work was supported by the U.S. Department of Veterans Affairs (CDA-2B6674W), the Burroughs Wellcome Fund (1009855), the American Heart Association/Stroke Association (0875016N) and departmental funds from the UCSF Department of Neurology. We would also like to thank Roy Tangsombatvisit for assistance with the design and the manufacturing of the reach boxes.
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