The supination assessment task: An automated method for quantifying forelimb rotational function in rats

Abstract

Background: Neurological injuries or disease can impair the function of motor circuitry controlling forearm supination, and recovery is often limited. Preclinical animal models are essential tools for developing therapeutic interventions to improve motor function after neurological damage. Here we describe the supination assessment task, an automated measure of quantifying forelimb supination in the rat.

New method: Animals were trained to reach out of a slot in a cage, grasp a spherical manipulandum, and supinate the forelimb. The angle of the manipulandum was measured using a rotary encoder. If the animal exceeded the predetermined turn angle, a reward pellet was delivered. This automated task provides a large, high-resolution dataset of turn angle over time. Multiple parameters can be measured including success rate, peak turn angle, turn velocity, area under the curve, and number of rotations per trial. The task provides a high degree of flexibility to the user, with both software and hardware parameters capable of being adjusted.

Results: We demonstrate the supination assessment task can effectively measure significant deficits in multiple parameters of rotational motor function for multiple weeks in two models of ischemic stroke.

Comparison with existing methods: Preexisting motor assays designed to measure forelimb supination in the rat require high-speed video analysis techniques. This operant task provides a high-resolution, quantitative end-point dataset of turn angle, which obviates the necessity of video analysis.

Conclusions: The supination assessment task represents a novel, efficient method of evaluating forelimb rotation and may help decrease the cost and time of running experiments.

Keywords: Automated task; Forelimb; Motor function; Operant behavior; Stroke; Supination.

Figure 1

Behavioral apparatus. (A) Solidworks model of behavioral cage and device. (B) View from inside of the behavioral cage. Aperture dimensions and location restricts use to right forelimb only. Pellet trough is located on the left side of the front wall. (C) Close-up of manipulandum. (D) View of device located inside of the cage at the initial training position of −0.5” inside of cage wall. (E) Close-up of device fully retracted outside of the cage, at the final training location 0.5” from inside of cage wall. (F) Sequential illustration of animal reaching, grasping, and rotating the manipulandum.

Figure 2

Experimental timeline and behavioral training. (A) Timeline of experiment. Training was performed twice daily. One week represents 5 days of training or 10 behavioral sessions. (B) Peak turn angle of individual trials taken from one session during the adaptive training. Each point represents the peak turn angle of a single trial. The horizontal black dotted line at 75 degrees represents the maximum threshold for Cohort B, and the large gray dashed line indicates the adaptive threshold within one behavioral session. (C) Example session during static training with the horizontal black dotted line at 75 degrees indicating the static threshold. (D) A single, representative trial from a pre-lesion animal during an adaptive training session. The horizontal gray dashed line indicates the turn angle success threshold. The leftmost arrow indicates when a pellet reward is delivered once the turn angle crosses the success threshold, and the rightmost arrow shows the peak turn angle of the trial. (E) A single trial from a pre-lesion animal during a static training session, with the arrow indicating a successful trial attempt in which the turn angle exceeded the threshold.

Figure 3

Experiment 1: Ischemic lesion of motor cortex impairs multiple measures of task performance. (A) Peak turn angle and (B) success rate of animals in Cohort A was significantly reduced compared to pre-lesion at all time points following lesion. (C) Number of trials performed per day showed a transient reduction during Post, but returned to pre-lesion levels during Weeks 1-4. (D) The maximum turn velocity, calculated as the maximum of the derivative of the turn angle, exhibited a transient reduction following injury but did not reach significance at Week 4. All plots show group averages (N=7) in black lines and light gray lines represent individual animals. Error bars indicate SEM. Significant differences were determined by paired t-tests and are noted as *p<0.05, **p<0.01, ***p<0.001.

Figure 4

Turn angle measurements from a single animal and group turn angle histograms. (A) Trial signals overlaid from one pre-lesion animal during a behavioral session. Gray lines represent individual trial signals, and thick black line indicates average turn angle at each sample. (B) Pre-lesion group histogram of peak turn angle from Cohort A. (C) Trial signals and average overlaid from one post-lesion behavioral session. (D) Post-lesion group histogram of peak turn angle from Cohort A. (E) Trial signals and average overlaid from one session during the fourth week of post-injury training. (F) Group histogram from the fourth week of post-injury training.

Figure 5

Reconstructions detailing the extent of ischemic damage from the smallest, representative, and largest lesions observed. Numbers denote distance from bregma in mm.

Figure 6

Experiment 2: Combined cortical and subcortical lesion impairs multiple measures of task performance. (A) Peak turn angle and (B) success rate was significantly reduced at all time points following injury. (C) Number of trials performed per day showed a transient reduction but returned to pre-lesion levels during Weeks 1-4. (D) The maximum turn velocity exhibited a transient reduction following injury through Week 2. All plots show group averages (N=7) in black lines and light gray lines represent individual animals. Error bars indicate SEM. Significant differences were determined by paired t-test and are noted as * p<0.05, ** p<0.01, *** p<0.001.

Figure 7

Adaptive training increases trial counts while providing an equivalent measure of performance compared to static thresholds. (A) Animals perform significantly more trials per day during adaptive training compared to static training. (B) Peak turn angle was not significantly different between adaptive and static thresholding sessions.