Novel application of a Radial Water Tread maze can distinguish cognitive deficits in mice with traumatic brain injury

Abstract

Introduction: The use of forced-swim, rat-validated cognition tests in mouse models of traumatic brain injury (TBI) raises methodological concerns; such models are vulnerable to a number of confounding factors including impaired motor function and stress-induced non-compliance (failure to swim). This study evaluated the ability of a Radial Water Tread (RWT) maze, designed specifically for mice, that requires no swimming to distinguish mice with controlled cortical impact (CCI) induced TBI and Sham controls.

Methods: Ten-week-old, male C57BL6/J mice were randomly assigned to receive either Sham (n=14) or CCI surgeries (n=15). Mice were tested for sensorimotor deficits via Gridwalk test and Noldus CatWalk gait analysis at 1 and 32days post-injury. Mice received RWT testing at either 11days (early time point) or 35days (late time point) post-injury.

Results: Compared to Sham-treated animals, CCI-induced TBI resulted in significant impairment in RWT maze performance. Additionally, CCI injured mice displayed significant deficits on the Gridwalk test at both 1day and 32days post-injury, and impairment in the CatWalk task at 1day, but not 32days, compared to Shams.

Conclusions: The Radial Water Tread maze capitalizes on the natural tendency of mice to avoid open areas in favor of hugging the edges of an apparatus (thigmotaxis), and replaces a forced-swim model with water shallow enough that the animal is not required to swim, but aversive enough to motivate escape. Our findings indicate the RWT task is a sensitive species-appropriate behavioral test for evaluating spatial memory impairment in a mouse model of TBI.

Keywords: Behavioral testing; Cognitive testing; Controlled-cortical impact; Traumatic brain injury; Water maze.

Fig. 1.

Radial water tread maze (A) and schematic (B). The maze consists of a 32-inch galvanized steel tub with nine exits, each 1 ½ inch above the apparatus floor. Of these exits, eight terminate after roughly 1 in. (decoy exits), and one leads to a heated safety box hidden behind a 90 degree angle bend to prevent visual confirmation of escape route. Upon reaching the safety box, subjects received a food incentive and 1-min rest. The apparatus is filled with one inch of cold water (12–14 °C) to motivate escape behavior, and lined with five unique visual cues for spatial orientation.

Fig. 2.

Radial Water Tread Maze successfully distinguishes between Sham and TBI mice at both early and late time points. (A) 11 days post-injury Sham mice had significantly reduced latency (time to complete maze in seconds) than TBI mice on days 5 and 12. Significant group differences were also apparent during the initial acquisition period consisting of testing days 1 through 4 (B) 35 days post-injury Sham mice had significantly reduced latency (time to complete maze in seconds) than TBI mice on day 12 only. There were no group differences during the acquisition period. Data points represent group means (± SEM). Significance is reported as p < 0.05 (*), p < 0.01 (**) and p < 0.001 (***).

Fig. 3.

CatWalk Gait Analysis differentiates between Sham and TBI mice on a variety of parameters 1 day, but not 32 days, post-injury. Bars represent group means (± SEM). Significance is reported as p < 0.05 (*), p < 0.01 (**) and p < 0.001 (***). (A) Cadence, (B) Average Speed (cm/s), (C) Swing (s), (D) Swing Speed (cm/s). RF: right front paw, RH: right hind paw, LF: left front paw, LH: left hind paw.

Fig. 4.

Significant contralateral foot fault bias in TBI compared to Sham mice 1 and 32 days post-injury. Bars represent group means (± SEM). Significance is reported as p < 0.05 (*).

Fig. 5.

Cognitive deficits in long term memory retention are detectable by Radial Water Tread maze at both early and late time points following TBI, while CCI-induced sensorimotor deficits measured by Catwalk Gait Analysis returned to control levels by 32 days post-injury. (A) RWT maze long term test (day 12) at 11 and 35 days post-injury, and (B) Average speed measured by Catwalk Gait Analysis at 1 and 32 days post-injury. Data points represent group means (± SEM). Significance is reported as p < 0.05 (*) and p < 0.01 (**).