Mice are increasingly being used in behavioral neuroscience, largely replacing rats as the behaviorist's animal of choice. Before aspects of behavior such as emotionality or cognition can be assessed, however, it is vital to determine whether the motor capabilities of e.g. a mutant or lesioned mouse allow such an assessment. Performance on a maze task requiring strength and coordination, such as the Morris water maze, might well be impaired in a mouse by motor, rather than cognitive, impairments, so it is essential to selectively dissect the latter from the former. For example, sensorimotor impairments caused by NMDA antagonists have been shown to impair water maze performance(2). Motor coordination has traditionally been assessed in mice and rats by the rotarod test, in which the animal is placed on a horizontal rod that rotates about its long axis; the animal must walk forwards to remain upright and not fall off. Both set speed and accelerating versions of the rotarod are available. The other three tests described in this article (horizontal bar, static rods and parallel bars) all measure coordination on static apparatus. The horizontal bar also requires strength for adequate performance, particularly of the forelimbs as the mouse initially grips the bar just with the front paws. Adult rats do not perform well on tests such as the static rods and parallel bars (personal observations); they appear less well coordinated than mice. I have only tested male rats, however, and male mice seem generally less well coordinated than females. Mice appear to have a higher strength:weight ratio than rats; the Latin name, Mus musculus, seems entirely appropriate. The rotarod, the variations of the foot fault test(12) or the Catwalk (Noldus)(15) apparatus are generally used to assess motor coordination in rats.
Objective: Assessment of motor coordination by measuring ability of mice to traverse elevated static rods of varying diameters
Gather these items before starting the experiment. Check off items as you prepare.
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Bring mice to the experimental room before testing to ensure they are fully awake
Note: Timing is important for consistent arousal levels
“For all tests, bring mice to the experimental room 5-20 min before testing, to ensure they are fully awake”
Configure rotarod with appropriate speed settings before placing mouse
Note: Settings must be consistent across trials
“Set the rotarod with a start speed of 4 rpm, acceleration rate 20 rpm/min”
Hold mouse by tail and place on rotating rod facing away from direction of rotation at 45 degrees below horizontal, then release when almost touching rod just forward of top dead center
Note: Angle of approach is critical to prevent mouse from grasping flanges
“Holding the mouse by the tail, and place it on the rotating rod, facing away from the direction of rotation so it has to walk forward to stay upright. This is easiest to do if the mouse is brought up towards the rod at an angle of 45° below horizontal”
Hold mouse in one hand, lower it onto a thin dowel parallel to long axis at 30 degrees angle with head downwards, then lower mouse and dowel between flanges and pull dowel away so mouse grasps rod
Note: This method is described as probably easier and more reliable
“Holding the mouse in one hand, lower it on to the dowel, parallel to the long axis. The dowel is angled with the mouse's head downwards about 30° to give it more time to grip the rotarod once it is released”
Start acceleration 10 seconds after placing mouse on rod, but only if mouse is facing forward; if not, wait until it faces forward before starting acceleration
Note: Timing of acceleration start is critical for consistent measurement
“At 10 sec after placing the mouse on the rod, start acceleration (as long as the mouse is facing forward: if not, wait till it does face forward before starting acceleration)”
Note the speed at which mouse falls off rod. If fall occurs before 10 seconds, note time and retry up to three times total, recording speed at first fall after 10 second point
Note: Falls before 5 seconds due to poor experimenter placement should not be recorded. Falls before 10 seconds are recorded but not used for final scoring
“note the speed at which the mouse falls off. If it falls off before 10 sec, note the time of fall and try again, up to three times in total, recording the speed at the first fall after the 10 sec point. However, falls before 5 sec which are due to poor placing by the experimenter should not be recorded”
Calculate mean speed at fall from all valid trials. If mouse fails to grip in 10 seconds three times, assign score of 4 rpm
Note: Mean speed corrects for extra practice from failed runs. Example: fall at 4 rpm then 12 rpm = (4+12)/2 = 8 rpm
“The mean speed at fall is the datum; rather than using the maximum speed, this corrects for the extra practice the mouse receives during the failed runs. If a mouse fails to grip in 10 sec three times assign it a score of 4 rpm”
Note if mouse stops walking forward and grips rod firmly, causing passive somersault. Record speed when first inversion occurs
Note: This is a behavioral observation that may indicate need for rod diameter or ridge adjustment
“One problem is that mice sometimes stop walking forward and grip the rod firmly instead, so that they passively somersault round, although most eventually fall off. It might therefore be useful to also note the speed when the first such inversion occurs”
Prepare horizontal bar apparatus, starting with 2 mm bar as mice find it easiest to grasp
Note: Test on 2 mm bar first before progressing to thicker bars if using triple-bar version
“As mice find it easiest to grasp the narrow 2 mm bar, it is advisable to test them first on this one”
Hold mouse by tail, place on bench in front of apparatus, slide backwards about 20 cm to align perpendicular to bar, rapidly raise and let grasp bar at central point with forepaws only, release tail and start stopclock simultaneously
Note: Technique is critical; some mice grip better if tail is released suddenly
“Holding the mouse by the tail, place it on the bench in front of the apparatus, slide it quickly backwards about 20 cm (this aligns it perpendicular to the bar), rapidly raise it and let it grasp the horizontal bar at the central point with its forepaws only, and release the tail, simultaneously starting the stopclock”
Measure time until mouse falls from bar or until one forepaw touches an end column. Maximum test time is 30 seconds
Note: Criterion is either fall or forepaw touching column
“The criterion point is either a fall from the bar before the mouse reaches one of the end columns of the bar, or the time till one forepaw touches a column. Maximum test time (cut-off time) is 30 sec”
If mouse fails to grasp bar properly on first attempt due to experimenter technique, retry after brief rest. If mouse falls before 5 seconds and not due to poor placement, repeat up to three times to get >5 second score. If >5 seconds on second attempt, do not do third trial
Note: Best score is taken as datum. Mice repeatedly failing to support >5 seconds score only 1
“If the mouse fails to grasp the bar properly first time and this appears to be attributable to the experimenter's technique, rather than the mouse, try again (after a brief rest while another one or two mice are tested) and do not record this fall. If the mouse falls before 5 sec and this is apparently not due to poor placing by the experimenter, repeat up to three times”
Score based on time intervals: 1-5 sec = 1 point; 6-10 sec = 2 points; 11-20 sec = 3 points; 21-30 sec = 4 points; after 30 sec = 5 points; forepaw on support without falling = 5 points
Note: First two intervals are smaller as mice are less likely to fall once they master task
“Falling between 1-5 sec = 1; Falling between 6-10 sec = 2; Falling between 11-20 sec = 3; Falling between 21-30 sec = 4; Falling after 30 sec = 5; Placing one forepaw on a bar support without falling = 5”
If using triple-bar version and mouse scores 5 on 2 mm bar, test on thicker bars (4 mm and 6 mm) after brief rest period. Final score is cumulated total from all bars tested
Note: Scoring system for 4 and 6 mm bars is same as 2 mm bar. Example: 5 on 2mm + 3 on 4mm = 8 total
“If the triple-bar version is being used, if the mouse scores 5 on this first 2 mm bar it can then be tested on thicker bars, after a brief rest period while another one or two mice are tested. The final score is the cumulated total”
Place mouse at far end of widest rod (35 mm diameter) with nose tip one head's length from end
Note: Start with largest diameter rod and progress to smaller rods
“Place the mouse at the far end of the widest rod (nose tip one head's length from the end is ideal)”
Measure orientation time: time taken for mouse to orient 180 degrees from starting position towards shelf
Note: Orientation is dependent on mouse staying upright
“Take two measures: orientation time (time taken to orientate 180° from the starting position towards the shelf)”
Measure transit time: time taken to travel to shelf end with nose beyond 10 cm mark from shelf end of rod
Note: Maximum test time is 120 seconds
“transit time (the time taken to travel to the shelf end (nose beyond the 10 cm mark from the shelf end of the rod)”
If mouse turns upside down and clings below rod, assign maximum orientation score of 120 seconds for statistical purposes. Do not test on smaller rods; assign transit time maximum value
Note: Upside-down transit indicates poorer coordination than upright transit
“if it turns upside down and clings below the rod, arbitrarily assign it (for statistical purposes) the maximum orientation score of 120 sec. Do not test it on smaller rods; also the transit time becomes the maximum value”
If mouse falls or reaches maximum test time (120 seconds) after orienting, do not test on smaller rods. Assign falling mice 120 for that rod and subsequent rods, assuming they would fall from narrower rod
Note: This is a conservative scoring approach
“If, after orienting, the mouse falls or it reaches the maximum test time (arbitrarily set at 120 sec) do not test it on smaller rods. For statistical purposes, assign mice falling are assigned 120 for that particular rod and for subsequent ones”
Note if mouse turns upside down during test. For successful transit and orientation, mouse must stay upright on rod
Note: Upside-down behavior is recorded as event
“If the mouse turns upside down, also note this event; for successful transit as well as orientation it must stay upright on the rod”
After testing on one rod, return mouse to home cage to rest while testing another mouse, then place on next smaller rod
Note: Rest period allows recovery between rods
“Remove the mouse after it reaches the end of the rod or falls. After testing on one rod return the mouse to the home cage to rest while you test another mouse. Then place it on the next smaller size rod”
If mouse falls off rod after being on it for less than 5 seconds, replace and allow another attempt (up to maximum of three trials) as early fall could be due to faulty placement. Use best result
Note: Falls after more than 5 seconds result in stopping testing on smaller rods
“Stop testing if the mouse falls off a rod after being on it for more than 5 sec. If it fell off in less than 5 sec replace it and allow another attempt (as falling within 5 sec could be due to faulty placing by the experimenter), for a maximum of three trials, and use the best result”
Place mouse in center of two bars with longitudinal axis perpendicular to bars; both front paws on one bar, both hind paws on other bar
Note: This positioning is novel for mice and tests coordination
“Place the mouse in the center of the two bars with its longitudinal axis perpendicular to that of the bars; both front paws should be on one bar, both hind paws on the other bar”
Measure time taken until mouse orients 90 degrees to start position
Note: Similar scoring to static rods test
“Scoring is similar to that for the static rods. Take two measures: the time taken until the mouse orients 90° to the start position”
Measure time until mouse reaches one of end supports after orienting
Note: Maximum test time is 120 seconds (implied from static rods protocol)
“and the time until it subsequently reaches one of the end supports”
Note if mouse turns upside down during test. Orientation and transit must be achieved while upright
Note: Similar to static rods protocol
“If the mouse turns upside down, also note this event. As for the static rods test, orientation and transit must be”
Return mouse to home cage after each motor test to allow recovery of muscular strength and return to normal arousal levels
Note: General rule for all tests
“As a general rule, to allow recovery of muscular strength and a return to normal levels of arousal, rest the mice by a return to the home cage after each motor test”
Clean and sterilize equipment between each mouse tested
Note: Important for hygiene and preventing disease transmission
“Also, be sure to clean and sterilize the equipment between each mouse tested”
Text mentions testing hundreds of mice, both normal and mutant, with various treatments including pharmacological agents and genetically modified animals