Motor Functions

Peromance of many behavioural tests depends on animal's locomotor abilities. For instance, some gene-modified mice such as staggerer, lurcher, weaver, and wobbler suffer from locomotor abnormalities that may affect performance in behavioural tasks, particularly when time is measured as the dependent variable. For these reasons, tests of motor performance should be conducted on transgenic and knockout mice to ensure that abnormal responses, particularly in learning and memory tasks, are not due to non-cognitive motor abnormalities.

Tremor Test

Procedure

Each mouse is placed inside the holder. Tremor resulted in vibration of the speaker surface and the resulting signal is amplified before passing through an analog-to-digital converter that assigned voltage equivalents to the vibrations transmitted to the speaker. Voltage recordings are made over a 22-second period at a rate of 454 recordings per second.

The Tremor Monitor System records, reviews, analyzes and reports rapid repetitive movements in mice. The Tremor Monitor differentiates tremor events from ambulatory/stereotyped movements. The user can define long and short tremor events. The system utilizes an ultra sensitive movement sensor to record continuous movement waveforms at 128Hz for up to 30 minutes.

Beam Test

Procedure

Mice are placed in the middle of a narrow, graspable runway and are examined for maneuverability between two stable platforms located at either end.

Mice are scored as follows:

1 - crosses easily without undue effort, can reverse on 3-mm edge, can reach platform from distance of 15 cm easily.

2 - reaches stable platform with substantial difficulty, can reach platform from distances of 7 cm, tremor typically evident.

3 - extreme difficulty in edge navigation, cannot make progress toward platform, but can maintain grip on edge for a minimum of 8-10 seconds.

4 - cannot maintain grip on edge for 8-10 seconds.

 Grip Test

Procedure

This procedure is used to measure the muscle strength of both fore and hind limbs.

Forelimb measurement: Gently lower the mouse over the top of the grid so that only its front paws can grip the grid. Keep the torso horizontal and pull the mouse back steadily (not jerking) until the grip is released down the complete length of the grid. Ensure that the animal does not grab onto the upper edge of the grid first as it’s lowered down (will result in higher than normal reading). When the animal releases the grid, the maximal grip strength value of the animal is displayed on the screen. Make a note of this value on the record sheet. Repeat this procedure to obtain a further 4 forelimb grip strength measurements.

Forelimb and hind limb measurement: Gently lower the mouse over the top of the grid so that both its front paws and hind paws can grip the grid. Keep the torso parallel to the grid and pull the mouse back steadily (not jerking) until the grip is released down the complete length of the grid. Ensure that the animal does not grab onto the upper edge of the grid first as it’s lowered down (will result in higher than normal reading). Make a note of the value displayed on the screen on the record sheet. Repeat this procedure to obtain a further 4 forelimb and hind limb grip strength measurements.

Catalepsy

Procedure

A mouse is gently scruffed between a thumb and a forefinger and quickly lifted up above the table (the experimentator's hand is fixed at the elbow) simultaneously releasing the tail.

Affected mice are usually rigid with their paws moved wide apart, sometimes one paw is raised, digits widely apart, the body and head are tense, and the tail kept upright towards the body. There is an expressed muscular rigidity, which is evidence for the development of a catatonic-like state. When mice are forced to change the position of their paws and tail, they returned to their previous position. The mouse will not react to weak tactile stimulation and noise.

The time of immobility before the first genesis of motor paroxysm (the motor agitation) is estimated (and/or count number of paroxysms during 10 minutes and duration of immobility).

Foot Pattern

Procedure

Mice are first trained to walk through the dark tunnel which is then lined with the clean white paper. All four feet are then dipped into non-toxic ink and the mouse is allowed to walk through the tunnel again. Their feet are wiped and the mice is returned to their home cage. Once the footprint is dried, it is scanned and uploaded to a special software that performs analysis.

If a mouse has an abnormal gait, a video recording it is useful for further analysis. The gait analysis can be informative. WT mice have a regular, alternating gait. Variation from this pattern can indicate ataxia or morphological defect that causes an abnormal gait.

Vertical Pole

Procedure

Each mouse is placed head upwards at the centre of a round pole that is inclined at 90° and performance is determined by the latency(s) of the mouse to turn downwards and completely descend the pole. In a habituation period one day prior to testing, each mouse is allowed to attempt to descend the pole. Each testing session lasts for a maximum of 180 seconds.

During testing, the following scores are applied:

0–20 second latency (scored 1)

21–40 second latency (scored 2)

41–60 second latency (scored 3)

more than 60 second latency (scored 4)

sliding down the pole immediately (scored 5)

freezing and never descending the pole (scored 6)

falling off the pole immediately or when trying to turn and descend at any time (scored 7)

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