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Grid Test

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The grid test is a straightforward, cost-effective method commonly employed to assess long-term behavioral deficits in mice, particularly in Parkinson’s research. Several versions of the test exist, and various modifications are available to facilitate video-based grading. MazeEngineers provides the standard grid test in two forms: the traditional horizontal grid test and a vertical grid test variant.

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Description

Version 1

32 cm x 20 cm x 50 cm (L x W x H)

Openings: 1.1 x 1.1 cm diameter openings

Version 2

41 cm x 41 cm x 41 cm (L x W x H)

Each grid cell 3.5Ɨ3.5 cm

Grid Test
Vertical Grid Test
Horizontal Grid Test

Introduction

The Grid test is employed to assess neuromuscular strength and coordination in rodents and is frequently used in conjunction with other assessments, such as the Rotarod and Gait test. Initially utilized by Tillerson et al. in 2002 to examine motor deficits in a murine model of Parkinson’s disease, the Grid test has evolved. Kim et al. modified the original design in 2010 by replacing the rods with clear plexiglass, facilitating easier data scoring. There are two primary versions of the Grid test: the Vertical Grid test and the Horizontal Grid test. These variants feature grid mesh positioned at fixed 90-degree angles relative to the surface.

The Grid test evaluates muscular strength by measuring the rodents’ ability to cling to the inverted mesh and assesses motor coordination through their locomotion in this inverted position. Since motor deficits are a key behavioral symptom of Parkinson’s disease, the Grid test is valuable for detecting subtle behavioral impairments in rodent models of the condition.

Apparatus and Equipment

The Horizontal Grid apparatus, as described by Tillerson et al. (2002) and Tillerson and Miller (2003), features a 12 x 12 cm mesh with grid openings measuring 0.5 x 0.5 cm. The grid is elevated 20 cm above the surface to prevent the subjects from jumping off. It is enclosed by 3-inch high walls made of durable, opaque plexiglass, which do not interfere with the subjectā€™s performance. Additionally, a bar crosses the gridā€™s width at its center and is connected to poles on each side, enabling the grid to be rotated.

Training Protocol

The Grid test apparatus is thoroughly cleaned before and after each use to maintain hygiene and accuracy. It is equipped with proper lighting to ensure clear visibility. Automated tracking and recording tools, such as Noldus Ethovision XT, can be employed to aid in data collection and analysis.

No prior training is required for the task. The procedure involves lifting the rodent by its tail and positioning it in the center of the grid. Once the rodent has securely grasped the mesh with all four paws, its tail is released. The grid is then flipped upside down, and the subject is monitored for 30 seconds while it hangs from the inverted mesh. Trials are conducted as needed to ensure reliable results.

The subjects were administered L-DOPA post 28 days of either 7.5 or 15 mg/kg MPTP injection, and their performance was evaluated on the Horizontal Grid test. A significant improvement on step distance scores for both MPTP dosages was observed in comparison to the pre-L-DOPA scores. Further, a significant decrease in percentage wall time was also observed on treatment with L-DOPA. (Tillerson and Miller, 2003)

The subjects were administered either 7.5 or 15 mg/kg MPTP injections and their behavioral performance was evaluated on the Grid test. A sustained decline in step length of the MPTP subjects was observed over the course of 30 days. In comparison to the controls, the MPTP treated subjects showed an overall increase of percentage wall time and an increase in forepaw faults on the grid (Tillerson and Miller, 2003).

Data Analysis

The following data can be collected during the Horizontal Grid test.

  • Fall latency value: Time the rodent hangs on the grid.
  • Percentage successful (Hang test): Determined as the maximum time hanging/30 s x 100.
  • Sum of forepaw step distance: Summation of the distance of each successful forepaw step taken. Length of each forepaw step is calculated as

Ā 

Step distance (grids covered/step) = āˆš (width)2+(length)2

  • The total number of forepaw steps: Count of the number of successful forepaw steps taken before the subject falls off the apparatus.
  • Average forepaw step distance: Obtained by dividing the sum of forepaw step lengths by the number of forepaw steps taken.
  • Hang time: The duration that the subject hangs from the horizontal grid, with a maximum of 30 s.
  • Percentage wall time: The time spent in physical contact with the surrounding wall divided by the total time on the grid.
  • Percentage forepaw faults: The number of unsuccessful forepaw steps divided by the total number of attempted forepaw steps. An unsuccessful step is defined as an attempt to step or place the forepaw during a weight shifting (place shifting) movement in which the paw slipped from its destined position and had to be replaced on the grid by the animal to regain weight-bearing control.

The following sample graphs show the comparison of Grid Test measures of subjects treated with different doses of MPTP before and after administration of L-DOPA

The following sample graph shows the variation of Percentage Contact Wall score across the test days.

The sample graph below shows the Percentage of the Successful Hangtest score of two groups treated with two different dosages of MPTP and saline-treated subjects.

Strengths & Limitations

The Grid test is highly effective for evaluating neuromuscular strength and motor coordination in rodent models of Parkinsonā€™s disease. It is also applicable for assessing motor performance in various other rodent models. Unlike the Vertical and Horizontal Grid tests, the Grid test accommodates a broader range of inclinations. This makes it particularly useful for detecting muscular dysfunction and assessing the impact of pharmacological treatments. Additionally, the test can be adapted to study age-related neuromuscular decline and to investigate nerve regeneration or damage.

Performing multiple trials using the Grid test may lead to muscle fatigue in the subjects. Additionally, the performance of the subjects can be influenced by their weight, so having a sizable group of subjects with similar weights is crucial for obtaining consistent results. Rest periods between trials are necessary to mitigate fatigue and ensure accurate measurements. Other factors, such as the subjectā€™s age and sex, may also impact performance. Furthermore, the rod that crosses the grid could complicate the assessment of motor deficits.

Summary and Key Points

  • The Grid test evaluates motor deficits by inverting the subject on a grid mesh and evaluating their hang performance and motor coordination.
  • Unlike the Horizontal Grid test and Vertical Grid test, the Grid test allows different angles of inclinations, thus making it more adaptable to different types of investigation.
  • Using the Grid test may be difficult for untrained investigators.
  • The test doesnā€™t require any stimuli as rodents are known to grip on to materials instinctively.
  • The subjectā€™s performance is also dependent on its weight.

References

Kim ST, Son HJ, Choi JH, Ji IJ, Hwang O (2010).Ā Vertical grid test and modified horizontal grid test are sensitive methods for evaluating motor dysfunctions in the MPTP mouse model of Parkinsonā€™s disease. Brain Res. 1306:176-83. doi: 10.1016/j.brainres.2009.09.103.

Tillerson, J.L., Caudle, W.M., Reverson, M.E., Miller, G.W., (2002).Ā Detection of behavioral impairments correlated to neurochemical deficits in mice treated with moderate doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine.Ā Exp. Neurol. 178, 80ā€“90.

Tillerson, J.L., Miller, G.W., (2003).Ā Grid performance test to measure behavioral impairment in the MPTP-treated mouse model of parkinsonism. J. Neurosci. Methods 123, 189ā€“200.

Additional information

Version

Version 1, Version 2

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