In Parkinson’s disease and movement disorders in general, sensitive and reliable behavioral assays are essential for testing novel potential therapeutics. Here, we describe a manageable battery of sensorimotor tests for mice that are sensitive to varying degrees of injury to the nigrostriatal system and useful for preclinical studies.
Sensitive and reliable behavioral outcome measures are essential to the evaluation of potential therapeutic treatments in preclinical trials for many neurodegenerative diseases. In Parkinson’s disease, sensorimotor tests sensitive to varying degrees of nigrostriatal dysfunction are fundamental for testing the efficacy of potential therapeutics. Reliable and quite elegant sensorimotor measures exist for rats, however many of these tests measure sensorimotor asymmetry within the rat and are not entirely suitable for the newer genetic mouse models of PD. We have put together a battery of sensorimotor tests inspired by the sensitive tests in rats and adapted for mice. The test battery highlighted in this study is chosen for a) its sensitivity in a wide variety of mouse models of PD, b) its ease in implementing into a study, and c) its low expense. These tests have proven useful in characterizing novel genetic mouse models of PD as well as in testing potential disease-modifying therapies.
Parkinson’s disease (PD) is a debilitating neurodegenerative disorder primarily characterized by the progressive loss of dopaminergic neurons in the substantia nigra and the development of Lewy body inclusions in central and peripheral systems. Patients suffer from sensorimotor impairments, including bradykinesia, tremor, rigidity, and postural instability that worsen over time. Although rare, familial forms of the disease discovered over the last 15 years have led to the identification of important novel targets for potential disease-modifying therapeutics. Mutations in genes encoding alpha-synuclein, parkin, DJ-1, LRRK2, and ATP13A2 among others mark the development of a new “generation” of animal models of PD, genetic mouse models.
Excellent non-drug-induced behavioral measures exist for the extensively studied unilateral 6-hydroxydopamine (6-OHDA) rat model of PD. These include tests for limb-use asymmetry, movement initiation, somatosensory neglect, reaching abilities, and more recently ultrasonic vocalizations1-6. These tests are sensitive to varying degrees of nigrostriatal dopamine neuron loss and have been used extensively to evaluate the efficacy of various types of potential therapeutics7-11. However, with the genetic mouse models there is not a clear consensus on the best sensorimotor tests to use or how many to use. This is problematic when characterizing a novel genetic mouse model, in preclinical studies, and when trying to make comparisons between models. Over the past decade we have worked to put together a battery of sensorimotor tests for mice similar to what has been used successfully in rats. The tests described in this article have been used to help characterize numerous genetic mouse models of PD and are currently used in preclinical studies testing novel potential therapeutics12.
The most common tests used to assess motor function in mice are activity in the open field and the rotarod test of coordination13. Although both of these tests are automated, relatively easy to use and provide information on sensorimotor function, they often lack the sensitivity needed to detect subtle alterations in the nigrostriatal dopamine system. For example, parkin deficient mice with subtle alterations in dopamine function do not display impairments on the rotarod but do display motor impairments on a challenging beam test14. In addition, mice treated with moderate doses of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) do not show impairments on the rotarod but do have significant alterations in gait and impairments on an inverted grid test15. Therefore, studies that use only the rotarod for phenotypic assessment may miss more subtle impairments. An optimal approach, in our opinion, to behavioral characterization is one that includes a battery of tests that are sensitive to different aspects of sensory and motor function, and subtle changes in basal ganglia function13-15. Here we describe how to measure and analyze sensorimotor function in mice using a challenging beam traversal test, a test of spontaneous activity in the cylinder, and a response to sensory stimuli test.
Optimally mice should be tested during their active (dark) cycle. The mice in our laboratory are maintained on a reverse light/dark cycle that enables us to conveniently test the mice during their active period (and ours). Testing is not started until at least one hour into the dark cycle. However, it is not always possible for an investigator to maintain a separate mouse room with a reverse light cycle. In that case, all three tests can be performed during the light cycle but keep in mind that time to traverse on the beam, number of steps and rears in the cylinder, and contact and removal times may be longer when tested during this time.
All three tests described below can be performed by one experimenter, but for those who are not as experienced handling and working with mice or have little to no experience measuring behavior in mice then an additional experimenter may be needed. In this case the second experimenter can assist with the challenging beam test by placing mice on the beam while the other experimenter records the trial or in the adhesive removal test the second experimenter can run the timer while the other places the sticker on the snout and places the mouse in the cage.
1. Challenging Beam Traversal Procedure
2. Analysis of Beam Video
3. Spontaneous Activity in the Cylinder Procedure
4. Analysis of Spontaneous Activity
5. Adhesive Removal
The challenging beam, spontaneous activity in the cylinder, and adhesive removal tests are all highly useful assays of sensorimotor function in mice. We have found alterations in sensorimotor function using these tests in multiple genetic and toxin mouse models of Parkinson’s disease including parkin knockout, parkin Q311X, Pitx3-aphakia, alpha-synuclein overexpressing, and unilateral 6-hydroxydopamine mice14, 16-19. Here we show data collected from mice overexpressing human wildtype alpha-synuclein under the Thy1 promoter (Thy1-aSyn) and Pitx3-aphakia mice 18,20. On the challenging beam we reliably detect increased errors per step in Thy1-aSyn compared to wildtype mice (Figure 1). In the same line of mice we also repeatedly detect a robust decrease in hindlimb stepping in the cylinder (Figure 2)12, 16, 21. In the adhesive removal test Pitx3-aphakia mice with a profound decrease in nigrostriatal dopamine neurons show significantly increased time to contact compared to wildtype controls (Figure 3).
Figure 1. Errors on the challenging in Wildtype (n=13) and Thy1-aSyn (n=4) at 4 months of age. A) Errors per step, mean of five trials. B) Mean errors at each beam width. ** represents p<0.01 respectively compared to Wildtype mice. Student’s t-test.
Figure 2. Hindlimb stepping in the cylinder in Wildtype (n=13) and Thy1-aSyn (n=4) mice at 4 months of age. * represents p<0.05 compared to Wildtype. Student’s t-test.
Figure 3. Contact time in Wildtype (n=10) and Pitx3-aphakia (n=12) mice at 4 weeks of age. ** represents p<0.01 compared to Wildtype. Mann-Whitney U.
Test | Parameters | Analysis Options |
Challenging Beam | Errors | Beam Widths (Errors only) Mean of 5 Trials Individual Trials |
Time | ||
Steps | ||
Spontaneous Activity | Forelimb Steps | Mean Forelimb/Hindlimb Ratio |
Hindlimb Steps | ||
Rears | Mean | |
Grooming Time | Mean | |
Adhesive Removal | Contact time | Mean Median Best/Worst Score Removal time Contact time score |
Removal time |
Table 1. Sensorimotor function Test Battery: Analysis Options.
In the present study we show how to perform and analyze three useful tests of sensorimotor function in mice. These include the challenging beam, spontaneous activity in the cylinder, and response to sensory stimuli (adhesive removal). These tests were chosen for the following reasons 1) we and others have found them to be highly sensitive to varying degrees of nigrostriatal dopaminergic dysfunction in genetic mouse models14,16-18, 2) only a short amount of training is required for the beam and handling for the response to sensory stimuli tests and once trained the assays can be performed in one test session, and 3) the price of the equipment needed to perform the tests is quite low compared to purchasing more automated equipment such as the rotarod and open field chambers.
The challenging beam test is not only useful at detecting motor performance and coordination deficits in genetic mouse models of PD but is also useful in uncovering impairments in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated and 6-hydroxydopamine-treated mice and norepinephrine deficient mice19, 23-25. In addition, we find the challenging beam to be less influenced by body weight compared to other tests of motor performance and coordination (rotarod and pole test). This is particularly beneficial when working with aged male mice that can weigh up to 50+ grams. Similar to the beam, alterations in spontaneous activity are reliably observed in parkin knockout, PQ311X, Thy1-aSyn, Pitx3-aphakia, and LRRK2 mice14, 16-18, 26. The adhesive removal test is also sensitive to genetic manipulation including parkin knockout, parkin Q311X, Thy1-aSyn, and DJ-1 knockout mutations in mice14,16, 17, 22. In the unilateral 6-hydroxydopamine-treated mouse the adhesive removal test is performed in a manner similar to how it is typically done with rats1,2. The adhesive label is placed on each forepaw using a forcep and the time to remove the label is recorded. We found that 6-hyrdoxydopamine-treated mice will remove the label from the unaffected limb prior to removing the label on the affected limb 19.
This test battery is easy to implement in aging studies using chronic treatments but it is also easy to use in pharmacological studies. Once animals are trained and ready for testing a test station for each assay can be set up. The animals are then run in the same order on each test. The drug of interest can be administered and once the desired drug peak concentration is reached each mouse can be tested on the beam and then moved to the cylinder for three minutes and then to the adhesive removal test. We found this strategy to work well when testing different dopamine agonists in mice18, 21. Both the beam and adhesive removal tests are amenable to repeated testing, however spontaneous activity in the cylinder is affected by repeated testing resulting in reduced activity over time16. Depending on how robust the deficit is in the mouse you may still be able to detect differences with repeated testing in the cylinder16. In general, habituation and reduced activity is observed as soon as the 2nd exposure to the cylinder however, we find that we can get sufficient activity levels when we run the spontaneous activity test immediately following beam traversal in pharmacological studies18,21. The number of spontaneous activity testing sessions to include in a study will be dependent on mouse strain (some are definitely more active than others) and treatment duration. In our pharmacological studies in mice on a mixed C57BL/6 X DBA background we measured activity between 2-4 times and the testing sessions were separated by one week21.
The beam and cylinder tests do require post-testing analysis of videorecorded behaviors. For this aspect of the analysis it is particularly important to have raters that are blind to the experimental conditions. When we train new raters in the laboratory we have the person score behavior on videotapes previously analyzed by an expert rater from the lab. The criteria are explained and shown to the new rater and then the person begins to score the previously analyzed tapes on their own. The scores are then compared to the expert’ ratings. The person is not allowed to rate new data until they are within 95-98% accuracy of the expert. All data is then randomly spot-checked for accuracy by an expert rater.
The battery of tests described in this study is designed to assess sensorimotor function in mice. However, whenever characterizing a novel mouse model of disease it is always important to do a basic examination of the animal as well. Body weight and temperature should be monitored throughout testing and any abnormal behaviors should be noted, like the removal of vibrissae or clasping of the hindlimbs when picked up by the tail. Basic neurological assessments are described elsewhere in detail27-29.
The authors have nothing to disclose.
This work is funded by NIH/NINDS NS07722-01 and the Gardner Family Center for Parkinson’s Disease and Movement Disorders.
Material Name | Company | Dimensions | Comments |
Challenging beam apparatus | Starks Plastics | Segment 1= 3.5 cm Segment 2= 2.5 cm Segment 3= 1.5 cm Segment 4= 0.5 cm |
Contact information: 11276 Sebring Dr. Forest Park ,OH 45240 USA Ph +1 (513) 541-4591 Fax +1 (513) 541-6773 |
Cylinder | Starks Plastics | 15.5 cm diameter 12.7 cm height |
Contact information: 11276 Sebring Dr. Forest Park ,OH 45240 USA Ph +1 (513) 541-4591 Fax +1 (513) 541-6773 |
Mesh Grid Wiring | Ace Hardware | 1 cm2 | |
Mouse Cages | Ancare | 19 x 29 x 12.7 cm | |
Glass | Ace Hardware | 19 cm2 | |
Mirror | Ace Hardware | 18 x 13 cm | |
Camcorder | Sony HDR-HC9 | ||
MiniDV Tapes | Sony DVC premium | 90 min long play | |
Labels | AveryColor Coding Labels | 6.35 mm diameter (1/4″ Round) |