Our protocol provides a detailed method for a reliable induction and comprehensive rating of levodopa-induced dyskinesia in a rat model of Parkinson's disease. The main advantage of our dyskinesia rating scale is that it allows for quantification of both the intensity of a given abnormal involuntary movement and the amount of time spent exhibiting that behavior. Dependable animal models of levodopa-induced dyskinesia are critical in realizing the final goal of finding effective treatments to reduce or eliminate the side effect in individuals with Parkinson's disease.
Start the preparation for the experiment by weighing rats weekly to calculate the appropriate drug quantity based on the weight changes. Provide the rats with nutritionally complete and highly palatable treats. On the first day of L-DOPA treatment, transfer rats to single housing supplied with institutional Animal Care and Use Committee approved enrichment.
And maintain rats into the single housing throughout the study to avoid peer interference with the behavioral assessments. On the dyskinesia rating days, remove water bottles, food racks, and the enrichment in the cage to avoid interference with the behavioral assessments, and place the cages on a steel wire rack at an approximately 45 degree angle, then flip the identification tags upward. Before the L-DOPA injection, add the appropriate volume of sterile saline to the pre-weigh lyophilized L-DOPA and benserazide mix in the amber vial and shake well for 10 seconds.
Immediately after the preparation, fill the required volume of the L-DOPA-Benserazide mix for each animal in individual syringes mounted with a 26 gauge needle and label each syringe with an individual animal identification. After bringing the first cage to the injection bench, remove the rat from its cage to place it on the injection surface. Use the nondominant hand to restrain the head and shoulders of the rat with the palm against the surface and scruff the skin on the back overlying the scapulae with the thumb and forefinger.
Use the dominant hand to inject L-DOPA volume into the subcutaneous space between the fingers, keeping the needle parallel to the body to avoid intramuscular injection. Post injection, move the rat into the cage. Next, set the timer for one to two minutes and repeat the procedure injecting one rat every one to two minutes until all the rats are injected.
On the rating day, position a timer next to the cage to observe levodopa-induced dyskinesia or LID behavior intensity while estimating the frequency of any given behavior during the rating period. Rate the intensity and frequency of the dystonic and hyperkinetic dyskinesia movements including the initial onset of LID behavior, peak behavior and the phase of decline at the desired number of time points. If using one minute rating intervals, set a timer for one minute to rate the first rat and continue the rating through all the rats at one minute intervals.
The LID rating for abnormal involuntary behaviors in the Parkinsonian rats was categorized to include intensity and frequency of the behaviors. A range of abnormal involuntary movements, including dystonic, hyperkinetic, and stereotypic behaviors were observed in rats. The representative analysis provides an example of the data presented as peak dose LID over the entire experimental timeline and dosage schedule.
The peak dose LID was defined as a time when the group average LID score was the greatest. Additionally, the LID rating data was examined over each daily rating time course at different L-DPOA concentrations with the groups combined and plotted as individual animals. Postmortem tissue from behaviorally evaluated subjects can be used to explore molecular mechanisms associated with levodopa-induced dyskinesias, and the impact of therapeutic interventions on such molecular mechanisms.
Animal models of levodopa-induced dyskinesia have been useful in elucidating several mechanisms thought to underlie this behavioral malady. Such understanding has led to preclinical and clinical evaluation of several targets.
