This study investigates the effects of levodopa on rats with Parkinson's disease, focusing on the induction of dyskinesias. The methodology includes the injection of levodopa and a dopamine conversion inhibitor to observe behavioral changes over time.
Take a syringe filled with levodopa, a dopamine precursor, and a dopamine conversion inhibitor.
Inject this solution into the subcutaneous tissue of a restrained rat with Parkinson's disease, exhibiting damaged dopamine-producing neurons.
In the rat, the inhibitor binds to dopamine-producing enzymes and prevents the premature conversion of levodopa into dopamine.
Levodopa enters the bloodstream, crosses the blood-brain barrier via amino acid channels, and enters the nondamaged dopamine-producing neurons.
The enzymes in these neurons convert levodopa into dopamine, an excitatory neurotransmitter, and release it into the synapse.
Dopamine binds to its receptors on the post-synaptic neurons, triggering signal transmission.
Repeat the injections periodically to increase dopamine production.
Over time, excessive dopamine leads to overstimulation of its receptors and excessive neuronal signaling, which eventually disrupts the rat's body movements.
Place the rat in a cage and observe its behavior. The rat exhibits involuntary, repetitive body movements, known as dyskinesias, induced by levodopa.
Before the L-DOPA injection, add the appropriate volume of sterile saline to the pre-weighed, 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 non-dominant 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.
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