Pramipexole- and methamphetamine-induced reward-mediated behavior in a rodent model of Parkinson's disease and controls.

Pramipexole (PPX) is a dopamine agonist that is FDA-approved for treatment of motor dysfunction in Parkinson's disease and restless leg syndrome. In a subpopulation of treated patients, PPX can lead to impulsive-compulsive disorders including behavioral addictions and dopamine dysregulation syndrome, a phenomenon that mirrors drug addiction. Regardless of this clinical picture, the capacity of PPX to regulate reward-mediated behaviors remains unclear and has not been evaluated in an animal model of Parkinson's disease. To fill this gap, we examined the rewarding potential of PPX in parkinsonian-like rats using conditioned place preference (CPP) and also evaluated associated motor behaviors. Methamphetamine (meth) and saline served as positive and negative controls, respectively. To model Parkinson's disease, the neurotoxin 6-OHDA was injected bilaterally into the dorsolateral striatum. The resulting lesions were verified functionally using a forelimb adjusting step and post mortem immunohistochemical staining of striatal tyrosine hydroxylase. Three pairings of meth (1mg/kg, ip), paired with a unique context, induced CPP in both 6-OHDA-treated and sham-operated rats; saline pairings had no effect. Three pairings of (±)PPX at 2mg/kg ip (equal to 1mg/kg of the active racimer) induced CPP in 6-OHDA-treated rats, but a higher dose (4 mg/kg, ip (±)PPX) was needed to induce CPP in sham rats. In all rats, acute administration of 2mg/kg (±)PPX decreased locomotor activity; the behavior was normalized by the third (±)PPX administration. In summary, these findings reveal that (±)PPX has motor and rewarding effects and suggest the parkinsonian brain state may be more sensitive to the rewarding, but not motoric effects.