Impulsive-compulsive behaviours and striatal neuroactivity in mildly parkinsonian rats under D2/3 agonist and L-DOPA treatment

Dopamine replacement therapy for Parkinson's disease can induce impulsive-compulsive behaviours (ICBs). Here we compare the D2/3 agonist ropinirole and L-DOPA, given alone or combined, with regard to their potential to induce ICBs in rats sustaining bilateral striatal injections of 6-hydroxydopamine. Daily treatment with ropinirole (2.5 mg/kg), L-DOPA (24.0 mg/kg), or their combination was given for six weeks while animals were examined using tests of compulsive checking and motor stereotypies not previously used in the ICB literature. Independently of L-DOPA cotreatment, ropinirole induced a stereotyped hyperactivity pattern, compulsive checking, and maladaptive choices in the rat version of the Iowa gambling task. Compared to both L-DOPA and vehicle, ropinirole elicited a distinct pattern of striatal neuroactivity, shifting the expression of a cellular activity marker from dorsolateral to centro-medial regions. Our results reveal quite distinct profiles of ICBs and striatal activation upon treatment with ropinirole or L-DOPA, providing clues of therapeutic relevance to Parkinson's ICBs.