[Motivation and apathy in Parkinson's disease: implication of dopaminergic D3 receptors]

Dopamine D3 Receptors: A Potential Target to Treat Motivational Deficits in Parkinson's Disease

Parkinson's disease (PD), which is traditionally viewed as a motor disorder involving the degeneration of dopaminergic (DA) neurons, has recently been identified as a quintessential neuropsychiatric condition. Indeed, a plethora of non-motor symptoms may occur in PD, including apathy. Apathy can be defined as a lack of motivation or a deficit of goal-directed behaviors and results in a pathological decrease of self-initiated voluntary behavior. Apathy in PD appears to fluctuate with the DA state of the patients, suggesting a critical role of DA neurotransmission in the pathophysiology of this neuropsychiatric syndrome. Using a lesion-based approach, we developed a rodent model which exhibits specific alteration in the preparatory component of motivational processes, reminiscent to apathy in PD. We found a selective decrease of DA D₃ receptors (D₃R) expression in the dorsal striatum of lesioned rats. Next, we showed that inhibition of D₃R neurotransmission in non-lesioned animals was sufficient to reproduce the motivational deficit observed in our model. Interestingly, we also found that pharmacologically targeting D₃R efficiently reversed the motivational deficit induced by the lesion. Our findings, among other recent data, suggest a critical role of D₃R in parkinsonian apathy and highlight this receptor as a promising target for treating motivational deficits.

La motivation dans tous ses K

La motivation peut être définie comme la fonction qui oriente et active le comportement. Nous résumons dans cette revue les acquis récents des neurosciences concernant les bases cérébrales des fonctions motivationnelles. En clinique neuropsychiatrique, les troubles de la motivation sont fréquents et actuellement évalués par des échelles qui ne renseignent pas sur les mécanismes sous-jacents. Nous présentons ici une nouvelle approche, dite computationnelle. Elle consiste à phénotyper le comportement des patients dans des tests de motivation, au moyen de modèles computationnels. Ces phénotypes computationnels caractérisent l’état du patient et pourraient aider au suivi et à la personnalisation du traitement.