Subtype-Specific Roles of Nigrostriatal Dopaminergic Neurons in Motor and Associative Learning

Abstract

Nigrostriatal dopaminergic neurons (DANs) in the substantia nigra pars compacta (SNc) comprise distinct subtypes defined by unique gene expression profiles and anatomical characteristics. However, their specific contributions to motor and non-motor functions remain elusive. Using Calbindin 1 (Calb1) and Aldehyde dehydrogenase 1a1 (Aldh1a1) as molecular markers, we investigated the functions of these nigrostriatal DAN subtypes in mice. Through intersectional genetics and chemogenetic manipulation, we selectively inhibited Calb1+ or Aldh1a1+ DANs by stereotactically delivering an adeno-associated viral vector (AAV-CreOn-FlpOn-hM4Di-P2A-mCherry) into the SNc of ThFlp; Calb1IRESCre or ThFlp; Aldh1a1CreERT2 double knock-in (KI) mice. This approach enabled subtype-specific neuronal inhibition via designer receptors exclusively activated by designer drugs (DREADD). Following DREADD ligand administration, both Calb1+ and Aldh1a1+ DAN-inhibited mice exhibited significant reduction in voluntary movement and impaired motor skill learning, demonstrating their essential roles in motor function. However, only Calb1+ DAN inhibition affected early associative-learning behavior, suggesting a unique role in reinforcement learning. These findings establish Calb1+ and Aldh1a1+ nigrostriatal DANs as key regulators of movement and motor learning, with Calb1+ neurons additionally modulating reward-based associative learning. This study advances our understanding of the functional heterogeneity of nigrostriatal DAN subtypes and identifies potential therapeutic targets for addressing motor and non-motor deficits in Parkinsons disease.