Subtype-specific roles of nigrostriatal dopaminergic neurons in motor and associative learning

Define the subtype-specific contributions of nigrostriatal dopaminergic neurons (DANs) to motor and non-motor behaviors by comparing Calbindin 1-positive (Calb1 ⁺) and Aldehyde dehydrogenase 1a1-positive (Aldh1a1 ⁺) DANs.

Intersectional genetic strategy and chemogenetic inhibition were applied to selectively silence Calb1 ⁺ or Aldh1a1 ⁺ DANs in mice. An adeno-associated viral vector (AAV-CreOn-FlpOn-hM4Di-P2A-mCherry) was stereotactically delivered into the substantia nigra pars compacta of double knock-in lines Th ^Flp; Calb1 ^IRESCre or Th ^Flp; Aldh1a1 ^CreERT2. Following expression, subtype-specific neuronal inhibition was induced with a designer receptor exclusively activated by designer drugs (DREADD) ligand, and the mice were assessed in assays of voluntary movement, motor skill learning, and early associative learning behavior.

Chemogenetic inhibition of either Calb1 ⁺ or Aldh1a1 ⁺ DANs produced a marked reduction in voluntary movement and impaired acquisition of motor skills, indicating that both subtypes are necessary for normal motor function and learning. In contrast, only inhibition of Calb1 ⁺ DANs altered early associative-learning performance, revealing a dissociable, subtype-specific role for Calb1 ⁺ neurons in reinforcement-related behavior that was not observed with Aldh1a1 ⁺ neuron inhibition.

Both Calb1 ⁺ and Aldh1a1 ⁺ nigrostriatal DANs are key regulators of movement and motor learning, with Calb1 ⁺ neurons additionally modulating reward-based associative learning. These findings highlight the functional heterogeneity of nigrostriatal DAN subtypes and identify potential therapeutic targets for addressing motor and non-motor deficits in Parkinson's disease.