Abstract

Modulation of corticostriatal plasticity alters the information flow throughout basal ganglia circuits and represents a fundamental mechanism for motor learning, action selection, and reward. Synaptic plasticity in the striatal direct- and indirect-pathway spiny projection neurons (dSPNs and iSPNs) are dichotomically regulated by two distinct networks of GPCR signaling cascades. While it is well-known that dopamine D2 and adenosine A2a receptors bidirectionally regulate iSPN plasticity, it remains unclear how D1 signaling modulation of synaptic plasticity is counteracted by a dSPN-specific Gi signaling. Here, we show that striatal dynorphin selectively suppresses long-term potentiation (LTP) through Kappa Opioid Receptor (KOR) in dSPNs. Both KOR antagonism and conditional deletion of dynorphin in dSPNs enhance LTP counterbalancing with different levels of D1 receptor activation. Behaviorally, mice lacking dynorphin specifically in dSPNs show normal motor behavior and reward-based learning, but enhanced flexibility during reversal learning. These findings support a model in which D1R and KOR signaling bidirectionally modulate synaptic plasticity in striatal direct pathways and behavior.