Altered Striatal Acetylcholine Dynamics across Dopamine Loss and L-DOPA Treatment

L-DOPA remains the most effective therapy for Parkinsons disease (PD), yet its chronic use often induces involuntary movements known as L-DOPA-induced dyskinesia (LID). While abnormal cholinergic interneuron (ChI) activity is a hallmark of both PD and LID, emerging evidence suggests that the temporal organization of acetylcholine (ACh) signaling, rather than its overall magnitude, may determine its functional impact. Under physiological conditions, ChIs exhibit intrinsic delta-frequency activity reflected in coordinated, slow oscillations of extracellular ACh, which are thought to organize striatal network function and movement pattering. To determine how dopamine (DA) depletion and L-DOPA treatment reshape these ACh dynamics, we used in vivo GRAB-ACh fiber photometry in the unilateral 6-OHDA mouse model. DA depletion disrupted slow ACh rhythmicity, reducing delta-band regularity while increasing higher-frequency phasic activity. Acute L-DOPA broadly suppressed ACh activity across frequencies, partially normalizing this imbalance, but without restoring slow temporal structure. In addition, chronic L-DOPA treatment, associated with established dyskinesia, further impaired delta-band coordination in the DA-depleted striatum during the ON state, while OFF-state activity retained lesion-associated features. The anti-dyskinetic agent amantadine restored low-frequency temporal structure both before and after L-DOPA exposure. Together, these findings reveal a state-dependent reorganization of striatal ACh dynamics, characterized by a shift from coordinated slow oscillations to irregular phasic activity following DA loss, and a further breakdown of slow temporal organization during dyskinetic states. These results highlight the temporal structure of cholinergic signaling as a critical and underappreciated dimension of striatal function in PD and LID.