Cortical Intra-Layer Hypersynchronization in Levodopa-Induced Dyskinesia Mouse Model.

BACKGROUND

Levodopa (l-dopa)-induced dyskinesia (LID) is a common and difficult complication in Parkinson's disease (PD) patients. It may result from hyperactivation of the primary motor cortex (M1) due to hypoactivation of the basal ganglia (BG) output nuclei. Electrophysiological evidences are sparse, mainly due to technological limitations related to the poor ability to simultaneously acquire data from many neurons of the different involved regions. We exploited the Neuropixels technology to overcome these obstacles.

METHODS

Extracellular Neuropixels recordings were acquired from awake head-restrained mice in wild-type (WT), parkinsonian, and LID conditions. Activity was recorded from M1 and the motor striatum simultaneously and compared for each mouse in four conditions: control (WT with and without l-dopa), hemiparkinsonian (6-hydroxydopamine model), and LID states.

RESULTS

Neural firing rates in M1 were decreased in PD and increased in LID as expected. Focusing on the quiet periods, the firing rates between the different conditions were similar. LID was associated with cortical intra-layer hypersynchronization, a phenomenon not previously described. The overall synchrony was significantly increased between neurons of Layers 2, 3, and 5 in M1 in LID compared to PD state. Inter-layer cross-correlation was increased in LID, compared to PD state, between Layer 5 of M1 and the striatum. These changes in functional connectivity were absent in WT mice receiving l-dopa.

CONCLUSIONS

Our single-cell recordings from thousands of neurons provide insight into cortical network changes in LID. We found that LID is associated with intra-layer hypersynchronization of neurons within the motor cortex, which may be an intrinsic network feature within the cortico-BG loop.