Altered M2 Cortex - Superior Colliculus visual perception circuit in Huntington's Disease
The premotor cortical area -M2 cortex in rodents- connection to the striatum is involved in movement and prominently affected in Huntingtons Disease (HD). M2 cortex also projects to the superior colliculus (SC), implicated in oculomotor functions (i.e. saccades) and visual perception. Here, we investigated the contribution of M2 cortex - SC circuit to HD physiopathology in male mice. Using fMRI, we observed that M2 cortex functional connectivity with the SC was the most prominently affected circuit in the symptomatic R6/1 HD mouse model. Structural alterations were also detected by tractography and viral tracing. HD mice showed decreased defensive behavioral responses towards an unexpected visual stimuli, such as a moving robo-beetle, and decreased locomotion upon unexpected flash of light. Additionally, optogenetic M2 cortex - SC stimulation promoted avoidance responses towards the robo-beetle in WT, but not HD mice. Though, DWI measurements in vivo and ex vivo electrophysiological responses to optogenetic and electrical stimuli in the SC suggested preserved brain structure. Finally, GCamp6f fluorescence recordings with fiber photometry indicated that aberrant M2 cortex engagement might be the underlying mechanism of visual perception alterations in HD. Collectively, our findings point to a key role of M2 cortex - SC circuit alterations in HD pathophysiology.