ABS 046: Mapping Secondary Motor Cortex Projections in Murine Models of Parkinson's Disease

Angel R. Varghese ¹ , Zoe Fokakis ¹ ² , J. Andrew Hardaway ¹ , Laura Volpicelli-Daley ²

¹ Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham
² Center for Neurodegeneration and Experimental Therapeutics, University of Alabama at Birmingham

Van Wickle (2025) Volume 1, ABS 046

Introduction: Parkinson's disease (PD) is a neurodegenerative disorder that is an increasing health concern, affecting more than 8.5 million individuals globally. Symptoms of PD include cognitive deficits and motor impairments, such as postural imbalance, walking difficulties, and bradykinesia. These symptoms are strongly associated with the lack of dopaminergic neurons in the substantia nigra and alpha-synuclein aggregation throughout the brain. In PD, there is significant alpha-synuclein aggregation in the secondary motor cortex (M2) glutamatergic neurons, which project into the striatum. We are studying the effects of this glutamatergic corticostriatal disruption by recording neuronal activity in the striatum during stimulation of M2 via ChrimsonR-tdTomato by using in vivo fiber photometry. Through stereotaxic surgery, the ChrimsonR-tdTomato red fluorescent virus is bilaterally injected into the M2 and will indicate expression through stimulation experiments. The retroCre bilaterally injected into the striatum will mark the M2 neuron’s axons that project into this region with fluorescence. These experiments will confirm the association between the M2 and striatum, and the expression of axons found in other regions will reveal areas also affected by PD. Additionally, we will learn more about how the reduced striatal glutamate release impacts the performance of the mice through stimulation experiments. We are studying the effects of this corticostriatal Lewy pathology (LP) by recording glutamatergic activity via iGluSnFR3 in the dorsomedial striatum (DMS) during stimulation of M2 via ChrimsonR-tdTomato through in vivo optogenetics and fiber photometry. C57BL/6J mice are injected with pre-formed fibrils of α-synuclein (PFFs) or monomeric α-synuclein (controls) before undergoing optogenetic stimulation of M2 while glutamatergic activity is recorded. The glutamate releases in the striatum will be examined microscopically after sections have undergone IHC staining. Our work will enhance understanding of how LP affects the M2-striatal connection and reduces striatal glutamate release, influencing mice performance in behavioral assays.

Methods: Through stereotaxic surgery, the ChrimsonR-tdTomato red fluorescent virus is bilaterally injected into the M2 and will indicate expression through stimulation experiments. The retroCre bilaterally injected into the striatum will mark the M2 neuron’s axons that project into this region with fluorescence. Under wide-field microscopy, the projections between the M2 and striatum and expression of axons found in other regions will be traced to reveal areas also affected by PD. Additionally, we will use optogenetic stimulation to study the impact of reduced striatal glutamate release. We will record glutamatergic activity via iGluSnFR3 in the DMS during stimulation of M2 via ChrimsonR-tdTomato through in vivo optogenetics and fiber photometry. C57BL/6J mice are injected with pre-formed fibrils of α-synuclein (PFFs) or monomeric α-synuclein (controls) before undergoing optogenetic stimulation of M2 while glutamatergic activity is recorded. The glutamate releases in the striatum will be examined microscopically after sections have undergone IHC staining.

Results: The M2 and DMS projections were visualized, and this connection between brain regions can be confirmed. We were also able to trace the collateral axons from the M2 that projected into the primary and secondary somatosensory cortices, lateral preoptic area, and ventral pallidum. Through optogenetic stimulation, we studied the dose-dependent effect on striatal glutamate release in the DMS with regards to temporal progression of PD in the mice. The varying laser frequencies during stimulation administered to the M2 resulted in significant differences in glutamatergic responses, with 20Hz at Week 9 displaying the most significant reduction in glutamate release.

Discussion: A more comprehensive understanding of M2’s role in Parkinson’s disease can be achieved by tracing additional collateral axons to identify targeted regions beyond the DMS. Additionally, using fiber photometry, we can assess glutamate activity in PFF-injected mice during behavioral assays like open field, serial order tasks, and running wheel. Using more goal-directed behaviors and interactive stimuli, we expect a better understanding of the impact of reduced striatal glutamatergic response in the DMS in mice performance.