Osting, S. | bioRxiv Science

bioRxiv2026

Levodopa induced dyskinesia severity is linked to distinct microstructural alterations in nigrostriatal and brainwide neural circuits

Dopaminergic replacement therapy via L-DOPA is the major medical therapy for Parkinsons Disease. Long-term L-DOPA administration is known to cause dyskinetic movements, L-DOPA Induced Dyskinesia (LID). It remains unclear if the LID related, maladaptive changes in brain structure/function are localized to neural circuits within the nigrostriatal DA system or have brainwide impact. We employed multi-shell diffusion magnetic resonance imaging and correlational tractography to investigate structural brain networks associated with daily administration of L-DOPA and the development of LID in the unilateral 6-hydroxydopamine rat model. 53% of rats receiving L-DOPA therapy developed severe LID. Tractography found brainwide statistical maps positively and negatively associated with LID severity highlighted by bilateral neural circuits contained in the lesioned nigrostriatal system as well as others including the cerebellum and prefrontal cortex. These results suggest that systemic dysfuntion in brainwide neural circuits forms the mechanistic basis the maladaptive changes underlying LID.

neuroscience↗

bioRxiv2024

Assessing changes in whole-brain structural connectivity in the unilateral 6-hydroxydopamine rat model of Parkinson's Disease using diffusion imaging and tractography

I.Parkinsons disease (PD) is a multifactorial, progressive neurodegenerative disease that has a profound impact on those it afflicts. Its hallmark pathophysiology is characterized by degeneration of dopaminergic neurons in the midbrain which trigger a host of motor and non- motor symptoms. Many preclinical research efforts utilize unilateral lesion models to assess the neural mechanisms of PD and explore new therapeutic approaches because these models produce similar motor symptoms to those of PD patients. The goal of this work is to examine changes in brain structure resulting from a unilateral lesion both within the nigrostriatal system, where dopaminergic neurons are lost, and throughout the brain. Using multi-shell diffusion magnetic resonance imaging and correlational tractography, we assessed microstructural changes throughout the brain resulting from unilateral injection of 6-hydroxydopamine (6-OHDA) in the median forebrain bundle (MFB). Following lesioning, the PD phenotype was confirmed using behavioral and histological assessment. Correlational tractography found networks of fiber tracts that were either positively or negatively correlated with lesion status throughout the brain. Analyzing patterns of intra- and inter-hemispheric connectivity between the positively and negatively correlated fiber tracts revealed two separate neural networks. The first contained only negatively correlated fibers in the lesioned hemisphere consistent with the local effects of the lesion (i.e. dopaminergic depletion in the nigrostriatal system). The second contained systematically overlapping fiber tracts in the lesioned and non-lesioned hemispheres including the olfactory system and cerebellum, which we suggest are indicative of adaptive mechanisms to compensate for the lesion. Taken together, these results suggest that correlational tractography is a reasonable tool to examine whole brain structural changes in rodent models of neurodegenerative disease, and may have future translational value as a diagnostic tool for patients with PD.

neuroscience↗