Histo-radiological correlations in an early-stage model of a Parkinson's disease

The study aims to establish histo-radiological correlates in a bilateral 6-OHDA rat model of Parkinson's disease. A total of 37 Wistar rats were included, distributed into a model group (n = 19) that received injection of low doses of the toxin into the substantia nigra (SN) while the remaining animals, considered as control group received saline injections. A protocol lasting 2 months was setup including motor and sensorimotor evaluations, multi-sequence magnetic resonance imaging with T2w images, echo gradient imaging (T2*w) used to compute R2* maps and resting-state functional imaging. Lastly, after animals' sacrifice, dopaminergic degeneration as well as ferritin quantification were done. While behavioural analyses did not reveal significant differences between the groups, dopaminergic degeneration showed neurons loss estimated at 53 % in the SN and 45 % in the striatum in the 6-OHDA group. In the same way, ferritin quantification showed an increase in this group. In terms of imaging, the results showed no structural changes but an increase of R2* values in the substantia nigra as well as an increase in functional connectivity involving this structure in the 6-OHDA group. The association analyses showed negative correlation between the dopaminergic neurons in the SN and the corresponding R2* values as well as with the functional connectivity involving this structure. Values from R2* maps were also positively correlated with ferritin quantification in the SN. Taken all together, the experimental design as well as the obtained results suggest that SN R2* and functional connectivity are potential biomarkers of early disease stages.