Differential degradation of motor deficits during gradual dopamine depletion with 6-hydroxydopamine in mice

Abstract

Parkinson’s disease (PD) is a movement disorder whose cardinal motor symptoms arise due to the progressive loss of dopamine. Although this dopamine loss typically progresses slowly over time, currently there are very few animal models that enable incremental dopamine depletion over time within the same animal. This type of gradual dopamine depletion model would be useful in studies aimed at the prodromal phase of PD, when dopamine levels are pathologically low but motor symptoms have not yet presented. Utilizing the highly characterized neurotoxin 6-hydroxydopamine (6-OHDA), we have developed a paradigm to gradually deplete dopamine levels in the striatum over a user-defined time course – spanning weeks to months – in C57BL/6 mice. Dopamine depletions were achieved by administration of five low dose injections (0.75 µg) of 6-OHDA through an implanted intracranial bilateral cannula targeting the medial forebrain bundle. Levels of dopamine within the striatum declined linearly with successive injections, quantified using tyrosine hydroxylase immunostaining and high-performance liquid chromatography. Behavioral testing was carried out at each time point to study the onset and progression of motor impairments as a function of dopamine loss over time. We found that spontaneous locomotion, measured in an open field, was robust to loss of dopamine until ~70% of striatal dopamine was lost. Beyond this point, additional dopamine loss caused a sharp decline in motor performance, reaching a final level comparable to that of acutely depleted mice. Similarly, although rearing behavior was more sensitive to dopamine loss and declined linearly as a function of dopamine levels, it eventually declined to levels similar to that seen in acutely depleted mice. In contrast, motor coordination, measured on a vertical pole task, was only moderately impaired in gradually depleted mice, despite severe impairments observed in acutely depleted mice. These results demonstrate the importance of the temporal profile of dopamine loss on the magnitude and progression of behavioral impairments. Our gradual depletion model thus establishes a new paradigm with which to study how circuits respond and adapt to dopamine loss over time, information which could uncover important cellular events during the prodromal phase of PD that ultimately impact the presentation or treatability of behavioral symptoms.

Neuroprotective effect of Portulaca oleracea extracts against 6-hydroxydopamine-induced lesion of dopaminergic neurons

“…Here, the administration of both extracts produced a nearly 70% increase in preservation of dopaminergic cells. It is in agreement with the reports that spontaneous locomotion, measured in an open field, is impaired in a manner closely related to striatal dopamine depletion after 6-OHDA in rodents (Kirik et al 1998, Willard et al 2015.…”

Beneficial Effect of Chronic Treatment with Extracts from Rhodiola Rosea L. and Curcuma Longa L. on the Immunoreactivity of Animals Subjected to a Chronic Mild Stress Model

“…Rearing behavior is known to be more sensitive to dopamine loss and should decline linearly as a function of dopamine levels. 28 It could be speculated that in the present study neither the CMS procedure nor the two extracts used have affected the dopamine levels to that extend to cause a sharp vertical motor defi cit.…”

Cell-specific pallidal intervention induces long-lasting motor recovery in dopamine-depleted mice

“…Brains were retrieved, fixed in 4% PFA for 24 hr before being placed in a 30% sucrose solution. Brains were sliced at 30 μm thickness and prepared for the appropriate incubations, as described previously 50 . Primary antibody included rabbit anti-GFP (1:1000, Millipore 06-896), Mouse anti-HuC/D (1:200, Molecular Probes A21271), mouse anti-NeuN (1:100, Millipore MAB377), rabbit anti-TH (1:1000, Pel-Freez P40101-0), at room temperature for 24 hours or at 4°C for 48 h when using rabbit anti-PV (1:1000, Swant PV 27).…”