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Dose-dependent loss of motor function after unilateral medial forebrain bundle rotenone lesion in rats: a cautionary
Alexander Klein1, Darryl C Gidyk, Alexandra M Shriner
1Canadian Centre for Behavioural Neuroscience, Department of Neuroscience, University of Lethbridge, Lethbridge, Alberta T1K 3M4, Canada. kleina@cardiff.ac.uk
Abstract:
The organic pesticide rotenone is a neurotoxin suspected to cause Parkinson's disease (PD) symptoms by selectively targeting and compromising the survival of dopaminergic neurons. Rotenone in rodent models reproduces key features of human PD by impairing the mitochondrial electron transport chain, leading to intracellular alpha-synuclein aggregates and functional impairments typical for PD. The present study characterized the dose-response relationship of standard rotenone concentrations in motor impairments in a rat model. Rats received a single medial forebrain bundle injection of 4, 8, or 12μg of rotenone. Animals were assessed in skilled limb use, skilled and non-skilled walking and exploratory activity as well as drug-induced rotation. The results revealed rotational bias and stable impairments in skilled walking and gross motor function up to five weeks post injection. However, transient motor deficits facilitated rapid improvement of skilled reaching success. Mainly the temporal aspects of skilled and non-skilled motor performance were responsive to different rotenone concentrations. By contrast, drug-induced rotation and nigral TH+ cell loss were not influenced by different rotenone doses. Rats infused with 8μg and 12μg seemed to have reached a ceiling effect in motor deficits as they were not distinguishable in behavioral measures. Most strikingly, the stereological and morphological analyses revealed non-specific toxicity of vehicle and rotenone infusions that caused macroscopic lesions beyond nigral boundaries. These findings suggest that sensitivity of comprehensive motor tests to subtle modulation of dopamine function is independent of dopamine cell loss per se. Furthermore, caution is advised concerning non-specific toxicity of rotenone and vehicle substances in experimental animal models.
Insights
Rotenone pesticide exposure causes motor deficits in rats, but dose-response effects are complex and not always linked to dopamine neuron loss. Non-specific toxicity from rotenone and vehicle requires caution in Parkinson's disease (PD) research.
Area of Science:
- Neuroscience
- Toxicology
- Parkinson's Disease Research
Background:
- Rotenone, an organic pesticide, is a neurotoxin linked to Parkinson's disease (PD) symptoms.
- It selectively targets dopaminergic neurons, impairs mitochondrial function, and causes alpha-synuclein aggregation in rodent models.
Purpose of the Study:
- To characterize the dose-response relationship of rotenone in inducing motor impairments in a rat model.
- To investigate the correlation between rotenone concentration, motor deficits, and dopaminergic neuron loss.
Main Methods:
- Rats received medial forebrain bundle injections of 4, 8, or 12μg of rotenone.
- Motor function was assessed via skilled limb use, walking, exploratory activity, and drug-induced rotation.
- Stereological and morphological analyses evaluated nigral cell loss and tissue damage.
Main Results:
- Rotenone induced rotational bias and persistent motor impairments for up to five weeks.
- Temporal aspects of motor performance, but not drug-induced rotation or cell loss, responded to rotenone doses.
- Higher rotenone doses (8μg and 12μg) showed a ceiling effect in motor deficits.
- Non-specific toxicity and macroscopic lesions were observed, independent of rotenone dose.
Conclusions:
- Motor test sensitivity to dopamine modulation may not directly correlate with dopamine cell loss.
- Non-specific toxicity of rotenone and vehicle substances necessitates careful consideration in experimental models.
- Findings highlight the complexity of rotenone's effects and advise caution in PD research.
