Pain perception in acute model mice of Parkinson's disease induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

Background: Pain is the most prominent non-motor symptom observed in patients with Parkinson's disease (PD). However, the mechanisms underlying the generation of pain in PD have not been well studied. We used a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model of PD to analyze the relationship between pain sensory abnormalities and the degeneration of dopaminergic neurons. Results: The latency to fall off the rotarod and the total distance traveled in round chamber were significantly reduced in MPTP-induced PD mice, consistent with motor dysfunction. MPTP-treated mice also showed remarkably shorter nociceptive response latencies compared to saline-treated mice and the subcutaneous injection of L-3,4-dihydroxyphenylalanine (L-DOPA) partially reversed pain hypersensitivity induced by MPTP treatment. We found that degeneration of cell bodies and fibers in the substantia nigra pars compacta and the striatum of MPTP-treated mice. In addition, astrocytic and microglial activation was seen in the subthalamic nucleus and neuronal activity was significantly increased in the striatum and globus pallidus. However, we did not observe any changes in neurons, astrocytes, and microglia of both the dorsal and ventral horns in the spinal cord after MPTP treatment. Conclusions: These results suggest that the dopaminergic nigrostriatal pathway may have a role in inhibiting noxious stimuli, and that abnormal inflammatory responses and neural activity in basal ganglia is correlated to pain processing in PD induced by MPTP treatment.