1-Methyl-4-phenyl-1,2,3,6 tetrahydropyridine/probenecid impairs intestinal motility and olfaction in the early stages of Parkinson's disease in mice.

Parkinson's disease (PD) is a progressive neurodegenerative disorder accompanied by movement deficits with selective degeneration of dopaminergic neurons in the substantia nigra (SN). Recent studies indicate that early diagnosis of PD has important implications for the disease-modifying strategy for PD showing not only some dopaminergic neuronal damage but also non-motor symptoms, which occur several years before the onset of motor symptoms. However, studies on the relationship between non-motor symptoms and its underlying mechanisms from the early to the late phase of PD are unknown. Here, we aimed to show alterations in the non-motor symptoms of PD, including colonic dysmotility and impaired olfaction, and the related factors by intraperitoneal injections of 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) plus probenecid (MPTP/p). A mouse model of the early stage of PD was developed by systemic administration of MPTP (25 mg/kg, i.p.) and probenecid (100 mg/kg, i.p.) at 3.5-day intervals for a total of 10 injections. We performed motor and non-motor behavioral tests after 3 (called asymptomatic) and 10 (called symptomatic) injections of MPTP/p compared with the untreated (called control) group. We found that there were motor disturbances at the symptomatic stage, while impairments in intestinal motility and olfaction were observed from the asymptomatic stage. We also found the reduction of dopaminergic neuronal cell numbers in the SN and striatal dopamine transporter levels starting from the asymptomatic stage. At both asymptomatic and symptomatic stages, we demonstrated alterations in the expression of several proteins that are associated with non-motor deficits in the mouse ileum or olfactory bulb compared with the control group. Our findings in chronic MPTP/p-induced mice suggest their potential use as an animal model for the early stage of PD as well as a significant correlation between changes in relevant factors and symptoms.