Subcutaneous rotenone rat model of Parkinson's disease: Dose exploration study

Subcutaneous administration of rotenone has recently attracted attention because of its convenience, simplicity and efficacy in replicating features of Parkinson's disease (PD) in animal models. However, the wide range of doses reported in the literature makes it difficult to evaluate the effectiveness of this technique objectively. The aim of the present study was to identify the optimum dose of subcutaneous rotenone for establishing a model of PD. We injected male Wistar rats subcutaneously with one of three doses of rotenone (1.5, 2, or 2.5mg/kg) daily for 5 weeks. Rotenone caused a dose-dependent increase in α-synuclein in the substantia nigra. Furthermore, at 2 and 2.5mg/kg, rotenone caused a significant decrease in the number of tyrosine hydroxylase-immunoreactive neurons in the substantia nigra, and dopamine in the striatum. However, mortality at 2.5mg/kg was 46.7%, compared with just 6.7% at 2mg/kg; the high mortality observed at 2.5mg/kg would limit its application. The 2mg/kg dose showed no detrimental effect on body weight after 5 weeks of daily injections. Furthermore, rats in the 2mg/kg group showed a longer latency to descend from a horizontal bar and a grid wall, decreased rearing, and shorter latency to fall from a rotarod than rats that received vehicle or saline. Mitochondrial damage, observed by transmission electron microscopy, was also evident at this dose. Together, our data indicate that daily subcutaneous injection of 2mg/kg rotenone in rats facilitates the formation of α-synuclein and reproduces the typical features of PD, while maintaining low mortality.