The Effect Of Microinjection Of Rotenone Into The SN On The Electroactivity Of Striatum And Ventrolateral Thalamus Neurons In Rats

Recently it was extensively concerned that the neurotoxicological effect of rotenone that could induce Parkinson's disease (PD), since it was widely used as an pesticide. Otherwise, the method of systemically exposure was mostly used in past studies, which mainly focused on observing the special pathological change of the central nerve system and motor disorder of the animals after the exposure of rotenone. It was rarely reported that electroactivity mechanism involved in the basal ganglia and the motor thalamus, which was related to the pathological change of motor disorder of PD.In the present study, it was checked that whether microinjection of rotenone into brain could induce the behavior change similar to PD and the special pathological change of the dopaminergic (DA-ergic) neurons in substantia nigra pars compacta (SNc). Furthermore, it was investigated the effect of the exposure of rotenone on the electroactivity of the striatum and the ventrolatral thalamus nuclei (VL) neurons, in order to analyze the nerve mechanism involving in the motor disorder of PD.The principal results were as folio wings:1. After 21 days exposure of 2μg, 3μg and μg rotenone, latencies of rats' moving on the vertical grid were significantly increased compared to both the control group and the same group before exposure. Moreover, along with the increase of exposure dose of rotenone, moving latencies increased correspondingly. The numbers of rats' sliding down the inclined plane were significantly increased after the exposure of rotenone. In the open-field test, both the number of the rats' dipping into holes and time of rearing were significantly decreased compared to the same group before exposure, which moreover presented the dose-effect relation. Tremor symptom was observed in half of the exposure animals.2. The results of the TH-immunohistochemistry test showed that the numbers of TH-positive neuron in SNc reduced significantly after the exposure of rotenone. Furthermore, loss of TH-positive neuron increased along with the increase of exposure dose of rotenone. The surviving neurons presented the degenerating characteristic such as shrinking of cell body and disappearing of neurite.3. The firing patterns of the striatum neurons were changed after rotenone exposure . Compared to the control group, the neurons with the regular and irregular firing decreased significantly. Otherwise, the neurons with the compound bursting firing increased significantly. Compared to the control group, the evoked activity of the striatum neurons responding to the stimulation of motor cortex increased accordingly, but the evoked latency reduced after the exposure of rotenone.4. Compared to the control group, ventrolateral thalamus neurons with the II-type firing patterns increased after the exposure of rotenone, and the firing rate of spontaneous discharge decreased generally, and then the power spectrum of neurons activity assembled into the areas of low frequencies. After the exposure of rotenone, the numbers of excitatory VL neurons responding to the stimulation of the motor cortex were decreased compared to the control group, but the evoked latency was significantly increased.Results above indicated that microinjection of rotenone into the SNc could induce typical PD symptoms in rats such as slow moving, rigidity and tremor et al. It could also cause the degeneration of the DA-ergic neuron in the SNc. The exposure of rotenone could bring on enhancement of spontaneous activity of the striatum neurons and increase of excitatory effect of their response to stimulation of motor cortex. It indicated that the increased activity of striatum neuron might be correlative with motor disorder of PD. The increased bursting fire of VL neurons suggested that the activity of VL nuclei might be involving with the behavior change of PD such as the kinesthesia and tremor. The present work built firstly an example of the PD model by microinjection of rotenone into the central nerve system; secondly it took the theory basis on the operation on striatum and VL for PD patients; thirdly it also provided evidences on striatum and the VL nuclei involving in the motor control.