[Effects of electrical stimulation of the parafascicular nucleus on the neuronal activities of the subthalamic nucleus and the ventromedial nucleus in rats].

The present study was designed to investigate the function and mechanism of high-frequency stimulation (HFS) of the parafascicular nucleus (PF) used as a therapeutic approach for Parkinson's disease (PD). PD rat model was built by injecting 6-hydroxydopamine (6-OHDA) into the substartia nigra pars compacta of adult male Sprague-Dawley rats. Using the ethological methods, we examined the effect of electrical stimulation of PF on the apomorphine-induced rotational behavior in PD rats. Moreover, Electrophysiological recordings were made in rats to investigate the effects of electrical stimulation of PF on the neuronal activities of the subthalamic nucleus (STN) and the ventromedial nucleus (VM). Our results showed that one week after HFS (130 Hz, 0.4 mA, 5 s) of PF, there was significant improvement in apomorphine-induced rotational behavior in PD rats. HFS of PF caused an inhibition of the majority of neurons (84%) recorded in the STN in PD rats. The majority of cells recorded in the VM of the thalamus responded to the HFS with an increase in their unitary discharge activity (81%). These effects were in a frequency-dependent manner. Only stimulus frequencies above 50 Hz were effective. Furthermore, employing microelectrophoresis, we demonstrated that glutamatergic and GABAergic afferent nerve fibers converged on the same STN neurons. These results show that the HFS of PF induces a reduction of the excitatory glutamatergic output from the PF which in turn results in deactivation of STN neurons. The reduction in tonic inhibitory drive from the basal ganglia induces a disinhibition of activity in the VM, a motor thalamic nucleus. In conclusion, the results suggest that HFS of PF may produce a therapeutic effect in PD rats, which is mediated by the nuclei of PF, STN and VM.