Electrical activation of the pedunculopontine tegmental nucleus modulates the neuronal activities of the subthalamic nucleus and the substantia nigra pars reticulata in anesthetized rats

The subthalamic nucleus (STN), substantia nigra pars reticulata (SNr), and pedunculopontine tegmental nucleus (PPTg) are reciprocally connected brain regions that play significant roles in the motor control. However, the electrophysiological relationship among the STN, SNr, and PPTg remains controversial. The present study was designed to further explore the mutual electrophysiological relationship of these brain regions from the perspective of the PPTg-STN-SNr neural circuit. The neuronal activities in the STN and SNr were simultaneously recorded while the PPTg was stimulated in anesthetized rats. The activation of PPTg induced excitatory responses of both the STN and SNr neurons. Comparisons of excitation latencies between the STN and SNr were made to distinguish the excitation evoked from the PPTg-STN-SNr pathway. Additionally, two types of excitatory responses and various inhibitory responses with different latencies in the SNr were recorded. The SNr responses could also be classified into five different response categories, which might attribute to projections within different neural circuits. Neuronal recordings were analyzed in different electrophysiological features (i.e., interspike interval [ISI] mode, ISI asymmetry index, ISI coefficient of variance, firing rate, burst index, and trough peak duration), and different response patterns of neurons had their specific features in neuronal activities. These findings indicated the complex interactions among the STN, SNr, and PPTg electrophysiologically, and provided insights into exploring information transmission mechanisms underlying these circuits.