The firing activity of presumed cholinergic and non-cholinergic neurons of the pedunculopontine nucleus in 6-hydroxydopamine-lesioned rats: An in vivo electrophysiological study

Several studies have shown that the neuronal activity of the pedunculopontine nucleus is increased in Parkinson's disease. In the present study, the changes were examined in the firing rate and firing pattern of presumed cholinergic and non-cholinergic neurons in the pedunculopontine nucleus of 6-hydroxydopamine-lesioned rats by using extracellular recording. In the lesioned rats, the mean firing rate of both presumed cholinergic and non-cholinergic neurons in the pedunculopontine nucleus increased significantly compared to normal rats. With regard to firing pattern, the majority of presumed cholinergic and non-cholinergic neurons fired regularly in normal rats. After substantia nigra pars compacta-lesion, the percentage of presumed non-cholinergic neurons exhibiting irregular pattern increased significantly compared to normal rats, while having no significant change in the firing pattern of presumed cholinergic neurons. Collectively, these results indicate that the presumed cholinergic and non-cholinergic neurons in the pedunculopontine nucleus are overactive in 6-hydroxydopamine-lesioned rats, particularly, presumed non-cholinergic neuron firing is more irregular, which suggests that the firing activity of presumed cholinergic and non-cholinergic neurons is affected by the different afferents from the basal ganglia and related structures.