Firing activity of locus coeruleus noradrenergic neurons increases in a rodent model of Parkinsonism

To investigate the changes in the firing activity of noradrenergic neurons in the locus coeruleus (LC) in a rat model of Parkinson disease (PD).2 and 4 weeks after unilateral lesion of the nigrostriatal pathway in the rat by local injection of 6-hydroxydopamine (6-OHDA) into the right substantia nigra pars compacta (SNc), the firing activity of noradrenergic neurons in LC was recorded by extracellular single unit recording.The firing rate of LC noradrenergic neurons increased significantly 2 and 4 weeks after 6-OHDA lesions compared to normal rats, respectively (P < 0.05). The percentage of irregularly firing neurons was obviously higher than that of normal rats during the fourth week after SNc lesion (P < 0.05).LC noradrenergic neurons are overactive and more irregular in 6-OHDA-lesioned rats. These changes suggest an implication of the LC in the pathophysiological mechanism of PD.