Objective To study the changes in neuronal activity of the zone incerta(ZI)following the unilateral lesion of the nigrostriatal pathway.Methods Electrophysiological recordings of ZI neurons were made in normal rats and in two groups of rats at different time intervals after injection of 6-hydrodopamine(6-OHDA)into the pars compacta of substantia nigra by extracellular recording in vivo.Results The results showed a significant increase in the mean firing rate of ZI during the second and fourth weeks after 6-OHDA lesion [n=32,(3.6±2.2)Hz,P<0.001;n=35,(9.3±6.6)Hz,P<0.001,respectively] compared to that of normal rats [n=39,(9.2±5.2)Hz].However,no significant change was observed between two groups of 6-OHDA-lesioned rats.With regard to firing pattern,7.7%(3/39)of ZI neurons discharged regularly,82.1%(32/39)irregularly and 10.3%(4/39)in bursts in normal rats.During the second week after 6-OHDA lesion,the regular,irregular and bursting firing neurons recorded in the ZI were 9.4%(3/32),59.4%(19/32)and 31.3%(10/32),and during fourth week,the regular,irregular and bursting firing neurons were 14.3%(5/35),57.1%(20/35)and 28.6%(10/35),respectively.The firing pattern of the neurons in the three different groups did not change significantly.Conclusion These results suggest that the firing rate of ZI neurons in 6-OHDA-lesioned rats is increased significantly,which may contribute to the pathophysiology of Parkinson’s disease. Objective To study the changes in neuronal activity of the zone in certa (ZI) following the unilateral lesion of the nigrostriatal pathway. Methods Electrophysiological recordings of ZI neurons were made in normal rats and in two groups of rats at different time intervals after injection of 6- hydrodopamine (6-OHDA) into the pars compacta of substantia nigra by extracellular recording in vivo. Results of the results showed a significant increase in the mean firing rate of ZI during the second and fourth weeks after 6-OHDA lesion [n = 32, ( N = 35, (9.3 ± 6.6) Hz, P <0.001, respectively] compared to that of normal rats [n = 39, (9.2 ± 5.2) Hz] change was observed between two groups of 6-OHDA-lesioned rats. Regard regard to firing pattern, 7.7% (3/39) of ZI neurons discharged regularly, 82.1% (32/39) irregularly and 10.3% (4/39) in bursts in normal rats. During the second week after 6-OHDA lesion, the regular, irregular and bursting firing neurons recorded in the ZI were 9.4% (3/32), 59.4 (19/32) and 31.3% (10/32), and during the fourth week, the regular, irregular and bursting firing neurons were 14.3% (5/35), 57.1% (20/35) and 28.6% 35), respectively. The firing pattern of the neurons in the three different groups did not change significantly. Conlusion These results suggest that the firing rate of ZI neurons in 6-OHDA-lesioned rats is more significantly, which may contribute to the pathophysiology of Parkinson’s disease.