SUBSTANTIA-NIGRA PARS RETICULATA SINGLE-UNIT ACTIVITY IN NORMAL AND 60HDA-LESIONED RATS - EFFECTS OF INTRASTRIATAL APOMORPHINE AND SUBTHALAMIC LESIONS

The spontaneous activity and the response to intrastriatal application of apomorphine of substantia nigra pars reticulata (SNpr) single unit s was studied in four experimental groups of rats: (1) normal rats; (2 ) subthalamic nucleus (STN) lesioned rats; (3) rats bearing a 6-hydrox ydopamine (6OHDA) lesion; and (4) 6OHDA-lesioned animals with an addit ional STN lesion. Thirty-eight percent of units from 6OHDA-lesioned ra ts showed a bursting pattern of spontaneous activity, which was never found in normal rats. STN lesions had no effect on the spontaneous act ivity of SNpr units from normal rats, but reduced the percentage of bu rst units in 6OHDA-lesioned animals. Intrastriatal apomorphine produce d responses in 62% of SNpr units from normal rats and 85% of units fro m 6OHDA-lesioned animals (P < 0.05). In addition, the modifications in the firing rate and in the coefficient of variation of the interspike intervals induced by intrastriatal apomorphine were significantly gre ater for the units isolated from 6OHDA-lesioned rats. In particular, i t was noted that all the burst units responded to apomorphine, showing the highest changes in firing rate and coefficient of variation. Howe ver, intrastriatal apomorphine did not always turn the activity of bur st units into a more physiological pattern. STN lesions reduced the pe rcentage of units responding to intrastriatal apomorphine in normal ra ts. In 6OHDA-lesioned rats, STN lesions reduced the number of responsi ve units, and their change in mean firing rate and coefficient of vari ation. Our results show that the STN participates in the genesis of th e bursting pattern of activity of SNpr units in 6OHDA-lesioned rats, a nd that STN lesions can partially revert the abnormal spontaneous and apomorphine-induced responses of SNpr units in these animals. (C) 1997 Wiley-Liss, Inc.