Multiple single-unit recordings in the striatum of freely moving animals: effects of apomorphine and D-amphetamine in normal and unilateral 6-hydroxydopamine-lesioned rats

Ensembles of striatal neurons were recorded in freely moving normal and uni lateral 6-hydroxydopamine (6-OHDA)-lesioned rats using chronically implante d electrode arrays. Animals received bilateral striatal implants of two 16- microwire arrays 1 week before recordings. Identified striatal neurons were categorized as medium spiny-like and large aspiny-like based on a combinat ion of their activity autocorrelations and firing rates. Baseline firing ra tes of medium spiny-like neurons in the 6-OHDA-lesioned striata were signif icantly faster than were firing rates of the same neurons in the intact hem ispheres of 6-OHDA-lesioned rats or normal animals. However, firing rates o f large aspiny-like neurons were faster in both hemispheres of the 6-OHDA-l esioned rats as compared to normal animals. Interestingly, firing rates of neurons in all groups decreased by fivefold or greater under urethane anest hesia, although the relative firing rates between hemispheres were unchange d. D-Amphetamine (5.0 mg/kg, s.c.) increased the firing rates of both types of striatal neurons by twofold or greater in normal rats and in the intact hemispheres of 6-OHDA-lesioned animals. By contrast, this treatment did no t alter neuron firing in the 6-OHDA-lesioned striata. Apomorphine (0.05 mg/ kg, s.c.) did not affect neuronal firing rates either in normal rat striatu m or in the unlesioned hemispheres of 6-OHDA-lesioned animals. However, it did significantly increase the firing rate of the medium spiny-like neurons in 6-OHDA-lesioned striata. These results demonstrate that the dopaminergi c innervation of the striatum differentially influences two electrophysiolo gically distinct sets of striatal neurons in freely moving rats. (C) 1999 E lsevier Science B.V. All rights reserved.