Fig. 12.
Autoreceptor-mediated inhibition of firing in SNc DA cells. a, Cumulative dose–response curves illustrating that the DA D2-class receptor agonist quinpirole induced a dose-dependent decrease in firing activity in both HRs and LRs [dose effect, F(10,190) = 80.4;p < 0.001]. This inhibition was attenuated in HRs compared with LRs [group effect,F(1,19) = 5.3; p < 0.04; group × dose interaction,F(10,190) = 4.1; p< 0.001]. The ANCOVA considering the basal firing rate (quinpirole dose 0) as the covariate [group effect,F(1,18) = 4.1; p = 0.06; group × dose interaction,F(9,171) = 4.5; p< 0.001] indicates that these differences were not entirely caused by difference in basal firing activity. Each pointrepresents the mean ± SEM of each group. b, Representative rate histograms showing examples of recordings from an HR or LR rat. Note the greater doses of quinpirole required to suppress the firing of SNc DA neurons in HR animals compared with LR animals. The effects of quinpirole were reversed by the D2-class receptor antagonist eticlopride (100 μg/kg, i.v.). Arrowheadsindicate the time points at which quinpirole or eticlopride was administered; numbers indicate the infusion dose (in micrograms per kilogram).