Summary of DA receptor agonist modulation in wild type and DA receptor KO mice. A. The mean change in Ca2+ responses is shown for the full data set (bars are colored to indicate main effect). Asterisks mark significant differences. The quinpirole inhibition seen in WT and D3 KO mice was completely abolished in D2 KO mice (p < 0.05). B. The incidence of DA modulation was assessed using the 5% criterion (see text). Numbers in parentheses indicate the total number of varicosities and cells recorded, respectively. While D1 stimulation with SKF81297 produced facilitation in almost all instances, D2 stimulation with quinpirole produced both inhibition and facilitation. Quinpirole facilitation seen in WT and D2 KO mice was completely abolished in D3 KO mice.