All neurons of three distinct neurochemical subtypes of DARPP-32, NOS, or CB in IM express D1 receptors. A–C, Three high magnification fields through the IM show D1 receptor expression in all neurons (red and yellow arrows). D–F, In the same fields some neurons express DARPP-32, NOS, or CB (yellow arrows). G–I, All neurons expressing one of the three distinct neurochemical subtypes of IM neurons express D1 (yellow arrows).