(a), D2 receptors appear to be located presynaptically on gluta­matergic fibers of the corticostriatial pathway. (b), D2 receptors are located presynaptically on the DA-ergic fibers of the nigrostriatial pathway. (c), both D1 and D2 receptors are located on the cell bodies of the nigrostriatial pathway (SNC).(e), the vast majority of D1 receptors of the SNR are located presynaptically on the GABA-ergic fibers of the striatonigral pathway.