Figure 1.

Psychostimulant-induced activation of ERK1/2 in Drd1a knock-out and DARPP-32 knock-out mice. Effects of d-amphetamine treatment (10 mg/kg) are compared between wild-type and Drd1a KO mice and between wild-type and DARPP-32 KO mice, in which DARPP-32-IR in the striatum is absent. Activation of ERK1/2 is indicated in coronal brain sections by neurons displaying immunoreactive phosphorylated ERK1/2 (phospho-ERK1/2-IR). In the dorsolateral striatum (a) and in the dorsomedial striatum (b), the numbers of scattered neurons with d-amphetamine-induced immunoreactive phospho-ERK1/2 is similar in the wild-type and Drd1a KO and DARPP-32 KO animals. In the shell of the nucleus accumbens (c), there are numerous d-amphetamine-induced phospho-ERK1/2-immunoreactive neurons in the wild-type mice, whereas in both the Drd1a KO and DARPP-32 KO mice, the numbers of such neurons is markedly reduced. These data indicate that psychostimulant activation of ERK1/2 mediated by Drd1a and DARPP-32 is restricted to the nucleus accumbens.