Unlike cocaine, amphetamine acutely increases p-ERK in the VTA,19 and like cocaine, it increases p-ERK in the dorsal striatum20,21 and NAc.22 Amphetamine also induces striatal expression of preproenkephalin and preprodynorphin through an ERK-dependent mechanism, since this response is attenuated by systemic or intrastriatal injection of MEK inhibitors.20 Nicotine, like cocaine, also increases p-ERK in the prefrontal cortex and amygdala.23
