 Cocaine, methamphetamine, heroin, and other psychoactive drugs have been shown to decrease c-fos production in the mesocortical pathway (prefrontal cortex) as well as in the mesolimbic reward pathway (nucleus accumbens).c-Fos repression by ΔFosB's AP-1 complex within the D1-type medium spiny neurons of the nucleus accumbens acts as a molecular switch that enables the chronic induction of ΔFosB, thus allowing it to accumulate more rapidly.As such, the c-Fos promoter finds utilization in drug addiction research in general, as well as with context-induced relapse to drug-seeking and other behavioral changes associated with chronic drug taking.