Homozygous transgenic mice are viable and fertile. These mice express a truncated variant of the Fosb transcription factor. The expressed variant is a highly stable isoform found to be induced in the brain (nucleus accumbens) with repeated exposure to commonly abused drugs, such as amphetamine, morphine, nicotine, and phencyclidine. Transcription is directed by a tetracycline-responsive promoter element (TRE). In bitransgenic mice produced by breeding a mouse carrying this transgene with a transgenic mouse expressing tetracycline-controlled transactivator protein (tTA), Fosb expression can be negatively regulated with the tetracycline analog, doxycycline.