Cocaine addiction is frequently modeled in rats using drug self-administration, extinction, and reinstatement. However the precise brain structures involved in extinction in cocaine seeking behavior are currently unknown. In this study, we investigated whether the nucleus accumbens (NA) shell is involved in the extinction process in cocaine seeking behavior. Male rats underwent surgery, where intravenous catheters were implanted in the rat, followed by cannulas entered in the brain aimed at the NAshell. After surgery, rats went into self-administration for two weeks, where a lever press produced a cocaine infusion combined with a light and a tone. Rats then underwent extinction training in which lever presses no longer produced the drug or cues. On the first 5 days of extinction, rats underwent 15 min extinction sessions, immediately after which they received microinjections of the AMPA receptor potentiator PEPA into the NAshell. On subsequent days, they underwent 2-h extinction sessions to assess retention from the earlier extinction training. Then, rats underwent five days of 30 minute cued extinction sessions. Immediately before each cued session during those five days, rats received microinjections of the AMPA glutamate receptor antagonist CNQX into the NAshell. In both experiments, microinjections into the NAshell had no effect on subsequent retention of the extinction training. These results are inconsistent with past studies and suggest future studies will need to alter the protocol in order to investigate the role of the NAshell in extinction learning. "