Figure 2.

Chronic cocaine increases expression of ΔFosB in frontal cortex. Panels indicate ΔFosB-positive cells in animals that were self-administering saline (a–c; n = 5), yoked to animals self-administering cocaine (d–f; n = 5), or self-administering cocaine (g–i; n = 6). Compared with saline self-administering animals, increased numbers of ΔFosB-positive cells were observed in the PrLC and OFC after yoked and self-administered cocaine. Within the OFC only, a much greater increase was seen after self-administration compared with forced administration of cocaine. Chronic intraperitoneal (IP) cocaine injections (n = 6) caused similar levels of ΔFosB induction in both brain regions as seen with yoked cocaine infusions. No significant increases were seen in M1, an area of frontal cortex not associated with addiction. Data shown are mean + SEM. * indicates significant difference from saline controls (p < 0.05); # indicates a significant difference from yoked cocaine administration (p < 0.05).