Plasma corticosterone concentration of self-administration (SA), yoked-cocaine (YC) and yoked-saline (YS) rats. The average number of injections during the session was 24 ± 5. Blood samples were collected 15 min before the session and immediately after. Plasma was separated from the red blood cells in 1 minute after blood collection. N=7-8 in each group.
* Significantly different from the pre-session sample, P<0.01,
& Significantly different from SA and YC groups, P<0.05.