FIGURE 6

Corticosterone (CORT) responses to nicotine self-administration (SA) and to mild foot shock stress in Lewis rats. In the experiments shown in (a) and (b), blood samples were collected through a femoral cannula on the first and third days of nicotine SA at the time of the first active lever press (0 min), and 15, 30, 45, and 60 min thereafter. On the first day, nicotine SA induced significant increases in CORT levels (a) compared to rats self-administering vehicle (repeated-measures ANOVA showed main effects: treatment, F_1,8=9.96, p<0.01; time, F_4,32=4.96, p<0.01). On the third day of nicotine SA (b), CORT was not significantly increased by the first dose of nicotine (F_1,8=3.74, p>0.05). (c) shows CORT responses to mild foot shock stress (FSS). On the 20th day of nicotine SA, baseline blood samples were collected 45 and 60 min after the first active lever press of the day (shown as -15 and 0 min) and then FSS was administered. The delivery of FSS in the vehicle SA group was paired with the nicotine SA rats. Mild FSS (0.6 mA, randomly delivered 5 times per 5 min) significantly increased CORT levels (main effect of time: F_5,88=4.37, p<0.01). Nicotine SA significantly amplified the CORT response to FSS (main effect of treatment: F_1,16=8.50, p<0.01). Hormone concentrations were expressed as meanSEM.