Following the initial 6-day training period ShA animals continued with 1-hour self-administration sessions and LgA animals were given 6 hr daily sessions. When examining the number of infusions taken during the first hour of each of these sessions (), both the ShA [One-way ANOVA, day, F(15,240)=1.86, p=.03] and LgA groups [day, F(15,224)=4.89, p<.0001] animals increased their cocaine intake over time. However, the effect was much greater in the LgA group than the ShA group, as indicated by a significant group by time interaction [main effect of group, F(1,15)=16.49, p=0.0003, main effect of day, F(15,435)=12.87, p<0.0001, group by day interaction, F(15,435)=2.90, p=0.0002]. In addition, the LgA animals exhibit a significant increase in the number of infusions over the entire session over the course of self-administration ().
Figure 2 A. Mean (+/− SEM) number of cocaine infusions during the first hour of each self-administration session in Experiment I. Both the short (ShA, 1 hr sessions) and the long (LgA, 6 hr sessions) access groups increased their intake over time, but (more ...) Sustained Attention Performance
Animals were trained on the sustained attention task for approximately 8 weeks prior to drug self-administration and animals assigned to the LgA, ShA and no-drug groups were matched based on training performance (). Twenty-four hours following the final self-administration session animals in the LgA group were markedly impaired on the sustained attention task, as illustrated by a significant decrease in VI relative to no-drug controls. In contrast, the ShA group did not differ from control [Overall ANOVA, main effect of group, comparing all groups, F(2,80)= 11.49, p=0.0001, group by signal length interaction, F(4,80)= 5.68, p=.0004. Individual group comparisons: LgA vs. ND, group, F(1,50)= 17.13, p=0.0003, interaction, F(2,50)=11.59, p<.0001; LgA vs. ShA, group, F(1,58)=12.56, p=0.0014, interaction, F(2,58)=4.36, p=0.0172; ]. At this point in time the performance of animals in the LgA group was impaired with respect to their ability to detect signals as well as to respond correctly to non-signal events [Signal Trials Overall ANOVA, interaction, F(4,90)= 6.92, p<.0001. Individual group comparisons: LgA vs. ND, F(2,50)=13.57, p<.0001; LgA vs. ShA, F(2,58)=5.37, p=0.007. Non-signal Trials ANOVA, F(2,40)=4.28, p=0.02; *, differs from ShA and No Drug groups as determined by Fisher’s Tests; ]. Fourteen days following the last self-administration session the LgA animals were still impaired relative to the control group, as indicated by a significant decrease in VI [Overall ANOVA, group, F(2,80)= 4.78, p=.01, interaction, F(4,80)= 4.28, p=0.004. Individual group comparisons: LgA vs. ND, group, F(1,50)=5.48, p=.028; LgA vs. ShA, group, F(1,58)=5.69, p=0.016; ]. However, by 14 days of withdrawal the deficit was due primarily to an increase in the number of false alarms (“claims” for signals on non-signal trials), as there was no longer a significant effect of prior self-administration on signal trial performance.
Figure 3 The effect of extended vs. limited access to self-administered cocaine on performance on the sustained attention task as a function of time following the last self-administration session. The top three panels show the data expressed as a vigilance index (more ...)
Following the test on day 14, animals were tested daily for an additional 7 days. Throughout this retraining period, there were no group differences on signal trials, i.e., in the relative number of hits (). However, the LgA group continued to show a significant deficit on non-signal trials relative to the control and ShA groups throughout this period [Overall ANOVA, group, F(2,240)= 3.80, p=0.03. Individual group comparisons: LgA vs. ND, group, F(1,150)=4.15, p=0.05, LgA vs. ShA, group, F(1,174)=4.1, p=0.05; ]. It is important to note that there were no group differences in either response latencies or the number of omissions at any point in time, indicating that all animals were equally motivated to perform the task ().
Figure 4 The effect of one week of “retraining” on the sustained attention task beginning 14 days after the last self-administration session. Data are shown as percent correct responses (a) on signal trials in which the signal duration was 500 (more ...)
Figure 5 The effect of extended vs. limited access to self-administered cocaine on response latency and omission rate (Mean ± SEM) as a function of time following the last self-administration session in Experiment I. There were no group differences on (more ...)