Figure 1.
Timeline of behavioural training and testing.
In Experiment 1 (panel A) we examined the effects of the speed of intravenous cocaine delivery on the acquisition, persistence and AMPH-induced potentiation of operant responding for a cocaine-paired cue. In Experiment 2 (panel B) we determined whether cues paired with rapid self-administered cocaine infusions would acquire conditioned reinforcing properties sooner than cues paired with slower cocaine infusions. s, seconds; SAL, saline; AMPH, amphetamine.
Figure 2.
In Experiment 1, there were no differences in the amount of cocaine exposure, cocaine-cue exposure, or number of days to reach each infusion criterion between the 5- and 90-s groups.
Total drug intake (panel A), number of cue-cocaine pairings (panel B) and days to reach infusion criteria (panel C). Note that total drug intake includes cocaine taken during self-administration training, when all rats self-administered cocaine injections delivered over 5 seconds. Rats were required to meet infusion criteria 10–25 for 2 days each and infusion criterion 30 for 5 days. Values are mean ± SEM. n's = 5/group. s, seconds. CS, conditioned stimulus; UCS; unconditioned stimulus.
Figure 3.
A cue paired with either rapid or slower cocaine injections acquires similar conditioned rewarding properties, and these properties abate with time.
Presses on the CR and NCR levers on Day 1 (panel A), Days 10–11 (panel B) and Day 30 (panel C) of withdrawal from self-administered cocaine in the 5- and 90-s groups. Values are mean ± SEM. n's = 5/group. s, seconds; CR, conditioned reward lever; NCR, non-conditioned reward lever. *p<0.05 compared with NCR within the same group.
Figure 4.
Amphetamine potentiates CR, but not NCR, lever presses in both the 5- and 90-s groups.
Presses on the CR and NCR levers following an acute injection of saline (panel A), 0.25 (panel B) and 0.5 (panel C) mg/kg amphetamine. Values are mean ± SEM. n's = 5/group. s, seconds; CR, conditioned reward lever; NCR, non-conditioned reward lever; AMPH, amphetamine. *p<0.05 compared with NCR within the same group. α p<0.05 compared with CR under saline.
Figure 5.
In Experiment 2, there were no differences in the amount of cocaine exposure, cocaine-cue exposure, or the number of days to reach each ratio/infusion criterion between the 5- and 90-s groups.
Total drug intake (panel A), number of cue-cocaine pairings (panel B) and days to reach ratio/infusion criteria (panel C) in the 5- and 90-s groups. Rats were required to meet the FR 1 and FR 2 criteria as well as infusion criteria 10–15 for 2 days each, and to meet infusion criterion 20 for 21 days. Values are mean ± SEM. n's = 6–7/group. s, seconds. CS, conditioned stimulus; UCS; unconditioned stimulus. FR; fixed ratio.
Figure 6.
In both the 5- and 90-s groups, discrimination between the CR and NCR levers is observed following extensive (panel B) but not limited (panel A) cocaine self-administration experience.
Limited self-administration experience consisted of 3 self-administration sessions. Extensive self-administration experience consisted of 24 self-administration sessions. Values are mean ± SEM. n's = 6–7/group. s, seconds; CR, conditioned reward lever; NCR, non-conditioned reward lever; SA, cocaine self-administration. *p<0.05 compared with NCR within the same group.