Figure 3.
Conditioned heroin withdrawal decreased the excitability of brain reward systems. a, Percentage change from baseline ICSS thresholds (±SEM) in control rats after saline injection on the preconditioning day (saline), during the four cue/injection pairings (naloxone + cues), and on the test day (saline + cues). b, Percentage change from baseline ICSS thresholds (±SEM) in 1 h rats. Saline did not alter the lowering of reward thresholds observed after heroin intake during 1 h self-administration sessions. However, naloxone (30 μg/kg) administration and cue presentation reversed heroin-induced lowering of reward thresholds. ∗p < 0.05, main effect of naloxone/cues compared with thresholds observed after saline injection, one-way repeated measures ANOVA. On the test day, cue presentation and vehicle did not alter the lowering of reward thresholds observed after heroin intake during 1 h self-administration sessions. c, Percentage change from baseline ICSS thresholds (±SEM) in 23 h rats. Saline did not alter the already elevated baseline reward thresholds in 23 h rats. However, naloxone (30 μg/kg) administration and cue presentation raised reward thresholds above their already elevated baseline levels in 23 h rats. ∗p < 0.05, main effect of naloxone/cues compared with thresholds observed after saline injection, one-way repeated measures ANOVA. On the test day, cue presentation and vehicle significantly elevated reward thresholds in 23 h rats. ∗p < 0.05, paired t test compared with thresholds on the saline day.
