Article Figures & Data
Figures
- Figure 1.
Histological analysis of intra-mPFC microinjection sites. A, Microphotograph of a representative injector placement within the PLC division of the mPFC. B, Schematic representation of select intra-PLC injector locations; ♦ = 500 ng WIN 55, 212-2 versus 5 mg/kg morphine group, ◊ = 500 ng AM 251 versus 0.05 mg/kg morphine group.
- Figure 2.
Effects of intra-PLC CB1 receptor activation on morphine CPP conditioning. A, Bilateral intra-PLC micro-infusions of the CB1 receptor agonist WIN 55,212-2 (50 and 500 ng/0.5 μl), dose-dependently produced a morphine aversion against a sub-reward threshold conditioning dose of morphine (0.05 mg/kg, i.p.). Both vehicle controls and rats receiving a lower dose of WIN 55,212-2 (50 ng/0.5 μl; n = 7) display no significant preference for either environment. Conversely, animals receiving the higher dose of WIN 55,212-2 (500 ng/0.5 μl; n = 8) display a significant aversion to morphine-paired environments. B, Bilateral intra-PLC microinfusions of WIN 55,212-2 (500 ng/0.5 μl; n = 8) or vehicle (n = 7) versus a supra-reward threshold dose of morphine (5.0 mg/kg, i.p.) similarly switches the rewarding properties of morphine into aversion, with rats demonstrating robust CPA for morphine-paired environments. C, In control rats receiving intra-PLC WIN 55,212-2 (500 ng/0.5 μl; n = 8) versus vehicle, no preference for either environment is observed. *p < 0.05; **p < 0.01, for this and all subsequent figures.
- Figure 3.
Effects of intra-PLC CB1 receptor blockade on morphine CPP conditioning. A, Bilateral intra-PLC microinfusions of the CB1 receptor antagonist, AM251 (50 ng/0.5 μl; n = 8, or 500 ng/0.5 μl; n = 7) dose-dependently potentiated the rewarding effects of morphine relative to vehicle controls that displayed no significant preference for either environment. B, Conversely, bilateral intra-PLC microinfusions of AM251 (500 ng/0.5 μl) versus a supra-reward threshold dose of morphine (5.0 mg/kg, i.p) has no effect on morphine reward conditioning, with both drug (n = 8) and vehicle control (n = 8) groups demonstrating robust morphine environment CPP. C, In control rats receiving intra-PLC AM251 (500 ng/0.5 μl; n = 8) versus vehicle, no preference for either environment is observed.
- Figure 4.
Behavioral effects of intra-PLC CB1 receptor activation or blockade on morphine place conditioning. A, Summary of the bidirectional behavioral effects of intra-PLC AM-251 (50–500 ng/0.5 μl) or WIN 55,212-2 (50–500 ng/0.5 μl) on sub-threshold morphine (0.05 mg/kg, i.p.) reward or aversion effects, presented as difference scores (time in drug minus saline-paired environments). B, Summary of the effects of intra-PLC AM 251 (500 ng/0.5 μl) or WIN 55 212-2 (500 ng/0.5 μl) on supra-reward threshold (5.0 mg/kg, i.p.) morphine.
- Figure 5.
Effects of DA receptor blockade on intra-PLC mediated modulation of opiate motivational processing. A, Rats treated with intra-PLC vehicle demonstrate robust CPP for environments paired with supra-reward threshold morphine (n = 8). Relative to vehicle pretreated controls (n = 8), pretreatment with the broad-spectrum DA receptor antagonist α-flu (0.8 mg/kg, i.p.) blocked the ability of intra-PLC WIN 55,212-2 (500 ng/0.5 μl; n = 7) to induce a behavioral morphine aversion to a supra-reward threshold conditioning dose of morphine (5.0 mg/kg, i.p.). B, Rats treated with intra-PLC vehicle demonstrated no preference for environments paired with sub-reward threshold morphine (n = 8). In contrast, rats treated with intra-PLC AM251 (n = 7) demonstrated a strong morphine CPP (p < 0.01; B). However, in rats pretreated with α-flu (n = 8), the ability of intra-PLC CB1 receptor blockade to potentiate the rewarding properties of morphine is blocked.
- Figure 6.
Effects of intra-VTA κ- or μ-opiate receptor blockade on CB1 receptor-mediated modulation of opiate reward and aversion behaviors. A, Relative to rats receiving intra-PLC WIN 55,212-2 (500 ng/0.5 ml) versus supra-reward threshold morphine (n = 8), intra-PLC administration of WIN 55,212-2 (500 ng/0.5 μl) following intra-VTA administration of the KOR antagonist nor-BNI [50 (n = 8) or 500 (n = 6) ng/0.5 μl] dose-dependently blocks the ability of intra-PLC CB1 activation to switch morphine reward signaling into aversion. However, intra-VTA administration of a MOR antagonist, cyprodime (500 ng/0.5 μl; n = 6) fails to reverse the effects of intra-PLC CB1 activation. Intra-VTA administration of the highest effective dose of nor-BNI (500 ng/0.5 μl) does not produce any behavioral motivational effects in and of itself (n = 8; right). B, Intra-PLC administration of AM251 (500 ng/0.5 μl) following intra-VTA administration of the MOR antagonist cyprodime [50 (n = 7) or 500 (n = 7) ng/0.5 μl] dose-dependently blocks the ability of intra-PLC CB1 receptor blockade to potentiate sub-reward threshold morphine effects, relative to intra-PLC AM251 alone (n = 8). In contrast, intra-VTA administration of the KOR antagonist, nor-BNI (500 ng/0.5 μl; n = 6) fails to reverse the effects of intra-PLC CB1 blockade. Intra-VTA administration of the highest effective dose of cyprodime (500 ng/0.5 μl) does not produce any behavioral motivational effects in and of itself (n = 8; right).
- Figure 7.
Histological analysis of intra-VTA microinfusion locations. A, Microphotograph showing representative bilateral intra-VTA infusion locations. B, Schematic summary of intra-VTA microinjector locations; ● = intra-VTA nor-BNI (500 ng/0.5 μl); □ = intra-VTA cyprodime (500 ng/05 μl). C, Schematic summary showing relative intra-VTA cannulae placement locations relative to behavioral CPP index score (total time in saline environment + total time in morphine environment/total time in morphine environment; de Jaeger et al., 2013) for rats receiving the behaviorally effective doses of either intra-VTA cyprodime or nor-BNI.
