Table 1.

Behavioral designs for experiments 1–4

GroupStage IStage IITest
+ = 0.8 mA
+ = 0.4 mA
Experiment 1
    Control–saline
    Control–morphine
    Control–naloxone
    Block–salineCxt: +++Cxt: CS + CS+Cxt, CS
    Block–morphineCxt: +++
    Unblock–salineCxt: +++
    Unblock–naloxoneCxt: +++
Experiment 2
    Saline–salineCxt: +++
    Morphine–morphineCxt: +++
    Saline–morphineCxt: +++Cxt: CS + CS+Cxt, CS
    Morphine–salineCxt: +++
Experiment 3
    Control–saline
    Block–salineCxt: +++
    Unblock–salineCxt: +++
    Block–DAMGOCxt: +++
    Block–DPDPECxt: +++Cxt: CS + CS+Cxt, CS
    Unblock–CTAPCxt: +++
    Unblock–naltrindoleCxt: +++
    Unblock–CTAP CPuCxt: +++
Experiment 3b
    Control–saline
    Block–salineCxt: +++
    Unblock–salineCxt: +++
    Unblock–2.5 μg of naltrindoleCxt: +++Cxt: CS + CS+
    Unblock–7.5 μg of naltrindoleCxt: +++
    Unblock–10 μg of naltrindoleCxt: +++
Experiment 4
    Control–saline
    Control–U50488
    Control–Nor-BNI
    Block–salineCxt: +++Cxt: CS + CS+Cxt, CS
    Block–U50488Cxt: +++
    Block–Nor-BNICxt: +++

  • Cxt, Context; +++, +++, three footshocks.