Figure 2.

(A) Prevention of blocking by infusions of the μ-opioid receptor agonist DAMGO, and prevention of unblocking by the μ-opioid receptor antagonist CTAP, upon infusion into the Acb prior to stage 2 training. Infusions of a δ-opioid receptor agonist (DPDPE) or antagonist (Nalt [Naltrindole]) were without effect. (B) μ-opioid receptors in the Acb regulate indirect predictive fear learning. Infusions of a μ-opioid receptor agonist prior to the first (morphine–saline) stage 2 trial prevents blocking, whereas infusion prior to the second trial (saline–saline) does not. (Reprinted with permission from The Society for Neuroscience © 2006, Iordanova et al. [2006b]).