Figure 1.

Stress-induced odorant aversion is dynorphin/KOR mediated. A, Schematic of the odorant-stress aversion paradigm. B, Odorant aversion scores (odorant side minus control side) show that, in the absence of stress pairing, the odorant does not elicit aversion (the odorant is neutral). Mice previously experiencing stress paired with odorant showed significant aversion to subsequent odorant exposure, and norBNI pretreated mice did not develop odorant aversion despite stress pairing. **p < 0.01, significantly different from saline/stress group. C, Pdyn(+/+), but not Pdyn(−/−), mice developed significant aversion to odorant. *p < 0.05, significantly different from Pdyn(−/−) group. D, Pairing of the neutral odorant with cocaine injection produced significant place preference for the odorant compartment that was not blocked by norBNI pretreatment. E, κ-Opioid receptor stimulation caused a dose-dependent increase in the odorant-aversion score. When odorant was paired with either 0, 2.5, 5, or 10 mg/kg of the selective κ-opioid receptor agonist U50,488, mice showed an increased aversion to the odorant when subsequently presented with the odorant alone in the T-maze (n = 4–8 animals per group).