Opioid κ receptors correlate with the development of conditioned suppression of motility in mice

Mice exhibited a marked suppression of motility (conditioned suppression) when placed in the same environment in which they had previously received an electric footshock. The conditioned suppression of motility was potentiated by U-69,593, a selective κ (non-μ) agonist. This effect of U-69,593 was antagonized by MR-2266, a κ antagonist. Additionally, in contrast to U-69,593, MR-2266 alone attenuated the conditioned suppression of motility. These results suggest that the activation of κ receptors may be responsible for the development of conditioned suppression of motility.