This experimental drug candidate is under development as a κ-opioid receptor agonist for pain management with fewer adverse side effects.

These two receptors "work together" to form a conformation to block the recruitment of a protein family known as the β-arrestins.

[1] These proteins are responsible for the regulation of GPCR's and they cause the internalization of the receptor to prevent further activation, leading to an increased tolerance to opioid drugs.

If they spent more time away from the conditioned side of the box, they had a negative experience, typically withdrawal symptoms.

This means that the mice spent more time on the side of the box used for the conditioning experiments, indicating that they were receiving a pleasurable stimulus from the drug.