Selective breeding for oral opioid acceptance or rejection in rats.

Lines of rats were selectively bred to diverge bidirectionally from a randomly bred control line in the propensity to self-administer an opioid orally. These lines seek or avoid the high-potency opioid etonitazene in a situation in which it is presented continuously as a choice with water. Over seven generations, preferences were measured and selection pressure imposed to develop the accepting and rejecting lines. These animals represent the only contemporary selective breeding program for opioid preference or self-administration, and hold the promise of being a useful resource in the drug-abuse field.