A rapid and inexpensive technique for assessing the reinforcing effects of opiate drugs

Adult male Sprague-Dawley rats were placed in an apparatus consisting of 2 distinctive interconnected chambers. Choice preferences developed and stabilized over three 30 min exposures. Central injection of morphine or an enkephalin analogue in conjunction with placement upon the nonpreferred side caused a preference shift which was not evident in control subjects. Classical conditioning of opiate effects to distinctive environments may offer a novel means of assessing the hedonic effects of these compounds.