Precipitated morphine withdrawal induces a conditioned aversion in the preweaning rat.

Opiate abstinence in the adult of many species, including humans, alters autonomic function and motor behavior, and induces a negative affective state. The neurobehavioral bases of each consequence of opiate withdrawal differs. Little attention has been paid to the issue of drug withdrawal in infants, although it is a common consequence of the maternal use of illegal and legal drugs. Infant rats as young as 7 days of age that experience opiate withdrawal show an abstinence syndrome consisting of developmentally appropriate behaviors that differ from those of the adult rat, including fewer autonomic signs. Unlike the adult, there are no data in the infant on whether or not opiate withdrawal induces a negative affective state. We treated infant rats twice daily for seven days with either morphine or saline. Pups were injected with naltrexone or saline and exposed to a novel odor. After conditioning, pups were given the option of spending time with the conditioned odor or in a neutral environment. Fourteen day old pups, but not 7 day old animals, chronically treated for 7 days with morphine and conditioned with naltrexone, showed a significant avoidance of the conditioned odor. This suggests that a conditioned aversion had formed, a result similar to that shown for adult animals.