Ontogeny of methamphetamine-induced and cocaine-induced one-trial behavioral sensitization in preweanling and adolescent rats.

The ontogenetic profile of psychostimulant-induced one-trial behavioral sensitization has not been determined. The purpose of this study was to systematically assess the ontogeny of methamphetamine-induced and cocaine-induced behavioral sensitization across the preweanling and adolescent periods. To this end, rats were injected with methamphetamine, cocaine, or saline in either an activity chamber or home cage during the preweanling [postnatal day (PD) 12, PD 16, or PD 20], preadolescent (PD 24), or adolescent (PD 34) periods. One day later, rats were challenged with the same psychostimulant and locomotion was measured in an activity chamber. The results showed that methamphetamine produced one-trial locomotor sensitization on PD 13 and PD 17; whereas, cocaine-induced behavioral sensitization was only evident on PD 21. The sensitized responding of preweanling rats was not influenced by environmental context. Interestingly, preadolescent and adolescent rats did not exhibit locomotor sensitization. The latter result is generally consistent with past studies showing that rats from the middle and late adolescent periods do not exhibit cocaine-induced one-trial behavioral sensitization. The present results show that methamphetamine, as well as cocaine, can produce one-trial context-independent behavioral sensitization during early ontogeny, but sensitized responding is only apparent within a narrow developmental window.