Ontogenetic differences in response to d-amphetamine: two-way avoidance, intertrial responses, and locomotor activity.

In Experiment 1, 15-, 17-, 21-, 36-, and 90-day-old rats were injected with either physiological saline, 0.5-, 1.0-, 4.0-, 8.0-, or 16.0-mg/kg of d-amphetamine sulfate and 20-min later they were allowed to explore a two-way avoidance apparatus for 8 min. Immediately following adaptation, they were given a single session of 100 two-way avoidance trials. In general, in all ages, there was a dose related increase in avoidance on the first block of trials. However, across trials avoidance of the two youngest ages decreased, avoidance responding by 21-day-old animals remained relatively constant, and avoidance of the oldest ages increased. In the three youngest ages, avoidance and intertrial responses had a similar pattern, but in older ages there was little relationship between avoidance and intertrial responses. Shuttle crossings during adaptation were increased more by higher doses in younger rats than adults. In Experiment 2, para-hydroxyamphetamine (1.0, 4.0, 16.0 mg/kg) did not alter two-way avoidance, intertrial responses, or crossings during adaptation in 15-, 17-, 21-, 36-, or 90-day-old rats. The age-dependent behavioral effects of d-amphetamine may be due to maturation of central nervous system catecholaminergic neurons.