Age-related differences in impulsivity among adolescent and adult Sprague-Dawley rats

Abstract

Adolescence is an ontogenetic period characterized by numerous hormonal, neural, and behavioral changes. In animal models, adolescents exhibit greater levels of novelty-seeking behavior and risk-taking relative to adults, behaviors associated in humans with increases in impulsivity and elevated propensities to engage in drug and alcohol seeking behaviors. The current series of experiments sought to explore possible age-related differences in impulsivity when indexed using delay discounting in adolescent (postnatal day [P] 25-27) and adult (P68-71) female (Experiment 1) and male (Experiment 2) Sprague-Dawley rats. In both experiments, adolescents exhibited significantly greater levels of impulsive-like behavior in this test relative to adults-even when data were adjusted to account for baseline differences in activity levels (i.e., general nose-poking behavior) across age. Taken together, these results extend to both sexes previous findings of adolescent-associated elevations in impulsivity observed among male mice using delay discounting, as well as among male rats using other procedures to index impulsivity. That these age differences were observed among both male and female rats suggests that impulsivity may be a pervasive feature of adolescence, and contributes to the expression of risky behaviors during this ontogenetic period.

Fig. 1

Percentage of long-delay hole pokes (%LDH) [number of long-delay pokes/(total rewarded pokes) * 100] are shown for female (F) adolescent (ADOL) and adult rats from Experiment 1 during (a) training and (b) testing. Bottom panels depict %LDH for adolescent and adult males (M) from Experiment 2, also during (c) training and (d) testing. Asterisks (*) denote a significant main effect of age, with adolescents overall exhibiting a lower ratio of LDH pokes relative to adults. Indifference point (INDIFF PT) values (in seconds, ± standard error of the mean) for animals from both experiments are also included in the figure legend.