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Adolescence has been described as an important period to acquire social competences required for adult life. It has been suggested that early stress experiences could affect the development of the brain at different levels. These changes in the brain during adolescence may be related with the development of psychopathologies such as depression and social anxiety in adulthood. In the first experiment, we examined long-term effects of repeated social stress during adolescence on adult social approach-avoidance behavior. For that purpose, adolescent male Wistar rats were exposed twice at postnatal day (Pnd) 45 and Pnd48 to the resident-intruder paradigm followed by three times psychosocial threat with the same resident. Three weeks after the last psychosocial threat experience the animals were behaviorally tested in a social approach-avoidance test. Socially stressed animals spent less time in the interaction zone with an unfamiliar male adult rat. These data suggest that animals exposed to social stress during adolescence show a higher level of social anxiety in adulthood. In the second experiment, we investigated whether these long-term effects of social stress during adolescence on behavior draw a parallel with changes in brain monoamine content, biosynthesis and turnover. Using the same experimental design as in the first experiment, HPLC analysis of various brain regions showed that there were no differences in monoamine content, monoamine biosynthesis and monoamines activity in the prefrontal cortex, hippocampus, hypothalamus and striatum in adulthood. These results indicate that long-lasting changes in social behavior following social stress during adolescence are not accompanied by changes in brain monoamine content, biosynthesis and turnover.

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Responses to some psychoactive substances seem to differ between adolescents and adults. Bupropion, an antidepressant which is also used for smoking cessation, induces a dose-dependent increase in locomotor activity in adult mice, although its behavioral actions in adolescents have not been evaluated. In the present study the effects of acute bupropion administration (5, 10, 15 and 20 mg/kg) on locomotor activity were examined in early adolescent (postnatal day (pnd): 29-31 days), late adolescent (pnd: 47-49 days) and adult (pnd > 70 days) male NMRI mice, using an infrared photocell system. Locomotion was recorded for a total period of 90 min. Results indicated that there were significant differences in motor activity counts between the three ages evaluated, with late adolescents being more active than early adolescents. Bupropion (at doses 20, 15 and 10 mg/kg) induced a significant increase in locomotion, but there was no significant interaction between age and treatment. This suggests that the locomotor-stimulating effects of bupropion can be observed at different ages (early adolescence, late adolescence and adulthood), although the detailed analysis of the temporal course of locomotion changes induced by different bupropion doses reflected some differences between ages. The lowest dose (5 mg/kg) failed to induce hyperactivity in either adolescent or adult mice.

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