Age and Sex Differences in the Acquisition and Maintenance of Intravenous Amphetamine Self-Administration in Rats

Drug abuse peaks during adolescence, and exposure to drugs during adolescence predicts drug abuse in adulthood. Nevertheless, adolescence is not widely studied in animal models of drug intake. Moreover, few studies have investigated sex differences in drug-reinforced behavior during adolescence. We studied age- and sex-differences in acquisition and maintenance of amphetamine self-administration in Sprague-Dawley rats. Adolescent males took more amphetamine than adult males, supporting the hypothesis that adolescents are more sensitive to amphetamine. A high rate of “inappropriate” active lever presses among periadolescent males suggests impulsive behavior. In the maintenance phase of testing, young adult males failed to work as hard as adult males. In contrast, young adult females worked harder than adult females. Comparing sex groups, young adult females worked harder than age-matched males to obtain amphetamine. These results will ultimately help to form effective treatment and prevention programs for drug dependent individuals of all ages and both sexes

The Effects Of Early Corticosterone Treatment On The Development Of The Avian Song Control System

Stress has long lasting effects on physiology, development, behavior, reproductive success and survival. These effects are mediated by glucocorticoids, such as corticosterone (Cort), via glucocorticoid receptors (GR), though the exact mechanisms underlying these effects are unknown. Early developmental stress affects the size of the avian song control nuclei (particularly HVC; proper name) and song quality in many songbirds, suggesting a direct link between brain and behavior. HVC is required for song learning and production. The complexity of the male zebra finch (Taeniopygia guttata) courtship song is important in female mate choice. Although the mechanisms behind the effects of developmental stress on song nuclei size and song quality are unknown, it is likely that elevated levels of Cort via GR within brain song nuclei play a significant role. We investigated the distribution, quantity, and subcellular-localization of GR- immunoreactive (GR-ir) neurons in the brains of male zebra finches 10 days post-hatch and in adulthood using immunohistochemistry. There was wide distribution of GR-ir neurons including two song nuclei HVC and robust nucleus of the arcopallium (RA). Distribution did not vary between the two ages but there were significant differences in the overall number of GR-ir neurons and their subcellular localization. We hypothesized that early Cort treatment would reduce song quality and HVC size in adult males. We inserted Cort implants in males at four days post-hatch and quantified the effects of early Cort treatment on adult song quality. Early Cort treatment decreased song similarity between the tutor and tutee’s songs and resulted in poorer copies of tutor song, but did not alter mean amplitude or song duration. Early Cort treatment reduced the HVC size in both juvenile and adult birds. This result suggests that the effect of developmental stress on the HVC size may be mediated through Cort via activation of GR within HVC as a mechanism by which HVC size and song quality are altered in developmentally stressed birds. These results suggest a potential role for Cort in mediating adverse effects of developmental stress in adult male zebra finches and highlight the developmental plasticity of the zebra finch brain