Background: The initial response to nicotine is an important predictor of subsequent use. Multiple factors may alter this response including genetics and age of first use. Here we investigated the influence of age, genetics, and their interaction on nicotine sensitivity. We then examined whether these factors influence the relationship between initial behavioral responses and voluntary nicotine consumption in adulthood. Methods: We measured initial nicotine responses, including nicotine-induced locomotor depression and hypothermia following an acute intraperitoneal injection (0, 0.5, or 1 mg/kg), during early-adolescence, middle-adolescence, late-adolescence, or adulthood. Thirty-five days after the initial testing, mice were assessed for voluntary oral nicotine consumption. Results: Early-adolescent mice were more resistant to nicotine-induced hypothermia and locomotor depression than later ages, further hypothermia was influenced by genetics. In the DBA/2J strain, early-adolescent mice were insensitive to nicotine-induced hypothermia, but this response developed at later ages. In contrast, C57BL/6J mice were sensitive at all ages, but sensitivity increased across developmental age. There was little evidence of a relationship between initial behavioral response and choice nicotine consumption. Conclusion: By understanding how age of exposure and genetics influence initial nicotine behavioral responses, we have a greater understanding of factors that make adolescents differentially sensitive to the effects of this drug.
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