Figure 3.

Animals pre-exposed to nicotine during periadolescence and postadolescence differed for transcript levels of different subunits of the nAChRs in the ventral midbrain. Results are expressed as fold changes from the matched vehicle-pretreated controls. An upregulation of the α5, α6, and β2 subunits was found in animals pretreated with nicotine during periadolescence. In contrast, no significant changes were found in animals that received the same nicotine pretreatment but during postadolescence, with the exception of the β3 subunit that was similarly increased in both groups. **p < 0.001 in comparison with animals pretreated during postadolescence.