Adolescent and adult male rats differ in expression of three nicotinic receptor subtypes and in the response of these subtypes to chronic nicotine exposure

Smokers who begin as adolescents have an increased likelihood of dependence to nicotine and other drugs of abuse; this may be due in part to biological differences in the response of adult and adolescent brains to nicotine. Our aim was to use quantitative autoradiography to compare expression of three subtypes of nicotinic receptor (nAChR) in brains of adolescent and adult rats, and the response of each subtype to chronic nicotine exposure. Male Sprague-Dawley rats were administered saline or nicotine (6 mg/kg/day, free base) via osmotic minipumps for 14 days, either as adolescents (PN days 29–42) or adults (PN days 69–82), and brain sections prepared for quantitative autoradiography. Adjacent sections were labeled with [125I]A-85,380 (β2* nAChRs), [125I]-Y0-α-conotoxin MII (α6* nAChRs), or [125I] α-bungarotoxin (α7 nAChRs). Binding was quantified by densitometry and compared by ANOVA. Adolescents had consistently greater binding to β2* nAChRs (in 17 of 23 brain regions) and α7 nAChRs (in 14 of 40 regions...