Regulation of α4β2α5 nicotinic acetylcholinergic receptors in rat cerebral cortex in early and late adolescence: Sex differences in response to chronic nicotine

Abstract

Chronic nicotine administration in animals, and smoking in humans, causes up-regulation of α4β2* neuronal nicotinic receptors (nAChRs), which has been hypothesized to contribute to the addictive actions of nicotine. We used a rat model to test whether such up-regulatory effects differ in adolescents versus adults, and in males versus females. Following chronic treatment with nicotine or saline via subcutaneous osmotic minipumps, we measured α4β2 and α4β2α5 nAChRs in cerebral cortex using [3H]epibatidine to label assembled nAChRs, and selective antibodies to measure the individual subunits via immunoprecipitation. For the first time, we provide a detailed characterization of the response of both α4β2 and α4β2α5 nAChRs in female adolescent rat cerebral cortex. We found differences in nicotine-induced up-regulation between males and females in early adolescence that are absent in both late adolescence and adulthood. Males showed significant up-regulation at PN28 which was absent in age-matched females. These results demonstrate sex differences in the susceptibility of α4β2* nAChRs to the effects of chronic nicotine exposure in the cerebral cortex based on age.

Keywords: Adolescence; Chronic nicotine; Immunoprecipitation; Nicotinic receptor subtypes; α5 subunit.

Figure 1. Male Immunoprecipitation and Specific Binding of nAChRs (Double Column)

Immunoprecipitation of [³H]EB-labeled nAChRs using subunit specific antibodies in the cerebral cortex of male rats at PN28 (a), PN42 (b), and PN84 (c) following chronic treatment with either nicotine or saline control. Specific binding of [³H]EB in the cerebral cortex of male rats at (d) PN28, (e) PN42, and (f) PN84 after chronic treatment with either nicotine or saline control. N=6–12, statistical significance determined with ANOVA, *p<0.05, **p<0.01, ***p<0.001.

Figure 2. Female Immunoprecipitation and Specific Binding of nAChRs (Single Column)

Immunoprecipitation of [3H]EB-labeled nAChRs using subunit specific antibodies in the cerebral cortex of female rats at PN28 (a), PN42 (b), and PN84 (c) following chronic treatment with either nicotine or saline control. Specific binding of [3H]EB in the cerebral cortex of female rats at (d) PN28, (e) PN42, and (f) PN84 after chronic treatment with either nicotine or saline control. N=6–11, statistical significance determined with ANOVA,*p<0.05, **p<0.01, ***p<0.001.