Three approaches to investigating an epigenetic basis to nicotine consumption in adolescent mice: Agouti viable yellow programming, methyl donor supplementation, and maternal care

The heterogeneity of adolescent nicotine consumption of inbred mice in controlled conditions suggests a possible epigenetic etiology of individual differences in nicotine use (Chapter 1). This dissertation research approached the association between adolescent nicotine consumption and epigenetics through analysis of coat color in the agouti viable yellow ( Avy) mouse model, responses to developmental exposure to dietary methyl donor compounds, and observation of maternal care. Four major hypotheses were tested: 1) Does perinatal nicotine exposure influence expression of the environmentally sensitive epiallele, Avy , as indicated by coat color? Results showed that spectrum of agouti coat color was not influenced by continuous exposure to 200 mug/ml or 50 mug/ml nicotine in parental drinking water from 2 weeks before conception to weaning (Chapter 2). 2) Are individual differences in early embryonic epigenetic programming, as indicated by extremes of coat color in Avy /a mice, associated with subsequent adolescent nicotine intake? Results showed that neither extreme yellow mice nor fully mottled pseudoagouti mice were different from black or mottled littermates in their oral nicotine consumption on a three bottle choice test at age 36-42 days (Chapter 2). 3) Does dietary methyl donor availability---which can increase DNA methylation---alter adolescent nicotine consumption? Initial experiments indicated that mice born of parents fed a standard Methyl Supplemented diet during conception, gestation, and lactation showed lower adolescent nicotine consumption than offspring of control diet-fed litters. The effect included interactions with perinatal nicotine exposure (200 mug/ml free base nicotine in dams' drinking water) and test day such that methyl diet blocked the perinatal nicotine-induced increase in adolescent nicotine consumption, especially in the first days of the test. Subsequent experiments evaluated the timing of methyl diet and two concentrations of perinatal nicotine exposure (50 and 200 mug/ml). The 3-5% reduction in adolescent nicotine consumption was consistent across all groups of mice receiving methyl diet during brain development, including an additional group of C57BL/6J mice. Although the effects were not significant in each wave, the overall effect of methyl diet across studies was significant. (Chapter 3) 4) Are individual differences in maternal care, particularly licking and grooming of neonatal pups, associated with differences in adolescent nicotine consumption? Individual lick counts observed during 4 hours of sampling per day on postnatal days 1-8 were not associated with subsequent adolescent nicotine consumption in four litters of Avy/a and a/a littermate mice (Chapter 4). The failure to detect macroscopic factors associated with the emergence of adolescent nicotine consumption is consistent with the hypothesis that cumulative stochastic molecular events are responsible for the divergence of dizygotic-but-genetically-identical littermates in nicotine use phenotypes.