No abstract

People are very likely to start psychoactive drug use during adolescence, an earlier onset being associated with a higher risk of developing addiction later in life. In experiment I, Pre-(postnatal day (pnd) 23-35), Mid-(pnd 36-48), or Post-(pnd 49-61) adolescent mice underwent a restricted-drinking period (2 h/day for 12 days), one bottle containing water and the other containing nicotine (10 mg/l) or water. After this period, Mid-adolescents showed prominent exploration and reduced anxiety in the plus-maze. This ontogenetic profile was dampened by nicotine consumption. After 2 months, these mice were tested in a novel environment (30 min/day for 3 days). Locomotor-habituation profiles were specifically disrupted by nicotine consumption during Mid-adolescence, suggesting this age as a critical period. In experiment II, Mid-adolescent (pnd 35-44) and adult (pnd 470) mice were pretreated with nicotine (0, 0.03, 0.10, 0.30 mg/kg/day for 10 days). Acute nicotine administration had opposite effects on anxiety in adolescents and adults. At 2 months after pretreatment, we measured levels of AMPA GluR2/3 subunits, thought to be involved in the control of addictive behaviors. Nicotine exposure during Mid-adolescence dose-dependently downregulated these subunits in the striatum and hippocampus, but comparable exposure during adulthood had either opposite or no effects. NMDA NR2A/B subunits were affected by nicotine, but without agerelated differences. The present data identified a nicotine-vulnerable age window, characterized by long-term disruption of locomotor habituation and downregulation of AMPA receptors. These findings support neurobiological vulnerability to drugs in adolescent humans.

In view of the need for easily accessible biomarkers, we evaluated in ADHD children the epigenetic status of the 5'-untranslated region (UTR) in the SLC6A3 gene, coding for human dopamine transporter (DAT). We analysed buccal swabs and sera from 30 children who met DSM-IV-TR criteria for ADHD, assigned to treatment according to severity. Methylation levels at six-selected CpG sites (among which, a CGGCGGCGG and a CGCG motif), alone or in combination with serum titers in auto-antibodies against dopamine transporter (DAT aAbs), were analysed for correlation with CGAS scores (by clinicians) and Conners' scales (by parents), collected at recruitment and after 6 weeks. In addition, we characterized the DAT genotype, i.e., the variable number tandem repeat (VNTR) polymorphisms at the 3'-UTR of the gene. DAT methylation levels were greatly reduced in ADHD patients compared to control, healthy children. Within patients carrying at least one DAT 9 allele (DAT 9/x), methylation at positions CpG2 and/or CpG6 correlated with recovery, as evident from delta-CGAS scores as well as delta Conners' scales ('inattentive' and 'hyperactive' subscales). Moreover, hypermethylation at CpG1 position denoted severity, specifically for those patients carrying a DAT 10/10 genotype. Intriguingly, high serum DAT-aAbs titers appeared to corroborate indications from high CpG1 versus high CpG2/CpG6 levels, likewise denoting severity versus recovery in DAT 10/10 versus 9/x patients, respectively. These profiles suggest that DAT 5'UTR epigenetics plus serum aAbs can serve as suitable biomarkers, to confirm ADHD diagnosis and/or to predict the efficacy of treatment.