A unique role for striatal serotonergic systems in the withdrawal from adolescent nicotine administration.
Adolescent smokers experience more severe withdrawal symptoms upon smoking cessation than do adults, even when daily smoking has occurred for only a short period or with low levels of consumption. Animal models of nicotine withdrawal indicate involvement of striatal serotonin (5-HT) systems in nicotine reward, withdrawal and craving. We evaluated indices of striatal 5-HT and dopamine (DA) synaptic activity, neurotransmitter levels and turnover (metabolite/transmitter ratio), after continuous nicotine infusions to adolescent rats from postnatal days 30 to 47, using a dose rate (6 mg/kg/day) that produces plasma levels typical of smokers. Withdrawal was accompanied by a significant and persistent loss of striatal 5-HT synaptic activity, evidenced by an initial decline in turnover followed by a reduction in 5-HT content without a compensatory increase in turnover. Similar effects were seen for striatal DA activity. These effects were superimposed on a loss of stimulatory 5-HT cellular responses and promotion of inhibitory responses as identified in an earlier work with this model. None of these alterations was seen during withdrawal in adult rats given the same regimen. The unique adolescent withdrawal effects were not seen when the adolescent nicotine treatment period was shortened to early adolescence (days 30-37), even if the administration paradigm was changed to twice-daily injections to maximize withdrawal stress. Our results are consistent with unique effects of adolescent nicotine withdrawal on striatal 5-HT and DA systems, and point to a potential for serotonin-specific reuptake inhibitors as alternatives to nicotine replacement therapy for smoking cessation in adolescents.
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