Adolescent exposure to nicotine results in reinforcement enhancement but does not affect adult responding in rats

Abstract

Background Adolescence is a period of development associated with a peak in an organism’s responsiveness to reward. Epidemiological data indicate that the initiation of smoking is high during adolescence and that earlier age of onset is associated with increased incidence of dependence as adults. In rats, nicotine is known to have primary reinforcing and reinforcement enhancing effects. Although the primary reinforcing effects of nicotine have been demonstrated in adolescent rats (self-administration), less is known about its reinforcement enhancing effects during this period. Moreover, the impact of adolescent nicotine exposure on its reinforcement enhancing effects during adulthood has not yet been examined. The objectives of this study were to assess whether 1) nicotine enhances operant responding for an unconditioned visual reinforcer (VS) in adolescent rats, and 2) exposure to nicotine during adolescence affects responsiveness to the VS in adulthood. Methods Rats were exposed to nicotine (0.32 mg/kg, subcutaneous injection) or saline during adolescence (Postnatal day 29–42) and adulthood. Nose-poking for the VS was assessed under fixed and progressive ratio schedules. Results Nicotine increased responding for the VS during adolescence. Adolescent nicotine exposure failed to significantly affect adult responsiveness for the VS, regardless of adult nicotine exposure, but early exposure to the VS affected responsiveness to the VS in adulthood. Conclusions Nicotine exhibits reinforcement enhancing effects in adolescent rats. Long-term effects of adolescent nicotine on reinforcement enhancement are minimal, but the impact of early exposure to the VS and/or the primary reinforcing effects of nicotine requires further investigation.

Adolescent nicotine induces persisting changes in development of neural connectivity

“…Bracken et al (2011) recently confirmed that adolescent nicotine induces adult nicotine sensitization in the rat. In addition to lasting changes in sensitization, adolescent nicotine leads to enhanced self-administration of nicotine in adult mice (Adriani et al, 2006) and rats ; this, however, was not confirmed by Weaver et al, (2012) in rats.…”

Effects of Monoamine Oxidase Inhibition on the Reinforcing Properties of Low-Dose Nicotine

“…We used a procedure that is well established in our laboratory, in which rats respond for a moderately reinforcing VS and receive non-contingent nicotine (Caggiula et al, 2009;Donny et al, 2003;Rupprecht et al, 2015;Weaver et al, 2012). We showed that MAO inhibition decreased the threshold nicotine dose required for reinforcement enhancement.…”

“…The nicotine dose was increased across sessions: 0.03 mg/kg (10 sessions), 0.1 mg/kg (5 sessions), and 0.3 mg/kg (4 sessions). The first two doses (0.03, 0.1 mg/kg) are relatively low s.c. doses of nicotine not expected to enhance the value of the VS on their own (unpublished observations), and the highest nicotine dose (0.3 mg/kg) is a dose in the range expected to enhance the value of the VS (Buffalari et al, 2014;Weaver et al, 2012;Wing and Shoaib, 2010). For this experiment, sessions were conducted 5 days per week.…”

Consequences of adolescent use of alcohol and other drugs: Studies using rodent models

“…Generally speaking, decreases in drug reward sensitivity are often associated with compensatory increases in drug self-administration under relatively low levels of response effort (see Koob & LeMoal, 2006). Indeed, age-specific enhancement of self-administration of nicotine (Adriani et al, 2003, 2006) and cocaine (McQuown et al, 2007; Dao et al, 2011) has sometimes (albeit not always – see Weaver et al, 2012; Levin et al, 2011) been reported after adolescent exposure to nicotine, with these effects generally restricted to exposures during early-mid adolescence, and not late adolescence or adulthood. This enhanced self-administration does not extend to all types of rewards given that similar effects were not evident when animals were given the opportunity to self-administer sucrose pellets (McQuown et al, 2007).…”