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Low dose nicotine and antagonism of ?2 subunit containing nicotinic acetylcholine receptors have similar effects on affective behavior in mice.

ABSTRACT: Nicotine leads to both activation and desensitization (inactivation) of nicotinic acetylcholine receptors (nAChRs). This study tested the hypothesis that nicotine and a selective antagonist of ?2*nAChRs would have similar effects on affective behavior. Adult C57BL/6J male mice were tested in a conditioned emotional response (CER) assay which evaluates the ability of an aversive stimulus to inhibit goal-directed behavior. Mice lever-pressed for a saccharin reinforcer according to a variable schedule of reinforcement during sessions in which two presentations of a compound light/tone conditioned stimulus (CS) co-terminated with a 0.1 or 0.3 mA, 0.5 s footshock unconditioned stimulus (US). During testing in the absence of the US, mice received doses of i.p. nicotine (0, 0.0032, 0.01, 0.032, 0.1 mg/kg) or a selective ?2 subunit containing nAChR (?2*nAChR) antagonist dihydro-beta-erythroidine (0, 0.1, 0.3, 1.0, 3.0 mg/kg DH?E). There was a dose-dependent effect of nicotine revealing that only low doses (0.01, 0.032 mg/kg) increased CER suppression ratios (SR) in these mice. DH?E also dose-dependently increased SR at the 3 mg/kg dose. In ethological measures of fear-/anxiety-like behavior, these doses of nicotine and DH?E significantly reduced digging behavior in a marble burying task and 0.3 mg/kg DH?E promoted open-arm activity in the elevated plus maze. Doses of nicotine and DH?E that altered affective behavior had no effect on locomotor activity. Similar to previous reports with anxiolytic drugs, low dose nicotine and DH?E reversed SR in a CER assay, decreased digging in a marble burying assay and increased open arm activity in the elevated plus maze. This study provides evidence that inactivation of ?2*nAChRs reduces fear-like and anxiety-like behavior in rodents and suggests that smokers may be motivated to smoke in part to desensitize their ?2*nAChRs. These data further identify ?2*nAChR antagonism as a potential therapeutic strategy for relief of negative affect and anxiety.

SUBMITTER: Anderson SM

PROVIDER: S-EPMC3492489 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Low dose nicotine and antagonism of β2 subunit containing nicotinic acetylcholine receptors have similar effects on affective behavior in mice.

Anderson Shawn M SM Brunzell Darlene H DH

PloS one 20121107 11

Nicotine leads to both activation and desensitization (inactivation) of nicotinic acetylcholine receptors (nAChRs). This study tested the hypothesis that nicotine and a selective antagonist of β2*nAChRs would have similar effects on affective behavior. Adult C57BL/6J male mice were tested in a conditioned emotional response (CER) assay which evaluates the ability of an aversive stimulus to inhibit goal-directed behavior. Mice lever-pressed for a saccharin reinforcer according to a variable sched ...[more]

PMID: 23144922

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Project description:Midbrain dopamine (DA) neurons are considered a critical substrate for the reinforcing and sensitizing effects of nicotine and tobacco dependence. While the role of the α4 and β2 subunit containing nicotinic acetylcholine receptors (α4β2∗nAChRs) in mediating nicotine effects on DA release and DA neuron activity has been widely explored, less information is available on their role in the morphological adaptation of the DA system to nicotine, eventually leading to dysfunctional behaviors observed in nicotine dependence. In particular, no information is available on the role of α6∗nAChRs in nicotine-induced structural plasticity in rodents and no direct evidence exists regarding the occurrence of structural plasticity in human DA neurons exposed to nicotine. To approach this problem, we used two parallel in vitro systems, mouse primary DA neuron cultures from E12.5 embryos and human DA neurons differentiated from induced pluripotent stem cells (iPSCs) of healthy donors, identified using TH+ immunoreactivity. In both systems, nicotine 1-10 μM produced a dose-dependent increase of maximal dendrite length, number of primary dendrites, and soma size when measured after 3 days in culture. These effects were blocked by pretreatments with the α6∗nAChR antagonists α-conotoxin MII and α-conotoxin PIA, as well as by the α4β2nAChR antagonist dihydro-β-erythroidine (DHβE) in both mouse and human DA neurons. Nicotine was also ineffective when the primary DA neurons were obtained from null mutant mice for either the α6 subunit or both the α4 and α6 subunits of nAChR. When pregnant mice were exposed to nicotine from gestational day 15, structural plasticity was also observed in the midbrain DA neurons of postnatal day 1 offspring only in wild-type mice and not in both null mutant mice. This study confirmed the critical role of α4α6∗nAChRs in mediating nicotine-induced structural plasticity in both mouse and human DA neurons, supporting the translational relevance of neurons differentiated from human iPSCs for pharmacological studies.

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Low dose nicotine and antagonism of ?2 subunit containing nicotinic acetylcholine receptors have similar effects on affective behavior in mice.

Publications

Low dose nicotine and antagonism of β2 subunit containing nicotinic acetylcholine receptors have similar effects on affective behavior in mice.

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