Habenular α5 nicotinic receptor subunit signalling controls nicotine intake

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Genetic variation in CHRNA5, the gene encoding the α5 nicotinic acetylcholine receptor subunit, increases vulnerability to tobacco addiction and lung cancer, but the underlying mechanisms are unknown. Here we report markedly increased nicotine intake in mice with a null mutation in Chrna5. This effect was ‘rescued’ in knockout mice by re-expressing α5 subunits in the medial habenula (MHb), and recapitulated in rats through α5 subunit knockdown in MHb. Remarkably, α5 subunit knockdown in MHb did not alter the rewarding effects of nicotine but abolished the inhibitory effects of higher nicotine doses on brain reward systems. The MHb extends projections almost exclusively to the interpeduncular nucleus (IPN). We found diminished IPN activation in response to nicotine in α5 knockout mice. Further, disruption of IPN signalling increased nicotine intake in rats. Our findings indicate that nicotine activates the habenulo-interpeduncular pathway through α5-containing nAChRs, triggering an inhibitory motivational signal that acts to limit nicotine intake.

At a glance


  1. Increased nicotine intake in [agr]5* knockout mice.
    Figure 1: Increased nicotine intake in α5* knockout mice.

    a, Data are presented as mean (± s.e.m.) number of nicotine infusions earned across a range of nicotine doses. Two-way ANOVA: genotype, F(1,91) = 28.57, P<0.0001; dose, F(6,91) = 13.69, P<0.0001; interaction, F(6,75) = 2.55, P<0.05; n = 10–11 per group. b, Data from a are presented as mean (± s.e.m.) total nicotine intake at each dose. Genotype, F(1,91) = 67.98, P<0.0001; dose, F(6,91) = 39.06, P<0.0001; interaction, F(6,791 = 14.25, P<0.0001. **P<0.01, ***P<0.001 compared with wild-type mice at the same nicotine dose.

  2. /`Rescue/' of [agr]5* nAChRs in the habenulo-interpeduncular tract normalizes nicotine intake.
    Figure 2: ‘Rescue’ of α5* nAChRs in the habenulo-interpeduncular tract normalizes nicotine intake.

    a, Mean (± s.e.m.) nicotine infusions in Lenti-Control mice. Genotype, F(1,22) = 7.70, P<0.05; dose, F(2,22) = 19.34, P<0.0001; interaction, F(2,22) = 3.75, P<0.05. **P<0.01 between genotypes. b, Mean (± s.e.m.) nicotine infusions in Lenti-CHRNA5 mice. Genotype, F(1,28) = 0.17, not significant (NS); dose, F(2,28) = 16.05, P<0.0001; interaction, F(2,28) = 0.36, NS; n = 6–9 per group. c, GFP immunostaining confirmed MHb virus delivery. Hipp, hippocampus; LHb, lateral habenula; LV, lateral ventricle; MHb, medial habenula. Scale bars, 500 μm (left), 200μm (right). d, GFP-labelled cells in MHb, 4′,6-diamidino-2-phenylindole (DAPI)-counterstained in left panel, extend into the fasciculus retroflexus (Fr). Scale bar, 200μm. e, GFP-positive axons detected in IPN. Left panel is labelled with vesicular acetylcholine transporter (VAChT) (red) to identify the IPN. Scale bars, 50μm (left), 10μm (right).

  3. [agr]5* nAChRs in the habenulo-interpeduncular tract control nicotine intake and its reward-inhibiting effects in rats.
    Figure 3: α5* nAChRs in the habenulo-interpeduncular tract control nicotine intake and its reward-inhibiting effects in rats.

    a, Nicotine self-administration in rats injected with Lenti-Control or Lenti-α5-shRNA in the MHb. Data are presented as mean (± s.e.m.) number of nicotine infusions earned. Lentivirus, F(1,60) = 21.07, P<0.01; dose, F(6,60) = 3.84, P<0.01; interaction, F(6,60) = 1.57, NS; ; n = 5–7 per group. b, Intracranial self-stimulation thresholds in rats. Data are presented as mean (± s.e.m.) percentage change from baseline reward threshold. Lentivirus, F(1,60) = 13.23, P<0.001; dose, F(5,60) = 6.38, P<0.0001; interaction, F(5,60) = 4.19, P<0.01. *P<0.05, **P<0.01 and ***P<0.001 indicate statistically significant differences between groups; n = 6–8 per group.

  4. Nicotine-induced activation of the IPN in mice.
    Figure 4: Nicotine-induced activation of the IPN in mice.

    a, Photomicrograph of IPN showing Fos immunoreactivity in wild-type (left) and α5 knockout (right) mice following saline (top), 0.5mgkg−1 nicotine (centre), or 1.5mgkg−1 nicotine (bottom); n = 5 per group. Scale bar, 100μm. b, Cell density was quantified with unbiased stereology. Data are presented as the mean (± s.e.m.) density of Fos-immunoreactive cells (number per mm3). Genotype, F(1,24) = 13.50, P<0.01; drug, F(2,24) = 21.13, P<0.0001; interaction, F(2,24) = 8.64, P<0.01. ***P<0.001 compared with saline treatment; ****P<0.001 compared with knockout mice at the same nicotine dose.

  5. Disruption of IPN or MHb signalling increases nicotine intake in rats.
    Figure 5: Disruption of IPN or MHb signalling increases nicotine intake in rats.

    ad, All data are presented as mean (± s.e.m.) number of nicotine infusions earned. a, Lidocaine infused into the IPN increased nicotine intake in rats; **P<0.01. b, Lidocaine into the MHb increased nicotine intake in rats self-administering a high unit dose (0.12mgkg−1 per infusion); *P<0.05. c, LY235959 infused into the IPN increased nicotine intake in rats (n = 9). F(3,24) = 6.08, P<0.01. *P<0.05 and **P<0.01 compared to control. d, LY235959 (10ng per side) into the MHb increased nicotine intake in rats responding for a high unit dose (0.12mgkg−1 per infusion; n = 5); *P<0.05.


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  1. Laboratory for Behavioral and Molecular Neuroscience, Department of Molecular Therapeutics, The Scripps Research Institute—Scripps Florida, Jupiter, Florida 33458, USA

    • Christie D. Fowler,
    • Qun Lu,
    • Paul M. Johnson &
    • Paul J. Kenny
  2. Institute of Behavioral Genetics, University of Colorado, Boulder, Colorado 80309, USA

    • Michael J. Marks


C.D.F., Q.L., P.M.J. and M.J.M. performed all experiments; M.J.M. also provided essential reagents and assisted in manuscript editing; C.D.F. and P.J.K. designed the experiments, performed the statistical analyses and wrote the manuscript.

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