Roles of metabotropic signaling of nicotine receptors in the development and maintenance of nicotine reward through regulation of dopamine D3 receptor expression.
Study Goal
The researchers aimed to investigate the interaction between α4β2 nAChR and dopamine receptors, particularly D3R, and how nicotine exposure during adolescence affects nicotine reward and relapse in adulthood.
Results Summary
Nicotine exposure in adolescent rats increased α4β2 nAChR and D3R expression, with elevated D3R levels persisting into adulthood. D3R knockout mice showed reduced nicotine reward effects, and cellular studies linked D3R upregulation to a signaling cascade involving Src, Syk, PKC, and NF-κB.
Population
Adolescent rats and mice (wild-type and D3R knockout).
Effective Dosage
Not specified
Duration
Not specified
Interactions
Interaction between α4β2 nAChR and dopamine D2/D3 receptors noted.
| Intervention | Direction | Endpoint | Population | Dosage | Impact | Claim # |
|---|---|---|---|---|---|---|
nicotine exposure | increase | nicotine's rewarding effects | adolescent rats | - | induced a sustained increase | #1 |
nicotine treatment | increase | expression levels of α4β2 nAChR | - | - | increased | #2 |
nicotine treatment | increase | expression levels of dopamine D2/D3 receptors (D2R, D3R) | - | - | increased | #3 |
nicotine exposure | increase | expression of α4β2 nAChR | adolescent rats | - | enhanced | #4 |
nicotine exposure | increase | expression of D3R | adolescent rats | - | enhanced | #5 |
nicotine exposure | increase | elevated level of D3R | adolescent rats | - | persisted into adulthood | #6 |
D3R knockout | decrease | CPP scores | mice | - | showed significantly lower | #7 |
- | increase | D3R expression | - | - | was attributed to enhanced | #8 |
- | increase | D3R promoter activity | - | - | enhanced | #9 |
The α4β2 nicotinic acetylcholine receptor (nAChR), an ionophore, has been suggested to signal through metabotropic pathways and interact with other receptor families, such as dopamine receptors. In this study, the interaction between α4β2 nAChR and dopamine receptors was investigated through in vivo and in vitro studies. Nicotine exposure in adolescent rats is known to induce a sustained increase in nicotine's rewarding effects which was assessed by conditioned place preference (CPP) assay. The expression levels of α4β2 nAChR and dopamine D2/D3 receptors (D2R, D3R) increased after nicotine treatment. To determine which of these two dopamine receptors was increased by nicotine treatment, a newly developed ligand with high selectivity for D3R was used in the radioligand binding assay. Although the expression of both α4β2 nAChR and D3R was enhanced by nicotine exposure during adolescence, only the elevated level of D3R persisted into adulthood. In experiments conducted on mice, D3R knockout mice showed significantly lower CPP scores in adulthood compared to wild-type mice. Cellular studies showed that an increase in D3R expression was attributed to enhanced D3R promoter activity, regulated by a signaling cascade composed of Src, Syk, PKC, and NF-κB. These results demonstrate that the metabotropic signaling pathway is involved in the interaction between α4β2 nAChR and D3R, and also suggest how nicotine reward initiated in adolescence could relapse after a long abstinence period. Given the significance of adolescent nicotine exposure on nicotine addiction, this study is thought to offer a novel mechanistic perspective for understanding nicotine reward and relapse.