Tribute to: Self-administered nicotine activates the mesolimbic dopamine system through the ventral tegmental area [William Corrigall, Kathleen Coen and Laurel Adamson, Brain Res. 653 (1994) 278-284]

Nicotine sensitization (part 1): estradiol or tamoxifen is required during the induction phase and not the expression phase to enable locomotor sensitization to nicotine in female rats

RATIONALE

Nicotine sensitization involves two functionally distinct phases: induction and expression. Estradiol enhances nicotine sensitization in female rats, but it is not known whether this enhancement is specific to one or both phases.

OBJECTIVES

We investigated the effects of estradiol selectively during the induction and the expression of nicotine sensitization.

METHODS

Ovariectomy (OVX) rats were administered E2 during the induction (2 injection days) and/or the expression phase (9 days later) of nicotine sensitization. The selective estrogen receptor modulator tamoxifen (agonist of ERα and ERß, agonist of the g-coupled estradiol receptor GPER1) also was used to elucidate receptor candidates for the effects of E2 on nicotine sensitization.

RESULTS

Gonadally intact female rats exhibited expression of nicotine sensitization after a 9-day delay, whereas OVX females did not. Administration of E2 limited to the induction phase of nicotine sensitization rescued expression of nicotine sensitization in OVX females. Tamoxifen during induction did not alter expression of sensitization in gonadally intact female rats, and, like E2, was sufficient to reverse the dampening effects of OVX on expression of sensitization.

CONCLUSIONS

The enhancing effects of E2 on nicotine sensitization occur during the induction phase of nicotine sensitization, although require a delay to produce the effects on locomotor activity to nicotine, and may involve non-canonical estrogen pathways (e.g., activation of GPER1).

Genetic correlations between nicotine reinforcement-related behaviors and propensity toward high or low alcohol preference in two replicate mouse lines

Common genetic factors may contribute to the high comorbidity between tobacco smoking and alcohol use disorder. Here, we assessed behavioral and biological effects of nicotine in replicate mouse lines selectively bred for high (HAP2/3) or low alcohol preference (LAP2/3). In Experiment 1, free-choice (FC) oral nicotine and quinine intake were assessed in HAP2/3 and LAP2/3 mice. Effects of nicotinic acetylcholine receptor blockade by mecamylamine on nicotine intake in HAP2 mice were also examined. In Experiment 2, HAP2/3 and LAP2/3 mice were tested for differences in sensitivity to nicotine-induced taste conditioning. In Experiment 3, the effects of a single nicotine injection on nucleus accumbens (NAc) and dorsal striatum monoamine levels in HAP2/3 and LAP2/3 mice were tested. In Experiment 1, HAP2/3 mice showed greater nicotine intake and intake ratio than LAP2/3 mice. There were no line differences in quinine intake. Mecamylamine reduced nicotine intake and intake ratio in HAP2 mice. In Experiment 2, HAP2/3 mice showed weaker nicotine-induced conditioned taste aversion (CTA) compared with LAP2/3 mice. In Experiment 3, nicotine treatment increased NAc dopamine turnover across both HAP2/3 and LAP2/3 mouse lines. These results show that there is a positive genetic correlation between oral alcohol intake (high alcohol intake/preference selection phenotype) and oral nicotine intake and a negative genetic correlation between oral alcohol intake and sensitivity to nicotine-induced CTA.

Role of trace amine-associated receptor 1 in nicotine's behavioral and neurochemical effects

Nicotine addiction and abuse remains a global health issue. To date, the fundamental neurobiological mechanism of nicotine addiction remains incompletely understood. Trace amine-associated receptor 1 (TAAR1) is thought to directly modulate dopaminergic system and are thought to be a neural substrate underlying addictive-like behaviors. We aimed to investigate the role of TAAR1 in nicotine addictive-like behaviors. TAAR1 expression after nicotine treatment was evaluated by western blotting. c-Fos immunofluorescence and in vivo fast-scan cyclic voltammetry were used to examine the activation of brain regions and dopamine release, respectively. We then thoroughly and systematically examined the role of TAAR1 in mediating nicotine-induced sensitization, nicotine discrimination, nicotine self-administration, nicotine demand curve, and the reinstatement of nicotine-seeking. Local pharmacological manipulation was conducted to determine the role of TAAR1 in the nucleus accumbens (NAcs) in the reinstatement of nicotine-seeking. We found that the expression of TAAR1 protein was selectively downregulated in the NAc, with no change in either dorsal striatum or prefrontal cortex. TAAR1 activation was sufficient to block nicotine-induced c-Fos expression in the NAc, while also reducing nicotine-induced dopamine release in the NAc. Systemic administration of TAAR1 agonists attenuated the expression and development of nicotine-induced sensitization, nicotine self-administration, the reinstatement of nicotine-seeking, and increased the elasticity of nicotine demand curve, while intra-NAc infusions of a TAAR1 agonist was sufficient to attenuate nicotine reinstatement. Moreover, TAAR1-knockout rats showed augmented cue-induced and drug-induced reinstatement of nicotine-seeking. These results indicated that modulation of TAAR1 activity regulates nicotine addictive-like behaviors and TAAR1 represents a novel target towards the treatment of nicotine addiction.

Insights Into Nicotinic Receptor Signaling in Nicotine Addiction: Implications for Prevention and Treatment

BACKGROUND

Nicotinic acetylcholine receptors (nAChRs) belong to the Cys-loop ligandgated ion-channel (LGIC) superfamily, which also includes the GABA, glycine, and serotonin receptors. Many nAChR subunits have been identified and shown to be involved in signal transduction on binding to them of either the neurotransmitter acetylcholine or exogenous ligands such as nicotine. The nAChRs are pentameric assemblies of homologous subunits surrounding a central pore that gates cation flux, and they are expressed at neuromuscular junctions throughout the nervous system.

METHODS AND RESULTS

Because different nAChR subunits assemble into a variety of pharmacologically distinct receptor subtypes, and different nAChRs are implicated in various physiological functions and pathophysiological conditions, nAChRs represent potential molecular targets for drug addiction and medical therapeutic research. This review intends to provide insights into recent advances in nAChR signaling, considering the subtypes and subunits of nAChRs and their roles in nicotinic cholinergic systems, including structure, diversity, functional allosteric modulation, targeted knockout mutations, and rare variations of specific subunits, and the potency and functional effects of mutations by focusing on their effects on nicotine addiction (NA) and smoking cessation (SC). Furthermore, we review the possible mechanisms of action of nAChRs in NA and SC based on our current knowledge.

CONCLUSION

Understanding these cellular and molecular mechanisms will lead to better translational and therapeutic operations and outcomes for the prevention and treatment of NA and other drug addictions, as well as chronic diseases, such as Alzheimer's and Parkinson's. Finally, we put forward some suggestions and recommendations for therapy and treatment of NA and other chronic diseases.