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.

The claustrum connects with a broad range of cortical areas including the prefrontal cortex (PFC). However, the function of the claustrum (CLA) and its neural projections remains largely unknown. Here, we elucidated the role of the neural projections from the CLA to the PFC in regulating impulsivity in male rats. We first identified the CLA-PFC pathway by retrograde tracer and virus expression. By using immunofluorescent staining of the c-Fos-positive neurons, we showed that chemogenetic activation and inhibition of the CLA-PFC pathway reduced and increased overall activity of the PFC, respectively. In the 5-choice serial reaction time task (5-CSRTT), we found that chemogenetic activation and inhibition of the CLA-PFC pathway increased and reduced the impulsive-like behavior (i.e., premature responses), respectively. Furthermore, chemogenetic inhibition of the CLA-PFC pathway prevented methamphetamine-induced impulsivity, without affecting methamphetamine-induced hyperactivity. In contrast to the role of CLA-PFC pathway in selectively regulating impulsivity, activation of the claustrum disrupted attention in the 5-CSRTT. These results indicate that the CLA-PFC pathway is essential for impulsivity. This study may shed light on the understanding of impulsivity-related disorders such as drug addiction.

Impulsivity is an important personality trait associated with several clinical syndromes including drug abuse. While repeated drug exposure is known to increase certain behavioral responses, such as locomotion, to subsequent drug exposure, few studies have examined whether such sensitization develops for impulsive behavior. In the current study we tested the effects of methamphetamine acutely, during the course of, and upon discontinuation of chronic methamphetamine treatment on impulsive behavior in two models, the 5-choice serial reaction time task (5-CSRTT) and the delay-discounting task which measure impulsive action and impulsive choice, respectively. We also examined whether the trace amine-associated receptor 1 (TAAR1) agonist RO5263397 attenuated methamphetamine-induced effects in parallel tests. Acute methamphetamine dose-dependently increased premature responses in the 5-CSRTT and shifted the delay function upward in delay discounting. Up to 40 days of methamphetamine treatment did not significantly alter the dose-effect curve of methamphetamine-induced premature responses, but produced a significant effect in the delay-discounting task. RO5263397 attenuated acute methamphetamine-induced premature responses, but this effect became non-significant over the course of chronic treatment. RO5263397 did not significantly alter the delay-discounting performance. Discontinuation of methamphetamine treatment increased premature responses, which was attenuated by RO5263397, but did not significantly alter the delay discounting function. These results suggest that acute discontinuation from prolonged methamphetamine treatment increases impulsivity, which can be reduced by a TAAR1 agonist.

Background and Purpose Trace amine‐associated https://www.guidetopharmacology.org/GRAC/ObjectDisplayForward?objectId=3641 receptors play critical roles in regulating dopamine transmission. Previous studies showed that pharmacologically or genetically manipulating the activity of https://www.guidetopharmacology.org/GRAC/ObjectDisplayForward?objectId=3641 receptors modulates addiction‐like behaviours associated with psychostimulants. However, little is known about whether https://www.guidetopharmacology.org/GRAC/ObjectDisplayForward?objectId=3641 receptor modulation would regulate the behavioural effects of opioids. Experimental Approach Effects of the selective https://www.guidetopharmacology.org/GRAC/ObjectDisplayForward?objectId=3641 receptor partial agonist RO5263397 on the addiction‐related and antinociceptive effects of morphine were systematically assessed in male rats and mice. Key Results RO5263397 attenuated the expression of morphine‐induced behavioural sensitization in wildtype but not https://www.guidetopharmacology.org/GRAC/ObjectDisplayForward?objectId=3641 receptor knockout mice. RO5263397 shifted the dose‐effect curve of morphine self‐administration downward and reduced the breakpoint in a progressive ratio schedule of reinforcement but did not affect food self‐administration in rats. RO5263397 decreased the cue‐ and drug‐induced reinstatement of morphine‐seeking behaviour in rats. RO5263397 alone did not trigger reinstatement of morphine‐seeking behaviour or change locomotor activity in rats with a history of morphine self‐administration. However, RO5263397 did not affect the expression of morphine‐induced conditioned place preference in mice or rats. RO5263397 did not affect naltrexone‐precipitated jumping behaviour or naltrexone‐induced conditioned place aversion in morphine‐dependent mice. Furthermore, RO5263397 did not affect the analgesic effects of morphine in an acute nociception model in mice and a chronic pain model in rats. Conclusion and Implications These results indicated that https://www.guidetopharmacology.org/GRAC/ObjectDisplayForward?objectId=3641 receptor activation selectively attenuated the reinforcing, but not withdrawal or antinociceptive effects of morphine, suggesting that selective https://www.guidetopharmacology.org/GRAC/ObjectDisplayForward?objectId=3641 receptor agonists might be useful to combat opioid addiction, while sparing the analgesic effects.

Nicotine addiction is a leading avoidable brain disorder globally. Although nicotine induces a modest reinforcing effect, which is important for the initial drug use, the transition from nicotine use to nicotine addiction involves the mechanisms responsible for the negative consequences of drug abstinence. Recent study suggested that trace amine-associated receptor 1 (TAAR1) is a promising pharmacological target for the modulation of positive reinforcing effects of nicotine. However, whether TAAR1 plays a part in the negative reinforcement of nicotine withdrawal remains to be determined. Here, using a long-access (LA) self-administration model, we investigated whether LA rats show increased nicotine intake and withdrawal symptoms in comparison with saline and ShA rats and then tested the effect of TAAR1 partial agonist RO5263397 on nicotine withdrawal effects. We found that rats from long-access group showed significant abstinence-induced anxiety-like behaviour, mechanic hypersensitivity, increased number of precipitated withdrawal signs and higher motivation for the drug, while rats from short-access did not differ from saline group. TAAR1 partial agonist RO5263397 significantly reduced the physical and motivational withdrawal effects of nicotine in LA rats, as reflected by increased time spent on the open arm in the elevated plus maze (EPM) test, normalized paw withdrawal threshold, decreased withdrawal signs and motivation to self-administer nicotine.This study indicates that activation of TAAR1 attenuates the negative-reinforcing effects of nicotine withdrawal and further suggests TAAR1 as a promising target to treat nicotine addiction.