Recalled first reactions to inhaling nicotine predict the level of physical dependence

Distinct populations suppress or escalate intake of cocaine paired with aversive quinine

Background

Only a subset of individuals who encounter drugs of abuse become habitual users. Aversive subjective effects like coughing and unpleasant taste are predictors for continued use. While several preclinical studies have explored self-administration involving aversive cues, none have simultaneously introduced aversion with the initial drug self-administration. We aimed to develop a clinically relevant model by pairing intravenous cocaine with intraoral quinine self-administration from the outset and investigating whether repeated exposure to an aversive stimulus would alter its hedonic value under laboratory conditions.

Methods

Twenty-seven male and female Sprague Dawley rats self-administered intravenous/intraoral (cocaine/quinine) for 2 hr/day over 14 days. This was followed by a 1-day quinine-only extinction session, a 3-day return to self-administration, and an intraoral infusion session to assess quinine taste reactivity (TR).

Results

We identified three distinct groups. The first self-administered very little cocaine, while the second sharply escalated cocaine intake. Both groups had similar aversive TR to quinine, suggesting that the escalating group did not habituate to the aversive cue but pursued drug despite it. We also identified a third group with high initial intake that decreased over time. This decrease predicted high aversive TR, and we argue this group may represent individuals who "overindulge" on their first use and subsequently find self-administration to be aversive.

Conclusions

Our novel model mimics real-world variability in initial interactions with drugs of abuse and yields three distinct groups that differ in self-administration patterns and aversive cue valuation.

Association of pleasant sensations at cigarette smoking initiation with subsequent tobacco product use among U.S. adolescents

Approximately 20% of high school students and 7% of middle school students in the United States used tobacco products in 2016. One factor that may contribute to tobacco use is pleasant sensations - typically characterized as physiological reinforcement such as a dopamine response, or as social reinforcement such as social acceptance. In the present study, the Wave 1 (2013-2014) of the Population Assessment of Tobacco and Health (PATH) Study was analyzed to examine the influence of pleasant sensations at cigarette smoking initiation on current use of other tobacco products among adolescents. While those who reported higher unpleasant sensations at cigarette smoking initiation were less likely to report current use of any tobacco product(s) (Odds Ratio [OR] = 0.70), those who reported higher pleasant sensations at cigarette initiation were more likely to report current use of any tobacco product(s) (OR = 2.12) - including: cigarettes (OR = 2.09), cigars (OR = 1.58), hookah (OR = 1.37), and e-cigarettes (OR = 1.37). Based on these findings, interventions for smoking education and further surveillance may benefit adolescents who report higher pleasant sensations at cigarette smoking initiation.

Young Adult Perceptions Surrounding Hookah Use

Objective

We aimed to improve understanding of young adults' perceptions and interpretations of the contexts surrounding use.

Methods

We conducted focus groups with young adult hookah users (ages 18-28) to examine hookah-use experiences and risk perceptions.

Results

Two dominant themes that emerged from the discussions were the social aspects of use (eg, "ending up" at a hookah café while out with friends), and the mental and physiological reactions to use (eg, relaxation and a "high" feeling). Participants often argued that because they only used hookah every few weeks, hookah use was much less dangerous than cigarette use.

Conclusions

Findings suggest that hookah research should account for heuristic processing and point to several areas where better health communication and stricter regulatory policies are needed.

Symptoms during Adolescents' First Use of Cigarettes and E-Cigarettes: A Pilot Study

Symptoms adolescents experience during their first time using a cigarette predict their current use, but little is known regarding the symptoms experienced during first e-cigarette use. We conducted a pilot study to understand the symptoms adolescents experience when they first tried cigarettes and e-cigarettes and the associations between these symptoms and current use. Participants were 41 adolescents in two U.S. cities who had tried cigarettes or e-cigarettes. We asked adolescents to recall the symptoms they experienced during their first cigarette or e-cigarette and categorized symptoms as negative (felt bad, coughing/chest pain, bad taste, upset stomach, dizzy/lightheaded) or positive (felt relaxed, rush/buzz). Adolescents reported fewer negative symptoms for first e-cigarette than first cigarette use (all p < 0.05). Current cigarette smoking was associated with endorsing fewer negative symptoms (OR = 0.49, 95% CI = [0.25, 0.95]) and more positive symptoms (OR = 7.11, 95% CI = [1.47, 34.33]) at first cigarette use. First e-cigarette use symptoms were not associated with current e-cigarette use. Adolescents reported fewer negative symptoms from first e-cigarette than from first cigarette, and e-cigarette symptoms did not influence use as they do for cigarettes. Additional research is needed to confirm these findings in longitudinal studies.

Evidence of Altered Brain Responses to Nicotine in an Animal Model of Attention Deficit/Hyperactivity Disorder

Introduction

Individuals with attention deficit/hyperactivity disorder (ADHD) are susceptible to earlier and more severe nicotine addiction. To shed light on the relationship between nicotine and ADHD, we examined nicotine's effects on functional brain networks in an animal model of ADHD.

Methods

Awake magnetic resonance imaging was used to compare functional connectivity in adolescent (post-natal day 44 ± 2) males of the spontaneously hypertensive rat (SHR) strain and two control strains, Wistar-Kyoto and Sprague-Dawley (n = 16 each). We analyzed functional connectivity immediately before and after nicotine exposure (0.4 mg/kg base) in naïve animals, using a region-of-interest approach focussing on 16 regions previously implicated in reward and addiction.

Results

Relative to the control groups, the SHR strain demonstrated increased functional connectivity between the ventral tegmental area (VTA) and retrosplenial cortex in response to nicotine, suggesting an aberrant response to nicotine. In contrast, increased VTA-substantia nigra connectivity in response to a saline injection in the SHR was absent following a nicotine injection, suggesting that nicotine normalized function in this circuit.

Conclusions

In the SHR, nicotine triggered an atypical response in one VTA circuit while normalizing activity in another. The VTA has been widely implicated in drug reward. Our data suggest that increased susceptibility to nicotine addiction in individuals with ADHD may involve altered responses to nicotine involving VTA circuits.

Implications

Nicotine addiction is more common among individuals with ADHD. We found that two circuits involving the VTA responded differently to nicotine in animals that model ADHD in comparison to two control strains. In one circuit, nicotine normalized activity that was abnormal in the ADHD animals, while in the other circuit nicotine caused an atypical brain response in the ADHD animals. The VTA has been implicated in drug reward. Our results would be consistent with an interpretation that nicotine may normalize abnormal brain activity in ADHD, and that nicotine may be more rewarding for individuals with ADHD.

Severity of dependence modulates smokers' functional connectivity in the reward circuit: a preliminary study

RATIONALE

Nicotine dependence is characterized as a neural circuit dysfunction, particularly with regard to the reward circuit. Although dependence severity moderates cue reactivity in the brain regions involved in reward processing, the direction of its influence remains controversial.

OBJECTIVES

Investigating the functional organization of the reward circuit may provide complementary information. Here, we used resting-state functional connectivity (rsFC) to evaluate the integrity of the reward circuit in smokers with different severities of nicotine dependence.

METHODS

Totals of 65 smokers and 37 non-smokers underwent resting-state functional magnetic resonance imaging (fMRI). The smokers were divided into low-dependent (FTND < 5, n = 26) and high-dependent smoker groups (FTND ≥ 5, n = 39) based on their nicotine-dependence severity (as measured by the Fagerström test for nicotine dependence [FTND]). The region of interest (ROI)-wise rsFC within the reward circuit was compared between smokers and non-smokers as well as between low-dependent and high-dependent smokers and then correlated with smokers' FTND scores.

RESULTS

Widespread rsFC attenuation was observed in the reward circuit of smokers compared with non-smokers. Compared with low-dependent smokers, high-dependent smokers showed greater rsFC between the right amygdala and the left nucleus accumbens (NAcc) as well as between the bilateral hippocampus. Furthermore, a positive correlation between the inter-hippocampus rsFC and the severity of nicotine dependence (FTND) was detected among all smokers (r = 0.416, p = 0.001).

CONCLUSIONS

Our results indicate a dysfunction of the reward circuit in nicotine-dependent individuals. Moreover, our study improves the understanding of the neuroplastic changes that occur during the development of nicotine dependence.