The fMRI BOLD response to unisensory and multisensory smoking cues in nicotine-dependent adults

Deciphering olfactory receptor binding mechanisms: a structural and dynamic perspective on olfactory receptors

Olfactory receptors, classified as G-protein coupled receptors (GPCRs), have been a subject of scientific inquiry since the early 1950s. Historically, investigations into the sensory mechanisms of olfactory receptors were often confined to behavioral characteristics in model organisms or the expression of related proteins and genes. However, with the development of cryo-electron microscopy techniques, it has gradually become possible to decipher the specific structures of olfactory receptors in insects and humans. This has provided new insights into the binding mechanisms between odor molecules and olfactory receptors. Furthermore, due to the rapid advancements in related fields such as computer simulations, the prediction and exploration of odor molecule binding to olfactory receptors have been progressively achieved through molecular dynamics simulations. Through this comprehensive review, we aim to provide a thorough analysis of research related to the binding mechanisms between odor molecules and olfactory receptors from the perspectives of structural biology and molecular dynamics simulations. Finally, we will provide an outlook on the future of research in the field of olfactory receptor sensory mechanisms.

Parameter Space and Potential for Biomarker Development in 25 Years of fMRI Drug Cue Reactivity: A Systematic Review

Importance

In the last 25 years, functional magnetic resonance imaging drug cue reactivity (FDCR) studies have characterized some core aspects in the neurobiology of drug addiction. However, no FDCR-derived biomarkers have been approved for treatment development or clinical adoption. Traversing this translational gap requires a systematic assessment of the FDCR literature evidence, its heterogeneity, and an evaluation of possible clinical uses of FDCR-derived biomarkers.

Objective

To summarize the state of the field of FDCR, assess their potential for biomarker development, and outline a clear process for biomarker qualification to guide future research and validation efforts.

Evidence Review

The PubMed and Medline databases were searched for every original FDCR investigation published from database inception until December 2022. Collected data covered study design, participant characteristics, FDCR task design, and whether each study provided evidence that might potentially help develop susceptibility, diagnostic, response, prognostic, predictive, or severity biomarkers for 1 or more addictive disorders.

Findings

There were 415 FDCR studies published between 1998 and 2022. Most focused on nicotine (122 [29.6%]), alcohol (120 [29.2%]), or cocaine (46 [11.1%]), and most used visual cues (354 [85.3%]). Together, these studies recruited 19 311 participants, including 13 812 individuals with past or current substance use disorders. Most studies could potentially support biomarker development, including diagnostic (143 [32.7%]), treatment response (141 [32.3%]), severity (84 [19.2%]), prognostic (30 [6.9%]), predictive (25 [5.7%]), monitoring (12 [2.7%]), and susceptibility (2 [0.5%]) biomarkers. A total of 155 interventional studies used FDCR, mostly to investigate pharmacological (67 [43.2%]) or cognitive/behavioral (51 [32.9%]) interventions; 141 studies used FDCR as a response measure, of which 125 (88.7%) reported significant interventional FDCR alterations; and 25 studies used FDCR as an intervention outcome predictor, with 24 (96%) finding significant associations between FDCR markers and treatment outcomes.

Conclusions and Relevance

Based on this systematic review and the proposed biomarker development framework, there is a pathway for the development and regulatory qualification of FDCR-based biomarkers of addiction and recovery. Further validation could support the use of FDCR-derived measures, potentially accelerating treatment development and improving diagnostic, prognostic, and predictive clinical judgments.

Evidence for a hijacked brain reward system but no desensitized threat system in quitting-motivated smokers: An fMRI study

BACKGROUND AND AIMS

Several aspects of how quitting-motivated tobacco use disorder (TUD) subjects and never-smokers differ in terms of reward and threat processing remain unresolved. We aimed to examine aberrant reward and threat processes in TUD and the association with smoking characteristics.

DESIGN

A between- and within-subjects functional magnetic resonance imaging (fMRI) experiment with a 2 (groups) × 4 (stimulus type) factorial design. The experimental paradigm had four conditions: pictures of (1) cigarettes served as drug-related-positive cues, (2) food as alternative reward cues, (3) long-term consequences of smoking as drug-related-negative cues and (4) neutral pictures as control.

SETTING/PARTICIPANTS

Adult participants (n = 38 TUD subjects and n = 42 never-smokers) were recruited in Berlin, Germany.

MEASUREMENTS

As contrasts of primary interest, the interactions of group × stimulus-type were assessed. Significance threshold correction for multiple testing was carried out with the family-wise error method. Correlation analyses were used to test the association with smoking characteristics.

FINDINGS

The 2 × 2 interaction of smoking status and stimulus type revealed activations in the brain reward system to drug-related-positive cues in TUD subjects (between-subjects effect: P-values ≤ 0.036). As a response to drug-related-negative cues, TUD subjects showed no reduced activation of the aversive brain network. Within the TUD group, a significant negative association was found between response of the aversive brain system to drug-related-negative cues (within-subjects effect: P-values ≤ 0.021) and the number of cigarettes smoked per day (right insula r = -0.386, P = 0.024; left insula r = -0.351, P = 0.042; right ACC r = -0.359, P = 0.037).

CONCLUSIONS

Moderate smokers with tobacco use disorder appear to have altered brain reward processing of drug-related-positive (but not negative) cues compared with never smokers.

Efectos de algunas señales visuales y olfativas sobre el consumo de cigarrillo y el ansia para fumar

Las señales inductoras para el consumo (SIC) son uno de los factores que inciden en que un fumador encienda, o no, el próximo cigarrillo. Las SIC impactan más a los fumadores no dependientes de la nicotina (FND) que a los fumadores dependientes (FD). Los FND no son dependientes de la nicotina y sus niveles de monóxido de carbono tienden a ser más bajos. Los FD muestran niveles de nicotina y monóxido de carbono más altos (dependientes). Este estudio evaluó el nivel de ansia de los individuos frente a imágenes relacionadas con el producto (cigarrillos y cajetilla de cigarrillos) y si existen diferencias entre inductores visuales y olfativos en relación con el consumo de cigarrillo. Los FD muestran niveles de nicotina y monóxido de carbono más altos. Los participantes mostraron mayor ansia ante las imágenes que presentaban cigarrillos saliendo de la cajetilla. No se hallaron diferencias entre inductores visuales y olfativos en relación con el consumo de cigarrillo. No obstante, la ocurrencia de fumar fue mayor en FD que en FND. Por eso, es importante clasificar el tipo de fumador en futuras investigaciones que pretendan evaluar esta población. 

Encoding the Odor of Cigarette Smoke

The encoding of odors is believed to begin as a combinatorial code consisting of distinct patterns of responses from odorant receptors (ORs), trace-amine associated receptors (TAARs), or both. To determine how specific response patterns arise requires detecting patterns in vivo and understanding how the components of an odor, which are nearly always mixtures of odorants, give rise to parts of the pattern. Cigarette smoke, a common and clinically relevant odor consisting of >400 odorants, evokes responses from 144 ORs and 3 TAARs in freely behaving male and female mice, the first example of in vivo responses of both ORs and TAARs to an odor. As expected, a simplified artificial mimic of cigarette smoke odor tested at low concentration to identify highly sensitive receptors evokes responses from four ORs, all also responsive to cigarette smoke. Human subjects of either sex identify 1-pentanethiol as the odorant most critical for perception of the artificial mimic; and in mice the OR response patterns to these two odors are significantly similar. Fifty-eight ORs respond to the headspace above 25% 1-pentanethiol, including 9 ORs responsive to cigarette smoke. The response patterns to both cigarette smoke and 1-pentanethiol have strongly responsive ORs spread widely across OR sequence diversity, consistent with most other combinatorial codes previously measured in vivo The encoding of cigarette smoke is accomplished by a broad receptor response pattern, and 1-pentanethiol is responsible for a small subset of the responsive ORs in this combinatorial code.SIGNIFICANCE STATEMENT Complex odors are usually perceived as distinct odor objects. Cigarette smoke is the first complex odor whose in vivo receptor response pattern has been measured. It is also the first pattern shown to include responses from both odorant receptors and trace-amine associated receptors, confirming that the encoding of complex odors can be enriched by signals coming through both families of receptors. Measures of human perception and mouse receptor physiology agree that 1-pentanethiol is a critical component of a simplified odorant mixture designed to mimic cigarette smoke odor. Its receptor response pattern helps to link those of the artificial mimic and real cigarette smoke, consistent with expectations about perceptual similarity arising from shared elements in receptor response patterns.

Encoding the Odor of Cigarette Smoke

The encoding of odors is believed to begin as a combinatorial code consisting of distinct patterns of responses from odorant receptors (ORs), trace-amine associated receptors (TAARs), or both. To determine how specific response patterns arise requires detecting patterns in vivo and understanding how the components of an odor, which are nearly always mixtures of odorants, give rise to parts of the pattern. Cigarette smoke, a common and clinically relevant odor consisting of >400 odorants, evokes responses from 144 ORs and 3 TAARs in freely behaving male and female mice, the first example of in vivo responses of both ORs and TAARs to an odor. As expected, a simplified artificial mimic of cigarette smoke odor tested at low concentration to identify highly sensitive receptors evokes responses from four ORs, all also responsive to cigarette smoke. Human subjects of either sex identify 1-pentanethiol as the odorant most critical for perception of the artificial mimic; and in mice the OR response patterns to these two odors are significantly similar. Fifty-eight ORs respond to the headspace above 25% 1-pentanethiol, including 9 ORs responsive to cigarette smoke. The response patterns to both cigarette smoke and 1-pentanethiol have strongly responsive ORs spread widely across OR sequence diversity, consistent with most other combinatorial codes previously measured in vivo The encoding of cigarette smoke is accomplished by a broad receptor response pattern, and 1-pentanethiol is responsible for a small subset of the responsive ORs in this combinatorial code.SIGNIFICANCE STATEMENT Complex odors are usually perceived as distinct odor objects. Cigarette smoke is the first complex odor whose in vivo receptor response pattern has been measured. It is also the first pattern shown to include responses from both odorant receptors and trace-amine associated receptors, confirming that the encoding of complex odors can be enriched by signals coming through both families of receptors. Measures of human perception and mouse receptor physiology agree that 1-pentanethiol is a critical component of a simplified odorant mixture designed to mimic cigarette smoke odor. Its receptor response pattern helps to link those of the artificial mimic and real cigarette smoke, consistent with expectations about perceptual similarity arising from shared elements in receptor response patterns.

Different Food Odors Control Brain Connectivity in Impulsive Children

BACKGROUND

Impulsivity is a complex multi-dimensional combination of behaviors which include: ineffective impulse control, premature decision-making and inability to delay gratification.

OBJECTIVE

The aim of this work was to explore how food odor perception and its emotional value is affected in impulsive children.

METHODS

Here we compared two cohorts of impulsive and control children with ages between 10 and 16 years. Both groups underwent a functional magnetic resonance imaging experiment, in which foodrelated odor-cues were presented to all of them.

RESULTS

Differences in regions of blood oxygen level dependent activation, as well as connectivity, were calculated. Activations were significant for all odors in the impulsive group in the temporal lobe, cerebellum, supplementary motor area, frontal cortex, medial cingulate cortex, insula, precuneus, precentral, para-hippocampal and calcarine cortices.

CONCLUSION

Connectivity results showed that the expected emotional reward, based on odor perceived and processed in temporal lobes, was the main cue driving responses of impulsive children. This was followed by self-consciousness, the sensation of interaction with the surroundings and feelings of comfort and happiness, modulated by the precuneus together with somatosensory cortex and cingulum. Furthermore, reduced connectivity to frontal areas as well as to other sensory integration areas (piriform cortex), combined to show different sensory processing strategies for olfactory emotional cues in impulsive children. Finally, we hypothesize that the cerebellum plays a pivotal role in modulating decision-making for impulsive children.

Multisensory Environments to Measure Craving During Functional Magnetic Resonance Imaging

There are limited functional magnetic resonance imaging (fMRI) studies that measure alcohol craving with multisensory environments. Researchers are faced with a two-fold challenge: to recreate a naturalistic environment during an MRI scan and to produce paradigms that mimic real-life conditions involved with craving. Craving is a multifaceted psychological construct and techniques such as fMRI provide an alternative way to measure craving and to have a better understanding of its complexity. Most studies to date have implemented visual stimuli to measure craving and only a few studies have investigated gustation and olfaction. Moving forward, there needs to be greater attention on the ways in which we measure craving and the use of multisensory environments during fMRI. By going beyond examining subjective craving responses, and investigating neurobiological responses such as brain activity during fMRI, can potentially lead to better treatments for alcohol use disorder. Further, there needs to be additional consideration on standardizing how we measure craving, which will allow for a more unified approach amongst researchers.

Increased network centrality as markers of relapse risk in nicotine-dependent individuals treated with varenicline

Identifying smokers at high risk of relapse could improve the effectiveness of cessation therapies. Although altered regional brain function in smokers has been reported, whether the whole-brain functional organization differs smokers with relapse vulnerability from others remains unclear. Thus, the goal of this study is to investigate the baseline functional connectivity differences between relapsers and quitters. Using resting-state fMRI, we acquired images from 57 smokers prior to quitting attempts. After 12-week treatment with varenicline, smokers were divided into relapsers (n=36) and quitters (n=21) (quitter: continuously abstinent for weeks 9-12). The smoking cessation outcomes were cross-validated by self-reports and expired carbon monoxide. We then used eigenvector centrality (EC) mapping to identify the functional connectivity differences between relapsers and quitters. When compared to quitters, increased EC in the right dorsolateral prefrontal cortex (DLPFC), left middle temporal gyrus (MTG) and cerebellum anterior lobe was observed in relapsers. In addition, a logistic regression analysis of EC data (with DLPFC, MTG and cerebellum included) predicted relapse with 80.7% accuracy. These findings suggest that the DLPFC, MTG and cerebellum may be important substrates of smoking relapse vulnerability. The data also suggest that relapse-vulnerable smokers can be identified before quit attempts, which could enable personalized treatment and improve smoking cessation outcomes.

The neurobiological and behavioral overlaps of nicotine and food addiction

Both cigarette smoking and obesity are significant public health concerns and are associated with increased risk of early mortality. It is well established that the mesolimbic dopamine pathway is an important component of the reward system within the brain and is implicated in the development of addiction. Indeed, nicotine and highly palatable foods are capable of altering dopamine release within this system, engendering addictive like responses in susceptible individuals. Although additional research is warranted, findings from animal and human literature have elucidated many of neuroadaptions that occur from exposure to nicotine and highly palatable foods, leading to a greater understanding of the underlying mechanisms contributing to these aberrant behaviors. In this review we present the findings taken from preclinical and clinical literature of the known effects of exposure to nicotine and highly palatable foods on the reward related circuitry within the brain. Further, we compare the neurobiological and behavioral overlaps between nicotine, highly palatable foods and obesity. Lastly, we examine the stigma associated with smoking, obesity and food addiction, and the consequences stigma has on the overall health and wellbeing of an individual.