Neuropsychiatric characterization of individuals with inhalant use disorder and polysubstance use according to latent profiles of executive functioning

Harms associated with inhalant misuse in adolescent females - a review of the pre-clinical and clinical evidence

BACKGROUND

Inhalant misuse, or the misuse of products containing toluene is common in adolescents, and is associated with diverse physiological and psychological harms. Females comprise over half those who misuse inhalants in adolescence, however, the majority of the evidence has been derived from male-only or mixed-sex studies without exploration of sex differences. Female adolescence is a critical maturational period with potential for growth, reproductive, cognitive and psychological harms that may lead to long-term health consequences. We therefore summarise evidence of female-specific harms arising from inhalant misuse.

METHODS

We synthesised pre-clinical and clinical studies of inhalant misuse which were conducted in females, or where sex-differences were reported, into a narrative literature review.

RESULTS

Females experience growth impairments and metabolic dysfunction arising from inhalant misuse, but data on sex-differences are inconclusive. Inhalant misuse in early adolescence may impact menarche and subsequent reproductive capacity, but studies have predominantly focused on the effects of inhalants on offspring rather than on the exposed female. There is limited evidence of sex-differences in relation to cognitive outcomes following exposure to inhalants in pre-clinical models. Females are at an increased risk of psychological harms associated with inhalant misuse, particularly depression and suicidal behaviour.

CONCLUSIONS

The type and magnitude of harms associated with inhalant misuse are sex-specific, but data are limited. We recommend that both pre-clinical and clinical studies of inhalant misuse include both males and females, and should specifically test for and report sex-differences. This can be used to build an evidence base for screening and interventions tailored to females.

Exploring the prevalence of substance-induced neurocognitive disorder among polysubstance users, adding subjective and objective evidence of cognitive impairment

The objective of this study was to explore the prevalence of substance-induced neurocognitive disorder (NCD) in a sample of polysubstance users, adding both objective- and subjective cognitive impairment.

METHOD

We collected cross-sectional data from 33 community-based residential facilities in Mexico City. Montreal Cognitive Assessment was used for measurement of objective cognitive impairment, and a DSM-5-based interview for subjective impairment. Years and days of recent use of alcohol, marijuana, cocaine and inhalants were collected for regression analyses.

RESULTS

753 participants were analyzed; from these, 50.5% show objective impairment, 71% and 58.5% self-reported any cognitive deficit and cognitive decline, respectively. Between 21.8%-36.5% would qualify for NCD when integrating both objective- and subjective impairment (deficit or decline). Significant weak associations were found between objective impairment and subjective deficits in all cognitive domains except social cognition. Regression models adding both objective- and subjective measures explained more variation in the years of alcohol, inhalant and cocaine use, and in recent marijuana use, than the objective measure alone, but associations were inconsistent.

CONCLUSION

Though significant in proportion, the prevalence of NCD in this population can only be partially related to substance use. Further integrative approaches are needed to refine the epidemiology of this disorder.

Default Mode Network Efficiency Is Correlated With Deficits in Inhibition in Adolescents With Inhalant Use Disorder

It is well established that alterations in cognitive function and damage to brain structures are often found in adolescents who have substance use disorder (SUD). However, deficits in executive cognitive functioning in adolescents related to the vulnerability and consumption of such substances are not well known. In this study, we use graph theoretic analysis to compare the network efficiency in the resting state for three networks-default mode network (DMN), salience network (SN) and fronto-parietal network (FPN)-between inhalant-consuming adolescents and a control group (12 to 17 years old). We analyzed whether the efficiency of these functional networks was related to working memory, mental flexibility, inhibition of response, and sequential planning. We found that, when compared to the control group, inhalant-consuming adolescents presented with important deficits in communication among brain regions that comprise the DMN, SN, and FPN networks. DMN is the most affected network by inhalant abuse during adolescence. The mediation analyses suggested that the relationship between inhalant abuse and inhibitory control and sequential planning was partly mediated by DMN efficiency.

Testing whether cognitive reserve as measured by self-rating of stimulating activities moderates the association of polysubstance use and neurocognitive disorder

Introduction: The objectives were to identify a latent factor of cognitive reserve (CR) assessed by self-rating of cognitively stimulating activities, to analyze the association between this factor and educational attainment, and to test whether CR moderates the association between polysubstance use and neurocognitive disorder (NCD). Methods: Cross-sectional data of 753 participants was collected in Mexico City. A questionnaire for self-rating of stimulating activities (work/education, leisure, physical, social, usual- and current environments) was designed. Confirmatory factor analysis was performed to test unifactoriality. This CR factor was then used within a structural equation model of moderation between recent- and years of substance use and indicators of NCD (Montreal Cognitive Assessment and an interview for subjective cognitive deficits). Results: We found acceptable goodness-of-fit values for the unifactorial model, but no association of this factor with educational attainment, nor with recent- and years of substance use (suggesting independence of CR and severity of neuropathology). We did not find a moderation effect of CR between substance use and indicators of NCD; CR was negatively associated with subjective cognitive deficits only. Conclusions: Moderation effect of self-rated CR should be further tested using direct measures of substance-induced neuropathology. Measurement of self-rated CR may complement self-reported cognitive examination.

The Abused Inhalant Toluene Impairs Medial Prefrontal Cortex Activity and Risk/Reward Decision-Making during a Probabilistic Discounting Task

Inhalant (e.g., toluene) misuse is linked to behavioral and cognitive deficits in humans, yet preclinical studies of the effect of inhalants on higher-order cognition are limited. We addressed this gap in the literature by examining the effect of toluene vapor exposure on risk/reward decision-making in male and female Sprague-Dawley rats using a probabilistic discounting task. In this task, rodents chose a risky/large reward or a safe/small reward, with the odds of risky reinforcement descending or ascending throughout the test session. We observed a dose-dependent, sex-independent deficit in behavioral flexibility during probabilistic discounting caused by acute toluene exposure. Rats exposed to toluene vapor during adolescence and tested as adults performed comparably to air-treated controls and were susceptible to the effects of an acute toluene challenge. These behavioral flexibility deficits observed suggests dysfunctional medial prefrontal cortex (mPFC) activity. To address this hypothesis, we virally expressed the genetically encoded calcium sensor GCaMP6f in glutamatergic mPFC neurons and monitored calcium transients in real-time using in vivo fiber photometry. mPFC activity peaked before either lever press during free-choice trials in toluene- and air-treated animals. During forced-choice trials, GCaMP6f transients shifted from pre-risky to pre-safe choice, an effect mitigated by acute toluene exposure. mPFC activity decreased during rewarded trials, with larger decreases following risky/large wins compared with safe/small wins. Toluene-treated animals also had decreased mPFC activity during rewarded trials, but there was no distinction between risky/large wins and safe/small wins. These results provide physiological evidence for mPFC-dependent behavioral deficits caused by toluene.SIGNIFICANCE STATEMENT Inhalants (e.g., toluene) are an understudied class of drugs of abuse that cause devastating behavioral and cognitive deficits in humans. Understanding the neurobiological interactions of toluene vapor using animal models is important for developing effective treatment strategies for inhalant addicts. Here we find that toluene vapor reduces behavioral flexibility in rodents making risk/reward-based decisions. The medial prefrontal cortex (mPFC) drives behavioral flexibility during this type of decision-making and we show that toluene reduces the ability of mPFC neurons to track optimal choices as reward probabilities change. Toluene also reduces these neurons' ability to distinguish between small and large rewards. A combination of these factors likely leads to the impaired performance in probabilistic discounting following acute toluene exposure.