The Effects of Alcohol and Cannabis Co-Use on Neurocognitive Function, Brain Structure, and Brain Function

White Matter Differences in Early-Stage Alcohol Use Disorder: Diffusion Tensor and Neurite Orientation Dispersion and Density Measures of Structural Integrity

BACKGROUND

Alcohol use disorder (AUD) is prevalent during young adulthood, and this risk may be linked to aberrations in neurodevelopmental processes. Prior studies examining white matter (WM) integrity in young adult individuals with AUD have shown considerable variability. This is due in part because traditional tensor related metrics such as fractional anisotropy are subject to limitations in estimation precision at sites of crossing or curving fibres. In response, to better understand differences in WM integrity of young adults with AUD, this study sought to uniquely employ two WM integrity measurement domains.

METHODS

Twenty-five participants (n = 14 female) diagnosed with AUD and 33 social drinkers (n = 19 female) underwent structural and diffusion-weighted imaging. Diffusion-weighted images were processed to extract diffusion tensor (DTI) and neurite orientation dispersion and density (NODDI) metrics in major WM tracts for comparison between the two groups.

RESULTS

We identified decreased axial diffusivity in portions of frontolimbic and corticostriatal WM tracts, and increased orientation dispersion at overlapping tracts in participants with AUD relative to social drinkers.

CONCLUSIONS

These results may represent early-stage neural immune system activation and axonal reorganization targeting frontolimbic and corticostriatal WM tracts, therein associated with behaviours linked to AUD. This is the first study combining DTI and NODDI metrics to identify early-stage indicators of alcohol-related neurobiological pathology in young adults with AUD compared to social drinkers.

The effects of moderate alcohol and THC co-use during male and female rat adolescence on AKT-GSK3ß signaling in adulthood

Alcohol and cannabis are often taken in combination, and extensive co-use has been linked to enduring changes in cognitive and metabolic functioning. The underlying mechanisms for these effects are unclear, but we recently demonstrated that co-administration of ethanol and delta-9-tetrahydrocannbinol (THC) to adolescent rats caused lasting adaptations in GABA and glycogen synthase kinase 3ß (GSK3ß) signaling in the medial prefrontal cortex (mPFC). As a ubiquitous protein kinase, GSK3ß is downstream to the protein kinase B (also known as AKT) pathway that is activated by insulin receptor signaling in a main control center for metabolism and energy homeostasis, the mediobasal hypothalamus (MBH). Our goal here was to investigate if volitional co-use of low to moderate levels of ethanol and THC would impact the total and phosphorylated levels (p) of AKT and GSK3ß in the mPFC and MBH. Peri-adolescent Long Evans rats [postnatal day (P) 30-47] consumed 10 % ethanol, cookies laced with THC (3-10 mg/kg/day), both drugs, or vehicle controls. On P114, we modeled re-exposure to a behaviorally relevant dose of THC by challenging rats (i.p.) with 5 mg/kg THC (or vehicle) and sacrificed them 30 min later. Western blot analysis revealed that THC challenge increased pAKT and pGSK3ß compared to control similarly across all treatment groups, sexes, and brain regions; no effects on total levels of AKT or GSK3ß were found. Previously reported behavioral results from these rats showed no differences in working memory assessed in adulthood. Although future studies will be necessary to determine the role of exposure dose on drug-induced adaptations in AKT and GSK3ß signaling, the current findings suggest that moderate volitional co-use of alcohol and THC may not produce long-term deficits that persist into adulthood.

Adolescent Alcohol Exposure Dysregulates Developing Cortical GABA Circuits

Adolescence is a critical developmental period during which physical, behavioral, and neurobiological maturation occurs. Within the brain, the prefrontal cortex is one of the last brain regions to undergo remodeling, often into adulthood. These relatively late developmental changes leave the prefrontal cortex uniquely vulnerable to insults beginning in adolescence-including alcohol exposure. Adolescents initiate alcohol consumption at a high rate, increasing the risk of lasting consequences through impairing the typical development of the prefrontal cortex. In this chapter, we discuss the development of prefrontal circuitry and the current literature investigating how alcohol influences prefrontal development. We primarily focus on preclinical studies in rodent models, which allow for the study of specific populations of neurons in the prefrontal cortex. We identify several future directions for adolescent alcohol research, including greater focus on neuropeptides and stronger understanding of sex differences in brain maturation and alcohol consumption.

The effects of simultaneous alcohol and cannabis use on subjective drug effects: A narrative review across methodologies

Over 75% of young adults who use cannabis also report drinking alcohol, leading to increased risks that include impaired cognition, substance use disorders, and more heavy and frequent substance use. Studies suggest that subjective responses to either alcohol or cannabis can serve as a valuable indicator for identifying individuals at risk of prolonged substance use and use disorder. While laboratory studies show additive effects when alcohol and cannabis are used together, the impact of co-using these substances, specifically with respect to cannabidiol, on an individual's subjective experience remains unclear. This narrative review explores the effects of simultaneous alcohol and cannabis (SAM) use on subjective drug effects, drawing from qualitative research, laboratory experiments, and naturalistic studies. Experimental findings are inconsistent regarding the combined effects of alcohol and cannabis, likely influenced by factors such as dosage, method of administration, and individual substance use histories. Similarly, findings from qualitative and naturalistic studies are mixed regarding subjective drug effects following SAM use. These discrepancies may be due to recall biases, variations in assessment methods, and the measurement in real-world contexts of patterns of SAM use and related experiences. Overall, this narrative review highlights the need for more comprehensive research to understand more fully subjective drug effects of SAM use in diverse populations and settings, emphasizing the importance of frequent and nuanced assessment of SAM use and subjective responses in naturalistic settings.

Emotion Recognition and Self-Reported Emotion Processing in Alcohol and Cannabis Co-Using Young Adults

Alcohol and cannabis use are each associated with impairments in emotion recognition accuracy, which may promote interpersonal problems. It is unclear if emotion recognition or self-reported emotion processing differs between young adult alcohol and cannabis co-users (ACCs) and healthy controls (HCs). This study examined whether ACCs and HCs differed in their emotion recognition across two different behavioral tasks with static or dynamic faces and determined if there were differences in self-reported socio-emotional processing and alexithymia. 22 ACCs (mean age = 21.27 ± 1.75) and 25 HCs (mean age = 21.48 ± 2.68), matched on age, sex, and IQ, completed the Metrisquare Emotion Recognition Task and CANTAB Emotion Recognition Task. The ACCs and HCs were compared on task accuracy and self-reported measures, including the Social Emotional Questionnaire (SEQ) and the Perth Alexithymia Questionnaire (PAQ). No significant main effects of the Group variable or the Emotion-Group interaction variable were present for either task. The ACCs had lower SEQ (p = 0.014) and higher PAQ (p = 0.024) scores relative to the HCs, indicating greater difficulties in socio-emotional processing and identifying one's own emotions, respectively. Understanding the behavioral correlates of the self-reported difficulties in emotion processing reported by ACCs is needed to develop interventions to reduce these symptoms and promote healthy socio-emotional functioning in this population.

Tobacco and alcohol co-use: Lifestyle and sociodemographic factors, and personality aspects as potential predictors in the "Seguimiento Universidad de Navarra" cohort

Tobacco and alcohol co-use are two major lifestyle modifiable risk factors. Understanding the determinants of both behaviors helps to develop interventions to prevent these exposures. However, previous studies have focused on predictors of individual tobacco or alcohol use. This study aims to explore the potential predictors of tobacco and alcohol co-use among Spanish university graduates from the "Seguimiento Universidad de Navarra" (SUN) cohort study. A total of 7175 participants who were co-users of tobacco and alcohol were selected for this cross-sectional analysis. Their mean age was 39.1 years (12.04 SD) and 57.3% were women. Univariate regression models were used to select the potential predictors of tobacco and alcohol co-use, and the areas under the ROC curves (AUC) were calculated. Multivariable logistic regression models were used to create a predictive model. Baseline potential predictors included sociodemographic factors, lifestyle habits, and perceived personality aspects. In the multivariable model, the main significant potential predictors of tobacco and alcohol co-use were driving under the influence of alcohol (odds ratio [OR] = 1.65 [1.43-1.90]), drinking 1-2 cups of coffee daily (OR = 1.50 [1.24-1.84]), drinking three or more cups of coffee daily (OR = 1.61 [1.35-1.91]), and doing more physical activity than recommended (OR = 1.18 [1.02-1.34]) when compared with the reference group. Conversely, those who were married (OR = 0.87 [0.75-0.99], ate at home 7 days a week (OR = 0.69 [0.60-0.80]), or had a high perceived level of competitiveness (OR = 0.83 [0.72-0.95]) had a lower risk of co-use (AUC 0.61 [confidence interval 95% 0.59-0.63]), compared to the reference group. These results could be used by healthcare professionals, especially nurses, to effectively assess patients at higher risk of tobacco and alcohol co-use. [Correction added on 16 February 2024, after first online publication: The abstract section has been revised to provide more clarity in this version.].

Effects of combined exposure to ethanol and delta-9-tetrahydrocannabinol during adolescence on synaptic plasticity in the prefrontal cortex of Long Evans rats

Significant exposure to alcohol or cannabis during adolescence can induce lasting disruptions of neuronal signaling in brain regions that are later to mature, such as the medial prefrontal cortex (mPFC). Considerably less is known about the effects of alcohol and cannabis co-use, despite its common occurrence. Here, we used male and female Long-Evans rats to investigate the effects of early-life exposure to ethanol, delta-9-tetrahydrocannabinol (THC), or their combination on high frequency stimulation (HFS)-induced plasticity in the prelimbic region of the mPFC. Animals were injected daily from postnatal days 30-45 with vehicle or THC (escalating doses, 3-20 mg/kg) and allowed to drink vehicle (0.1% saccharin) or 10% ethanol immediately after each injection. In vitro brain slice electrophysiology was then used to record population responses of layer V neurons following HFS in layer II/III after 3-4 weeks of abstinence. We found that THC exposure reduced body weight gains observed in ad libitum fed rats, and reduced intake of saccharin and ethanol. Compared to controls, there was a significant reduction in HFS-induced long-term depression (LTD) in rats exposed to either drug alone, and an absence of LTD in rats exposed to the drug combination. Bath application of indiplon or AR-A014418, which enhance GABAA receptor function or inhibit glycogen synthase kinase 3β (GSK3β), respectively, suggested the effects of ethanol, THC or their combination were due in part to lasting adaptations in GABA and GSK3β signaling. These results suggest the potential for long-lasting adaptations in mPFC output following co-exposure to alcohol and THC.

Effects of combined exposure to ethanol and delta-9-tetrahydrocannabinol during adolescence on synaptic plasticity in the prefrontal cortex of Long Evans rats

Significant exposure to alcohol or cannabis during adolescence can induce lasting disruptions of neuronal signaling in brain regions that are later to mature, such as the medial prefrontal cortex (mPFC). Considerably less is known about the effects of alcohol and cannabis co-use, despite its common occurrence. Here, we used male and female Long-Evans rats to investigate the effects of early-life exposure to ethanol, delta-9-tetrahydrocannabinol (THC), or their combination on high frequency stimulation (HFS)-induced plasticity in the prelimbic region of the mPFC. Animals were injected daily from postnatal days 30 to 45 with vehicle or THC (escalating doses, 3-20 mg/kg) and allowed to drink vehicle (0.1% saccharin) or 10% ethanol immediately after each injection. In vitro brain slice electrophysiology was then used to record population responses of layer V neurons following HFS in layer II/III after 3-4 weeks of abstinence. We found that THC exposure reduced body weight gains observed in ad libitum fed rats, and reduced intake of saccharin and ethanol. Compared to controls, there was a significant reduction in HFS-induced long-term depression (LTD) in rats exposed to either drug alone, and an absence of LTD in rats exposed to the drug combination. Bath application of indiplon or AR-A014418, which enhance GABAA receptor function or inhibit glycogen synthase kinase 3β (GSK3β), respectively, suggested the effects of ethanol, THC or their combination were due in part to lasting adaptations in GABA and GSK3β signaling. These results suggest the potential for long-lasting adaptations in mPFC output following co-exposure to alcohol and THC.

Sex moderates effects of alcohol and cannabis co-use on alcohol and stress reactivity

BACKGROUND

Simultaneous or concurrent use (co-use) of alcohol and cannabis is associated with greater use of both substances over time, academic difficulties, more severe substance use consequences, and adverse impacts on cognitive functioning than the use of a single substance or no substance use. This study examined potential neural mechanisms underlying co-use behaviors in comparison to single substance use. Specifically, we compared alcohol cue reactivity and stress-cue reactivity among individuals who reported frequent same-day co-use of alcohol and cannabis and individuals who reported only alcohol use.

METHODS

The sample included 88 individuals (41 women) who reported only alcohol use and 24 individuals (8 women) who reported co-use of alcohol and cannabis on at least 50% of drinking occasions. All participants completed fMRI stress and alcohol cue reactivity tasks. Because of known sex effects on stress reactivity and alcohol cue reactivity, we tested sex by co-use interactions.

RESULTS

During alcohol cue presentation, co-users had less activation in the thalamus and dorsomedial prefrontal cortex than alcohol-only users, effects that were driven by differences in responses to neutral cues. Examination of stress cue reactivity revealed sex by co-use interactions in the lingual gyrus, with women co-users showing a greater difference between negative and neutral cue reactivity than all other groups. In addition, women co-users had greater connectivity between the nucleus accumbens and both the medial orbitofrontal cortex and the rostral anterior cingulate cortex during negative cue presentation than the other groups.

CONCLUSIONS

These results provide preliminary evidence of enhanced stress cue reactivity in individuals reporting co-use of alcohol and cannabis, particularly women co-users.