Associations between regular cannabis use and brain resting-state functional connectivity in adolescents and adults

The role of sex in the association between cannabis use disorder and resting-state functional connectivity

While Cannabis use disorder (CUD) is twice as prevalent in males, females transition more quickly from heavy use to CUD and experience more severe withdrawal. These clinically relevant sex differences contrast the lack of knowledge about the underlying brain mechanisms. This study investigated the relationship between CUD and resting-state functional brain connectivity (RSFC), assessing potential sex differences herein. RSFC of the Salience Network (SN), Basal Ganglia Network (BGN), Executive Control Network (ECN), and Default Mode Network (DMN) was compared between 152 individuals (76 males) with CUD and 114 matched controls (47 males). Within the CUD group, relationships between RSFC and heaviness of cannabis use, age of onset, and CUD symptom severity, along with their associations with sex, were investigated. CUD and control groups showed similar RSFC across all networks, regardless of sex. In the CUD group, heavier cannabis use correlated with higher RSFC across all networks and earlier age of onset was related to higher RSFC in the anterior SN, BGN, left ECN, and dorsal DMN. These associations were similar for males and females. CUD severity was related to higher RSFC in the anterior SN, which was moderated by sex, with a positive association seen only in males. In conclusion, CUD may not necessarily be associated with altered RSFC. Individual use characteristics such age of onset and severity of use may determine the potential impact of cannabis use on RSFC in a largely similar way in males and females.

Central Executive Network drives delta-9-tetrahydrocannabinol (THC)-induced nonlinear changes in large-scale functional connectivity in adolescent nonhuman primates

Adolescent cannabinoid exposure has been implicated in enduring modifications to adult brain circuitry; however, well-controlled, systematic analyses investigating dose-dependent effects of chronic delta-9-tetrahydrocannabinol (THC) exposure on brain connectivity are lacking. It is hypothesized that large-scale intrinsic networks, such as default mode (DMN), central executive (CEN), and salience networks (SN), are critically involved in vulnerability to deficits in cognitive processing often associated with adolescent cannabis use. The present study aimed to elucidate the effects of chronic THC exposure on functional connectivity (FC) of these putative large-scale networks in nonhuman primates. Separate groups of adolescent squirrel monkeys (aged 2.0-yrs [female] and 2.5-yrs [male]) were administered intramuscular injections of vehicle or THC daily (0.32 or 3.2mg/kg) for 6-months during adolescence. Resting state functional connectivity from scans conducted in awake subjects was measured before dosing, at 6-months of chronic dosing, and 60-days following discontinuation of daily THC exposure. Utilizing two distinct analytical methodologies, we observed a non-linear, dosage-dependent alteration in DMN-CEN FC across scan intervals. Specifically, exposure to a low THC dosage increased FC during chronic exposure compared to both the pre-dosing and discontinuation periods. This pattern, however, was not observed in either the vehicle or high THC dosage groups. Dual-regression unveiled a similar non-linear effect within the CEN, but not DMN, suggesting the effect on DMN-CEN FC may be driven by modifications within the CEN. Taken together, these results suggest adolescent THC exposure differentially affects large-scale brain networks and contributes to a nuanced understanding of CEN's role in disrupting brain connectivity following chronic THC exposure.

Cannabis flower, concentrates, and edibles: a narrative review comparing prevalence of use, methods of consumption, and cannabis use disorder outcomes

BACKGROUND

Cannabis use has increased in prevalence over the past several decades, and novel forms of cannabis (e.g., concentrates and edibles) have become readily available.

OBJECTIVE

The purpose of this narrative review was to compare the prevalence of use, methods of consumption, and risk for cannabis use disorder outcomes across cannabis forms to better understand the diversifying landscape of cannabis products and practices.

METHODS

The electronic database PubMed was used to find relevant articles with keyword searches related to the prevalence of use, methods of consumption, and risk for cannabis use disorder for three major forms of cannabis (flower, concentrates, and edibles).

RESULTS

Use of all three major forms is prevalent among many cannabis users, but there are differences in user demographics and methods of consumption. Use of cannabis concentrates may be associated with a greater risk for cannabis use disorder. Given the historical predominance of cannabis flower use, many outcomes have not been compared with concentrates or edibles. Furthermore, form-specific longitudinal data is lacking.

CONCLUSIONS

Given the more recent emergence of novel cannabis products, comparisons of the long-term outcomes of use for each form are needed to advance the development of more informed harm reduction practices that are common to and specific to each form of cannabis.

Acute effects of different types of cannabis on young adult and adolescent resting-state brain networks

Adolescence is a time of rapid neurodevelopment and the endocannabinoid system is particularly prone to change during this time. Cannabis is a commonly used drug with a particularly high prevalence of use among adolescents. The two predominant phytocannabinoids are Delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD), which affect the endocannabinoid system. It is unknown whether this period of rapid development makes adolescents more or less vulnerable to the effects of cannabis on brain-network connectivity, and whether CBD may attenuate the effects of THC. Using fMRI, we explored the impact of vaporized cannabis (placebo, THC: 8 mg/75 kg, THC + CBD: 8 mg/75 kg THC & 24 mg/75 kg CBD) on resting-state networks in groups of semi-regular cannabis users (usage frequency between 0.5 and 3 days/week), consisting of 22 adolescents (16-17 years) and 24 young adults (26-29 years) matched for cannabis use frequency. Cannabis caused reductions in within-network connectivity in the default mode (F[2,88] = 3.97, P = 0.022, η² = 0.018), executive control (F[2,88] = 18.62, P < 0.001, η² = 0.123), salience (F[2,88] = 12.12, P < 0.001, η² = 0.076), hippocampal (F[2,88] = 14.65, P < 0.001, η² = 0.087), and limbic striatal (F[2,88] = 16.19, P < 0.001, η² = 0.102) networks compared to placebo. Whole-brain analysis showed cannabis significantly disrupted functional connectivity with cortical regions and the executive control, salience, hippocampal, and limbic striatal networks compared to placebo. CBD did not counteract THC's effects and further reduced connectivity both within networks and the whole brain. While age-related differences were observed, there were no interactions between age group and cannabis treatment in any brain network. Overall, these results challenge the assumption that CBD can make cannabis safer, as CBD did not attenuate THC effects (and in some cases potentiated them); furthermore, they show that cannabis causes similar disruption to resting-state connectivity in the adolescent and adult brain.

Accelerated aging in people living with HIV: The neuroimmune feedback model

People living with HIV (PLWH) experience earlier onset of aging-related comorbidities compared to their counterparts without HIV. This paper lays out a theoretical model to explain why PLWH experience accelerated aging. Briefly, the model is structured as follows. PLWH experience disproportionately heavy burdens of psychosocial stress across the life course. This psychosocial stress increases risks for depressive symptoms and problematic substance use. Depressive symptoms and problematic substance use interfere with long-term adherence to antiretroviral therapy (ART). Lower ART adherence, in turn, exacerbates the elevated systemic inflammation stemming from HIV infection. This inflammation increases risks for aging-related comorbidities. Systemic inflammation also reduces connectivity in the brain's central executive network (CEN), a large-scale brain network that is critical for coping with stressful circumstances. This reduced capacity for coping with stress leads to further increases in depressive symptoms and problematic substance use. Together, these changes form a neuroimmune feedback loop that amplifies the impact of psychosocial stress on aging-related comorbidities. In this paper, I review the existing evidence relevant to this model and highlight directions for future research.