An Investigation of Neurochemical Changes in Chronic Cannabis Users

Impact of cannabis use on brain metabolism using 31P and 1H magnetic resonance spectroscopy

PURPOSE

This prospective cross-sectional study investigated the influence of regular cannabis use on brain metabolism in young cannabis users by using combined proton and phosphorus magnetic resonance spectroscopy.

METHODS

The study was performed in 45 young cannabis users aged 18-30, who had been using cannabis on a regular basis over a period of at least 2 years and in 47 age-matched controls. We acquired 31P MRS data in different brain regions at 3T with a double-resonant 1H/31P head coil, anatomic images, and 1H MRS data with a standard 20-channel 1H head coil. Absolute concentration values of proton metabolites were obtained via calibration from tissue water as an internal reference, whereas a standard solution of 75 mmol/l KH2PO4 was used as an external reference for the calibration of phosphorus signals.

RESULTS

We found an overall but not statistically significant lower concentration level of several proton and phosphorus metabolites in cannabis users compared to non-users. In particular, energy-related phosphates such as adenosine triphosphate (ATP) and inorganic phosphate (Pi) were reduced in all regions under investigation. Phosphocreatine (PCr) showed lowered values mainly in the left basal ganglia and the left frontal white matter.

CONCLUSION

The results suggest that the increased risk of functional brain disorders observed in long-term cannabis users could be caused by an impairment of the energy metabolism of the brain, but this needs to be verified in future studies.

The metabotropic glutamate receptor 5 as a biomarker for psychiatric disorders

The role of glutamate system in the etiology and pathophysiology of psychiatric disorders has gained considerable attention in the past two decades, including dysregulation of the metabotropic glutamatergic receptor subtype 5 (mGlu5). Thus, mGlu5 may represent a promising therapeutic target for psychiatric conditions, particularly stress-related disorders. Here, we describe mGlu5 findings in mood disorders, anxiety, and trauma disorders, as well as substance use (specifically nicotine, cannabis, and alcohol use). We highlight insights gained from positron emission tomography (PET) studies, where possible, and discuss findings from treatment trials, when available, to explore the role of mGlu5 in these psychiatric disorders. Through the research evidence reviewed in this chapter, we make the argument that, not only is dysregulation of mGlu5 evident in numerous psychiatric disorders, potentially functioning as a disease "biomarker," the normalization of glutamate neurotransmission via changes in mGlu5 expression and/or modulation of mGlu5 signaling may be a needed component in treating some psychiatric disorders or symptoms. Finally, we hope to demonstrate the utility of PET as an important tool for investigating mGlu5 in disease mechanisms and treatment response.

The relationship between cannabis use and taurine: A MRS and metabolomics study

Taurine is an essential amino acid. It has been shown to be neuroprotective including protecting against the neurotoxic effects of glutamate. The goal of the current study was to examine the relationship between CB use and taurine measured in brain using magnetic resonance spectroscopy (MRS), and peripherally from a urine sample. Two experiments are presented. The first is a reanalysis of published data that examined taurine and glutamate in the dorsal anterior cingulate of a CB user group and non-user group using MRS. The second experiment, in a separate CB user group, used metabolomics analysis to measure taurine levels in urine. Because body composition has been associated with the pharmacokinetics of cannabis and taurine levels, a moderation model was examined with body composition included as the covariate. The MRS study found taurine levels were correlated with glutamate in both groups and taurine was correlated with frequency of CB use in the CB user group. The moderation model demonstrated significant effects of CB use and BMI; the interaction was marginally significant with lower BMI individuals showing a positive relationship between CB use and taurine. A similar finding was observed for the urine analysis. Both CB use and weight, as well as the interaction were significant. In this case, individuals with higher weight showed an association between CB use and taurine levels. This study shows the feasibility and potential importance of examining the relationship between taurine and CB use as it may shed light on a mechanism that underlies the neuroprotective effects of CB.

Examination of gamma-aminobutyric acid and glutamate-glutamine levels in association with impulsive behavior in adolescent marijuana users

BACKGROUND

Adolescent marijuana (MJ) use has been associated with alterations in brain structure and function as well as behavior. Examination of neurochemical correlates such as GABA (gamma-aminobutyric acid) and Glx (glutamate + glutamine) in MJ users remains limited. Impulsivity, identified as a risk factor and consequence of MJ use, has been associated with GABA and Glx levels in healthy and clinical populations. However, this relationship has not been investigated in MJ users. In this study, we examined levels of GABA and Glx in the anterior cingulate cortex (ACC) and its relationship with impulsive behavior in MJ-using adolescents and healthy controls.

METHODS

Healthy control subjects (HC; N = 21) and MJ-using adolescents (N = 18) completed a metabolite-edited ¹H MRS exam to measure ACC GABA and Glx levels, a structured clinical interview to assess MJ use, and the Barratt Impulsivity Scale (BIS-11) to evaluate impulsive behavior.

RESULTS

Adolescent MJ users had significantly lower tissue-corrected GABA (with macromolecules; GABA+) levels (p = 0.029) compared to HC's. No significant between-group differences were observed in ACC Glx levels. Assessment of impulsive behavior demonstrated no significant between-group differences in motor, non-planning, attention, and total impulsivity scores. Additionally, impulsivity measures and tissue-corrected GABA+ or Glx levels were not significantly correlated in either group.

CONCLUSION

Lower GABA levels in MJ users may indicate alterations in excitatory-inhibitory mechanisms critical for neurodevelopment. Although no significant relationships were observed between impulsive measures and GABA or Glx levels in both groups, further investigations are needed examining the relationship between neurochemical correlates, behavior, and adolescent MJ use.

Differential Cognitive Performance in Females and Males with Regular Cannabis Use

OBJECTIVES

Preclinical and clinical studies suggest that males and females may be differentially affected by cannabis use. This study evaluated the interaction of cannabis use and biological sex on cognition, and the association between observed cognitive deficits and features of cannabis use.

METHODS

Cognitive measures were assessed in those with regular, ongoing, cannabis use (N = 40; 22 female) and non-using peers (N = 40; 23 female). Intelligence, psychomotor speed, and verbal working memory were measured with the Wechsler Abbreviated Scale of Intelligence, Digit Symbol Test, and Digit Span and Hopkins Verbal Learning Test, respectively. Associations between cognitive measures and cannabis use features (e.g., lifetime cannabis use, age of initiation, time since last use of cannabis, recent high-concentration tetrahydrocannabinoid exposure) were also evaluated.

RESULTS

No main effects of group were observed across measures. Significant interactions between group and biological sex were observed on measures of intelligence, psychomotor speed, and verbal learning, with greatest group differences observed between males with and without regular cannabis use. Psychomotor performance was negatively correlated with lifetime cannabis exposure. Female and male cannabis use groups did not differ in features of cannabis use.

CONCLUSIONS

Findings suggest that biological sex influences the relationship between cannabis and cognition, with males potentially being more vulnerable to the neurocognitive deficits related to cannabis use.

Which came first: Cannabis use or deficits in impulse control?

Impulse control deficits are often found to co-occur with substance use disorders (SUDs). On the one hand, it is well known that chronic intake of drugs of abuse remodels the brain with significant consequences for a range of cognitive behaviors. On the other hand, individual variation in impulse control may contribute to differences in susceptibility to SUDs. Both of these relationships have been described, thus leading to a "chicken or the egg" debate which remains to be fully resolved. Does impulsivity precede drug use or does it manifest as a function of problematic drug usage? The link between impulsivity and SUDs has been most strongly established for cocaine and alcohol use disorders using both preclinical models and clinical data. Much less is known about the potential link between impulsivity and cannabis use disorder (CUD) or the directionality of this relationship. The initiation of cannabis use occurs most often during adolescence prior to the brain's maturation, which is recognized as a critical period of development. The long-term effects of chronic cannabis use on the brain and behavior have started to be explored. In this review we will summarize these observations, especially as they pertain to the relationship between impulsivity and CUD, from both a psychological and biological perspective. We will discuss impulsivity as a multi-dimensional construct and attempt to reconcile the results obtained across modalities. Finally, we will discuss possible avenues for future research with emerging longitudinal data.

The neuropharmacology of cannabinoid receptor ligands in central signaling pathways

The endocannabinoid system is a complex neuronal system involved in a number of biological functions, like attention, anxiety, mood, memory, appetite, reward, and immune responses. It is at the centre of scientific interest, which is driven by therapeutic promise of certain cannabinoid ligands and the changing legalization of herbal cannabis in many countries. The endocannabinoid system is a modulatory system, with endocannabinoids as retrograde neurotransmitters rather than direct neurotransmitters. Neuropharmacology of cannabinoid ligands in the brain can therefore be understood in terms of their modulatory actions through other neurotransmitter systems. The CB₁ receptor is chiefly responsible for effects of endocannabinoids and analogous ligands in the brain. An overview of the neuropharmacology of several cannabinoid receptor ligands, including endocannabinoids, herbal cannabis and synthetic cannabinoid receptor ligands is given in this review. Their mechanism of action at the endocannabinoid system is described, mainly in the brain. In addition, effects of cannabinoid ligands on other neurotransmitter systems will also be described, such as dopamine, serotonin, glutamate, noradrenaline, opioid, and GABA. In light of this, therapeutic potential and adverse effects of cannabinoid receptor ligands will also be discussed.

Olfactory Neuroepithelium Cells from Cannabis Users Display Alterations to the Cytoskeleton and to Markers of Adhesion, Proliferation and Apoptosis

Cannabis is the third most commonly used psychoactive substance of abuse, yet it also receives considerable attention as a potential therapeutic drug. Therefore, it is essential to fully understand the actions of cannabis in the human brain. The olfactory neuroepithelium (ON) is a peripheral nervous tissue that represents an interesting surrogate model to study the effects of drugs in the brain, since it is closely related to the central nervous system, and sensory olfactory neurons are continually regenerated from populations of stem/progenitor cells that undergo neurogenesis throughout life. In this study, we used ON cells from chronic cannabis users and healthy control subjects to assess alterations in relevant cellular processes, and to identify changes in functional proteomic pathways due to cannabis consumption. The ON cells from cannabis users exhibited alterations in the expression of proteins that were related to the cytoskeleton, cell proliferation and cell death, as well as, changes in proteins implicated in cancer, gastrointestinal and neurodevelopmental pathologies. Subsequent studies showed cannabis provoked an increase in cell size and morphological alterations evident through β-Tubulin III staining, as well as, enhanced beta-actin expression and a decrease in the ability of ON cells to undergo cell attachment, suggesting abnormalities of the cytoskeleton and cell adhesion system. Furthermore, these cells proliferated more and underwent less cell death. Our results indicate that cannabis may alter key processes of the developing brain, some of which are similar to those reported in mental disorders like DiGeorge syndrome, schizophrenia and bipolar disorder.

Evidence That Cannabis Exposure, Abuse, and Dependence Are Related to Glutamate Metabolism and Glial Function in the Anterior Cingulate Cortex: A 1H-Magnetic Resonance Spectroscopy Study

There is evidence that long-term cannabis use is associated with alterations to glutamate neurotransmission and glial function. In this study, 26 long-term cannabis users (males=65.4%) and 47 non-cannabis using healthy controls (males=44.6%) underwent proton magnetic resonance spectroscopy (¹H-MRS) of the anterior cingulate cortex (ACC) in order to characterize neurometabolite alterations in cannabis users and to examine associations between neurometabolites, cannabis exposure, and cannabis use behaviors. Myo-inositol, a marker of glial function, and glutamate metabolites did not differ between healthy controls and cannabis users or cannabis users who met criteria for DSM5 cannabis use disorder (n=17). Lower myo-inositol, a putative marker of glial function, was related to greater problematic drug use (F_1,22 = 11.95, p=.002; Cohen's f=0.59, large effect; Drug Abuse Screening Test) and severity of cannabis dependence (F_1,22 = 6.61, p=.17; Cohen's f=0.44, large effect). Further, past-year cannabis exposure exerted different effects on glutamate and glutamate+glutamine in males and females (glutamate: F_1,21 = 6.31, p=.02; glutamate+glutamine: F_1,21 = 7.20, p=.014), such that greater past-year cannabis exposure was related to higher concentrations of glutamate metabolites in male cannabis users (glutamate: F_1,14 = 25.94, p=.00016; Cohen's f=1.32, large effect; glutamate+glutamine: F_1,14 = 23.24, p=.00027, Cohen's f=1.24, large effect) but not in female cannabis users (glutamate: F_1,6 = 1.37, p=0.78; glutamate+glutamine: F_1,6 = 0.001, p=.97). The present results extend existing evidence of altered glial function and glutamate metabolism with cannabis use by providing evidence linking problematic drug use behaviors with glial function as measured with myo-inositol and recent chronic cannabis exposure to alterations in glutamate metabolism. This provides novel directions for the interrogation of the impact of cannabis use on brain neurochemistry.