Cerebellar white-matter changes in cannabis users with and without schizophrenia

THC improves behavioural schizophrenia-like deficits that CBD fails to overcome: a comprehensive multilevel approach using the Poly I:C maternal immune activation

Prenatal infections and cannabis use during adolescence are well-recognized risk factors for schizophrenia. As inflammation and oxidative stress (OS) contribute to this disorder, anti-inflammatory drugs have been proposed as potential therapies. This study aimed to evaluate the association between delta-9-tetrahydrocannabinol (THC) and schizophrenia-like abnormalities in a maternal immune activation (MIA) model. Additionally, we assessed the preventive effect of cannabidiol (CBD), a non-psychotropic/anti-inflammatory cannabinoid. THC and/or CBD were administered to Saline- and MIA-offspring during periadolescence. At adulthood, THC-exposed MIA-offspring showed significant improvements in sensorimotor gating deficits. Structural and metabolic brain changes were evaluated by magnetic resonance imaging, revealing cortical shrinkage in Saline- and enlargement in MIA-offspring after THC-exposure. Additionally, MIA-offspring displayed enlarged ventricles and decreased hippocampus, which were partially reverted by both cannabinoids. CBD prevented THC-induced reduction in the corpus callosum, despite affecting white matter structure. Post-mortem studies revealed detrimental effects of THC, including increased inflammation and oxidative stress. CBD partially reverted these pro-inflammatory alterations and modulated THC's effects on the endocannabinoid system. In conclusion, contrary to expectations, THC exhibited greater behavioural and morphometric benefits, despite promoting a pro-inflammatory state that CBD partially reverted. Further research is needed to elucidate the underlying mechanisms involved in the observed benefits of THC.

Consensus paper of the WFSBP task force on cannabis, cannabinoids and psychosis

OBJECTIVES

The liberalisation of cannabis laws, the increasing availability and potency of cannabis has renewed concern about the risk of psychosis with cannabis.

METHODS

The objective of the WFSBP task force was to review the literature about this relationship.

RESULTS

Converging lines of evidence suggest that exposure to cannabis increases the risk for psychoses ranging from transient psychotic states to chronic recurrent psychosis. The greater the dose, and the earlier the age of exposure, the greater the risk. For some psychosis outcomes, the evidence supports some of the criteria of causality. However, alternate explanations including reverse causality and confounders cannot be conclusively excluded. Furthermore, cannabis is neither necessary nor sufficient to cause psychosis. More likely it is one of the multiple causal components. In those with established psychosis, cannabis has a negative impact on the course and expression of the illness. Emerging evidence also suggests alterations in the endocannabinoid system in psychotic disorders.

CONCLUSIONS

Given that exposure to cannabis and cannabinoids is modifiable, delaying or eliminating exposure to cannabis or cannabinoids, could potentially impact the rates of psychosis related to cannabis, especially in those who are at high risk for developing the disorder.

Cannabis smoking increases the risk of suicide ideation and suicide attempt in young individuals of 11-21 years: A systematic review and meta-analysis

BACKGROUND

Cannabis is the most frequently consumed drug around the world. Its use has been associated with increased suicide behaviors; nonetheless, the association of cannabis smoking and suicide behaviors in adolescents has not yet been established. The aim of this systematic review and meta-analysis was to evaluate the risk of suicide attempt, suicidal ideation or suicide planning in individuals of 11-21 years of age who smoke cannabis.

METHODS

We performed an online searched using PubMed, EBSCO and Science Direct databases, up to July 2021. We calculated odds ratio with 95% confidence intervals to evaluate the association between suicide attempt, suicidal ideation or suicide planning and cannabis smoking in individuals of 11-21 years of age.

RESULTS

Twenty studies reported suicide attempts in 34,859 young individuals, suicidal ideation in 26, 937 individuals, and suicide planning in 9054 young individuals. We found an increased risk of suicide attempt in cannabis smokers than in non-cannabis users (OR: 2.33; 95% CI: 1.78-3.05; Z p value; <0.0001; I² = 97.12%), as well as a significant association between cannabis smoking and suicidal ideation (OR: 2.04; 95%CI: 1.64-2.53; Z p value: <0.001; I²: 94.88) and suicide planning (OR: 1.674; 95% CI: 1.554-1.804; Z p value: 0.000; I²: 92.609). Subgroup analyses showed that American teens have an increased risk of suicidal ideation; the meta-regression analysis revealed that age was negatively associated with the risk of suicide attempt.

CONCLUSIONS

This meta-analysis shows that cannabis smoking increased the risk of suicide attempt, suicidal ideation and suicide planning in young individuals of 11-21 years of age. The high risk of suicide behaviors could vary depending on the population studied; therefore, more studies are necessary to corroborate the risk of presenting suicide behaviors in individuals of 11-21 years of age who smoke cannabis.

The Link Between Cannabis Use and Violent Behavior in the Early Phase of Psychosis: The Potential Role of Impulsivity

INTRODUCTION

Recently, the literature has shown that Cannabis Use (CU) was a risk factor for Violent Behavior (VB) in patients with psychosis, and those in the early phase of psychosis (EPP). These findings are relevant because of the high prevalence of CU in this EPP, and the potential for prevention during this phase of illness. However, there is still a lack of clear explanations, supported by empirical evidence, about what underlies the link between CU and VB against other.

METHOD

This viewpoint reviews the scientific literature on the link between CU and VB, and the involvement of impulsivity in this relationship. This last point will be addressed at clinical and neurobiological levels.

RESULTS

Recent studies confirmed that CU is particularly high in the EPP, and is a risk factor for VB in the EPP and schizophrenia. Studies have also shown that impulsivity is a risk factor for VB in psychosis, is associated with CU, and may mediate the link between CU and VB. Research suggests a neurobiological mechanism, as CU affects the structures and function of frontal areas, known to play a role in impulsive behavior.

CONCLUSION

Scientific evidence support the hypothesis of an involvement of impulsivity as a variable that could mediate the link between CU and aggression, particularly, when CU has an early onset. However, this hypothesis should be confirmed with longitudinal studies and by taking into account confounding factors. The studies highlight the relevance of early prevention in the EPP, in addition to interventions focusing on psychotic disorders.

Timing dysfunction and cerebellar resting state functional connectivity abnormalities in youth at clinical high-risk for psychosis

BACKGROUND

Consistent with pathophysiological models of psychosis, temporal disturbances in schizophrenia spectrum populations may reflect abnormal cortical (e.g. prefrontal cortex) and subcortical (e.g. striatum) cerebellar connectivity. However, few studies have examined associations between cerebellar connectivity and timing dysfunction in psychosis populations, and none have been conducted in youth at clinical high-risk (CHR) for psychosis. Thus, it is currently unknown if impairments in temporal processes are present in CHR youth or how they may be associated with cerebellar connectivity and worsening of symptoms.

METHODS

A total of 108 (56 CHR/52 controls) youth were administered an auditory temporal bisection task along with a resting state imaging scan to examine cerebellar resting state connectivity. Positive and negative symptoms at baseline and 12 months later were also quantified.

RESULTS

Controlling for alcohol and cannabis use, CHR youth exhibited poorer temporal accuracy compared to controls, and temporal accuracy deficits were associated with abnormal connectivity between the bilateral anterior cerebellum and a right caudate/nucleus accumbens striatal cluster. Poor temporal accuracy accounted for 11% of the variance in worsening of negative symptoms over 12 months.

CONCLUSIONS

Behavioral findings suggest CHR youth perceive durations of auditory tones as shortened compared to objective time, which may indicate a slower internal clock. Poorer temporal accuracy in CHR youth was associated with abnormalities in brain regions involved in an important cerebellar network implicated in prominent pathophysiological models of psychosis. Lastly, temporal accuracy was associated with worsening of negative symptoms across 12 months, suggesting temporal dysfunction may be sensitive to illness progression.

Sex and dependence related neuroanatomical differences in regular cannabis users: findings from the ENIGMA Addiction Working Group

Males and females show different patterns of cannabis use and related psychosocial outcomes. However, the neuroanatomical substrates underlying such differences are poorly understood. The aim of this study was to map sex differences in the neurobiology (as indexed by brain volumes) of dependent and recreational cannabis use. We compared the volume of a priori regions of interest (i.e., amygdala, hippocampus, nucleus accumbens, insula, orbitofrontal cortex (OFC), anterior cingulate cortex and cerebellum) between 129 regular cannabis users (of whom 70 were recreational users and 59 cannabis dependent) and 114 controls recruited from the ENIGMA Addiction Working Group, accounting for intracranial volume, age, IQ, and alcohol and tobacco use. Dependent cannabis users, particularly females, had (marginally significant) smaller volumes of the lateral OFC and cerebellar white matter than recreational users and controls. In dependent (but not recreational) cannabis users, there was a significant association between female sex and smaller volumes of the cerebellar white matter and OFC. Volume of the OFC was also predicted by monthly standard drinks. No significant effects emerged the other brain regions of interest. Our findings warrant future multimodal studies that examine if sex and cannabis dependence are specific key drivers of neurobiological alterations in cannabis users. This, in turn, could help to identify neural pathways specifically involved in vulnerable cannabis users (e.g., females with cannabis dependence) and inform individually tailored neurobiological targets for treatment.

Associations between cognition and white matter microstructure in first-episode antipsychotic-naïve patients with schizophrenia and healthy controls: A multivariate pattern analysis

BACKGROUND

Cognitive functions have been associated with white matter (WM) microstructure in schizophrenia, but most studies are limited by examining only select cognitive measures and single WM tracts in chronic, medicated patients. It is unclear if the cognition-WM relationship differs between antipsychotic-naïve patients with schizophrenia and healthy controls, as differential associations have not been directly examined. Here we examine if there are differential patterns of associations between cognition and WM microstructure in first-episode antipsychotic-naïve patients with schizophrenia and healthy controls, and we characterize reliable contributors to the pattern of associations across multiple cognitive domains and WM regions, in order to elucidate white matter contribution to the neural underpinnings of cognitive deficits.

METHODS

Thirty-six first-episode antipsychotic-naïve patients with schizophrenia and 52 matched healthy controls underwent cognitive tests and diffusion-weighted imaging on a 3T Magnetic Resonance Imaging scanner. Using a multivariate partial least squares correlation analysis, we included 14 cognitive variables and mean fractional anisotropy values of 48 WM regions.

RESULTS

Initial analyses showed significant group differences in both measures of WM and cognition. There was no group interaction effect in the pattern of associations between cognition and WM microstructure. The combined analysis of patients and controls lead to a significant pattern of associations (omnibus test p = .015). Thirty-four regions and seven cognitive functions contributed reliably to the associations.

CONCLUSIONS

The lack of an interaction effect suggests similar associations in first-episode antipsychotic-naïve patients with schizophrenia and healthy controls. This, together with the differences in both WM and cognitive measurements, supports the involvement of WM in cognitive deficits in schizophrenia. Our findings add to the field by showing a coherent picture of the overall pattern of association between cognition and WM. These findings increase our understanding of the impact of WM on cognition, contributing to the search for neuromarkers of cognitive deficits in schizophrenia.

Characterizing psychosis-relevant phenomena and cognitive function in a unique population with isolated, chronic and very heavy cannabis exposure

BACKGROUND

The literature on psychosis-relevant outcomes in cannabis users does not adequately address the confounding effects of other substance use/misuse and psychiatric disorders.

METHODS

We studied a unique population for whom cannabis use is central and necessary to their way of life. They are forbidden from using other substances, including tobacco and alcohol. Their use of cannabis is heavy, chronic, and begins early. The cases were compared with matched controls who did not use cannabis, alcohol, or drugs. The controls were from the same location and shared similar beliefs and lifestyle, except for cannabis use. Attenuated psychosis-relevant phenomena were assessed with the Schizotypal Personality Questionnaire (SPQ) and cognitive functioning with a culture-neutral computerized cognitive battery.

RESULTS

Fifteen cases and 12 matched controls were studied. The cases averaged >30 000 lifetime cannabis exposures. Relative to controls, the cases had significantly higher mean (s.d.) SPQ scores 24 (14.32) v. 13 (8.92), p = 0.031; and poorer cognitive performance, reflected by a lower mean (s.d.) composite cognitive score -0.23 (0.32) v. +0.28 (0.52), p = 0.03. Moderate to large effect sizes were noted for differences in tests of attention, psychomotor speed, working memory, cognitive flexibility, visuo-spatial processing, and verbal memory. A subsample of cases had higher SPQ scores and worse cognitive performance than their siblings not using cannabis.

CONCLUSION

Heavy, chronic, and early cannabis use that is not confounded by other drug use is associated with psychosis-relevant phenomena and cognitive deficits. The findings are relevant to the evolving attitudes and laws about cannabis.

Cannabis, Cannabinoids, and Brain Morphology: A Review of the Evidence

Cannabis and cannabinoid-based products are increasingly being accepted and commodified globally. Yet there is currently limited understanding of the effect of the varied cannabinoid compounds on the brain. Exogenous cannabinoids interact with the endogenous cannabinoid system that underpins vital functions in the brain and body, and they are thought to perturb key brain and cognitive function. However, much neuroimaging research has been confined to observational studies of cannabis users, without examining the specific role of the various cannabinoids (Δ⁹-tetrahydrocannabinol, cannabidiol, etc.). This review summarizes the brain structural imaging evidence to date associated with cannabis use, its major cannabinoids (e.g., Δ⁹-tetrahydrocannabinol, cannabidiol), and synthetic cannabinoid products that have emerged as recreational drugs. In doing so, we seek to highlight some of the key issues to consider in understanding cannabinoid-related brain effects, emphasizing the dual neurotoxic and neuroprotective role of cannabinoids, and the need to consider the distinct role of the varied cannabinoids in establishing their effect on the brain.

Adolescent cannabinoid exposure interacts with other risk factors in schizophrenia: A review of the evidence from animal models

Many factors and their interaction are linked to the aetiology of schizophrenia, leading to the development of animal models of multiple risk factors and adverse exposures. Differentiating between separate and combined effects for each factor could better elucidate schizophrenia pathology, and drive development of preventative strategies for high-load risk factors. An epidemiologically valid risk factor commonly associated with schizophrenia is adolescent cannabis use. The aim of this review is to evaluate how early-life adversity from various origins, in combination with adolescent cannabinoid exposure interact, and whether these interactions confer main, synergistic or protective effects in animal models of schizophrenia-like behavioural, cognitive and morphological alterations. Patterns emerge regarding which models show consistent synergistic or protective effects, particularly those models incorporating early-life exposure to maternal deprivation and maternal immune activation, and sex-specific effects are observed. It is evident that more research needs to be conducted to better understand the risks and alterations of interacting factors, with particular interest in sex differences, to better understand the translatability of these preclinical models to humans.

Neuroanatomical alterations in people with high and low cannabis dependence

OBJECTIVES

We aimed to investigate whether severity of cannabis dependence is associated with the neuroanatomy of key brain regions of the stress and reward brain circuits.

METHODS

To examine dependence-specific regional brain alterations, we compared the volumes of regions relevant to reward and stress, between high-dependence cannabis users (CD+, n = 25), low-dependence cannabis users (CD-, n = 20) and controls (n = 37).

RESULTS

Compared to CD- and/or controls, the CD+ group had lower cerebellar white matter and hippocampal volumes, and deflation of the right hippocampus head and tail.

CONCLUSION

These findings provide initial support for neuroadaptations involving stress and reward circuits that are specific to high-dependence cannabis users.

Cerebellar alterations in cannabis users: A systematic review

Cannabis is the most used illicit substance in the world. As many countries are moving towards decriminalization, it is crucial to determine whether and how cannabis use affects human brain and behavior. The role of the cerebellum in cognition, emotion, learning, and addiction is increasingly recognized. Because of its high density in CB1 receptors, it is expected to be highly affected by cannabis use. The aim of this systematic review is to investigate how cannabis use affects cerebellar structure and function, as well as cerebellar-dependent behavioral tasks. Three databases were searched for peer-reviewed literature published until March 2018. We included studies that focused on cannabis effects on cerebellar structure, function, or cerebellar-dependent behavioral tasks. A total of 348 unique records were screened, and 40 studies were included in the qualitative synthesis. The most consistent findings include (1) increases in cerebellar gray matter volume after chronic cannabis use, (2) alteration of cerebellar resting state activity after acute or chronic use, and (3) deficits in memory, decision making, and associative learning. Age of onset and higher exposure to cannabis use were frequently associated with increased cannabis-induced alterations. Chronic cannabis use is associated with alterations in cerebellar structure and function, as well as with deficits in behavioral paradigms that involve the cerebellum (eg, eyeblink conditioning, memory, and decision making). Future studies should consider tobacco as confounding factor and use standardized methods for assessing cannabis use. Paradigms exploring the functional activity of the cerebellum may prove useful as monitoring tools of cannabis-induced impairment.

Beneficial and deleterious effects of cannabinoids in the brain: the case of ultra-low dose THC

This article reviews the neurocognitive advantages and drawbacks of cannabinoid substances, and discusses the possible physiological mechanisms that underlie their dual activity. The article further reviews the neurocognitive effects of ultra-low doses of ∆9-tetrahydrocannabinol (THC; 3-4 orders of magnitude lower than the conventional doses) in mice, and proposes such low doses of THC as a possible remedy for various brain injuries and for the treatment of age-related cognitive decline.

Does regular cannabis use affect neuroanatomy? An updated systematic review and meta-analysis of structural neuroimaging studies

Regular cannabis use is associated with adverse cognitive and mental health outcomes that have been ascribed to aberrant neuroanatomy in brain regions densely innervated with cannabinoid receptors. Neuroanatomical differences between cannabis users and controls have been assessed in multiple structural magnetic resonance imaging (sMRI) studies. However, there is heterogeneity in the results leading to cautious interpretation of the data so far. We examined the sMRI evidence to date in human cannabis users, to establish more definitely whether neuroanatomical alterations are associated with regular cannabis use. The regional specificity and association with cannabis use indices (i.e. cumulative dosage, duration) were also explored. We systematically reviewed and meta-analysed published sMRI studies investigating regional brain volumes (cortical, subcortical and global) in cannabis users and non-user controls. Three electronic databases were searched (PubMed, Scopus, and PsycINFO). A total of 17 meta-analyses were conducted (one for each cortical, subcortical and global volume) using the generic inverse variance method, whereby standardised mean difference in volume was calculated between users and non-users. Exploratory meta-regressions were conducted to investigate the association between cannabis use indices and regional brain volumes. A total of 30 articles were eligible for inclusion, contributing 106 effect sizes across 17 meta-analyses. Regular cannabis users had significantly smaller volumes of the hippocampus (SMD = 0.14, 95% CIs [0.02, 0.27]; Z = 2.29, p = 0.02, I² = 74%) and orbitofrontal cortex {medial (SMD = 0.30, 95% CIs [0.15, 0.45]; Z = 3.89, p = 0.0001, I² = 51%), lateral (SMD = 0.19, 95% CIs [0.07, 0.32]; Z = 3.10, p = 0.002, I² = 26%)} relative to controls. The volumes of the hippocampus and orbitofrontal cortex were not significantly associated with cannabis duration and dosage. Our findings are consistent with evidence of aberrance in brain regions involved in reward, learning and memory, and motivation circuits in the regular use of substances other than cannabis, pointing to commonality in neurobiological abnormalities between regular users of cannabis and of other substances.

Neuroimaging Studies in Patients With Mental Disorder and Co-occurring Substance Use Disorder: Summary of Findings

Introduction: More than half of psychiatric patients have comorbid substance use disorder (dual diagnosis) and this rate, confirmed by many epidemiological studies, is substantially higher compared to general population. Combined operation of self-medication mechanisms, common etiological factors, and mutually causative influences most likely accounts for comorbidity, which, despite its clinical prevalence, remains underrepresented in psychiatric research, especially in terms of neuroimaging. The current paper attempts to review and discuss all existing methodologically sustainable structural and functional neuroimaging studies in comorbid subjects published in the last 20 years. Methods: Performing a systematic PubMed/MEDLINE, Web of Science, and Cochrane databases search with predefined key-words and selection criteria, 43 structural and functional neuroimaging studies were analyzed. Results: Although markedly inconsistent and confounded by a variety of sources, available data suggest that structural brain changes are slightly more pronounced, yet not qualitatively different in comorbid patients compared to non-comorbid ones. In schizophrenia (SZ) patients, somewhat greater gray matter reduction is seen in cingulate cortex, dorsolateral prefrontal and frontotemporal cortex, limbic structures (hippocampus), and basal ganglia (striatum). The magnitude of structural changes is positively correlated to duration and severity of substance use, but it is important to note that at least in the beginning of the disease, dual diagnosis subjects tend to show less brain abnormalities and better cognitive functioning than pure SZ ones suggesting lower preexisting neuropathological burden. When analysing neuroimaging findings in SZ and bipolar disorder subjects, dorsolateral prefrontal, cingular, and insular cortex emerge as common affected areas in both groups which might indicate a shared endophenotypic (i.e., transdiagnostic) disruption of brain networks involved in executive functioning, emotional processing, and social cognition, rendering affected individuals susceptible to both mental disorder and substance misuse. In patients with anxiety disorders and substance misuse, a common neuroimaging finding is reduced volume of limbic structures (n. accumbens, hippocampus and amygdala). Whether this is a neuropathological marker of common predisposition to specific behavioral symptoms and drug addiction or a result from neuroadaptation changes secondary to substance misuse is unknown. Future neuroimaging studies with larger samples, longitudinal design, and genetic subtyping are warranted to enhance current knowledge on comorbidity.

Are cannabis-using and non-using patients different groups? Towards understanding the neurobiology of cannabis use in psychotic disorders

A substantial body of credible evidence has accumulated that suggest that cannabis use is an important potentially preventable risk factor for the development of psychotic illness and its worse prognosis following the onset of psychosis. Here we summarize the relevant evidence to argue that the time has come to investigate the neurobiological effects of cannabis in patients with psychotic disorders. In the first section we summarize evidence from longitudinal studies that controlled for a range of potential confounders of the association of cannabis use with increased risk of developing psychotic disorders, increased risk of hospitalization, frequent and longer hospital stays, and failure of treatment with medications for psychosis in those with established illness. Although some evidence has emerged that cannabis-using and non-using patients with psychotic disorders may have distinct patterns of neurocognitive and neurodevelopmental impairments, the biological underpinnings of the effects of cannabis remain to be fully elucidated. In the second and third sections we undertake a systematic review of 70 studies, including over 3000 patients with psychotic disorders or at increased risk of psychotic disorder, in order to delineate potential neurobiological and neurochemical mechanisms that may underlie the effects of cannabis in psychotic disorders and suggest avenues for future research.

Age of onset of cannabis use and decision making under uncertainty

Objective

Cannabis, like other substances, negatively affects health, inducing respiratory problems and mental and cognitive alterations. Memory and learning disorders, as well as executive dysfunctions, are also neuropsychological disorders associated to cannabis use. Recent evidence reveals that cannabis use during adolescence may disrupt the normal development of the brain. This study is aimed to analyze possible differences between early-onset and late-onset cannabis consumers.

Method

We used a task based on a card game with four decks and different programs of gains/losses. A total of 72 subjects (19 women; 53 men) participated in the study; they were selected through a purposive sampling and divided into three groups: early-onset consumers, late-onset consumers, and control (non-consumers). The task used was the “Cartas” program (computerized version based on the Iowa Gambling Task (IGT)), with two versions: direct and inverse. The computational model “Prospect Valence Learning” (PVL) was applied in order to describe the decision according to four characteristics: utility, loss aversion, recency, and consistency.

Results

The results evidence worst performance in the IGT in the early-onset consumers as compared to late-onset consumers and control. Differences between groups were also found in the PVL computational model parameters, since the process of decision making of the early-onset consumers was more influenced by the magnitude of the gains-losses, and more determined by short-term results without loss aversion.

Conclusions

Early onset cannabis use may involve decision-making problems, and therefore intervention programs are necessary in order to reduce the prevalence and delay the onset of cannabis use among teenagers.

Chronic oxycodone induces axonal degeneration in rat brain

BACKGROUND

Chronic opioid therapy for non-malignant pain conditions has significantly increased over the last 15 years. Recently, the correlation between opioid analgesics and alternations in brain structure, such as leukoencephalopathy, axon demyelination, and white matter lesions, has been demonstrated in patients with a history of long-term use of prescription opioids. The exact mechanisms underlying the neurotoxic effect of opioids on the central nervous system are still not fully understood. We investigated the effect of chronic opioids using an animal model in which female rats were orally gavaged with 15 mg/kg of oxycodone every 24 h for 30 days. In addition we tested oxycodone, morphine and DAMGO in breast adenocarcinoma MCF7 cells, which are known to express the μ-opioid receptor.

RESULTS

We observed several changes in the white matter of animals treated with oxycodone: deformation of axonal tracks, reduction in size of axonal fascicles, loss of myelin basic protein and accumulation of amyloid precursor protein beta (β-APP), suggesting axonal damages by chronic oxycodone. Moreover, we demonstrated activation of pro-apoptotic machinery amid suppression of anti-apoptotic signaling in axonal tracks that correlated with activation of biomarkers of the integrated stress response (ISR) in these structures after oxycodone exposure. Using MCF7 cells, we observed induction of the ISR and pro-apoptotic signaling after opioid treatment. We showed that the ISR inhibitor, ISRIB, suppresses opioid-induced Bax and CHOP expression in MCF7 cells.

CONCLUSIONS

Altogether, our data suggest that chronic opioid administration may cause neuronal degeneration by activation of the integrated stress response leading to induction of apoptotic signaling in neurons and also by promoting demyelination in CNS.

The details of structural disconnectivity in psychotic disorder: A family-based study of non-FA diffusion weighted imaging measures

BACKGROUND

Diffusion tensor imaging (DTI) studies in psychotic disorder have shown reduced FA, often interpreted as disturbed white matter integrity. The observed 'dysintegrity' may be of multifactorial origin, as changes in FA are thought to reflect a combination of changes in myelination, fiber organization and number of axons. Examining the structural substrate of the diffusion tensor in individuals with (risk for) psychotic disorder may provide better understanding of the underlying structural changes.

METHODS

DTI scans were acquired from 85 patients with psychotic disorder, 93 siblings of patients with psychotic disorder and 80 controls. Cross-sectional group comparisons were performed using Tract-Based Spatial Statistics (TBSS) on six DTI measures: axial diffusivity (AXD), radial diffusivity (RD), mean diffusivity (MD), and the case linear (CL), case planar (CP) and case spherical (CS) tensor shape measures.

RESULTS

AXD did not differ between the groups. RD and CS values were significantly increased in patients compared to controls and siblings, with no significant differences between the latter two groups. MD was higher in patients compared to controls (but not siblings), with no difference between siblings and controls. CL was smaller in patients than in siblings and controls, and CP was smaller in both patients and siblings as compared to controls.

CONCLUSION

The differences between individuals with psychotic disorder and healthy controls, derived from detailed diffusion data analyses, suggest less fiber orientation and increased free water movement in the patients. There was some evidence for association with familial risk expressed by decreased fiber orientation.

A case for motor network contributions to schizophrenia symptoms: Evidence from resting-state connectivity

Though schizophrenia (SCZ) is classically defined based on positive symptoms and the negative symptoms of the disease prove to be debilitating for many patients, motor deficits are often present as well. A growing literature highlights the importance of motor systems and networks in the disease, and it may be the case that dysfunction in motor networks relates to the pathophysiology and etiology of SCZ. To test this and build upon recent work in SCZ and in at-risk populations, we investigated cortical and cerebellar motor functional networks at rest in SCZ and controls using publically available data. We analyzed data from 82 patients and 88 controls. We found key group differences in resting-state connectivity patterns that highlight dysfunction in motor circuits and also implicate the thalamus. Furthermore, we demonstrated that in SCZ, these resting-state networks are related to both positive and negative symptom severity. Though the ventral prefrontal cortex and corticostriatal pathways more broadly have been implicated in negative symptom severity, here we extend these findings to include motor-striatal connections, as increased connectivity between the primary motor cortex and basal ganglia was associated with more severe negative symptoms. Together, these findings implicate motor networks in the symptomatology of psychosis, and we speculate that these networks may be contributing to the etiology of the disease. Overt motor deficits in SCZ may signal underlying network dysfunction that contributes to the overall disease state. Hum Brain Mapp 38:4535-4545, 2017. © 2017 Wiley Periodicals, Inc.

Neurobiological underpinnings and modulating factors in schizophrenia spectrum disorders with a comorbid substance use disorder: A systematic review

Recently there is a growing interest in the interaction of schizophrenia spectrum disorders (SSD) and substance use disorders (SUD), a condition named dual schizophrenia spectrum disorders (SSD+). While previous research has focused on clinical and cognitive aspects, little is known about the impact of comorbidity in the brain structure and functions. Evidence suggests that dual diagnosis patients, including SSD+, show a better neurocognitive functioning during the first years of illness, followed by a serious long-term decline. The initial search retrieved 94 articles, 12 were excluded for being redundant and 49 for not fulfilling the selection criteria. Thirty-three structural and functional neuroimaging studies that compare SSD and SSD+ patients were included. Both groups exhibited more brain alterations, in comparison to only SUD patients and healthy controls. SSD+ patients are less cognitively and emotionally impaired than non-dual SSD, but worse than healthy controls. The neurobiological alterations are prominent in SSD+ after five years of illness or longer. Moreover, SUD characteristics are important modulating factors, contrary to clinical severity or specific SSD diagnosis.

Adverse Structural and Functional Effects of Marijuana on the Brain: Evidence Reviewed

The growing use and legalization of cannabis are leading to increased exposures across all age groups, including in adolescence. The touting of its medicinal values stems from anecdotal reports related to treatment of a broad range of illnesses including epilepsy, multiple sclerosis, muscle spasms, arthritis, obesity, cancer, Alzheimer disease, Parkinson disease, post-traumatic stress, inflammatory bowel disease, and anxiety. However, anecdotal data and the high level of interest in this treatment must not obscure objective assessments of any potential and realized short- and long-term adverse effects of cannabis, particularly with respect to age of onset and chronicity of exposure. This critical review focuses on evidence-based research designed to assess both therapeutic benefits and harmful effects of cannabis exposure and is combined with an illustration of the neuropathologic findings in a fatal case of cannabis-induced psychosis. The literature and reported case provide strong evidence that chronic cannabis abuse causes cognitive impairment and damages the brain, particularly white matter, where cannabinoid 1 receptors abound. Contrary to popular perception, there are few objective data supporting preferential use of cannabis over conventional therapy for restoration of central nervous system structure and function in disease states such as multiple sclerosis, epilepsy, or schizophrenia. Additional research is needed to determine if subsets of individuals with various neurological and psychiatric diseases derive therapeutic benefits from cannabis.

Endocannabinoids in brain plasticity: Cortical maturation, HPA axis function and behavior

Marijuana use during adolescence has reached virtually every strata of society. The general population has the perception that marijuana use is safe for mature people and therefore is also safe for developing adolescents. However, both clinical and preclinical research shows that marijuana use, particularly prior to age 16, could have long-term effects on cognition, anxiety and stress-related behaviors, mood disorders and substance abuse. These effects derive from the role of the endocannabinoid system, the endogenous cannabinoid system, in the development of cortex, amygdala, hippocampus and hypothalamus during adolescence. Endocannabinoids are necessary for normal neuronal excitation and inhibition through actions at glutamate and GABA terminals. Synaptic pruning at excitatory synapses and sparing of inhibitory synapses likely results in changes in the balance of excitation/inhibition in individual neurons and within networks; processes which are necessary for normal cortical development. The interaction between prefrontal cortex (PFC), amygdala and hippocampus is responsible for emotional memory, anxiety-related behaviors and drug abuse and all utilize the endogenous cannabinoid system to maintain homeostasis. Also, endocannabinoids are required for fast and slow feedback in the normal stress response, processes which mature during adolescence. Therefore, exogenous cannabinoids, such as marijuana, have the potential to alter the course of development of each of these major systems (limbic, hypothalamic-pituitary-adrenal (HPA) axis and neocortex) if used during the critical period of brain development, adolescence. This article is part of a Special Issue entitled SI: Adolescent plasticity.

Effects of Marijuana Use on Brain Structure and Function: Neuroimaging Findings from a Neurodevelopmental Perspective

Marijuana, behind only tobacco and alcohol, is the most popular recreational drug in America with prevalence rates of use rising over the past decade. A wide range of research has highlighted neurocognitive deficits associated with marijuana use, particularly when initiated during childhood or adolescence. Neuroimaging, describing alterations to brain structure and function, has begun to provide a picture of possible mechanisms associated with the deleterious effects of marijuana use. This chapter provides a neurodevelopmental framework from which recent data on brain structural and functional abnormalities associated with marijuana use is reviewed. Based on the current data, we provide aims for future studies to more clearly delineate the effects of marijuana on the developing brain and to define underlying mechanisms of the potential long-term negative consequences of marijuana use.

The Role of Cannabinoids in Neuroanatomic Alterations in Cannabis Users

The past few decades have seen a marked change in the composition of commonly smoked cannabis. These changes primarily involve an increase of the psychoactive compound ∆(9)-tetrahydrocannabinol (THC) and a decrease of the potentially therapeutic compound cannabidiol (CBD). This altered composition of cannabis may be linked to persistent neuroanatomic alterations typically seen in regular cannabis users. In this review, we summarize recent findings from human structural neuroimaging investigations. We examine whether neuroanatomic alterations are 1) consistently observed in samples of regular cannabis users, particularly in cannabinoid receptor-high areas, which are vulnerable to the effects of high circulating levels of THC, and 2) associated either with greater levels of cannabis use (e.g., higher dosage, longer duration, and earlier age of onset) or with distinct cannabinoid compounds (i.e., THC and CBD). Across the 31 studies selected for inclusion in this review, neuroanatomic alterations emerged across regions that are high in cannabinoid receptors (i.e., hippocampus, prefrontal cortex, amygdala, cerebellum). Greater dose and earlier age of onset were associated with these alterations. Preliminary evidence shows that THC exacerbates, whereas CBD protects from, such harmful effects. Methodologic differences in the quantification of levels of cannabis use prevent accurate assessment of cannabis exposure and direct comparison of findings across studies. Consequently, the field lacks large "consortium-style" data sets that can be used to develop reliable neurobiological models of cannabis-related harm, recovery, and protection. To move the field forward, we encourage a coordinated approach and suggest the urgent development of consensus-based guidelines to accurately and comprehensively quantify cannabis use and exposure in human studies.

Impact of adolescent marijuana use on intelligence: Results from two longitudinal twin studies

Marijuana is one of the most commonly used drugs in the United States, and use during adolescence--when the brain is still developing--has been proposed as a cause of poorer neurocognitive outcome. Nonetheless, research on this topic is scarce and often shows conflicting results, with some studies showing detrimental effects of marijuana use on cognitive functioning and others showing no significant long-term effects. The purpose of the present study was to examine the associations of marijuana use with changes in intellectual performance in two longitudinal studies of adolescent twins (n = 789 and n = 2,277). We used a quasiexperimental approach to adjust for participants' family background characteristics and genetic propensities, helping us to assess the causal nature of any potential associations. Standardized measures of intelligence were administered at ages 9-12 y, before marijuana involvement, and again at ages 17-20 y. Marijuana use was self-reported at the time of each cognitive assessment as well as during the intervening period. Marijuana users had lower test scores relative to nonusers and showed a significant decline in crystallized intelligence between preadolescence and late adolescence. However, there was no evidence of a dose-response relationship between frequency of use and intelligence quotient (IQ) change. Furthermore, marijuana-using twins failed to show significantly greater IQ decline relative to their abstinent siblings. Evidence from these two samples suggests that observed declines in measured IQ may not be a direct result of marijuana exposure but rather attributable to familial factors that underlie both marijuana initiation and low intellectual attainment.

Neurobiological underpinnings of sensation seeking trait in heroin abusers

Neurobiological investigation of heroin revealed that abusers of this highly addictive substance show dysregulation in brain circuits for reward processing and cognitive control. Psychologically, personality traits related to reward processing and cognitive control differed between heroin abusers and non-abusers. Yet, there is no direct evidence on the relationship between these neurobiological and psychological findings on heroin abusers, and whether such relationship is altered in these abusers. The present study filled this research gap by integrating findings obtained via magnetic resonance imaging (structural volume and resting-state functional connectivity) and self-reported personality trait measures (Zuckerman׳s Sensation Seeking Scale and Barratt Impulsivity Scale) on 33 abstinent heroin users and 30 matched healthy controls. The key finding is a negative relationship between high sensation seeking tendency and midbrain structural volume in the heroin users. Importantly, there was stronger coupling between the midbrain and ventromedial prefrontal cortex and weaker coupling between the midbrain and dorsolateral prefrontal cortex in heroin users. Our findings offer significant insight into the neural underpinning of sensation seeking in heroin users. Importantly, the data shed light on a novel relationship between the mesolimbic-prefrontal pathway of the reward system and the high sensation seeking personality trait in heroin abusers.

Longitudinal changes in white matter microstructure after heavy cannabis use

Diffusion tensor imaging (DTI) studies of cannabis users report alterations in brain white matter microstructure, primarily based on cross-sectional research, and etiology of the alterations remains unclear. We report findings from longitudinal voxelwise analyses of DTI data collected at baseline and at a 2-year follow-up on 23 young adult (18-20 years old at baseline) regular cannabis users and 23 age-, sex-, and IQ-matched non-using controls with limited substance use histories. Onset of cannabis use was prior to age 17. Cannabis users displayed reduced longitudinal growth in fractional anisotropy in the central and parietal regions of the right and left superior longitudinal fasciculus, in white matter adjacent to the left superior frontal gyrus, in the left corticospinal tract, and in the right anterior thalamic radiation lateral to the genu of the corpus callosum, along with less longitudinal reduction of radial diffusion in the right central/posterior superior longitudinal fasciculus, corticospinal tract, and posterior cingulum. Greater amounts of cannabis use were correlated with reduced longitudinal growth in FA as was relatively impaired performance on a measure of verbal learning. These findings suggest that continued heavy cannabis use during adolescence and young adulthood alters ongoing development of white matter microstructure, contributing to functional impairment.

Daily marijuana use is not associated with brain morphometric measures in adolescents or adults

Recent research has suggested that marijuana use is associated with volumetric and shape differences in subcortical structures, including the nucleus accumbens and amygdala, in a dose-dependent fashion. Replication of such results in well controlled studies is essential to clarify the effects of marijuana. To that end, this retrospective study examined brain morphology in a sample of adult daily marijuana users (n = 29) versus nonusers (n = 29) and a sample of adolescent daily users (n = 50) versus nonusers (n = 50). Groups were matched on a critical confounding variable, alcohol use, to a far greater degree than in previously published studies. We acquired high-resolution MRI scans, and investigated group differences in gray matter using voxel-based morphometry, surface-based morphometry, and shape analysis in structures suggested to be associated with marijuana use, as follows: the nucleus accumbens, amygdala, hippocampus, and cerebellum. No statistically significant differences were found between daily users and nonusers on volume or shape in the regions of interest. Effect sizes suggest that the failure to find differences was not due to a lack of statistical power, but rather was due to the lack of even a modest effect. In sum, the results indicate that, when carefully controlling for alcohol use, gender, age, and other variables, there is no association between marijuana use and standard volumetric or shape measurements of subcortical structures.

Cannabis and psychopathology: The meandering journey of the last decade

Since its inception cannabis has been observed to be associated with various psycho-pathology. In this paper, the authors have reviewed the advancement made in this area over the last decade. The association between cannabis and schizophrenia has been researched more intensively. The controversy regarding the reliability, clinical utility, and the existence of a cannabis withdrawal syndrome has also been settled. Recent studies also buttressed the possibility of acute and chronic effect of cannabis on various cognitive functions. There has been a plethora of research regarding the treatment for cannabis use disorders. But the new and most interesting area of research is concentrated on the endocannabinoid system and its contribution in various psychiatric disorders.

Effects of cannabis on impulsivity: a systematic review of neuroimaging findings

We conducted a systematic review to assess the evidence for specific effects of cannabis on impulsivity, disinhibition and motor control. The review had a specific focus on neuroimaging findings associated with acute and chronic use of the drug and covers literature published up until May 2012. Seventeen studies were identified, of which 13 met the inclusion criteria; three studies investigated acute effects of cannabis (1 fMRI, 2 PET), while six studies investigated non-acute functional effects (4 fMRI, 2 PET), and four studies investigated structural alterations. Functional imaging studies of impulsivity studies suggest that prefrontal blood flow is lower in chronic cannabis users than in controls. Studies of acute administration of THC or marijuana report increased brain metabolism in several brain regions during impulsivity tasks. Structural imaging studies of cannabis users found differences in reduced prefrontal volumes and white matter integrity that might mediate the abnormal impulsivity and mood observed in marijuana users. To address the question whether impulsivity as a trait precedes cannabis consumption or whether cannabis aggravates impulsivity and discontinuation of usage more longitudinal study designs are warranted.

Endocannabinoid signalling and the deteriorating brain

Ageing is characterized by the progressive impairment of physiological functions and increased risk of developing debilitating disorders, including chronic inflammation and neurodegenerative diseases. These disorders have common molecular mechanisms that can be targeted therapeutically. In the wake of the approval of the first cannabinoid-based drug for the symptomatic treatment of multiple sclerosis, we examine how endocannabinoid (eCB) signalling controls--and is affected by--normal ageing and neuroinflammatory and neurodegenerative disorders. We propose a conceptual framework linking eCB signalling to the control of the cellular and molecular hallmarks of these processes, and categorize the key components of endocannabinoid signalling that may serve as targets for novel therapeutics.

Cannabis and adolescent brain development

Heavy cannabis use has been frequently associated with increased rates of mental illness and cognitive impairment, particularly amongst adolescent users. However, the neurobiological processes that underlie these associations are still not well understood. In this review, we discuss the findings of studies examining the acute and chronic effects of cannabis use on the brain, with a particular focus on the impact of commencing use during adolescence. Accumulating evidence from both animal and human studies suggests that regular heavy use during this period is associated with more severe and persistent negative outcomes than use during adulthood, suggesting that the adolescent brain may be particularly vulnerable to the effects of cannabis exposure. As the endocannabinoid system plays an important role in brain development, it is plausible that prolonged use during adolescence results in a disruption in the normative neuromaturational processes that occur during this period. We identify synaptic pruning and white matter development as two processes that may be adversely impacted by cannabis exposure during adolescence. Potentially, alterations in these processes may underlie the cognitive and emotional deficits that have been associated with regular use commencing during adolescence.

The Cannabis Pathway to Non-Affective Psychosis may Reflect Less Neurobiological Vulnerability

There is a high prevalence of cannabis use reported in non-affective psychosis. Early prospective longitudinal studies conclude that cannabis use is a risk factor for psychosis, and neurochemical studies on cannabis have suggested potential mechanisms for this effect. Recent advances in the field of neuroscience and genetics may have important implications for our understanding of this relationship. Importantly, we need to better understand the vulnerability × cannabis interaction to shed light on the mediators of cannabis as a risk factor for psychosis. Thus, the present study reviews recent literature on several variables relevant for understanding the relationship between cannabis and psychosis, including age of onset, cognition, brain functioning, family history, genetics, and neurological soft signs (NSS) in non-affective psychosis. Compared with non-using non-affective psychosis, the present review shows that there seem to be fewer stable cognitive deficits in patients with cannabis use and psychosis, in addition to fewer NSS and possibly more normalized brain functioning, indicating less neurobiological vulnerability for psychosis. There are, however, some familiar and genetic vulnerabilities present in the cannabis psychosis group, which may influence the cannabis pathway to psychosis by increasing sensitivity to cannabis. Furthermore, an earlier age of onset suggests a different pathway to psychosis in the cannabis-using patients. Two alternative vulnerability models are presented to integrate these seemingly paradoxical findings.

Structural brain differences in alcohol-dependent individuals with and without comorbid substance dependence

BACKGROUND

Over 50% of individuals with alcohol use disorders (AUD) also use other substances; brain structural abnormalities observed in alcohol dependent individuals may not be entirely related to alcohol consumption. This MRI study assessed differences in brain regional tissue volumes between short-term abstinent alcohol dependent individuals without (ALC) and with current substance use dependence (polysubstance users, PSU).

METHODS

Nineteen, one-month-abstinent PSU and 40 ALC as well as 27 light-drinkers (LD) were studied on a 1.5 T MR system. Whole brain T1-weighted images were segmented automatically into regional gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) volumes. MANOVA assessed group differences of intracranial volume-normalized tissue volumes of the frontal, parietal, occipital, and temporal lobes and regional subcortical GM volumes. The volumetric measures were correlated with neurocognitive measures to assess their functional relevance.

RESULTS

Despite similar lifetime drinking and smoking histories, PSU had significantly larger normalized WM volumes than ALC in all lobes. PSU also had larger frontal and parietal WM volumes than LD, but smaller temporal GM volumes and smaller lenticular and thalamic nuclei than LD. ALC had smaller frontal, parietal, and temporal GM, thalamic GM and cerebellar volumes than LD. ALC had more sulcal CSF volumes than both PSU and LD.

CONCLUSION

One-month-abstinent ALC and PSU exhibited different patterns of gross brain structural abnormalities. The larger lobar WM volumes in PSU in the absence of widespread GM volume loss contrast with widespread GM atrophy in ALC. These structural differences may demand different treatment approaches to mitigate specific functionally relevant brain abnormalities.

Modulation of brain structure by catechol-O-methyltransferase Val(158) Met polymorphism in chronic cannabis users

Neuroimaging studies have shown that chronic consumption of cannabis may result in alterations in brain morphology. Recent work focusing on the relationship between brain structure and the catechol-O-methyltransferase (COMT) gene polymorphism suggests that functional COMT variants may affect brain volume in healthy individuals and in schizophrenia patients. We measured the influence of COMT genotype on the volume of four key regions: the prefrontal cortex, neostriatum (caudate-putamen), anterior cingulate cortex and hippocampus-amygdala complex, in chronic early-onset cannabis users and healthy control subjects. We selected 29 chronic cannabis users who began using cannabis before 16 years of age and matched them to 28 healthy volunteers in terms of age, educational level and IQ. Participants were male, Caucasians aged between 18 and 30 years. All were assessed by a structured psychiatric interview (PRISM) to exclude any lifetime Axis-I disorder according to Diagnostic and Statistical Manual for Mental Disorders-Fourth Edition. COMT genotyping was performed and structural magnetic resonance imaging data was analyzed by voxel-based morphometry. The results showed that the COMT polymorphism influenced the volume of the bilateral ventral caudate nucleus in both groups, but in an opposite direction: more copies of val allele led to lesser volume in chronic cannabis users and more volume in controls. The opposite pattern was found in left amygdala. There were no effects of COMT genotype on volumes of the whole brain or the other selected regions. Our findings support recent reports of neuroanatomical changes associated with cannabis use and, for the first time, reveal that these changes may be influenced by the COMT genotype.

Δ9-tetrahydrocannabinol prevents methamphetamine-induced neurotoxicity

Methamphetamine (METH) is a potent psychostimulant with neurotoxic properties. Heavy use increases the activation of neuronal nitric oxide synthase (nNOS), production of peroxynitrites, microglia stimulation, and induces hyperthermia and anorectic effects. Most METH recreational users also consume cannabis. Preclinical studies have shown that natural (Δ9-tetrahydrocannabinol, Δ9-THC) and synthetic cannabinoid CB1 and CB2 receptor agonists exert neuroprotective effects on different models of cerebral damage. Here, we investigated the neuroprotective effect of Δ9-THC on METH-induced neurotoxicity by examining its ability to reduce astrocyte activation and nNOS overexpression in selected brain areas. Rats exposed to a METH neurotoxic regimen (4×10 mg/kg, 2 hours apart) were pre- or post-treated with Δ9-THC (1 or 3 mg/kg) and sacrificed 3 days after the last METH administration. Semi-quantitative immunohistochemistry was performed using antibodies against nNOS and Glial Fibrillary Acidic Protein (GFAP). Results showed that, as compared to corresponding controls (i) METH-induced nNOS overexpression in the caudate-putamen (CPu) was significantly attenuated by pre- and post-treatment with both doses of Δ9-THC (−19% and −28% for 1 mg/kg pre- and post-treated animals; −25% and −21% for 3 mg/kg pre- and post-treated animals); (ii) METH-induced GFAP-immunoreactivity (IR) was significantly reduced in the CPu by post-treatment with 1 mg/kg Δ9-THC1 (−50%) and by pre-treatment with 3 mg/kg Δ9-THC (−53%); (iii) METH-induced GFAP-IR was significantly decreased in the prefrontal cortex (PFC) by pre- and post-treatment with both doses of Δ9-THC (−34% and −47% for 1 mg/kg pre- and post-treated animals; −37% and −29% for 3 mg/kg pre- and post-treated animals). The cannabinoid CB1 receptor antagonist SR141716A attenuated METH-induced nNOS overexpression in the CPu, but failed to counteract the Δ9-THC-mediated reduction of METH-induced GFAP-IR both in the PFC and CPu. Our results indicate that Δ9-THC reduces METH-induced brain damage via inhibition of nNOS expression and astrocyte activation through CB1-dependent and independent mechanisms, respectively.

The cerebellum and addiction: insights gained from neuroimaging research

Although cerebellar alterations have been consistently noted in the addiction literature, the pathophysiology of this link remains unclear. The cerebellum is commonly classified as a motor structure, but human functional neuroimaging along with clinical observations in cerebellar stroke patients and anatomical tract tracing in non-human primates suggests its involvement in cognitive and affective processing. A comprehensive literature search on the role of the cerebellum in addiction was performed. This review article (1) considers the potential role of the cerebellum in addiction; (2) summarizes the cerebellar structural alterations linked to addiction; (3) presents the functional neuroimaging evidence linking the cerebellum with addiction; and (4) proposes a model for addiction that underscores the role of the cerebellum. The data implicate the cerebellum as an intermediary between motor and reward, motivation and cognitive control systems, as all are relevant etiologic factors in addiction. Furthermore, consideration of these findings could contribute to deeper and more sophisticated insights into normal reward and motivational function. The goal of this review is to spread awareness of cerebellar involvement in addictive processes, and to suggest a preliminary model for its potential role.

Chronic effects of cannabis use on the auditory mismatch negativity

BACKGROUND

Cannabis use is associated with the development of psychotic symptoms and increased risk for schizophrenia. The mismatch negativity (MMN) is a brain event-related potential marker of change detection thought to index glutamatergic N-methyl-D-aspartate receptor-mediated neurotransmission, which is known to be deficient in schizophrenia. This study examined auditory MMN in otherwise healthy chronic cannabis users compared with nonuser control subjects.

METHODS

Forty-two chronic cannabis users and 44 nonuser healthy control subjects completed a multi-feature MMN paradigm, which included duration, frequency, and intensity deviants (deviants 6%; standards 82%). The MMN was compared between users and control subjects as well as between long- and short-term users and age- and gender-matched control subjects. Associations between MMN, cannabis use measures, and symptoms were examined.

RESULTS

The MMN amplitude was significantly reduced to frequency but not duration or intensity deviants in overall cannabis users relative to control subjects. Frequency MMN was similarly attenuated in short- and long-term users relative to control subjects. Long-term users also exhibited reduced duration MMN relative to control subjects and short-term users and this was correlated with increased duration of exposure to cannabis and increased psychotic-like experiences during intoxication. In short-term users, a younger age of onset of regular cannabis use and greater frequency of use were associated with greater psychotic-like experiences and symptomatic distress.

CONCLUSIONS

These results suggest impaired sensory memory that might reflect N-methyl-D-aspartate receptor dysfunction in chronic cannabis users. The pattern of MMN alterations in cannabis users differed from that typically observed in patients with schizophrenia, indicating overlapping but distinct underlying pathology.

Epidemiological, neurobiological, and genetic clues to the mechanisms linking cannabis use to risk for nonaffective psychosis

Epidemiological studies have shown that the association between cannabis and psychosis is robust and consistent across different samples, with compelling evidence for a dose-response relationship. Because longitudinal work indicates that cannabis use precedes psychotic symptoms, it seems reasonable to assume a causal relationship. However, more work is needed to address the possibility of gene-environment correlation (for example, genetic risk for psychosis causing onset of cannabis use). Moreover, knowledge about underlying biological mechanisms linking cannabis use and psychosis is still relatively limited. In order to understand how cannabis use may lead to an increased risk for psychosis, in the present article we (a) review the epidemiological, neurobiological, and genetic evidence linking cannabinoids and psychosis, (b) assess the quality of the evidence, and finally (c) try to integrate the most robust findings into a neurodevelopmental model of cannabis-induced psychosis and identify the gaps in knowledge that are in need of further investigation.

Neuropathology of substance use disorders

Addictions to licit and illicit drugs are chronic relapsing brain disorders that affect circuits that regulate reward, motivation, memory, and decision-making. Drug-induced pathological changes in these brain regions are associated with characteristic enduring behaviors that continue despite adverse biopsychosocial consequences. Repeated exposure to these substances leads to egocentric behaviors that focus on obtaining the drug by any means and on taking the drug under adverse psychosocial and medical conditions. Addiction also includes craving for the substances and, in some cases, involvement in risky behaviors that can cause death. These patterns of behaviors are associated with specific cognitive disturbances and neuroimaging evidence for brain dysfunctions in a diverse population of drug addicts. Postmortem studies have also revealed significant biochemical and/or structural abnormalities in some addicted individuals. The present review provides a summary of the evidence that has accumulated over the past few years to implicate brain dysfunctions in the varied manifestations of drug addiction. We thus review data on cerebrovascular alterations, brain structural abnormalities, and postmortem studies of patients who abuse cannabis, cocaine, amphetamines, heroin, and "bath salts". We also discuss potential molecular, biochemical, and cellular bases for the varied clinical presentations of these patients. Elucidation of the biological bases of addiction will help to develop better therapeutic approaches to these patient populations.

Mismatch negativity: translating the potential

The mismatch negativity (MMN) component of the auditory event-related potential has become a valuable tool in cognitive neuroscience. Its reduced size in persons with schizophrenia is of unknown origin but theories proposed include links to problems in experience-dependent plasticity reliant on N-methyl-d-aspartate glutamate receptors. In this review we address the utility of this tool in revealing the nature and time course of problems in perceptual inference in this illness together with its potential for use in translational research testing animal models of schizophrenia-related phenotypes. Specifically, we review the reasons for interest in MMN in schizophrenia, issues pertaining to the measurement of MMN, its use as a vulnerability index for the development of schizophrenia, the pharmacological sensitivity of MMN and the progress in developing animal models of MMN. Within this process we highlight the challenges posed by knowledge gaps pertaining to the tool and the pharmacology of the underlying system.

Cannabis use and brain structural alterations of the cingulate cortex in early psychosis

As cannabis use is more frequent in patients with psychosis than in the general population and is known to be a risk factor for psychosis, the question arises whether cannabis contributes to recently detected brain volume reductions in schizophrenic psychoses. This study is the first to investigate how cannabis use is related to the cingulum volume, a brain region involved in the pathogenesis of schizophrenia, in a sample of both at-risk mental state (ARMS) and first episode psychosis (FEP) subjects. A cross-sectional magnetic resonance imaging (MRI) study of manually traced cingulum in 23 FEP and 37 ARMS subjects was performed. Cannabis use was assessed with the Basel Interview for Psychosis. By using repeated measures analyses of covariance, we investigated whether current cannabis use is associated with the cingulum volume, correcting for age, gender, alcohol consumption, whole brain volume and antipsychotic medication. There was a significant three-way interaction between region (anterior/posterior cingulum), hemisphere (left/right cingulum) and cannabis use (yes/no). Post-hoc analyses revealed that this was due to a significant negative effect of cannabis use on the volume of the posterior cingulum which was independent of the hemisphere and diagnostic group and all other covariates we controlled for. In the anterior cingulum, we found a significant negative effect only for the left hemisphere, which was again independent of the diagnostic group. Overall, we found negative associations of current cannabis use with grey matter volume of the cingulate cortex, a region rich in cannabinoid CB1 receptors. As this finding has not been consistently found in healthy controls, it might suggest that both ARMS and FEP subjects are particularly sensitive to exogenous activation of these receptors.