Acute changes in cerebral blood flow after smoking marijuana

Task-independent acute effects of delta-9-tetrahydrocannabinol on human brain function and its relationship with cannabinoid receptor gene expression: A neuroimaging meta-regression analysis

The neurobiological mechanisms underlying the effects of delta-9-tetrahydrocannabinol (THC) remain unclear. Here, we examined the spatial acute effect of THC on human regional brain activation or blood flow (hereafter called 'activation signal') in a 'core' network of brain regions from 372 participants, tested using a within-subject repeated measures design under experimental conditions. We also investigated whether the neuromodulatory effects of THC are related to the local expression of the cannabinoid-type-1 (CB1R) and type-2 (CB2R) receptors. Finally, we investigated the dose-response relationship between THC and key brain substrates. These meta-analytic findings shed new light on the localisation of the effects of THC in the human brain, suggesting that THC has neuromodulatory effects in regions central to many cognitive tasks and processes, related to dose, with greater effects in regions with higher levels of CB1R expression.

Considerations for Cannabinoids in Perioperative Care by Anesthesiologists

Increased usage of recreational and medically indicated cannabinoid compounds has been an undeniable reality for anesthesiologists in recent years. These compounds’ complicated pharmacology, composition, and biological effects result in challenging issues for anesthesiologists during different phases of perioperative care. Here, we review the existing formulation of cannabinoids and their biological activity to put them into the context of the anesthesia plan execution. Perioperative considerations should include a way to gauge the patient’s intake of cannabinoids, the ability to gain consent properly, and vigilance to the increased risk of pulmonary and airway problems. Intraoperative management in individuals with cannabinoid use is complicated by the effects cannabinoids have on general anesthetics and depth of anesthesia monitoring while simultaneously increasing the potential occurrence of intraoperative hemodynamic instability. Postoperative planning should involve higher vigilance to the risk of postoperative strokes and acute coronary syndromes. However, most of the data are not up to date, rending definite conclusions on the importance of perioperative cannabinoid intake on anesthesia management difficult.

The Yin and Yang of Cannabis: A Systematic Review of Human Neuroimaging Evidence of the Differential Effects of Δ9-Tetrahydrocannabinol and Cannabidiol

Cannabidiol (CBD) and Δ9-tetrahydrocannabinol (THC) have been the most investigated cannabinoids at the human and preclinical levels, although the neurobiological mechanisms underlying their effects remain unclear. Human experimental evidence complemented by observational studies suggests that THC may have psychotogenic effects while CBD may have antipsychotic effects. However, whether their effects on brain function are consistent with their opposing behavioral effects remains unclear. To address this, here we synthesize neuroimaging evidence investigating the acute effects of THC and CBD on human brain function using a range of neuroimaging techniques, with an aim to identify the key brain substrates where THC and CBD have opposing effects. After a systematic search, a review of the available studies indicated marked heterogeneity. However, an overall pattern of opposite effect profiles of the two cannabinoids was evident with some degree of consistency, primarily attributed to the head-to-head challenge studies of THC and CBD. While head-to-head comparisons are relatively few, collectively the evidence suggests that opposite effects of THC and CBD may be present in the striatum, parahippocampus, anterior cingulate/medial prefrontal cortex, and amygdala, with opposite effects less consistently identified in other regions. Broadly, THC seems to increase brain activation and blood flow, whereas CBD seems to decrease brain activation and blood flow. Given the sparse evidence, there is a particular need to understand the mechanisms underlying their opposite behavioral effects because it may not only offer insights into the underlying pathophysiological mechanisms of psychotic disorders but also suggest potentially novel targets and biomarkers for drug discovery.

A systematic review of neuroimaging and acute cannabis exposure in age-of-risk for psychosis

Acute exposure to cannabis has been associated with an array of cognitive alterations, increased risk for neuropsychiatric illness, and other neuropsychiatric sequelae including the emergence of acute psychotic symptoms. However, the brain alterations associating cannabis use and these behavioral and clinical phenotypes remains disputed. To this end, neuroimaging can be a powerful technique to non-invasively study the impact of cannabis exposure on brain structure and function in both humans and animal models. While chronic exposure studies provide insight into how use may be related to long-term outcomes, acute exposure may reveal interesting information regarding the immediate impact of use and abuse on brain circuits. Understanding these alterations could reveal the connection with symptom dimensions in neuropsychiatric disorders and, more specifically with psychosis. The purpose of the present review is to: 1) provide an update on the findings of pharmacological neuroimaging studies examining the effects of administered cannabinoids and 2) focus the discussion on studies that examine the sensitive window for the emergence of psychosis. Current literature indicates that cannabis exposure has varied effects on the brain, with the principal compounds in cannabis (delta-9-tetrahydrocannabinol and cannabidiol) altering activity across different brain regions. Importantly, we also discovered critical gaps in the literature, particularly regarding sex-dependent responses and long-term effects of chronic exposure. Certain networks often characterized as dysregulated in psychosis, like the default mode network and limbic system, were also impacted by THC exposure, identifying areas of particular interest for future work investigating the potential relationship between the two.

Acute and chronic effects of Δ9-tetrahydrocannabinol (THC) on cerebral blood flow: A systematic review

Acute and chronic exposure to cannabis and its main psychoactive component, Δ⁹-tetrahydrocannabinol (THC), is associated with changes in brain function and cerebral blood flow (CBF). We therefore sought to systematically review the literature on the effects of THC on CBF following PRISMA guidelines. Studies assessing the acute and chronic effects of THC on CBF, perfusion and volume were searched in the PubMed database between January 1972 and June 2019. We included thirty-four studies, which altogether investigated 1259 humans and 28 animals. Acute and chronic THC exposure have contrasting and regionally specific effects on CBF. While acute THC causes an overall increase in CBF in the anterior cingulate cortex, frontal cortex and insula, in a dose-dependent manner, chronic cannabis use results in an overall reduction in CBF, especially in the prefrontal cortex, which may be reversed upon prolonged abstinence from the drug. Future studies should focus on standardised methodology and longitudinal assessment to strengthen our understanding of the region-specific effects of THC on CBF and its clinical and functional significance.

Delta-9-tetrahydrocannabinol intoxication is associated with increased prefrontal activation as assessed with functional near-infrared spectroscopy: A report of a potential biomarker of intoxication

The primary psychoactive compound in cannabis, Δ9-tetrahydrocannabinol (THC), binds to cannabinoid receptors (CB1) present in high concentrations in the prefrontal cortex (PFC). It is unknown whether the PFC hemodynamic response changes with THC intoxication. We conducted the first double-blind, placebo-controlled, cross-over study of the effect of THC intoxication on functional near infrared spectroscopy (fNIRS) measures of PFC activation. Fifty-four adult, regular (at least weekly) cannabis users received a single oral dose of synthetic THC (dronabinol; 5-50 mg, dose individually tailored to produce intoxication) and identical placebo on two visits at least one week apart. fNIRS recordings were obtained during a working memory task (N-Back) at three timepoints: before THC/placebo, at 100 min (when peak effects were expected), and at 200 min after THC/placebo administration. Functional data were collected using a continuous-wave NIRS device, with 8 sources and 7 detectors arrayed over the forehead, resulting in 20 channels covering PFC regions. Participants also completed frequent heart rate measures and subjective ratings of intoxication. Approximately half of participants reported significant intoxication. Intoxication ratings were not correlated with dose of THC. Increases in heart rate significantly correlated with intoxication ratings after THC dosing. Results indicated that 100 min after THC administration, oxygenated hemoglobin (HbO) response significantly increased from pre-dose HbO levels throughout the PFC in participants who reported significant intoxication. Changes in HbO response significantly correlated with self-reported intoxication at 100 min after THC administration. Among those who reported intoxication, HbO response decreased at 200 min after THC, when intoxication had largely resolved, compared to the peak THC time point. This study demonstrates that THC intoxication causes increased PFC activity, and fNIRS of the PFC can measure this effect. Increased neural activation in PFC represents a potential biomarker for cannabis intoxication.

The neuropsychopharmacology of cannabis: A review of human imaging studies

The laws governing cannabis are evolving worldwide and associated with changing patterns of use. The main psychoactive drug in cannabis is Δ⁹-tetrahydrocannabinol (THC), a partial agonist at the endocannabinoid CB₁ receptor. Acutely, cannabis and THC produce a range of effects on several neurocognitive and pharmacological systems. These include effects on executive, emotional, reward and memory processing via direct interactions with the endocannabinoid system and indirect effects on the glutamatergic, GABAergic and dopaminergic systems. Cannabidiol, a non-intoxicating cannabinoid found in some forms of cannabis, may offset some of these acute effects. Heavy repeated cannabis use, particularly during adolescence, has been associated with adverse effects on these systems, which increase the risk of mental illnesses including addiction and psychosis. Here, we provide a comprehensive state of the art review on the acute and chronic neuropsychopharmacology of cannabis by synthesizing the available neuroimaging research in humans. We describe the effects of drug exposure during development, implications for understanding psychosis and cannabis use disorder, and methodological considerations. Greater understanding of the precise mechanisms underlying the effects of cannabis may also give rise to new treatment targets.

Residual Effects of THC via Novel Measures of Brain Perfusion and Metabolism in a Large Group of Chronic Cannabis Users

Given the known vascular effects of cannabis, this study examined the neurophysiological factors that may affect studies of brain activity in cannabis users. We conducted a systematic evaluation in 72 h abstinent, chronic cannabis users (N=74) and nonusing controls (N=101) to determine the association between prolonged cannabis use and the following neurophysiological indicators: (1) global and regional resting cerebral blood flow (CBF), (2) oxygen extraction fraction (OEF), and (3) cerebral metabolic rate of oxygen (CMRO₂). We found that cannabis users had greater global OEF and CMRO₂ compared with nonusers. Regionally, we found higher CBF in the right pallidum/putamen of the cannabis users compared with nonusers. Global resting CBF and regional CBF of right superior frontal cortex correlated positively with creatinine-normalized Δ9-tetrahydrocannabinol (THC) levels. These findings demonstrate residual effects of cannabis use whereby global and regional brain metabolism are altered in those with prolonged cannabis exposure. These neurophysiological alterations should be considered in both research and clinical applications.

Using Functional Near-Infrared Spectroscopy to Measure Effects of Delta 9-Tetrahydrocannabinol on Prefrontal Activity and Working Memory in Cannabis Users

Intoxication from cannabis impairs cognitive performance, in part due to the effects of Δ9-tetrahydrocannabinol (THC, the primary psychoactive compound in cannabis) on prefrontal cortex (PFC) function. However, a relationship between impairment in cognitive functioning with THC administration and THC-induced change in hemodynamic response has not been demonstrated. We explored the feasibility of using functional near-infrared spectroscopy (fNIRS) to examine the functional changes of the human PFC associated with cannabis intoxication and cognitive impairment. Eighteen adult regular cannabis users (final sample, n = 13) performed a working memory task (n-back) during fNIRS recordings, before and after receiving a single dose of oral synthetic THC (dronabinol; 20–50 mg). Functional data were collected using a continuous-wave NIRS device, in which 8 Sources and 7 detectors were placed on the forehead, resulting in 20 channels covering PFC regions. Physiological changes and subjective intoxication measures were collected. We found a significant increase in the oxygenated hemoglobin (HbO) concentration after THC administration in several channels on the PFC during both the high working memory load (2-back) and the low working memory load (0-back) condition. The increased HbO response was accompanied by a trend toward an increased number of omission errors after THC administration. The current study suggests that cannabis intoxication is associated with increases in hemodynamic blood flow to the PFC, and that this increase can be detected with fNIRS.

A Structural Analysis of Attitudes toward Alcohol and Marijuana Use

Male and female undergraduates (N = 316) completed affective, cognitive, and global evaluations of alcohol and marijuana use. The discriminant validity of the attitude components was supported. As predicted, relationships between global attitude and the affective component varied across use experience groups; for both drugs, the affective component was more related to the global scale among the most experienced users. Attitude components predicted current marijuana use in a manner that was consistent with the analyses of attitude structure. However, the affective and cognitive attitude scales were relatively poor predictors of current alcohol use, suggesting that additional information may contribute to global attitude for alcohol use. Thus, similarities on attitude structure emerged across drugs, but the ability of the attitude components to predict use behavior differentiated the drug types.

Structural and functional imaging studies in chronic cannabis users: a systematic review of adolescent and adult findings

Background

The growing concern about cannabis use, the most commonly used illicit drug worldwide, has led to a significant increase in the number of human studies using neuroimaging techniques to determine the effect of cannabis on brain structure and function. We conducted a systematic review to assess the evidence of the impact of chronic cannabis use on brain structure and function in adults and adolescents.

Methods

Papers published until August 2012 were included from EMBASE, Medline, PubMed and LILACS databases following a comprehensive search strategy and pre-determined set of criteria for article selection. Only neuroimaging studies involving chronic cannabis users with a matched control group were considered.

Results

One hundred and forty-two studies were identified, of which 43 met the established criteria. Eight studies were in adolescent population. Neuroimaging studies provide evidence of morphological brain alterations in both population groups, particularly in the medial temporal and frontal cortices, as well as the cerebellum. These effects may be related to the amount of cannabis exposure. Functional neuroimaging studies suggest different patterns of resting global and brain activity during the performance of several cognitive tasks both in adolescents and adults, which may indicate compensatory effects in response to chronic cannabis exposure.

Limitations

However, the results pointed out methodological limitations of the work conducted to date and considerable heterogeneity in the findings.

Conclusion

Chronic cannabis use may alter brain structure and function in adult and adolescent population. Further studies should consider the use of convergent methodology, prospective large samples involving adolescent to adulthood subjects, and data-sharing initiatives.

Weed or wheel! FMRI, behavioural, and toxicological investigations of how cannabis smoking affects skills necessary for driving

Marijuana is the most widely used illicit drug, however its effects on cognitive functions underlying safe driving remain mostly unexplored. Our goal was to evaluate the impact of cannabis on the driving ability of occasional smokers, by investigating changes in the brain network involved in a tracking task. The subject characteristics, the percentage of Δ(9)-Tetrahydrocannabinol in the joint, and the inhaled dose were in accordance with real-life conditions. Thirty-one male volunteers were enrolled in this study that includes clinical and toxicological aspects together with functional magnetic resonance imaging of the brain and measurements of psychomotor skills. The fMRI paradigm was based on a visuo-motor tracking task, alternating active tracking blocks with passive tracking viewing and rest condition. We show that cannabis smoking, even at low Δ(9)-Tetrahydrocannabinol blood concentrations, decreases psychomotor skills and alters the activity of the brain networks involved in cognition. The relative decrease of Blood Oxygen Level Dependent response (BOLD) after cannabis smoking in the anterior insula, dorsomedial thalamus, and striatum compared to placebo smoking suggests an alteration of the network involved in saliency detection. In addition, the decrease of BOLD response in the right superior parietal cortex and in the dorsolateral prefrontal cortex indicates the involvement of the Control Executive network known to operate once the saliencies are identified. Furthermore, cannabis increases activity in the rostral anterior cingulate cortex and ventromedial prefrontal cortices, suggesting an increase in self-oriented mental activity. Subjects are more attracted by intrapersonal stimuli ("self") and fail to attend to task performance, leading to an insufficient allocation of task-oriented resources and to sub-optimal performance. These effects correlate with the subjective feeling of confusion rather than with the blood level of Δ(9)-Tetrahydrocannabinol. These findings bolster the zero-tolerance policy adopted in several countries that prohibits the presence of any amount of drugs in blood while driving.

Altered cerebral blood flow and neurocognitive correlates in adolescent cannabis users

RATIONALE

The effects of adolescent marijuana use on the developing brain remain unclear, despite its prevalence. Arterial spin labeling (ASL) is a noninvasive imaging technique that characterizes neurovascular status and cerebral blood flow (CBF), potentially revealing contributors to neuropathological alterations. No studies to date have looked at CBF in adolescent marijuana users.

OBJECTIVES

This study examined CBF in adolescent marijuana users and matched healthy controls at baseline and after 4 weeks of monitored abstinence.

METHODS

Heavy adolescent marijuana users (n = 23, >200 lifetime marijuana use days) and demographically matched controls (n = 23) with limited substance exposure underwent an ASL brain scan at an initial session and after 4 weeks of sequential urine toxicology to confirm abstinence.

RESULTS

Marijuana users showed reduced CBF in four cortical regions including the left superior and middle temporal gyri, left insula, left and right medial frontal gyrus, and left supramarginal gyrus at baseline; users showed increased CBF in the right precuneus at baseline, as compared to controls (corrected p values < 0.05). No between group differences were found at follow-up.

CONCLUSIONS

Marijuana use may influence CBF in otherwise healthy adolescents acutely; however, group differences were not observed after several weeks of abstinence. Neurovascular alterations may contribute to or underlie changes in brain activation, neuropsychological performance, and mood observed in young cannabis users with less than a month of abstinence.

Evidence for involvement of the insula in the psychotropic effects of THC in humans: a double-blind, randomized pharmacological MRI study

The main reason for recreational use of cannabis is the 'high', the primary psychotropic effect of Δ9-tetrahydrocannabinol (THC). This psychoactive compound of cannabis induces a range of subjective, physical and mental reactions. The effect on heart rate is pronounced and complicates bloodflow-based neuroimaging of psychotropic effects of THC. In this study we investigated the effects of THC on baseline brain perfusion and activity in association with the induction of 'feeling high'. Twenty-three subjects participated in a pharmacological MRI study, where we applied arterial spin labelling (ASL) to measure perfusion, and resting-state functional MRI to assess blood oxygen level-dependent signal fluctuation as a measure of baseline brain activity. Feeling high was assessed with a visual analogue scale and was compared to the imaging measures. THC increased perfusion in the anterior cingulate cortex, superior frontal cortex, and insula, and reduced perfusion in the post-central and occipital gyrus. Baseline brain activity was altered, indicated by increased amplitude of fluctuations in resting-state functional MRI signal after THC administration in the insula, substantia nigra and cerebellum. Perfusion changes in frontal cortex were negatively correlated with ratings of feeling high, suggesting an interaction between cognitive control and subjective effects of THC. In conclusion, an acute THC challenge altered baseline brain perfusion and activity, especially in frontal brain areas involved in cognitive and emotional processes, and the insula, associated with interoceptive awareness. These changes may represent the THC-induced neurophysiological correlates of feeling high. The alterations in baseline brain perfusion and activity also have relevance for studies on task-related effects of THC on brain function.

Neuroimaging in cannabis use: a systematic review of the literature

BACKGROUND

We conducted a systematic review to assess the evidence for specific effects of cannabis on brain structure and function. The review focuses on the cognitive changes associated with acute and chronic use of the drug.

METHOD

We reviewed literature reporting neuroimaging studies of chronic or acute cannabis use published up until January 2009. The search was conducted using Medline, EMBASE, LILACS and PsycLIT indexing services using the following key words: cannabis, marijuana, delta-9-tetrahydrocannabinol, THC, cannabidiol, CBD, neuroimaging, brain imaging, computerized tomography, CT, magnetic resonance, MRI, single photon emission tomography, SPECT, functional magnetic resonance, fMRI, positron emission tomography, PET, diffusion tensor MRI, DTI-MRI, MRS and spectroscopy.

RESULTS

Sixty-six studies were identified, of which 41 met the inclusion criteria. Thirty-three were functional (SPECT/PET/fMRI) and eight structural (volumetric/DTI) imaging studies. The high degree of heterogeneity across studies precluded a meta-analysis. The functional studies suggest that resting global and prefrontal blood flow are lower in cannabis users than in controls. The results from the activation studies using a cognitive task are inconsistent because of the heterogeneity of the methods used. Studies of acute administration of THC or marijuana report increased resting activity and activation of the frontal and anterior cingulate cortex during cognitive tasks. Only three of the structural imaging studies found differences between users and controls.

CONCLUSIONS

Functional neuroimaging studies suggest a modulation of global and prefrontal metabolism both during the resting state and after the administration of THC/marijuana cigarettes. Minimal evidence of major effects of cannabis on brain structure has been reported.

Biomarkers for the effects of cannabis and THC in healthy volunteers

An increasing number of novel therapeutic agents are targeted at cannabinoid receptors. Drug development programmes of new cannabinoid drugs may be facilitated by the identification of useful biomarkers. This systemic literature review aims to assess the usefulness of direct biomarkers for the effects of cannabis and tetrahydrocannabinol (THC) in healthy volunteers. One hundred and sixty-five useful articles were found that investigated the acute effects of cannabis or THC on the central nervous system (CNS) and heart rate in healthy volunteers. Three hundred and eighteen tests (or test variants) were grouped in test clusters and functional domains, to allow their evaluation as a useful biomarker and to study their dose-response effects. Cannabis/THC affected a wide range of CNS domains. In addition to heart rate, subjective effects were the most reliable biomarkers, showing significant responses to cannabis in almost all studies. Some CNS domains showed indications of depression at lower and stimulation at higher doses. Subjective effects and heart rate are currently the most reliable biomarkers to study the effect of cannabis. Cannabis affects most CNS domains, but too many different CNS tests are used to quantify the drug-response relationships reliably. Test standardization, particularly in motor and memory domains, may reveal additional biomarkers.

Perfusion magnetic resonance imaging in psychiatry

INTRODUCTION

Cerebral perfusion imaging using magnetic resonance imaging (MRI) is widely used in the research and clinical fields to assess the profound changes in blood flow related to ischemic events such as acute stroke, chronic steno-occlusive disease, vasospasm, and abnormal vessel formations from congenital conditions or tumoral neovascularity. With continuing improvements in the precision of MRI-based perfusion techniques, it is increasingly feasible to use this tool in the study of the subtle brain perfusion changes occurring in psychiatric illnesses. This article aims to review the existing literature on applications of perfusion MRI in psychiatric disorder and substance abuse research. The article also provides a brief introductory overview of dynamic susceptibility contrast MRI and arterial spin labeling techniques. An outlook of necessary steps to bring perfusion MRI into the realm of clinical psychiatry as a diagnostic tool is brought forth. Opportunities for research in unexplored disorders and with higher field strengths are briefly examined.

METHODS

PubMed, ISI Web of Knowledge & Scopus were used to search the literature and cross reference several neuropsychiatric disorders with a search term construct, including "magnetic resonance imaging," "dynamic susceptibility contrast," "arterial spin labeling," perfusion or "cerebral blood flow" or "cerebral blood volume" or "mean transit time." The list of disorders used in the search included schizophrenia, depression and bipolar disorder, dementia and Alzheimer's disease, Parkinson's disease, posttraumatic stress disorder, autism, Asperger disease, attention deficit, Tourette syndrome, obsessive-compulsive disorder, Huntington's disease, bulimia nervosa, anorexia nervosa, and substance abuse. For each disorder for which perfusion MRI studies were found, a brief overview of the disorder symptoms, treatment, prevalence, and existing models is provided, and previous findings from nuclear medicine-based perfusion imaging are overviewed. Findings of perfusion MRI studies are then summarized, and overlap of findings are discussed. Overarching conclusions are made, or an outlook for future work in the area is offered, where appropriate.

RESULTS

Despite the now fairly broad availability of perfusion MRI, only a limited number of studies were found using this technology. The search produced 13 studies of schizophrenia, 7 studies in major depression, 12 studies in Alzheimer's disease, and 2 studies in Parkinson's disease. Drug abuse and other disorders have mainly been studied with nuclear medicine-based perfusion imaging. The literature concerning the use of perfusion imaging in psychiatry has not been reviewed in the last 5 years or more. The use of MRI for perfusion measurements in psychiatry has not been reviewed in 10 years.

CONCLUSIONS

Although MRI-based perfusion imaging in psychiatry has mainly been used as a research tool, a path is progressively being cleared for its application in clinical diagnostic and treatment monitoring. The precision of perfusion MRI methods now rivals that of nuclear medicine-based perfusion imaging techniques. Because of their noninvasive nature, arterial spin labeling methods have gained popularity in studies of neuropsychiatric disorders such as schizophrenia, depression, Alzheimer's, and Parkinson's diseases. Perfusion imaging measurements have yet to be included within the diagnostic criteria of neuropsychiatric disorders despite having shown to have great discriminant power in specific disorders. As this young methodology continues to improve and research studies demonstrate the correlation of measured perfusion abnormalities to microcirculatory abnormalities and neuropsychiatric symptomatology, the idea of including such a test within diagnostic criteria for certain mental illnesses becomes increasingly plausible.

Differences in regional blood volume during a 28-day period of abstinence in chronic cannabis smokers

Cerebral blood volume (CBV) studies have provided important insight into the effects of illicit substances such as cannabis. The present study examined changes in regional blood volume in the frontal and temporal lobe, and the cerebellum during 28 days of supervised abstinence from cannabis. Dynamic susceptibility contrast MRI (DSCMRI) data were collected on 15 current, long-term cannabis users between 6 and 36 h after the subjects' last reported cannabis use (Day 0), and again after 7 and 28 days of abstinence. Resting state CBV images were also acquired on 17 healthy comparison subjects. The present findings demonstrate that at Day 7, cannabis users continued to display increased blood volumes in the right frontal region, the left and right temporal regions, and the cerebellum. However, after 28 days of abstinence, only the left temporal area and cerebellum showed significantly increased CBV values in cannabis users. These findings suggest that while CBV levels begin to normalize with continued abstinence from cannabis, specifically in frontal areas, other temporal and cerebellar brain regions show slower CBV decreases.

Acute and non-acute effects of cannabis on brain functioning and neuropsychological performance

Cannabis has an ancient history of human use and is currently one of the most commonly used drugs worldwide. Understanding its impact on neurobehavioral functioning is of significant public health concern. In recent decades, substantial progress has been made in understanding the impact of cannabis use on neurobehavioral functioning. This has been fueled, in part, by characterization of an endocannabinoid signaling system in the brain through which cannabis exerts its psychoactive effects. Acute intoxication with cannabis causes marked changes in subjective mental status, brain functioning, and neuropsychological performance. Some of these changes are consistently detected and well characterized, yet others are not. Changes in brain functioning and neuropsychological performance are also reported after abstinence, but appear to be mild, circumscribed, and transient. On the other hand, functional neuroimaging often reveals subtle differences in the brain functioning of abstinent cannabis users compared with controls. The persistence and clinical significance of these differences, however, remains to be determined. Neuropsychological deficits and differences in brain functioning are most consistently observed only among frequent, heavy users, who are those most likely addicted to cannabis. The dire impact of drug addiction on a person's life and everyday functioning suggests that the large number of individuals addicted to cannabis experience substantial negative effects from its use. This manuscript reviews the scientific literature on the aforementioned topics in detail, providing evidence for converging findings, and highlighting areas in need of further investigation.

Inhibition of 2-arachidonoylglycerol catabolism modulates vasoconstriction of rat middle cerebral artery by the thromboxane mimetic, U-46619

BACKGROUND AND PURPOSE

Cerebrovascular smooth muscle cells express the CB1 cannabinoid receptor and CB1 agonists produce vasodilatation of the middle cerebral artery (MCA). The thromboxane A2 mimetic, U-46619, increased the content of the endocannabinoid, 2-arachidonoylglycerol (2-AG) in the MCA and 2-AG moderated the vasoconstriction produced by U46619 in this tissue. The purposes of this study were to examine the extent to which 2-AG is catabolized by cerebral arteries and to determine whether blockade of 2-AG inactivation potentiates its feedback inhibition of U-44619-mediated vasoconstriction.

EXPERIMENTAL APPROACH

The diameters of isolated, perfused MCA from male rats were measured using videomicroscopy.

KEY RESULTS

Exogenous 2-AG produces a CB1 receptor-dependent and concentration-related increase in the diameter of MCA constricted with 5-HT. The E (max) for 2-AG dilation is increased 4-fold in the presence of the metabolic inhibitors 3-(decylthio)-1,1,1-trifluropropan-2-one (DETFP), URB754 and URB597. To examine the role of catabolism in the effects of endogenous 2-AG, vasoconstriction induced by U-46619 was studied. DETFP and URB754, but not the fatty acid amide hydrolase inhibitor, URB597, significantly increased the EC(50) for U-46619. These data support a physiological role for endocannabinoid feedback inhibition in the effects of U-46619 and indicate that endogenously produced 2-AG is also efficiently catabolized within the MCA.

CONCLUSIONS AND IMPLICATIONS

MCA express mechanisms for the efficient inactivation of 2-AG, providing further support for an endocannabinoid feedback mechanism that opposes thromboxane-mediated vasoconstriction. These data suggest that potentiation of endogenously produced 2-AG could be a novel therapeutic approach to the treatment of thrombotic stroke.

Cannabinoid modulation of electrically evoked pH and oxygen transients in the nucleus accumbens of awake rats

Cannabinoid receptors have been implicated in the regulation of blood flow in the cerebral vasculature. Because the nucleus accumbens (NAc) shows high levels of central cannabinoid receptor 1 (CB1) expression we examined the effects of cannabinoids on the local transient alkaline shifts and increases in extracellular oxygen induced by electrical stimulation of the medial forebrain bundle (MFB) in conscious animals. These changes result from increases in cerebral blood flow (CBF) and metabolism in the NAc that are evoked by the stimulation. Oxygen and pH changes were monitored using fast-scan cyclic voltammetry at carbon-fiber microelectrodes in the NAc of freely moving rats. Administration of the cannabinoid receptor agonist WIN55,212-2 potently inhibited extracellular oxygen and pH changes, an effect that was reversed and prevented by pre-treatment with the CB1 receptor antagonists SR141716A and AM251. The effects on pH following WIN55,212-2 were similar to those following nimodipine, a recognized vasodilator. When AM251 was injected alone, the amplitude of electrically evoked pH shifts was unaffected. Administration of AM404 and VDM11, endocannabinoid transport inhibitors, partially inhibited pH transients in a CB1 receptor-dependent manner. The present findings suggest that CB1 receptor activation modulates changes in two well-established indices of local blood flow and metabolism resulting from electrically evoked activation of ascending fibers. Although endogenous cannabinoid tone alone is not sufficient to modify these responses, uptake blockade demonstrates that the system has the potential to exert CB1-specific effects similar to those of full agonists.

Dronabinol reduces signs and symptoms of idiopathic intracranial hypertension: a case report

A case is presented in which a woman diagnosed with a longstanding history of idiopathic intracranial hypertension reported improvement of frontal headaches, photophobia, transient blindness, enlarged blind spots, and tinnitus after smoking marijuana. All these symptoms and signs were associated with increased intracranial pressure (220-425 mm of water). Treatment with dronabinol at a dose of 10 mg twice a day, then reduced to 5 mg twice a day, relieved all of her symptoms. Previously noted papilledema and enlargement of blind spots also resolved, and this, in the absence of psychoactive effect or weight gain.

Cannabinoids and prefrontal cortical function: Insights from preclinical studies

Marijuana use has been associated with disordered cognition across several domains influenced by the prefrontal cortex (PFC). Here, we review the contribution of preclinical research to understanding the effects of cannabinoids on cognitive ability, and the mechanisms by which cannabinoids may affect the neurochemical processes in the PFC that are associated with these impairments. In rodents, acute administration of cannabinoid agonists produces deficits in working memory, attentional function and reversal learning. These effects appear to be largely dependent on CB1 cannabinoid receptor activation. Preclinical studies also indicate that the endogenous cannabinoid system may tonically regulate some mnemonic processes. Effects of cannabinoids on cognition may be mediated via interaction with neurochemical processes in the PFC and hippocampus. In the PFC, cannabinoids may alter dopaminergic, cholinergic and serotonergic transmission. These mechanisms may underlie cognitive impairments observed following marijuana intake in humans, and may also be relevant to other disorders of cognition. Preclinical research will further enhance our understanding of the interactions between the cannabinoid system and cognitive functioning.

Recent cannabis abuse decreased stress-induced BOLD signals in the frontal and cingulate cortices of cocaine dependent individuals

Previous neuroimaging studies showed that use of marijuana can alter patterns of cortical activation during rest or a task challenge. We used functional magnetic resonance imaging to examine whether recent cannabis abuse contributed to stress-induced blood-oxygen-level-dependent (BOLD) contrast in a group of cocaine-dependent individuals. Emotional stress was induced using the script-guided imagery paradigm, in which subjects imagined being in a real-life stressful situation and, as a control, in a neutral situation, while BOLD signals of their brain were acquired with a 1.5 T scanner. Abstinent cocaine-dependent subjects with recent marijuana abuse (n=8) were compared with abstinent cocaine-dependent subjects who had not abused marijuana recently (n=18). The two groups were otherwise matched in their demographic characteristics and drug use history. All subjects were abstinent for at least 15 days and drug free as confirmed by urine drug screening before the imaging session. Recent cannabis abusers demonstrated hypo-activation in frontal cortical areas including the perigenual anterior cingulate during increased emotional stress. In contrast, at the same statistical threshold, no brain regions showed increased activation in recent cannabis abusers compared with non-abusers. The group difference in the perigenual anterior cingulate remained even when lifetime cocaine and alcohol consumption was accounted for in covariance analysis. These results provide evidence that recent cannabis abuse is associated with decreased activation in the frontal cortex during an emotional stress task. The results suggest an abnormal cognitive control mechanism during affective processing in association with heavy cannabis use.

Acute delta9-tetrahydrocannabinol-induced deficits in reversal learning: neural correlates of affective inflexibility

Despite concerns surrounding the possible adverse effects of marijuana on complex cognitive function, the processes contributing to the observed cognitive deficits are unclear, as are the causal relationships between these impairments and marijuana exposure. In particular, marijuana-related deficits in cognitive flexibility may affect the social functioning of the individual and may contribute to continued marijuana use. We therefore examined the ability of rats to perform affective and attentional shifts following acute administration of Delta(9)-tetrahydrocannabinol (THC), the primary psychoactive marijuana constituent. Administration of 1 mg/kg THC produced marked impairments in the ability to reverse previously relevant associations between stimulus features and reward presentation, while the ability to transfer attentional set between dimensional stimulus properties was unaffected. Concurrent in situ hybridization analysis of regional c-fos and ngfi-b expression highlighted areas of the prefrontal cortex and striatum that were recruited in response to both THC administration and task performance. Furthermore, the alterations in mRNA expression in the orbitofrontal cortex and striatum were associated with the ability to perform the reversal discriminations. These findings suggest that marijuana use may produce inelasticity in updating affective associations between stimuli and reinforcement value, and that this effect may arise through dysregulation of orbitofrontal and striatal circuitry.

A role for cannabinoid CB1 receptors in mood and anxiety disorders

Mood and anxiety disorders, the most prevalent of the psychiatric disorders, cause immeasurable suffering worldwide. Despite impressive advances in pharmacological therapies, improvements in efficacy and side-effect profiles are needed. The present literature review examines the role that the endocannabinoid system may play in these disorders and the potential value of targeting this system in the search for novel and improved medications. Cannabis and its major psychoactive component (-)-trans-delta9-tetrahydrocannabinol, have profound effects on mood and can modulate anxiety and mood states. Cannabinoid receptors and other protein targets in the central nervous system (CNS) that modulate endocannabinoid function have been described. The discovery of selective modulators of some of these sites that increase or decrease endocannabinoid neurotransmission, primarily through the most prominent of the cannabinoid receptors in the CNS, the CB1 receptors, combined with transgenic mouse technology, has enabled detailed investigations into the role of these CNS sites in the regulation of mood and anxiety states. Although data point to the involvement of the endocannabinoid system in anxiety states, the pharmacological evidence seems contradictory: both anxiolytic- and anxiogenic-like effects have been reported with both endocannabinoid neurotransmission enhancers and blockers. Due to advances in the development of selective compounds directed at the CB1 receptors, significant progress has been made on this target. Recent biochemical and behavioural findings have demonstrated that blockade of CB1 receptors engenders antidepressant-like neurochemical changes (increases in extracellular levels of monoamines in cortical but not subcortical brain regions) and behavioural effects consistent with antidepressant/antistress activity in rodents.

[Brain effects of cannabis--neuroimaging findings]

Cannabis is the most widely used illicit drug. Despite this, only a small number of studies have investigated the long-term neurotoxic consequences of cannabis use. Structural and functional neuroimaging techniques are powerful research tools to investigate possible cannabis-induced pathophysiological changes. A computer literature review was conducted in the MEDLINE and PsycLIT databases between 1966 and November of 2004 with the search terms 'cannabis', 'marijuana', 'neuroimaging', 'magnetic resonance', 'computed tomography', 'positron emission tomography', 'single photon emission computed tomography", 'SPET', 'MRI' and 'CT'. Structural neuroimaging studies have yielded conflicting results. Most studies report no evidence of cerebral atrophy or regional changes in tissue volumes, and one study suggested that long-term users who started regular use on early adolescence have cerebral atrophy as well as reduction in gray matter. However, several methodological shortcomings limit the interpretation of these results. Functional neuroimaging studies have reported increases in neural activity in regions that may be related with cannabis intoxication or mood-change effects (orbital and mesial frontal lobes, insula, and anterior cingulate) and decreases in activity of regions related with cognitive functions impaired during acute intoxication. The important question whether residual neurotoxic effects occur after prolonged and regular use of cannabis remains unclear, with no study addressing this question directly. Better designed neuroimaging studies, combined with cognitive evaluation, may be elucidative on this issue.

U-46619 but not serotonin increases endocannabinoid content in middle cerebral artery: evidence for functional relevance

Cerebral vascular smooth muscle cells express the CB(1) cannabinoid receptor, and CB(1) receptor agonists produce vasodilation of cerebral arteries. The purpose of this study was to determine whether vasoconstriction of rat middle cerebral artery (MCA) results in the local formation of endocannabinoids (eCBs), which, via activation of CB(1) receptors, oppose the vasoconstriction in a feedback manner. The thromboxane A(2) (TXA(2)) mimetic U-46619 significantly increased N-arachidonylethanolamine (AEA) and 2-arachidonylglycerol (2-AG) content of isolated MCA, whereas 5-hydroxytrypamine (5-HT) decreased AEA and 2-AG content. If eCBs play a feedback role in the regulation of MCA tone, then CB(1) receptor antagonists should enhance the constriction of MCA produced by U-46619 but not 5-HT. U-46619 caused concentration-dependent constrictions of endothelium-denuded MCA. Two CB(1) receptor antagonists SR-141716 and AM-251 decreased the EC(50) value for U-46619 to constrict endothelium-denuded MCA without affecting the maximal effect. A low concentration of CB(1) receptor agonist Win-55212-2 (30 nM) produced vasodilation of MCAs constricted with low but not saturating concentrations of U-46619. SR-141716 had no effect on the 5-HT concentration-contraction relationship. These data suggest that TXA(2) receptor activation increases MCA eCB content, which, via activation of CB(1) receptors, reduces the constriction produced by moderate concentrations of the TXA(2) agonist. Although 5-HT-induced vasoconstriction is reduced by exogenous CB(1) receptor agonist, activation of 5-HT receptors does not increase eCB content. These results suggest that MCA production of eCBs is not regulated by constriction per se but likely via a signaling pathway that is specific for TXA(2) receptors and not 5-HT receptors.

Cannabis use and cerebrovascular disease

BACKGROUND

Cannabis is the most commonly abused illicit drug and is often considered innocuous. However, cases of acute onset neurologic dysfunction occurring in relation to cannabis use have been described and corresponding cerebral imaging studies have documented focal ischemic changes and vessel abnormalities.

REVIEW SUMMARY

This article reviews all reported cases of presumed cannabis related cerebral ischemic events in the medical literature, as well as pertinent human and animal experimental studies on the cardiovascular and cerebrovascular effects of cannabis.

CONCLUSIONS

Cannabis use seems to have been causally related to several instances of cerebral ischemia and infarction. Proposed etiologic mechanisms have included cerebral vasospasm, cardioembolization, and systemic hypotension with impaired cerebral autoregulation, but most of the available data points to a vasospastic process. The exact relation of cannabis to cerebrovascular disease remains to be determined.

Postural syncope after marijuana: a transcranial Doppler study of the hemodynamics

Twenty-nine volunteers participated in a randomized, double-blind, placebo-controlled study. Cerebral blood velocity (CBV), pulse rate, blood pressure (BP), skin perfusion (SP) on forehead and plasma delta9 tetrahydrocannabinol (THC) levels were quantified during reclining and standing for 10 min before and after THC infusions and marijuana smoking. Both THC and marijuana induced postural dizziness, with 28% reporting severe symptoms. Intoxication and dizziness peaked immediately after drug. The severe dizziness group showed the most marked postural drop in CBV and BP and showed a drop in pulse rate after an initial increase during standing. Postural dizziness was unrelated to plasma levels of THC and other indices.

Acute marihuana (THC) exposure produces a "transient" topographic quantitative EEG profile identical to the "persistent" profile seen in chronic heavy users

In two published pilot studies and a controlled replication using screened normals, chronic marihuana (THC) use was associated with a unique topographic quantitative EEG profile, consisting of significant elevations of Absolute and Relative Power and Coherence of alpha activity over the bilateral frontal cortex as well as a significant decrease in alpha frequency. This report attempts to establish the causal influence of THC in the above findings by the transient production of this exact quantitative EEG profile in subjects who did not display it at the beginning. Using paced smoking of marihuana with high and low dose THC content and placebo marihuana in a counterbalanced design under double blind conditions, all four of the topographic features of chronic THC exposure were produced as transient effects by THC but not by placebo.

Time course of tetrahydrocannabinol-induced changes in regional cerebral blood flow measured with positron emission tomography

While several studies are available on the immediate effects of marijuana and its active ingredient tetrahydrocannabinol (THC) on regional cerebral blood flow (rCBF), we examined the effects of intravenous infusion of THC on rCBF and behavior over a 120-min. period using positron emission tomography. Indices of rCBF, intoxication and physiology were measured at baseline and 30, 60, 90 and 120 min. after a 20-min. intravenous infusion of 0.15 or 0.25 mg/min. of THC, or placebo given to 47 subjects. The rCBF remained increased up to 120 min. after the high-dose THC infusion. Significant increases were seen in global perfusion and in the frontal, insular and anterior cingulate regions. Changes were greater in the right hemisphere. After the high dose, cerebellar flow was increased at both 30 and 60 min. The anterioposterior ratio of cortical rCBF increased in both hemispheres, and remained significantly greater than in the placebo condition until 120 min. in the right hemisphere. Intoxication peaked at 30 min. and remained elevated at 120 min. THC had significant effects on global CBF and rCBF, and feeling intoxicated accounted for changes in rCBF better than plasma level of THC.

Cardiovascular system effects of marijuana

Marijuana and delta9-tetrahydrocannabinol (THC) increase heart rate, slightly increase supine blood pressure, and on occasion produce marked orthostatic hypotension. Cardiovascular effects in animals are different, with bradycardia and hypotension the most typical response. Cardiac output increases, and peripheral vascular resistance and maximum exercise performance decrease. Tolerance to most of the initial cardiovascular effects appears rapidly. With repeated exposure, supine blood pressure decreases slightly, orthostatic hypotension disappears, blood volume increases, heart rate slows, and circulatory responses to exercise and Valsalva maneuver are diminished, consistent with centrally mediated, reduced sympathetic, and enhanced parasympathetic activity. Receptor-mediated and probably nonneuronal sites of action account for cannabinoid effects. The endocannabinoid system appears important in the modulation of many vascular functions. Marijuana's cardiovascular effects are not associated with serious health problems for most young, healthy users, although occasional myocardial infarction, stroke, and other adverse cardiovascular events are reported. Marijuana smoking by people with cardiovascular disease poses health risks because of the consequences of the resulting increased cardiac work, increased catecholamine levels, carboxyhemoglobin, and postural hypotension.

Delta 9-tetrahydrocannabinol-induced alterations in limbic system glucose use in the rat

The effects of Delta9-tetrahydrocannabinol (THC) on neural activity in the rat were investigated using [14C]2-deoxyglucose autoradiography to measure local cerebral glucose use. Overall, THC reduced glucose use at 5 mg/kg and slightly increased it at 1 mg/kg. Significant reductions were seen at the higher dose in regions of the hippocampus and limbic system, and in structures associated with sensory and sensorimotor process ing, consistent with the effects of THC on memory, sensory perception and motor control. Glucose use was increased in the shell of the nucleus accumbens at 1 mg/kg but not reduced at 5 mg/kg. This may reflect increases in activity in mesolimbic reward pathways which at the higher dose are mitigated by reduced glutamatergic outflow from the hippocampus.

Neurobehavioural consequences of substance abuse and HIV infection

Although our understanding of how human immunodeficiency virus (HIV)-related neurobehavioural deficits develop is nascent and preliminary, some clues have emerged which may clarify lingering uncertainties. In particular, HIV seems to yield brain dysfunction by mediating pathological changes upon neuronal function. HIV also compromises immunological integrity, thereby resulting in secondary infections that may further increase brain dysfunction. Notably, many individuals with HIV tend to be current or past abusers of drugs, and, in some cases, their drug use may have actually presented a pathway for initial HIV infection. Similar to HIV, many drugs tend to yield pathological changes upon neuronal function. Further paralleling HIV, some drugs seem to compromise immune function, which in turn may yield secondary detrimental effects upon the brain. Yet, despite the relatively high comorbidity rates of HIV infection and substance abuse, few investigations have addressed the potential interaction between these two factors upon neurobehavioural status. Towards this end, the present paper reviews the existing literature concerning neuropsychological effects of HIV and substance use, and suggests potential mechanisms whereby substance use may potentiate and exacerbate the onset and severity of neurobehavioural abnormalities in HIV infection.

A literature review of the consequences of prenatal marihuana exposure. An emerging theme of a deficiency in aspects of executive function

In spite of marihuana being the most widely used illegal drug among women of reproductive age, there is a relative paucity of literature dealing with the neurobehavioral consequences in offspring--particularly the longer-term effects. However, there is a degree of consistency in the limited data, both across cross-sectional reports and longitudinally, where offspring have been followed for a number of years. Two cohort studies fall into the latter category; one involving a low-risk sample and, the other, a high-risk sample. Global IQ is not impacted by prenatal marihuana exposure but aspects of executive function (EF)--in particular, attentional behavior and visual analysis/hypothesis testing--appear to be negatively associated with in utero cannabis exposure in children beyond the toddler stage. This hypothesized influence of prenatal marihuana on EF is examined and discussed relative to effects (or lack of effects) across different ages in the offspring, cannabinoid receptors, and the extant general marihuana and prefrontal literature.

Regional cerebral blood flow and depersonalization after tetrahydrocannabinol administration

OBJECTIVE

The aim of this study was to examine the relationship between depersonalization induced by tetrahydrocannabinol (THC), and regional brain activation.

METHOD

Cerebral blood flow (CBF) was measured by means of positron emission tomography (PET) in 59 normal right-handed volunteers before and following intravenous infusions of THC.

RESULTS

After THC, CBF showed a global increase which was more marked in the right hemisphere, frontal lobes and anterior cingulate.

CONCLUSION

Regression analyses showed positive correlations between the right frontal and anterior cingulate and depersonalization.

Cannabinoid CB1 receptor of cat cerebral arterial muscle functions to inhibit L-type Ca2+ channel current

The CB1 subtype of the cannabinoid receptor is present on neurons in the brain and mediates the perceptual effects of Delta9-tetrahydrocannabinol and other cannabinoids. We found that cat cerebral arterial smooth muscle cells (VSMC) contain the protein for the CB1 receptor and express a cDNA that has >98% amino acid homology to the CB1 cDNA expressed in rat and human neurons. Activation of the CB1 cannabinoid receptor has been shown to decrease the opening of N-type voltage-gated Ca2+ channels in neurons through a pertussis toxin-sensitive GTP-binding protein. In the present study we tested the hypothesis that activation of the cannabinoid CB1 receptor in cerebral VSMC inhibits voltage-gated Ca2+ channels and results in cerebral vasodilation. The predominant Ca2+ current identified in cat cerebral VSMC is a voltage-gated, dihydropyridine-sensitive, L-type Ca2+ current. The cannabimimetic drug WIN-55,212-2 (10-100 nM) induced concentration-dependent inhibition of peak L-type Ca2+ current, which reached a maximum of 82 +/- 4% at 100 nM (n = 14). This effect was mimicked by the putative endogenous CB1-receptor agonist anandamide, which produced a concentration-related reduction of peak L-type Ca2+ current with a maximum inhibition (at 300 nM) of 39 +/- 4% (n = 12). The inhibitory effects of both ligands on peak L-type Ca2+ currents were abolished by pertussis toxin pretreatment and application of the CB1-receptor antagonist SR-141716A (100 nM, n = 5). Both WIN-55,212-2 and anandamide produced concentration-dependent relaxation of preconstricted cerebral arterial segments that was abolished by SR-141716A. These results indicate that the CB1 receptor is expressed in cat cerebral VSMC and that the cerebral vasculature is one of the targets for endogenous cannabinoids. These findings suggest that the CB1 receptor and its endogenous ligand may play a fundamental role in the regulation of cerebral arterial tone and reactivity by modulating the influx of Ca2+ through L-type Ca2+ channels.

Cerebellar activity and disturbed time sense after THC

Because marijuana continues to be the most commonly used illicit drug, its effects on the brain function are of major interest. We utilized positron emission tomography (PET) and magnetic resonance imaging (MRI) to study the effects of delta-9-tetrahydrocannabinol (THC) infusion on brain blood flow and its behavioral correlates in 46 volunteers. Consistent with previous reports, there was a significant increase in cortical and cerebellar blood flow following THC, but not all subjects showed this effect. Those who showed a decrease in cerebellar CBF also had a significant alteration in time sense. The relationship between decreased cerebellar flow and impaired time sense is of interest because the cerebellum has been linked to an internal timing system.

Differential effects on cognitive functioning in 9- to 12-year olds prenatally exposed to cigarettes and marihuana

Cognitive performance was examined in 131 9-12-year-old children for whom prenatal marihuana and cigarette exposure had been ascertained. The subjects, participants in an ongoing longitudinal study, were from a low-risk, predominantly middle class sample. The tasks included the WISC-III and a series of tests assessing aspects of cognition subsumed under the rubric of executive function. Consistent with results obtained at earlier ages, discriminant function analysis revealed a dose-dependent association, which remained after controlling for potential confounds (including secondhand smoke), between prenatal cigarette exposure and lower global intelligence scores with the verbal subtests of the WISC maximally discriminating among levels of in utero exposure. In contrast, prenatal marihuana exposure was not associated with global intelligence or the verbal subtests. Rather, this drug was negatively associated with the executive function tasks that require impulse control and visual analysis/hypothesis testing and with a number of WISC subtests requiring the same abilities. The interpretation of these results is discussed in terms of executive function and is related to earlier observations of this sample and to the extant prefrontal and general marihuana literature.

Marijuana intoxication and brain activation in marijuana smokers

OBJECTIVE AND METHOD

The acute effects of delta9 tetrahydrocannabinol (THC) on cerebral blood flow (CBF) were studied in human subjects. Regional CBF was measured with 15O-water and Positron Emission Tomography (PET) in 32 volunteers with a history of exposure to marijuana. Scans were performed before and after intravenous (I.V.) infusion of either of two doses of THC or a placebo, given under double blind conditions.

RESULTS

THC but not placebo increased CBF especially in the frontal regions bilaterally, insula and cingulate gyrus and sub-cortical regions with somewhat greater effects in the right hemisphere. While most regions showed significant change at 60 minutes for the lower dose group, the higher dose group had significant change at 30 and 60 minutes. There was a highly significant change in the anterior/posterior ratio for the two THC groups reflecting minimal change in occipital flow but significant increases in frontal flow. Self ratings of THC intoxication showed significant effects, and regression analysis indicated it correlated most markedly with the right frontal region.

CONCLUSION

Behavioral manifestations of marijuana intoxication may be associated with increased functional activity of the brain especially the frontal cortex, insula and cingulate gyrus.

Alzheimer's disease risk factors as related to cerebral blood flow

Inconsistencies within results of case-control studies on Alzheimer's disease risk factors led to a search of the literature for a potential cofactor. Reduced cerebral blood flow was selected and literature was surveyed for evidence of a cerebral blood flow linkage with the more than 40 putative risks. Alcohol abuse, depression, head trauma, underactivity, old age, sleep disturbance, glucose utilization, Down's syndrome, and Parkinson's disease are risk factors where an association with reduced cerebral blood flow is documented. Studies were cited showing that improved cerebral blood flow is associated with factors thought to be helpful in Alzheimer's disease, such as education or occupational attainment, exercise, headache, smoking, and arthritis/anti-inflammatory drugs to the extent that aspirin is used. Sugar consumption is identified as a potential risk factor with glucose management in Alzheimer's disease also shown to involve reduced cerebral blood flow. An hypothesis is developed showing how compromised regional cerebral blood flow could fit as a cofactor for genetic, autoimmune, and neurotoxic aspects of Alzheimer's disease.

Effects of marijuana on performance of a computerized cognitive-neuromotor test battery

To evaluate the sensitivity of a computerized cognitive-neuromotor test battery in assessing the effects of marijuana (delta-9-tetrahydrocannabinol [THC]), we conducted a study of 10 healthy male volunteers who were experienced marijuana smokers. After extensive training on the performance tasks, each subject was tested on three separate days after smoking a cigarette containing either 1.75% THC, 3.55% THC, or placebo according to a randomized double-blind repeated measures design. Testing was carried out before smoking and 30, 90, and 150 minutes after smoking the cigarette. Of the five tasks employed, the digit-symbol substitution test with memory and the reaction time task were the measures most sensitive to effects of marijuana. We examined the usefulness of the coefficient of variation and effect size as indices of sensitivity to be used across different types of tasks.