The absence of substance use was determined by self-report and confirmed by urine toxicology and breathalyzer test at screening, and on the days of MR and PET imaging. Participants were asked to abstain from food, nicotine, and caffeinated beverages after midnight on the day prior to the imaging study until after completion of the scan. Blood samples were collected at the time of tracer injection and processed immediately after collection in the laboratory, which is adjacent to the scan room and frozen at −80°Celsius until analyzed, as previously described.OMAR was prepared in high specific activity . The radio tracer was infused over 1 minute through the antecubital vein. The radioactivity concentration in blood from the radial artery was measured continuously using an automated system for the first 7 min after radio tracer administration and manually drawn and counted thereafter. Discrete samples were acquired at selected times and measured on a gamma counter to determine radioactivity concentration in whole blood and plasma. Five discrete blood samples were analyzed for the fraction of unchanged OMAR and its radio metabolites using a column-switching high pressure liquid chromatography method. Listmode emission data were collected for 120 minutes after radiotracer administration using the High Resolution Research Tomograph ,hydroponic stands a dedicated brain PET scanner with spatial resolution better than 3 mm. Head motion was measured using the Polaris Vicra optical tracking system and incorporated into PET image reconstruction with all corrections.

The PET images were registered to subject-specific T1-weighted magnetic resonance images acquired on a 3 Tesla Trio imaging system . Anatomical MR images were in turn nonlinearly registered to an MR template where regions of interest were defined. Regional time activity curves were extracted from the dynamic PET data and analyzed using the multi-linear analysis method with metabolite-corrected arterial input functions and cutoff time t*=30 minutes. The kinetic analysis yielded regional estimates of total volume of distribution , the equilibrium ratio of radioligand concentration in tissue relative to arterial plasm, which is directly proportional to CB1 receptor availability. Seventy-two participants were recruited into the study and 60 completed the protocol. Reasons for exclusion were previous medication exposure and medical reasons that would interfere with correct interpretation of the collected data . Table 1 shows demographic, trauma, and clinical characteristics of the HC, TC, and PTSD groups whose data were used for analyses.OMAR injection parameters, age, sex, education, nature of trauma histories, and body mass index did not differ among the groups; there was a greater proportion of white individuals in the HC than TC and PTSD groups. The PTSD group was significantly more likely than the HC and TC groups to currently smoke cigarettes, and to have a lifetime history of mood or anxiety disorder, and alcohol or drug abuse, but the groups did not differ with respect to lifetime and current alcohol use and nicotine dependence. The PTSD group scored higher on the MADRS and HAM-A relative to both control groups, and on the CAPS relative to the TC group.We found that PTSD is associated with a ubiquitously expressed large magnitude elevation in OMAR VT values, which quantitatively reflects CB1 receptor availability.

Notably, this elevation was found in an amygdala-hippocampal-cortico-striatal neural circuit implicated in PTSD, as well as in brain regions outside this circuit. These results suggest greater brain-wide CB1 receptor availability in individuals with PTSD relative to control participants with and without histories of trauma exposure. Reduced peripheral anandamide levels in PTSD complemented the brain OMAR VT results, suggesting that the elevated CB1 receptor availability in PTSD may result from a combination of both receptor up regulation and low receptor occupancy by anandamide. The lack of displacement of CB1 radioligands by agonists which has been attributed to a large receptor reserve suggests that increased OMAR VT values are explained to the most part by receptor up regulation in response to low anandamide levels rather than low receptor occupancy by anandamide. This idea is substantiated by data showing that CB1 receptor up-regulation in response to low stress-induced synaptic anandamide availability was prevented by enhanced anandamide signaling. OEA levels were higher in HC relative to TC and PTSD participants in the current study, but groups did not differ with respect to 2-AG and PEA levels. Taken together, these data suggest that abnormal CB1 receptor-mediated anandamide signaling is implicated in the etiology of PTSD. The sex-related results of the current study accord with animal data demonstrating sex differences in CB1 receptor regulation, with stress-related up-regulation of CB1 receptors observed predominantly in female animals. We also found abnormally low cortisol levels in trauma survivors, corroborating prior work. Another key contribution of the current study is the finding that collective consideration of all three of the biomarkers examined— OMAR VT, anandamide, and cortisol—was highly accurate in classifying PTSD, with nearly 85% of PTSD cases correctly classified and overall classification accuracy approaching 90%.

Results of this study advance the extant literature in three important ways: they contribute to extant knowledge regarding the etiology of PTSD; they identify candidate biomarkers that may be used to support clinical decision-making regarding diagnostic classification of PTSD; and they provide a promising neurobiological rationale to develop novel, evidence-based pharmacotherapies for PTSD.Our results of reduced peripheral anandamide levels together with a compensatory up regulation of CB1 receptors in PTSD suggest lower anandamide tone in PTSD. Notably, elevated rates of cannabis abuse/dependence among individuals with PTSD have been reported. Such findings substantiate, at least in part, emerging evidence that synthetic cannabinoid receptor agonists50 or plant-derived cannabinoids such as marijuana51 may possess some benefits in individuals with PTSD by helping relieve haunting nightmares and other symptoms of PTSD. However, such data do not allow the conclusion that self medication with cannabis with its primary psychoactive constituent tetrahydrocannabinol should be recommended for the treatment of PTSD, as direct activation of CB1 receptors with plant-derived cannabinoids over an extended period of time leads to down-regulation of CB1 receptors, which may in turn result in a depression-like phenotype in certain individuals and increase risk of addiction. Another important finding in this study is the sex differences in anandamide levels and OMAR VT values in both the HC and PTSD groups. Animal data showing higher CB1 receptor levels in male relative to female animals and receptor fluctuations during the estrous cycle together with changes in affinity of agonist binding highlight the importance of careful considerations of gender and menstrual cycle phase in assessments of CB1 receptor availability in imaging studies. In addition, we believe, that a conclusive interpretation of the CB1 receptor profile in males and females requires a broad and dynamic perspective rather than a single observation in a cross-sectional study with a single time point. Our results are largely in agreement with a previous study that used the CB1 PET tracer MK-9470 to investigate the effects of age and gender. That report found greater plasma parent fraction and higher normalized brain uptake in men,grow table which is consistent with our findings. However, because of the nearly irreversible uptake kinetics of the radio tracer and the lack of significant gender differences in the metabolite-corrected input function in the initial cohort that underwent arterial blood sampling, the MK-9470 study used brain SUV as the final outcome metric of tracer binding. We performed kinetic analysis of OMAR data using metabolite-corrected arterial input functions in all participants. This methodology provided estimates of VT, which – in contrast to SUV, which was greater in men than women – was reduced in men compared to women. Thus, our measurements are compatible with those of the previously reported MK-9470 data and the discrepant interpretations appear to be accounted for by different endpoints centered on our use of arterial input functions in kinetic analyses rather than the simplified outcome of normalized brain concentration.

If, as our results suggest, women show higher CB1 receptor availability than men already under basal, non-stress conditions, then they may be at increased risk for PTSD when exposed to trauma. This finding may thus provide a neurobiological explanation for why women are at greater risk for developing PTSD following exposure to various types of trauma than men even when sexual trauma—which is more common in women—is excluded. To date, drug development in PTSD has been opportunistic, building almost entirely on empirical observations with drugs approved for other indications. The data reported herein are the first of which we are aware of to demonstrate the critical role of CB1 receptors and endocannabinoids in the etiology of PTSD in humans. As such, they provide a foundation upon which to develop and validate informative biomarkers of PTSD vulnerability, as well as to guide the rational development of the next generation of evidence-based treatments for PTSD. Blocking anandamide deactivation or re-uptake, both of which will increase synaptic anandamide availability, may lead to a more circumscribed and beneficial spectrum of biological responses than those produced by direct CB1 receptor activation. This is of particular interest for the development of mechanism-based novel pharmacotherapies for PTSD, as emerging data have revealed that enhanced anandamide signaling can curb the effects of chronic stress, possibly by maintaining normal amygdala function via extinction-driven reductions in fear resulting in improved stress-reactivity in humans. Although researchers in sociology, cultural studies, and anthropology have attempted, for the last 20 years, to re-conceptualize ethnicity within post-modernist thought and debated the usefulness of such concepts as “new ethnicities,” researchers within the field of alcohol and drug use continue to collect data on ethnic groups on an annual basis using previously determined census formulated categories. Researchers use this data to track the extent to which ethnic groups consume drugs and alcohol, exhibit specific alcohol and drug using practices and develop substance use related problems. In so doing, particular ethnic minority or immigrant groups are identified as high risk for developing drug and alcohol problems. In order to monitor the extent to which such risk factors contribute to substance use problems, the continuing collection of data is seen as essential. However, the collection of this epidemiological data, at least within drug and alcohol research, seems to take place with little regard for either contemporary social science debates on ethnicity, or the contemporary on-going debates within social epidemiology on the usefulness of classifying people by race and ethnicity . While the conceptualization of ethnicity and race has evolved over time within the social sciences, “most scholars continue to depend on empirical results produced by scholars who have not seriously questioned racial statistics” . Consequently, much of the existing research in drug and alcohol research remains stuck in discussions about concepts long discarded in mainstream sociology or anthropology, yielding robust empirical data that is arguably based on questionable constructs . Given this background, the aim of this paper is to outline briefly how ethnicity has been operationalized historically and continues to be conceptualized in mainstream epidemiological research on ethnicity and substance use. We will then critically assess this current state of affairs, using recent theorizing within sociology, anthropology, and health studies. In the final section of the paper, we hope to build upon our ”cultural critique” of the field by suggesting a more critical approach to examining ethnicity in relation to drug and alcohol consumption. According to Kertzer & Arel , the development of the nation states in the 19th century went hand in hand with the development of national statistics gathering which was used as a way of categorizing populations and setting boundaries across pre-existing shifting identities. Nation states became more and more interested in representing their population along identity criteria, and the census then arose as the most visible means by which states could depict and even invent collective identities . In this way, previous ambiguous and context-dependent identities were, by the use of the census technology, ‘frozen’ and given political significance. “The use of identity categories in censuses was to create a particular vision of social reality. All people were assigned to a single category and hence conceptualized as sharing a common collective identity” , yet certain groups were assigned a subordinate position. In France, for example, the primary distinction was between those who were part of the nation and those who were foreigners, whereas British, American, and Australian census designers have long been interested in the country of origin of their residents.