Background The widespread use of cannabis, the increasing legalization of “medical” cannabis, the increasing potency of cannabis and the growing recreational use of synthetic cannabinoid 1 receptor (CB1R) full agonists underscores the importance of elucidating the effects of cannabinoids on the CB1R system. Exposure to cannabinoids is known to result in CB1R downregulation. However, the precise time course of changes in CB1R availability in cannabis dependent subjects (CDs) following short and intermediate term abstinence has not been determined. Methods Using High Resolution Research Tomography (HRRT) and [11C]OMAR, CB1R availability as indexed by the volume of distribution (VT) [11C]OMAR was measured in male CDs (n=11) and matched healthy controls (HCs) (n=19). CDs were scanned at baseline (while they were neither intoxicated nor in withdrawal), and after 2 days and 28 days of monitored abstinence. HCs were scanned at baseline and a subset (n=4) was rescanned 28 days later. Results Compared to HCs, [11C]OMAR VT was 15% lower in CDs (effect size Cohen’s d=−1.11) at baseline in almost all brain regions. However, these group differences in CB1R availability were no longer evident after just 2 days of monitored abstinence from cannabis. There was a robust negative correlation between CB1R availability and withdrawal symptoms after 2 days of abstinence. Finally, there were no significant group differences in CB1R availability in CDs after 28 days of abstinence. Conclusions Cannabis dependence is associated with CB1R downregulation, which begins to reverse surprisingly rapidly upon termination of cannabis use and may continue to increase over time.

clinicaltrials.gov Identifier: NCT01421342.

High-resolution (11)C-PBR28 PET can visualize focal areas where microglial activation is known to be present and has good test-retest reproducibility in the human brain. (11)C-PBR28 PET is likely to be valuable for monitoring both MS disease evolution and response to therapeutic strategies that target microglial activation.

BACKGROUND Several lines of evidence suggest the presence of abnormalities in the endocannabinoid (eCB) system in schizophrenia (SCZ). However, there are limited in vivo measures of the eCB system in SCZ. METHODS Twenty five male SCZ subjects (SCZs), 18 antipsychotic treated [SCZ-MED] and 7 antipsychotic free [SCZ-UNMED]) were compared to 18 age- matched male healthy control subjects (HCs). Subjects underwent one Positron Emission Tomography (PET) scan each with the cannabinoid receptor-1 (CB1R) selective radiotracer [11C]OMAR on the High Resolution Research Tomography (HRRT) scanner. Regional volume of distribution (VT) values were determined using kinetic modeling of PET data as a measure of CB1R availability. Group differences in mean composite [11C]OMAR VT values were compared between SCZs and HCs. Exploratory comparisons of CB1R availability within 15 brain regions were also conducted. All analyses were covaried for age and body mass index. RESULTS SCZs showed significantly (p =0.02) lower composite [11C]OMAR VT relative to HCs (~12% difference, effect size d= 0.73). [11C]OMAR VT was significantly (all ps <0.05) lower in SCZs in the amygdala, caudate, posterior cingulate cortex, hippocampus, hypothalamus and insula. Composite [11C]OMAR VT was greater in HCs> SCZ-MED>SCZ-UNMED. Furthermore, composite [11C]OMAR VT was greater in HCs> SCZ smokers (n=11) > SCZ non-smokers (n=14). CONCLUSIONS CB1R availability is lower in males SCZs compared to HCs. Furthermore, antipsychotics and tobacco use may increase CB1R availability in this population. The findings of the study provide further evidence supporting the hypothesis that alterations in the eCB system might contribute to the pathophysiology of SCZ.