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Docosahexaenoic acid (DHA) shows anti-inflammatory/proresolution effects in the brain. Higher red blood cell (RBC) DHA in humans is associated with improved cognitive performance and a lower risk for suicide. Here, we hypothesized that binding to the 18 kDa translocator protein (TSPO), a proxy for microglia levels, will be higher in individuals with low DHA relative to high DHA levels. We also postulated that higher TSPO would predict poor cognitive performance and impaired stress resilience.RBC DHA screening was performed in 320 healthy males. [sup11/supC]PBR28 positron emission tomography was used to measure binding to TSPO in 38 and 32 males in the lowest and highest RBC DHA quartiles. Volumes of distribution expressed relative to total plasma ligand concentration (VsubT/sub) was derived using an arterial input function-based kinetic analysis in 14 brain regions.[sup11/supC]PBR28 VsubT/subwas significantly lower (by 12% and 20% in C/T and C/C rs6971 genotypes) in males with low RBC DHA than in males with high RBC DHA. Regional VsubT/subwas correlated positively and negatively with RBC DHA and serum triglycerides, respectively. No relationships between VsubT/suband cognitive performance or stress resilience measures were present.Contrary to our hypothesis, we found lower TSPO binding in low-DHA than in high-DHA subjects. It is unclear as to whether low TSPO binding reflects differences in microglia levels and/or triglyceride metabolism in this study. Future studies with specific targets are necessary to confirm the effect of DHA on microglia. These results underscore the need to consider lipid parameters as a factor when interpreting TSPO positron emission tomography clinical findings.

Background Positron emission tomography studies have demonstrated less dopamine D2/3 receptor availability and blunted psychostimulant-induced dopamine release in cocaine-dependent subjects (CDSs). No studies in CDSs have reported the in vivo status of D2/3 and dopamine release in the cortex. Basic and functional imaging studies suggest a role for prefrontal cortical dopaminergic abnormalities in impaired executive function and relapse in cocaine dependence. We used [11C]FLB 457 positron emission tomography and amphetamine to measure cortical D2/3 receptors and dopamine release in CDSs. Methods [11C]FLB 457 and positron emission tomography were used to measure D2/3 receptor binding potential in cortical regions of interest in recently abstinent CDSs (n = 24) and healthy control subjects (n = 36) both before and after 0.5 mg kg−1 of oral d-amphetamine. Binding potential relative to nondisplaceable uptake (BPND) and binding potential relative to total plasma concentration (BPP) were derived using an arterial input function-based kinetic analysis. Cortical dopamine release in regions of interest was measured as the change in BPND and BPP after amphetamine. Results Baseline D2/3 receptor availability (BPP and BPND) and amphetamine-induced dopamine release (ΔBPND and ΔBPP) were significantly lower in the cortical regions in CDSs compared with healthy control subjects. Fewer D2/3 receptors and less dopamine release in CDSs were not associated with performance on working memory and attention tasks. Conclusions The results of this study suggest that deficits in dopamine D2/3 transmission involve the cortex in cocaine dependence. Further studies to understand the clinical relevance of these findings are warranted.

OBJECTIVE: An imbalance between neuropeptides that promote stress and resilience, such as corticotrophin-releasing factor (CRF) and nociceptin, has been postulated to underlie relapse in addiction. The objective of this study was to develop a paradigm to image the in vivo interaction between stress-promoting neuropeptides and nociceptin receptors (NOP) in humans. METHODS: [(11)C]NOP-1A PET was used to measure the binding to NOP receptors at baseline (BASE) and following an intravenous hydrocortisone challenge (POST-CORT) in 19 healthy controls. Hydrocortisone was used as a challenge because in microdialysis studies it has been shown to increase CRF release in extrahypothalamic brain regions such as the amygdala. [(11)C]NOP-1A total distribution volume (V(T)) in eleven regions (ROIs) were measured using a two-tissue compartment kinetic analysis. The primary outcome measure was hydrocortisone-induced ΔV(T) calculated as (V(T POST-CORT) - V(T BASE)) / V(T BASE). RESULTS: Hydrocortisone led to an acute increase in plasma cortisol levels. Regional [(11)C]NOP-1A V(T) was on average 11 to 16% higher in the POST-CORT compared to BASE condition (linear mixed model, condition, p = 0.005; region, p < 0.001, condition*region, p < 0.001). Independent t-tests in all ROIs were statistically significant and survived multiple comparison correction. Hydrocortisone-induced ΔV(T) was significantly negatively correlated with baseline V(T) in several ROIs. CONCLUSIONS: Hydrocortisone administration increases NOP receptor availability. Increased NOP in response to elevated cortisol might suggest a compensatory mechanism in the brain to counteract CRF/stress. The [(11)C]NOP-1A and hydrocortisone imaging paradigm should allow for the examination of interactions between stress-promoting neuropeptides and NOP in addictive disorders. (In Vivo Imaging of Corticotropin-releasing Factor - Nociceptin Receptor Interactions, https://clinicaltrials.gov/ct2/show/NCT03302416 ClinicalTrials.gov Identifier: )

Positron emission tomography studies have demonstrated less dopamine D[Baseline DThe results of this study suggest that deficits in dopamine D

Background The neuropeptide transmitter nociceptin, which binds to the nociceptin/orphanin FQ peptide (NOP) receptor, is a core component of the brain's antistress system. Nociceptin exerts its antistress effect by counteracting the functions of corticotropin-releasing factor, the primary stress-mediating neuropeptide in the brain. Basic investigations support a role for medications that target nociceptin receptors in the treatment of alcohol use disorders. Thus, it is of high interest to measure the in vivo status of NOP receptors in individuals with alcohol use disorders. Methods Here, we used [11C]NOP-1A and positron emission tomography to measure the in vivo binding to NOP receptors in 15 alcohol-dependent humans as identified by DSM-IV and 15 healthy control subjects matched for age, sex, and smoking status. Alcohol-dependent individuals with no comorbid psychiatric, medical, or drug abuse disorders were scanned following 2 weeks of outpatient monitored abstinence (confirmed with three times per week urine alcohol metabolite testing). [11C]NOP-1A distribution volume in regions of interest (including the amygdala, hippocampus, and midbrain, striatal, and prefrontal cortical subdivisions) was measured with kinetic analysis using the arterial input function. Results Regional [11C]NOP-1A distribution volume in alcohol dependence was not significantly different compared with healthy control subjects. No relationship between [11C]NOP-1A distribution volume and other clinical measures (including duration and severity of alcohol abuse, craving, and anxiety or depressive symptoms) were significant after correction for the multiple hypotheses tested. Conclusions The results of this study do not support alterations in the binding to NOP receptors in alcohol dependence. However, this finding does not necessarily rule out alterations in nociceptin transmission in alcohol dependence.

Addiction is composed of three phases: intoxication, withdrawal, and craving. Negative reinforcement, strengthening a behaviour by removing an aversive stimulus, has been associated with the withdrawal phase. An imbalance of neurotransmitters within the brain's stress (nociceptin, neuropeptide Y) and anti-stress (CRF, norepinephrine, etc.) system is attributed to negatively reinforced compulsive behaviours associated with relapse. Similarly, post-traumatic stress disorder is characterized by an overactive stress system. In a PTSD mouse model, rodents exhibited impaired cued-fear memory consolidation when nociceptin transmission was blocked. Furthermore, a single-nucleotide polymorphism has been identified between women diagnosed with PTSD and the severity of PTSD symptoms, suggesting a genetic basis. Therefore, it is critical to understand the functions and interactions between the brain's stress and anti-stress neurotransmitters, specifically nociceptin. This paper will examine the hypothalamic-pituitary-adrenocortical axis, evaluate the functions of corticotropin-releasing-factor and nociceptin, discuss nociceptin's role as an anxiolytic or anxiogenic, and discuss PET-imaging studies-all of which targeted nociceptin receptors (NOP-R). Finally, the discussion of pharmacological interventions will be proposed as preventative or therapeutic treatments for those suffering from PTSD and substance-use disorders.

Nociceptin/orphanin FQ (N/OFQ) is an antistress neuropeptide transmitter in the brain that counteracts corticotropin-releasing factor (CRF)-mediated stress and anxiety symptoms during drug and alcohol withdrawal. It also inhibits the release of a wide array of neurotransmitters, including dopamine and glutamate, which allows for it to block the rewarding properties of cocaine. Chronic cocaine administration in rodents has been shown to decrease N/OFQ and increase nociceptive opioid peptide (NOP) receptors in the nucleus accumbens. No previous studies have reported on the in vivo status of NOP in chronic cocaine-abusing humans.[A significant increase in [Increased NOP in cocaine use disorder suggests an adaptive response to decreased N/OFQ, or increased CRF transmission, or both. Future studies should examine the interactions between CRF and NOP to elucidate their role in negative reinforcement and relapse. NOP agonist medications to enhance N/OFQ should be explored as a therapeutic to treat cocaine use disorder.

Objective:Nociceptin/orphanin FQ (N/OFQ) is an antistress neuropeptide transmitter in the brain that counteracts corticotropin-releasing factor (CRF)-mediated stress and anxiety symptoms during dru...

Background Posttraumatic stress disorder (PTSD) is a stress disorder that develops in only some individuals following a traumatic event. Data suggest that a substantial fraction of women recover after sexual violence. Thus, the investigation of stress and antistress neuropeptides in this sample has the potential to inform the neurochemistry of resilience following trauma. Nociceptin is an antistress neuropeptide in the brain that promotes resilience in animal models of PTSD. Methods [11C]NOP-1A positron emission tomography was used to measure the in vivo binding to nociceptin receptors in 18 college women who had experienced sexual violence irrespective of whether they met DSM-5 diagnostic criteria for PTSD. [11C]NOP-1A data from 18 healthy control subjects were also included to provide a contrast with the sexual violence group. [11C]NOP-1A total distribution volume (VT) in the regions of interest were measured with kinetic analysis using the arterial input function. The relationships between regional VT and Clinician-Administered PTSD Scale for DSM-5 total symptom and subscale severity were examined using correlational analyses. Results No differences in [11C]NOP-1A VT were noted between the sexual violence and control groups. VT in the midbrain and cerebellum were positively correlated with PTSD total symptom severity in the past month before positron emission tomography. Intrusion/re-experiencing and avoidance subscale symptoms drove this relationship. Stratification of subjects by a DSM-5 PTSD diagnosis and contrasting their VT with that in control subjects showed no group differences. Conclusions Decreased midbrain and cerebellum nociceptin receptors are associated with less severe PTSD symptoms. Medications that target nociceptin should be explored to prevent and treat PTSD.

Phosphodiesterase-10a (PDE10a) is located exclusively in medium spiny neurons (MSN). Rodent studies show an increase in striatal MSN spine density following exposure to cocaine. These increases in MSN spine density are suggested to underlie neurobiological changes which contribute to cocaine self-administration. No postmortem or imaging studies have confirmed this finding in humans. Here, we hypothesized an increase in the MSN marker PDE10a in subjects with cocaine use disorder ("cocaine users") compared to controls. PDE10a availability was measured with [11 C]IMA107 and positron emission tomography in 15 cocaine users and 15 controls matched for age, gender, and nicotine status. Cocaine users with no comorbid psychiatric, medical, or drug abuse disorders were scanned following two weeks of outpatient-monitored abstinence. [11 C]IMA107 binding potential relative to nondisplaceable uptake (BPND ) in the regions of interest was derived with the simplified reference tissue method. No significant effect of diagnosis on BPND was demonstrated using linear mixed modeling with [11 C]IMA107 BPND as the dependent variable and regions of interest as a repeated measure. There were no significant relationships between BPND and clinical rating scales. To the extent that PDE10a is a valid proxy for MSN spine density, these results do not support its increase in recently abstinent cocaine users.

Postmortem studies in schizophrenia reveal alterations in gene products that regulate the release and extracellular persistence of GABA. However, results of in vivo studies of schizophrenia measuring total tissue GABA with magnetic resonance spectroscopy (MRS) have been inconsistent. Neither the postmortem nor the MRS studies directly address the physiological properties of GABA neurotransmission. The present study addresses this question through an innovative positron emission tomography (PET) paradigm.The binding of [(11)C]flumazenil, a benzodiazepine-specific PET radiotracer, was measured before and after administration of tiagabine (0.2 mg/kg of body weight), a GABA membrane transporter (GAT1) blocker, in 17 off-medication patients with schizophrenia and 22 healthy comparison subjects. Increased extracellular GABA, through GAT1 blockade, enhances the affinity of GABAA receptors for benzodiazepine ligands, detected as an increase in [(11)C]flumazenil tissue distribution volume (VT).[(11)C]Flumazenil VT was significantly increased across all cortical brain regions in the healthy comparison group but not in the schizophrenia group. This lack of effect was most prominent in the antipsychotic-naive schizophrenia group. In this subgroup, [(11)C]flumazenil ΔVT in the medial temporal lobe was correlated with positive symptoms, and baseline [(11)C]flumazenil VT in the medial temporal lobe was negatively correlated with visual learning. In the healthy comparison group but not the schizophrenia group, [(11)C]flumazenil ΔVT was positively associated with gamma-band oscillation power.This study demonstrates, for the first time, an in vivo impairment in GABA transmission in schizophrenia, most prominent in antipsychotic-naive individuals. The impairment in GABA transmission appears to be linked to clinical symptoms, disturbances in cortical oscillations, and cognition.

Background Consistent with postmortem data, in a recent positron emission tomography study, we demonstrated less [ 11 C]-(+)-dihydrotetrabenazine ([ 11 C]DTBZ) binding to striatal vesicular monoamine transporter type 2 (VMAT2) in cocaine abusers compared with control subjects. A major limitation of these between-group comparison human studies is their inability to establish a causal relationship between cocaine abuse and lower VMAT2. Furthermore, studies in rodents that evaluated VMAT2 binding before and after cocaine self-administration do not support a reduction in VMAT2. Methods To clarify these discrepant VMAT2 findings and attribute VMAT2 reduction to cocaine abuse, we imaged four rhesus monkeys with [ 11 C]DTBZ positron emission tomography before and after 16 months of cocaine self-administration. [ 11 C]DTBZ binding potential in the striatum was derived using the simplified reference tissue method with the occipital cortex time activity curve as an input function. Results Chronic cocaine self-administration led to a significant (25.8 ± 7.8%) reduction in [ 11 C]DTBZ binding potential. Conclusions In contrast to the cocaine rodent investigations that do not support alterations in VMAT2, these results in nonhuman primates clearly demonstrated a reduction in VMAT2 binding following prolonged exposure to cocaine. Lower VMAT2 implies that fewer dopamine storage vesicles are available in the presynaptic terminals for release, a likely factor contributing to decreased dopamine transmission in cocaine dependence. Future studies should attempt to clarify the clinical significance of lower VMAT2 in cocaine abusers, for example, its relationship to relapse and vulnerability to mood disorders.

SEP-227162 [R(-)-O-desmethylvenlafaxine] is an enantiomer of the venlafaxine metabolite O-desmethylvenlafaxine (ODV, Pristiq™, Wyeth). This study compared the serotonin transporter (SERT) occupancy achieved by SEP-227162 and ODV, at daily doses of 25, 50, 100, and 150 mg using [11 C]DASB positron emission tomography (PET). Sixteen healthy male subjects participated in one of four dose groups (N = 4 per group) during which they were administered two doses of the study drug (SEP-227162 or ODV). For each study drug, total daily doses of 25, 50, 100, and150 mg were studied. Subjects underwent three PET scans with [11 C]DASB. A baseline, off-medication, scan was performed prior to dosing and a [11 C]DASB PET scan was performed after 72 hr at each dose level. [11 C]DASB binding potential (BPND ) was calculated using the simplified reference tissue method. SERT occupancy was calculated as the change in BPND (ΔBPND ) from baseline scan to the on-medication scan relative to the baseline BPND value. SEP-227162 and ODV significantly reduced regional distribution volumes and region BPND values in a dose-dependent manner. Across all doses ODV produced significantly greater SERT occupancy than SEP-227162 (ANOVA F = 21.8, df = 1,23, p < .001). The total daily dose required to provide 50% SERT occupancy was 24.8 mg for SEP-227162 and 14.4 mg for ODV. In vitro data suggests a ratio of 3.3:1 for binding at human SERT for SEP-227162 relative to ODV. Our study suggests a ratio of 1.7:1, highlighting the value of in vivo imaging in the drug development process.

Background Receptor imaging studies have reported increased amphetamine-induced dopamine release in subjects with schizophrenia (SCH) relative to healthy control subjects (HCs). A limitation of these studies, performed with D2/3 antagonist radiotracers, is the failure to provide information about D2/3 receptors configured in a state of high affinity for the agonists (i.e., D2/3 receptors coupled to G proteins [D2/3 HIGH]). The endogenous agonist dopamine binds with preference to D2/3 HIGH receptors relative to D2/3 LOW receptors, making it critical to understand the status of D2/3 HIGH receptors in SCH. Methods D2/3 agonist positron emission tomography radiotracer [11C]N-propyl-norapomorphine ([11C]NPA) binding potential (BPND) was measured in 14 off-medication subjects with SCH and 14 matched HCs at baseline and after the administration of 0.5 mg kg–1 oral D-amphetamine. The amphetamine-induced change in BPND (ΔBPND) was calculated as the difference between BPND in the postamphetamine condition and BPND in the baseline condition and was expressed as a percentage of BPND at baseline. Results A trend-level increase was observed in comparing baseline [11C]NPA BPND (repeated-measures analysis of variance, F1,26 = 3.34, p = .08) between the SCH and HC groups. Amphetamine administration significantly decreased BPND in all striatal regions across all subjects in both groups. No differences were observed in [11C]NPA ΔBPND (repeated-measures analysis of variance, F1,26 = 1.9, p = .18) between HCs and subjects with SCH. Amphetamine significantly increased positive symptoms in subjects with SCH (19.5 ± 5.3 vs. 23.7 ± 4.1, paired t test, p Conclusions This study provides in vivo indication of a role for postsynaptic factors in amphetamine-induced psychosis in SCH.

BACKGROUND: The neuropeptide transmitter nociceptin, which binds to the nociceptin/orphanin FQ peptide (NOP) receptor, is a core component of the brain's anti-stress system. Nociceptin exerts its anti-stress effect by counteracting the functions of corticotropin releasing factor, the primary stress-mediating neuropeptide in the brain. Basic investigations support a role for medications that target nociceptin receptors in the treatment of alcohol use disorders. Thus, it is of high interest to measure the in vivo status of NOP receptors in individuals with alcohol use disorders. METHODS: Here, we used [(11)C]NOP-1A and PET to measure the in vivo binding to NOP receptors in 15 DSM-IV alcohol-dependent humans and 15 healthy controls matched for age, gender, and smoking status. Alcohol-dependent individuals with no comorbid psychiatric, medical, or drug abuse disorders were scanned following two weeks of outpatient monitored abstinence (confirmed with 3×/week urine alcohol metabolite testing). [(11)C]NOP-1A distribution volume (V(T)) in regions of interest (including the amygdala, hippocampus, midbrain, striatal, and prefrontal cortical subdivisions) were measured with kinetic analysis using the arterial input function. RESULTS: Regional [(11)C]NOP-1A V(T) in alcohol-dependence was not significantly different compared to healthy controls. No relationship between [(11)C]NOP-1A V(T) and other clinical measures (including duration and severity of alcohol abuse, craving, anxiety or depressive symptoms) were significant after correction for the multiple hypotheses tested. CONCLUSIONS: The results of this study do not support alterations in the binding to NOP receptors in alcohol dependence. However, this finding does not necessarily rule out alterations in nociceptin transmission in alcohol dependence.

ONO-2952, a novel antagonist of translocator protein 18 kDa (TSPO), binds with high affinity to TSPO in rat brain and human tumor cell line membrane preparations. This study used the TSPO-specific PET radioligand [

Basic investigations link a Val158Met polymorphism (rs4680) in the catechol-O-methyltransferase (COMT) gene to not only its enzymatic activity, but also to its dopaminergic tone in the prefrontal cortex. Previous PET studies have documented the relationship between COMT Val158Met polymorphism and D1 and D2/3 receptor binding potential (BP), and interpreted them in terms of dopaminergic tone. The use of baseline dopamine D1 and D2/3 receptor binding potential (BPND) as a proxy for dopaminergic tone is problematic because they reflect both endogenous dopamine levels (a change in radiotracer's apparent affinity) and receptor density. In this analysis of 31 healthy controls genotyped for the Val158Met polymorphism (Val/Val, Val/Met, and Met/Met), we used amphetamine-induced displacement of [11C]FLB 457 as a direct measure of dopamine release. Our analysis failed to show a relationship between COMT genotype status and prefrontal cortical dopamine release. COMT genotype was also not predictive of baseline dopamine D2/3 receptor BPND.

Positron emission tomography (PET) studies performed with [(11) C]raclopride have consistently reported lower binding to D(2/3) receptors and lower amphetamine-induced dopamine (DA) release in cocaine abusers relative to healthy controls. A limitation of these studies that were performed with D(2/3) antagonist radiotracers such as [(11) C]raclopride is the failure to provide information that is specific to D(2/3) receptors configured in a state of high affinity for the agonists (i.e., D(2/3) receptors coupled to G-proteins, D(2/3 HIGH) ). As the endogenous agonist DA binds with preference to D(2/3 HIGH) relative to D(2/3 LOW) receptors (i.e., D(2/3) receptors uncoupled to G-proteins) it is critical to understand the in vivo status of D(2/3 HIGH) receptors in cocaine dependence. Thus, we measured the available fraction of D(2/3) (HIGH) receptors in 10 recently abstinent cocaine abusers (CD) and matched healthy controls (HC) with the D(2/3) antagonist and agonist PET radiotracers [(11) C]raclopride and [(11) C]NPA.[(11) C]raclopride and [(11) C]NPA binding potential (BP) (BP(ND) ) in the striatum were measured with kinetic analysis using the arterial input function. The available fraction of D(2/3 HIGH) receptors, i.e., % R(HIGH) available = D(2/3 HIGH) /(D(2/3 HIGH) + D(2/3 LOW) ) was then computed as the ratio of [(11) C]NPA BP(ND) /[(11) C]raclopride BP(ND) .No differences in striatal [(11) C]NPA BP(ND) (HC = 1.00 ± 0.17; CD = 0.97 ± 0.17, P = 0.67) or available % R(HIGH) (HC = 39% ± 5%; CD = 41% ± 5%, P = 0.50) was observed between cocaine abusers and matched controls.The results of this [(11) C]NPA PET study do not support alterations in D(2/3 HIGH) binding in the striatum in cocaine dependence.

Studies in nonhuman primates and humans have demonstrated that amphetamine-induced dopamine release in the cortex can be measured with [(11)C]FLB 457 and PET imaging. This technique has been successfully used in recent clinical studies to show decreased dopamine transmission in the prefrontal cortex in schizophrenia and alcohol dependence. Here, we present data from a cohort of twelve healthy controls in whom an oral amphetamine challenge (0.5 mg kg(−1)) did not lead to a significant reduction in [(11)C]FLB 457 BP(ND) (i.e., binding potential relative to non-displaceable uptake). Two factors that likely contributed to the inability to displace [(11)C]FLB 457 BP(ND) in this cohort relative to successful cohorts are: (1) the acquisition of the baseline and post-amphetamine scans on different days as opposed to the same day and (2) the initiation of the post-amphetamine [(11)C]FLB 457 scan at ~ 5 hours as opposed to ~ 3 hours following oral amphetamine. Furthermore, we show [(11)C]FLB 457 reproducibility data from a legacy dataset to support greater variability in cortical BP(ND) when the test and re-test scans are acquired on different days as compared to the same day. These results highlight the methodological challenges that continue to plague the field with respect to imaging dopamine release in the cortex.

ONO-2952, a novel antagonist of translocator protein 18 kDa (TSPO), binds with high affinity to TSPO in rat brain and human tumor cell line membrane preparations. This study used the TSPO-specific PET radioligand [11 C]PBR28 to confirm binding of ONO-2952 to brain TSPO in human subjects, and evaluate brain TSPO occupancy and its relationship with ONO-2952 plasma concentration. Sixteen healthy subjects received a single oral dose of 200, 60, 20, or 6 mg ONO-2952 (n = 4 per dose). Two PET scans with [11 C]PBR28 were conducted ≤7 days apart: at baseline and 24 h after ONO-2952 administration. [11 C]PBR28 regional distribution volume (VT ) was derived with kinetic modeling using the arterial input function and a two tissue compartment model. Nonspecific binding (VND ) was obtained on an individual basis for each subject using linear regression as the x-intercept of the Lassen plot. The binding potential relative to VND (BPND ) was derived as the difference between VT in the ROI (VT ROI) and VND , normalized to VND ; BPND = (VT ROI - VND )/VND . TSPO occupancy was calculated as the change in BPND (ΔBPND ) from individual's baseline scan to the on-medication scan to the baseline BPND value. TSPO occupancy by ONO-2952 was dose dependent between 20-200 mg, approaching saturation at 200 mg both in the whole brain and in 15 anatomic regions of interest (ROI). Estimated Ki values ranged from 24.1 to 72.2 nM. This open-label, single-center, single-dose study demonstrated engagement of ONO-2952 to brain TSPO. The relationship between pharmacokinetics and TSPO occupancy observed in this study support the hypothesis that ONO-2952 could potentially modulate neurosteroid production by binding to brain TSPO.

Basic studies have demonstrated that optimal levels of prefrontal cortical dopamine are critical to various executive functions such as working memory, attention, inhibitory control, and risk/reward decisions, all of which are impaired in addictive disorders such as alcoholism. Based on this and imaging studies of alcoholism that have demonstrated less dopamine in the striatum, the authors hypothesized decreased dopamine transmission in the prefrontal cortex in persons with alcohol dependence.To test this hypothesis, amphetamine and [11C]FLB 457 positron emission tomography were used to measure cortical dopamine transmission in 21 recently abstinent persons with alcohol dependence and 21 matched healthy comparison subjects. [11C]FLB 457 binding potential, specific compared to nondisplaceable uptake (BPND), was measured in subjects with kinetic analysis using the arterial input function both before and after 0.5 mg kg-1 of d-amphetamine.Amphetamine-induced displacement of [11C]FLB 457 binding potential (ΔBPND) was significantly smaller in the cortical regions in the alcohol-dependent group compared with the healthy comparison group. Cortical regions that demonstrated lower dopamine transmission in the alcohol-dependent group included the dorsolateral prefrontal cortex, medial prefrontal cortex, orbital frontal cortex, temporal cortex, and medial temporal lobe.The results of this study, for the first time, unambiguously demonstrate decreased dopamine transmission in the cortex in alcoholism. Further research is necessary to understand the clinical relevance of decreased cortical dopamine as to whether it is related to impaired executive function, relapse, and outcome in alcoholism.

Positron emission tomography (PET) imaging studies in cocaine abusers have shown that low dopamine release in the striatum following an amphetamine challenge is associated with higher relapse rates. One possible mechanism that might lead to lower amphetamine-induced dopamine release is low availability of dopamine storage vesicles in the presynaptic terminals for release. Consistent with this hypothesis, postmortem studies have shown low levels of vesicular monoamine transporter, type 2 (VMAT2), the membrane protein that regulates the size of the vesicular dopamine pool, in cocaine abusers relative to healthy subjects. To confirm the postmortem findings, the authors used PET and the VMAT2 radioligand [¹¹C]-(+)-dihydrotetrabenazine (DTBZ) to assess the in vivo VMAT2 availability in a group of 12 recently abstinent cocaine-dependent subjects and matched healthy comparison subjects.[¹¹C]DTBZ nondisplaceable binding potential (BP(ND)) was measured by kinetic analysis using the arterial input function or, if arterial input was unavailable, by the simplified reference tissue method.[¹¹C]DTBZ BP(ND) was significantly lower in the cocaine abusers than in the comparison subjects in the limbic striatum (10.0% lower), associative striatum (-13.4%), and sensorimotor striatum (-11.5%).The results of this in vivo PET study confirm previous in vitro reports of low VMAT2 availability in the striatum of cocaine abusers. It also suggests a compensatory down-regulation of the dopamine storage vesicles in response to chronic cocaine abuse and/or a loss of dopaminergic terminals. Further research is necessary to understand the clinical relevance of this observation to relapse and outcome in abstinent cocaine abusers.

Evidence indicates that synchronization of cortical activity at gamma-band frequencies, mediated through GABA-A receptors, is important for perceptual/cognitive processes. To study GABA signaling in vivo, we recently used a novel positron emission tomography (PET) paradigm measuring the change in binding of the benzodiazepine (BDZ) site radiotracer [(11)C]flumazenil associated with increases in extracellular GABA induced via GABA membrane transporter (GAT1) blockade with tiagabine. GAT1 blockade resulted in significant increases in [(11)C]flumazenil binding potential (BPND) over baseline in the major functional domains of the cortex, consistent with preclinical studies showing that increased GABA levels enhance the affinity of GABA-A receptors for BDZ ligands. In the current study we sought to replicate our previous results and to further validate this approach by demonstrating that the magnitude of increase in [(11)C]flumazenil binding observed with PET is directly correlated with tiagabine dose. [(11)C]flumazenil distribution volume (VT) was measured in 18 healthy volunteers before and after GAT1 blockade with tiagabine. Two dose groups were studied (n = 9 per group; Group I: tiagabine 0.15 mg/kg; Group II: tiagabine 0.25 mg/kg). GAT1 blockade resulted in increases in mean (± SD) [(11)C]flumazenil VT in Group II in association cortices (6.8 ± 0.8 mL g-1 vs. 7.3 ± 0.4 mL g-1;p = 0.03), sensory cortices (6.7 ± 0.8 mL g-1 vs. 7.3 ± 0.5 mL g-1;p = 0.02) and limbic regions (5.2 ± 0.6 mL g-1 vs. 5.7 ± 0.3 mL g-1;p = 0.03). No change was observed at the low dose (Group I). Increased orbital frontal cortex binding of [(11)C]flumazenil in Group II correlated with the ability to entrain cortical networks (r = 0.67, p = 0.05) measured via EEG during a cognitive control task. These data provide a replication of our previous study demonstrating the ability to measure in vivo, with PET, acute shifts in extracellular GABA.

Genetic, pharmacologic, and physiological data suggest that individuals with anorexia nervosa (AN) have altered striatal dopamine (DA) function.We used an amphetamine challenge and positron emission tomography [(11) C]raclopride paradigm to explore DA striatal transmission in 10 recovered (REC) AN compared with 9 control women (CW).REC AN and CW were similar for baseline, postamphetamine [(11) C]raclopride binding potential (BP(ND) ) and change (Δ) in BP(ND) for all regions. In CW, ventral striatum Δ BP(ND) was associated with euphoria (r = -0.76; p = 0.03), which was not found for REC AN. Instead, REC AN showed a significant relationship between anxiety and Δ BP(ND) in the precommissural dorsal caudate (r = -0.62, p = 0.05).REC AN have a positive association between endogenous DA release and anxiety in the dorsal caudate. This finding could explain why food-related DA release produces anxiety in AN, whereas feeding is pleasurable in healthy participants.

In a recent positron emission tomography (PET) study, we demonstrated the ability to measure amphetamine-induced dopamine (DA) release in the human cortex with the relatively high affinity dopamine D2/3 radioligand [(11)C]FLB 457. Herein we report on reproducibility and reliability of [(11)C]FLB 457 binding potential relative to non-displaceable uptake (BP(ND)) following an acute amphetamine challenge. Ten healthy human subjects were studied twice with [(11)C]FLB 457 following an acute amphetamine (oral, 0.5 mg kg(-1) dose) challenge on two-separate days approximately one week apart. D2/3 receptor binding parameters were estimated using a two-tissue compartment kinetic analysis in the cortical regions of interest and cerebellum (reference region). The test-retest variability and intraclass correlation coefficient were assessed for distribution volume (V(T)), binding potential relative to plasma concentration (BP(P)), and BP(ND) of [(11)C]FLB 457. The test-retest variability of [(11)C]FLB 457 V(T), BP(P) and BP(ND) were ≤ 17%, 22% and 11% respectively. These results, which are consistent with the published test-retest variability for this ligand measured under baseline conditions demonstrate that the post-amphetamine [(11)C]FLB 457 BP(ND) is reproducible. These data further support the use [(11)C]FLB 457 and amphetamine to characterize cortical dopamine transmission in neuropsychiatric disorders.