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R F Dannals

Publications and source records attributed to R F Dannals.

At least 55 records · Page 3Linked to original sources
PubMed1998

Brain opioid receptor measurements by positron emission tomography in normal cycling women: relationship to luteinizing hormone pulsatility and gonadal steroid hormones.

The regulation of central mu-opioid receptors in women during the menstrual cycle was explored with positron emission tomography and the selective radiotracer [11C]carfentanil. Ten healthy women were studied twice, during their follicular and luteal phases. Plasma concentrations of estradiol, progesterone, testosterone, and beta-endorphin were determined immediately before scanning. LH pulsatility was measured over the 9 h preceding each of the two positron emission tomography scans. No significant differences in the binding potential of mu-opioid receptors (binding capacity/Kd) were observed between phases of the menstrual cycle. However, significant negative correlations were observed between circulating levels of estradiol during the follicular phase and mu-receptor binding measures in the amygdala and hypothalamus, two regions thought to be involved in the regulation of GnRH pulsatility. LH pulse amplitude was positively correlated with mu binding in the amygdala, whereas LH pulse number was negatively correlated with binding in this same region. No significant associations were noted between LH pulse measures and the hypothalamus for this sample. These results suggest that amygdalar mu-opioid receptors exert a modulatory effect on GnRH pulsatility, and that circulating levels of estradiol also regulate central mu-opioid function.

Adult↗
PubMed1998

Investigation of angiotensin II/AT1 receptors with carbon-11-L-159,884: a selective AT1 antagonist.

UNLABELLED: Antagonists of the angiotensin II AT1 receptor subtype have been recently introduced for treatment of arterial hypertension and for pharmacological studies of these receptors. The purpose of this work was to label such an antagonist with 11C and test the applicability of the radioligand for PET studies. METHODS: The potent and selective nonpeptide AT1 antagonist L-159,884 was labeled with 11C and injected intravenously into six dogs. Renal accumulation and kinetics of the radioligand were imaged with PET at baseline and after receptor blockade with 1 mg/kg MK-996. Time-activity curves were derived from the renal cortex and were analyzed by the Gjedde-Patlak plot to obtain the influx rate constant of the radioligand. RESULTS: There was selective radioligand binding in the kidneys, mainly located in the cortex. Within the time interval between 95 and 115 min postinjection, the radioactivity retained in the kidneys was 109 +/- 27 and 42 +/- 4 nCi/ml/mCi of the injected dose for the control and inhibition studies, respectively. The influx rate constant of the radioligand decreased from a baseline of 0.0298 +/- 0.0156 to a post-MK-996 value of 0.0098 +/- 0.0052. CONCLUSION: These results demonstrate distinct binding of 11C-L-159,884 in the renal cortex with a specific binding component suitable for quantitative PET imaging of angiotensin II/AT1 receptors.

Angiotensin II↗
PubMed1997

A simple probe measures the pharmacokinetics of[125I]RTI-55 in mouse brain in vivo.

A simple external radiation detector system was used to assess brain dopamine and serotonin transporters in mice in vivo using [125I]RTI-55. The results were compared to ex vivo dissection data. Methyl 3beta-(4-iodophenyl) tropane-2beta-carboxic acid methyl ester (RTI-55 or beta-CIT), a high-affinity cocaine antagonist, binds to presynaptic dopamine and serotonin transporters in the brain. Radiotracer accumulation increased for the first 150 min after intravenous injection and then remained constant. When unlabeled RTI-55 was injected, either before or 60 min after radiotracer administration, a significant decrease in tracer accumulation was observed. [125I]RTI-55 binding was also displaced by blocking doses of 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-[3-phenylpropyl]piperazine dihydrochloride (GBR 12909) and paroxetine. The results were similar to the ex vivo dissection data. The results demonstrate the feasibility of using the probe detector system to study the presynaptic transporter system in vivo in the mouse brain. The technique is applicable to other cerebral neurotransmitter systems.

Absorptiometry, Photon↗
PubMed1997

[125/123I]IPH: a radioiodinated analog of epibatidine for in vivo studies of nicotinic acetylcholine receptors.

Tomographic imaging of central nicotinic acetylcholine receptors (nAChRs) via single photon emission computed tomography (SPECT) has been hampered by the lack of a radioligand with suitable in vivo binding characteristics. Therefore, a novel analog of epibatidine, (+/-)-exo-2-(2-iodo-5-pyridyl)-7-azabicyclo[2.2.1]heptane (IPH), labeled with [(125)I] or [(123)I] was evaluated as an in vivo marker of central nicotinic acetylcholine receptors (nAChRs). [(125)I]IPH showed substantial brain penetration (4.2% of the injected dose at 30 min) and a cerebral biodistribution in mice consistent with the in vivo labeling of nAChRs (% injected dose/gram of thalamus, superior colliculi >> cerebellum). [(125)I]IPH binding sites were shown to be saturable with unlabeled IPH (ED50 approximately 1 microg/kg). The uptake of [(125)I]IPH was blocked significantly by the nicotinic agonists, cytisine, lobeline, and (-)-nicotine, but not by the noncompetitive nAChR antagonist, mecamylamine. Antagonists of muscarinic (scopolamine), serotonin (ketanserin), and opioid (naloxone) receptors had no significant effect on [(125)I]IPH binding. A preliminary SPECT imaging study with [(123)I]IPH in a baboon showed [(123)I]IPH to localize in nAChR-rich areas of brain (thalamus > frontal cortex > cerebellum). [(123)I]IPH binding in baboon brain was also displaced (35-45% displacement) by a challenge dose of cytisine showing that a well-characterized nicotinic agonist effectively competes for [(123)I]IPH binding sites. [(123)I]IPH seems well suited for imaging studies of nAChRs and, to our knowledge, is the first SPECT agent that has allowed for the visualization of nAChRs in primate brain.

Animals↗
PubMed1997

Imaging of delta- and mu-opioid receptors in temporal lobe epilepsy by positron emission tomography.

The involvement of opioid neurotransmitter systems in seizure mechanisms is well documented. In previous positron emission tomography (PET) studies in patients with unilateral temporal lobe epilepsy, we have found evidence for differential regulation of the opioid-receptor subtypes. The present study extends our previous observations to delta-opioid receptors by using the delta-receptor-selective antagonist [11C]methylnaltrindole ([11C]MeNTI). Paired measurements of delta- and mu-opioid receptor binding and metabolic activity were performed with PET using [11C]MeNTI and [11C]carfentanil ([11C]CFN) and [18F]fluorodeoxyglucose ([18F]FDG), respectively. Binding of [11C]MeNTI and [11C]CFN increased and [18F]FDG uptake decreased in the temporal cortex (TC) ipsilateral to the focus. Decreases in [18F]FDG uptake were more widespread regionally than were increases in opioid receptors. Increases in the delta- and mu-receptor binding showed different regional patterns. Increases in mu-receptor binding were confined to the middle aspect of the inferior TC, whereas binding of delta receptors increased in the mid-inferior TC and anterior aspect of the middle and superior TC. The increase in delta receptors suggests their anticonvulsant action, as previously shown for the delta-receptor subtype, whereas the different regional pattern of receptor alterations suggest the distinct roles of different opioid-receptor subtypes in seizure phenomena.

Adult↗
PubMed1997

Time course of 5-HT2A receptor occupancy in the human brain after a single oral dose of the putative antipsychotic drug MDL 100,907 measured by positron emission tomography.

MDL 100,907 is a potent and selective antagonist of 5-HT2A serotonin receptors. Animals studies suggest that MDL 100,907 may behave as an atypical antipsychotic drug. Positron emission tomograph (PET) using [11C]NMSP as the radiotracer was used to define the time course of 5-HT2 receptor occupancy in the human frontal cerebral cortex after a single oral dose of MDL 100,907 (10 or 20 mg) in nine healthy subjects. After the baseline scan each subject was studied three times post dosing at various time points. 5-HT2 occupancies were in the range of 70 and 90% after each dose. While the occupancy remains in this range over 24 hours after 20 mg MDL 100,907, it decreases by about 20% at 24 hours compared to the timepoint at 8 hours, when only 10 mg are administered (p < 0.05). Our results should allow determination of the appropriate dosing regimen for future trials in schizophrenic patients.

Adult↗
PubMed1997

Quantification of neuroreceptors in the living human brain: IV. Effect of aging and elevations of D2-like receptors in schizophrenia and bipolar illness.

In a previous study of 10 drug-naive schizophrenic patients, the density of D2 dopamine receptors was found to be elevated in the caudate nucleus. The study raised questions about the influence of the age of the patients, the relationship of receptor density to psychosis, and the accuracy of the method used to obtain this evidence. Using positron emission tomography and constrained analysis of the brain uptake of the radioligand N-[11C]methyl-spiperone ([11C]NMSP), we tested four questions: Were the assumptions underlying the quantitation valid? Is there an age decline of the density of D2-like dopamine receptors in drug-naive schizophrenia and bipolar illness? If so, is it different from that observed in normal aging? Are D2-like dopamine receptors elevated at any age in either drug-naive schizophrenic or psychotic bipolar illness patients? NMSP and haloperidol partition volumes and plasma protein fractions were not significantly different among patient groups and normal volunteers. The model-derived assay of radioligand metabolites in plasma was confirmed by high-performance liquid chromatography in the patient groups. D2-like dopamine receptors declined with age, and the slope did not differ significantly between the schizophrenic patients, bipolar affective illness patients, and normal controls. Taking the effect of age into account, increases in D2 dopamine receptor density were found in seven psychotic patients with bipolar affective illness compared with seven nonpsychotic patients and 24 control subjects as well as in 22 drug-naive schizophrenic patients compared with the 24 control subjects.

Adult↗
PubMed1997

Cerebral glucose utilization is reduced in second test session.

Cerebral glucose utilization was higher during the first positron emission tomography (PET) session than during the second session, as assayed using the PET [18F]fluorodeoxyglucose method in male human volunteers. This difference was due largely to data from subjects with low-trait anxiety, since subjects with high anxiety showed similar metabolism in both PET sessions. High-anxiety subjects showed greater right/ left ratios of cerebral metabolism than low-anxiety subjects, particularly during the second PET session. These findings suggest that the level of anxiety may be an important variable to consider in PET studies using multiple sessions.

Adult↗
PubMed1997

PET study of competition between intravenous cocaine and [11C]raclopride at dopamine receptors in human subjects.

OBJECTIVE: Animal data suggest that the strong euphoriant effects of cocaine are related to the drug's enhancement of available dopamine at the synaptic cleft. The authors' goal was to determine whether this mechanism is the same in humans because the development of putative pharmacological agents for treatment of cocaine dependence depends on this knowledge. METHOD: Positron emission tomography with [11C]raclopride was used to examine the effects of the intravenous administration of 48 mg of cocaine (a typical "street" dose) on the occupancy of dopamine 2 receptors in the putamen of 11 self-identified intravenous drug abusers. RESULTS: All 11 subjects reported subjective stimulation and euphoria in response to cocaine administration. Radioligand occupancy at dopamine receptors was decreased significantly after cocaine administration, suggesting that higher dopamine concentrations were competing at the receptor site. CONCLUSIONS: These results support the concept of dopamine system involvement in human cocaine abuse.

Adult↗
PubMed1997

[125I]IPH, an epibatidine analog, binds with high affinity to neuronal nicotinic cholinergic receptors.

An analog of epibatidine (EB) was synthesized with an iodine atom in the 2 position of the pyridyl ring. This analog, (+/-)-exo-2-(2-iodo-5-pyridyl)-7-azabicyclo[2.2.1]heptane (IPH), as well as its two stereoisomers, displayed high affinity for neuronal nicotinic receptors; therefore, radioiodinated IPH, [125I]IPH, was synthesized with specific radioactivities consistently > 1000 Ci/mmol, and its properties as a radioligand for neuronal nicotinic receptors were evaluated. The characteristics of [125I]IPH binding in tissue homogenates appeared to be virtually identical to those reported for [3H]epibatidine binding; but the high specific radioactivity of [125I]IPH greatly facilitated measurements of nicotinic receptors in tissues with relatively low receptor densities and/or where tissues are in limited supply. Autoradiography with [125I]IPH provided clear localization of nicotinic receptors in brain and adrenal gland after film exposure times of < or = 2 days. We conclude that [125I]IPH will be a very useful radioligand for the study of neuronal nicotinic receptors in brain and in peripheral ganglia.

Animals↗
PubMed1997

D2-like dopamine receptor density in Tourette syndrome measured by PET.

UNLABELLED: Tourette syndrome (TS) is a chronic neurologic disorder characterized by the presence of involuntary motor and phonic tics. There is evidence that TS is associated with an abnormality of the dopaminergic system, involving postsynaptic D2 receptors. We tested the hypothesis that D2-like dopamine receptors are elevated in TS. METHODS: Twenty-nine adult patients with TS were studied by PET imaging with [11C]3-N-methylspiperone ([11C]NMSP). Two methods of data analysis were used. The first was a caudate-to-cerebellar ratio, measured at 45 min. The second method, applied in 20 subjects, was a two-PET scan procedure. Both used high specific activity [11C]NMSP, but the second scan was preceded by a dose of unlabeled haloperidol, which partially occupied the D2-like dopamine receptors. This was done to provide an absolute measure of receptor density (Bmax). All patients were compared to age- and sex-matched controls. RESULTS: Neither group showed significant differences from their control group in caudate-to-cerebellar ratio. However, the two-PET scan Bmax measurement demonstrated that 4 of the 20 patients had significantly elevated D2-like receptors. In this group of 20 patients, multiple linear regression analysis revealed a trend between the severity of vocal tics and Bmax values. This Bmax measure also revealed a significant (p < 0.05) association with performance on the Wisconsin Card Sorting Test. CONCLUSION: These findings suggest that not all patients with TS have an abnormality of D2-like receptors, but a subgroup of TS subjects has a significant D2-like dopamine receptor elevation. These findings also support the importance of applying a more quantitative method for Bmax determination to PET imaging analysis. The Bmax findings in the subgroup do not exclude an effect of intrasynaptic dopamine competition, but this effect may be less likely due to the high affinity of [11C]NMSP.

Adult↗
PubMed1997

Fluorine-18-FPH for PET imaging of nicotinic acetylcholine receptors.

UNLABELLED: Visualization of central nicotinic acetylcholine receptors (nAChRs) with modern PET or SPECT imaging techniques has been hampered by the lack of a radioligand with suitable in vivo binding characteristics (i.e., high target-to-nontarget ratios and kinetics appropriate for the half-life of the tracer and imaging modality used). This paper describes in vivo binding, kinetics and pharmacology of a highly potent 18F-labeled analog of epibatidine, (+/-)-exo-2-(2-[18F]fluoro-5-pyridyl)-7-azabicyclo[2.2.1]heptane ([18F]FPH), in the mouse brain with the view towards application of this tracer for PET imaging of nAChR in human brain. METHODS: Fluorine-18-FPH was administered intravenously to mice, and time-activity curves were determined for several regions in the brain and other organs. Saturation and pharmacology of [18F]FPH binding was demonstrated in vivo by preinjecting unlabeled FPH or other drugs with known pharmacological action before [18F]FPH was injected. The effect of the drugs on [18F]FPH accumulation was evaluated. RESULTS: [18F]FPH was rapidly incorporated into the mouse brain; peak activity (2.4% of the injected dose) was measured at 5 min after intravenous administration, followed by washout to 1.1% injected dose (ID) at 60 min. Highest concentrations of 18F occurred at 15 min in areas known to contain high densities of nAChR ¿e.g., thalamus [9.7% of injected dose per gram tissue (ID/g¿] and superior colliculus (8.3% ID/g)]. Accumulation of the 18F tracer in hippocampus, striatum, hypothalamus and cortical areas was intermediate (5.0, 5.6, 4.2 and 5.6% ID/g, respectively) and low in the cerebellum (2.8% ID/g). The distribution of [18F]FPH in the mouse brain matched that of other in vivo nAChR probes such as 3H-labeled epibatidine or norchloroepibatidine, [3H](-)-nicotine and [3H]cytisine and that of nAChR densities determined in postmortem autoradiographic studies in rodents. Preinjection of blocking doses of unlabeled epibatidine, (-)-nicotine, lobeline and cytisine significantly inhibited [18F]FPH binding in thalamus and superior colliculus, but not in cerebellum, whereas drugs that interact with binding sites other than acetylcholine recognition sites of nAChR (e.g., mecamylamine, scopolamine, N-methylspiperone and ketanserin) had no effect on [18F]FPH accumulation in any of the brain regions examined. CONCLUSION: Fluorine-18-FPH labels nAChR in vivo in the mouse brain. Because of its high uptake into the brain and high ratios of specific-to-nonspecific binding, this radioligand appears to be ideally suited for PET imaging of nAChR in the mammalian brain.

Animals↗
PubMed1997

Longer occupancy of opioid receptors by nalmefene compared to naloxone as measured in vivo by a dual-detector system.

UNLABELLED: Surgical procedures usually involve the administration of narcotic drugs as anesthetics or adjuvants. To reverse the effects of anesthesia, opioid antagonists such as naloxone are commonly used. Due to its short lasting effects, patients receiving naloxone must be monitored carefully. Nalmefene, a pure opiate antagonist with a longer duration of action than naloxone, has shown promise in the reversal of opioid anesthesia. METHODS: A simple dual-detector positron radiation detector system and [11C]carfentanil were used to compare the duration of blockade of cerebral mu opioid receptors by naloxone and nalmefene in eight normal volunteers. Carbon-11-carfentanil brain kinetics were monitored for 5 min and 2, 4, 8 and 24 hr after the administration of either nalmefene (1 mg or 1 microg/kg) or naloxone (2 mg or 2 microg/kg). Blood samples were obtained at the same times for plasma determinations. RESULTS: Clearance half-times from opioid receptors were 28.7 +/- 5.9 hr for 1 mg of nalmefene and 2.0 +/- 1.6 hr for 2 mg of naloxone. Brain clearance times were about 21.1 and 3.4 times slower than plasma clearance times for nalmefene and naloxone, respectively. CONCLUSION: These findings suggest that the prolonged effects of nalmefene are related to the slow dissociation of nalmefene from opioid receptors, which are not reflected in the plasma curve. This longer blockade of opioid receptors by nalmefene represents an advantage in the clinical management of postsurgical reversal of narcotic anesthesia and opioid side effects as well as the reversal of opioid overdose.

Adult↗
PubMed1997

Imaging nicotinic acetylcholine receptors with fluorine-18-FPH, an epibatidine analog.

UNLABELLED: Nicotinic acetylcholine receptors (nAChRs) have been implicated in a variety of central processes, such as learning and memory and analgesia. These receptors also mediate the reinforcing properties of nicotine in tobacco products and are increased in postmortem samples of brains of smokers. On the other hand, brains of individuals who have died from dementia of the Alzheimer type show abnormally low densities of nAChRs. In this study, the distribution and kinetics of [(+/-)-exo-2-(2-[18F] fluoro-5-pyridyl)-7-azabicyclo[2.2.1]heptane (18F-FPH), a high-affinity nAChR agonist, was evaluated in a baboon using PET. METHODS: After intravenous injection of 5 mCi [185 MBq] 18F-FPH into a 25-kg anesthetized baboon, sequential quantitative tomographic data were acquired over a period of 150 min. Regions of interest were placed and time-activity curves were generated. Brain kinetics of the radiotracer were calculated, and the in vivo regional binding in the baboon brain was compared with the known in vitro regional distribution of nAChRs in the rat and human brain. RESULTS: Brain activity reached a plateau within 60 min after injection of the tracer, and the binding was reversible. Elimination of 18F-FPH was relatively rapid from the cerebellum (clearance t[1/2] = 3 hr), intermediate from the hypothalamus/midbrain (t[1/2] = 7 hr) and slow from the thalamus (t[1/2] = 16 hr). Radioactivity due to 18F-FPH at 130 min postinjection was highest in the thalamus and hypothalamus/midbrain, intermediate in the neocortex and hippocampus and lowest in the cerebellum. Subcutaneous injection of 1 mg/kg cytisine 45 min after injection of the radiotracer reduced brain activity at 130 min by 67%, 64%, 56% and 52% of control values in the thalamus, hypothalamus/midbrain, hippocampus and cerebellum, respectively. The regional binding of 18F-FPH at 130 min was highly correlated with the known densities of nAChR measured in vitro in human (r = 0.81) and rat brain (r = 0.90). CONCLUSION: These results demonstrate the feasibility of imaging nAChRs in vivo. Fluorine-18-FPH appears to be a suitable tracer to study nAChRs in the human brain.

Animals↗
PubMed1996

Brain metabolism patterns are sensitive to attentional effort associated with a tone recognition task.

Using positron emission tomography with the tracer 18-fluoro-D-deoxyglucose, we assessed regional cerebral glucose utilization patterns (rCMRglu) associated with three performance levels in a forced choice, tone recognition task. Four normal subjects responded with one hand when they heard a high-frequency tone (1500 Hz), and with the other hand when they recognized a low-frequency tone (750 Hz). The EASY (EAS) condition accuracy average was 96%, the INTERMEDIATE level accuracy averaged 89%, and the DIFFICULT (DIF) recognition task accuracy average was 77%. Statistical parametric mapping (SPM94) analysis revealed that the DIF minus EAS contrast is associated with a marked metabolic elevation in the right middle and inferior temporal gyri and the gyrus fusiformis. The EAS minus DIF contrast revealed greater rCMRglu in the right medial geniculate body. Enhanced activity in right temporal lobe structures may reflect a role in auditory memory and "image" visualization. The medial geniculate enhancement may reflect tone frequency assessment.

Adult↗
PubMed1996

Dopamine transporters are markedly reduced in Lesch-Nyhan disease in vivo.

Dopamine (DA) deficiency has been implicated in Lesch-Nyhan disease (LND), a genetic disorder that is characterized by hyperuricemia, choreoathetosis, dystonia, and compulsive self-injury. To establish that DA deficiency is present in LND, the ligand WIN-35,428, which binds to DA transporters, was used to estimate the density of DA-containing neurons in the caudate and putamen of six patients with classic LND. Comparisons were made with 10 control subjects and 3 patients with Rett syndrome. Three methods were used to quantify the binding of the DA transporter so that its density could be estimated by a single dynamic positron emission tomography study. These approaches included the caudate- or putamen-to-cerebellum ratio of ligand at 80-90 min postinjection, kinetic analysis of the binding potential [Bmax/(Kd x Vd)] using the assumption of equal partition coefficients in the striatum and the cerebellum, and graphical analysis of the binding potential. Depending on the method of analysis, a 50-63% reduction of the binding to DA transporters in the caudate, and a 64-75% reduction in the putamen of the LND patients was observed compared to the normal control group. When LND patients were compared to Rett syndrome patients, similar reductions were found in the caudate (53-61%) and putamen (67-72%) in LND patients. Transporter binding in Rett syndrome patients was not significantly different from the normal controls. Finally, volumetric magnetic resonance imaging studies detected a 30% reduction in the caudate volume of LND patients. To ensure that a reduction in the caudate volume would not confound the results, a rigorous partial volume correction of the caudate time activity curve was performed. This correction resulted in an even greater decrease in the caudate-cerebellar ratio in LND patients when contrasted to controls. To our knowledge, these findings provide the first in vivo documentation of a dopaminergic reduction in LND and illustrate the role of positron emission tomography imaging in investigating neurodevelopmental disorders.

Adolescent↗
PubMed1996

Imaging of delta opioid receptors in human brain by N1'-([11C]methyl)naltrindole and PET.

Recently, we have developed the positron emitting radiotracer N1'-([11C]methyl)naltrindole ([11C]MeNTI) and demonstrated its high selectivity for delta opioid receptors in the mouse brain [Lever et al. (1992) Eur. J. Pharmacol., 216:449-450]. In the present study, we examined the selectivity of [11C]MeNTI for the delta opioid receptor in the human brain, using positron emission tomography (PET). The regional kinetics and distribution as well as the pharmacology confirmed the selectivity of [11C]MeNTI for delta opioid receptor in the human brain. First, the regional kinetics of [11C]MeNTI are in accordance with the density of the delta opioid receptor. Rapid washout in receptor-poor areas and prolonged retention in receptor-rich areas were observed. Second, the regional distribution of [11C]MeNTI correlated well (r = 0.91) with the in vitro distribution of delta opioid sites but not with mu or kappa site densities (r < or = 0.008 or r < or = 0.014, respectively). [11C]MeNTI binding was highest in regions of the neocortex (insular, parietal, frontal, cingulate, and occipital), caudate nucleus, and putamen. Binding was intermediate in the amygdala and lowest in the cerebellum and thalamus. Third, studies using the competitive antagonist naltrexone demonstrated the inhibition of [11C]MeNTI binding. Naltrexone inhibition of [11C]MeNTI binding was most effective in delta receptor-rich regions, and its inhibitory potency correlated well (r = 0.88) with the regional distribution of delta opioid sites. [11C]MeNTI is the first radioligand which selectively labels delta opioid receptors in vivo in the human brain following systemic administration. The availability of [11C]MeNTI will enable a receptor specific analysis of the role of [11C]MeNTI receptors in normal and abnormal human brain.

Adult↗