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

Long-term trends in total administered radiation dose from brain [18F]FDG-PET in children with drug-resistant epilepsy

PURPOSE

To assess the trends in administered 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG) doses, computed tomography (CT) radiation doses, and image quality over the last 15 years in children with drug-resistant epilepsy (DRE) undergoing hybrid positron emission tomography (PET) brain scans.

METHODS

We retrospectively analyzed data from children with DRE who had [18F]FDG-PET/CT or magnetic resonance scans for presurgical evaluation between 2005 and 2021. We evaluated changes in injected [18F]FDG doses, administered activity per body weight, CT dose index volume (CTDIvol), and dose length product (DLP). PET image quality was assessed visually by four trained raters. Conversely, CT image quality was measured using region-of-interest analysis, normalized by signal-to-noise (SNR) and contrast-to-noise ratio (CNR).

RESULTS

We included 55 children (30 male, mean age: 9 ± 6 years) who underwent 61 [18F]FDG-PET scans (71% as PET/CT). Annually, the injected [18F]FDG dose decreased by ~ 1% (95% CI: 0.92%-0.98%, p < 0.001), with no significant changes in administered activity per body weight (p = 0.51). CTDIvol and DLP decreased annually by 16% (95% CI: 9%-23%) and 15% (95% CI: 8%-21%, both p < 0.001), respectively. PET image quality improved by 9% year-over-year (95% CI: 6%-13%, p < 0.001), while CT-associated SNR and CNR decreased annually by 7% (95% CI: 3%-11%, p = 0.001) and 6% (95% CI: 2%-10%, p = 0.008), respectively.

CONCLUSION

Our findings indicate stability in [18F]FDG administered activity per body weight alongside improvements in PET image quality. Conversely, CT-associated radiation doses reduced. These results reaffirm [18F]FDG-PET as an increasingly safer and higher-resolution auxiliary imaging modality for children with DRE. These improvements, driven by technological advancements, may enhance the diagnostic precision and patient outcomes in pediatric epilepsy surgery.

Contribution of the opioid system to depression and to the therapeutic effects of classical antidepressants and ketamine

Major depressive disorder (MDD) afflicts approximately 5 % of the world population, and about 30-50 % of patients who receive classical antidepressant medications do not achieve complete remission (treatment resistant depressive patients). Emerging evidence suggests that targeting opioid receptors mu (MOP), kappa (KOP), delta (DOP), and the nociceptin/orphanin FQ receptor (NOP) may yield effective therapeutics for stress-related psychiatric disorders. As depression and pain exhibit significant overlap in their clinical manifestations and molecular mechanisms involved, it is not a surprise that opioids, historically used to alleviate pain, emerged as promising and effective therapeutic options in the treatment of depression. The opioid signaling is dysregulated in depression and numerous preclinical studies and clinical trials strongly suggest that opioid modulation can serve as either an adjuvant or even an alternative to classical monoaminergic antidepressants. Importantly, some classical antidepressants require the opioid receptor modulation to exert their antidepressant effects. Finally, ketamine, a well-known anesthetic whose extremely efficient antidepressant effects were recently discovered, was shown to mediate its antidepressant effects via the endogenous opioid system. Thus, although opioid system modulation is a promising therapeutical venue in the treatment of depression further research is warranted to fully understand the benefits and weaknesses of such approach.

A Molecular Toolbox of Positron Emission Tomography Tracers for General Anesthesia Mechanism Research

With appropriate radiotracers, positron emission tomography (PET) allows direct or indirect monitoring of the spatial and temporal distribution of anesthetics, neurotransmitters, and biomarkers, making it an indispensable tool for studying the general anesthesia mechanism. In this Perspective, PET tracers that have been recruited in general anesthesia research are introduced in the following order: 1) ¹¹C/¹⁸F-labeled anesthetics, i.e., PET tracers made from inhaled and intravenous anesthetics; 2) PET tracers targeting anesthesia-related receptors, e.g., neurotransmitters and voltage-gated ion channels; and 3) PET tracers for studying anesthesia-related neurophysiological effects and neurotoxicity. The radiosynthesis, pharmacodynamics, and pharmacokinetics of the above PET tracers are mainly discussed to provide a practical molecular toolbox for radiochemists, anesthesiologists, and those who are interested in general anesthesia.

The Role of SPECT and PET in Epilepsy

OBJECTIVE. The purpose of this article is to summarize the role of molecular imaging of the brain by use of SPECT, FDG PET, and non-FDG PET radiotracers in epilepsy. CONCLUSION. Quantitative image analysis with PET and SPECT has increased the diagnostic utility of these modalities in localizing epileptogenic onset zones. A multi-modal platform approach integrating the functional imaging of PET and SPECT with the morphologic information from MRI in presurgical evaluation of epilepsy can greatly improve outcomes.

A Survey of Molecular Imaging of Opioid Receptors

The discovery of endogenous peptide ligands for morphine binding sites occurred in parallel with the identification of three subclasses of opioid receptor (OR), traditionally designated as μ, δ, and κ, along with the more recently defined opioid-receptor-like (ORL1) receptor. Early efforts in opioid receptor radiochemistry focused on the structure of the prototype agonist ligand, morphine, although N-[methyl-¹¹C]morphine, -codeine and -heroin did not show significant binding in vivo. [¹¹C]Diprenorphine ([¹¹C]DPN), an orvinol type, non-selective OR antagonist ligand, was among the first successful PET tracers for molecular brain imaging, but has been largely supplanted in research studies by the μ-preferring agonist [¹¹C]carfentanil ([¹¹C]Caf). These two tracers have the property of being displaceable by endogenous opioid peptides in living brain, thus potentially serving in a competition-binding model. Indeed, many clinical PET studies with [¹¹C]DPN or [¹¹C]Caf affirm the release of endogenous opioids in response to painful stimuli. Numerous other PET studies implicate μ-OR signaling in aspects of human personality and vulnerability to drug dependence, but there have been very few clinical PET studies of μORs in neurological disorders. Tracers based on naltrindole, a non-peptide antagonist of the δ-preferring endogenous opioid enkephalin, have been used in PET studies of δORs, and [¹¹C]GR103545 is validated for studies of κORs. Structures such as [¹¹C]NOP-1A show selective binding at ORL-1 receptors in living brain. However, there is scant documentation of δ-, κ-, or ORL1 receptors in healthy human brain or in neurological and psychiatric disorders; here, clinical PET research must catch up with recent progress in radiopharmaceutical chemistry.

Is There a Role for GPCR Agonist Radiotracers in PET Neuroimaging?

Positron emission tomography (PET) is a molecular imaging modality that enables in vivo exploration of metabolic processes and especially the pharmacology of neuroreceptors. G protein-coupled receptors (GPCRs) play an important role in numerous pathophysiologic disorders of the central nervous system. Thus, they are targets of choice in PET imaging to bring proof concept of change in density in pathological conditions or in pharmacological challenge. At present, most radiotracers are antagonist ligands. In vitro data suggest that properties differ between GPCR agonists and antagonists: antagonists bind to receptors with a single affinity, whereas agonists are characterized by two different affinities: high affinity for receptors that undergo functional coupling to G-proteins, and low affinity for those that are not coupled. In this context, agonist radiotracers may be useful tools to give functional images of GPCRs in the brain, with high sensitivity to neurotransmitter release. Here, we review all existing PET radiotracers used from animals to humans and their role for understanding the ligand-receptor paradigm of GPCR in comparison with corresponding antagonist radiotracers.

Molecular Targets of Cannabidiol in Neurological Disorders

Cannabis has a long history of anecdotal medicinal use and limited licensed medicinal use. Until recently, alleged clinical effects from anecdotal reports and the use of licensed cannabinoid medicines are most likely mediated by tetrahydrocannabinol by virtue of: 1) this cannabinoid being present in the most significant quantities in these preparations; and b) the proportion:potency relationship between tetrahydrocannabinol and other plant cannabinoids derived from cannabis. However, there has recently been considerable interest in the therapeutic potential for the plant cannabinoid, cannabidiol (CBD), in neurological disorders but the current evidence suggests that CBD does not directly interact with the endocannabinoid system except in vitro at supraphysiological concentrations. Thus, as further evidence for CBD's beneficial effects in neurological disease emerges, there remains an urgent need to establish the molecular targets through which it exerts its therapeutic effects. Here, we conducted a systematic search of the extant literature for original articles describing the molecular pharmacology of CBD. We critically appraised the results for the validity of the molecular targets proposed. Thereafter, we considered whether the molecular targets of CBD identified hold therapeutic potential in relevant neurological diseases. The molecular targets identified include numerous classical ion channels, receptors, transporters, and enzymes. Some CBD effects at these targets in in vitro assays only manifest at high concentrations, which may be difficult to achieve in vivo, particularly given CBD's relatively poor bioavailability. Moreover, several targets were asserted through experimental designs that demonstrate only correlation with a given target rather than a causal proof. When the molecular targets of CBD that were physiologically plausible were considered for their potential for exploitation in neurological therapeutics, the results were variable. In some cases, the targets identified had little or no established link to the diseases considered. In others, molecular targets of CBD were entirely consistent with those already actively exploited in relevant, clinically used, neurological treatments. Finally, CBD was found to act upon a number of targets that are linked to neurological therapeutics but that its actions were not consistent withmodulation of such targets that would derive a therapeutically beneficial outcome. Overall, we find that while >65 discrete molecular targets have been reported in the literature for CBD, a relatively limited number represent plausible targets for the drug's action in neurological disorders when judged by the criteria we set. We conclude that CBD is very unlikely to exert effects in neurological diseases through modulation of the endocannabinoid system. Moreover, a number of other molecular targets of CBD reported in the literature are unlikely to be of relevance owing to effects only being observed at supraphysiological concentrations. Of interest and after excluding unlikely and implausible targets, the remaining molecular targets of CBD with plausible evidence for involvement in therapeutic effects in neurological disorders (e.g., voltage-dependent anion channel 1, G protein-coupled receptor 55, CaV3.x, etc.) are associated with either the regulation of, or responses to changes in, intracellular calcium levels. While no causal proof yet exists for CBD's effects at these targets, they represent the most probable for such investigations and should be prioritized in further studies of CBD's therapeutic mechanism of action.

Low-frequency electroacupuncture suppresses focal epilepsy and improves epilepsy-induced sleep disruptions

Background

The positive effects of acupuncture at Feng-Chi acupoints on treating epilepsy and insomnia have been well-documented in ancient Chinese literature. However, there is a lack of scientific evidence to elucidate the underlying mechanisms behind these effects. Our previous study demonstrated that high-frequency (100 Hz) electroacupuncture (EA) at Feng-Chi acupoints deteriorates both pilocarpine-induced focal epilepsy and sleep disruptions. This study investigated the effects of low-frequency (10 Hz) EA on epileptic activities and epilepsy-induced sleep disruptions.

Results

In rats, the Feng-Chi acupoint is located 3 mm away from the center of a line between the two ears. Rats received 30 min of 10 Hz EA stimuli per day before each day’s dark period for three consecutive days. Our results indicated that administration of pilocarpine into the left CeA at the beginning of the dark period induced focal epilepsy and decreased both rapid eye movement (REM) sleep and non-REM (NREM) sleep during the consequent light period. Low-frequency (10 Hz) EA at Feng-Chi acupoints suppressed pilocarpine-induced epileptiform EEGs, and this effect was in turn blocked by naloxone (a broad-spectrum opioid receptor antagonist), but not by naloxonazine (a μ-receptor antagonist), naltrindole (a δ-receptor antagonist) and nor-binaltorphimine (a κ-receptor antagonist). Ten Hz EA enhanced NREM sleep during the dark period, and this enhancement was blocked by all of the opioid receptor antagonists. On the other hand, 10 Hz EA reversed pilocarpine-induced NREM suppression during the light period, and the EA’s effect on the sleep disruption was only blocked by naloxonazine.

Conclusions

These results indicate that low-frequency EA stimulation of Feng-Chi acupoints is beneficial in improving epilepsy and epilepsy-induced sleep disruptions, and that opioid receptors in the CeA mediate EA’s therapeutic effects.

Development of (18)F-labeled radiotracers for neuroreceptor imaging with positron emission tomography

Positron emission tomography (PET) is an in vivo molecular imaging tool which is widely used in nuclear medicine for early diagnosis and treatment follow-up of many brain diseases. PET uses biomolecules as probes which are labeled with radionuclides of short half-lives, synthesized prior to the imaging studies. These probes are called radiotracers. Fluorine-18 is a radionuclide routinely used in the radiolabeling of neuroreceptor ligands for PET because of its favorable half-life of 109.8 min. The delivery of such radiotracers into the brain provides images of transport, metabolic, and neurotransmission processes on the molecular level. After a short introduction into the principles of PET, this review mainly focuses on the strategy of radiotracer development bridging from basic science to biomedical application. Successful radiotracer design as described here provides molecular probes which not only are useful for imaging of human brain diseases, but also allow molecular neuroreceptor imaging studies in various small-animal models of disease, including genetically-engineered animals. Furthermore, they provide a powerful tool for in vivo pharmacology during the process of pre-clinical drug development to identify new drug targets, to investigate pathophysiology, to discover potential drug candidates, and to evaluate the pharmacokinetics and pharmacodynamics of drugs in vivo.

An overview of PET neuroimaging

Over the past 35 years or so, PET brain imaging has allowed powerful and unique insights into brain function under normal conditions and in disease states. Initially, as PET instrumentation continued to develop, studies were focused on brain perfusion and glucose metabolism. This permitted refinement of brain imaging for important, non-oncologic clinical indications. The ability of PET to not only provide spatial localization of metabolic changes but also to accurately and consistently quantify their distribution proved valuable for applications in the clinical setting. Specifically, glucose metabolism brain imaging using (F-18) fluorodeoxyglucose continues to be invaluable for evaluating patients with intractable seizures for identifying seizure foci and operative planning. Cerebral glucose metabolism also contributes to diagnosis of neurodegenerative diseases that cause dementia. Alzheimer disease, dementia with Lewy bodies, and the several variants of frontotemporal lobar degeneration have differing typical patterns of hypometabolism. In Alzheimer disease, hypometabolism has furthermore been associated with poorer cognitive performance and ensuing cognitive and functional decline. As the field of radiochemistry evolved, novel radioligands including radiolabeled flumazenil, dopamine transporter ligands, nicotine receptor ligands, and others have allowed for further understanding of molecular changes in the brain associated with various diseases. Recently, PET brain imaging reached another milestone with the approval of (F-18) florbetapir imaging by the United States Federal Drug Administration for detection of amyloid plaque accumulation in brain, the major histopathologic hallmark of Alzheimer disease, and efforts have been made to define the clinical role of this imaging agent in the setting of the currently limited treatment options. Hopefully, this represents the first of many new radiopharmaceuticals that would allow improved diagnostic and prognostic information in these and other clinical applications, including Parkinson disease and traumatic brain injury.

Activation of amygdala opioid receptors by electroacupuncture of Feng-Chi (GB20) acupoints exacerbates focal epilepsy

BACKGROUND

The effect of seizure suppression by acupuncture of Feng-Chi (GB20) acupoints has been documented in the ancient Chinese literature, Lingshu Jing (Classic of the Miraculous Pivot), however, there is a lack of scientific evidence to prove it. This current study was designed to elucidate the effect of electroacupuncture (EA) stimulation of bilateral Feng-Chi (GB20) acupoints on the epileptic activity by employing an animal model of focal epilepsy.

METHODS

Administration of pilocarpine into the left central nucleus of amygdala (CeA) induced the focal epilepsy in rats. Rats received a 30-min 100 Hz EA stimulation of bilateral Feng-Chi acupoints per day, beginning at 30 minutes before the dark period and performing in three consecutive days. The broad-spectrum opioid receptor antagonist (naloxone), μ-receptor antagonist (naloxonazine), δ-receptor antagonist (naltrindole) and κ-receptor antagonist (nor-binaltorphimine) were administered directly into the CeA to elucidate the involvement of CeA opioid receptors in the EA effect.

RESULTS

High-frequency (100 Hz) EA stimulation of bilateral Feng-Chi acupoints did not suppress the pilocarpine-induced epileptiform electroencephalograms (EEGs), whereas it further increased the duration of epileptiform EEGs. We also observed that epilepsy occurred while 100 Hz EA stimulation of Feng-Chi acupoints was delivered into naïve rats. EA-induced augmentation of epileptic activity was blocked by microinjection of naloxone, μ- (naloxonazine), κ- (nor-binaltorphimine) or δ-receptor antagonists (natrindole) into the CeA, suggesting that activation of opioid receptors in the CeA mediates EA-exacerbated epilepsy.

CONCLUSIONS

The present study suggests that high-frequency (100 Hz) EA stimulation of bilateral Feng-Chi acupoints has no effect to protect against pilocarpine-induced focal epilepsy; in contrast, EA further exacerbated focal epilepsy induced by pilocarpine. Opioid receptors in the CeA mediated EA-induced exacerbation of focal epilepsy.

Pharmacological traits of delta opioid receptors: pitfalls or opportunities?

RATIONALE

Delta opioid receptors (DORs) have been considered as a potential target to relieve pain as well as treat depression and anxiety disorders and are known to modulate other physiological responses, including ethanol and food consumption. A small number of DOR-selective drugs are in clinical trials, but no DOR-selective drugs have been approved by the Federal Drug Administration and some candidates have failed in phase II clinical trials, highlighting current difficulties producing effective delta opioid-based therapies. Recent studies have provided new insights into the pharmacology of the DOR, which is often complex and at times paradoxical.

OBJECTIVE

This review will discuss the existing literature focusing on four aspects: (1) Two DOR subtypes have been postulated based on differences in pharmacological effects of existing DOR-selective ligands. (2) DORs are expressed ubiquitously throughout the body and central nervous system and are, thus, positioned to play a role in a multitude of diseases. (3) DOR expression is often dynamic, with many reports of increased expression during exposure to chronic stimuli, such as stress, inflammation, neuropathy, morphine, or changes in endogenous opioid tone. (4) A large structural variety in DOR ligands implies potential different mechanisms of activating the receptor.

CONCLUSION

The reviewed features of DOR pharmacology illustrate the potential benefit of designing tailored or biased DOR ligands.

Quantification of opioid receptor availability following spontaneous epileptic seizures: correction of [11C]diprenorphine PET data for the partial-volume effect

Previous positron emission tomography (PET) studies in refractory temporal lobe epilepsy (TLE) using the non-selective opioid receptor antagonist [(11)C]diprenorphine (DPN) did not detect any changes in mesial temporal structures, despite known involvement of the hippocampus in seizure generation. Normal binding in smaller hippocampi is suggestive of increased receptor concentration in the remaining grey matter. Correction for partial-volume effect (PVE) has not been used in previous DPN PET studies. Here, we present PVE-corrected DPN-PET data quantifying post-ictal and interictal opioid receptor availability in humans with mTLE. Eight paired datasets of post-ictal and interictal DPN PET scans and eleven test/retest control datasets were available from a previously published study on opioid receptor changes in TLE following seizures (Hammers et al., 2007a). Five of the eight participants with TLE had documented hippocampal sclerosis. Data were re-analyzed using regions of interest and a novel PVE correction method (structural functional synergistic-resolution recovery (SFS-RR); (Shidahara et al., 2012)). Data were denoised, followed by application of SFS-RR, with anatomical information derived via precise anatomical segmentation of the participants' MRI (MAPER; (Heckemann et al., 2010)). [(11)C]diprenorphine volume-of-distribution (VT) was quantified in six regions of interest. Post-ictal increases were observed in the ipsilateral fusiform gyri and lateral temporal pole. A novel finding was a post-ictal increase in [(11)C]DPN VT relative to the interictal state in the ipsilateral parahippocampal gyrus, not observed in uncorrected datasets. As for voxel-based (SPM) analyses, correction for global VT values was essential in order to demonstrate focal post-ictal increases in [(11)C]DPN VT. This study provides further direct human in vivo evidence for changes in opioid receptor availability in TLE following seizures, including changes that were not evident without PVE correction. Denoising, resolution recovery and precise anatomical segmentation can extract valuable information from PET studies that would be missed with conventional post-processing procedures.

From Acupuncture to Interaction between δ-Opioid Receptors and Na (+) Channels: A Potential Pathway to Inhibit Epileptic Hyperexcitability

Epilepsy is one of the most common neurological disorders affecting about 1% of population. Although the precise mechanism of its pathophysiological changes in the brain is unknown, epilepsy has been recognized as a disorder of brain excitability characterized by recurrent unprovoked seizures that result from the abnormal, excessive, and synchronous activity of clusters of nerve cells in the brain. Currently available therapies, including medical, surgical, and other strategies, such as ketogenic diet and vagus nerve stimulation, are symptomatic with their own limitations and complications. Seeking new strategies to cure this serious disorder still poses a big challenge to the field of medicine. Our recent studies suggest that acupuncture may exert its antiepileptic effects by normalizing the disrupted neuronal and network excitability through several mechanisms, including lowering the overexcited neuronal activity, enhancing the inhibitory system, and attenuating the excitatory system in the brain via regulation of the interaction between δ -opioid receptors (DOR) and Na(+) channels. This paper reviews the progress in this field and summarizes new knowledge based on our work and those of others.

Functional imaging: PET

Among various neuroimaging techniques used for the evaluation of children with intractable epilepsy, positron emission tomography (PET) employing various PET tracers plays a very important role, especially in localizing areas of focal cortical dysplasia. This is particularly important in infants, where incomplete myelination may limit the structural information provided by MRI. In children with tuberous sclerosis, PET can differentiate between epileptogenic and nonepileptogenic tubers, previously not thought to be possible with neuroimaging. PET may reveal cortical or subcortical abnormalities in various epilepsy syndromes, such as infantile spasms and Landau-Kleffner syndrome. Various other applications of PET have included the investigation of epileptic networks, secondary epileptic foci, dual pathology, and neuroinflammation. Finally, PET can also be used to evaluate various cognitive processes and their underlying neurological substrates and can help in addressing the issue of brain plasticity and reorganization, related to epilepsy.

The relationship between naloxone-induced cortisol and delta opioid receptor availability in mesolimbic structures is disrupted in alcohol-dependent subjects

Hypothalamic-pituitary-adrenal (HPA) axis responses following naloxone administration have been assumed to provide a measure of opioid receptor activity. Employing positron emission tomography (PET) using the mu opioid receptor (MOR) selective ligand [(11)C] carfentanil (CFN), we demonstrated that cortisol responses to naloxone administration were negatively correlated with MOR availability. In this study, we examined whether naloxone-induced cortisol and adrenocorticotropin (ACTH) responses in 15 healthy control and 20 recently detoxified alcohol-dependent subjects correlated with delta opioid receptor (DOR) availability in 15 brain regions using the DOR-selective ligand [(11)C] methyl-naltrindole (MeNTL) and PET imaging. The day after the scan, cortisol responses to cumulative doses of naloxone were determined. Peak cortisol and ACTH levels and area under the cortisol and ACTH curve did not differ by group. There were negative relationships between cortisol area under curve to naloxone and [(11)C] MeNTL-binding potential (BP(ND)) in the ventral striatum, anterior cingulate, fusiform cortices, temporal cortex, putamen and a trend in the hypothalamus of healthy control subjects. However, in alcohol-dependent subjects, cortisol responses did not correlate with [(11)C]MeNTL BP(ND) in any brain region. Plasma ACTH levels did not correlate with [(11)C]MeNTL BP(ND) in either group. The study demonstrates that naloxone provides information about individual differences in DOR availability in several mesolimbic structures. The data also show that the HPA axis is intimately connected with mesolimbic stress pathways through opioidergic neurotransmission in healthy subjects but this relationship is disrupted during early abstinence in alcohol-dependent subjects.

Current research on opioid receptor function

The use of opioid analgesics has a long history in clinical settings, although the comprehensive action of opioid receptors is still less understood. Nonetheless, recent studies have generated fresh insights into opioid receptor-mediated functions and their underlying mechanisms. Three major opioid receptors (μ-opioid receptor, MOR; δ-opioid receptor, DOR; and κ-opioid receptor, KOR) have been cloned in many species. Each opioid receptor is functionally sub-classified into several pharmacological subtypes, although, specific gene corresponding each of these receptor subtypes is still unidentified as only a single gene has been isolated for each opioid receptor. In addition to pain modulation and addiction, opioid receptors are widely involved in various physiological and pathophysiological activities, including the regulation of membrane ionic homeostasis, cell proliferation, emotional response, epileptic seizures, immune function, feeding, obesity, respiratory and cardiovascular control as well as some neurodegenerative disorders. In some species, they play an essential role in hibernation. One of the most exciting findings of the past decade is the opioid-receptor, especially DOR, mediated neuroprotection and cardioprotection. The upregulation of DOR expression and DOR activation increase the neuronal tolerance to hypoxic/ischemic stress. The DOR signal triggers (depending on stress duration and severity) different mechanisms at multiple levels to preserve neuronal survival, including the stabilization of homeostasis and increased pro-survival signaling (e.g., PKC-ERK-Bcl 2) and antioxidative capacity. In the heart, PKC and KATP channels are involved in the opioid receptor-mediated cardioprotection. The DOR-mediated neuroprotection and cardioprotection have the potential to significantly alter the clinical pharmacology in terms of prevention and treatment of life-threatening conditions like stroke and myocardial infarction. The main purpose of this article is to review the recent work done on opioids and their receptor functions. It shall provide an informative reference for better understanding the opioid system and further elucidation of the opioid receptor function from a physiological and pharmacological point of view.

Positron emission tomography imaging of mu- and delta-opioid receptor binding in alcohol-dependent and healthy control subjects

BACKGROUND

The endogenous opioid system plays a significant role in alcohol dependence. The goal of the current study was to investigate regional brain mu-opioid receptor (MOR) and delta-opioid receptor (DOR) availability in recently abstinent alcohol-dependent and age-matched healthy control men and women with positron emission tomography (PET) imaging.

METHODS

Alcohol-dependent subjects completed an inpatient protocol, which included medically supervised withdrawal and PET imaging on day 5 of abstinence. Control subjects completed PET imaging following an overnight stay. PET scans with the MOR-selective ligand [(11)C]carfentanil (CFN) were completed in 25 alcohol-dependent and 30 control subjects. Most of these same subjects (20 alcohol-dependent subjects and 18 controls) also completed PET scans with the DOR-selective ligand [(11)C]methylnaltrindole (MeNTL).

RESULTS

Volumes of interest and statistical parametric mapping analyses indicated that alcohol-dependent subjects had significantly higher [(11)C]CFN binding potential (BP(ND) ) than healthy controls in multiple brain regions including the ventral striatum when adjusting for age, gender, and smoking status. There was an inverse relationship between [(11)C]CFN BP(ND) and craving in several brain regions in alcohol-dependent subjects. Groups did not differ in [(11)C]MeNTL BP(ND) ; however, [(11)C]MeNTL BP(ND) in caudate was positively correlated with recent alcohol drinking in alcohol-dependent subjects.

CONCLUSIONS

Our observation of higher [(11)C]CFN BP(ND) in alcohol-dependent subjects can result from up-regulation of MOR and/or reduction in endogenous opioid peptides following long-term alcohol consumption, dependence, and/or withdrawal. Alternatively, the higher [(11)C]CFN BP(ND) in alcohol-dependent subjects may be an etiological difference that predisposed these individuals to alcohol dependence or may have developed as a result of increased exposure to childhood adversity, stress, and other environmental factors known to increase MOR. Although the direction of group differences in [(11)C]MeNTL BP(ND) was similar in many brain regions, differences did not achieve statistical significance, perhaps as a result of our limited sample size. Additional research is needed to further clarify these relationships. The finding that alcohol-dependent subjects had higher [(11)C]CFN BP(ND) is consistent with a prominent role of the MOR in alcohol dependence.

PET in Epilepsy and Other Seizure Disorders

Positron emission tomography (PET) imaging has been widely used in the evaluation and management of patients with seizure disorders. The ability of PET to measure cerebral function makes it ideal for studying the neurophysiologic correlates of seizure activity during ictal and interictal states. PET imaging is also useful for evaluating patients before surgical interventions to determine the best surgical method and maximize outcomes. Thus, PET will continue to play a major role not only in the clinical arena but in further investigations of the pathogenesis and management of various seizure disorders. This article reviews the literature regarding the current uses and indications for PET in the study and management of patients with seizure disorders.

PET imaging in pediatric neuroradiology: current and future applications

Molecular imaging with positron emitting tomography (PET) is widely accepted as an essential part of the diagnosis and evaluation of neoplastic and non-neoplastic disease processes. PET has expanded its role from the research domain into clinical application for oncology, cardiology and neuropsychiatry. More recently, PET is being used as a clinical molecular imaging tool in pediatric neuroimaging. PET is considered an accurate and noninvasive method to study brain activity and to understand pediatric neurological disease processes. In this review, specific examples of the clinical use of PET are given with respect to pediatric neuroimaging. The current use of co-registration of PET with MR imaging is exemplified in regard to pediatric epilepsy. The current use of PET/CT in the evaluation of head and neck lymphoma and pediatric brain tumors is also reviewed. Emerging technologies including PET/MRI and neuroreceptor imaging are discussed.

Preparation and radiosynthesis of [18F]FE@CFN (2-[18F]fluoroethyl 4-[N-(1-oxopropyl)-N-phenylamino]-1-(2-phenylethyl)-4-piperidinecarboxylate): a potential μ-opioid receptor imaging agent

PET imaging of the μ-opioid receptor (OR) is still restricted to [11C]carfentanil ([11C]CFN) but its use is limited due to its short half-life and high agonistic potency. Recently, the radiosynthesis of [18F]fluoroalkyl esters of CFN was proposed, unfortunately yielding products not suitable for human PET due to their low specific activities. Therefore, our rationale was to develop a reliable radiosynthesis of a [18F]fluoroethylated CFN derivative overcoming these drawbacks.

The [18F]fluoroethyl ester of carfentanil, [18F]FE@CFN (2-[18F]fluoroethyl 4-[N-(1-oxopropyl)-N-phenylamino]-1-(2-phenylethyl)-4-piperidinecarboxylate), and its corresponding inactive standard compound were prepared. Purification of [18F]FE@CFN was achieved via a simple solid phase extraction method. [18F]FE@CFN was prepared with excellent purity (> 98%) and sufficient yields. Specific activity surpassed the level required for safe administration. We therefore conclude that our simplified synthesis of [18F]FE@CFN, for the first time, overcomes the shortcomings of [11C]CFN and the previously suggested alternatives, namely, (1) longer half-life; (2) easy production and (3) adequate specific activity, should make a wider application possible. Hence, [18F]FE@CFN may become a valuable PET tracer for the imaging of the μ-OR in human brain and heart.

PET and SPECT in epilepsy: a critical review

Molecular imaging with ictal and interictal single-photon emission computed tomography (SPECT) as well as positron emission tomography (PET) rank among the established functional imaging tests for the presurgical evaluation of epileptic onset zone in patients with intractable partial epilepsy. In temporal lobe epilepsy the sensitivity of these methods was shown to be excellent, in particular if a multimodal platform is used, which combines the functional imaging with the additional morphological information of magnetic resonance imaging (MRI), but was lower in extra temporal lobe epilepsy. Functional imaging with SPECT and PET reflects seizure related changes of cerebral perfusion, glucose-metabolism and neuroreceptor status. In this review the usefulness of SPECT and PET imaging in clinical routine in epilepsy as well as the role of different neuroreceptor PET-tracer, which were used in epilepsy are discussed. The use of perfusion SPECT tracer allows the investigation of ictal activations, but the low temporal resolution of ictal perfusion SPECT often results in the detection of both the ictal onset zone as well as the propagation pathways, an area that has not always need to be resected in order to render a patient seizure free. The additional use of interictal PET with fluorine-18 fluorodeoxyglucose which measures regional cerebral metabolism or interictal perfusion SPECT enhance the informational value of ictal SPECT and were shown to be important tools to better define the ictal onset and surround inhibition zones. In recent years PET imaging of different cerebral neuroreceptor-systems inter alia GABA(A) receptors, serotonin receptors (5-HT(1A)), opioid receptors as well as dopamine receptors was used to investigate the neurochemical basis of epilepsy, the role of these neurotransmitters for the epileptogenesis as well as the spread of epileptic activity during seizures and partially entered in clinical routine. Currently some of these radioligands are also used to investigate new treatment approaches.

Imaging of opioid receptors in the central nervous system

In vivo functional imaging by means of positron emission tomography (PET) is the sole method for providing a quantitative measurement of mu-, kappa and delta-opioid receptor-mediated signalling in the central nervous system. During the last two decades, measurements of changes to the regional brain opioidergic neuronal activation--mediated by endogenously produced opioid peptides, or exogenously administered opioid drugs--have been conducted in numerous chronic pain conditions, in epilepsy, as well as by stimulant- and opioidergic drugs. Although several PET-tracers have been used clinically for depiction and quantification of the opioid receptors changes, the underlying mechanisms for regulation of changes to the availability of opioid receptors are still unclear. After a presentation of the general signalling mechanisms of the opioid receptor system relevant for PET, a critical survey of the pharmacological properties of some currently available PET-tracers is presented. Clinical studies performed with different PET ligands are also reviewed and the compound-dependent findings are summarized. An outlook is given concluding with the tailoring of tracer properties, in order to facilitate for a selective addressment of dynamic changes to the availability of a single subclass, in combination with an optimization of the quantification framework are essentials for further progress in the field of in vivo opioid receptor imaging.

Opioid Imaging

Many breakthrough scientific discoveries have been made using opioid imaging. Developments include the application of ever higher resolution whole-brain positron emission tomography (PET) scanners, the availability of several radioligands, the combination of PET with advanced structural imaging, advances in modeling macroparameters of PET ligand binding, and large-scale statistical analysis of imaging datasets. Suitable single-photon emission computed tomography (SPECT) tracers are lacking, but with the increase in the number of available PET (or PET/CT) cameras and cyclotrons thanks to the clinical successes of PET in oncology, PET may become widespread enough to overcome this. In the coming decade, there should be a more widespread application of the available techniques to patients and an impact in clinical medicine.

Effects of LiCl/pilocarpine-induced status epilepticus on rat brain mu and benzodiazepine receptor binding: regional and ontogenetic studies

Neurochemical studies document involvement of benzodiazepine (BDZ) and mu opioid receptors in seizure development and their possible age-related role during epileptogenesis. To study developmental changes of this role LiCl/pilocarpine status epilepticus (SE) was induced in P12, P25 and/or adult rats. This SE leads to epilepsy in all adult and subpopulation of immature rats. Using in vitro autoradiography, benzodiazepine (BDZ) and mu opioid receptor binding was evaluated 1 week (early phase of epileptogenesis) and 3 months (chronic phase) after SE in 27 brain structures involved in seizure generation and spread (amygdala, hippocampus, basal ganglia and thalamic nuclei). The pattern of receptor binding changes was related to the age at SE, interval after SE and to brain structures. Enhanced BDZ binding was found 1 week after SE in many cortical areas in P12 and also in the amygdala complex and dentate gyrus in both P12 and P25. No changes of BDZ binding occurred in adults at that time, but 3 months after SE a decrease of binding appeared in all evaluated areas in both adult and P25 but not P12 rats. This decrease did not reflect neuronal loss. mu opioid receptors were less significantly affected but clear tendency to decrease binding occurred in adult rats in various cortical, amygdala and thalamic regions early after SE. Changes were less expressed in immature rats. Our data support the hypothesis that age-related changes of receptor properties may participate in different functional consequences of SE including epileptogenesis (more common in older age groups) and behavioral changes.

Indium-Labeled Macrocyclic Conjugates of Naltrindole: High-Affinity Radioligands for In Vivo Studies of Peripheral δ Opioid Receptors

We have identified a series of hydrophilic indium-labeled DOTA and DO3A conjugates of naltrindole (NTI) that are suited to in vivo studies of peripheral delta opioid receptors. Indium(III) complexes, linked to the indole nitrogen of NTI by six- to nine-atom spacers, display high affinities (0.1-0.2 nM) and excellent selectivities for binding to delta sites in vitro. The [111In]-labeled complexes can be prepared in good isolated yields ( approximately 65%) with high specific radioactivities (>3300 mCi/mumol). The spacers serve as pharmacokinetic modifiers, and log D7.4 values range from -2.74 to -1.79. These radioligands exhibit a high level of specific binding (75-94%) to delta opioid receptors in mouse gut, heart, spleen, and pancreas in vivo. Uptakes of radioactivity are saturable by the non-radioactive complexes, inhibited by naltrexone, and blocked by NTI. Thus, these radiometal-labeled NTI analogues warrant further study by single-photon emission computed tomography.

Lung cancer: New surgical approaches

Over the past two decades, many surgical specialties have seen a dramatic shift from large, open operations with wide incisions towards more-minimal incisions and less-invasive procedures. Surgical techniques for lung cancer are no exception, and today, video-assisted thoracic surgical lobectomies are being performed with increasing frequency in large-volume thoracic practices. Despite these new surgical techniques, however, the most substantial innovations that have changed surgical outcomes occurred away from the operative theatre. In lung cancer, in particular, the last 20 years have witnessed the clinical debut of more sophisticated, more elegant and more accurate imaging modalities for improved screening, diagnostic and staging, such as the spiral CT scan, PET scan, PET/CT and the endobronchial ultrasound machine. This technology has been complimented by more targeted chemotherapeutic regimens, novel methods of administering more accurate and more concentrated doses of radiation therapy, and innovative local excisional methods, such as the Cyberknife and radiofrequency ablation. The result has been that surgical excision, although remaining the most effective local therapeutic modality in early-stage lung cancer, is no longer the 'lone ranger' treatment, but rather is part of a complex mosaic of multimodality therapy. As scientific advances continue to be translated into the clinic, this trend will inexorably continue with the advent of a molecular staging system using molecular markers and tumour profiling, which ultimately could enhance our ability to predict tumour chemosensitivity. In this brave new world, however, complete surgical resection of the lung cancer will continue to be critical.

PET tracer technology for monitoring focal epilepsies

Studies using positron emission tomography (PET) have advanced our pathophysiological and biochemical understanding of focal and generalized epilepsies. H(2) (15)O PET allows quantification of cerebral blood flow and (18)F-fluorodeoxyglucose-PET quantification of cerebral glucose metabolism. Neurotransmitters are directly responsible for modulating synaptic activity and newer PET tracers can provide information about synaptic activity and specific ligand-receptor relationships, which are important for epileptogenesis and the spread of epileptic activity.

Upregulation of opioid receptor binding following spontaneous epileptic seizures

Animal and limited human data suggest an important anticonvulsant role for opioid peptides and their receptors. We aimed to provide direct human in vivo evidence for changes in opioid receptor availability following spontaneous seizures. We scanned nine patients within hours of spontaneous temporal lobe seizures and compared their postictal binding of the non-subtype selective opioid receptor PET radioligand [11C]diprenorphine (DPN), quantified as a volume-of-distribution (VD), with interictal binding and with binding changes in 14 healthy controls, controlling for a range of behavioural variables associated with opioid action. A regionally specific increase of opioid receptor availability was evident in the temporal pole and fusiform gyrus ipsilateral to the seizure focus following seizures (Z 5.01, P < 0.001, 16 432 mm3). Within this region, there was a negative correlation between VD and log10 time since last seizure (r = -0.53, P < 0.03), compatible with an early increase and gradual return to baseline. [11C]DPN VD did not undergo systematic changes between time points in controls. This study provides direct human in vivo evidence for changes in opioid receptor availability over a time course of hours following spontaneous seizures, emphasizing an important role of the opioid system in seizure control.

Opioid Imaging

Many breakthrough scientific discoveries have been made using opioid imaging, particularly in the fields of pain, addiction and epilepsy research. Recent developments include the application of ever higher resolution whole-brain positron emission tomography (PET) scanners, the availability of several radioligands, the combination of PET with advanced structural imaging, advances in modeling macroparameters of PET ligand binding, and large-scale statistical analysis of imaging datasets. Suitable single-photon emission computed tomography (SPECT) tracers are lacking, but with the increase in the number of available PET (or PET/CT) cameras and cyclotrons thanks to the clinical successes of PET in oncology, PET may become widespread enough to overcome this limitation. In the coming decade, we hope to see a more widespread application of the techniques developed in healthy volunteers to patients and more clinical impact of opioid imaging.

Down-regulation of delta-opioid receptors in Na+/H+ exchanger 1 null mutant mouse brain with epilepsy

Mice lacking Na+/H+ exchanger 1 (NHE1) show a unique epilepsy phenotype although the underlying mechanisms remain unclear. Since expression of delta-opioid receptor (DOR) may be involved in control of epileptic activity, we conducted immunohistochemistry and autoradiography to investigate whether DOR expression is dys-regulated in the brain of NHE1 null mouse. Immunohistochemistry showed a decline in DOR expression in hippocampus and cortex. Autoradiographic results confirmed that the density of DOR was decreased in most cortical and hippocampal regions such as striate and temporal cortex, hippocampal CA1 and CA3 regions (reduced by 27.7 +/- 6.4%, 29.4 +/- 5.1%, 40.7 +/- 4.4% and 20.6 +/- 5.7%, respectively, P < 0.05). These data demonstrate that NHE1 null mutation leads to a reduction of DOR expression in the cortical and hippocampal regions, which provides a new clue for the genesis of epilepsy.

Neuroimaging of epilepsy: therapeutic implications

Neuroimaging has important applications in the diagnosis and treatment of patients with seizures and epilepsy. Having replaced computed tomography (CT) in many situations, MRI is the preferred imaging technique for patients with epilepsy. Advances in radionuclide-based techniques such as single-photon emission CT/positron emission tomography and electromagnetic source imaging with magnetoencephalography are providing new insights into the pathophysiology of epilepsy. In addition, techniques such as magnetic resonance spectroscopy are beginning to impact treatment. In this review, I discuss how these techniques are used in clinical practice but more importantly, how imaging findings play an increasing role in neurotherapeutics.

Imaging structure and function in refractory focal epilepsy

Over the past decade there have been many advances in data acquisition and analysis for structural and functional neuroimaging of people with epilepsy. New imaging sequences and analysis techniques have increased the resolution of images such that underlying structural pathology can be seen in many patients with "cryptogenic" epilepsy. When an epileptogenic lesion is present, antiepileptic drugs alone rarely prevent seizures. However, the success of surgical treatment is improved when a structural lesion has been identified. Lesions might not overlap with the area of the cortex generating seizures and may continue into areas sustaining normal functions. To prevent postsurgical morbidity, the spatial relation between functionally important areas and the epileptogenic lesion must be assessed before surgery. In this review we describe the potential of different neuroimaging techniques to show lesions, assess neuronal function, and assist with the prognosis of postsurgical outcome in patients with refractory focal epilepsy.

PET in seizure disorders

PET imaging has been widely used in the evaluation and management of patients with seizure disorders. The ability of PET to measure cerebral function is ideal for studying the neurophysiologic correlates of seizure activity during both ictal and interictal states. PET imaging is also valuable for evaluating patients before surgical interventions to determine the best surgical method and maximize outcomes. PET will continue to play a major role, not only in the clinical arena, but also in investigating the pathogenesis and treatment of various seizure disorders.

Qualitative and quantitative imaging of the hippocampus in mesial temporal lobe epilepsy with hippocampal sclerosis

MR imaging allows the in vivo detection of hippocampal sclerosis (HS) and has been instrumental in the delineation of the syndrome of mesial temporal lobe epilepsy with HS (mTLE-HS). MR features of HS include hippocampal atrophy with an increased T2 signal. Quantitative MR imaging accurately reflects the degree of hippocampal damage.Ictal single photon emission computed tomography (SPECT) in mTLE-HS shows typical perfusion patterns of ipsilateral temporal lobe hyperperfusion, and ipsilateral frontoparietal and contralateral cerebellar hypoperfusion. Interictal 18fluoro-2-deoxyglucose positron emission tomography (PET) shows multiregional hypometabolism, involving predominantly the ipsilateral temporal lobe. 11C-flumazenil PET shows hippocampal decreases in central benzodiazepine receptor density. Future strategies to study the etiology and pathogenesis of HS should include longitudinal MR imaging studies,MR studies in families with epilepsy and febrile seizures, stratification for genetic background, coregistration with SPECT and PET, partial volume correction and statistical parametric mapping analysis of SPECT and PET images.

Flumazenil positron emission tomography and other ligands for functional imaging

Most PET receptor studies in idiopathic generalized epilepsy conducted to date include only small numbers of patients and should be interpreted with caution. Differences between earlier and later studies can largely be explained by different inclusion criteria and improving methodology. The finding of some increase of GABAA receptor binding in IGE has a potential pathologic basis in microdysgenesis. Future studies aiming to elucidate the pathophysiology of IGEs may benefit from the use of subtype-specific opioid ligands, available now, and GABAB ligands, if and when they become available.

Central poststroke pain and reduced opioid receptor binding within pain processing circuitries: a [11C]diprenorphine PET study

Based on concepts that endogenous opioids participate in neural transmission of pain, the present study in central poststroke pain (CPSP) patients investigated changes in opioid receptor (OR) binding in neural structures centrally involved in the processing of pain. Five patients with central pain after lesions in the brain stem, thalamus or parietal cortex and twelve healthy volunteers underwent a [11C]diprenorphine positron emission tomography study. Binding potentials were calculated using a reference region model in all subjects. Statistical parametric mapping was applied for t-statistical analysis on voxel-basis. Binding potential values for each individual were extracted from a volume of interest at each identified significant peak. Spectral analysis was applied for quantification of global values. Significant regional reduced 11C-diprenorphine binding (corrected for multiple tests) was detected in contralateral thalamus, parietal, secondary somatosensory, insular and lateral prefrontal cortices, and along the midline in anterior cingulate, posterior cingulate and midbrain gray matter. Individual extracted binding values disclosed a reduced binding in these regions in all patients independent from the particular lesion site. The poststroke pain syndrome is associated with a characteristic pattern of reduced OR binding within the neural circuitry processing pain. It is suggested that an imbalance of excitatory-inhibitory mechanisms in certain brain structures, as evidenced in decreased [11C]diprenorphine binding, is one of the causes or the consequences of poststroke pain.

Pain activation of human supraspinal opioid pathways as demonstrated by [11C]-carfentanil and positron emission tomography (PET)

The role of the supraspinal endogenous opioid system in pain processing has been investigated in this study using positron emission tomography imaging of [11C]-carfentanil, a synthetic, highly specific mu opioid receptor (mu-OR) agonist. Eight healthy volunteers were studied during a baseline imaging session and during a session in which subjects experienced pain induced by applying capsaicin topically to the dorsal aspect of the left hand. A pain-related decrease in brain mu-OR binding was observed in the contralateral thalamus consistent with competitive binding between [11C]-carfentanil and acutely released endogenous opioid peptides. This decrease varied directly with ratings of pain intensity. These results suggest that the supraspinal mu-opioid system is activated by acute pain and thus may play a substantial role in pain processing and modulation in pain syndromes.

Evaluation of opioid peptide and muscarinic receptors in human epileptogenic neocortex: an autoradiography study

PURPOSE

The main goal of the present study was to evaluate possible alterations in opioid peptide and muscarinic receptors in human neocortical epileptic focus and the surrounding area removed from patients with pharmacologically resistant epilepsy and epilepsy secondary to cerebral lesion by tumor or other causes.

METHODS

In vitro quantitative autoradiography experiments were carried out to label mu, delta, and muscarinic receptors of neocortical epileptic focus and surrounding area obtained from patients with pharmacologically resistant primary epilepsy and epilepsy caused by tumors and angioma cavernosa, and compared with neocortex obtained from patients with dementia and tumors without epilepsy.

RESULTS

The mu receptor levels were lower in surrounding areas (-46%). The delta receptor binding was reduced in epileptic focus obtained from patients with epilepsy secondary to cerebral lesion (-25%) and surrounding areas (-31%). In contrast, muscarinic receptor levels were higher in the focus from patients with primary epilepsy (layers I-II, 52%; layers III-IV, 44%; layers V-VI, 36%).

CONCLUSIONS

It is suggested that the increased muscarinic receptors in the epileptic focus and the decreased mu and delta receptors in the surrounding area are associated with the initiation and propagation of seizure activity in human epileptogenic neocortex.

Impaired benzodiazepine receptor binding in peri-lesional cortex of patients with symptomatic epilepsies studied by [(11)C]-flumazenil PET

Individual benzodiazepine receptor (BZR) binding of peri-lesional cortex was investigated in symptomatic epilepsies. Eleven patients aged 19-44 years were studied whose diagnosis was established by medical history, clinical, electroencephalographic, and magnetic resonance imaging (MRI) findings. Three-dimensional [11C]-flumazenil (FMZ) positron emission tomography and MRI scans were obtained and coregistered. Lesions (five low-grade brain tumours, one AV malformation, one cavernoma, one cystic lesion of unknown aetiology, one traumatic brain injury, one post-operative and one post-haemorrhagic defect) were outlined on individual MRI scans. Adjacent to those lesions, and in homologous contralateral structures, FMZ binding was analysed in four pairs of cortical 9 x 9-mm regions of interest (ROIs) placed on transaxial and coronal slices, respectively, as well as in the lesion volume and its mirror region. Percentage asymmetry ratios were calculated and those at or outside the 90-110% range were operationally defined significant. Peri-lesional FMZ binding asymmetries ranged from 70 to 125%, lesional asymmetries from 38 to 82%. Only one patient showed no significant change, whilst nine exhibited significant reductions of FMZ binding in at least one ROI (3 x 1, 4 x 2, 1 x 3, 1 x 4), and significant increases were observed in two ROIs of another patient. Therefore, peri-lesional disturbances of BZR binding are common but variable in location. Because a close correlation between regional decreases in FMZ binding and spiking activity was recently demonstrated in neocortical epilepsies, abnormal peri-lesional FMZ binding may bear some relation to the mechanisms of epileptogenesis in symptomatic epilepsies.

Functional and anatomical localization of mu opioid receptors in the striatum, amygdala, and extended amygdala of the nonhuman primate

The subregional distribution of mu opioid receptors and corresponding G-protein activation were examined in the striatum, amygdala, and extended amygdala of cynomolgus monkeys. The topography of mu binding sites was defined using autoradiography with [(3)H]DAMGO, a selective mu ligand. In adjacent sections, the distribution of receptor-activated G proteins was identified with DAMGO-stimulated guanylyl 5'(gamma-[(35)S]thio)triphosphate ([(35)S]GTPgammaS) binding. Within the striatum, the distribution of [(3)H]DAMGO binding sites was characterized by a distinct dorsal-ventral gradient with a higher concentration of binding sites at more rostral levels of the striatum. [(3)H]DAMGO binding was further distinguished by the presence of patch-like aggregations within the caudate, as well as smaller areas of very dense receptor binding sites, previously identified in human striatum as neurochemically unique domains of the accumbens and putamen (NUDAPs). The amygdala contained the highest concentration of [(3)H]DAMGO binding sites measured in this study, with the densest levels of binding noted within the basal, accessory basal, paralaminar, and medial nuclei. In the striatum and amygdala, the distribution of DAMGO-stimulated G-protein activation largely corresponded with the distribution of mu binding sites. The central and medial nuclei of the amygdala, however, were notable exceptions. Whereas the concentration of [(3)H]DAMGO binding sites in the central nucleus of the amygdala was very low, the concentration of DAMGO-stimulated G-protein activation in this nucleus, as measured with [(35)S]GTPgammaS binding, was relatively high compared to other portions of the amygdala containing much higher concentrations of [(3)H]DAMGO binding sites. The converse was true in the medial nucleus, where high concentrations of binding sites were associated with lower levels of DAMGO-stimulated G-protein activation. Finally, [(3)H]DAMGO and [(35)S]GTPgammaS binding within the amygdala, particularly the medial nucleus, formed a continuum with the substantia innominata and bed nucleus of the stria terminalis, supporting the concept of the extended amygdala in primates.