[Show abstract][Hide abstract] ABSTRACT: In vivo imaging and quantification of amyloid-β plaque (Aβ) burden in small-animal models of Alzheimer's disease (AD) is a valuable tool for translational research such as developing specific imaging markers and monitoring new therapy approaches. Methodological constraints such as image resolution of positron emission tomography (PET) and lack of suitable AD models have limited the feasibility of PET in mice. In this study, we evaluated a feasible protocol for PET imaging of Aβ in mouse brain with [(11)C]PiB and specific activities commonly used in human studies. In vivo mouse brain MRI for anatomical reference was acquired with a clinical 1.5 T system. A recently characterized APP/PS1 mouse was employed to measure Aβ at different disease stages in homozygous and hemizygous animals. We performed multi-modal cross-validations for the PET results with ex vivo and in vitro methodologies, including regional brain biodistribution, multi-label digital autoradiography, protein quantification with ELISA, fluorescence microscopy, semi-automated histological quantification and radioligand binding assays. Specific [(11)C]PiB uptake in individual brain regions with Aβ deposition was demonstrated and validated in all animals of the study cohort including homozygous AD animals as young as nine months. Corresponding to the extent of Aβ pathology, old homozygous AD animals (21 months) showed the highest uptake followed by old hemizygous (23 months) and young homozygous mice (9 months). In all AD age groups the cerebellum was shown to be suitable as an intracerebral reference region. PET results were cross-validated and consistent with all applied ex vivo and in vitro methodologies. The results confirm that the experimental setup for non-invasive [(11)C]PiB imaging of Aβ in the APP/PS1 mice provides a feasible, reproducible and robust protocol for small-animal Aβ imaging. It allows longitudinal imaging studies with follow-up periods of approximately one and a half years and provides a foundation for translational Alzheimer neuroimaging in transgenic mice.
[Show abstract][Hide abstract] ABSTRACT: The Val(108/158)Met polymorphism of the catechol-O-methyltransferase gene (COMT) is known to interact with the function of various neuroreceptor systems in the brain. We have recently shown by post-mortem receptor autoradiography that the number of mu-opioid (MOP) receptor binding sites depends on the number of COMT Met(108/158) alleles in distinct human brain regions. We now investigated COMT Val(108/158)Met related levels of the MOP receptor protein and its endogenous ligands met-enkephalin and beta-endorphin in the human frontal cortex, thalamus and basal ganglia. Semiquantitative immunostaining and in situ hybridization were applied in a cohort of 17 human brain tissues from healthy donors. MOP receptor protein levels paralleled previous ligand binding results with a significantly higher MOP receptor expression in the mediodorsal nucleus of the thalamus of COMT Met(108/158) allele carriers. Also met-enkephalin peptide levels correlated with the genotype in this structure, with the lowest expression in COMT Met(108/158) homozygous individuals. Beta-endorphin was not detectable in the cortex, basal ganglia or thalamus, and therefore is unlikely to contribute to changes of the MOP receptor system. These results confirm the impact of the COMT Val(108/158)Met polymorphism on the MOP receptor system and may support the hypothesis of an enkephalin related turnover of MOP receptors at least in some brain structures.
No preview · Article · Nov 2011 · Neuroscience Letters
[Show abstract][Hide abstract] ABSTRACT: Over the last decades, functional imaging studies have fostered our knowledge of cerebral pain processing in humans. A lively interest has been focussing on possible opioidergic mechanisms of pain transmission and modulation. Today, reliable knowledge of the in vivo distribution of opioid receptors in healthy human subjects is available from positron emission tomography (PET) studies of opioidergic neurotransmission. Gender dependent differences in receptor distribution and ligand metabolism have been demonstrated. Moreover, an increasing number of studies are reporting alterations in receptor distribution patterns in states involving painful diseases. Various acute painful challenges have also been shown to induce measurable changes in receptor availability in multiple brain areas. The perigenual anterior cingulate cortex (ACC) has been identified as one brain region with a major impact on opioidergic pain modulation. Thereby, the ACC apparently executes cortical top-down control on brainstem structures in (exogenous) pharmacological opioid analgesia. In addition, accumulating evidence suggests that non-pharmacological treatment approaches also utilize similar endogenous opioid dependent pathways to exert pain modulation. This article summarizes our current knowledge of PET studies of the opioidergic system and outlines future perspectives.
[Show abstract][Hide abstract] ABSTRACT: Zusammenfassung In den letzten Jahrzehnten haben funktionelle Bildgebungsstudien unser Verständnis hinsichtlich der zentralnervösen Schmerzverarbeitung
beim Menschen deutlich verbessert. Besonderes Interesse wurde dabei auf opioiderge Mechanismen der Schmerztransmission und
Inhibition gerichtet. Hierdurch stehen heute umfassende Erkenntnise zur In-vivo-Verteilung von Opioidrezeptoren beim Menschen
zur Verfügung, und geschlechtsspezifische Unterschiede konnten gezeigt werden. Eine zunehmende Anzahl von Studien hat zudem
über veränderte Opioidrezeptorverteilungsmuster bei klinischen Schmerzzuständen berichtet. Durch experimentelle Schmerzreize
konnten ferner messbare Veränderungen der Opioidrezeptorbindung in multiplen Hirnarealen induziert werden. Der perigenuale
anteriore zinguläre Kortex (ACC) wurde hierbei als bedeutende Hirnregion im Rahmen der opioidergen Schmerzinhibition identifiziert.
Dieses Hirnareal beeinflusst offensichtlich durch kortikale Top-down-Mechanismen im Rahmen der opioidergen Analgesie die Funktion
von Hirnstammregionen. Zudem ergeben sich zunehmend Hinweise, dass auch durch nichtpharmakologische Therapieansätze ähnliche
endogene Opioidsignalwege aktiviert werden und hierdurch eine Schmerzinhibition ausgelöst werden kann. Diese Übersichtsarbeit
fasst den aktuellen Stand zu PET-Studien des opoidergen Systems zusammen und zeigt Perspektiven auf.
[Show abstract][Hide abstract] ABSTRACT: Three potent and selective (11)C-labelled NR2B antagonists have been synthesized and evaluated as PET ligands. The brain uptake of the compounds in mice varied substantially and was dominated by metabolism. One compound was found to have favourable uptake and retention in the brain, as well as a binding pattern consistent with the expression of the target receptor as measured by in vitro autoradiography. However, the metabolism of the compounds tested was too rapid to allow for in vivo imaging. (c) 2006 Elsevier Ltd. All rights reserved.
No preview · Article · Oct 2006 · Bioorganic & Medicinal Chemistry
[Show abstract][Hide abstract] ABSTRACT: The morphinane-derivate 6-O-(2-[(18)F]fluoroethyl)-6-O-desmethyldiprenorphine ([(18)F]FDPN) is a nonselective opioid receptor ligand currently used in positron emission tomography (PET). Correction for plasma metabolites of the arterial input function is necessary for quantitative measurements of [(18)F]FDPN binding. A study was undertaken to investigate if there are gender dependent differences in the rate of metabolism of [(18)F]FDPN.
The rate of metabolism of [(18)F]FDPN was mathematically quantified by fitting a bi-exponential function to each individual's dynamic metabolite data.
No statistically significant gender differences were found for age, weight, body mass index or dose. However, significant differences (p < 0.01) in two of the four kinetic parameters describing the rate of metabolism were found between the two groups, with women metabolizing [(18)F]FDPN faster than men. These differences were found in the contribution of the fast and slow kinetic components of the model describing the distribution of radioactive species in plasma, indicating a higher rate of enzyme-dependent degradation of [(18)F]FDPN in women than in men.
The findings reinforce the need for individualized metabolite correction during [(18)F]FDPN-PET scans and also indicate that in certain cases, grouping according to gender could be performed in order to minimize methodological errors of the input function prior to kinetic analyses.
[Show abstract][Hide abstract] ABSTRACT: The synthesis, evaluation, and molecular modeling of a series of 18F-labeled 4-anilidopiperidines with high affinities for the mu-opioid receptor (mu-OR) are reported. On the basis of the high brain uptake and selective retention in brain regions that contain a high concentration of the mu-OR, combined with a good metabolic stability, [18F]fluoro-pentyl carfentanil ([18F]4) and 2-(+/-)[18F]fluoropropyl-sufentanil ([18F]6) were selected as the lead compounds for further evaluation. The binding affinity to the human mu-OR was 0.74 and 0.13 nM for [18F]4 and [18F]6, respectively. In vitro autoradiography of [18F]4 and [18F]6 on rat brain sections produced patterns in accordance with the known distribution of mu-OR expression. Structure-activity relationships of the fluorinated compounds are discussed with respect to the interaction with an activated-state model of the mu-OR. Taken together, the in vivo and in vitro data indicate that [18F]4 and [18F]6 hold promise for studying the mu-opioid receptor in humans by means of positron emission tomography.
Full-text · Article · Jan 2006 · Journal of Medicinal Chemistry
[Show abstract][Hide abstract] ABSTRACT: Recent data from [(11)C]carfentanil ligand-PET indicate that in the human brain, the availability of mu-opioid (MOP) receptor binding sites is affected by the Val(108/158)Met polymorphism of the catechol-O-methyltransferase (COMT) gene. This prompted us to validate the impact of COMT Val(108/158)Met on MOP receptors in human post-mortem brain. [(3)H]DAMGO receptor autoradiography was performed in frontal cortex, basal ganglia, thalamus and cerebellum (8 Met/Met, 6 Met/Val, 3 Val/Val). With respect to genotype, numbers of MOP binding sites in COMT Met(108/158) homozygous and Val(108/158)Met heterozygous cases were higher than in Val(108/158) homozygous. Differences were significant in the caudate nucleus (Val/Met vs. Val/Val), nucleus accumbens (Val/Met vs. Val/Val) and the mediodorsal nucleus of the thalamus (Met/Met vs. Val/Val). In the thalamus, this was corroborated by DAMGO-stimulated [(35)S]GTPgammaS autoradiography. Moreover, stepwise multiple regression taking into account various covariables allowed to confirm the COMT genotype as the most predictive factor in this structure. As a mechanism how COMT might exert its action on MOP receptors, it has been suggested that at least in striatopallidal circuits COMT Val(108/158)Met impacts on enkephalin, which is capable of reciprocally regulating MOP receptor expression. Thus, we assessed preproenkephalin mRNA by in situ hybridization. In the striatum, mRNA levels were significantly higher in COMT Met(108/158) homozygous cases indicating that MOP binding sites and enkephalin are regulated in parallel. Moreover, the transcript was not detectable in the thalamus. Thus, mechanisms other than an enkephalin-dependent receptor turnover must be responsible for COMT-related differences in MOP binding site availability in the human brain.
[Show abstract][Hide abstract] ABSTRACT: The synthesis of an (18)F-labeled sufentanil analogue with apparent high mu-opioid receptor selectivity is reported. Intravenous injection of N-[4-(methoxymethyl)-1-[2-(2-thienyl)ethyl]-4-piperidinyl]-N-phenyl-2-(+/-)-[(18)F]fluoropropan-amide in mice resulted in high brain uptake and a regional brain activity distribution corresponding to the mu-opioid receptor expression pattern. The developed ligand is a promising tracer for extended protocols in mu-opioid receptor mapping and quantitation with positron emission tomography.
No preview · Article · May 2005 · Bioorganic & Medicinal Chemistry Letters
[Show abstract][Hide abstract] ABSTRACT: Ligand-PET studies are attracting increasing interest in experimental and clinical research. As the most elaborated of PET techniques, ligand-PET allows the demonstration of receptor distributions, and thus, the delineation of neurochemical pathologies in the disease state. Recent developments are promising that ligand-PET will even allow to characterize dynamic and short-term changes in neurotransmission and will tremendously add to the understanding of neurophysiology on the receptor level. In pain studies, mainly the mu-opioidergic agonist [(11)C]-carfentanil and the unspecific opioid receptor antagonist [(11)C]-diprenorphine are applied. Utilizing these ligands the thalamus, prefrontal and cingulate cortex, basal ganglia and midbrain structures have been shown to possess high amounts of opioidergic receptors in vivo and it is well accepted, that the receptor density is higher in projections of the medial than those of the lateral pain system. Changes in receptor availability were observed in patients suffering from chronic pain. Rheumatoid arthritis, trigeminal neuralgia and central poststroke pain (CPSP) all lead to decreased ligand binding in pain processing regions during the painful period in comparison to pain free intervals or healthy subjects. These decreases may either be the consequence of increased endogenous release or indicate receptor internalization/down-regulation or loss of neurons carrying these receptors. Recent studies also evidenced [(11)C]-carfentanil binding changes due to acute experimental pain. One possible interpretation of these changes is that the PET-ligand might be displaced by endogenous opioidergic ligands. One major region, where this "ligand displacement" was observed, was the thalamus. These findings highlight the importance of the opioidergic system in pain processing and the power of ligand-PET to advance the understanding of pain.
Full-text · Article · May 2005 · European Journal of Pain
[Show abstract][Hide abstract] ABSTRACT: Short-lasting unilateral neuralgiform headache with conjunctival injection and tearing (SUNCT) is a primary head-pain syndrome, which is often refractory to any medical treatment. Concerning the pathophysiology of SUNCT, hypothalamic involvement ipsilaterally to the pain has been suggested based on the clinical features and one functional imaging case report. Here we now report a new case with SUNCT and the concomitant cerebral activation pattern (fMRI) during the pain attacks. In addition to an activation of several brain structures known to be generally involved in pain processing, bilateral hypothalamic activation occurred during the pain attacks, arguing for a central origin of the headache. Interestingly, this patient became completely pain free after surgical decompression of the ipsilateral trigeminal nerve. We hypothesize that in this case with a central predisposition for trigeminal autonomic cephalgias, a peripheral trigger with ectopic excitation might have contributed to the clinical picture of SUNCT.
[Show abstract][Hide abstract] ABSTRACT: The neural basis of trait anxiety is poorly understood. In genetically selected hyperanxious (high anxiety-related behavior; HAB) rats, diazepam induces a stronger anxiolytic response than in hypoanxious (low anxiety-related behavior; LAB) rats. A screen for neuronal response differences to diazepam between HAB and LAB rats using pharmacologic fMRI (phMRI) at 7 T revealed a blunted diazepam-induced neuronal deactivation in the dorsomedial prefrontal cortex (dmPFC) of HABs. This was not due to reduced benzodiazepine (BDZ) receptor densities in this region. Instead, dmPFC tissue oxygenation at baseline was found to be significantly lower in HABs. This suggests a tonic relative hypoactivity under the highly stressful phMRI conditions, offering an explanation for the reduced responsivity to the neural depressant effect of diazepam in the sense of a floor effect. Subsequently, Fos immunoreactivity (Fos-IR) showed that ethologically relevant stressors also cause less dmPFC activation in HABs. In the context of an anxiety-inhibiting role of the dmPFC, we propose that failure to sufficiently activate this region in stressful situations may contribute to high trait anxiety.
[Show abstract][Hide abstract] ABSTRACT: Following the cloning of the novel nociceptin opioid receptor (NOP(1)) and the identification of its endogenous ligand orphanin FQ/nociceptin the distribution and functional role of the NOP(1) receptor system have been studied mainly in the rodent CNS. In the present study the regional distribution and splice variant expression of the NOP(1) receptor was investigated in the adult human brain using [(3)H]-nociceptin autoradiography, NOP(1) reverse transcriptase PCR and mRNA in situ hybridization. Ligand binding revealed strong expression of functional NOP(1) receptors in the cerebral cortex and moderate signals in hippocampus and cerebellum. Interestingly, the NOP(1) receptor specific ligand was also strongly bound in the human striatum. A matching pattern of mRNA expression was observed with high amounts of NOP(1) mRNA in the prefrontal and cingulate cortex as well as in the dentate gyrus of the hippocampus. mRNA levels in the Ammon's horn and cerebellar cortex were moderate and low in the striatum. A considerable expression of N-terminal NOP(1) splice variant mRNAs was not detectable in the human brain by means of in situ hybridization. This suggests that functional NOP(1) receptors in the human brain are encoded by N-terminal full length NOP(1) transcripts. The present data on the anatomical distribution of nociceptin binding sites and NOP(1) receptor mRNA contribute to the knowledge about opioid receptor systems in the human brain and may promote the understanding of function and pharmacology of the orphanin FQ/nociceptin receptor system in the human CNS.
[Show abstract][Hide abstract] ABSTRACT: GABA(B) receptors are widely expressed in the CNS. The distribution of the recently cloned GABA(B1) receptor is highly concordant with GABA(B) ligand binding sites, but experiments with transfected cell lines indicate that GABA(B1) has to heterodimerize with GABA(B2) to gain the functionality of a native GABA(B) receptor. Using in situ hybridization we investigated the expression of GABA(B1) and GABA(B2) mRNAs in the human brain. Both transcripts were detectable in prefrontal cortex, hippocampus and cerebellum with no apparent mismatch. A distinct expression of GABA(B1) was detected in putative Bergmann glia. In the human striatum GABA(B1) mRNA was expressed in moderate amounts, whereas the GABA(B2) mRNA signal was not clearly above background. According to our data, the current concept on GABA(B) receptor composition needs re-evaluation, at least for certain brain structures.
[Show abstract][Hide abstract] ABSTRACT: Metabotropic glutamate receptors (mGluR) have been shown to play a role in the modulation of acute and inflammatory pain. Additionally, we have recently detected time-dependent changes in the mRNA expression of several mGluR subtypes in thalamic nuclei of monoarthritic (MA) rats. In the present study, mGluR1, -3, -4, and -7 subtype mRNA expression was analyzed by in situ hybridization with radioactively labelled oligonucleotide probes in cerebral cortical regions of normal and MA rats at 2, 4, and 14 days of the disease. The mGluR1, -4, and -7 mRNAs were at background level in normal rats and did not change in MA animals. In contrast, mGluR3 mRNA expression was abundant in normal rats and was significantly increased in cortical areas of MA rats at all time points. Higher changes were detected bilaterally at 4 days, predominantly in layers IV/V, in the motor, primary, and secondary somatosensory cortices (average increases of 50-75%), but maximum rises occurred in the contralateral cingulate cortex (+138%). No changes were detected in the auditory cortex. The present data show an up-regulation of mGluR3 mRNA expression in the motor, somatosensory, and limbic cortices of MA rats. This possibly reflects the occurrence of central mechanisms counteracting the increased transmission of nociceptive input arising from the inflamed paw and the impaired motor behavior of these rats. Changes in the cingulate cortex may be related to the motivational-affective component of nociception.
No preview · Article · Mar 2001 · Journal of Neuroscience Research
[Show abstract][Hide abstract] ABSTRACT: Evidence for the involvement of metabotropic glutamate receptors (mGluR) in sensory processing has been emerging. Additionally, the differential distribution of distinct mGluR subtypes mRNA in particular thalamic nuclei of normal rats suggests that they could be involved in the processing of somatosensory information. In the present study, mGluR1, 3, 4 and 7 mRNAs expression was investigated by in situ hybridisation in selected brainstem and thalamic nuclei of adult monoarthritic rats at different time points of the disease (2, 4 and 14 days). Monoarthritic rats displayed behavioural and physical signs of painful arthritis at all time points. At 2 days of monoarthritis the mGluR1 mRNA expression was decreased mainly in the ventrobasal complex (VB) and in the posterior thalamic nuclei (Po) contralateral to the inflamed joint. The mGluR4 mRNA expression was also reduced, but minimum values were found at 4 days of monoarthritis, when no changes could be found in mGluR1 mRNA expression. At 14 days, mGluR4 mRNA expression was similar to controls, while mGluR1 mRNA was again reduced. Similar decreases of mGluR7 mRNA expression in the VB and Po were found at all time points, while mGluR3 mRNA expression was bilaterally increased in the reticular thalamic nucleus (Rt). In the brainstem no changes could be found in the expression of any mGluR subtype mRNA. The reduced expression of mGluR1, 4 and 7 transcripts in VB and Po, and the increases of mGluR3 mRNA in the Rt may contribute to counteract the increased noxious input arising from the periphery.
No preview · Article · Oct 2000 · Molecular Brain Research