Discriminative binding of tau PET tracers PI2620, MK6240 and RO948 in Alzheimer's disease, corticobasal degeneration and progressive supranuclear palsy brains.

Recent mechanistic and structural studies have challenged the classical tauopathy classification approach and revealed the complexity and heterogeneity of tau pathology in Alzheimer's disease (AD) and primary tauopathies such as corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP), progressing beyond distinct tau isoforms. In this multi-tau tracer study, we focused on the new second-generation tau PET tracers PI2620, MK6240 and RO948 to investigate this tau complexity in AD, CBD, and PSP brains using post-mortem radioligand binding studies and autoradiography of large and small frozen brain sections. Saturation binding studies indicated multiple binding sites for 3H-PI2620 in AD, CBD and PSP brains with different binding affinities (Kd ranging from 0.2 to 0.7 nM) and binding site densities (following the order: BmaxAD > BmaxCBD > BmaxPSP). Competitive binding studies complemented these findings, demonstrating the presence of two binding sites [super-high affinity (SHA): IC50(1) = 8.1 pM; and high affinity (HA): IC50(2) = 4.9 nM] in AD brains. Regional binding distribution studies showed that 3H-PI2620 could discriminate between AD (n = 6) and control cases (n = 9), especially in frontal cortex and temporal cortex tissue (p < 0.001) as well as in the hippocampal region (p = 0.02). 3H-PI2620, 3H-MK6240 and 3H-RO948 displayed similar binding behaviour in AD brains (in both homogenate competitive studies and one large frozen hemispherical brain section autoradiography studies) in terms of binding affinities, number of sites and regional patterns. Our small section autoradiography studies in the frontal cortex of CBD (n = 3) and PSP brains (n = 2) showed high specificity for 3H-PI2620 but not for 3H-MK6240 or 3H-RO948. Our findings clearly demonstrate different binding properties among the second-generation tau PET tracers, which may assist in further understanding of tau heterogeneity in AD versus non-AD tauopathies and suggests potential for development of pure selective 4R tau PET tracers.

Astroglial tracer BU99008 detects multiple binding sites in Alzheimer's disease brain.

With reactive astrogliosis being established as one of the hallmarks of Alzheimer's disease (AD), there is high interest in developing novel positron emission tomography (PET) tracers to detect early astrocyte reactivity. BU99008, a novel astrocytic PET ligand targeting imidazoline-2 binding sites (I2BS) on astrocytes, might be a suitable candidate. Here we demonstrate for the first time that BU99008 could visualise reactive astrogliosis in postmortem AD brains and propose a multiple binding site [Super-high-affinity (SH), High-affinity (HA) and Low-affinity (LA)] model for BU99008, I2BS specific ligands (2-BFI and BU224) and deprenyl in AD and control (CN) brains. The proportion (%) and affinities of these sites varied significantly between the BU99008, 2-BFI, BU224 and deprenyl in AD and CN brains. Regional binding studies demonstrated significantly higher 3H-BU99008 binding in AD brain regions compared to CN. Comparative autoradiography studies reinforced these findings, showing higher specific binding for 3H-BU99008 than 3H-Deprenyl in sporadic AD brain compared to CN, implying that they might have different targets. The data clearly shows that BU99008 could detect I2BS expressing reactive astrocytes with good selectivity and specificity and hence be a potential attractive clinical astrocytic PET tracer for gaining further insight into the role of reactive astrogliosis in AD.

Amyloid, tau, and astrocyte pathology in autosomal-dominant Alzheimer's disease variants: AßPParc and PSEN1DE9.

Autosomal-dominant Alzheimer's disease (ADAD) may be associated with atypical amyloid beta deposits in the brain. In vivo amyloid imaging using 11C-Pittsburgh compound B (PiB) tracer has shown differences in binding between brains from ADAD and sporadic Alzheimer's disease (sAD) patients. To gain further insight into the various pathological characteristics of these genetic variants, we performed large frozen hemisphere autoradiography and brain homogenate binding assays with 3H-PiB, 3H-MK6240-3H-THK5117, and 3H-deprenyl for detection of amyloid fibrils, tau depositions, and activated astrocytes, respectively, in two AßPParc mutation carriers, one PSEN1ΔE9 mutation carrier, and three sAD cases. The results were compared with Abeta 40, Abeta 42, AT8, and GFAP immunostaining, respectively, as well as with Congo red and Bielschowsky. PiB showed a very low binding in AßPParc. A high binding was observed in PSEN1ΔE9 and in sAD tissues but with different binding patterns. Comparable 3H-THK5117 and 3H-deprenyl brain homogenate binding was observed for AßPParc, PSEN1ΔE9, and sAD, respectively. Some differences were observed between 3H-MK6240 and 3H-THK5117 in ADAD. A positive correlation between 3H-deprenyl and 3H-THK5117 binding was observed in AßPParc, while no such correlation was found in PSEN1ΔE9 and sAD. Our study demonstrates differences in the properties of the amyloid plaques between two genetic variants of AD and sAD. Despite the lack of measurable amyloid fibrils by PiB in the AßPParc cases, high regional tau and astrocyte binding was observed. The lack of correlation between 3H-deprenyl and 3H-THK5117 binding in PSEN1ΔE9 and sAD in contrast of the positive correlation observed in the AßPParc cases suggest differences in the pathological cascade between variants of AD that warrant further exploration in vivo.

Characterization of MK6240, a tau PET tracer, in autopsy brain tissue from Alzheimer's disease cases.

PURPOSE: MK6240 is a second-generation tau PET tracer designed to detect the neurofibrillary tangles in the brains of patients with Alzheimer's disease (AD). The aim of the study was to characterize 3H-MK6240 in AD and control brain tissue and to compare its binding properties with those of first-generation tau PET tracers. METHODS: Saturation binding assays with 3H-MK6240 were carried out in the temporal and parietal cortices of AD brains to determine the maximum number of binding sites (Bmax) and the dissociation constants (Kd) at these sites. Competitive binding assays were carried out between 3H-MK6240 and unlabelled MK6240, AV-1451 (aka T807, flortaucipir) and THK5117, and between 3H-THK5351 and unlabelled MK6240. Regional binding studies with 3H-MK6240 were carried out in homogenates from six AD and seven control brains and, using autoradiography, on large frozen sections from two AD brains and one control brain. RESULTS: The saturation binding assays gave Bmax and Kd values of 59.2 fmol/mg and 0.32 nM in the temporal cortex and 154.7 fmol/mg and 0.15 nM in the parietal cortex. The competitive binding assays revealed two binding sites with affinities in the picomolar and nanomolar range shared by 3H-MK6240 and all the tested unlabelled compounds. There were no binding sites in common between 3H-THK5351 and unlabelled MK6240. Regional binding of 3H-MK6240 was significantly higher in AD brain tissue than in controls. Binding in brain tissue from AD patients with early-onset AD was significantly higher than in brain tissue from patients with late-onset AD. Binding of 3H-MK6240 was not observed in off-target regions. Autoradiography showed high regional cortical binding in the two AD brains and very low binding in the control brain. CONCLUSIONS: 3H-MK6240 has a high binding affinity for tau deposits in AD brain tissue but also has different binding characteristics from those of the first-generation tau tracers. This confirms the complexity of tau tracer binding on tau deposits with different binding affinities for different binding sites.

Tau PET imaging in neurodegenerative tauopathies-still a challenge.

The accumulation of pathological misfolded tau is a feature common to a collective of neurodegenerative disorders known as tauopathies, of which Alzheimer's disease (AD) is the most common. Related tauopathies include progressive supranuclear palsy (PSP), corticobasal syndrome (CBS), Down's syndrome (DS), Parkinson's disease (PD), and dementia with Lewy bodies (DLB). Investigation of the role of tau pathology in the onset and progression of these disorders is now possible due the recent advent of tau-specific ligands for use with positron emission tomography (PET), including first- (e.g., [18F]THK5317, [18F]THK5351, [18F]AV1451, and [11C]PBB3) and second-generation compounds [namely [18F]MK-6240, [18F]RO-948 (previously referred to as [18F]RO69558948), [18F]PI-2620, [18F]GTP1, [18F]PM-PBB3, and [18F]JNJ64349311 ([18F]JNJ311) and its derivative [18F]JNJ-067)]. In this review we describe and discuss findings from in vitro and in vivo studies using both initial and new tau ligands, including their relation to biomarkers for amyloid-ß and neurodegeneration, and cognitive findings. Lastly, methodological considerations for the quantification of in vivo ligand binding are addressed, along with potential future applications of tau PET, including therapeutic trials.

Cross-interaction of tau PET tracers with monoamine oxidase B: evidence from in silico modelling and in vivo imaging.

PURPOSE: Several tracers have been designed for tracking the abnormal accumulation of tau pathology in vivo. Recently, concerns have been raised about the sources of off-target binding for these tracers; inconclusive data propose binding for some tracers to monoamine oxidase B (MAO-B). METHODS: Molecular docking and dynamics simulations were used to estimate the affinity and free energy for the binding of several tau tracers (FDDNP, THK523, THK5105, THK5317, THK5351, T807 [aka AV-1451, flortaucipir], T808, PBB3, RO-948, MK-6240, JNJ-311 and PI-2620) to MAO-B. These values were then compared with those for safinamide (MAO-B inhibitor). PET imaging was used with the tau tracer [18F]THK5317 and the MAO-B tracer [11C]DED in five patients with Alzheimer's disease to investigate the MAO-B binding component of this first generation tau tracer in vivo. RESULTS: The computational modelling studies identified a binding site for all the tau tracers on MAO-B; this was the same site as that for safinamide. The binding affinity and free energy of binding for the tau tracers to MAO-B was substantial and in a similar range to those for safinamide. The most recently developed tau tracers MK-6240, JNJ-311 and PI-2620 appeared, in silico, to have the lowest relative affinity for MAO-B. The in vivo investigations found that the regional distribution of binding for [18F]THK5317 was different from that for [11C]DED, although areas of suspected off-target [18F]THK5317 binding were detected. The binding relationship between [18F]THK5317 and [11C]DED depended on the availability of the MAO-B enzyme. CONCLUSIONS: The developed tau tracers show in silico and in vivo evidence of cross-interaction with MAO-B; the MAO-B component of the tracer binding was dependent on the regional concentration of the enzyme.

Longitudinal tau and metabolic PET imaging in relation to novel CSF tau measures in Alzheimer's disease.

PURPOSE: Studies comparing CSF and PET tau biomarkers have included only commercial CSF assays examining specific phosphorylation sites (e.g. threonine 181, P-tau181p) and mid-domain tau (i.e. total tau, T-tau). Moreover, these studies did not examine CSF tau levels in relation to cerebral glucose metabolism. We thus aimed to examine CSF tau measures, using both commercial and novel assays, in relation to [18F]THK5317 (tau) and [18F]FDG PET (glucose metabolism). METHODS: Fourteen Alzheimer's disease (AD) patients (seven prodromal, seven dementia) underwent [18F]THK5317 and [18F]FDG PET studies, with follow-up performed in ten subjects (six prodromal, four dementia) after 17 months. In addition to commercial assays, novel measures capturing N-terminus+mid-domain (tau N-Mid) and C-terminally truncated (tau-368) fragments were included. RESULTS: While the levels of all forms of CSF tau were found to be inversely associated with baseline [18F]FDG uptake, associations with baseline [18F]THK5317 uptake varied in relation to the degree of isocortical hypometabolism ([18F]FDG SUVR). Changes in the levels of the novel CSF markers tracked longitudinal changes in tracer uptake better than changes in P-tau181p and T-tau levels, and improved concordance with dichotomized regional [18F]THK5317 measures. CONCLUSION: Our findings suggest that neurodegeneration may modulate the relationship between CSF and PET tau biomarkers, and that, by comparison to P-tau181p and T-tau, tau-368 and tau N-Mid may better capture tau pathology and synaptic impairment.

Signal peptide peptidase-like 2b modulates the amyloidogenic pathway and exhibits an Aß-dependent expression in Alzheimer's disease.

Alzheimer's disease (AD) is a multifactorial disorder driven by abnormal amyloid ß-peptide (Aß) levels. In this study, we investigated the role of presenilin-like signal peptide peptidase-like 2b (SPPL2b) in AD pathophysiology and its potential as a druggable target within the Aß cascade. Exogenous Aß42 influenced SPPL2b expression in human cell lines and acute mouse brain slices. SPPL2b and its AD-related substrate BRI2 were evaluated in the brains of AppNL-G-F knock-in AD mice and human postmortem AD brains. An early high cortical expression of SPPL2b was observed, followed by a downregulation in late AD pathology in AppNL-G-F mice, correlating with synaptic loss. To understand the consequences of pathophysiological SPPL2b dysregulation, we found that SPPL2b overexpression significantly increased APP cleavage, while genetic deletion reduced APP cleavage and Aß production. Notably, postmortem AD brains showed higher levels of SPPL2b's BRI2 substrate compared to healthy control samples. These results strongly support the involvement of SPPL2b in AD pathology. The early Aß-induced upregulation of SPPL2b may enhance Aß production in a vicious cycle, further aggravating Aß pathology. Therefore, SPPL2b emerges as a potential anti-Aß drug target.

A new single-photon emission computed tomography (SPECT) imaging agent for serotonin transporters: [(125)I]Flip-IDAM, (2-((2-((dimethylamino)methyl)-4-iodophenyl)thio)phenyl)methanol.

New ligands for in vivo brain imaging of serotonin transporter (SERT) with single photon emission tomography (SPECT) were prepared and evaluated. An efficient synthesis and radiolabeling of a biphenylthiol, FLIP-IDAM, 4, was accomplished. The affinity of FLIP-IDAM was evaluated by an in vitro inhibitory binding assay using [(125)I]-IDAM as radioligand in rat brain tissue homogenates (K(i) = 0.03 nM). New [(125)I]Flip-IDAM exhibited excellent binding affinity to SERT binding sites with a high hypothalamus to cerebellum ratio of 4 at 30 min post iv injection. The faster in vivo kinetics for brain uptake and a rapid washout from non-specific regions provide excellent signal to noise ratio. This new agent, when labeled with (123)I, may be a useful imaging agent for mapping SERT binding sites in the human brain.

Development of 11C-Labeled ASEM Analogues for the Detection of Neuronal Nicotinic Acetylcholine Receptors (α7-nAChR).

The homo-pentameric alpha 7 receptor is one of the major types of neuronal nicotinic acetylcholine receptors (α7-nAChRs) related to cognition, memory formation, and attention processing. The mapping of α7-nAChRs by PET pulls a lot of attention to realize the mechanism and development of CNS diseases such as AD, PD, and schizophrenia. Several PET radioligands have been explored for the detection of the α7-nAChR. 18F-ASEM is the most functional for in vivo quantification of α7-nAChRs in the human brain. The first aim of this study was to initially use results from in silico and machine learning techniques to prescreen and predict the binding energy and other properties of ASEM analogues and to interpret these properties in terms of atomic structures using 18F-ASEM as a lead structure, and second, to label some selected candidates with carbon-11/hydrogen-3 (11C/3H) and to evaluate the binding properties in vitro and in vivo using the labeled candidates. In silico predictions are obtained from perturbation free-energy calculations preceded by molecular docking, molecular dynamics, and metadynamics simulations. Machine learning techniques have been applied for the BBB and P-gp-binding properties. Six analogues of ASEM were labeled with 11C, and three of them were additionally labeled with 3H. Binding properties were further evaluated using autoradiography (ARG) and PET measurements in non-human primates (NHPs). Radiometabolites were measured in NHP plasma. All six compounds were successfully synthesized. Evaluation with ARG showed that 11C-Kln83 was preferably binding to the α7-nAChR. Competition studies showed that 80% of the total binding was displaced. Further ARG studies using 3H-KIn-83 replicated the preliminary results. In the NHP PET study, the distribution pattern of 11C-KIn-83 was similar to other α7 nAChR PET tracers. The brain uptake was relatively low and increased by the administration of tariquidar, indicating a substrate of P-gp. The ASEM blocking study showed that 11C-KIn-83 specifically binds to α7 nAChRs. Preliminary in vitro evaluation of KIn-83 by ARG with both 11C and 3H and in vivo evaluation in NHP showed favorable properties for selectively imaging α7-nAChRs, despite a relatively low brain uptake.

Leveraging the Client-Provider Interaction to Address Contraceptive Discontinuation: A Scoping Review of the Evidence That Links Them.

Despite considerable investment and effort, unmet need for contraception remains an obstacle to improved family planning outcomes. One influencing factor is the frequency of contraceptive discontinuation among users who desire to prevent pregnancy, often due to method-related concerns and side effects. Contraceptive users have the right to be supported during counseling to voluntarily choose methods that align with their individual needs and preferences. Contraceptive counseling, as a key component of quality of care, is particularly important for providers to reduce unmet need among their clients. This scoping review examined the state of the evidence on contraceptive counseling and its impact on discontinuation. The review first examines the association between quality of care and contraceptive discontinuation, then looks to what the current body of evidence suggests are women's contraceptive counseling priorities, and lastly, explores whether specific counseling tools and approaches have been evaluated with discontinuation as an outcome. The results identified general principles and priorities for good counseling including person-centeredness, client-tailored information exchange, clear and concise information on side effects and bleeding changes, reducing providers' implicit and explicit biases, and trust and respect between the client and provider. The review of the literature also found that evidence to support the use of specific counseling tools and approaches to reduce contraceptive discontinuation is insufficient; research should be designed to determine which specific elements of the client-provider interaction can be improved to significantly impact contraceptive discontinuation. This evidence could inform how the global community of practice might improve and leverage specific counseling approaches and tools to address the most common predictors of discontinuation.

Assessment of Tau Pathology as Measured by 18F-THK5317 and 18F-Flortaucipir PET and Their Relation to Brain Atrophy and Cognition in Alzheimer's Disease.

BACKGROUND: In Alzheimer's disease (AD), the abnormal aggregation of hyperphosphorylated tau leads to synaptic dysfunction and neurodegeneration. Recently developed tau PET imaging tracers are candidate biomarkers for diagnosis and staging of AD. OBJECTIVE: We aimed to investigate the discriminative ability of 18F-THK5317 and 18F-flortaucipir tracers and brain atrophy at different stages of AD, and their respective associations with cognition. METHODS: Two cohorts, each including 29 participants (healthy controls [HC], prodromal AD, and AD dementia patients), underwent 18F-THK5317 or 18F-flortaucipir PET, T1-weighted MRI, and neuropsychological assessment. For each subject, we quantified regional 18F-THK5317 and 18F-flortaucipir uptake within six bilateral and two composite regions of interest. We assessed global brain atrophy for each individual by quantifying the brain volume index, a measure of brain volume-to-cerebrospinal fluid ratio. We then quantified the discriminative ability of regional 18F-THK5317, 18F-flortaucipir, and brain volume index between diagnostic groups, and their associations with cognition in patients. RESULTS: Both 18F-THK5317 and 18F-flortaucipir outperformed global brain atrophy in discriminating between HC and both prodromal AD and AD dementia groups. 18F-THK5317 provided the highest discriminative ability between HC and prodromal AD groups. 18F-flortaucipir performed best at discriminating between prodromal and dementia stages of AD. Across all patients, both tau tracers were predictive of RAVL learning, but only 18F-flortaucipir predicted MMSE. CONCLUSION: Our results warrant further in vivo head-to-head and antemortem-postmortem evaluations. These validation studies are needed to select tracers with high clinical validity as biomarkers for early diagnosis, prognosis, and disease staging, which will facilitate their incorporation in clinical practice and therapeutic trials.

[18F]F15599, a novel 5-HT1A receptor agonist, as a radioligand for PET neuroimaging.

PURPOSE: The serotonin-1A (5-HT(1A)) receptor is implicated in the pathophysiology of major neuropsychiatric disorders. Thus, the functional imaging of 5-HT(1A) receptors by positron emission tomography (PET) may contribute to the understanding of its role in those pathologies and their therapeutics. These receptors exist in high- and low-affinity states and it is proposed that agonists bind preferentially to the high-affinity state of the receptor and therefore could provide a measure of the functional 5-HT(1A) receptors. Since all clinical PET 5-HT(1A) radiopharmaceuticals are antagonists, it is of great interest to develop a( 18)F labelled agonist. METHODS: F15599 (3-chloro-4-fluorophenyl-(4-fluoro-4{[(5-methyl-pyrimidin-2-ylmethyl)-amino]-methyl}-piperidin-1-yl)-methanone) is a novel ligand with high affinity and selectivity for 5-HT(1A) receptors and is currently tested as an antidepressant. In pharmacological tests in rat, it exhibits preferential agonist activity at post-synaptic 5-HT(1A) receptors in cortical brain regions. Here, its nitro-precursor was synthesised and radiolabelled via a fluoronucleophilic substitution. Radiopharmacological evaluations included in vitro and ex vivo autoradiography in rat brain and PET scans on rats and cats. Results were compared with simultaneous studies using [(18)F]MPPF, a validated 5-HT(1A) antagonist radiopharmaceutical. RESULTS: The chemical and radiochemical purities of [(18)F]F15599 were >98%. In vitro [(18)F]F15599 binding was consistent with the known 5-HT(1A) receptors distribution (hippocampus, dorsal raphe nucleus, and notably cortical areas) and addition of Gpp(NH)p inhibited [(18)F]F15599 binding, consistent with a specific binding to G protein-coupled receptors. In vitro binding of [(18)F]F15599 was blocked by WAY100635 and 8-OH-DPAT, respectively, prototypical 5-HT(1A) antagonist and agonist. The ex vivo and in vivo studies demonstrated that the radiotracer readily entered the rat and the cat brain and generated few brain radioactive metabolites. Remarkably, in microPET studies, [(18)F]F15599 notably displayed a pattern of brain labelling that did not correlate with in vitro observations. Thus, in cat, the highest binding was observed in dorsal raphe and cingulate cortex with little binding in other cortical regions and none in hippocampus. In vivo binding was abolished by WAY100635, indicating specific labelling of 5-HT(1A) receptors. CONCLUSION: [(18)F]F15599 is a radiofluorinated agonist presenting interesting characteristics for probing in vitro and in vivo the high-affinity states of the 5-HT(1A) receptors. Its differential labelling of 5-HT(1A) receptors in vitro and in vivo may result from its reported preferential interaction with receptors coupled to specific G-protein subtypes.

Looking for a 5-HT7 radiotracer for positron emission tomography.

In search of a serotonin 5-HT(7) radiotracer for positron emission tomography, we developed 1-[2-[(2S)-1-(phenylsulfonyl)pyrrolidin-2-yl]ethyl]piperidin-4-yl 4-fluorobenzoate. After labeling in good yield with fluorine-18 via nitro for fluorine exchange, preliminary biological experiments with autoradiographies failed to evidence any specific 5-HT(7) receptor delineation.

Functional correlates for 5-HT(1A) receptors in maternally deprived rats displaying anxiety and depression-like behaviors.

Maternal separation is known to induce long-term changes in neuroendocrine and emotional responsiveness to stress in a large variety of models. We examined an animal model of early deprivation in Sprague-Dawley rats consisting of separating litters from their mothers and littermates 3 h daily during postnatal days 2 to 15. In adulthood, maternally deprived rats in comparison with non-deprived controls exhibited an increase in anxiety and depression-related behaviors in the open-field and forced swim tests. Because serotonin (5-HT) 5-HT(1A) receptors seem to play an important role in the pathophysiology of major depression and in the mechanism of action of antidepressants, we investigated if 5-HT(1A) receptor function is altered in deprived rats. Although the hypothermic response to the 5-HT(1A) receptor agonist 8-OH-DPAT was increased in adult deprived rats compared to non-deprived control group, no differences between groups were found in the effect of the systemic 8-OH-DPAT administration on serotoninergic cell firing in dorsal raphe nucleus and in the 5-HT release at the ventral hippocampus levels. These results suggest that 5-HT(1A) receptors are not substantially affected in adult Sprague-Dawley rats that were subjected to a maternal deprivation 3 h daily during the neonatal period.

Management of acute postpartum pain in patients maintained on methadone or buprenorphine during pregnancy.

BACKGROUND: Empirical evidence is needed to guide adequate postpartum pain relief of methadone and buprenorphine stabilized patients. OBJECTIVES: To first determine the adequacy of pain control using non-opioid and opioid medication in participants stabilized on buprenorphine or methadone before a vaginal delivery. Second, to compare the amount of non-opioid and opioid medication needed for adequate pain control for buprenorphine-and methadone-maintained patients during the immediate postpartum period. METHODS: Pain control adequacy and amount of non-opioid and opioid medication needed in buprenorphine- (n = 8) and methadone-maintained (n = 10) patients over the first five days postpartum were examined. RESULTS: Pain ratings and number of opioid medication doses decreased over time in both medication groups. While the buprenorphine and methadone groups began with similar mean daily ibuprofen (IB) doses, the buprenorphine group decreased its IB use, while the methadone group increased its IB use. CONCLUSIONS AND SCIENTIFIC SIGNIFICANCE: Patients treated daily with either buprenorphine or methadone can have adequate pain control postpartum with opioid medication and IB. Pain control is dependent on the opioid-agonist medication in use at delivery, and must be individualized.

Tau positron emission tomography imaging in tauopathies: The added hurdle of off-target binding.

Ligands targeting tau for use with positron emission tomography have rapidly been developed during the past several years, enabling the in vivo study of tau pathology in patients with Alzheimer's disease and related non-Alzheimer's disease tauopathies. Several candidate compounds have been developed, showing good in vitro characteristics with respect to their ability to bind tau deposits; off-target binding, however, has also been observed. In this short commentary, we briefly summarize the available in vivo and in vitro evidence pertaining to their off-target binding and discuss the different approaches that are needed for the future development of tau positron emission tomography tracers.

Synthesis and biological evaluation in rat and cat of [18F]12ST05 as a potential 5-HT6 PET radioligand.

INTRODUCTION: 5-hydroxytryptamine (5-HT)6 receptors represent one of the more recently discovered serotoninergic receptor family. However, no 5-HT6 positron emission tomography (PET) radiotracer is currently used in clinical imaging studies. The purpose of this study was to propose the first fluorinated PET radiotracer for this brain receptor. METHODS: A new compound presenting in vitro high affinity towards the serotoninergic 5-HT6 receptor, N-[2-(1-[(4-fluorophenyl)sulfonyl]-1H-indol-4-yloxy)ethyl]-N,N-dimethylamine, was labelled with fluorine 18 via a nitro-/fluoronucleophilic substitution. Biological evaluations included (i) in vitro and ex vivo autoradiographies in rat brain and (ii) a PET scan on anaesthetized cat. RESULTS AND CONCLUSION: Although the radioligand showed excellent brain penetration, it did not reveal any specific binding to the 5-HT6 receptors indicating that this radiotracer is not suitable for mapping 5-HT6 receptors using PET.

Cortical laminar tau deposits and activated astrocytes in Alzheimer's disease visualised by 3H-THK5117 and 3H-deprenyl autoradiography.

Hyperphosphorylated tau protein deposits and, inflammatory processes are characteristic components of Alzheimer disease (AD) pathology. We here aimed to visualize in vitro the distribution of tau deposits and activated astrocytes across the cortical layers in autopsy AD brain tissue using the radiotracers 3H-THK5117 and 3H-deprenyl. 3H-THK5117 and 3H-deprenyl autoradiographies were carried out on frozen brain sections from three AD patients and one healthy control. 3H-THK5117 showed a distinct laminar cortical binding similar to 3H-deprenyl autoradiography, with an extensive binding in the superficial and deep layers of the temporal neocortices, whereas the middle frontal gyrus showed an even binding throughout the layers. Globally, eventhough some differences could be observed, AT8 (tau) and GFAP (astrocyte) immunostaining showed a laminar pattern comparable to their corresponding radiotracers within each AD case. Some variability was observed between the AD cases reflecting differences in disease phenotype. The similar laminar cortical brain distribution of tau deposits and activated astrocytes supports the hypothesis of a close pathological interconnection. The difference in regional binding patterns of 3H-THK5117 and AT8 antibody staining suggest additional tau binding sites detectable by 3H-THK5117.