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Fujinaga, M.

Publications and source records attributed to Fujinaga, M..

6 recordsLinked to original sources

Native receptor-targeted chemogenetics enables cell-type-specific inhibition of endogenous receptors in freely moving mice

Understanding brain function requires tools that allow precise manipulation of receptor signaling in defined cell types within intact neural circuits. Optogenetics and conventional chemogenetic approaches primarily enable cell-type-specific control of neuronal excitability using engineered receptors or ion channels. However, direct and reversible inhibition of endogenous neurotransmitter receptors in defined cell types has remained technically inaccessible. Here, we introduce native receptor-targeted chemogenetics (NARCH), a chemogenetic strategy that integrates structure-guided receptor engineering with allosteric ligand design to achieve reversible and temporally precise inhibition of endogenous receptor signaling with cell-type specificity in vivo. By applying NARCH to metabotropic glutamate receptor 1 (mGlu1), we demonstrate that mGlu1 signaling in cerebellar Purkinje cells is required for stabilization of motor learning across training sessions in freely moving mice. NARCH thus establishes a receptor-level chemogenetic framework for causal analysis of neural circuits and behavior.

neuroscience↗

Multimodal imaging for validation and optimization of ion channel-based chemogenetics in nonhuman primates

Chemogenetic tools provide an opportunity to manipulate neuronal activity and behavior selectively and repeatedly in nonhuman primates (NHPs) with minimal invasiveness. Designer Receptors Exclusively Activated by Designer Drugs are one example that is based on mutated muscarinic acetylcholine receptors. Another channel-based chemogenetic system available for neuronal modulation in NHPs uses Pharmacologically Selective Actuator Modules (PSAMs), which are selectively activated by Pharmacologically Selective Effector Molecules (PSEMs). To facilitate the use of the PSAM/PSEM system, the selection and dosage of PSEMs should be validated and optimized for NHPs. To this end, we used a multimodal imaging approach. We virally expressed excitatory PSAM (PSAM4-5HT3) in the striatum and the primary motor cortex of two macaque monkeys, and visualized its location through positron emission tomography (PET) with the reporter ligand [18F]ASEM. Chemogenetic excitability of neurons triggered by two PSEMs (uPSEM817 and uPSEM792) was evaluated using [18F]fluorodeoxyglucose-PET imaging, with uPSEM817 being more efficient than uPSEM792. Pharmacological magnetic resonance imaging showed that increased brain activity in the PSAM4-expressing region began approximately 13 min after uPSEM817 administration and continued for at least 60 min. Our multimodal imaging data provide valuable information regarding the manipulation of neuronal activity using the PSAM/PSEM system in NHPs, facilitating future applications. Significance statementLike other chemogenetic tools, the ion channel-based system called Pharmacologically Selective Actuator Module/Pharmacologically Selective Effector Molecule (PSAM/PSEM) allows remote manipulation of neuronal activity and behavior in living animals. Nevertheless, its application in non-human primates (NHPs) is still limited. Here, we used multi-tracer positron emission tomography (PET) imaging and pharmacological magnetic resonance imaging (MRI) to visualize an excitatory chemogenetic ion channel (PSAM4-5HT3) and validate its chemometric function in macaque monkeys. Our results provide the optimal agonist, dose, and timing for chemogenetic neuronal manipulation, facilitating the use of the PSAM/PSEM system and expanding the flexibility and reliability of circuit manipulation in NHPs in a variety of situations.

neuroscience↗

In vivo visualization of intracellular pH gradient in brain using PET imaging

Intracellular pH (pHi) is a valuable index for predicting hypoxic brain damage. However, no positron emission tomography (PET) probe is currently available for monitoring pHi in vivo. In this study, we developed a new approach for visualizing monoacylglycerol lipase (MAGL) activity in the brain. This approach used PET with a new probe [11C]HC-A, an azetidine carbamate inhibitor, whose uptake and residence depended on the pHi gradient was evaluated with in silico, in vitro, and in vivo assessments. Molecular dynamics simulations predicted that complex (complex-A) between HC-A and MAGL would be difficult to hydrolyze under acidic conditions. In vitro assessment using rat brain homogenate showed that [11C]HC-A reacted with MAGL to yield [11C]complex-A, which was rapidly hydrolyzed to liberate 11CO2. The 11CO2 liberation rate was slower at lower pH. In PET with [11C]HC-A using ischemic rats, the radioactivity clearance rate, which reflects the production rate of 11CO2 in the brain, was lower in a remarkably hypoxic area than in the contralateral region. In conclusion, we successfully visualized the pHi gradient in the brain using PET imaging.

neuroscience↗

Radiosynthesis and preclinical evaluation of a carbon-11 labeled PDE7 inhibitor for PET neuroimaging

BackgroundDysfunction of cyclic nucleotide phosphodiesterase 7 (PDE7) has been associated with excess intracellular cAMP concentrations, fueling pathogenic processes that are implicated in neurodegenerative disorders. The aim of this study was to develop a suitable PDE7-targeted positron emission tomography (PET) probe that allows non-invasive mapping of PDE7 in the mammalian brain. MethodsBased on a spiro cyclohexane-1,4-quinazolinone scaffold with known inhibitory properties towards PDE7, we designed and synthesized a methoxy analog that was suitable for carbon-11 labeling. Radiosynthesis was conducted with the respective desmethyl precursor using [11C]MeI. The resulting PET probe, codenamed [11C]26, was evaluated by cell uptake studies, ex vivo biodistribution and radiometabolite studies, as well as in vivo PET experiments in rodents and nonhuman primates (NHP). ResultsTarget compound 26 and the corresponding phenolic precursor were synthesized in 2-3 steps with overall yields of 49.5% and 12.4%, respectively. An inhibitory constant (IC50) of 31 nM towards PDE7 was obtained and no significant interaction with other PDE isoforms were observed. [11C]26 was synthesized in high molar activities (170 - 220 GBq/{micro}mol) with radiochemical yields of 34{+/-}7%. In vitro cell uptake of [11C]26 was 6-7 folds higher in PDE7 overexpressing cells, as compared to the controls, whereas an in vitro specificity of up to 90% was measured. Ex vivo metabolite studies revealed a high fraction of intact parent in the rat brain (98% at 5 min and 75% at 30 min post injection). Considerable brain penetration was further corroborated by ex vivo biodistribution and PET imaging studies - the latter showing heterogenic brain uptake. While marginal specific binding was observed by PET studies in rodents, a moderate, but dose-dependent, blockade was observed in the NHP brain following pretreatment with non-radioactive 26. ConclusionIn this work, we report on the preclinical evaluation of [11C]26 (codename [11C]P7-2104), a PDE7-targeted PET ligand that is based on a spiroquinazolinone scaffold. [11C]26 displayed promising in vitro performance characteristics, a moderate degree of specific binding in PET studies with NHP. Accordingly, [11C]26 will serve as a valuable lead compound for the development of a new arsenal of PDE7-targeted probes with potentially improved in vivo specificity.

neuroscience↗

In vivo visualization of propagating α-synuclein pathologies in mouse and marmoset models by a bimodal imaging probe, C05-05

Deposition of -synuclein fibrils is implicated in Parkinsons disease (PD) and dementia with Lewy bodies (DLB), while in vivo detection of -synuclein pathologies in these illnesses has been challenging. Here, we have developed a small-molecule ligand, C05-05, for visualizing -synuclein deposits in the brains of living subjects. In vivo optical and positron emission tomography (PET) imaging of mouse and marmoset models demonstrated that C05-05 captured a dynamic propagation of fibrillogenesis along neural pathways followed by disruptions of these structures. High-affinity binding of 18F-C05-05 to -synuclein aggregates in human brain tissues was also proven by in vitro assays. Notably, PET-detectable 18F-C05-05 signals were intensified in the midbrains of PD and DLB patients as compared to healthy controls, providing the first demonstration of visualizing -synuclein pathologies in these illnesses. Collectively, we propose a new imaging technology offering neuropathology-based translational assessments of PD and allied disorders towards diagnostic and therapeutic research and development.

neuroscience↗

Genetically targeted reporter imaging of deep neuronal network in the mammalian brain

Positron Emission Tomography (PET) allows biomolecular tracking, while PET monitoring of brain networks has been hampered by the lack of a suitable reporter. Here, we describe in vivo brain imaging that takes advantage of bacterial dihydrofolate reductase, ecDHFR, and its unique antagonist, TMP. In mice, peripheral administration of radiofluorinated and fluorescent TMP analogs enabled PET and intravital microscopy, respectively, of neuronal ecDHFR expressions. This technique is applicable to the visualization of neuronal ensemble activities elicited by chemogenetic manipulation in the mouse hippocampus. Notably, ecDHFR-PET offers mapping of neuronal projections in non-human primate brains, indicating the availability of ecDHFR-based tracking technologies for network monitoring. Finally, we demonstrate the utility of TMP analogs for PET assays of turnover and self-assembly of proteins tagged with ecDHFR mutants. Our findings may facilitate a broad spectrum of PET analyses of a mammalian brain circuit at molecular levels that were not previously applicable for technical reasons.

neuroscience↗