Ligand recognition and allosteric regulation of DRD1-Gs signaling complexes.

Dopamine receptors, including D1- and D2-like receptors, are important therapeutic targets in a variety of neurological syndromes, as well as cardiovascular and kidney diseases. Here, we present five cryoelectron microscopy (cryo-EM) structures of the dopamine D1 receptor (DRD1) coupled to Gs heterotrimer in complex with three catechol-based agonists, a non-catechol agonist, and a positive allosteric modulator for endogenous dopamine. These structures revealed that a polar interaction network is essential for catecholamine-like agonist recognition, whereas specific motifs in the extended binding pocket were responsible for discriminating D1- from D2-like receptors. Moreover, allosteric binding at a distinct inner surface pocket improved the activity of DRD1 by stabilizing endogenous dopamine interaction at the orthosteric site. DRD1-Gs interface revealed key features that serve as determinants for G protein coupling. Together, our study provides a structural understanding of the ligand recognition, allosteric regulation, and G protein coupling mechanisms of DRD1.

Risk factors of cytokine release syndrome: stress, catecholamines, and beyond.

Cytokine release syndrome (CRS) is a severe clinical syndrome marked by drastic elevation of inflammatory cytokines such as interleukin (IL)-1, IL-6, and tumor necrosis factor (TNF). Despite the current empirical therapeutic strategies, prediction of CRS onset and identification of high-risk individuals are not satisfactory due to poor understanding of the mechanisms underlying CRS-related immune dysfunction and risk factors for CRS. Recent studies have suggested that conditions such as stress, obesity, diabetes, and hypertension may contribute to the development of CRS. Here, we discuss potential connections between these conditions and CRS pathogenesis, with a focus on stress hormone catecholamine-mediated effects, hoping that the design of CRS therapeutic approaches ensues from a renewed perspective.

Impact of acute stress on murine metabolomics and metabolic flux.

Plasma metabolite concentrations and labeling enrichments are common measures of organismal metabolism. In mice, blood is often collected by tail snip sampling. Here, we systematically examined the effect of such sampling, relative to gold-standard sampling from an in-dwelling arterial catheter, on plasma metabolomics and stable isotope tracing. We find marked differences between the arterial and tail circulating metabolome, which arise from two major factors: handling stress and sampling site, whose effects were deconvoluted by taking a second arterial sample immediately after tail snip. Pyruvate and lactate were the most stress-sensitive plasma metabolites, rising ~14 and ~5-fold. Both acute handling stress and adrenergic agonists induce extensive, immediate production of lactate, and modest production of many other circulating metabolites, and we provide a reference set of mouse circulatory turnover fluxes with noninvasive arterial sampling to avoid such artifacts. Even in the absence of stress, lactate remains the highest flux circulating metabolite on a molar basis, and most glucose flux into the TCA cycle in fasted mice flows through circulating lactate. Thus, lactate is both a central player in unstressed mammalian metabolism and strongly produced in response to acute stress.

Dopamine and Norepinephrine Differentially Mediate the Exploration-Exploitation Tradeoff.

Dopamine (DA) and norepinephrine (NE) have been repeatedly implicated in neuropsychiatric vulnerability, in part via their roles in mediating the decision-making processes. Although two neuromodulators share a synthesis pathway and are coactivated under states of arousal, they engage in distinct circuits and modulatory roles. However, the specific role of each neuromodulator in decision-making, in particular the exploration-exploitation tradeoff, remains unclear. Revealing how each neuromodulator contributes to exploration-exploitation tradeoff is important in guiding mechanistic hypotheses emerging from computational psychiatric approaches. To understand the differences and overlaps of the roles of these two catecholamine systems in regulating exploration, a direct comparison using the same dynamic decision-making task is needed. Here, we ran male and female mice in a restless two-armed bandit task, which encourages both exploration and exploitation. We systemically administered a nonselective DA antagonist (flupenthixol), a nonselective DA agonist (apomorphine), a NE beta-receptor antagonist (propranolol), and a NE beta-receptor agonist (isoproterenol) and examined changes in exploration within subjects across sessions. We found a bidirectional modulatory effect of dopamine on exploration. Increasing dopamine activity decreased exploration and decreasing dopamine activity increased exploration. The modulatory effect of beta-noradrenergic receptor activity on exploration was mediated by sex. Reinforcement learning model parameters suggested that dopamine modulation affected exploration via decision noise and norepinephrine modulation affected exploration via sensitivity to outcome. Together, these findings suggested that the mechanisms that govern the exploration-exploitation transition are sensitive to changes in both catecholamine functions and revealed differential roles for NE and DA in mediating exploration.

Optical control of cell-surface and endomembrane-exclusive ß-adrenergic receptor signaling.

Beta-adrenergic receptors (ßARs) are G protein-coupled receptors (GPCRs) that mediate catecholamine hormone-induced stress responses, such as elevation of heart rate. Besides those that are plasma membrane-bound, endomembrane ßARs are also signaling competent. Dysregulation of ßAR pathways underlies severe pathological conditions. Emerging evidence indicates pathological molecular signatures in deeper endomembrane ßARs signaling, likely contributing to conditions such as cardiomyocyte hypertrophy and apoptosis. However, the lack of approaches to control endomembrane ß1ARs has impeded linking signaling with pathology. Informed by the ß1AR-catecholamine interactions, we engineered an efficient photolabile proligand (OptoIso) to trigger ßAR signaling exclusively in endomembrane regions using blue light stimulation. Not only does OptoIso undergo blue light deprotection in seconds, but also efficiently enters cells and allows examination of G protein heterotrimer activation exclusively at endomembranes. OptoIso also allows optical activation of plasma membrane ßAR signaling in selected single cells with native fidelity, which can be reversed by terminating blue light. Thus, OptoIso will be a valuable experimental tool to elicit spatial and temporal control of ßAR signaling in user-defined endomembrane or plasma membrane regions in unmodified cells with native fidelity.

Neuromelanin-sensitive MRI as a promising biomarker of catecholamine function.

Disruptions to dopamine and noradrenergic neurotransmission are noted in several neurodegenerative and psychiatric disorders. Neuromelanin-sensitive (NM)-MRI offers a non-invasive approach to visualize and quantify the structural and functional integrity of the substantia nigra and locus coeruleus. This method may aid in the diagnosis and quantification of longitudinal changes of disease and could provide a stratification tool for predicting treatment success of pharmacological interventions targeting the dopaminergic and noradrenergic systems. Given the growing clinical interest in NM-MRI, understanding the contrast mechanisms that generate this signal is crucial for appropriate interpretation of NM-MRI outcomes and for the continued development of quantitative MRI biomarkers that assess disease severity and progression. To date, most studies associate NM-MRI measurements to the content of the neuromelanin pigment and/or density of neuromelanin-containing neurons, while recent studies suggest that the main source of the NM-MRI contrast is not the presence of neuromelanin but the high-water content in the dopaminergic and noradrenergic neurons. In this review, we consider the biological and physical basis for the NM-MRI contrast and discuss a wide range of interpretations of NM-MRI. We describe different acquisition and image processing approaches and discuss how these methods could be improved and standardized to facilitate large-scale multisite studies and translation into clinical use. We review the potential clinical applications in neurological and psychiatric disorders and the promise of NM-MRI as a biomarker of disease, and finally, we discuss the current limitations of NM-MRI that need to be addressed before this technique can be utilized as a biomarker and translated into clinical practice and offer suggestions for future research.

Loss of adipose TET proteins enhances ß-adrenergic responses and protects against obesity by epigenetic regulation of ß3-AR expression.

ß-adrenergic receptor (ß-AR) signaling plays predominant roles in modulating energy expenditure by triggering lipolysis and thermogenesis in adipose tissue, thereby conferring obesity resistance. Obesity is associated with diminished ß3-adrenergic receptor (ß3-AR) expression and decreased ß-adrenergic responses, but the molecular mechanism coupling nutrient overload to catecholamine resistance remains poorly defined. Ten-eleven translocation (TET) proteins are dioxygenases that alter the methylation status of DNA by oxidizing 5-methylcytosine to 5-hydroxymethylcytosine and further oxidized derivatives. Here, we show that TET proteins are pivotal epigenetic suppressors of ß3-AR expression in adipocytes, thereby attenuating the responsiveness to ß-adrenergic stimulation. Deletion of all three Tet genes in adipocytes led to increased ß3-AR expression and thereby enhanced the downstream ß-adrenergic responses, including lipolysis, thermogenic gene induction, oxidative metabolism, and fat browning in vitro and in vivo. In mouse adipose tissues, Tet expression was elevated after mice ate a high-fat diet. Mice with adipose-specific ablation of all TET proteins maintained higher levels of ß3-AR in both white and brown adipose tissues and remained sensitive to ß-AR stimuli under high-fat diet challenge, leading to augmented energy expenditure and decreased fat accumulation. Consequently, they exhibited improved cold tolerance and were substantially protected from diet-induced obesity, inflammation, and metabolic complications, including insulin resistance and hyperlipidemia. Mechanistically, TET proteins directly repressed ß3-AR transcription, mainly in an enzymatic activity-independent manner, and involved the recruitment of histone deacetylases to increase deacetylation of its promoter. Thus, the TET-histone deacetylase-ß3-AR axis could be targeted to treat obesity and related metabolic diseases.

Human Brainstem and Cerebellum Atlas: Chemoarchitecture and Cytoarchitecture Paired to MRI.

Lesion localization is the basis for understanding neurologic disease, which is predicated on neuroanatomical knowledge carefully cataloged from histology and imaging atlases. However, it is often difficult to correlate clinical images of brainstem injury obtained by MRI scans with the details of human brainstem neuroanatomy represented in atlases, which are mostly based on cytoarchitecture using Nissl stain or a single histochemical stain, and usually do not include the cerebellum. Here, we report a high-resolution (200 µm) 7T MRI of a cadaveric male human brainstem and cerebellum paired with detailed, coregistered histology (at 2 µm single-cell resolution) of the immunohistochemically stained cholinergic, serotonergic, and catecholaminergic (dopaminergic, noradrenergic, and adrenergic) neurons, in relationship to each other and to the cerebellum. These immunohistochemical findings provide novel insights into the spatial relationships of brainstem cell types and nuclei, including subpopulations of melanin and TH+ neurons, and allows for more informed structural annotation of cell groups. Moreover, the coregistered MRI-paired histology helps validate imaging findings. This is useful for interpreting both scans and histology, and to understand the cell types affected by lesions. Our detailed chemoarchitecture and cytoarchitecture with corresponding high-resolution MRI builds on previous atlases of the human brainstem and cerebellum, and makes precise identification of brainstem and cerebellar cell groups involved in clinical lesions accessible for both laboratory scientists and clinicians alike.SIGNIFICANCE STATEMENT Clinicians and neuroscientists frequently use cross-sectional anatomy of the human brainstem from MRI scans for both clinical and laboratory investigations, but they must rely on brain atlases to neuroanatomical structures. Such atlases generally lack both detail of brainstem chemical cell types, and the cerebellum, which provides an important spatial reference. Our current atlas maps the distribution of key brainstem cell types (cholinergic, serotonergic, and catecholaminergic neurons) in relationship to each other and the cerebellum, and pairs this histology with 7T MR images from the identical brain. This atlas allows correlation of the chemoarchitecture with corresponding MRI, and makes the identification of cell groups that are often discussed, but rarely identifiable on MRI scan, accessible to clinicians and clinical researchers.

Deletion of the α2δ-1 calcium channel subunit increases excitability of mouse chromaffin cells.

High voltage-gated Ca2+ channels (HVCCs) shape the electrical activity and control hormone release in most endocrine cells. HVCCs are multi-subunit protein complexes formed by the pore-forming α1 and the auxiliary ß, α2δ and γ subunits. Four genes code for the α2δ isoforms. At the mRNA level, mouse chromaffin cells (MCCs) express predominantly the CACNA2D1 gene coding for the α2δ-1 isoform. Here we show that α2δ-1 deletion led to ∼60% reduced HVCC Ca2+ influx with slower inactivation kinetics. Pharmacological dissection showed that HVCC composition remained similar in α2δ-1-/- MCCs compared to wild-type (WT), demonstrating that α2δ-1 exerts similar functional effects on all HVCC isoforms. Consistent with reduced HVCC Ca2+ influx, α2δ-1-/- MCCs showed reduced spontaneous electrical activity with action potentials (APs) having a shorter half-maximal duration caused by faster rising and decay slopes. However, the induced electrical activity showed opposite effects with α2δ-1-/- MCCs displaying significantly higher AP frequency in the tonic firing mode as well as an increase in the number of cells firing AP bursts compared to WT. This gain-of-function phenotype was caused by reduced functional activation of Ca2+-dependent K+ currents. Additionally, despite the reduced HVCC Ca2+ influx, the intracellular Ca2+ transients and vesicle exocytosis or endocytosis were unaltered in α2δ-1-/- MCCs compared to WT during sustained stimulation. In conclusion, our study shows that α2δ-1 genetic deletion reduces Ca2+ influx in cultured MCCs but leads to a paradoxical increase in catecholamine secretion due to increased excitability. KEY POINTS: Deletion of the α2δ-1 high voltage-gated Ca2+ channel (HVCC) subunit reduces mouse chromaffin cell (MCC) Ca2+ influx by ∼60% but causes a paradoxical increase in induced excitability. MCC intracellular Ca2+ transients are unaffected by the reduced HVCC Ca2+ influx. Deletion of α2δ-1 reduces the immediately releasable pool vesicle exocytosis but has no effect on catecholamine (CA) release in response to sustained stimuli. The increased electrical activity and CA release from MCCs might contribute to the previously reported cardiovascular phenotype of patients carrying α2δ-1 loss-of-function mutations.

Effects of reversible SERCA inhibition on catecholamine exocytosis and intracellular [Ca2+] signaling in chromaffin cells from normotensive Wistar Kyoto rats and spontaneously hypertensive rats.

Intracellular Ca2+ ([Ca2+]i) signaling and catecholamine (CA) exocytosis from adrenal chromaffin cells (CCs) differ between mammalian species. These differences partly result from the different contributions of Ca2+-induced Ca2+-release (CICR) from internal stores, which boosts intracellular Ca2+ signals. Transient inhibition of the sarcoendoplasmic reticulum (SERCA) Ca2+ pump with cyclopiazonic acid (CPA) reduces CICR. Recently, Martínez-Ramírez et al. found that CPA had contrasting effects on catecholamine secretion and intracellular Ca2+ signals in mouse and bovine CCs, where it enhanced and inhibited exocytosis, respectively. After CPA withdrawal, exocytosis diminished in mouse CCs and increased in bovine CCs. These differences can be explained if mouse CCs have weak CICR and strong Ca2+ uptake, and the reverse is true for bovine CCs. Surprisingly, CPA slightly reduced the amplitude of Ca2+ signals in both mouse and bovine CCs. Here we examined the effects of CPA on stimulated CA exocytosis and Ca2+ signaling in rat CCs and investigated if it alters differently the responses of CCs from normotensive (WKY) or hypertensive (SHR) rats, which differ in the gain of CICR. Our results demonstrate that CPA application strongly inhibits voltage-gated exocytosis and Ca2+ transients in rat CCs, regardless of strain (SHR or WKY). Thus, despite the greater phylogenetic distance from the most recent common ancestors, suppression of endoplasmic reticulum (ER) Ca2+ uptake through CPA inhibits the CA secretion in rat CCs more similarly to bovine than mouse CCs, unveiling divergent evolutionary relationships in the mechanism of CA exocytosis of CCs between rodents. Agents that inhibit the SERCA pump, such as CPA, suppress catecholamine secretion equally well in WKY and SHR CCs and are not potential therapeutic agents for hypertension. Rat CCs display Ca2+ signals of varying widths. Some even show early and late Ca2+ components. Narrowing the Ca2+ transients by CPA and ryanodine suggests that the late component is mainly due to CICR. Simultaneous recordings of Ca2+ signaling and amperometry in CCs revealed the existence of a robust and predictable correlation between the kinetics of the whole-cell intracellular Ca2+ signal and the rate of exocytosis at the single-cell level.

Catecholamines Attenuate LPS-Induced Inflammation through ß2 Adrenergic Receptor Activation- and PKA Phosphorylation-Mediated TLR4 Downregulation in Macrophages.

Inflammation is a tightly regulated process involving immune receptor recognition, immune cell migration, inflammatory mediator secretion, and pathogen elimination, all essential for combating infection and restoring damaged tissue. However, excessive inflammatory responses drive various human diseases. The autonomic nervous system (ANS) is known to regulate inflammatory responses; however, the detailed mechanisms underlying this regulation remain incompletely understood. Herein, we aimed to study the anti-inflammatory effects and mechanism of action of the ANS in RAW264.7 cells. Quantitative PCR and immunoblotting assays were used to assess lipopolysaccharide (LPS)-induced tumor necrosis factor α (TNFα) expression. The anti-inflammatory effects of catecholamines (adrenaline, noradrenaline, and dopamine) and acetylcholine were examined in LPS-treated cells to identify the receptors involved. Catecholamines inhibited LPS-induced TNFα expression by activating the ß2 adrenergic receptor (ß2-AR). ß2-AR activation in turn downregulated the expression of Toll-like receptor 4 (TLR4) by stimulating protein kinase A (PKA) phosphorylation, resulting in the suppression of TNFα levels. Collectively, our findings reveal a novel mechanism underlying the inhibitory effect of catecholamines on LPS-induced inflammatory responses, whereby ß2-AR activation and PKA phosphorylation downregulate TLR4 expression in macrophages. These findings could provide valuable insights for the treatment of inflammatory diseases and anti-inflammatory drug development.

Role of catecholamine synthases in the maintenance of cancer stem-like cells in malignant peripheral nerve sheath tumors.

Malignant peripheral nerve sheath tumors (MPNSTs) are malignant tumors that are derived from Schwann cell lineage around peripheral nerves. As in many other cancer types, cancer stem cells (CSCs) have been identified in MPNSTs, and they are considered the cause of treatment resistance, recurrence, and metastasis. As an element defining the cancer stemness of MPNSTs, we previously reported a molecular mechanism by which exogenous adrenaline activates a core cancer stemness factor, YAP/TAZ, through ß2 adrenoceptor (ADRB2). In this study, we found that MPNST cells express catecholamine synthases and that these enzymes are essential for maintaining cancer stemness, such as the ability to self-renew and maintain an undifferentiated state. Through gene knockdown and inhibition of these enzymes, we confirmed that catecholamines are indeed synthesized in MPNST cells. The results confirmed that catecholamine synthase knockdown in MPNST cells reduces the activity of YAP/TAZ. These data suggest that a mechanism of YAP/TAZ activation by de novo synthesized adrenaline, as well as exogenous adrenaline, may exist in the maintenance of cancer stemness of MPNST cells. This mechanism not only helps to understand the pathology of MPNST, but could also contribute to the development of therapeutic strategies for MPNST.

65 years of research on dopamine's role in classical fear conditioning and extinction: A systematic review.

Dopamine, a catecholamine neurotransmitter, has historically been associated with the encoding of reward, whereas its role in aversion has received less attention. Here, we systematically gathered the vast evidence of the role of dopamine in the simplest forms of aversive learning: classical fear conditioning and extinction. In the past, crude methods were used to augment or inhibit dopamine to study its relationship with fear conditioning and extinction. More advanced techniques such as conditional genetic, chemogenic and optogenetic approaches now provide causal evidence for dopamine's role in these learning processes. Dopamine neurons encode conditioned stimuli during fear conditioning and extinction and convey the signal via activation of D1-4 receptor sites particularly in the amygdala, prefrontal cortex and striatum. The coordinated activation of dopamine receptors allows for the continuous formation, consolidation, retrieval and updating of fear and extinction memory in a dynamic and reciprocal manner. Based on the reviewed literature, we conclude that dopamine is crucial for the encoding of classical fear conditioning and extinction and contributes in a way that is comparable to its role in encoding reward.

Molecular characterization and distribution of motilin and motilin receptor in the Japanese medaka Oryzias latipes.

Motilin (MLN) is a peptide hormone originally isolated from the mucosa of the porcine intestine. Its orthologs have been identified in various vertebrates. Although MLN regulates gastrointestinal motility in tetrapods from amphibians to mammals, recent studies indicate that MLN is not involved in the regulation of isolated intestinal motility in zebrafish, at least in vitro. To determine the unknown function of MLN in teleosts, we examined the expression of MLN and the MLN receptor (MLNR) at the cellular level in Japanese medaka (Oryzias latipes). Quantitative PCR revealed that mln mRNA was limitedly expressed in the gut, whereas mlnr mRNA was not detected in the gut but was expressed in the brain and kidney. By in situ hybridization and immunohistochemistry, mlnr mRNA was detected in the dopaminergic neurons of the area postrema in the brain and the noradrenaline-producing cells in the interrenal gland of the kidney. Furthermore, we observed efferent projections of mlnr-expressing dopaminergic neurons in the lobus vagi (XL) and nucleus motorius nervi vagi (NXm) of the medulla oblongata by establishing a transgenic medaka expressing the enhanced green fluorescence protein driven by the mlnr promoter. The expression of dopamine receptor mRNAs in the XL and cholinergic neurons in NXm was confirmed by in situ hybridization. These results indicate novel sites of MLN activity other than the gastrointestinal tract. MLN may exert central and peripheral actions through the regulation of catecholamine release in medaka.

Role of ß-adrenergic signaling and the NLRP3 inflammasome in chronic intermittent hypoxia-induced murine lung cancer progression.

BACKGROUND: Obstructive sleep apnea (OSA), characterized by chronic intermittent hypoxia (CIH), is a prevalent condition that has been associated with various forms of cancer. Although some clinical studies suggest a potential link between OSA and lung cancer, this association remains uncertain, and the underlying mechanisms are not fully understood. This study investigated the role of the catecholamine-ß-adrenergic receptor (ßAR) and the NLRP3 inflammasome in mediating the effects of CIH on lung cancer progression in mice. METHODS: Male C57BL/6 N mice were subjected to CIH for four weeks, with Lewis lung carcinoma cells seeded subcutaneously. Propranolol (a ßAR blocker) or nepicastat (an inhibitor of catecholamine production) was administered during this period. Tumor volume and tail artery blood pressure were monitored. Immunohistochemical staining and immunofluorescence staining were employed to assess protein expression of Ki-67, CD31, VEGFR2, PD-1, PD-L1, and ASC specks in tumor tissues. ELISA was used to detect catecholamine and various cytokines, while western blot assessed the expression of cyclin D1, caspase-1, and IL-1ß. In vitro tube formation assay investigated angiogenesis. NLRP3 knockout mice were used to determine the mechanism of NLRP3 in CIH. RESULTS: CIH led to an increase in catecholamine. Catecholamine-ßAR inhibitor drugs prevented the increase in blood pressure caused by CIH. Notably, the drugs inhibited CIH-induced murine lung tumor growth, and the expression of Ki-67, cyclin D1, CD31, VEGFR2, PD-1 and PD-L1 in tumor decreased. In vitro, propranolol inhibits tube formation induced by CIH mouse serum. Moreover, CIH led to an increase in TNF-α, IL-6, IL-1ß, IFN-γ and sPD-L1 levels and a decrease in IL-10 in peripheral blood, accompanied by activation of NLRP3 inflammasomes in tumor, but these effects were also stopped by drugs. In NLRP3-knockout mice, CIH-induced upregulation of PD-1/PD-L1 in tumor was inhibited. CONCLUSIONS: Our study underscores the significant contribution of ß-adrenergic signaling and the NLRP3 inflammasome to CIH-induced lung cancer progression. These pathways represent potential therapeutic targets for mitigating the impact of OSA on lung cancer.

The evidence-based role of catecholaminergic PET tracers in Neuroblastoma. A systematic review and a head-to-head comparison with mIBG scintigraphy.

BACKGROUND: Molecular imaging is pivotal in staging and response assessment of children with neuroblastoma (NB). [123I]-metaiodobenzylguanidine (mIBG) is the standard imaging method; however, it is characterised by low spatial resolution, time-consuming acquisition procedures and difficult interpretation. Many PET catecholaminergic radiotracers have been proposed as a replacement for [123I]-mIBG, however they have not yet made it into clinical practice. We aimed to review the available literature comparing head-to-head [123I]-mIBG with the most common PET catecholaminergic radiopharmaceuticals. METHODS: We searched the PubMed database for studies performing a head-to-head comparison between [123I]-mIBG and PET radiopharmaceuticals including meta-hydroxyephedrine ([11C]C-HED), 18F-18F-3,4-dihydroxyphenylalanine ([18F]DOPA) [124I]mIBG and Meta-[18F]fluorobenzylguanidine ([18F]mFBG). Review articles, preclinical studies, small case series (< 5 subjects), case reports, and articles not in English were excluded. From each study, the following characteristics were extracted: bibliographic information, technical parameters, and the sensitivity of the procedure according to a patient-based analysis (PBA) and a lesion-based analysis (LBA). RESULTS: Ten studies were selected: two regarding [11C]C-HED, four [18F]DOPA, one [124I]mIBG, and three [18F]mFBG. These studies included 181 patients (range 5-46). For the PBA, the superiority of the PET method was reported in two out of ten studies (both using [18F]DOPA). For LBA, PET detected significantly more lesions than scintigraphy in seven out of ten studies. CONCLUSIONS: PET/CT using catecholaminergic tracers shows superior diagnostic performance than mIBG scintigraphy. However, it is still unknown if such superiority can influence clinical decision-making. Nonetheless, the PET examination appears promising for clinical practice as it offers faster image acquisition, less need for sedation, and a single-day examination.

The pivotal role of neuronal nitric oxide synthase in the release of 6-nitrodopamine from mouse isolated vas deferens.

6-Nitrodopamine (6-ND) is released from rat and human vas deferens and is considered a major mediator of both tissues contractility. The contractions induced by 6-ND are selectively blocked by both tricyclic antidepressants and α1-adrenoceptor antagonists. Endothelial nitric oxide synthase (eNOS) is the major isoform responsible for 6-ND release in mouse isolated heart, however the origin of 6-ND in the vas deferens is unknown. Here it was investigated by LC-MS/MS the basal release of 6-ND from isolated vas deferens obtained from control, eNOS-/-, nNOS-/-, and iNOS-/- mice. In addition, it was evaluated in vitro vas deferens contractility following electric field stimulation (EFS). Basal release of 6-ND was significantly reduced in nNOS-/- mice compared to control mice, but not decreased when the vas deferens were obtained from either eNOS-/- or iNOS-/- mice. Pre-incubation of the vas deferens with tetrodotoxin (1 µM) significantly reduced the basal release of 6-ND from control, eNOS-/-, and iNOS-/- mice but had no effect on the basal release of 6-ND from nNOS-/- mice. EFS-induced frequency-dependent contractions of the vas deferens, which were significantly reduced when the tissues obtained from control, eNOS-/- and iNOS-/- mice, were pre-incubated with l-NAME, but unaltered when the vas deferens was obtained from nNOS-/- mice. In addition, the EFS-induced contractions were significantly smaller when the vas deferens were obtained from nNOS-/- mice. The results clearly demonstrate that nNOS is the main NO isoform responsible for 6-ND release in mouse vas deferens and reinforces the concept of 6-ND as a major modulator of vas deferens contractility.

Impaired Dynamic Sarcoplasmic Reticulum Ca Buffering in Autosomal Dominant CPVT2.

BACKGROUND: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a potentially lethal cardiac arrhythmia syndrome triggered by catecholamines released during exercise, stress, or sudden emotion. Variants in the calsequestrin-2 gene (CASQ2), encoding the major calcium (Ca) binding protein in the sarcoplasmic reticulum (SR), are the second most common cause of CPVT. Recently, several CASQ2 gene variants, such as CASQ2-K180R, have been linked to an autosomal dominant form of Casq2-linked CPVT (CPVT2), but the underlying mechanism is not known. METHODS: A K180R mouse model was generated using CRIPSR/Cas9. Heterozygous and homozygous K180R mice were studied using telemetry ECG recordings in vivo. Ventricular cardiomyocytes were isolated and studied using fluorescent Ca indicators and patch clamp. Expression levels and localization of SR Ca-handling proteins were evaluated using Western blotting and immunostaining. Intra-SR Ca kinetics were quantified using low-affinity Ca indicators. RESULTS: K180R mice exhibit an autosomal dominant CPVT phenotype following exercise or catecholamine stress. Upon catecholamine stress, K180R ventricular cardiomyocytes exhibit increased spontaneous SR Ca release events, triggering delayed afterdepolarizations and spontaneous beats. K180R had no effect on levels of Casq2, Casq2 polymers, or other SR Ca-handling proteins. Intra-SR Ca measurements revealed that K180R impaired dynamic intra-SR Ca buffering, resulting in a more rapid rise of free Ca in the SR during diastole. Steady-state SR Ca buffering and total SR Ca content were not changed. Consistent with the reduced dynamic intra-SR buffering, K180R causes reduced SR Ca release refractoriness. CONCLUSIONS: CASQ2-K180R causes CPVT2 via a heretofore unknown mechanism that differs from CASQ2 variants associated with autosomal recessive CPVT2. Unlike autosomal recessive CASQ2 variants, K180R impairs the dynamic buffering of Ca within the SR without affecting total SR Ca content or Casq2 protein levels. Our data provide insight into the molecular mechanism underlying autosomal dominant CPVT2.

Obesity-induced tissue alterations resist weight loss: A mechanistic review.

Interventions aimed at weight control often have limited effectiveness in combating obesity. This review explores how obesity-induced dysfunction in white (WAT) and brown adipose tissue (BAT), skeletal muscle, and the brain blunt weight loss, leading to retention of stored fat. In obesity, increased adrenergic stimulation and inflammation downregulate ß-adrenoreceptors and impair catecholaminergic signalling in adipocytes. This disrupts adrenergic-mediated lipolysis, diminishing lipid oxidation in both white and brown adipocytes, lowering thermogenesis and blunting fat loss. Emerging evidence suggests that WAT fibrosis is associated with worse weight loss outcomes; indeed, limiting collagen and laminin-α4 deposition mitigates WAT accumulation, enhances browning, and protects against high-fat-diet-induced obesity. Obesity compromises mitochondrial oxidative capacity and lipid oxidation in skeletal muscle, impairing its ability to switch between glucose and lipid metabolism in response to varying nutrient levels and exercise. This dysfunctional phenotype in muscle is exacerbated in the presence of obesity-associated sarcopenia. Additionally, obesity suppresses sarcolipin-induced sarcoplasmic reticulum calcium ATPase (SERCA) activation, resulting in reduced oxidative capacity, diminished energy expenditure, and increased adiposity. In the hypothalamus, obesity and overnutrition impair insulin and leptin signalling. This blunts central satiety signals, favouring a shift in energy balance toward energy conservation and body fat retention. Moreover, both obese animals and humans demonstrate impaired dopaminergic signalling and diminished responses to nutrient intake in the striatum, which tend to persist after weight loss. This may result in enduring inclinations toward overeating and a sedentary lifestyle. Collectively, the tissue adaptations described pose significant challenges to effectively achieving and sustaining weight loss in obesity.

Testing preload responsiveness by the tidal volume challenge assessed by the photoplethysmographic perfusion index.

BACKGROUND: To detect preload responsiveness in patients ventilated with a tidal volume (Vt) at 6 mL/kg of predicted body weight (PBW), the Vt-challenge consists in increasing Vt from 6 to 8 mL/kg PBW and measuring the increase in pulse pressure variation (PPV). However, this requires an arterial catheter. The perfusion index (PI), which reflects the amplitude of the photoplethysmographic signal, may reflect stroke volume and its respiratory variation (pleth variability index, PVI) may estimate PPV. We assessed whether Vt-challenge-induced changes in PI or PVI could be as reliable as changes in PPV for detecting preload responsiveness defined by a PLR-induced increase in cardiac index (CI) ≥ 10%. METHODS: In critically ill patients ventilated with Vt = 6 mL/kg PBW and no spontaneous breathing, haemodynamic (PICCO2 system) and photoplethysmographic (Masimo-SET technique, sensor placed on the finger or the forehead) data were recorded during a Vt-challenge and a PLR test. RESULTS: Among 63 screened patients, 21 (33%) were excluded because of an unstable PI signal and/or atrial fibrillation and 42 were included. During the Vt-challenge in the 16 preload responders, CI decreased by 4.8 ± 2.8% (percent change), PPV increased by 4.4 ± 1.9% (absolute change), PIfinger decreased by 14.5 ± 10.7% (percent change), PVIfinger increased by 1.9 ± 2.6% (absolute change), PIforehead decreased by 18.7 ± 10.9 (percent change) and PVIforehead increased by 1.0 ± 2.5 (absolute change). All these changes were larger than in preload non-responders. The area under the ROC curve (AUROC) for detecting preload responsiveness was 0.97 ± 0.02 for the Vt-challenge-induced changes in CI (percent change), 0.95 ± 0.04 for the Vt-challenge-induced changes in PPV (absolute change), 0.98 ± 0.02 for Vt-challenge-induced changes in PIforehead (percent change) and 0.85 ± 0.05 for Vt-challenge-induced changes in PIfinger (percent change) (p = 0.04 vs. PIforehead). The AUROC for the Vt-challenge-induced changes in PVIforehead and PVIfinger was significantly larger than 0.50, but smaller than the AUROC for the Vt-challenge-induced changes in PPV. CONCLUSIONS: In patients under mechanical ventilation with no spontaneous breathing and/or atrial fibrillation, changes in PI detected during Vt-challenge reliably detected preload responsiveness. The reliability was better when PI was measured on the forehead than on the fingertip. Changes in PVI during the Vt-challenge also detected preload responsiveness, but with lower accuracy.