Ultra-high resolution spectral photon-counting CT outperforms dual layer CT for lung imaging: Results of a phantom study.

PURPOSE: The purpose of this study was to compare lung image quality obtained with ultra-high resolution (UHR) spectral photon-counting CT (SPCCT) with that of dual-layer CT (DLCT), at standard and low dose levels using an image quality phantom and an anthropomorphic lung phantom. METHODS: An image quality phantom was scanned using a clinical SPCCT prototype and an 8 cm collimation DLCT from the same manufacturer at 10 mGy. Additional acquisitions at 6 mGy were performed with SPCCT only. Images were reconstructed with dedicated high-frequency reconstruction kernels, slice thickness between 0.58 and 0.67 mm, and matrix between 5122 and 10242 mm, using a hybrid iterative algorithm at level 6. Noise power spectrum (NPS), task-based transfer function (TTF) for iodine and air inserts, and detectability index (d') were assessed for ground-glass and solid nodules of 2 mm to simulate highly detailed lung lesions. Subjective analysis of an anthropomorphic lung phantom was performed by two radiologists using a five-point quality score. RESULTS: At 10 mGy, noise magnitude was reduced by 29.1 % with SPCCT images compared to DLCT images for all parameters (27.1 ± 11.0 [standard deviation (SD)] HU vs. 38.2 ± 1.0 [SD] HU, respectively). At 6 mGy with SPCCT images, noise magnitude was reduced by 8.9 % compared to DLCT images at 10 mGy (34.8 ± 14.1 [SD] HU vs. 38.2 ± 1.0 [SD] HU, respectively). At 10 mGy and 6 mGy, average NPS spatial frequency (fav) was greater for SPCCT images (0.75 ± 0.17 [SD] mm-1) compared to DLCT images at 10 mGy (0.55 ± 0.04 [SD] mm-1) while remaining constant from 10 to 6 mGy. At 10 mGy, TTF at 50 % (f50) was greater for SPCCT images (0.92 ± 0.08 [SD] mm-1) compared to DLCT images (0.67 ± 0.06 [SD] mm-1) for both inserts. At 6 mGy, f50 decreased by 1.1 % for SPCCT images, while remaining greater compared to DLCT images at 10 mGy (0.91 ± 0.06 [SD] mm-1 vs. 0.67 ± 0.06 [SD] mm-1, respectively). At both dose levels, d' were greater for SPCCT images compared to DLCT for all clinical tasks. Subjective analysis performed by two radiologists revealed a greater median image quality for SPCCT (5; Q1, 4; Q3, 5) compared to DLCT images (3; Q1, 3; Q3, 3). CONCLUSION: UHR SPCCT outperforms DLCT in terms of image quality for lung imaging. In addition, UHR SPCCT contributes to a 40 % reduction in radiation dose compared to DLCT.

Photon-counting CT systems: A technical review of current clinical possibilities.

In recent years, computed tomography (CT) has undergone a number of developments to improve radiological care. The most recent major innovation has been the development of photon-counting detectors. By comparison with the energy-integrating detectors traditionally used in CT, these detectors offer better dose efficiency, eliminate electronic noise, improve spatial resolution and have intrinsic spectral sensitivity. These detectors also allow the energy of each photon to be counted, thus improving the sampling of the X-ray spectrum in multiple energy bins, to better distinguish between photoelectric and Compton attenuation coefficients, resulting in better spectral images and specific color K-edge images. The purpose of this article was to make the reader more familiar with the basic principles and techniques of new photon-counting CT systems equipped with photon-counting detectors and also to describe the currently available devices that could be used in clinical practice.

Characteristics of patients with difficult-to-treat rheumatoid arthritis: a descriptive retrospective cohort study.

BACKGROUND: In 2021, an EULAR task force published a definition of difficult-to-treat rheumatoid arthritis (D2T RA). Our current knowledge of D2T RA with the EULAR definition is based on European and Asian cohorts, and no North American cohort has yet to be published. The aim of this study was to compare D2T RA patients to non-D2T RA who are good responders to advanced therapy, and to describe their evolution in an university health center patient cohort. METHODS: This is a retrospective single centre study of the medical records of all adults with RA on at least one biologic or target synthetic DMARD (b/tsDMARD). D2T RA group was defined according to the EULAR definition of D2T RA. The non-D2T RA group was defined as a b/tsDMARD good responder who had low-disease activity or remission for at least one year on 1 or 2 b/tsDMARD mechanism of action. We compared the patients' comorbidities, and history of b/tsDMARD use. Descriptive statistics and proportions were calculated. Kaplan-Meier analysis with log-rank test was used to estimate and compare median survival. RESULTS: Among the 417 patients, 101 (24%) were D2T RA and 316 (76%) were non-D2T RA. D2T RA group was slightly younger (63 ± 9 years versus 65 ± 12 years, p = 0.045), more likely to have concomitant non-inflammatory pain (28% versus 8%, p < 0.0001) and to discontinue at least one b/tsDMARD due to intolerance (39% versus 10%, p < 0.0001). In the D2T RA group, JAK inhibitors were associated with longer drug continuation when used as the third b/tsDMARD. Fewer patients were using corticosteroid at their most recent follow-up in this Canadian cohort compared to others (16% versus from 29 to 74%). CONCLUSION: Concomitant non-inflammatory pain was more prevalent in D2T RA patients compared to b/tsDMARD good responder non-D2T RA patients. Steroid-sparing strategies is possible even in D2T RA patients. Future prospective research may compare JAK inhibitors with other mechanisms of action in D2T RA.

Dosimetric impact of 3D motion-compensated SPECT reconstruction for SIRT planning.

BACKGROUND: In selective internal radiation therapy, 99mTc SPECT images are used to optimize patient treatment planning, but they are affected by respiratory motion. In this study, we evaluated on patient data the dosimetric impact of motion-compensated SPECT reconstruction on several volumes of interest (VOI), on the tumor-to-normal liver (TN) ratio and on the activity to be injected. METHODS: Twenty-nine patients with liver cancer or hepatic metastases treated by radioembolization were included in this study. The biodistribution of 90Y is assumed to be the same as that of 99mTc when predictive dosimetry is implemented. A total of 31 99mTc SPECT images were acquired and reconstructed with two methods: conventional OSEM (3D) and motion-compensated OSEM (3Dcomp). Seven VOI (liver, lungs, tumors, perfused liver, hepatic reserve, healthy perfused liver and healthy liver) were delineated on the CT or obtained by thresholding SPECT images followed by Boolean operations. Absorbed doses were calculated for each reconstruction using Monte Carlo simulations. Percentages of dose difference (PDD) between 3Dcomp and 3D reconstructions were estimated as well as the relative differences for TN ratio and activities to be injected. The amplitude of movement was determined with local rigid registration of the liver between the 3Dcomp reconstructions of the extreme phases of breathing. RESULTS: The mean amplitude of the liver was 9.5 ± 2.7 mm. Medians of PDD were closed to zero for all VOI except for lungs (6.4%) which means that the motion compensation overestimates the absorbed dose to the lungs compared to the 3D reconstruction. The smallest lesions had higher PDD than the largest ones. Between 3D and 3Dcomp reconstructions, means of differences in lung dose and TN ratio were not statistically significant, but in some cases these differences exceed 1 Gy (4/31) and 8% (2/31). The absolute differences in activity were on average 3.1% ± 5.1% and can reach 22.8%. CONCLUSION: The correction of respiratory motion mainly impacts the lung and tumor doses but only for some patients. The largest dose differences are observed for the smallest lesions.

Liver Resection for Type IV Perihilar Cholangiocarcinoma: Left or Right Trisectionectomy?

How the side of an extended liver resection impacts the postoperative prognosis of advanced perihilar cholangiocarcinoma (PHC) is still controversial. We compared the outcomes of right (RTS) and left trisectionectomies (LTS) in Bismuth-Corlette (BC) type IV PHC resection. All patients undergoing RTS or LTS for BC type IV PHC in a single tertiary center between January 2012 and December 2019 were compared retrospectively. The endpoints were perioperative outcomes, long-term overall (OS), and disease-free survival (DFS). Among 67 hepatic resections for BC type IV PHC, 25 (37.3%) were LTS and 42 (63.7%) were RTS. Portal vein and artery resection rates were 40% and 52.4% (p = 0.29), and 24% and 0% (p < 0.001) in the LTS and RTS groups, respectively. The severe complication (Clavien−Dindo > IIIa) rate was comparable (36% vs. 21.5%, p = 0.357) while the postoperative liver failure (POLF) rate was lower in the LTS group (16% vs. 38%, p = 0.048). The R0 resection rate was similar between groups (81% vs. 92%; p = 0.154). The five-year OS rate was higher in the LTS group (66% vs. 30%, p = 0.009) while DFS was comparable (43% vs. 18%, p = 0.11). Based on multivariable analysis, the side of the trisectionectomy was an independent predictor of OS. Compared with RTS, LTS is associated with lower POLF and higher overall survival despite more frequent arterial reconstructions in type IV PHC. Although technically more demanding, LTS may be preferred in the treatment of advanced PHC.

Cyclobishelicenes: Shape-Persistent Figure-Eight Aromatic Molecules with Promising Chiroptical Properties.

Cyclobis[n]helicenes (n=3 or 5) are chiral D2 -symmetric π-conjugated macrocycles with stable lemniscular, or figure-eight, shapes. The conformational analysis of five different cyclobis[n]helicenes revealed that these molecules can only exist as their lemniscular conformers with high barriers to enantiomerization (>200 kJ mol-1 ). The enantiomers of a cyclobis[5]helicene were resolved by HPLC and their unusual chiroptical properties were attributed to the inherent chirality of their macrocyclic figure-eight.

Extended Right Hepatectomy and Inferior Vena Cava Graft Replacement for En Bloc Resection of Hepatocellular Carcinoma with Cavo-Hepatic Venous Confluence Invasion.

BACKGROUND: Hepatocellular carcinoma (HCC) associated with tumor extension in the portal vein, hepatic vein, or inferior vena cava (IVC) is traditionally considered an advanced stage of disease to which palliative radiotherapy or sorafenib chemotherapy is proposed.1,2 Recent studies have shown a significant survival benefit in patients treated with R0 liver resection.3-5 METHODS: We describe the case of a 45-year-old female patient presenting with a voluminous HCC developed in a non-cirrhotic liver with a tumor thrombus obstructing the retrohepatic IVC and the middle hepatic vein termination. Initial treatment included two cycles of selective internal radiation therapy with Yttrium 90 and sorafenib treatment for 1 year. Re-evaluation revealed a significant reduction of the tumor and compensative hypertrophy of the left liver lobe, enabling surgical resection. RESULTS: The procedure included anatomic right hepatic trisectionectomy with caudate lobectomy and retrohepatic IVC graft replacement. Total liver vascular exclusion with intrapericardial IVC control enabled en bloc R0 resection of the tumor and the floating tumor thrombus in the cavo-hepatic venous confluence. Total liver vascular exclusion duration was 20 min, for a total warm liver ischemia of 40 min. The duration of the operation was 240 min and blood loss was 700 mL. The patient was discharged on postoperative day 15 and was free of disease 6 months post-surgery. CONCLUSION: Liver surgery with complex vascular resections for HCC with major vascular invasion should be considered a valid therapeutic option in high-volume hepatobiliary centers.

Cyclic tris-[5]helicenes with single and triple twisted Möbius topologies and Möbius aromaticity.

A number of singly (180°) twisted, largely single-stranded and thus conformationally rather fragile, Möbius molecules have been synthesized within the last 15 years, which are aromatic with 4n electrons, thus violating the Hückel rule. Annulenes with significantly higher twist (e.g. 540°) that retain a full cyclic conjugation path have been elusive, mainly because of the high strain and loss of orbital overlap. Recently, a topological strategy was devised to project the "twist" into "writhe", thus reducing the strain. However, orbital overlap was still severely reduced within the flexible building blocks. We now present a single and a triple twisted annulene with fully conjugated peripheries. They are unique in their pronounced band shape and conformational robustness as they are made up of three fully kata-condensed [5]helicene fragments. The triple twisted molecule exhibits a strong diatropic ring current in the outer periphery, even though the π system includes 4n electrons. The diatropic current is counterbalanced by a paratropic current in the σ system, resulting in no net manifestation of macrocyclic aromaticity. The key step of the synthesis of both Möbius compounds is a Perkin condensation of complementary bifunctional bismaleates leading to a flexible macrocycle containing alternating benzene and biphenyl fragments. Subsequent photocyclization yields a separable mixture of rigid diastereomeric tris-helicene macrocycles of the above topologies.

Non-planar oligoarylene macrocycles from biphenyl.

Saddle- and propeller-shaped macrocycles are obtained by fourfold Perkin condensations in transient high dilution of 4,4'-bis(phenylglyoxylic acid) with either 4,4'-bis(phenylacetic acid) or p-phenylenediacetic acid, followed by four-fold oxidative photocyclizations. In the saddle-shaped tetraphenanthrylene, the angle between opposite phenanthrene planes is close to the value of 90° of an ideal saddle. In the two helicene fragments of the propeller-shaped double [5]helicene, the geometry of unsubstituted [5]helicene is preserved without major macrocycle-induced distortions.

Directed assembly of single colloidal gold nanowires by AFM nanoxerography.

Ultrathin gold nanowires (NWs) dispersed in hexane were prepared by chemical reduction of HAuCl4 in oleylamine, along with nanospheres (NSs), side products of the reaction. X-ray photoelectron spectroscopy and small-angle X-ray scattering evidenced a stabilization of these nano-objects by oleylammonium chloride surfactants. The directed assembly of these nano-objects on surfaces was performed by atomic force microscopy (AFM) nanoxerography in a few seconds. Selective assembly of gold NWs only occurred on positively charged patterns, while NSs assembled more specifically on the negatively charged ones. This sorting suggests that the strong electric field generated by the charge patterns induced a negative effective charge on the gold NWs and a weak positive effective charge on the NSs. Such difference could be explained by the ion organization at the colloid surface, monolayered in the case of NWs, and bilayered in the case of NSs. By adjusting the design of the positive patterns and the experimental conditions of development, single gold nanowires were successfully assembled by AFM nanoxerography on predefined sites of surfaces without damaging them, opening the way for future electrical and mechanical characterizations.

DiAs web monitoring: a real-time remote monitoring system designed for artificial pancreas outpatient trials.

BACKGROUND: Developments in an artificial pancreas (AP) for patients with type 1 diabetes have allowed a move toward performing outpatient clinical trials. "Home-like" environment implies specific protocol and system adaptations among which the introduction of remote monitoring is meaningful. We present a novel tool allowing multiple patients to monitor AP use in home-like settings. METHODS: We investigated existing systems, performed interviews of experienced clinical teams, listed required features, and drew several mockups of the user interface. The resulting application was tested on the bench before it was used in three outpatient studies representing 3480 h of remote monitoring. RESULTS: Our tool, called DiAs Web Monitoring (DWM), is a web-based application that ensures reception, storage, and display of data sent by AP systems. Continuous glucose monitoring (CGM) and insulin delivery data are presented in a colored chart to facilitate reading and interpretation. Several subjects can be monitored simultaneously on the same screen, and alerts are triggered to help detect events such as hypoglycemia or CGM failures. In the third trial, DWM received approximately 460 data per subject per hour: 77% for log messages, 5% for CGM data. More than 97% of transmissions were achieved in less than 5 min. CONCLUSIONS: Transition from a hospital setting to home-like conditions requires specific AP supervision to which remote monitoring systems can contribute valuably. DiAs Web Monitoring worked properly when tested in our outpatient studies. It could facilitate subject monitoring and even accelerate medical and technical assessment of the AP. It should now be adapted for long-term studies with an enhanced notification feature.

The relationship between agonist potency and AMPA receptor kinetics.

AMPA-type glutamate receptors are tetrameric ion channels that mediate fast excitatory synaptic transmission in the mammalian brain. When agonists occupy the binding domain of individual receptor subunits, this domain closes, triggering rearrangements that couple agonist binding to channel opening. Here we compare the kinetic behavior of GluR2 channels activated by four different ligands, glutamate, AMPA, quisqualate, and 2-Me-Tet-AMPA, full agonists that vary in potency by up to two orders of magnitude. After reduction of desensitization with cyclothiazide, deactivation decays were strongly agonist dependent. The time constants of decay increased with potency, and slow components in the multiexponential decays became more prominent. The desensitization decays of agonist-activated currents also contained multiple exponential components, but they were similar for the four agonists. The time course of recovery from desensitization produced by each agonist was described by two sigmoid components, and the speed of recovery varied substantially. Recovery was fastest for glutamate and slowest for 2-Me-Tet-AMPA, and the amplitude of the slow component of recovery increased with agonist potency. The multiple kinetic components appear to arise from closed-state transitions that precede channel gating. Stargazin increases the slow kinetic components, and they likely contribute to the biexponential decay of excitatory postsynaptic currents.

AMPA receptor binding cleft mutations that alter affinity, efficacy, and recovery from desensitization.

Glutamate binds to AMPA receptors within a deep cleft between two globular protein domains (domains 1 and 2). Once glutamate binds, the cleft closes, and agonist-bound structures of the isolated ligand binding core suggest that closure of the binding cleft is sufficiently complete that it essentially prevents ligand dissociation. There is also considerable evidence supporting the view that cleft closure is the initial conformational change that triggers receptor activation and desensitization, and it has been clearly demonstrated that there is a correlation between the degree of cleft closure and agonist efficacy. It is unknown, however, whether the stability of binding cleft closure also influences receptor-channel properties. The crystallographic structures indicate that closed-cleft conformations are stabilized by the formation of hydrogen bonds that involve amino acid side chains of residues in domains 1 and 2. We show here that mutations that disrupt one such cross-cleft hydrogen bond (in the AMPA receptor subunit GluR2) decrease both agonist affinity and efficacy. The same mutations also hasten recovery from desensitization. We conclude that the stability of binding cleft closure has a significant impact on AMPA receptor function and is a major determinant of the apparent affinity of agonists. The results suggest that the stability of cleft closure has been tuned so that glutamate dissociates as rapidly as possible yet remains a full agonist.

Reaction mechanism determines NMDA receptor response to repetitive stimulation.

At central excitatory synapses, N-methyl-D-aspartate (NMDA) receptors, which have a high affinity for glutamate, produce a slowly rising synaptic current in response to a single transmitter pulse and an additional current after a second, closely timed stimulus. Here we show, by examining the kinetics of transmitter binding and channel gating in single-channel currents from recombinant NR1/NR2A receptors, that the synaptic response to trains of impulses is determined by the molecular reaction mechanism of the receptor. The rate constants estimated for the activation reaction predict that, after binding neurotransmitter, receptors hesitate for approximately 4 ms in a closed high-affinity conformation before they either proceed towards opening or release neurotransmitter, with about equal probabilities. Because only about half of the initially fully occupied receptors become active, repetitive stimulation elicits currents with distinct waveforms depending on pulse frequency. This high-affinity/low-efficiency activation mechanism might serve as a link between stimulation frequency and the directionality of the ensuing synaptic plasticity.

Azithromycin monotherapy for patients hospitalized with community-acquired pneumonia: a 31/2-year experience from a veterans affairs hospital.

BACKGROUND: Current American Thoracic Society (ATS) community-acquired pneumonia treatment guidelines recommend azithromycin monotherapy for a limited subset of hospitalized patients. We evaluated the effectiveness of azithromycin monotherapy in a more generalized population of patients hospitalized with mild-to-moderate community-acquired pneumonia. METHODS: We reviewed medical records from a Veterans Affairs facility for patients admitted with community-acquired pneumonia between December 1, 1997, and June 30, 2001, comparing those receiving azithromycin monotherapy, other ATS-recommended antibiotics, and non-ATS-recommended antibiotics. We excluded patients with immunosuppression, metastatic cancer, or hospital-acquired pneumonia. Outcome measures included times to stability, meeting criteria for change to oral therapy, and eligibility for discharge; length of stay; intensive care unit transfer; and mortality. Outcomes were adjusted for pneumonia severity, skilled nursing facility status, and processes of care. RESULTS: A total of 442 patients were eligible for the study (221 in the azithromycin monotherapy group, 129 in the ATS group, and 92 in the non-ATS group). Times to clinical stability and to fulfilling early switch criteria were not statistically significantly different among the 3 groups. Mean time to fulfilling early discharge criteria was 2.48 days for patients receiving azithromycin monotherapy vs 2.84 days for those receiving ATS antibiotics (P =.008) and 2.58 days for those receiving non-ATS antibiotics (P =.64). Overall mean length of stay was shorter in the azithromycin monotherapy group (4.35 days) vs the ATS (5.73 days) (P =.002) and non-ATS (6.21 days) (P<.001) groups. Mortality, intensive care unit transfer, and readmission rates were similar across the groups. CONCLUSION: Azithromycin monotherapy is equally as efficacious as other ATS-recommended regimens for treating hospitalized patients with mild-to-moderate community-acquired pneumonia.

How AMPA receptor desensitization depends on receptor occupancy.

AMPA-type glutamate receptors mediate fast excitatory transmission at many central synapses, and rapid desensitization of these receptors can shape the decay of synaptic currents and limit the fidelity of high-frequency synaptic transmission. Here we use a combination of fast glutamate application protocols and kinetic simulations to determine how AMPA receptor desensitization depends on the number of subunits occupied by glutamate. We show that occupancy of a single subunit is sufficient to desensitize AMPA-type channels and that receptors with one to four glutamates bound enter desensitization at similar rates. We find that recovery from desensitization follows a similar sigmoid time course for channels with two to four glutamates bound but is faster and exponential for singly occupied channels. The results suggest that desensitization, at intermediate and high glutamate concentrations, is accompanied by two conformational changes that slow glutamate dissociation. We propose a kinetic scheme that accurately predicts several types of experimental results and differs significantly from previous models in the assignment of affinities for binding to closed and desensitized states. We conclude that desensitization involves a rearrangement that stabilizes the binding domains of one subunit in each dimer in a partially closed conformation. This stabilization likely results from an interaction at the dimer-dimer interface between the binding domains of adjacent subunits.

The expression of dominant-negative subunits selectively suppresses neuronal AMPA and kainate receptors.

Glutamate-gated ion channels are widely expressed in neurons where they serve a host of cellular functions. An appealing, but yet unexplored, way to delineate the functions of particular glutamate receptor subtypes is to direct the expression of dominant-negative and gain-of-function mutant subunits. We tested the ability of two dominant-negative subunits, an alpha-amino-3-hydroxy-5-methyl-isoxazolproprionic acid receptor subunit and a kainate receptor subunit, to silence recombinant and neuronal glutamate receptors. Co-expression studies in non-neuronal cells indicated that the inclusion of a single mutant subunit was sufficient to silence the receptor. When expressed in cerebellar granule cells, the dominant-negative subunits silenced native channels in a subtype-specific fashion. Immunocytochemical staining of control and transfected neurons, as well as studies with a gain-of-function glutamate receptor-1 mutant, indicated that the mutant subunits were expressed at levels roughly equal to the total abundance of related native subunits, and both dominant-negatives suppressed native channel expression 60-65% when tested 24 h post-transfection. If co-assembly of the mutant subunits with related native subunits is combinatorial, this level of suppression gives receptor half-lives of approximately 20 h.

A new way to rapidly create functional, fluorescent fusion proteins: random insertion of GFP with an in vitro transposition reaction.

BACKGROUND: The jellyfish green fluorescent protein (GFP) can be inserted into the middle of another protein to produce a functional, fluorescent fusion protein. Finding permissive sites for insertion, however, can be difficult. Here we describe a transposon-based approach for rapidly creating libraries of GFP fusion proteins. RESULTS: We tested our approach on the glutamate receptor subunit, GluR1, and the G protein subunit, alphas. All of the in-frame GFP insertions produced a fluorescent protein, consistent with the idea that GFP will fold and form a fluorophore when inserted into virtually any domain of another protein. Some of the proteins retained their signaling function, and the random nature of the transposition process revealed permissive sites for insertion that would not have been predicted on the basis of structural or functional models of how that protein works. CONCLUSION: This technique should greatly speed the discovery of functional fusion proteins, genetically encodable sensors, and optimized fluorescence resonance energy transfer pairs.

The speeding of EPSC kinetics during maturation of a central synapse.

Several factors contribute to the shape of excitatory postsynaptic currents (EPSCs) in CNS neurons, among them the kinetics of presynaptic release, transmitter clearance, and the properties and distribution of postsynaptic receptors. The decays of AMPA receptor-mediated EPSCs at rat cerebellar mossy fibre-granule cell (MF-gc) synapses follow a bi-exponential time-course. The fast component dominates the decay, accounting for 84-94% of the peak amplitude. Here we show that both components of decay, and also the risetimes, became faster during postnatal maturation. At adult, but not immature, synapses, the risetimes and decays of evoked multiquantal EPSCs were similar to those of monoquantal miniature (m)EPSCs. The faster risetimes at mature synapses reflected increased synchrony of multivesicular release, whereas the faster decays appeared to reflect changes in the properties of postsynaptic receptors. Inhibition of glutamate uptake was without effect on evoked EPSCs at both ages. Furthermore, after slowing receptor desensitization with cyclothiazide, the EPSCs at mature synapses decayed as slowly as EPSCs at immature synapses, suggesting that faster glutamate clearance does not account for the developmental speeding of EPSC decay. Our results support previous conclusions that glutamate clearance and receptor deactivation are important determinants of the fast decay component at immature synapses. Desensitization becomes increasingly important during development and plays a major role in shaping EPSC decay at mature synapses.