Performance evaluation of SimPET-L and SimPET-XL: MRI-compatible small-animal PET systems with rat-body imaging capability.

BACKGROUND: SimPET-L and SimPET-XL have recently been introduced with increased transaxial fields of view (FOV) compared with their predecessors (SimPET™ and SimPET-X), enabling whole-body positron emission tomography (PET) imaging of rats. We conducted performance evaluations of SimPET-L and SimPET-XL and rat-body imaging with SimPET-XL to demonstrate the benefits of increased axial and transaxial FOVs. PROCEDURES: The detector blocks in SimPET-L and SimPET-XL consist of two 4 × 4 silicon photomultiplier arrays coupled with 20 × 9 array lutetium oxyorthosilicate crystals. SimPET-L and SimPET-XL have an inner diameter (bore size) of 7.6 cm, and they are composed of 40 and 80 detector blocks yielding axial lengths of 5.5 and 11 cm, respectively. Each system was evaluated according to the National Electrical Manufacturers Association NU4-2008 protocol. Rat imaging studies, such as 18F-NaF and 18F-FDG PET, were performed using SimPET-XL. RESULTS: The radial resolutions at the axial center measured using the filtered back projection, 3D ordered-subset expectation maximization (OSEM), and 3D OSEM with point spread functions correction were 1.7, 0.82, and 0.82 mm FWHM in SimPET-L and 1.7, 0.91, and 0.91 mm FWHM in SimPET-XL, respectively. The peak sensitivities of SimPET-L and SimPET-XL were 6.30% and 10.4% for an energy window of 100-900 keV and 4.44% and 7.25% for a window of 250-750 keV, respectively. The peak noise equivalent count rate with an energy window of 250-750 keV was 249 kcps at 44.9 MBq for SimPET-L and 349 kcps at 31.3 MBq for SimPET-XL. In SimPET-L, the uniformity was 4.43%, and the spill-over ratios in air- and water-filled chambers were 5.54% and 4.10%, respectively. In SimPET-XL, the uniformity was 3.89%, and the spill-over ratio in the air- and water-filled chambers were 3.56% and 3.60%. Moreover, SimPET-XL provided high-quality images of rats. CONCLUSION: SimPET-L and SimPET-XL show adequate performance compared with other SimPET systems. In addition, their large transaxial and long axial FOVs provide imaging capability for rats with high image quality.

An aptamer-based magnetic resonance imaging contrast agent for detecting oligomeric amyloid-ß in the brain of an Alzheimer's disease mouse model.

The oligomeric amyloid-ß (oAß) is a reliable feature for an early diagnosis of Alzheimer's disease (AD). Therefore, the objective of this study was to demonstrate imaging of oAß deposits using our developed DNA aptamer called ob5 conjugated with gadolinium (Gd)-dodecane tetraacetic acid (DOTA) as a contrast agent for early diagnosis of AD using MRI. An oAß-specific aptamer was developed by amide bond formation and conjugated to Gd-DOTA MRI contrast agent and/or cyanine5 (cy5). We verified the performance of our new contrast agent with an AD mouse model using in vivo and ex vivo fluorescent imaging and animal MRI experiments. The presence of soluble Aß in 3xTg AD mice was detected using GdDOTA-ob5-cy5 probe ex vivo. Fluorescence intensities of the GdDOTA-ob5-cy5 contrast agent were high in the brains of 3xTg-AD mice, but relatively low in the brains of control mice. The GdDOTA-ob5 contrast agent had higher relaxivity than a clinically available contrast agent. T1-weighted MRI signals in 5-month-old 3xTg AD mice increased at 5 min, were prolonged until 10 min, then decreased 15 min after injecting the GdDOTA-ob5 contrast agent. Our targeted DNA aptamer GdDOTA-ob5 contrast agent could be potentially useful for validating the efficacy of a novel diagnostic contrast agent for selectively targeting neurotoxic oAß. It could ultimately be used for early diagnosis of AD.

Non-invasive In Vivo Brain Astrogenesis and Astrogliosis Quantification Using a Far-red E2-Crimson Transgenic Reporter Mouse.

Despite the adaptation of major clinical imaging modalities for small animals, optical bioluminescence imaging technology is the main approach readily reporting gene activity. Yet, in vivo bioluminescence monitoring requires the administration and diffusion of a substrate to the tissues of interest, resulting in experimental variability, high reagent cost, long acquisition time, and stress to the animal. In our study, we avoid such issues upon generating a new transgenic mouse (GFAP-E2crimson) expressing the far-red fluorescent protein E2-crimson under the control of the glial fibrillary acidic protein (GFAP) promoter. Using microscopy, we validated the selective expression of the reporter in the astrocyte cell population and by non-invasive in vivo fluorescence imaging its detection through the scalps and skulls of live animals. In addition, we performed a longitudinal study validating by in vivo imaging that the E2-crimson fluorescence signal is up-regulated, in pups during astrogenesis and in adult mice during astrogliosis upon kainic acid administration. Furthermore, upon crossing GFAP-E2crimson transgenic with 5XFAD Alzheimer's disease mice model, we were able to quantify the chronic inflammation triggered by amyloid deposit and aging over 18 months. As many diseases and conditions can trigger neuroinflammation, we believe that the GFAP-E2crimson reporter mice model delivers tremendous value for the non-invasive quantification of astrogliosis responses in living animals.

Connectome-based predictive models using resting-state fMRI for studying brain aging.

Changes in the brain with age can provide useful information regarding an individual's chronological age. studies have suggested that functional connectomes identified via resting-state functional magnetic resonance imaging (fMRI) could be a powerful feature for predicting an individual's age. We applied connectome-based predictive modeling (CPM) to investigate individual chronological age predictions via resting-state fMRI using open-source datasets. The significant feature for age prediction was confirmed in 168 subjects from the Southwest University Adult Lifespan Dataset. The higher contributing nodes for age production included a positive connection from the left inferior parietal sulcus and a negative connection from the right middle temporal sulcus. On the network scale, the subcortical-cerebellum network was the dominant network for age prediction. The generalizability of CPM, which was constructed using the identified features, was verified by applying this model to independent datasets that were randomly selected from the Autism Brain Imaging Data Exchange I and the Open Access Series of Imaging Studies 3. CPM via resting-state fMRI is a potential robust predictor for determining an individual's chronological age from changes in the brain.

Highly brain-permeable apoferritin nanocage with high dysprosium loading capacity as a new T2 contrast agent for ultra-high field magnetic resonance imaging.

High sensitivity at ultra-high field (UHF) and sufficient potential to penetrate the brain are the most desirable characteristics in the development of contrast agents (CAs) for magnetic resonance imaging (MRI). However, incorporating such qualities into a single nanocarrier is challenging. Herein, we report a new strategy for a highly brain-permeable MR CA with high sensitivity at UHF by loading dysprosium chelates (DyL) in apoferritin cavities (Apo-DyL). We also design the chelate ligand structure to increase DyL loading capacity within the apoferritin cavity. Using the intracerebroventricular (ICV) injection approach as a new delivery route for Apo-DyL, we demonstrate that apoferritin loaded with DyL can penetrate the brain-ventricular barrier and diffuse into the brain. This brain-permeable capability is unique to Apo-DyL, compared with other types of nanoparticles used in MRI. Apo-DyL also shows significant increase in MR sensitivity of DyL at UHF. Furthermore, based on brain tumor imaging at UHF, Apo-DyL can significantly enhance the tumor for a lower dose of the CA than the previously reported Gd- or Mn-loaded apoferritin nanoplatform. Therefore, Apo-DyL can be a novel nanoplatform that is a highly sensitive and versatile MR CA for UHF brain imaging.

A mouse model of subcortical vascular dementia reflecting degeneration of cerebral white matter and microcirculation.

Subcortical vascular dementia(SVaD) is associated with white matter damage, lacunar infarction, and degeneration of cerebral microcirculation. Currently available mouse models can mimic only partial aspects of human SVaD features. Here, we combined bilateral common carotid artery stenosis (BCAS) with a hyperlipidaemia model in order to develop a mouse model of SVaD; 10- to 12-week-old apolipoprotein E (ApoE)-deficient or wild-type C57BL/6J mice were subjected to sham operation or chronic cerebral hypoperfusion with BCAS using micro-coils. Behavioural performance (locomotion, spatial working memory, and recognition memory), histopathological findings (white matter damage, microinfarctions, astrogliosis), and cerebral microcirculation (microvascular density and blood-brain barrier (BBB) integrity) were investigated. ApoE-deficient mice subjected to BCAS showed impaired locomotion, spatial working memory, and recognition memory. They also showed white matter damage, multiple microinfarctions, astrogliosis, reduction in microvascular density, and BBB breakdown. The combination of chronic cerebral hypoperfusion and ApoE deficiency induced cognitive decline and cerebrovascular pathology, including white matter damage, multiple microinfarctions, and degeneration of cerebral microcirculation. Together, these features are all compatible with those of patients with SVaD. Thus, the proposed animal model is plausible for investigating SVaD pathophysiology and for application in preclinical drug studies.

Synthesis and Evaluation of Manganese(II)-Based Ethylenediaminetetraacetic Acid-Ethoxybenzyl Conjugate as a Highly Stable Hepatobiliary Magnetic Resonance Imaging Contrast Agent.

In this study, we designed and synthesized a highly stable manganese (Mn2+)-based hepatobiliary complex by tethering an ethoxybenzyl (EOB) moiety with an ethylenediaminetetraacetic acid (EDTA) coordination cage as an alternative to the well-established hepatobiliary gadolinium (Gd3+) chelates and evaluated its usage as a T1 hepatobiliary magnetic resonance imaging (MRI) contrast agent (CA). This new complex exhibits higher r1 relaxivity (2.3 mM-1 s-1) than clinically approved Mn2+-based hepatobiliary complex Mn-DPDP (1.6 mM-1 s-1) at 1.5 T. Mn-EDTA-EOB shows much higher kinetic inertness than that of clinically approved Gd3+-based hepatobiliary MRI CAs, such as Gd-DTPA-EOB and Gd-BOPTA. In addition, in vivo biodistribution and MRI enhancement patterns of this new Mn2+ chelate are comparable to those of Gd3+-based hepatobiliary MRI CAs. The diagnostic efficacy of the new complex was demonstrated by its enhanced tumor detection sensitivity in a liver cancer model using in vivo MRI.

Outcome of ultrasonographic imaging in infants with sacral dimple.

PURPOSE: Sacral dimples are a common cutaneous anomaly in infants. Spine ultrasonography (USG) is an effective and safe screening tool for patients with a sacral dimple. The aim of this study was to determine the clinical manifestations in patients with an isolated sacral dimple and to review the management of spinal cord abnormalities identified with USG. METHODS: We reviewed clinical records and collected data on admissions for a sacral dimple from March 2014 through February 2017 that were evaluated with spine USG by a pediatric radiologist. During the same period, patients who were admitted for other complaints, but were found to have a sacral dimple were also included. RESULTS: This study included 230 infants under 6-months-old (130 males and 100 females; mean age 52.8±42.6 days). Thirty-one infants with a sacral dimple had an echogenic filum terminale, and 57 children had a filar cyst. Twenty-seven patients had a low-lying spinal cord, and only one patient was suspected of having a tethered cord. Follow-up spine USG was performed in 28 patients, which showed normalization or insignificant change. CONCLUSION: In this study, all but one infant with a sacral dimple had benign imaging findings. USG can be recommended in infants with a sacral dimple for its convenience and safety.

Long-term prenatal stress increases susceptibility of N-methyl-D-aspartic acid-induced spasms in infant rats.

PURPOSE: Infantile spasms, also known as West syndrome, is an age-specific epileptic seizure. Most patients with this condition also exhibit delayed development. This study aimed to determine the effect of long-term prenatal stress on susceptibility to infantile spasms. METHODS: We subjected pregnant rats to acute or chronic immobilization stress. Resulting offspring received N-methyl-D-aspartic acid (15 mg/kg, intraperitoneally) on postnatal day 15, and their behaviors were observed 75 minutes after injection. The expression of KCC2 and GAD67 was also determined using immunohistochemistry. RESULTS: Exposure to long-term prenatal stress increased the frequency of spasms and decreased the latency to onset of spasms compared with offspring exposed to short-term prenatal stress. Expression of KCC2 and GAD67 also decreased in the group exposed to long-term prenatal stress compared with the group exposed to short-term prenatal stress. CONCLUSION: Our study suggests that exposure to long-term prenatal stress results in increased susceptibility to seizures.

In vivo stem cell tracking with imageable nanoparticles that bind bioorthogonal chemical receptors on the stem cell surface.

It is urgently necessary to develop reliable non-invasive stem cell imaging technology for tracking the in vivo fate of transplanted stem cells in living subjects. Herein, we developed a simple and well controlled stem cell imaging method through a combination of metabolic glycoengineering and bioorthogonal copper-free click chemistry. Firstly, the exogenous chemical receptors containing azide (-N3) groups were generated on the surfaces of stem cells through metabolic glycoengineering using metabolic precursor, tetra-acetylated N-azidoacetyl-d-mannosamine(Ac4ManNAz). Next, bicyclo[6.1.0]nonyne-modified glycol chitosan nanoparticles (BCN-CNPs) were prepared as imageable nanoparticles to deliver different imaging agents. Cy5.5, iron oxide nanoparticles and gold nanoparticles were conjugated or encapsulated to BCN-CNPs for optical, MR and CT imaging, respectively. These imageable nanoparticles bound chemical receptors on the Ac4ManNAz-treated stem cell surface specifically via bioorthogonal copper-free click chemistry. Then they were rapidly taken up by the cell membrane turn-over mechanism resulting in higher endocytic capacity compared non-specific uptake of nanoparticles. During in vivo animal test, BCN-CNP-Cy5.5-labeled stem cells could be continuously tracked by non-invasive optical imaging over 15 days. Furthermore, BCN-CNP-IRON- and BCN-CNP-GOLD-labeled stem cells could be efficiently visualized using in vivo MR and CT imaging demonstrating utility of our stem cell labeling method using chemical receptors. These results conclude that our method based on metabolic glycoengineering and bioorthogonal copper-free click chemistry can stably label stem cells with diverse imageable nanoparticles representing great potential as new stem cell imaging technology.

Molecular fMRI of Serotonin Transport.

Reuptake of neurotransmitters from the brain interstitium shapes chemical signaling processes and is disrupted in several pathologies. Serotonin reuptake in particular is important for mood regulation and is inhibited by first-line drugs for treatment of depression. Here we introduce a molecular-level fMRI technique for micron-scale mapping of serotonin transport in live animals. Intracranial injection of an MRI-detectable serotonin sensor complexed with serotonin, together with serial imaging and compartmental analysis, permits neurotransmitter transport to be quantified as serotonin dissociates from the probe. Application of this strategy to much of the striatum and surrounding areas reveals widespread nonsaturating serotonin removal with maximal rates in the lateral septum. The serotonin reuptake inhibitor fluoxetine selectively suppresses serotonin removal in septal subregions, whereas both fluoxetine and a dopamine transporter blocker depress reuptake in striatum. These results highlight promiscuous pharmacological influences on the serotonergic system and demonstrate the utility of molecular fMRI for characterization of neurochemical dynamics.

Localized Down-regulation of P-glycoprotein by Focused Ultrasound and Microbubbles induced Blood-Brain Barrier Disruption in Rat Brain.

Multi-drug resistant efflux transporters found in Blood-Brain Barrier (BBB) acts as a functional barrier, by pumping out most of the drugs into the blood. Previous studies showed focused ultrasound (FUS) induced microbubble oscillation can disrupt the BBB by loosening the tight junctions in the brain endothelial cells; however, no study was performed to investigate its impact on the functional barrier of the BBB. In this study, the BBB in rat brains were disrupted using the MRI guided FUS and microbubbles. The immunofluorescence study evaluated the expression of the P-glycoprotein (P-gp), the most dominant multi-drug resistant protein found in the BBB. Intensity of the P-gp expression at the BBB disruption (BBBD) regions was significantly reduced (63.2 ± 18.4%) compared to the control area. The magnitude of the BBBD and the level of the P-gp down-regulation were significantly correlated. Both the immunofluorescence and histologic analysis at the BBBD regions revealed no apparent damage in the brain endothelial cells. The results demonstrate that the FUS and microbubbles can induce a localized down-regulation of P-gp expression in rat brain. The study suggests a clinically translation of this method to treat neural diseases through targeted delivery of the wide ranges of brain disorder related drugs.

Molecular-level functional magnetic resonance imaging of dopaminergic signaling.

We demonstrate a technique for mapping brain activity that combines molecular specificity and spatial coverage using a neurotransmitter sensor detectable by magnetic resonance imaging (MRI). This molecular functional MRI (fMRI) method yielded time-resolved volumetric measurements of dopamine release evoked by reward-related lateral hypothalamic brain stimulation of rats injected with the neurotransmitter sensor. Peak dopamine concentrations and release rates were observed in the anterior nucleus accumbens core. Substantial dopamine transients were also present in more caudal areas. Dopamine-release amplitudes correlated with the rostrocaudal stimulation coordinate, suggesting participation of hypothalamic circuitry in modulating dopamine responses. This work provides a foundation for development and application of quantitative molecular fMRI techniques targeted toward numerous components of neural physiology.

In vivo imaging with a cell-permeable porphyrin-based MRI contrast agent.

Magnetic resonance imaging (MRI) with molecular probes offers the potential to monitor physiological parameters with comparatively high spatial and temporal resolution in living subjects. For detection of intracellular analytes, construction of cell-permeable imaging agents remains a challenge. Here we show that a porphyrin-based MRI molecular imaging agent, Mn-(DPA-C(2))(2)-TPPS(3), effectively penetrates cells and persistently stains living brain tissue in intracranially injected rats. Chromogenicity of the probe permitted direct visualization of its distribution by histology, in addition to MRI. Distribution was concentrated in cell bodies after hippocampal infusion. Mn-(DPA-C(2))(2)-TPPS(3) was designed to sense zinc ions, and contrast enhancement was more pronounced in the hippocampus, a zinc-rich brain region, than in the caudate nucleus, which contains relatively little labile Zn(2+). Membrane permeability, optical activity, and high relaxivity of porphyrin-based contrast agents offer exceptional functionality for in vivo imaging.

Chronic stress selectively reduces hippocampal volume in rats: a longitudinal magnetic resonance imaging study.

The notion of uncontrollable stress causing reduced hippocampal size remains controversial in the posttraumatic stress disorder literature, because human studies cannot discern the causality of effect. Here, we addressed this issue by using structural magnetic resonance imaging in rats to measure the hippocampus and other brain regions before and after stress. Chronic restraint stress produced approximately 3% reduction in hippocampal volume, which was not observed in control rats. This decrease was not signficantly correlated with baseline hippocampal volume or body weight. Total forebrain volume and the sizes of the other brain regions and adrenal glands were all unaffected by stress. This longitudinal, within-subjects design study provides direct evidence that the hippocampus is differentially vulnerable and sensitive to chronic stress.

Discriminative conditioning with different CS-US intervals produces temporally differentiated conditioned responses in the two eyes of the rabbit (Oryctolagus cuniculus).

The conditioned eyeblink response (CR) in rabbits is lateralized to the eye targeted by the unconditioned stimulus (US). However, a contralateral component has been reported during concurrent discriminative conditioning of the two eyes. The authors investigated CRs produced by both eyes during conditioning with 2 different interstimulus intervals (ISIs) in which a short conditioned stimulus (CS) was paired with a US to the left eye and a long CS was paired with a US to the right eye. Whether the 2 CSs were more or less similar (or identical), the short CS produced short-latency CRs in the left eye, whereas the long CS produced long-latency CRs in the right eye. The contralateral responses to a CS trained at one ISI were separable into temporal corollaries of the ipsilateral response (suggesting a bilaterality of the CR) versus those to a CS trained at another ISI (indicating generalization between the CSs). The results indicate that the neuronal substrates subserving CRs of the two eyes involve not only a dominant lateralization but also some avenue of bilaterality.

Bilateral nature of the conditioned eyeblink response in the rabbit: behavioral characteristics and potential mechanisms.

In Pavlovian eyeblink conditioning, the conditioned response (CR) is highly lateralized to the eye to which the unconditioned stimulus (US) has been directed. However, the initial conditioning of one eye can facilitate subsequent conditioning of the other eye, a phenomenon known as the intereye transfer (IET) effect. Because a conditioned emotional response (CER), as well as the eyeblink CR, is acquired during eyeblink conditioning and influences the development of the CR, the CER acquired in initial training can plausibly account for the IET effect. To evaluate this possibility, the present study utilized previously determined eyeblink conditioning procedures that effectively decouple the degree of CER and CR development to investigate the IET effect. In each of 3 experiments rabbits were initially trained with comparison procedures that differentially favored the development of the eyeblink CR or the CER, prior to a shift of the US to the alternate eye. The observed differences in the IET suggest that the effect depends largely on the specific development of eyeblink CRs rather than the CER. The neurobiological implications of this apparent bilaterality of the eyeblink CR are discussed.

Differential effects of cerebellar, amygdalar, and hippocampal lesions on classical eyeblink conditioning in rats.

Eyeblink conditioning has been hypothesized to engage two successive stages of nonspecific emotional (fear) and specific musculature (eyelid) learning, during which the nonspecific component influences the acquisition of the specific component. Here we test this notion by investigating the relative contributions of the cerebellum, the amygdala, and the hippocampus to the emergence of conditioned eyelid and fear responses during delay eyeblink conditioning in freely moving rats. Periorbital electromyography (EMG) and 22 kHz ultrasonic vocalization (USV) activities were measured concurrently from the same subjects and served as indices of conditioned eyeblink and fear responses, respectively. In control animals, conditioned EMG responses increased across training sessions, whereas USV responses were initially robust but decreased across training sessions. Animals with electrolytic lesions to their cerebellum (targeting the interpositus nucleus) were completely unable to acquire conditioned EMG responses but exhibited normal USV behavior, whereas animals with lesions to the amygdala showed decelerated acquisition of conditioned EMG responses and displayed practically no USV behavior. In contrast, hippocampal lesioned rats demonstrated facilitated acquisition of conditioned EMG responses, whereas the USV behavior was unaffected. The amygdalar involvement in eyeblink conditioning was examined further by applying the GABA(A) agonist muscimol directly into the amygdala either before or immediately after training sessions. Although pretraining muscimol infusions impaired conditioned EMG responses, post-training infusions did not. Together, these results suggest that, even during a simple delay eyeblink conditioning, animals learn about different aspects associated with the behavioral task that are subserved by multiple brain-memory systems that interact to produce the overall behavior.