These results suggest that phMRI may potentially prove useful to map DAR function non-invasively in multiple brain regions simultaneously.

Relative to common clinical magnetic field strengths, higher fields benefit functional brain imaging both by providing additional signal for high-resolution applications and by improving the sensitivity of endogenous contrast due to the blood oxygen level dependent (BOLD) mechanism, which has limited detection power at low magnetic fields relative to the use of exogenous contrast agent. This study evaluates the utility of iron oxide contrast agent for gradient echo functional MRI at 9.4 T in rodents using cocaine and methylphenidate as stimuli. Relative to the BOLD method, the use of high iron doses and short echo times provided a roughly twofold global increase in functional sensitivity, while also suppressing large vessel signal and reducing susceptibility artifacts. MRI is widely used to assess brain function in humans and animals due to a powerful combination of capabilities, including high spatiotemporal resolution, volumetric coverage, and the potential for noninvasive, longitudinal studies. Many of the target applications for fMRI in animal models are inherently challenging in terms of sensitivity. For instance, functional signals often are attenuated in disease or recovery states, such as the evolution of neuronal plasticity during recovery from stroke (1-3). Pharmacological stimuli can produce widespread, graded, dosedependent changes in local brain function; low-field blood oxygen level dependent (BOLD) signal is simply inadequate for detecting changes in many brain regions without averaging results from a very large number of animals (4,5).High magnetic field strengths provide numerous advantages for fMRI, as well as challenges (6). Sample polarization increases with magnetic field, providing additional signal that can be traded for higher spatial resolution. Functional changes in the BOLD relaxation rate also increase with field strength (7), making BOLD detection power more competitive with that provided by an exogenous agent (8). Moreover, paramagnetic deoxyhemoglobin shortens blood relaxation times at high field strengths, which should decrease spatially nonspecific signal associated with draining vessels. However, the time scale for relaxation of transverse magnetization using gradient echoes (T 2 *) becomes progressively shorter and more heterogeneous, especially in regions near magnetic susceptibility interfaces that arise at air-tissue and bone-tissue interfaces. Signal dropout and image distortion reduce some of the theoretical advantages of BOLD fMRI at high fields by forcing a choice between increased image artifacts or the reduced sensitivity that accompanies short gradient echo times or spin echo methods.Because of the limitations of BOLD sensitivity, many fMRI applications in animal models have employed exogenous contrast agents (1-3,9 -11), which experimentally have been shown to markedly improve fMRI sensitivity at magnetic field strengths up to 4.7 T (4,5,8,12-14). The use of exogenous agents with very long blood half lives for fMRI has been termed IRON fMRI (5), to denote the increas...

The use of functional magnetic resonance imaging (fMRI) techniques for evaluation of pharmacologic stimuli has great potential for understanding neurotransmitter dynamics for a number of brain disorders, such as drug abuse, schizophrenia, epilepsy, or neurodegeneration. Unfortunately, blood oxygenation level-dependent (BOLD) imaging at common fields strengths, such as 1.5 or 3 T, has very low sensitivity and contrast-to-noise ratios (CNRs). We demonstrate here the utility of using an intravascular superparamagnetic iron oxide contrast agent with a long plasma half-life for evaluation of hemodynamic changes related to dopaminergic stimuli using amphetamine or the cocaine analog 2␤-carbomethoxy-3␤-(4-fluorophenyl)tropane (CFT). We refer to this technique as increased relaxation with iron oxide nanoparticles (IRON). Results obtained here show that even at field strengths as high as 4.7 T, one can obtain increases in CNR by factors of 2-3 over BOLD imaging that lead to greater than an order of magnitude increase in statistical power with greatly increased sensitivity to hemodynamic changes in brain regions difficult to observe using BOLD imaging. Furthermore, use of the intravascular contrast agent allows for a meaningful physiologic parameter to be measured (relative cerebral blood volume (rCBV)), compared to conventional BOLD imaging. J. Magn. THE TECHNIQUE OF FUNCTIONAL MAGNETIC resonance imaging (fMRI) using either relative cerebral blood volume (rCBV) (1), blood oxygenation level-dependent (BOLD) (2,3), or T1-based cerebral blood flow (CBF) techniques (3,4) has led to a revolution in brain mapping. By far the most common application is the BOLD technique. Unfortunately, contrast-to-noise ratios (CNRs) of BOLD are low, especially at field strengths such as 1.5 T (5). In addition, BOLD contrast has no simple relationship to any unique physiologic parameter, although with appropriate calibration and modeling in ideal circumstances, it can be used to infer regional oxygen consumption (6,7). CNRs for flow-based MR measurements based upon T1 changes (3,4,8) are generally even lower than they are for BOLD.Conventional BOLD imaging is often sensitivity limited at field strengths such as 1.5 T. For example, percent signal changes in occipital cortex with photic stimulation protocols are on the order of 2%-3% with a standard gradient echo (GE) EPI acquisition (long TR, moderate TE (30 -50 msec)). Other stimuli of interest, particularly those associated with cognitive tasks, are most often smaller in magnitude and require intersubject averaging. This is obviously inappropriate for clinical studies where one might need data from individual patients. Use of BOLD for mapping of neuronal activation after a pharmacologic challenge has an even greater number of limitations than mapping task activation in conventional fMRI. Generally, pharmacologic stimuli have a longer and uncontrolled time duration, compared to task activation in fMRI (9). Due to the long time course of the pharmacodynamic changes that may take place, BOLD sig...

Water-suppressed chemical shift magnetic resonance imaging was used to detect neurochemical alterations in vivo in neurotoxin-induced rat models of Huntington's and Parkinson's disease. The toxins were: N-methyl-4-phenylpyridinium (MPP+), aminooxyacetic acid (AOAA), 3-nitropropionic acid (3-NP), malonate, and azide. Local or systemic injection of these compounds caused secondary excitotoxic lesions by selective inhibition of mitochondrial respiration that gave rise to elevated lactate concentrations in the striatum. In addition, decreased N-acetylaspartate (NAA) concentrations were noted at the lesion site over time. Measurements of lactate washout kinetics demonstrated that t1/2 followed the order: 3-NP approximately MPP+ >> AOAA approximately malonate, which parallels the expected lifetimes of the neurotoxins based on their mechanisms of action. Further increases in lactate were also caused by intravenous infusion of glucose. At least part of the excitotoxicity is mediated through indirect glutamate pathways because lactate production and lesion size were diminished using unilateral decortectomies (blockade of glutamatergic input) or glutamate antagonists (MK-801). Lesion size and lactate were also diminished by energy repletion with ubiquinone and nicotinamide. Lactate measurements determined by magnetic resonance agreed with biochemical measurements made using freeze clamp techniques. Lesion size as measured with MR, although larger by 30%, agreed well with lesion size determined histologically. These experiments provide evidence for impairment of intracellular energy metabolism leading to indirect excitotoxicity for all the compounds mentioned before and demonstrate the feasibility of small-volume metabolite imaging for in vivo neurochemical analysis.

Non-alcoholic steatohepatitis (NASH) is an increasing cause of chronic liver disease characterized by steatosis, inflammation, and fibrosis which can lead to cirrhosis, hepatocellular carcinoma, and mortality. Quantitative, noninvasive methods for characterizing the pathophysiology of NASH at both the preclinical and clinical level are sorely needed. We report here a multiparametric magnetic resonance imaging (MRI) protocol with the fibrogenesis probe Gd-Hyd to characterize fibrotic disease activity and steatosis in a common mouse model of NASH. Mice were fed a choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD) to induce NASH with advanced fibrosis. Mice fed normal chow and CDAHFD underwent MRI after 2, 6, 10 and 14 weeks to measure liver T1, T2*, fat fraction, and dynamic T1-weighted Gd-Hyd enhanced imaging of the liver. Steatosis, inflammation, and fibrosis were then quantified by histology. NASH and fibrosis developed quickly in CDAHFD fed mice with strong correlation between morphometric steatosis quantification and liver fat estimated by MRI (r = 0.90). Sirius red histology and collagen quantification confirmed increasing fibrosis over time (r = 0.82). Though baseline T1 and T2* measurements did not correlate with fibrosis, Gd-Hyd signal enhancement provided a measure of the extent of active fibrotic disease progression and correlated strongly with lysyl oxidase expression. Gd-Hyd MRI accurately detects fibrogenesis in a mouse model of NASH with advanced fibrosis and can be combined with other MR measures, like fat imaging, to more accurately assess disease burden.

No abstract

Cerebrovascular reactivity (CVR) deficits in adolescents with concussion may persist after resolution of neurological symptoms. Whether or not CVR deficits predict long term neurological function is unknown. We used adolescent mice closed head injury (CHI) models (54 g, 107 cm or 117 cm drop height), followed by blood oxygenation level dependent (BOLD)-functional MRI with CO2 challenge to assess CVR and brain connectivity. At one week, 3HD 107 cm mice showed delayed BOLD responses (p = 0.0074), normal striatal connectivity, and an impaired respiratory rate response to CO2 challenge (p = 0.0061 in ΔRmax). The 107 cm group developed rotarod deficits at 6 months (p = 0.02) and altered post-CO2 brain connectivity (3-fold increase in striatum to motor cortex correlation coefficient) by one year, but resolved their CVR and respiratory rate impairments, and did not develop cognitive or circadian activity deficits. In contrast, the 117 cm group had persistent CVR (delay time: p = 0.016; washout time: p = 0.039) and circadian activity deficits (free-running period: 23.7 hr in sham vs 23.9 hr in 3HD; amplitude: 0.15 in sham vs 0.2 in 3HD; peak activity: 18 in sham vs 21 in 3HD) at one year. Persistent CVR deficits after concussion may portend long-term neurological dysfunction. Further studies are warranted to determine the utility of CVR to predict chronic neurological outcome after mild traumatic brain injury.

Delivery of antibodies to monitor key biomarkers of retinopathy in vivo represents a significant challenge because living cells do not take up immunoglobulins to cellular antigens. We met this challenge by developing novel contrast agents for retinopathy, which we used with magnetic resonance imaging (MRI). Biotinylated rabbit polyclonal to chick IgY (rIgPxcIgY) and phosphorylthioate-modified oligoDNA (sODN) with random sequence (bio-sODN-Ran) were conjugated with NeutrAvidin-activated superparamagnetic iron oxide nanoparticles (SPION). The resulting Ran-SPION-rIgPxcIgY carries chick polyclonal to microtubule-associated protein 2 (MAP2) as Ran-SPIONrIgP/cIgY-MAP2, or to rhodopsin (Rho) as anti-Rho-SPIONRan. We examined the uptake of Ran-SPION-rIgP/ cIgY-MAP2 or SPION-rIgP/cIgY-MAP2 in normal C57black6 mice (n = 3 each, 40 mg/kg, i.c.v.); we found retention of Ran-SPION-rIgP/cIgY-MAP2 using molecular contrastenhanced MRI in vivo and validated neuronal uptake using Cy5-goat IgPxcIgY ex vivo. Applying this novel method to monitor retinopathy in a bilateral carotid artery occlusion-induced ocular ischemia, we observed pericytes (at d 2, using Gd-nestin, by eyedrop solution), significant photoreceptor degeneration (at d 20, using anti-Rho-SPION-Ran, eyedrops, P = 0.03, Student's t test), and gliosis in Müller cells (at 6 mo, using SPION-glial fibrillary acidic protein administered by intraperitoneal injection) in surviving mice (n ‡ 5). Molecular contrastenhanced MRI results were confirmed by optical and electron microscopy. We conclude that chimera and molecular contrast-enhanced MRI provide sufficient sensitivity for monitoring retinopathy and for theranostic applications.-Ren, J., Chen, Y. I., Mackey, A. M., Liu, P. K. Imaging rhodopsin degeneration in vivo in a new model of ocular ischemia in living mice. FASEB J. 30, 612-623 (2016). www.fasebj.org