Iris Yuwen Zhou^1,2, Abby Y Ding^1,2, Qi Li^3,4, Frank Yik Hin Lee^1,2, Shujuan J Fan^1,2, Kevin Chuen Wing Chan^1,2, Grainne M McAlonan^3,4, and Ed Xuekui Wu^1,2
1Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong SAR, China, People's Republic of, ²Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong SAR, China, People's Republic of, ³Department of Psychiatry, The University of Hong Kong, ⁴Centre for Reproduction Growth and Development, The University of Hong Kong

Fear conditioning is a widely used procedure to study the neural basis of learning and memory. To study the neurocircuits behind this paradigm, in vivo MEMRI was employed to investigate the neural response after subjection to fear-conditioning in mice. Compared to controls, fear-conditioned animals exhibited higher Mn-uptake in amygdala, hippocampus, paraventricular nucleus of hypothalamus and cingulate cortex, which are all highly-involved in the process of fear. The results provide insights to neurocircuits involved in fear-conditioning and consolidate the capability of MEMRI as an in vivo probe for mapping neural activity.

A-B-M-A Asad¹, Serene YL Tong¹, Ma Wei², Weiping Han², and Kai-Hsiang Chuang^1
1Magnetic Resonance Imaging Group, Singapore Bioimaging Consortium, A*STAR, Singapore, Singapore, ²Lab of Metabolic Medicine, Singapore Bioimaging Consortium, A*STAR, Singapore, Singapore

Leptin signaling in CNS plays an important role in regulating energy homeostasis which inhibits food intake and increases energy expenditure. To understand the CNS response to leptin, we used manganese enhanced MRI to observe dynamic changes in hypothalamic nuclei by Mn2+ as an Ca2+ activity dependent agent during fasting and peripheral leptin injection. We observed signal changes in arcuate, paraventricular, ventromedial and dorsomedial nuclei in hypothalamus. Injection of leptin suppressed signal significantly in most nuclei in fasted animals. In non-fasted animals, however, leptin injection increased signal in most nuclei but not arcuate. This method can be applied to study hypothalamic function in response to different metabolic signals and hypothalamic dysfunction in animal models of leptin resistance.

Margaret F Bennewitz¹, Michael K Nkansah¹, Tricia L Lobo², and Erik M Shapiro^1,2
1Department of Biomedical Engineering, Yale University, New Haven, CT, United States, ²Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, CT, United States

Inorganic manganese particles are attractive for molecular and cellular imaging due to their potential to provide bright contrast on MRI. We have fabricated pH-sensitive, poly(lactic-co-glycolic-acid) (PLGA) encapsulated manganese oxide (MnO) nanocrystals. Particles were fabricated at 140-nm and 1.7-m, and incorporated 15 to 20-nm MnO nanocrystals. Intact particles at physiological pH cause little MRI contrast, but following endocytosis into low pH compartments within cells, particles erode, and MnO dissolves to release Mn²⁺, causing cells to appear bright on MR images. The change in MRI properties is as high as 35-fold, making it the most dynamic ‘smart’ MRI contrast agent yet reported.

Shigeyoshi Saito¹, Sumitaka Hasegawa¹, Takako Furukawa¹, Tsuneo Saga¹, and Ichio Aoki^1
1Molecular Imaging Center (MIC), National Institute of Radiological Sciences (NIRS), Chiba, Chiba, Japan

Recent studies on the utility of manganese have shown that manganese-enhanced MRI (MEMRI) can detect cellular alterations in tumor models. We investigated the relationship between x-ray irradiation and Mn uptake in tumor cells and tested whether MEMRI can detect radiation-induced cell disturbances at an early stage. MEMRI is able to detect cell cycle arrest of tumor cells following radiation exposure. Reductions in Mn accumulation in the irradiated cells were observed both in vitro and in vivo. MEMRI may be suitable for evaluation of not only cell viability but also the acute stage of cell cycle alteration after radiotherapy.

Kamila Urszula Szulc¹, Brian J Nieman², Edward Jospeh Houston¹, Alexandra L Joyner³, and Daniel H Turnbull^1,4
1Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine, NYU School of Medicine, New York, NY, United States, ²Mouse Imaging Center, Hospital for Sick Children, Toronto, Canada, ³Developmental Biology Program, Sloan-Kettering Institute, New York, NY, United States, ⁴Radiology, NYU School of Medicine, New York, NY, United States

MEMRI approach is particularly well suited to visualize brain anatomy and it has been successfully used to do so in mice in vivo at embryonic to adult stages. Here, we have extended MEMRI for longitudinal studies of brain development in individual mice during the critical early postnatal period. Based on these data, a brain atlas was created, consisting of individual and average brains at 11 developmental stages, from postnatal day 1 (P1) to P11. The database generated in this project will serve as an important resource for future phenotypic MEMRI analyses of mutant mice with brain defects.

Ulrike Dydak^1,2, Jun Xu^1,2, Ashritha Epur², Xiangrong Li³, Seth Streitmatter¹, Li-Ling Long³, Wei Zheng¹, and Yue-Ming Jiang^4
1School of Health Sciences, Purdue University, West Lafayette, IN, United States, ²Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Indianapolis, IN, United States, ³Department of Radiology, Guangxi Medical University, Nanning, China, People's Republic of, ⁴Department of Health Toxicology, Guangxi Medical University, Nanning, China, People's Republic of

A 3D whole-brain T1-weigthed sequence was used to study the human brain structures showing T1 hyperintensities due to occupational Mn exposure in a cohort of smelters and welders. Brain regions showing Mn accumulation were compared to non-exposed controls as well as to a rat model of chronic Mn exposure. While the rat brain predominantly shows Mn accumulation in hippocampus, in humans Mn first accumulates in the globus pallidus. T1 hyperintensities were also found in subthalamic nucleus, pituitary gland, pineal stalk and cerebral peduncle. These differences need to be considered when using animal models to study chronic Mn exposure.

alexia Daoust^1,2, Emmanuel Luc Barbier^1,2, and Sylvain Bohic^1,3
1INSERM U836, Grenoble, France, ²Grenoble Institut des Neurosciences, Université Joseph Fourier, Grenoble, France, ³European Synchrotron Radiation Facility (ESRF), Grenoble, France

In MEMRI protocols, the cellular distribution remains still unclear. To obtain further insights, we imaged rat brains by MRI after IP and IC MnCl₂ injections. Then, using synchrotron X-ray microprobe, we mapped the distribution of Mn, Ca, Zn and Fe in rat hippocampus. The hippocampal distributions of Mn obtained by both techniques were in excellent agreement. At a cellular scale, Mn was distributed within the DG/hilus/CA3. After IC injection, Mn was preferentially located in hippocampal fissure, a structure rich in astrocytes. The presence of Mn also modifies the distribution of Fe and Zn.

Kevin M. Bennett¹, Shannon S. Olfers², and Vinodh Narayanan^2
1School of Biological and Health Systems Engineering, Arizona State University, Tempe, Az, United States, ²Developmental Neurogenetics Laboratory, Barrow Neurological Institute, Phoenix, Az, United States

Neurofibromatosis 1 (NF1) is a cogenital neurodegenerative disease. The goal of this work is to determine whether fast axonal transport rates in the CNS of mice heterozygous for the neurofibromin 1 (NF1) gene differ from those of WT controls. We used MEMRI to demonstrate that uptake of Mn2+ in the olfactory bulb in NF1 heterozygous mice is significantly lower than in wild-type, implicating RAS deregulation as a potential mechanism for deficits in NF. Animals treated with lovastatin have restored axonal transport, demonstrating that MEMRI may be useful to screen compounds to treat patients with NF1.

Umer Abdur Rahim Khan¹, Anne Bertrand^1,2, Hoang Minh Dung¹, Dmitry Novikov¹, Lindsay Kathleen Hill¹, Benjamin Winthrope Little¹, Hameetha B Rajamohamed Sait³, Mesha Shamsie¹, Einar M Sigurdsson³, and Youssef Zaim Wadghiri^1
1Radiology, New York University Langone Medical Center, New York, NY, United States, ²URA CEA-CNRS 2210, Mircen, Fontenay-Aux-Roses, France, ³Physiology & Neuroscience, New York University Langone Medical Center, New York, NY, United States

Amyloid Beta (A Beta) and tau play an essential role in the Alzheimer’s disease (AD) pathophysiology. There is in vitro evidence that A Beta oligomers can impair fast axonal transport. Crucially lacking are in vivo non invasive techniques to evaluate neuronal function. Track-Tracing Manganese Enhanced MRI (TT-MEMRI) is currently the only non invasive 4-D volumetric imaging technique to demonstrate neuronal transport perturbations. Applying MEMRI in a transgenic model (Tg2576) of A Beta pathology by expressing human APP mutation confirmed the deleterious effect of A Beta on neuronal transport measured by a decrease in the rate of signal change. We previously investigated a tau model (JNPL3) using a 7 day time-course period where we showed a significant decrease in neuronal transport function in Tg mice. In the present study, we sought to examine with the same approach an accelerated A Beta mouse model (Tg6799 5xFAD) expressing both APP and PS1 human mutations. Surprisingly, our results show significant decrease in neuronal conduction in the (C57/B6xSJL) WT mice with age contrasting with maintained transport function in Tg 5xFAD with age.

Yutong Liu¹, Larisa Poluektova², Balasrinivasa Sajja¹, Howard Gendelman², and Boska Michael^1
1Radiology, UNMC, Omaha, NE, United States, ²Pharmacology/Exp Neuroscience, UNMC, Omaha, NE, United States

Cross-linking chemicals including paraformaldehyde (PFA) and glutaraldehyde (GA) and focused beam microwave irradiation (FBMI) were evaluated to investigate the fixation methods that preserve in vivo manganese enhancement for ex vivo mouse brain MRI. T1 values were measured and T1-wt MRI was acquired at 24 hours after MnCl2 administration. The mice were then euthanized and brains were fixed for ex vivo MRI. The results demonstrated that the manganese enhancement was preserved by PFA and GA, but lost in FBMI fixed mice.