Byline: SATOMI KIKUTA, YUCHIO YANAGAWA, NORIYASU HOMMA, MAKOTO OSANAI Keywords: MRI; manganese; calcium imaging SUMMARY The activity-induced manganese-enhanced MRI (AIM-MRI) is one of the candidate methods for measuring the neuronal activity noninvasively in vivo. This method has the potential to measure the history of the neuronal activity, since the Mn.sub.2+ can enter the active neuron through voltage-dependent Ca.sub.2+ channels. However, the relation between the neuronal activity and the accumulation of Mn.sub.2+ in the cell has not been clear. At first, we confirmed that the longitudinal relaxation time of H.sub.+ (T.sub.1) measured by means of MRI apparatus was related to the [Mn.sub.2+] using the pseudo intracellular phantoms with various concentrations of Mn.sub.2+. The inverse of T.sub.1 (1/T.sub.1) was proportional to [Mn.sub.2+], thus [Mn.sub.2+] can be measured by MRI quantitatively. Next, we investigated the relation between the neuronal activity and the accumulation of Mn.sub.2+ in the striatal GABAergic neurons using the method of the Mn.sub.2+ quenching of Fura-2 LR, a family of Fura fluorescent Ca.sub.2+ indicators. The amount of the Ca.sub.2+ influx was correlated to the neuronal activity evoked by tetanic stimulations with various frequencies. In the same slice preparation, the amounts of the fluorescence quench induced by the tetanic stimulations under the condition of 50 I1/4M MnCl.sub.2 administration were recorded. As a result, the amount of the quench was proportional to the amount of the Ca.sub.2+ influx. These results suggested that a cell, which has higher activity, accumulated larger amount of Mn.sub.2+ in the neuron. Thus, our results supported that AIM-MRI can measure the history of the neuronal activities in the whole brain noninvasively in vivo. Biographical information: Satomi Kikuta (nonmember) was born on June 23, 1988. Kikuta graduated from the Course of Radiological Technology, Division of Health Sciences, School of Medicine, Tohoku University in March 2012. She started the third year of the second term of doctorate curriculum there in April 2014. Her current research focuses on neurological pathology and neurophysiology using calcium imaging, manganese-enhanced, behavioral testing, and other methods. Yuchio Yanagawa (nonmember) was born on December 28, 1955. Yanagawa graduated from the School of Medicine, Niigata University in 1982, and obtained the degree there in 1988. After working as a JSPS Postdoctoral Fellow, Research Associate at Kyushu University, Researcher at Beckman Research Institute (City of Hope), Research Associate at Tohoku University, and Assistant Professor at National Institute for Physiological Sciences, he joined Graduate School of Medicine, Gunma University as a Professor in 2004. He expertises in neuroscience. He studies physiology and disorders of inhibitory neurons using genetically modified animals. Noriyasu Homma (nonmember) completed the second term of doctorate curriculum at the Graduate School of Engineering, Tohoku University in 1995. Homma was a Visiting Professor at the University of Saskatchewan in 2000. He was an Assistant Professor at School of Medicine, Tohoku University in 2003 and an Associate Professor at the Cyber Science Center, Tohoku University in 2008. Currently, he is a Professor at Graduate School of Medicine, Tohoku University. His research involves optimal control, complex systems, intelligent systems, medical imaging, and other fields. He is a Doctor of Engineering. Makoto Osanai (member) was born on March 27, 1969. Osanai graduated from the Department of Physics, Faculty of Science, Nagoya University in March 1991, and obtained the degree there in 1996. After working at Kyorin University, Tokyo Medical, Dental University, Osaka University, and so far, he became an Associate Professor at Graduate School of Medicine, Tohoku University in 2009. He engages in neuroscience by calcium imaging, electrophysiology, simulations, and other approaches. He is a Doctor of Science.