J Neuro Res. 2019;97:923–932. wileyonlinelibrary.com/journal/jnr | 923 © 2019 Wiley Periodicals, Inc. 1 | INTRODUCTION The mammalian brain consumes a significant portion of the total body energy. In humans, while occupying a mere 2% of the body mass, the brain consumes up to 20% of the total body energy (Clarke & Sokoloff, 1999). Evidently, it is of prime importance to secure a stable supply of energy substrate to the brain. Glucose is the prime energy substrate in the brain and is constantly supplied by the blood. Hypo‐ or hyper‐glycemia results in malfunctioning of the brain and leads to loss of consciousness, as seen in diabetes mellitus. After taken up from the blood to a cell, glucose is converted to pyruvate for further energy metabolism. In mammalian cells, glucose can also be stored as glycogen, a highly branched polysaccharide that is readily broken down into glucose phosphate to meet metabolic demands. The functional role of cellular glycogen storage as an intermediate energy reservoir is well‐established in peripheral organs. For instance, in the liver, monosaccharides are supplied by the blood from the small intestine and eventually stored into glycogen. Hepatic glycogen serves as a buffer to sustain healthy levels of blood glucose (e.g., 90–130 mg/dl in humans). Excess glucose is stored in hepatocytes as glycogen, and glycogenolysis occurs to secrete glucose to the blood upon events of low blood glucose level. These operations are mediated by the pan‐ creas through insulin and glucagon signaling, respectively. In skeletal muscles, glycogen is mobilized as an initial phosphocreatine pool is depleted upon events of prolonged muscle contraction. Interestingly, while the liver and muscles are the two major sources of glycogen storage representing approximately 100 g (5%–6% of the organs fresh weight) and 400–500 g (1%–2% of muscle mass) of glycogen, Received: 17 November 2018 | Revised: 4 January 2019 | Accepted: 7 January 2019 DOI: 10.1002/jnr.24386 MINIREVIEW Glycogen distribution in mouse hippocampus Hajime Hirase 1,2,3 * | Sonam Akther 1,2 * | Xiaowen Wang 1 | Yuki Oe 1 *HH and SA contributed equally to this article. 1 RIKEN Center for Brain Science, Wako, Japan 2 Saitama University Brain Science Institute, Saitama, Japan 3 Center for Translational Neuromedicine, Faculty of Medical and Health Sciences, University of Copenhagen, Copenhagen, Denmark Correspondence Hajime Hirase and Yuki Oe, RIKEN Center for Brain Science, Wako, Saitama, Japan. Emails: hajime.hirase@riken.jp; yuki.oe@ riken.jp Funding information Japan Society for the Promotion of Science, Grant/Award Number: KAKENHI 16H01888, 16K10738, and 18H05150; Human Frontier Science Program, Grant/ Award Number: RGP0036/2014; Lundbeck Foundation Visiting Professorship ‐ Lundbeck Foundation Correction added on February 12, 2019, after first online publication: Funding information text have been changed from ‘Lundbeck Foundation Professorship ‐ Lundbeck Foundation’ to ‘Lundbeck Foundation Visiting Professorship ‐ Lundbeck Foundation’. Abstract The hippocampus is a limbic structure involved in the consolidation of episodic mem‐ ory. In the recent decade, glycogenolysis in the rodent hippocampus has been shown critical for synaptic plasticity and memory formation. Astrocytes are the primary cells that store glycogen which is subject to degradation in hypoglycemic conditions. Focused microwave application to the brain halts metabolic activities, and therefore preserves brain glycogen. Immunohistochemistry against glycogen on focused mi‐ crowave‐assisted brain samples is suitable for both macroscopic and microscopic in‐ vestigation of glycogen distribution. Glycogen immunohistochemistry in the hippocampus showed a characteristic punctate signal pattern that depended on hip‐ pocampal layers. In particular, the hilus is the most glycogen‐rich subregion of the hippocampus. Moreover, large glycogen puncta (>0.5 µm in diameter) observed in neuropil areas are organized in a patchy pattern consisting of puncta‐rich and ‐poor astrocytes. These observations are discussed with respect to distinct hippocampal neural activity states observed in live animals. KEYWORDS astrocytes, glycogen, hippocampus, neuromodulators, potassium