26 0090-2977/08/4001-0026 © 2008 Springer Science+Business Media, Inc. Neurophysiology, Vol. 40, No. 1, 2008 Neurodegenerative Changes in the Hippocampus within the Early Period of Experimental Diabetes Mellitus Yu. V. Lebed, 1 M. A. Orlovsky, 1 I. V. Lushnikova, 1 and G. G. Skibo 1 Neirofiziologiya/Neurophysiology, Vol. 40, No. 1, pp. 30-37, January-February, 2008. Received December 1, 2007. We studied the dynamics of modifications of the structure and architectonics in different zones of the pyramidal layer of the rat hippocampus within the early periods (3, 7, and 14 days) after induction of diabetes mellitus by streptozotocin. Using confocal immunofluorescence microscopy, we found neurons containing a specific protein, NeuN; a fluorescence dye, Hoechst 33258, allowed us to visualize the cell nuclei. The density of localization of neurons in the СА2 area decreased significantly on the 3rd day of development of diabetes. In the СА1 and СА3 areas, a significant decrease in this index was observed beginning from the 7th day. Within this time interval, we observed neurons with clear condensation of chromatin in the nuclei of these cells. The obtained data indicate that formation of appreciable neurodegenerative changes in the hippocampus occurs within the initial stages of development of experimental diabetes mellitus; this phenomenon can be a factor in the development of diabetic encephalopathy. Keywords: diabetes mellitus, hippocampus, neurodegeneration, streptozotocin. 1 Bogomolets Institute of Physiology, National Academy of Sciences of Ukraine, Kyiv, Ukraine. Correspondence should be addressed to Yu. V. Lebed (e-mail: lebed@biph.kiev.ua). INTRODUCTION Diabetes of types 1 and 2 induces serious complications related to functional and structural changes in the CNS [1-3]. Long-lasting diabetes mellitus is accompanied by the appearance of a syndrome that is qualified as diabetic encephalopathy [4]. In diabetic patients, the processes of memorization and learning are worsened [5, 6]. These patients demonstrate less successful solution of test tasks characterizing the level of attention and velocity of intellectual and motor processes than healthy subjects [7-9]. Such disorders can to a considerable extent be determined by dysfunction of the hippocampus that plays a key role in cognitive processes related first of all to the state of memory. Studies of molecular and cellular aspects of dysfunction of the hippocampus in diabetes were focused mostly on changes observed within late periods of this disease [10, 11]. Nevertheless, a few recent findings are indicative of the appearance of noticeable disorders in the hippocampus within the early periods (first weeks) of development of experimental diabetes [12-14]. Despite the urgency of this problem, injuries of the cerebral structures at early stages of diabetes mellitus remain relatively poorly studied. In this relation, we studied the dynamics of changes in the structure and architectonics of the pyramidal layer of the hippocampus within the early periods of development of experimental diabetes in rats. METHODS Experiments were carried out on 30 male Wistar rats (5 months old) weighing 190 to 240 g. Diabetes mellitus was induced in 14 animals by single i.p. injections of 45 mg/kg streptozotocin (Sigma-Aldrich, Germany) dissolved ex tempore in 0.5 ml of citrate buffer (0.1 M, pH 4.5) [15, 16]. The level of glycemia was estimated with the use of an express-analysis device; only rats with the level of glucose in the blood of 10 mM or greater were used in experiments. In one and the same day, rats of the experimental group were injected with streptozotocin, and animals of the control group ( n = 6) were injected with an analogous volume of citrate buffer. Tissue samples for histological studies were collected on the 3rd, 7th, and 14th days of streptozotocin-