[1]Institute of Neurobiology, Department of Drug Toxicology, Bulgarian Academy of Sciences, 1113 Sofa, Bulgaria;
[2]Institute of Cellular Biology and Neurobiology, National Research Council, I-00168 Rome, Italy;
[2]Institute of Cellular Biology and Neurobiology, National Research Council, I-00168 Rome, Italy;
[3]Laboratory of Cell Biology, Depart-ment of Anatomy and Histology, Medical University, BG-9002 Varna, Bulgaria;