[1] Med Univ Plovdiv, Dept Pharmacol Toxicol & Pharmacotherapy, Plovdiv 4002, Bulgaria
[2] Bulgarian Acad Sci BAS, Inst Neurobiol, Sofia 1113, Bulgaria
[3] Trakia Univ, Fac Med, Dept Anat, Stara Zagora 6003, Bulgaria
[4] Med Univ Plovdiv, Dept Bioorgan Chem, Plovdiv 4002, Bulgaria
[5] Med Univ Pleven, Dept Biol, Pleven 5800, Bulgaria