A. V. Kryuchkova - Junior Research Scientist, FSBIS SRI PCM FMBA of Russia, Moscow. E-mail: likkavolkhova@mail.ru
A. N. Inozemtsev - Dr.Sc. (Biol.), Leading Research Scientist, Head of Laboratory, Lomonosov Moscow State University, Moscow. E-mail: A_Inozemtsev@mail.ru
N. A. Loginova - Ph.D.(Biol.), Research Scientist, FSBI IHNA&NPh RAS, Moscow. E-mail: nadinvnd@yandex.ru
I. V. Zimina - Ph.D.(Biol.), Senior Research Scientist, FSBIS SRI PCM FMBA of Russia, Moscow. E-mail: Yangicher@yandex.ru
O. V. Belova - Dr.Sc. (Biol.), Head of Laboratory, FSBIS SRI PCM FMBA of Russia, Moscow. E-mail: olgabelova49@yandex.ru
V. Ya. Arion - Dr.Sc. (Biol.), Professor, Chief Research Scientist, FSBIS SRI PCM FMBA of Russia, Moscow. E-mail: vyaarion@yandex.ru
E. V. Loseva - Dr.Sc. (Biol.), Leading Research Scientist, FSBI IHNA&NPh RAS, Moscow. E-mail: losvnd@mail.ru

Mutual influence of the nervous and immune systems has being widely studied. We investigated effects of the peptide immunoactive drug of thymus Tactivin on passive avoidance (PA) conditioning and the c-fos expression in the rats brain. Rats-male Wistar (n = 48) were intraperitoneally injected by Tactivin (0.4 mg/kg). In the first series of experiments, the drug was administered during 5 days before the PA acquisition, in the second one for 10 days before the PA acquisition and then another 5 days before the brain extraction. Rats of control groups were injected with a saline solution. PA conditioning is analyzed in an apparatus that consists of a light compartment, a dark dangerous compartment in which foot shock was delivered and a dark safe one where rats were not punished. C-fos expression was assessed in the second series immunohistochemically in a total of 21 brain regions on the frontal sections at 2.52 mm and +0.95 mm from bregma levels (Paxinos, Watson, 2005). In the first series, Tactivin-treated animals least often chose the dangerous compartment and least time spent in it than the control ones. Tactivin had no effect in the second series. Tactivin increased c-fos expression in lateral septal nucleus, nucleus accumbens, dorsal dentate gyrus, ventromedial and lateral hypothalamic nuclei, and decreased it in dorsal CA1 hippocampal field. Thus, specific impact of Tactivin on structural-functional state of CNS is revealed. It is shown also that 5 day of Tactivin administration improved avoidance conditioning meanwhile its administration during 10 days may cancel this effect. The reported study was partly supported by RFBR, research project No.14-04-32087 mol_a.