ИСТИНА

The nature of functional specialization of hippocampal subfields along the rostrocaudal axis remains a matter of debate. Mapping of neuronal activity using c-Fos expression allows identification of the size and borders of active areas within the whole hippocampus. In the present work we assessed the zones which were activated by locomotion, environmental factors of novelty and visual information. C-Fos expression was measured at 8 levels along the rostrocaudal axis of the hippocampus. We tested C57BL/6 mice in 4 experiments. In the 1st experiment 4 groups were tested in different versions of the open field: novel arena x light condition, novel arena x dark condition, familiar arena x light condition or familiar arena x dark condition. In a 2nd experiment mice were tested in a familiar light open field with novel visual stimuli around the arena. In a 3rd experiment mice were tested in a light arena after 3 days of familiarization in the dark. In a 4th experiment free exploration was confined, mice were released into transparent cylinder in the familiar light arena. The caudal parts of CA3 and dental gyrus (DG) were activated in all free exploration groups irrespective of novelty and visual information. The confined condition reduced c-Fos expression in these regions. The rostral part of CA3 and DG were specifically activated in the light condition in novel arena. This effect was decreased in a familiar arena. When familiar environment was modified by addition of novel visual stimuli, a reactivation of rostral CA3 and DG was observed. CA1 (in all levels) was activated by exploring the novel arena in both light and dark conditions. However dark/light shift in familiar arena increased c-Fos activity in CA1. Thus various aspects of behaviour (response to novelty and/or visual information and exploration) differentially affected the hippocampal subfields along the rostrocaudal axis.