ИСТИНА

Exploratory behavior is a necessary component of cognitive mapping which is hippocampal dependent (O’Keefe & Nadel, 1978). Complete lesion of the hippocampus usually results in hyperactivity and impaired exploration in rats, but effects of partial hippocampal lesions were not always found, especially after ventral hippocampal lesions (e.g. Bannerman et al., 2003).The role of different hippocampal subregions in the control of exploration in mice and other rodents is poorly studied, although species-specific features of the functions along the septotemporal axis of the hippocampus are possible. The involvement of the caudal hippocampal subregion was assessed in a series of experiments where different aspects of locomotion in various types of open field were studied in C57BL/6 mice and bank voles (Clethrionomys glareolus). Using c-Fos as a marker of neuronal activity showed that the caudal hippocampus, including ventral and intermediate subregions is specifically activated during exploration. Selective cytotoxic (NMDA) lesions of this part significantly affected the character of locomotion in both species, and this alteration was context-specific, marked impairment (hyperactivity, decreased tortuosity, rearing, a change of path segment characteristics and others) was found in a large (220 cm diameter) arena. The size of the arena influenced only caudal hippocampal subfields; c-Fos expression was high in CA3 and dental gyrus in mice tested in the large arena. In the experiments with the large arena with contrasted context zones (wall/center, shadow/light and food/nofood) no decreased anxiety was found in caudal hippocampal lesioned mice, however they demonstrated a sharp nonflexible change in activity depending on the availability of food and especially arena lighting. Recent naturalistic experiments showed increased activation in both whole dental gyrus and the caudal CA-fields after homing in bank voles. These findings suggest a specific role of this hippocampus region in the control of exploration and context-dependent movement.