Аннотация:Functional heterogeneity of the hippocampus along its longitudinal axis has been found in many studies. However, the functional specificity of its different parts is still not entirely clear, especially the role of the caudal part in spatial behaviour. In the present work we addressed this issue by studying the effects of lesions of the caudal parts of hippocampus wild-caught bank voles (Clethrionomys glareolus). Previously we showed that voles perform the Morris water maze task better than laboratory mice and that they have a larger hippocampus, especially in the caudal region. Caudal bilateral cytotoxic (NMDA) lesions, about 1/3 of the whole hippocampus impaired exploratory behaviour in voles. The number of rears in open fields with and without 2 additional objects was reduced. Track segmentation showed an increased percentage of high-speed segments and a decreased percentage of middle-speed segments in lesioned voles compared to controls. Moreover lesioned voles learned the water maze task more slowly. However, no group differences were revealed in an enclosed T-maze spontaneous alternation task, although rostral and complete hippocampus lesions are known to impair spontaneous alternation in mice and rats. Thus caudal hippocampal lesions impaired spatial behaviour only if voles moved freely in the space of an arena but not in the narrow arms of the maze. Mapping of neuronal activity by c-Fos expression showed high activation in middle and caudal subregions of CA1, CA3 and dental gyrus after exploration of a familiar open field in both voles and C57BL/6 mice. c-Fos activity was significantly decreased when animal movement was restricted by putting it into a small transparent cylinder placed in the arena. Our data suggest that the caudal part of the hippocampus is involved in the control of spatial behaviour, but the effects are related to the size of the experimental space and the demands of the spatial task.