Kuptsov Pa

Features of the expression of the c-Fos gene along the rostrocaudal axis of the hippocampus in common voles after rapid training to solve a spatial task

The level of expression of the c-Fos protein in neurons was used as a measure of the activation of transcription in the hippocampus of common voles (Microtus arvalis Pall.) after rapid spatial training. Stained Fos-positive cells were counted on 20 brain sections along the rostrocaudal axis of the hippocampus. Voles were trained to find the exit to their home cages through one of the arms of a modified eight-arm radial maze (using a 2-h series of six trials on one day). Animals were initially trained to leave the home cage via an arm not connected to the maze. Voles of the “active” control group were passed through the isolated arm into the home cage six times on the experimental day. Animals for the “passive” control for c-Fos levels were collected from their home cages. Significant increases in c-Fos expression in voles trained in the maze and the active control group, as compared with passive controls, were seen in all areas studied (hippocampal fields CA1 and CA3 and the dentate fascia). At the same time, a significant increase in the number of c-Fos-positive neurons in voles trained in the maze, as compared with the active controls, was noted only in the caudal hippocampus, no differences being seen in the rostral part. The greatest levels of activation were seen in the dentate fascia and field CA3. These results provide evidence for the heterogeneous functioning of the hippocampus along the rostrocaudal axis during training of voles to solve a spatial task.

Inhomogeneous Rostrocaudal Activation of the Hippocampus in Mice after Exploration of a Novel Space

Hippocampal activity in C57BL/6 mice was studied during exploration of novel spaces of different levels of complexity and learning by neuromapping using the induction of c-Fos protein by nervous activity. c-Fos-immunopositive neurons were counted at eight levels along the whole of the rostrocaudal axis of the hippocampus. In experiment 1, mice were given six opportunities on a single day to find the entrance to the home cage through one of the arms of a modified eight-arm radial maze. Animals of the active control group were released into the home cage via an isolated arm. Mice tested in the eight-arm maze showed an inhomogeneous increase in c-Fos expression along the rostrocaudal axis: activation in the caudal part of fields CA1 and CA3 and the dentate fascia was significantly greater than that in the rostral part. In experiment 2, animals were tested in a novel open field. In this situation, the increase in expression in the caudal part of field CA1 was greater than that in the rostral part, though in field CA3 and the dentate fascia there was uniform activation over the whole rostrocaudal extent. Both experiments identified positive correlations between the density of c-Fos-positive neurons and measures of investigative activity. These data provide evidence that placing of animals in a novel space leads to inhomogeneous activation of the hippocampal field along its rostrocaudal axis.