Fos Imaging Reveals Differential Patterns of Hippocampal and Parahippocampal Subfield Activation in Rats in Response to Different Spatial Memory Tests

Abstract

We compared neuronal activation, as measured by Fos staining, during different spatial tasks in two experiments. The counts of Fos-stained neurons in the hippocampus increased as the spatial demands of the tasks increased, the tasks having been carefully matched for other factors. In Experiment 1, matched groups of rats either ran a standard eight-arm radial maze task or were trained to run up and down just one arm of the maze; the number of runs and rewards was identical in both conditions. In Experiment 2, rats were trained on the eight-arm maze but in different rooms. On the critical test day, both groups were run in the same room so that one group now performed with novel landmarks. All hippocampal subfields (dentate gyrus, CA3, CA1, dorsal, ventral, and caudal subiculum) showed a relative increases in c-fos activation in the eight-arm (Experiment 1) and novel room (Experiment 2) conditions, the sole exception being the ventral subiculum in Experiment 2. Although increased c-fos activation was found in both dorsal and ventral hippocampus, in Experiment 2 the relative increase was significantly greater in the dorsal hippocampus. Parahippocampal cortices responded heterogeneously: the perirhinal cortex failed to show increased activation in both experiments, in contrast to the entorhinal and postrhinal cortices. Subsequent comparisons confirmed that the perirhinal and postrhinal cortices responded in qualitatively different ways, the perirhinal cortex differing from the rest of the hippocampal formation. These experiments, which provide the first analysis of hippocampal Fos production during tests of allocentric spatial working memory, reveal that all components of the hippocampus are activated, but that under certain conditions the dorsal hippocampus is disproportionately involved.

The rat perirhinal cortex: A review of anatomy, physiology, plasticity, and function

“…This dissociation between hippocampal and perirhinal function was conserved across rat strains (Futter et al, 2006) and species (Pihlajamä ki et al, 2004;Buckley, 2005;Kö hler et al, 2005). Furthermore, immediate early gene imaging supports these lesion studies whereby c-Fos levels are increased in the hippocampus but not the perirhinal cortex during spatial learning tasks and they are increased in the perirhinal cortex but not the hippocampus during recognition tasks (Vann et al, 2000a;Aggleton and Brown, 2005).…”

“…Functional differences between the perirhinal and postrhinal cortices have also been demonstrated; there is differential activity between the postrhinal and perirhinal cortices following spatial memory tasks (Vann et al, 2000a). Lesions of the postrhinal cortex do not result in substantial changes in place cell firing in the area CA1 (Nerad et al, 2009) whereas lesions of the perirhinal cortex result do cause disruption of CA1 place cell function (Muir and Bilkey, 2001).…”

Recruitment of adult-generated neurons into functional hippocampal networks contributes to updating and strengthening of spatial memory

“…At this age, new cells exhibit unique characteristics that make them particularly inclined to modification by experience (6,8,10,11). One day after spatial navigation in the water maze (i.e., 10 days after BrdU injections), we found more BrdU-labeled cells in the DG of both Spatial ϪPF and Swim animals compared with Cage control mice [F (2,15) ϭ 6.01; P Ͻ 0.05; Fig. 1B and Table S1].…”

A Role of Fos Expression in the CA3 Region of the Hippocampus in Spatial Memory Formation in Rats

“…The expression of c-fos is induced by a variety of stimuli (Smith et al 1992;Melia et al 1994;Duncan et al 1996) and after some forms of learning (McCabe and Horn 1994;Radulovic et al 1998;Wan et al 1999;Vann et al 2000). Accordingly, Fos expression is considered a mechanism by which brief stimuli can trigger long-term changes in gene expression and alter the structural and functional properties of nerve cells (Goelet et al 1986;Morgan and Curran 1991).…”