Effect of chronic stress on dorsal CA1 place cell activities in freely moving mice

Abstract

Chronic stress impairs hippocampal mnemonic functions. Although stress effects on hippocampal spatial memory have been well studied in rodents, much less is known about its effects on hippocampal place cell activities in behaving animals. Place cell encodes the animal’s location in a given environment and is believed to be crucial for spatial memory and navigation. Recent studies revealed that acute stress significantly altered firing rates of place cell activities in CA1 hippocampus and showed slight effects on the water maze test. In this study, we investigated whether the chronic restraint stress (6 hr/a day for 21 days) would also affect CA1 pyramidal cell firing properties. First, we confirmed that the chronic restraint stress significantly impaired the spatial learning performance on 7 days water maze test. CA1 pyramidal cells were recorded in an open-field cylindrical chamber. On the inside of the chamber, a rectangular white card board was installed as a local cue. Cue arrangements were identical in sessions 1 and 3 while a local cue was 90° rotated in session 2. The stress group showed the low similarities in the same environments (sessions 1 and 3) compared to the control group. In the stress group, average firing rate of the place cells was significantly reduced while place fields were larger, and the spatial coherence was significantly lower than the control group. The stress group showed that the peak time of the Inter-spike interval (ISI) was significantly longer than the control group. These results suggest that chronic stress can produce alterations in hippocampal place cell activities, which might contribute to impairments in spatial learning and memory.