Relocating cued goals induces population remapping in CA1 related to memory performance in a two‐platform water task in rats

Abstract

The activity of CA1 neurons in the rodent hippocampus represents multiple aspects of learning episodes, including cue and place information. Previous reports on cue and place representation in CA1 have examined activity in single neurons and population recordings during free exploration of an environment or when actions are directed to either cue or place aspects of memory tasks. To better understand cue and place memory representation in CA1, and how these interact during goal-directed navigation, we investigated population activity in CA1 during memory encoding and retrieval in a novel water task with two visibly distinct platforms, using mRNA for immediate early genes Arc and Homer1a as markers of neural activity. After training, relocating cues to new places induces an extensive, perhaps global, remapping of the memory code that is accompanied by altered navigation and rapid learning of new cue-place information. In addition, we have found a significant relationship between the extent of reactivation and overall cue choice accuracy. These findings demonstrate an important relationship between population remapping in CA1 and memory-guided behavior.

Place navigation in the Morris water task results in greater nuclear Arc mRNA expression in dorsal compared to ventral CA1

“…Brains were postfixed in 4% PFA for approximately 4 hr and then transferred to 30% sucrose in PBS with 0.02% sodium azide for at least 48 hr before cryosectioning. Following sectioning at 40 μm thickness, a 1/12 section series was mounted onto Superfrost Plus microscope slides, labeled with antisense Arc mRNA probes, and nuclei were counterstained with DAPI (see detailed methods;Lee, LeDuke, Chua, McDonald, & Sutherland, 2018). Following Arc mRNA and DAPI labeling, we collected z-stack images following systematic-random sampling principles using the optical fractionator method in Olympus Fluoview and StereoInvestigator software packages (see detailed methods;Lee et al, 2018).…”

“…Following sectioning at 40 μm thickness, a 1/12 section series was mounted onto Superfrost Plus microscope slides, labeled with antisense Arc mRNA probes, and nuclei were counterstained with DAPI (see detailed methods;Lee, LeDuke, Chua, McDonald, & Sutherland, 2018). Following Arc mRNA and DAPI labeling, we collected z-stack images following systematic-random sampling principles using the optical fractionator method in Olympus Fluoview and StereoInvestigator software packages (see detailed methods;Lee et al, 2018). This approach allowed us to collect unbiased population estimates of DAPI and Arc mRNA labels across the entire CA1 hippocampal axis.By contrast to the behavioral effects of changes to goal location and context, we failed to find an effect of treatment on the probability of Arc mRNA expression in CA1 shown in the proportion of Arc:DAPI across the entire CA1 axis (Figure2c; One-way ANOVA: F(1, 21) = 1.578, p = .2299).…”

Calcium Imaging Reveals Fast Tuning Dynamics of Hippocampal Place Cells and CA1 Population Activity during Free Exploration Task in Mice

“…It is known that several types of spatial representation remapping may occur between different navigating sessions, including full, partial and rate remapping [ 33 , 34 ]. However, the retention of the cognitive maps was also observed [ 3 , 35 ].…”

Behaviour-driven Arc expression is greater in dorsal than ventral CA1 regardless of task or sex differences

“…A total of 24 Long Evans rats weighing between 300 and 350 grams were used in the present experiments, including 12 females and 12 males (Charles River, Raleigh, NC). Previous work in our lab and others have determined such group sizes provide adequate statistical power for within-animal and across-group comparisons for behavioural and cellular levels of analysis [8,10,31,32]. Following their arrival at the University of Lethbridge, animals were allowed at least 1 week to acclimatize to colony room conditions and were handled 5 minutes each day by the experimenter for 5 days before the start of the experiment.…”