We monitored somatic Ca 2+ dynamics in three Ocean-GCaMP6f mice (177, 180, and 198 = 555 cells in total) and three Island-GCaMP6f mice (196, 196, and 199 = 591 cells in total), as each animal ran freely for 90 min in a familiar open field ( Fig. For both cohorts of mice, we implanted a microendoscope probe ( 11) into dorsal MEC and performed Ca 2+ imaging using a miniaturized, head-mounted fluorescence microscope as the mice freely explored a square arena (100 × 100 cm) ( Fig. Because Cre expression in the EC of these mice is specific for island cells ( 5), GCaMP6f expression in the MEC was restricted to the Calbindin/Wfs1-positive island cells ( Fig. To study island cells, we injected AAV2/5-Syn-DIO-GCaMP6f virus into the superficial layer of MEC of Wfs1-Cre transgenic mice ( 5) ( Fig.
Because ocean cells but not island cells project to the DG ( 5), GCaMP6f expression in the MEC was restricted to the Reelin-positive ocean cell populations ( Fig. We injected retrogradely transported adenoassociated virus (AAV)2/5-Syn-GCaMP6f virus into the dorsal DG of WT C57BL6 mice ( Fig. To study ocean cells, we make use of the fluorescent calcium sensor GCaMP6f ( 10). A dichotomy of activity properties in island and ocean cells gives insight into how different downstream spatial functions in hippocampus arise. Here, we are able to selectively monitor the Ca 2+ dynamics of either island or ocean cells in freely exploring mice and, in doing so, resolve whether both populations contain grid cells and, if so, whether their spatial coding properties differ or not.
In previous literature, it has been suggested that specific types of spatially modulated cells, particularly grid cells, may be differentially contributed by the two cell types however, this remains controversial in the literature ( 8, 9) owing to the difficulty of directly monitoring island and ocean cells during behavior. To date, few studies have investigated the relationship between anatomy and spatial coding in EC thus, there is very little known about how ocean cells and island cells differ in their coding of space. Given this clear morphological, genetic, and anatomical dichotomy of ECII excitatory cells, we wondered whether they differ in their activity patterns.
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