Determinants of different deep and superficial CA1 pyramidal cell dynamics during sharp-wave ripples

Abstract

Sharp-wave ripples represent a prominent synchronous activity pattern in the mammalian hippocampus during sleep and immobility. GABAergic interneuronal types are silenced or fire during these events, but the mechanism of pyramidal cell (PC) participation remains elusive. We found opposite membrane polarization of deep (closer to stratum oriens) and superficial (closer to stratum radiatum) rat CA1 PCs during sharp-wave ripples. Using sharp and multi-site recordings in combination with neurochemical profiling, we observed a predominant inhibitory drive of deep calbindin (CB)-immunonegative PCs that contrasts with a prominent depolarization of superficial CB-immunopositive PCs. Biased contribution of perisomatic GABAergic inputs, together with suppression of CA2 PCs, may explain the selection of CA1 PCs during sharp-wave ripples. A deep-superficial gradient interacted with behavioral and spatial effects to determine cell participation during sleep and awake sharp-wave ripples in freely moving rats. Thus, the firing

Investigation of the hippocampal information processing in freely moving rats

“…After the recordings, the electrode tracks were determined by histological reconstruction ( Figure 1A; Table S1). The CA1-CA2 border was identified by the widening of the pyramidal layer and the larger size of the neurons in the CA2 region and further validated by immunolabeling by the CA2-specific marker PCP4 Valero et al, 2015). The CA3 region was divided into three subregions ( Figure 1B): CA3a (closest to CA2), CA3b, and CA3c (see Supplemental Experimental Procedures).…”

“…Segmentation of the different regions and subregions were made according to physiological criteria (Diba and Buzsaki, 2008;Royer et al, 2010), difference in the width of the pyramidal layer and larger size of the neurons in the CA2 region compare to CA1, and finally the extensive recurrent collateral and negligible mossy fiber inputs in CA2 compare to CA3 (Lorente de Nó, 1947;Tamamaki et al, 1988;Jones and McHugh, 2011). Post-hoc immunohistological validation of the electrode locations was confirmed with the help of PCP4 antibody staining Valero et al, 2015).…”

“…Cellular layers and dendritic domains were identified with Current Source Density (CSD) analysis and Independent Component Analysis (ICA) of the LFPs (Fernandez-Ruiz and Herreras, 2013) assisted by physiological features such as the reversal of sharp-waves (Ylinen et al, 1995) and depth versus amplitude profile of theta oscillations ). We used a specific histological marker (anti-PCP4 antibody, Sigma HPA005792) to identify post-hoc the CA2 region Valero et al, 2015), helped by the visual inspection of the thicker pyramidal layer and wider and sparser cell bodies compared to CA1 in the histological sections (Lorente de Nó, 1947; . The CA1 region was divided into three equally wide subregions: CA1 proximal (next to the border of CA2), CA1 distal (close to the subiculum) and CA1 intermediate (in the middle).…”

“…For histological evaluation, brains were sliced into 70 μm thick slices (Leica Vibratome), with a 45º angle from the midline to capture the plane parallel to the implanted electrodes. Slices with visible traces of electrode shanks locations were immunolabelled with PCP4 (specific CA2 region marker) Valero et al, 2015). For this process, slices were washed three times in PBS-Tx 1% (Triton X-100 -laboratory grade, Sigma 9002-93-1), then blocked with 3% bovine serum albumin in PBS-Tx and then exposed to overnight incubation (at room temperature) with the primary antibody solution containing rabbit anti-PCP4 (1:300, Sigma HPA005792).…”

“…2014; Varga et al, 2012). Since in a previous study ripple-suppressed CA1 pyramidal cells were located in deep CA1 pyramidal layer (Valero et al, 2015), we investigated SPW-R-related spiking of neurons as function of their depth location in the CA2 pyramidal layer. The vertical distribution of the recording sites of the silicon probe shanks allowed us to simultaneously sample both superficial and deep neurons.…”