Interlamellar CA1 network in the hippocampus

Abstract

To understand the cellular basis of learning and memory, the neurophysiology of the hippocampus has been largely examined in thin transverse slice preparations. However, the synaptic architecture along the longitudinal septo-temporal axis perpendicular to the transverse projections in CA1 is largely unknown, despite its potential significance for understanding the information processing carried out by the hippocampus. Here, using a battery of powerful techniques, including 3D digital holography and focal glutamate uncaging, voltage-sensitive dye, two-photon imaging, electrophysiology, and immunohistochemistry, we show that CA1 pyramidal neurons are connected to one another in an associational and wellorganized fashion along the longitudinal axis of the hippocampus. Such CA1 longitudinal connections mediate reliable signal transfer among the pyramidal cells and express significant synaptic plasticity. These results illustrate a need to reconceptualize hippocampal CA1 network function to include not only processing in the transverse plane, but also operations made possible by the longitudinal network. Our data will thus provide an essential basis for future computational modeling studies on information processing operations carried out in the full 3D hippocampal network that underlies its complex cognitive functions.longitudinal axons | CA1 association fibers | sequence memory | DHR

Membrane Potential Dynamics of CA1 Pyramidal Neurons during Hippocampal Ripples in Awake Mice

“…First, CA1 pyramidal neurons are known to have sparse recurrent connections (Deuchars and Thomson, 1996, Yang et al, 2014). The phase-locked firing of CA1 neurons during ripples would produce rhythmic excitatory inputs in the recurrently connected CA1 cells.…”

Distinct hippocampal functional networks revealed by tractography-based parcellation

“…Having stressed the differences between antHC and postHC connectivity to the rest of the brain, it is important to keep in mind that there are also prominent longitudinal intrahippocampal fibers connecting both segments (Sloviter and Lømo 2012;Yang et al 2014). These intrahippocampal connections might facilitate the integration of information stemming from antHC and postHC subregions (Patel et al 2013;Strange et al 2014).…”

Flexible theta sequence compression mediated via phase precessing interneurons

“…CA1 pyramidal cells make few direct connections with one another (Anderson et al, 2007) (but see Yang et al, 2014), suggesting that phase precession in CA1 arises through some combination of intrinsic cellular properties, external inputs to the circuit and local interactions between pyramidal cells and interneurons. Major sources of input to CA1 include spatially modulated signals from CA3 and from the entorhinal cortex, and temporally patterned GABAergic inputs from the medial septum, which target hippocampal interneurons and act as a pacemaker to entrain theta oscillations in the circuit (Freund and Antal, 1988).…”