Long-term depression is differentially expressed in distinct lamina of hippocampal CA1 dendrites.

Camin Dean,Saheeb Ahmed,Binu Ramachandran

doi:10.3389/fncel.2015.00023

Camin Dean, Saheeb Ahmed + Show 1 more

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https://doi.org/10.3389/fncel.2015.00023

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Abstract

Information storage in CA1 hippocampal pyramidal neurons is compartmentalized in proximal vs. distal apical dendrites, cell bodies, and basal dendrites. This compartmentalization is thought to be essential for synaptic integration. Differences in the expression of long-term potentiation (LTP) in each of these compartments have been described, but less is known regarding potential differences in long-term depression (LTD). Here, to directly compare LTD expression in each compartment and to bypass possible differences in input-specificity and stimulation of presynaptic inputs, we used global application of NMDA to induce LTD. We then examined LTD expression in each dendritic sub-region—proximal and distal apical, and basal dendrites—and in cell bodies. Interestingly, we found that distal apical dendrites exhibited the greatest magnitude of LTD of all areas tested and this LTD was maintained, whereas LTD in proximal apical dendrites was not maintained. In basal dendrites, LTD was also maintained, but the magnitude of LTD was less than in distal apical dendrites. Blockade of inhibition blocked LTD maintenance in both distal apical and basal dendrites. Population spikes recorded from the cell body layer correlated with apical dendrite field EPSP (fEPSP), where LTD was maintained in distal dendrites and decayed in proximal dendrites. On the other hand, LTD of basal dendrite fEPSPs was maintained but population spike responses were not. Thus E-S coupling was distinct in basal and apical dendrites. Our data demonstrate cell autonomous differential information processing in somas and dendritic sub-regions of CA1 pyramidal neurons in the hippocampus, where LTD expression is intrinsic to distinct dendritic regions, and does not depend on the nature of stimulation and input specificity.

Highlights

Long-term potentiation (LTP) and long-term depression (LTD) of synaptic strength are thought to represent the cellular mechanism by which learning and memory formation occur (Bliss and Collingridge, 1993; Malenka, 1994b)
In this study we investigated whether distinct branches of hippocampal CA1 pyramidal neurons have cell-intrinsic postsynaptic differences in LTD expression
To date only a couple www.frontiersin.org of studies have compared LTD expression in distinct dendritic was found between apical and basal dendrite LTD, regions—in one LTD was maintained in distal but not proximal proximal and distal dendrites were not distinguished in this apical dendrites (Parvez et al, 2010), and in another, no difference study (Pavlowsky and Alarcon, 2012)

Summary

Introduction

Long-term potentiation (LTP) and long-term depression (LTD) of synaptic strength are thought to represent the cellular mechanism by which learning and memory formation occur (Bliss and Collingridge, 1993; Malenka, 1994b). In the hippocampus NMDA receptors are crucial for LTP and LTD at the Schaffer collateral-pyramidal synapse of the CA1 region—one of the best-studied plasticity models in the mammalian brain (Dudek and Bear, 1992; Mulkey and Malenka, 1992). Hippocampal CA1 pyramidal neurons have distinct compartmentalized domains with distinct inputs, signaling cascades and plasticity mechanisms thought to be crucial for synaptic integration (Spruston, 2008). These domains consist of basal dendrites extending into the stratum oriens, the pyramidal cell body layer in stratum pyramidale, proximal apical dendrites and distal apical dendrites in stratum radiatum. In a comparison of dopamine-induced LTP in basal and distal apical dendrites, expression of LTP in basal dendrites required L-type voltage-gated calcium channels, and expression of LTP in distal apical dendrites required BDNF (Navakkode et al, 2012)

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