Kv4.2 potassium channels segregate to extrasynaptic domains and influence intrasynaptic NMDA receptor NR2B subunit expression

Walter A Kaufmann,Jeanne M Nerbonne,Ko Matsui,Andreas Jeromin,Francesco Ferraguti

doi:10.1007/s00429-012-0450-1

Abstract

Neurons of the intercalated cell clusters (ITCs) represent an important relay site for information flow within amygdala nuclei. These neurons receive mainly glutamatergic inputs from the basolateral amygdala at their dendritic domains and provide feed-forward inhibition to the central nucleus. Voltage-gated potassium channels type-4.2 (Kv4.2) are main players in dendritic signal processing and integration providing a key component of the A currents. In this study, the subcellular localization and distribution of the Kv4.2 was studied in ITC neurons by means of light- and electron microscopy, and compared to other types of central principal neurons. Several ultrastructural immunolocalization techniques were applied including pre-embedding techniques and, most importantly, SDS-digested freeze-fracture replica labeling. We found Kv4.2 densely expressed in somato-dendritic domains of ITC neurons where they show a differential distribution pattern as revealed by nearest neighbor analysis. Comparing ITC neurons with hippocampal pyramidal and cerebellar granule cells, a cell type- and domain-dependent organization in Kv4.2 distribution was observed. Kv4.2 subunits were localized to extrasynaptic sites where they were found to influence intrasynaptic NMDA receptor subunit expression. In samples of Kv4.2 knockout mice, the frequency of NR1-positive synapses containing the NR2B subunit was significantly increased. This indicates a strong, yet indirect effect of Kv4.2 on the synaptic content of NMDA receptor subtypes, and a likely role in synaptic plasticity at ITC neurons.

Highlights

The intercalated cell clusters (ITCs) of the amygdala are composed of densely packed GABAergic neurons that areBrain Struct Funct (2013) 218:1115–1132 distributed around the basolateral complex (Busti et al 2011; Millhouse 1986)
When analyzing Kv4.2 immunolabeling in the ITCs at higher resolution, it appeared enriched in the neuropil and sparse in cell bodies (Fig. 1b, c)
Apart from the tight clustering of immunoparticles with nearest neighbor distance (NND) below 40 nm, which was detected in all preparations, we found homogeneously distributed Kv4.2 subunits in the dendrites of ITC neurons and randomly distributed subunits in the dendrites of CA1 pyramidal neurons

Summary

Introduction

The intercalated cell clusters (ITCs) of the amygdala are composed of densely packed GABAergic neurons that areBrain Struct Funct (2013) 218:1115–1132 distributed around the basolateral complex (Busti et al 2011; Millhouse 1986). ITC neurons are characterized by a small soma (8–19 lm in diameter), a flattened dendritic tree and high density of dendritic spines (Pape and Pare 2010) These neurons strongly express l-opioid and dopamine type I receptors (Jacobsen et al 2006; Likhtik et al 2008), and they are uniform with respect to active and passive membrane properties (Busti et al 2011). They prevent initiation of dendritic action potentials, limit back-propagation of action potentials into dendrites and modulate excitatory postsynaptic potentials (Cai et al 2004; Hoffman et al 1997; Johnston et al 2003) Since they operate in a voltage range where other channels are closed, even subtle changes in the activity of these channels can have large repercussions in the overall excitability and firing properties of the cells expressing them

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Conclusion