Target- and input-dependent organization of AMPA and NMDA receptors in synaptic connections of the cochlear nucleus Journal Article


Author(s): Rubio, Maía E; Fukazawa, Yugo; Kamasawa, Naomi; Clarkson, Cheryl; Molnár, Elek; Shigemoto, Ryuichi
Article Title: Target- and input-dependent organization of AMPA and NMDA receptors in synaptic connections of the cochlear nucleus
Affiliation IST Austria
Abstract: We examined the synaptic structure, quantity, and distribution of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)- and N-methyl-D-aspartate (NMDA)-type glutamate receptors (AMPARs and NMDARs, respectively) in rat cochlear nuclei by a highly sensitive freeze-fracture replica labeling technique. Four excitatory synapses formed by two distinct inputs, auditory nerve (AN) and parallel fibers (PF), on different cell types were analyzed. These excitatory synapse types included AN synapses on bushy cells (AN-BC synapses) and fusiform cells (AN-FC synapses) and PF synapses on FC (PF-FC synapses) and cartwheel cell spines (PF-CwC synapses). Immunogold labeling revealed differences in synaptic structure as well as AMPAR and NMDAR number and/or density in both AN and PF synapses, indicating a target-dependent organization. The immunogold receptor labeling also identified differences in the synaptic organization of FCs based on AN or PF connections, indicating an input-dependent organization in FCs. Among the four excitatory synapse types, the AN-BC synapses were the smallest and had the most densely packed intramembrane particles (IMPs), whereas the PF-CwC synapses were the largest and had sparsely packed IMPs. All four synapse types showed positive correlations between the IMP-cluster area and the AMPAR number, indicating a common intrasynapse-type relationship for glutamatergic synapses. Immunogold particles for AMPARs were distributed over the entire area of individual AN synapses; PF synapses often showed synaptic areas devoid of labeling. The gold-labeling for NMDARs occurred in a mosaic fashion, with less positive correlations between the IMP-cluster area and the NMDAR number. Our observations reveal target- and input-dependent features in the structure, number, and organization of AMPARs and NMDARs in AN and PF synapses.
Keywords: Synapses; Electron microscopy; Dorsal cochlear nucleus; GluN1; RRID: AB_94946; RRID: nif-0000-30467; SDS-freeze fracture immunolabeling; Ventral cochlear nucleus
Journal Title: Journal of Comparative Neurology
Volume: 522
Issue 18
ISSN: 0021-9967
Publisher: Wiley-Blackwell  
Date Published: 2014-07-29
Start Page: 4023
End Page: 4042
URL:
DOI: 10.1002/cne.23654
Notes: The authors thank Sanae Hara for technical help with some of the sample preparations and Jennifer Chikar for proof editing the article.
Open access: yes (repository)