Calcium binding proteins and the AMPA glutamate receptor subunits in gerbil cochlear nucleus

The alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) glutamate receptors mediate fast excitatory synaptic transmission in the central nervous system. The GluR2 subunit confers calcium impermeability to AMPA receptors. Various calcium binding proteins play a role in calcium regulation within the neurons. This study sought to identify possible relationships between calcium binding proteins and glutamate receptor subunits, especially GluR2, in gerbil cochlear nucleus neurons. Our immunohistochemical observations reveal no particular correlation between GluR2 and calbindin; all the cell types show labeling for all the antibodies studied except calretinin. There was coincidence of strong GluR4 and strong parvalbumin staining in octopus cells, although calbindin was also present in these cells. This study suggests a possible relationship between parvalbumin and predominantly GluR4 containing receptors, even when calbindin is present. The absence of a strong inverse correlation between the presence of ionotropic AMPA receptor subunit GluR2 and calbindin suggests a more significant role of non-AMPA ionotropic glutamate receptors or other voltage-gated channels in the regulation of calcium in the neurons of cochlear nucleus. Alternatively, more detailed analysis of receptor composition at particular synapses and the subcellular localization of specific calcium binding proteins may be required.