Cellular and subcellular distribution of AMPA-type glutamate receptor subunits and metabotropic glutamate receptor 1 alpha in the cochlear nucleus ofthe horseshoe bat (Rhinolophus rouxi)

Ionotropic alpha -amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) sel ective glutamate receptors (GluRs) are the main mediators of fast excitator y neurotransmission and composed of a variable combination of four differen t subunits (GluR1-4). The metabotropic glutamate receptor 1 alpha (mGluR1 a lpha) is involved in plastic synaptic events, Since horseshoe bats strongly depend on temporal cues for acoustic imaging by echolocation and exhibit p rominent species specific specializations of the cochlear nucleus (CN), the subunit distribution of AMPA selective GluRs and the distribution of mGluR 1 alpha was studied at the light and electron microscopic level with preemb edding immunocytochemistry. Immunoreactivity to GluR1 was low throughout th e CN. All types of projection neurons of the ventral CN expressed distinct GluR2/3 and GluR4 immunoreactivity with GluR4-labeling especially prominent in multipolar and octopus cell-like neurons of the posteroventral CN. The AMPA and metabotropic receptor inventory of the laminated ventral subdivisi on of the dorsal CN (DCNv) agreed with that reported in other mammals, wher eas the specialized dorsal non-laminated subdivision of DCN (DCNd) lacked t he prominent labeling for GluR2/3 and mGluR1 alpha that characterizes cartw heel cells of DCNv. Distinct GluR2/3 and GluR4 immunoreactivity combined wi th low expression of mGluR1 alpha immunoreactivity was characteristic for f usiform cells of DCNv and DCNd. Tuberculoventral cells of both the deep DCN v and the DCNd exhibited light to moderate GluR2/3 and GluR4 immunoreactivi ty. The staining patterns in DCNd thus indicate a loss of cerebellar-like m icrocircuits and a conservation of frequency specific circuitry of the deep and fusiform cell layers of the mammalian DCN. (C) 2001 Elsevier Science B .V. All rights reserved.