Occurrence of glutamate receptor subunit 1-containing aggresome-like structures during normal development of rat spinal cord interneurons

During a developmental study of the expression of alpha -amino-3-hydroxy-5- methyl-4-isoxazolepropionate (AMPA) -type glutamate receptor subunits in ra t spinal cord, we observed the existence of cytoplasmic inclusion bodies wi th positive immunoreactivity to glutamate receptor subunit 1 (GluR1) but no t to other glutamate receptor subunits. GluR1-positive bodies have a diamet er of between 1 and 3 Lm and can be seen widely distributed throughout spin al cord gray matter, with the exception of the ventral horn region. They tr ansiently appear within a definite developmental time-period between embryo nic day 19 and postnatal day 17 and are only associated with neuronal cells . Ultrastructural analysis revealed that these inclusions were located adja cent to the nucleus and consisted of amorphous material without any limitin g membrane. Immunocytochemical analysis revealed that the inclusions displa yed positive immunoreactivity to ubiquitin, HSP70, and 20S proteasome. All these data indicate that GluR1-containing inclusions display all the ultras tructural and immunocytochemical characteristics of the recently described structure, which have been given the name aggresomes. Further studies are n eeded to determine the biological significance of these normally occurring aggresome-like inclusions, because aggresomes are usually considered in a p athologic context. (C) 2002 Wiley-Liss, Inc.