CALRETININ-CONTAINING NEURONS IN RAT CEREBELLAR GRANULE CELL-CULTURES

Using an antiserum against calretinin, a calcium-binding protein, we d iscovered two distinct neuronal cell types that stain intensely in enr iched cerebellar granule cells. One neuronal cell type resembles unipo lar brush cells, whereas the other resembles Lugaro cells. During earl y culture times, these calretinin-positive neurons are most numerous b ut represent less than one percent of the total neuronal population. I n cultured cells, calretinin mRNA levels peak at day three in vitro, f ollowed by a rapid decline to undetectable levels by day six in vitro. However, calretinin-immunoreactive neurons are observed up to 29 days in vitro. Excitotoxic concentrations of glutamate receptor agonists f ailed to elicit an excitotoxic response on the intensely staining calr etinin-positive neurons, whereas greater than 95% of the cerebellar gr anule cells were susceptible to the excitotoxic actions of the glutama te receptor agonists. To distinguish between the two possibilities tha t calretinin-positive neurons either do not express glutamate receptor s or they are not susceptible to the excitotoxic effects of glutamate receptor agonists, we performed immunocytochemistry using glutamate re ceptor antibodies to detect the presence of receptor protein. We found that the AMPA/kainate glutamate receptor (GluR(2)R(3)) colocalized wi th calretinin, suggesting that calretinin-immunoreactive neurons expre ss the AMPA/kainate receptor; cerebellar granule cells, which are know n to express this receptor, were also immunoreactive for the GluR(2)R( 3) receptor. Copyright (C) 1997 Elsevier Science Inc.