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The unfolded protein response (UPR) has been reported during normal development of cortical neurons and cerebellar white matter and may also contribute to the pathogenesis of neurological conditions, such as Marinesco‐Sjogren syndrome and Borna virus infection, which result in cerebellar defects. The UPR is initiated when the processing capacity of the endoplasmic reticulum (ER) is overwhelmed. Misfolded proteins accumulate and can activate ER stress sensors; PKR‐like endoplasmic reticulum kinase (PERK), inositol‐requiring enzyme 1 (IRE1), activated transcription factor 6 (ATF6) and their downstream targets glucose‐regulated protein 78 (GRP78), glucose‐regulated protein 94 (GRP94) and protein disulfide isomerase (PDI). In order to provide a fuller appreciation of the possible importance of ER stress‐associated proteins in the context of cerebellar disease, we have profiled the expression of ER stress sensors and their downstream targets in the developing cerebellar cortex in postnatal rat. Activation of PERK and IRE1 stress sensors was observed for the first time in normally developing granule cell precursors. A second proliferative pPERK‐positive population was also detected in the internal granular layer (IGL). In general, the density of UPR protein‐positive cells was found to decrease significantly when profiles in early and late postnatal ages were compared. These data may be relevant to studies of medulloblastoma and warrant further investigation. [ABSTRACT FROM AUTHOR]