Constitutive expression of the 25-kDa heat shock protein Hsp25 reveals novel parasagittal bands of Purkinje cells in the adult mouse cerebellar cortex

Despite the reported absence of the 25‐kDa heat shock protein Hsp25 in the rodent cerebellum, we have determined that Hsp25 is constitutively expressed in a subset of Purkinje cells in the adult cerebellum of the mouse. No other cerebellar neurons are Hsp25 immunoreactive, but there is weak staining associated with blood vessels. In the vermis, Hsp25‐immunoreactive Purkinje cells are confined to two regions: one in lobules VI/VII, the other in lobules IX/X. In each region, only a subset of the Purkinje cells is immunoreactive. These cells are grouped in five parasagittal bands arranged symmetrically about the midline. The boundaries of these expression domains correspond to transverse zones previously inferred from other expression patterns. A third Hsp25‐immunopositive domain is seen in the paraflocculus and flocculus. Again, only a subset of Purkinje cells within the paraflocculus and flocculus express Hsp25, revealing three distinct bands. Previous descriptions of compartmentation antigens have not differentiated between adult populations of Purkinje cells in these regions, suggesting that Hsp25 is a novel compartmentation antigen in the adult cerebellum. J. Comp. Neurol. 416:383–397, 2000. © 2000 Wiley‐Liss, Inc.