Postnatal development of unipolar brush cells in the cerebellar cortex of cat

The postnatal developmental distribution pattern of metabotropic glutamate receptor (mGluR1a) immunoreactive unipolar brush cells (UBCs) was studied in the cerebellar cortex of kittens. On the day of birth (P0) UBCs are already present in the white matter in lobule X of the vermis, but only a few of these cell seemed to migrate to the deeper region of the internal granular layer. By the end of the first week (P8) UBCs were seen to invade the white matter + internal granular layer of lobules IX, VIII, I, and II of the vermis, and they spread further in the transitory area medio-laterally from the vermis toward the cerebellar hemispheres. By P15, UBCs appeared in lobules III and VII of the vermis, as well as in corresponding lobules of the neocerebellum, with especially high numbers in lobule VII. By P22, UBCs migrated further after their medio-lateral course in the neocerebellum, and began to invade lobules V and VI. At P62 the amount of UBCs in midsagittal planes of early developing vermal lobules (I, II, VII-X) resembled the P132 or adult pattern. The medio-lateral migration and incorporation of UBCs into the late-developing cerebellar lobules V and VI was completed only by P132, when the spatial distribution of UBCs in both the vermal and neocerebellar lobules was comparable to that seen in the 1 year old young adult cat. Although by P132 the postnatal migration of the vast majority of UBCs seemed to be completed, in the cerebellum of adult cats a few migrating UBCs could still be observed in the white matter of the cerebellar lobules, and beneath the ependyma of the fourth ventricle. It is concluded that during ontogenesis the migration course of UBCs follows essentially the developmental sequence of cerebellar lobules, although the incorporation of UBCs into the internal granular layer continues until 4 months postnatally, i.e., much beyond the apparent completion (about two months postnatally) of cytoarchitectonic built up of the cerebellar cortex of kittens.