Tyrosine phosphorylation in the postnatal rat brain: A developmental, immunohistochemical study

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Abstract
We have used antibodies against phosphotyrosine to probe 50-μm cerebellar sections from rats of various ages as well as sections of adult brainstem, cerebrum, and olfactory bulb to investigate the developmental appearance of this phosphorylation system as revealed by light microscopy. While the overall intensity of staining in the cerebellum was highest at 7 days, the pattern of staining in the adult is quite disparate from that seen in younger animals. From 10 to 21 days postnatal, staining is associated primarily with the white matter and/or the lower premigratory zone of the external granular layer and adjacent formative molecular layer. While the temporal and spatial appearance of phosphotyrosine immunoreactivity corresponds well to the established patterns of axonal growth in these areas, we cannot at the light level ascertain whether the immunoreactivity is intrinsic or extrinsic to the growing fibers. In animals 28 days and older, however, staining is restricted to a subpopulation of multipolar cells distributed throughout the cerebellum, as well as the olfactory bulb, cerebrum, and brainstem. The phosphotyrosine-positive cells in the adult cerebellum are not comparable to glial-fibrillary-acidic-protein-immunoreactive elements with regard to morphology or distribution, and they fail to colocalize with neuronal somata stained with anti-microtubule-protein-2 antibodies. While it appears that the radial fibers of the Bergmann glia in the external granular layer stain at 7 days, there is no staining detected in the mitotically active neuroblasts of this layer at any age. We conclude that in the immature cerebellum, the majority of tyrosine phosphorylation detectable by this method may be involved in the formation and growth of axonal processes. In the adult rat cerebellum, however, it is most likely that detectable tyrosine phosphorylation occurs in the somata and processes of a neuroglial subpopulation.

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