An immunohistochemical study of the fetal sheep neocortex and cerebellum with antibodies against nervous system-specific proteins.

The topographical distribution of glial fibrillary acidic protein (GFAP), vimentin, neuron-specific enolase (NSE) and neurofilament (NF) proteins in the developing neocortex and cerebellum of sheep fetuses of different gestational ages (60-149 days) was described. For comparison, brain tissues from a lamb and two adult sheep were included in this study. In the walls of the developing cerebral hemispheres GFAP- and vimentin-immunoreactive radial glial fibres were demonstrated. From 80 days of gestation onwards a continuous decrease of radial fibres occurred which was accompanied by an increase of GFAP-positive mature astrocytes. In Bergmann glial fibres of the cerebellum, which are the equivalent of radial fibres in the telencephalon, both GFAP and vimentin were detectable in fetuses and adult sheep. With polyclonal antibodies against NSE and NF proteins (NF-M, NF-H) prominent staining of neuronal fibre tracts was seen in fetuses of all gestational ages studied. In the neocortex, staining for NF-L did not occur before day 80 of gestation. With monoclonal antibodies against phosphorylated NF-H (clone SMI 31), however, reaction of neocortical fibre tracts was first seen at 85 days of gestation, and cytoplasmic staining of single neocortical neurons was first found in a 149-day-old fetus. Several fixatives and proteolytic pretreatment were examined for their effects on preservation and re-establishment of marker protein expression, respectively. GFAP and vimentin in radial glial fibres were not demonstrable without pretrypsinization of tissue sections. The most intensive staining of NF proteins with polyclonal antisera was seen in brains fixed in Bouin's fluid.