Bibliothek

Notizen: Abstract This study examines the early organization of glial cells, together with the expression of chondroitin sulfate proteoglycans in the developing thalamus of ferrets. Glia were identified with antibodies against vimentin and glial fibrillary acidic protein and the chondroitin sulfate proteoglycans were identified by using an antibody against chondroitin sulfate side chains. Our results reveal three striking features of early thalamic development. First, there is a distinct population of glial fibrillary acidic protein-immunoreactive astrocytes (first seen at E30) that resides in the perireticular thalamic nucleus of the primordial internal capsule. These glial fibrillary acidic protein-immunoreactive astrocytes of the perireticular nucleus are transient and form a conspicuous feature of the early developing forebrain. They are first apparent well before any glial fibrillary acidic protein-immunoreactive astrocytes are seen in other regions of the thalamus (at about P8). Further, unlike in other thalamic regions, these peculiar perireticular astrocytes do not express vimentin before they express glial fibrillary acidic protein. Second, in the reticular thalamic nucleus, the radial glial cells express glial fibrillary acidic protein; they are the only ones to do so in the thalamus during development. The glial fibrillary acidic protein-immunoreactive radial glial cells of the reticular nucleus form a rather distinct band across the developing thalamus at these early stages (E30–P1). Finally, and preceding the expression of glial fibrillary acidic protein, the radial glial cells of the reticular nucleus, unlike those in other thalamic regions, are associated closely with the expression of chondroitin sulfate proteoglycans (E20–E30). Later (after E30), the expression of the chondroitin sulfate proteoglycans in the reticular nucleus declines sharply. The significance of this finding is related to the early organization of the cortico-fugal and cortico-petal pathways.

Notizen: Abstract We have explored two aspects of internal capsule development that have not been described previously, namely, the development of glia and of blood vessels. To these ends, we used antibodies to glial fibrillary acidic protein (GFAP) and to vimentin (to identify astrocytes and to radial glia) and Griffonia simplicifolia (lectin; to identify microglia and blood vessels). Further, we made intracardiac injections of Evans Blue to examine the permeability of this dye in the vessels of the internal capsule during neonatal development. Our results show that large numbers of radial glia, astrocytes and microglia are not labelled with these markers in the white matter of the internal capsule until about birth; very few are labelled earlier, during the critical stages of corticofugal and corticopetal axonal ingrowth (E15–E20). The large glial labelling in the internal capsule at birth is accompanied by a dense vascular innervation of the capsule; as with the glia, very few labelled patent vessels are seen earlier. After intracardiac injections of Evans Blue, we find that the blood vessels of the internal capsule are not particularly permeable to Evans Blue. At each age examined (P0, P5, P15), blood vessels are outlined very clearly and there is no diffuse haze of fluorescence within the extracellular space, which is indicative of a leaky vessel. There are three striking differences between the glial environment of the internal capsule and that of the adjacent thalamus. First, the internal capsule is never rich with radial glial fibres (vimentin- and GFAP-immunoreactive) during development (except at P0), whereas the thalamus has many radial fibres from very early development (E15–E17). Second, astrocytes (vimentin- and GFAP-immunoreactive) first become apparent in the internal capsule (E20–P0) well before they do in the thalamus (P15). Third, the internal capsule houses a large transient population of amoeboid microglia (P0–P22), whereas the thalamus does not; only ramified microglia are seen in the thalamus. In summary, our results indicate that all three types of glia in the internal capsule are associated closely with the vasculature, suggesting they may play a role in the development of the blood–brain barrier among the vessels in this white matter region of the forebrain.