Immunohistochemical, ultrastructural & immunoelectron microscopic study of glial fibrillary acidic protein in corpora amylacea.

Brain tissues from 10 patients (of non-neurological disease) were studied for the presence of corpora amylacea (CA) using light microscopy (LM), immunohistochemistry (IH) for localisation of glial fibrillary acidic protein (GFAP) and transmission electron microscopy (TEM). Immunoelectron microscopy (IEM) by post-embedding technique using colloidal gold was also performed in two of these patients for more precise localisation of GFAP. Three types of immunoreactivity were noted by IH under LM; some CA were completely negative for GFAP (type III), while others showed positivity, which was either diffuse (type I) or confined to the periphery (rim positivity-type II). TEM showed variable sizes in electron dense material in the centre associated with different amounts of glial filaments (GFs) at the periphery. Thus the different types of IH staining appeared to corroborate with the presence and amount of GFs in CA. The sensitive technique of IEM confirmed the presence of GFAP in all CA irrespective of their IH typing at LM. It is suggested that CA formation in astrocytes is associated with progressive fragmentation and disintegration of GFs with resulting increase in the accumulation of electron dense GFAP-negative material. As more and more of GFs get incorporated and disintegrated, it results in increase in the size of the CA. Thus, the present study clearly demonstrates that GFAP in the GFs contributes to the composition of CA.