Detection and Localization of Glial Fibrillary Acidic Protein in the Mouse Ileum by Immunocytochemical Staining Techniques
This study was done in response to the recent finding of Jessen and Mirsky (1980) of glial fibrillary acidic protein (GFAP) in the myenteric (Auerbach's) and submucous (Meissner's) plexi of the ileum of rats by an immunofluorescent staining technique. Previously, this protein had been known to be characteristic of central nervous system (CNS) astrocytes and tanycytes. Morphologically indistinguishable GFAP immunoreactive structures were found by this author in both the brain and the appropriate plexi of the ileum of mice using an indirect immunostaining technique (Jessen and Mirsky) with a fluorescein conjugated marker molecule serum. Two additional immunostaining techniques were employed, an indirect peroxidase and a peroxidase antiperoxidase (PAP) method. The latter of the two is known to be more sensitive and specific in staining for substances such as GFAP and both methods give permanent descriptions of the substance studied. These techniques also revealed structures in mouse and cat ileum tissue analogous to those found by immunofluorescence. Further, random sampling of the large and small intestine of mice showed morphologically indistinguishable structures to those found in the ileum. A number of controls were done to test both antibody and method specificity, and all of the results showed absence of nonspecific staining. Whole body sections of neonatal mice were also done to look at changes in GFAP distribution in development. Underdeveloped GFAP immunoreactive species were found in the ileum and brain while a highly developed area was found in the optic disc and an area of the heart identified as the sinoatrial node. In conclusion, there appears to be GFAP-containing glia-like cells in mouse and cat submucous and myenteric plexi of the gastrointestinal tract that immunostain with the same intensity as astrocytes and tanycytes of the CNS. The function of these cells is essentially undetermined, though these GFAP immunoreactive species appear more closely related to CNS glial cells than Schwann cells.