Immunccytochemical Localization of Angiotensinogen in Rat Brain: Dependence of Neuronal Immunoreactivity on Method of Tissue Processing

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Abstract
There is disagreement between laboratories on the presence and location of angiotensinogen immunostaining in neuronal cells. We examined this issue by using different antisera and histological procedures to stain for angiotensinogen in brains from normal, colchicine-treated and nephrectomized rats. Five different antisera from three laboratories were used to stain sections of paraffin-embedded tissue, frozen sections and Vibratome sections of cerebral cortex, thalamus, hypothalamus, brainstem and cerebellum. All five antisera and all three tissue treatments were effective in showing angiotensinogen staining in glial cells, with the most intense staining being achieved in Vibratome sections. All five antisera gave identical results. Neuronal staining was also found with all antisera but mostly in paraffin-embedded sections, with occasional light staining in frozen sections. No neuronal staining was observed in Vibratome sections. Neuronal staining was frequently perivascular, tended to have a more variable anatomical localization, and to occasionally lack bilateral symmetry in coronal sections. These results provide an explanation for the disagreement between laboratories on the presence and location of angiotensinogen immunostaining in neuronal cells. Taken together with the limited concordance between published sites of angiotensinogen and angiotensin II staining, and the recent demonstration by hybridization in situ of a specifically glial cell localization of angiotensinogen mRNA, our own results suggest a need for caution in the interpretation of neuronal staining with anti-angiotensinogen antisera.