MONOAMINE OXIDASE-B IN ASTROCYTES

In the present report we describe the astrocytic localization and cont ent of monoamine oxidase-B (MAO-B) by means of a H-3-L-deprenyl emulsi on autoradiography in primary cultures of rat astrocytes, in cryosecti oned astrocytoma surgical specimen, and in cryosections of human spina l cords from patients dying in amyotrophic lateral sclerosis (ALS) and controls. The occurrence of MAO-B enzyme protein depends on the degre e of cellular differentiation as demonstrated by studies on astrocytes in primary cultures analyzed at two different stages of maturation. H ighly differentiated cells exhibited high relative enzyme concentratio n whereas glioblasts lacked or showed very low contents of MAO-B enzym e. This was further substantiated by studies performed on human astroc ytoma tissue using H-3-L-deprenyl emulsion autoradiography in combinat ion with immunohistochemical detection of glial fibrillary acidic prot ein (GFAP). Regional increases of MAO-B concentration were found in AL S lumbar sections with quantitative H-3-L-deprenyl autoradiography. On the basis of results obtained from double staining for GFAP and MAO-B , the increase in MAO-B seemed to be due to an increased number of ast rocytes as well as an increased content of MAO-B in reactive species o f astrocytes. A cell culture model has been used that produces cells w ith morphology and GFAP-content similar to reactive cells. These astro cytes exhibited high relative content of the MAO-B enzyme protein. In the light of the presented data, taking into account the finding that a subpopulation of reactive cells contained low levels of MAO-B, a het erogeneity among reactive astrocytes was observed.