Tyrosine phosphatase SHP-1 immunoreactivity increases in a subset of astrocytes following deafferentation of the chicken auditory brainstem

Proliferation of astrocytes is a dramatic response of the central nervous s ystem (CNS) to injury and disease. Such proliferation results in the format ion of the neural/glial scar and the reconstitution of the glial limitans. However, not all astrocytes enter the proliferative cycle following injury, and for those that do, the period of cell division is limited. Little atte ntion has focused on the events that regulate the duration and extent of as trocyte proliferation following damage, but clearly control mechanisms are in place as CNS injury does not result in the continuous astrocyte prolifer ation seen in glial tumorigenesis. Protein tyrosine phosphorylation has bee n implicated in both astrocyte proliferation and differentiation and plays an important role in the regulation of the cell cycle in a number of differ ent systems. We have found a small subset of astrocytes in the chick audito ry brainstem that are immunopositive for the protein tyrosine phosphatase S HP-1. SHP-1 appears to negatively regulate cellular division in the hematop oietic system and is involved in the mitogenic response to various growth f actors. Following cochlea removal, there is a marked increase within the au ditory brainstem nucleus, nucleus magnocellularis (NM), in both in the numb er of SHP-1-positive astrocytes and the length of their immunopositive fibe rs. Significantly, those animals showing the greatest increases in SHP-1 im munoreactivity do not exhibit large amounts of astrocyte proliferation. We hypothesize that the expression of SHP-1 plays a role in negatively regulat ing the mitotic behavior of astrocytes following deafferentation. (C) 2000 Wiley-Liss, Inc.