A CHRONOLOGICAL STUDY OF THE EXPRESSION OF GLIAL FIBRILLARY ACIDIC PROTEIN AND CALBINDIN-D-28K BY REACTIVE ASTROCYTES IN THE ELECTRICALLY LESIONED RAT-BRAIN

Immunoreactivity of neuronal and glial marker proteins of reactive ast rocytes around the electrically damaged pyramidal layer and stratum ra diatum of the hippocampal CA1 region and corpus callosum was chronolog ically studied in electrically lesioned rat brains. A monoclonal antib ody against calbindin-D-28 k (CD28-Ab) and a polyclonal antibody again st glial fibrillary acidic protein (GFAP-Ab) were used for immunostain ing. Immunoreactivity of CD28 and GFAP in the reactive astrocytes was detected in brains 1-6 weeks post-lesion but not in non-lesioned brain s. The number of immunohistochemically stained reactive astrocytes aro und the electrically damaged areas were counted and then compared with the number of those in the same areas of non-lesioned brains. The num ber of CD28- and GFAP-immunoreactive astrocytes began to increase arou nd the lesion from 1-3 weeks following lesion in the pyramidal layer o f the hippocampal CA1 region and from 1-4 weeks following lesion in th e stratum radiatum of the hippocampal CA1 region and corpus callosum. These immunoreactive astrocytes could be observed for 6 weeks (the max imum survival time studied) in all areas of the lesioned brains studie d. The increase in the number of reactive astrocytes might have been i nduced by the stimulatory effects of neurotrophic factors, or growth f actors, produced around the lesioned site. The constancy in the number of reactive astrocytes after 3 and 4 weeks in the lesioned areas may have been due to the termination of the initial phase of the repair pr ocess, i.e. space-filling. Reactive astrocytes which were stained by G FAP-Ab were separated into two groups, based on the presence of CD28, i.e. CD28-positive and CD28-negative reactive astrocytes. The presence of CD28 might confer certain functions via calcium-mediated mechanism s on CD28-positive astrocytes in addition to the constructive role med iated by GFAP.