LEARNING-INDUCED EXPRESSION OF MENINGEAL EPENDYMIN MESSENGER-RNA AND DEMONSTRATION OF EPENDYMIN IN NEURONS AND GLIAL-CELLS

The turnover of a CNS-specific cell adhesion glycoprotein, ependymin, has earlier been found to increase during periods of neuronal plastici ty. Here, ependymin mRNA expression was analyzed by semiquantitative i n situ hybridization in goldfish. Learning of an active avoidance resp onse resulted in a significant increase in ependymin mRNA expression 2 0 min to 4 h after acquisition of the task. In contrast, yoked control animals that were exposed to the same numbers of conditioned and unco nditioned stimuli in a random, unpaired manner exhibited a strong down -regulation of ependymin mRNA. Hybridization signals were also increas ed by injection of anti-ependymin antiserum into brain ventricles. Epe ndymin mRNA was exclusively localized to reticular-shaped fibroblasts of the inner endomeningeal cell layer. Immunoelectron microscopic inve stigation, however, revealed ependymin also in distinct neuronal and g lial cell populations in which no ependymin mRNA had been detected. Up take of meningeal protein factors into glial and neuronal cells may th erefore be of functional importance for plastic adaptations of the CNS .