Possible role of S-100 in glia—Neuronal signalling involved in activity-dependent plasticity in the developing mammalian cortex

Using Western blot analyses and a quantitative ELISA, we identified the presence and developmental accumulation of the astroglial S-100 protein(s) in rat and cat visual cortex. There is a steep rise in the S-100 content, comprising mainly S-100β, during the time period of highest cortical malleability in both species. A possible role of the astroglial S-100 protein(s) in experience-dependent plasticity of the visual cortex of kittens was tested by infusing antiserum against this protein during the critical period for cortical malleability. Following 1 week of monocular deprivation, the ocular dominance of single cells in the visual cortex was investigated. The vast majority of cells in the hemispheres infused with anti-S-100 serum maintained binocular responses. This finding suggests that extracellular S-100 protein is essential for ocular-dominance plasticity. Infusion of S-100β during the critical period of cortical malleability had no effect on deprivation-induced ocular-dominance plasticity, but interfered with the experience-dependent refinement of orientation selectivity of visual cortical neurons. It is suggested that S-100β may play an important role in the refinement of cortical circuitries by selectively affecting active or activated neuronal compartments. As S-100β is synthesized in astroglial cells, the effects on neuronal plasticity imply that glia-neuronal information transfer occurs during activity-dependent plasticity. Possible underlying mechanisms are discussed on the basis of current knowledge on the S-100 protein family, especially S-100β (Marshak, 1990).