IMMUNOMAGNETIC REMOVAL OF NEURONS FROM DEVELOPING CHICK OPTIC TECTUM RESULTS IN GLIAL PHENOTYPIC INSTABILITY

The ability of embryonic day 12 and 13 optic tectum cells to replace d epleted A2B5(+) cells and neurons was tested by immunomagnetic cell se paration. Nearly all purified surface A2B5(-) cells were identified as glia by immunoreactivity for either glutamine synthetase of galactoce rebroside. Most (almost-equal-to 80%) of the purified A2B5(-) cells be came A2B5(+) after 1 day in culture, although no increase in the perce ntage of A2B5(+) cells (from 45%) was observed in control cultures of unpurified cells. Long-term monolayer cultures from purified cells con tained A2B5(+) cells with mostly flattened glial-like or round process -free morphology, whereas those from unpurified cells contained many A 2B5(+) neurons. The non-neuronal A2B5(+) cells frequently reacted with antibodies against glial fibrillary acidic protein and another marker expressed by embryonic brain glia, 5A11. Additionally, some flattened glia-like cells exhibited elaborate networks of anti-neurofilament-M- reactive filaments. We believe these unusual phenotypes, which appeare d only in cultures of purified A2B5(-) cells, arose in response to the immunomagnetic removal of neurons. In conjunction with previous findi ngs, we conclude that the abnormal phenotypes in purified cell culture s represent glia that were unsuccessful in attempting to replenish the depleted neuronal population. This may reflect restricted development al potentials that arise during brain ontogeny.