EVIDENCE THAT THE INFLUENCE OF GANGLION-CELL AXONS ON ASTROCYTE MORPHOLOGY IS MEDIATED BY ACTION SPIKE ACTIVITY DURING DEVELOPMENT

In many mammal retinas, the morphology of astrocytes is strongly influ enced by nearby axons of ganglion cells. Astrocyte processes stretch a long the axons, fine extensions of the processes contact node-like spe cialisation of the axon membrane and the morphology of the adult astro cyte is strongly determined by this relationship. The mechanism which attracts astrocyte processes to contact specific regions of the axon m embrane is not known however. This study presents evidence that in the neonatal cat blocking the impulse activity of ganglion cells with the Na+-channel blocker tetrodotoxin (TTX) leads to a loss of the axon-re lated morphology of astrocytes. The morphological change induced in as trocytes by TTX was greater in younger animals and could not be detect ed in the adult. Conversely, if the TTX block was maintained for 4 pos tnatal weeks the changes induced in astrocytes persisted at least to 1 3 weeks. The TTX-induced loss of axon-related morphology in astrocytes suggests that the signal by which axons attract astrocyte processes t o contact the axonal membrane in ways which modify astrocyte morpholog y is released by action spike activity during development. (C) 1998 El sevier Science B.V. All rights reserved.