Can A1 reactive astrocytes induce formation of functional synapses in vitro? We cultured purified retinal ganglion cells (RGCs) with resting or A1 reactive astrocytes and quantified synapse number by double immunostaining for pre- and post-synaptic proteins (Fig. 2a, Extended Data Fig. 5). RGCs cultured with A1s had 50% less synapses compared to those grown with control astrocytes (Fig. 2b). When RGCs were cultured with control astrocytes to induce synapse formation and then cultured with A1s, synapse number significantly decreased by about 40%, suggesting that A1s are either unable to maintain these synapses or actively disassemble them.
