Astrocytes induce formation of excitatory synapses by secreting GPCG4/620, SPARCL121, and thrombospondins (THBS1/2)22, so we next investigated whether reactive astrocytes still produce these factors. Quantitative PCR showed decreased Gpc6 and Sparcl1, while simultaneously showing increased expression of Thbs1/2 (Fig. 2c). This increase in thrombospondins (which should increase synaptic number) suggests the decreased synapse number may reflect an A1-induced toxicity to synapses (see below). To determine effects of A1 reactive astrocytes on synapse function we used whole-cell patch clamp recording on RGCs cultured with resting astrocytes or A1s. RGCs cultured with A1s had significantly decreased frequency and amplitude of miniature excitatory postsynaptic currents when compared to RGCs cultured with resting astrocytes (Fig. 2d–g). Taken together these results show A1 reactive astrocytes induce formation of fewer synapses, and the few synapses they do induce are significantly weaker when compared to those produced by healthy resting astrocytes.
