3B-D). Whereas all large and symmetric EGFP+ donor cells exhibited passive membrane currents and linear current to voltage (I/V) curves, another population of smaller EGFP+ human cells with compact, asymmetrically branched morphologies manifested a much higher input resistance (147.8 ± 11.7MΩ, n=14). These donor cells manifested voltage-gated currents and depolarization-triggered outward currents with delayed activation (Fig. 3B), and expressed a human epitope of chondroitin sulfate proteoglycan NG2, identifying them as persistent glial progenitors (Fig. 2G) (Kang et al., 2010; Robel et al., 2011). Together, these histological and electrophysiological analyses supported the notion that a large proportion of engrafted human cells differentiated into protoplasmic astrocytes, forming a functional syncytium with their murine host, and that these were accompanied by large numbers of co-engrafted NG2+ human glial progenitors.
