erbB4 receptors are required to maintain SynCAM1 expression in hypothalamic astrocytes. A, SynCAM1 protein levels are decreased in GFAP-DNerbB4 hypothalamic astrocytes in culture. Protein extracts were probed with SynCAM1 monoclonal antibody 3E1 and anti-glyceraldehyde-3-phosphate dehydrogenase (GAPDH) antibodies. B, Densitometric analysis of blot shown in A. ***, P < 0.01 vs. WT astrocytes. C, SynCAM1-isoform 4 mRNA levels in hypothalamic astrocytes assessed by real-time RT-PCR increases 8 h after stimulating erbB4 receptors with NRGβ1 (3 nm). *, P < 0.05. D, SynCAM1 protein levels increased in hypothalamic astrocytes after 16 h of NRGβ1 treatment. *, P < 0.05. E, NRGβ1 (3 nm, 8 h) increases SynCAM1 promoter activity in BAS 8.1 astrocyte progenitor cells transiently expressing human erbB4 (herb4) receptors, and this effect is abolished by overexpression of a DNerbB4 receptor. ***, P < 0.01 vs. all other groups. Numbers in parentheses above bars are number of independent observations per group, and vertical lines are sem.