(A) Representative images of Glast and Gfap immunostaining of WT and .T1 KO astrocytes co-cultured with WT neurons. Sholl analysis revealed decreased complexity of .T1 KO astrocytes at the (B) total (Glast) and C) branch (Gfap) levels. (D) Schematic of timeline of AAV-Cre injections and morphology analysis. (E,F) Egfp-Cre+ astrocytes exhibited decreased astrocyte volume and complexity in. T1fl/fl animals compared to WT Egfp-Cre+ astrocytes. (G) Representative images of confocal (green, top) and Imaris reconstruction (blue, bottom). (H) Schematic of timeline to generate astrocyte-specific cKO animals. (I) QPCR analysis of isolated astrocytes revealed specific loss of TrkB.T1 isoform and no change in TrkB.FL isoform expression. (J) QPCR analysis of sequentially isolated astrocytes, neurons, and microglia reveal astrocyte-specific loss of TrkB.T1. (K) Representative confocal images of TrkB.T1 immunoreactivity in cWT and cKOs reveals loss of TrkB.T1 protein expression. (L) Representative images of confocal (green, top) and Imaris reconstructions (blue, bottom) of cWT and .T1 cKO astrocytes. (M, N) .T1 cKO astrocytes exhibited decreased morphological complexity in comparison to cWT astrocytes. (O) QPCR analysis of WT and .T1 cKO PND25 cortex demonstrates decreased mRNA expression of mature astrocytic genes Slc1a2 (Glt1), Kcnj10 (Kir4.1), and Aq4 (Aqp4), with no change in Gja1 (Cx43) expression. Data represented as mean + /- SEM, n = 4–7 animals for image analysis, with at least n = 3 cells per animal; n = 6 animals for qPCR analysis in I; three animals for qPCR analysis in J; *p<0.05, **p<0.01, ***p<0.0001. Each data point represents an individual cell in E and M, and an individual animal in I, J, and O.