Loss of collagen XIX leads to impaired inhibitory synapse formation in mouse CTX. (A–D) Immunostaining for Syt2 and VGluT1 in layer V of pfCTX in P11 WT controls (Ctl) and col19a1−/− mutants (KO). (B and D) High-magnification images of Syt2-immunostaining from layer V of pfCTX in P11 WT controls (Ctl) and col19a1−/− mutants. A–D depict Syt2-immunolabeling; A′ and C′ depict VGluT1-immunolabeling; A″ and C″ depict merged overlay of Syt2 and VGluT1 immunolabeling. Bars: (A″) 25 µm; (B) 5 µm. (E–H) Area occupied by VGluT1 and Syt2 immunoreactivity (IR) in layer V of pfCTX and vCTX in P11 control and KO. Data are mean ± SEM; n = 4. *, Differs from control by P < 0.001 by Student’s t test. ns, no statistical difference by Student’s t test. (I) Area occupied by Syt2 IR in layer V of vCTX in P56 control and KO. Data are mean ± SEM; n = 4. *, Differs from controls by P < 0.001 by Student’s t test. (J–M) Mean fluorescence intensity of VGluT1 and Syt2 IR in layer V of pfCTX and vCTX in P11 control and KO. Data are mean ± SEM; n = 4. *, Differs from control by P < 0.001 by Student’s t test. ns, no statistical difference by Student’s t test. (N) Mean fluorescence intensity of Syt2 IR in layer V of vCTX in P56 control and KO. Data are mean ± SEM; n = 4. *, Differs from control by P < 0.001 by Student’s t test. (O–R) Western blots show reduced levels of GAD65/67 and Syt2 (but not VGluT1) in protein extracts (O and P) and synaptosome fractions (sy; Q and R) from KO CTX versus control (dashed line). Data are mean ± SEM; n = 4. *, Differs from control by P < 0.001 by Student’s t test.