Both at P6 and P15, the total number of Nissl-stained cells (Figure 3E; P6: control: 438 ± 35, ThVGdKO: 446 ± 26, p = 0.3; P15: control: 378.6 ± 42, ThVGdKO: selleck chemical 365 ± 45, p = 0.15) and caspase-3 positive cells (data not shown) were not different in control and ThVGdKO mice, indicating there was no obvious cell proliferation or apoptosis defects in ThVGdKO mice. CUX1 (aka CUTL1 or CDP) is a transcription factor expressed in superficial layers of somatosensory cortex that clearly delineates the bottom of L4 (Nieto et al., 2004). As with Nissl staining, there was no difference in the laminar expression of CUX1 at P6

(Figures 3F and 3H). However, there were fewer cells labeled with CUX1 at P15 (Figures

3G, 3I, and 3K), and the thickness of CUX1-expressing superficial layers was significantly reduced in ThVGdKO mice (control: 39% ± 3% of cortical thickness; ThVGdKO: 30% ± 4%; p < 0.01; Figures 3G, 3I, and 3J), consistent with the lamination defects observed with Nissl stain. These results suggest that in the prolonged absence of glutamatergic input from the thalamus, the relative thickness of infragranular layers (L5) of the cortex expands at the expense of granular and supragranular layers (L2/3 and L4) during the second week after birth. Because Sert-Cre is expressed in all the thalamic sensory relay nuclei ( Zhuang et al., 2005), including the visual thalamus Entinostat in vivo (dorsal

lateral geniculate nucleus or dLGN) and the auditory thalamus (medial geniculate nucleus or MGN), we wondered whether laminar development in visual and auditory cortex was similarly impaired as in the somatosensory cortex. However, we did not observe any obvious cortical laminar cytoarchitecture defects in the visual or auditory and cortex of ThVGdKO mice ( Figures S2A–S2F). Sert-Cre expression is much weaker in the dLGN and MGN in comparison to the somatosensory thalamus (ventrobasal or VB; Figures S3A–S3O), and accordingly Vglut2 mRNA and VGLUT2 protein levels were only modestly decreased in the dLGN (68.9% of control mRNA levels) and MGN (48.4% of control mRNA levels) of ThVGdKO mice at P12. In contrast, Vglut2 mRNA in the VB was only 13.5% of control levels (p < 0.001 for the difference between dLGN, MGN, and VB), and VGLUT2 protein levels were down to 20% of control already at P4. This is consistent with the earlier and stronger expression of SERT in the VB relative to the other thalamic relay nuclei ( Lebrand et al., 1998) and is probably responsible for sparing the auditory cortex and visual cortex from the laminar changes observed in the somatosensory cortex of ThVGdKO mice. We generated a second model of disrupted neurotransmitter release to confirm and expand our understanding of the role of thalamocortical neurotransmission on somatosensory cortex development.