Figure 4. Loss of Bhlhb5 Function Disrupts Post-Synaptic Vibrissal Barrels in Somatosensory Cortex.

(A,A’) HRP-immunohistochemistry for SERT on P7 tangential cortical sections. Thalamocortical afferents segregate into vibrissal specific “hollows”, but with less intense staining and indistinct borders in Bhlhb5-nulls (wild type n=7; Bhlhb5-nulls n=7).

(B,B’) HRP-immunohistochemistry for SERT on P6 coronal sections reveals normal thalamocortical afferents in the internal capsule (black arrowheads), but not in barrel cortex (asterisks) of Bhlhb5-nulls (wild type n=3; Bhlhb5-nulls n=3).

(C,C’) In situ hybridization for RORβ on P5 coronal sections reveals absent expression medially in caudal motor cortex (asterisks), but disorganized expression laterally in the barrel region of the somatosensory cortex (black arrowheads; magnified views in insets) suggesting a post-synaptic disruption of vibrissal barrels in layer IV of Bhlhb5-nulls (wild type n=3; Bhlhb5-nulls n=3).

(D,D’) Nissl staining on tangential sections confirms robust disruption of cytoarchitectonic barrels with only a faint vibrissal pattern in Bhlhb5-nulls (wild type n=3; Bhlhb5-nulls n=3).

(E–G and E’–G’) Confocal microscopy on SERT immunolabeled sections counterstained with Sytox Green nucleic acid stain (Sytox Grn) reveals near absence of septa (white arrowheads) in Bhlhb5-nulls (wild type n=3; Bhlhb5-nulls n=3).

Scale Bars: 250 µm (A,A’), 1 mm (B,B’,C,C’), 100 µm (D–G and D’–G’). Insets in (C,C’) not to scale.