Figure 2

Thalamocortical innervation of the P7.5 Dicer null cortex. (A) Schematic diagram indicating DiI crystal placement in the ventrobasal thalamus and cerebral peduncle for tracing of corticothalamic and corticopeduncular projections (orange circles) and in the somatosensory cortex (yellow circle) to reveal corticofugal, corticopetal and callosal projections. (B-C) Crystal placement in the cortex (denoted by black asterisk) revealed thalamocortical connections that descend ventrolaterally to the VB. The axons change their fasciculation at the striato-cortical junction (see arrow in C) and extend in thicker fascicles through the striatum (arrow in B). (D, E) and (H, I) DiI crystal placement (see arrow) in the ventrobasal thalamus of the wild-type (D, E) and Dicer null (H, I) cortex. (F, G) Magnification of boxed area in (E) showing retrogradely labelled layer 5 and some layer 6 cortical projection neurons in the wild-type. (J, K) Magnification of boxed area in (I) showing the presence of deep layer specific thalamocortical projections that maintain some degree of fasciculation as they progress within the cortical plate. (K) DAPI stained image showing the reduced thickness of the cortical plate, loss of lamination and hugely reduced hippocampus in the Dicer null cortex. (L, M, O-P) DiI crystal placement (see arrow) in the cerebral peduncle of the wild-type (L, M) and Dicer null (O, P) cortex. (N, Q) Magnification of boxed areas in (L) and (P), respectively, showing the retrograde labelling of layer 5 cortical neurons in the wildtype. (Q) There are no backlabelled cells apparent from similar cerebral peduncle crystal placements in the Dicer null, suggesting reduced corticofugal projections. White star depicts the cortical plate. Four brains from each genotype were analysed. CP, cerebral peduncle; CPu; caudate putamen, CTX, cortex; GP, globus pallidus; Hip, Hippocampus; S1, somatosensory nucleus; SCB, striatocortical boundary; VB, ventrobasal thalamus. Scale bars: 100 μm.