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. 2017 Dec 5;11:111. doi: 10.3389/fnana.2017.00111

FIGURE 9.

FIGURE 9

First appearance of lamination in the insula at midgestation (21GW). (A) The anatomy of a Nissl-stained hemisphere near the limen insulae. The arrow points to the inferior circular sulcus (iCSI) between the rostro-ventral insula and the temporal lobe. This region, shown in B (Reelin) and C (Tbr1), represents the transition between the ventral periallocortical insula and the dorsal isocortical insula. (B) The periallocortical insula lacks the Reelin+ plexus of the Cajal–Retzius cells in the lower marginal zone (arrowheads), characteristic of isocortex, although Cajal–Retzius cells are present all over the outer marginal zone. (C) A prominent layer V shows cytoplasmic Tbr1 staining, while the subplate has nuclear staining. At a more caudal level, MAP2 reveals a few pyramidal cells in layers V and III in the anterior insula (D), which are much smaller and less numerous compared to the Betz cells in layer V of the primary motor cortex (E). In F, Tbr1 marks the subplate (SP), which is continuous with the subplate of the adjacent temporal cortex (TC), although narrower and more compressed than the latter. CN, caudate nucleus; P, putamen; SVZ, SVZ of the temporal horn which opens at more caudal levels. Bars: in A: 400 μm; in C, for B,C,F: 160 μm; in D, for D and E: 75 μm.