Radial glia cells and Tela Attachement Sites Confirm Medial, Dorsal, and Thalamic Eminence Identification. We performed triple fluorescence immunostains against parvalbumin (PV), GFP, and GFAP in the brains of Tg(vGlut2a:GFP) counterstained against DAPI. (A1–C2): A1 shows different aspects of a rostral section highlighting that one large parvalbumin- (PV-) positive tela attachment site is located at the ventricular site of the dorsal pallium and pallial amygdala (white arrows in A1,A2,B,C1). The tela choroidea is fused (green arrows in A1,A2,B,C1) with the proliferative stem cell layer of the dorsolateral zone (“Dl”) supporting its medial pallial (“hippocampal”) identity. The nLOT tract shows a characteristic indentation (A2,C2) and no GFAP stained cell somata at its lateralmost aspect corroborating this area as the pial, not ventricular site. Notably, all radial glia of the candidate dorsal pallium do send their processes towards the pallial-subpallial border (PBS). These radial glia are attached to the topographically ventral side of the nLOT next to those of the medial pallium. Radial glia of the nLOT are not visible in this orientation suggesting that their radial domain is different from pallial zones. This finding supports the interpretation that the vGlut2a-driven GFP domain is a derivative of the EmT. (D1A–D2B) At mid-telencephalic sections, both radial glia cells and tela attachments show the same distribution. At the point where proliferative zones of the DM and medial pallium (MP) meet and grow over the dorsal pallium, a reduced number of radial glia cells of the dorsal pallium are visible. Radial glia of both MP and DM cut through the territory of DP and send their processes beneath the nLOT. The probable diencephalic attachment site of the tela choroidea is located at the nLOT (gray arrows in D1b,D2b). Again, there are no GFAP-positive glia cell somata at the most lateral cell groups corroborating its pial nature. The nLOT in this orientation shows no radial glia processes supporting their postulated EmT origin. At caudalmost sections, the study identifies the diencephalic -telencephalic junction (DTJ) that comprises territories formerly assigned to the telencephalon such as the posterior medial amygdala (MeAp/EmTr) and the vGlut2a-driven GFP positive nLOT territory that spans a region next to the MeAp/EmTr to the lateral (pial) surface (blue arrows in E1-E3). The BNSM was formerly identified as a derivative of the EmT in zebrafish and is often mistaken as the entopeduncular nuleus proper (ENv) Mueller and Guo 2009). Note, that the tela choroidea is attached to the MeAp/EmTr indicating its periventricular site (E1,F1).
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