Fig. 1. The transient intermediate plexiform layer (TIPL), a plexiform layer-like structure in the developing rat retina. (A, B) Two examples of a distinct type of cells found in postnatal day (PD) 7 (A) and PD 10 (B) rat retinas immunostained for substance P (SP) receptor. Their processes ramify and form a plexus in the TIPL in the proximal or middle of the inner nuclear layer (INL). OPL, outer plexiform layer; IPL, inner plexiform layer; GCL, ganglion cell layer. (C) Lower magnification view of PD 7 rat retina immunostained for SP receptor. The TIPL is seen to be a dot line within the INL, not a continuous band. (D) Light micrograph of PD 7 rat retina stained with toluidine blue showing the presence of the TIPL (double arrows) in the INL. (E, F) Electron micrograph shows that the TIPL is located at the border between the bipolar (BZ) and amacrine cell zone (AZ) of the INL (E) and is composed of numerous cell processes in higher magnification view (F). Scale bars=10 µm in A, B; 25 µm in C, D; 1 µm in E, F.
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