The earliest detailed description of the rat placenta and its development was published in the late nineteenth century. Since that time numerous rat placental studies have been carried out, focusing on a variety of topics ranging from fine structural details and vasculature analysis to placental protein transport and genetic regulatory mechanisms. The rat placenta is an inverted yolk sac that exhibits a discoid shape and develops in layers. In its early stages, rat placenta development is very similar to the process of placental development in another common laboratory animal, the mouse.

The rat placenta tissue section illustrated in the digital image above was labeled with wheat germ agglutinin (WGA) conjugated to Texas Red. WGA, which selectively binds to N-acetylglucosamine and N-acetylneuraminic (sialic acid) residues, is often used to target the Golgi network in fixed cells and tissues. The specimen was also labeled with Alexa Fluor 488 conjugated to phalloidin (targeting F-actin) and Hoechst 33342 (targeting DNA in the nucleus). Images were recorded in grayscale with a 12-bit digital camera coupled to a Nikon Eclipse 80i microscope equipped with bandpass emission fluorescence filter optical blocks. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.