A composite photomicrograph of a representative PGE2 injection (100 ng of PGE2 in 100 nl of vehicle). A composite photomicrograph of a representative PGE2 injection (100 ng of PGE2 in 100 nl of vehicle). The injection site (black arrow) is evident as a cluster of fluorescent beads on the boundary between the VMPO and the ventrolateral POA. An image of the rhodamine-labeled microsphere epifluorescence was digitally superimposed on the corresponding dark-field image. Scale bar, 500 μm. Thomas E. Scammell et al. J. Neurosci. 1996;16:6246-6254 ©1996 by Society for Neuroscience