Figure 5. In situ hybridization histochemistry using either exonic or intronic probe technology to detect cytoplasmic LHRH mRNA or primary transcript (LHRH hn/mRNA) in the brains of cycling female rats. These photos depict dark-field photomicrographs of the inverted "V" characterizing the LHRH neuronal system distributed in the MPOA surrounding the OVLT (top panels) of LHRH mRNA (left panels) and LHRH hn/mRNA (right panels). Animals were deeply anesthetized and rapidly perfused with 4% paraformaldehyde in the afternoon of proestrus and brain sections were dipped into NTB-2 nuclear emulsion to reveal the presence of silver grains depicted in these photos. Note the robust difference in the agglomeration of silver grains for cytoplasmic LHRH mRNA (bottom left panel) and heteronuclear RNA (bottom right panel). (Taken from Nappi and Rivest, ref. 183.)