Although CD200 is concluded so far as an immunosuppressive molecule, it also an adhesion molecule that contains two immunoglobulin superfamily domains and present on neurons. Systemic examinations on distributions of these molecules in the hippocampus have not been carried out and their expressions during development remain unknown. In the present study, we demonstrated a differential immunoreactivity of CD200 in the intact hippocampus of adult rats, which was dependent on their distributions, in particular those in the substrata of the stratum moleculare of the dentate gyrus. ImmunoEM study illustrated that CD200 reaction products in the hippocampus were patchy in the cytoplasmic membrane of neurons and significantly at the postsynaptic dense plaque. In the developing hippocampus, laminated CD200 profiles in each stratum were not found until postnatal day 7 and reached the adult form at postnatal day 28. The fiber tracts of the hippocampus such as fimbria and alveus lost their CD200 progressively with age. Western blotting data indicate a significant fall of CD200 amount at 10-day postnatal hippocampus.
