LAUSR

The study demonstrates the astroglial and gliovascular structures of the area postrema (AP) in three planes, and compares them to our former findings on the subfornical organ (SFO) and the organon vasculosum laminae terminalis (OVLT). The results revealed long glial processes interconnecting the AP with deeper areas of brain stem. The laminin and β‐dystroglycan immunolabeling altered along the vessels indicating alterations of the gliovascular relations. These and the distributions of glial markers displayed similarities to the SFO and OVLT. In every organ, there was a central area with vimentin‐ and nestin‐immunopositive glia, whereas GFAP and the water‐channel aquaporin 4 were found at the periphery. This separation supports different functions of the two regions. The presence of nestin may indicate stem cell capabilities, whereas aquaporin 4 has been suggested by other studies to be a possible participant of osmoperception. Numerous S100‐immunopositive glial cells were found approximately evenly distributed in both parts of the AP. Frequency of glutamine synthetase‐immunoreactive cells was similar in the surrounding brain tissue in contrast to that found in the OVLT and SFO. Our findings on the three sensory circumventricular organs (AP, OVLT, and SFO) are compared in parallel.