Abstract
The area postrema (AP) is one of the circumventricular organs, which is located on the dorsal surface of the medulla oblongata at the caudal end of the forth ventricle. In our previous studies, we showed that AP neurons could be divided into three subpopulations, such as cells displaying the hyperpolarization-activated cation current (Ih), cells displaying the fast transient outward current (fast Ito) and cells displaying the slow transient outward current (slow Ito). In this study, we investigated morphological properties of each subpopulation of AP neurons. Slices containing cells recorded with Neurobiotin-containing electrodes were fixed in 4% paraformaldehyde and 0.2% picric acid in 0.1 M phosphate buffer (pH 7.4) from overnight to 5 days. After rinses with phosphate-buffered saline (PBS, pH 7.4), these slices were treated with 0.1% H2O2 for 20 minutes and Triton-X100 (0.4 - 0.5% in PBS) for 2 to 3 hours. They were rinsed in PBS and then incubated in the Vectastain ABC Reagent (Vector Laboratories Inc. Burlingame, CA) in PBS for 2 to 3 hours. After rinses with PBS, slices were reacted with diaminobenzidine (DAB) and H2O2 (0.003%) in PBS to visualize the injected cells. The morphology of the successfully stained cells was identified on light microscopic observation. AP neurons were found to be small cell size, i.e. cell diameter around 10-15 μm. Cells displaying the slow Ito typically showed a larger diameter than other subpopulations. The difference in the cell size was consistent with the difference in the electrical capacitance. [Jpn J Physiol 54 Suppl:S199 (2004)]
