Immunohisto-and immunocytochemical localizations of tyrosine hydroxylase (TH) were studied in the area postrema of hamster brain. By immunohistochemistry, TH-positive neurons with thick, smooth nerve processes were seen to be situated in close apposition to the blood vessels, and they were of oval-shaped, almost unipolar types.
By immunocytochemistry, TH-positive reaction products were observed within the cytoplasm and granular vesicles but not in either the nucleus nor Golgi area of the TH-positive neurons. From the size of the granular vesicles, TH-positive cells in the area postrema were divided into two types of neurons, cells containing small granular vesicles (about 100 nm in diameter), and cells containing both small and large granular vesicles (larger than 150 nm in diameter). Small numbers of neurons with TH-negative reaction, were also found. These TH-negative neurons were agranular.