The localization of 5‐hydroxytryptamine in chromaffin cells of the leech body wall

The present study is an analysis of the sites of uptake of radioactive 5‐HT into the leech body wall. Two sites of uptake are noted: (1) the axons and nerve terminals containing large dense core vesicles and (2) the type I cells of the vasofibrous tissue. Both of these cell types are chromaffin cells in that they contain vesicles or granules with cores that reduce dichromate salts. Chemicla analysis indicates that most of the radioactivity in the body wall at the time of sacrifice is 5‐HT. Thus, these two cell types acquire 5‐HT when it is present in the extracellular environment and presumably store it in the cores of the vesicles of granules that characterize these cells. This acquisition of 5‐HT may be an impotrant method of inactivation for 5‐HT. In addition, the fine structure of the vasofibrous tissues is described here for the first time. There are two types of cells in the vasofibrous tissue, rather than one as previously thought, and the electorn microscope clearly shows that the fibrils of vasofibrous tissue are not pigmented capillaries.