The localisation of the extraneuronal monoamine transporter (EMT) in rat brain.

The extraneuronal monoamine transporter plays an important role in the inactivation of monoamine transmitters. A basal extraneuronal tissue expression of this transporter has been reported, but it is also expressed in CNS glia. As little is known about the expression pattern and the function of the extraneuronal monoamine transporter in the brain, we performed a detailed investigation. Firstly, a northern blot analysis of different rat organs revealed that the transporter is strongly expressed in placenta, lung and heart and less prominently in the whole brain, brain stem, intestine, testis, epididymis, stomach, kidney and skeletal muscle. It was not expressed in cerebellum, liver and embryo. Using an in situ hybridization to the rat brain, we detected a marked and highly confined expression of the extraneuronal monoamine transporter in the area postrema, but in no other brain areas. These findings were confirmed by polyclonal antibodies against rat extraneuronal monoamine transporter showing an intensive signal in the area postrema, although a few cells in the cerebellum and the brain stem also showed a signal. Additionally, a partly overlapping expression pattern of the monoamine oxidase-B was detected. Summarizing, we firstly describe a marked and highly confined expression of the extraneuronal monoamine transporter in the rat area postrema by in situ hybridisation which may play a role in physiological functions of this circumventricular organ such as emesis, food intake and the regulation of cardiovascular functions.