TISSUE DISTRIBUTION AND IMMUNOCYTOCHEMICAL LOCALIZATION OF NEUROTROPHIN-3 IN THE BRAIN AND PERIPHERAL-TISSUES OF RATS

The tissue distribution of neurotrophin-3 (NT-3) was investigated in r ats at 1 month of age using a newly established, sensitive two-site en zyme immunoassay system for NT-3, as well as the immunocytochemical lo calization of this protein. The immunoassay for NT-3 enabled us to qua ntify NT-3 at levels > 3 pg per assay. In the rat brain, NT-3 was dete ctable only in the olfactory bulb (0.54 ng/g wet weight), cerebellum ( 0.71 ng/g), septum (0.91 ng/g), and hippocampus (6.3 ng/g). By contras t, NT-3 was widely distributed in peripheral tissues. Appreciable leve ls of NT-3 were also found in the thymus (31 ng/g), heart (38 ng/g), d iaphragm (21 ng/g), liver (45 ng/g), pancreas (892 ng/g), spleen (133 ng/g), kidney (40 ng/g), and adrenal gland (46 ng/g). An antibody spec ific for NT-3 bound to pyramidal cells in the CA2-CA4 regions of the h ippocampus, to A cells in the islets of Langerhans in the pancreas, to unidentified cells in the red pulp of the spleen, to liver cells, and to muscle fibers in the diaphragm from rats at 1 month of age. Molecu lar masses of NT-3-immunoreactive proteins in the hippocampus and panc reas were 14 and 12 kDa, respectively. Thus, in rats, NT-3 was detecte d in restricted regions of the brain and in the visceral targets of th e nodose ganglia at high concentrations. Our present results suggest t hat NT-3 not only functions as a classical target-derived neurotrophic factor but also can play other roles.