Distribution of trkB tyrosine kinase immunoreactivity in the rat central nervous system

Recent evidence suggests that trkB tyrosine kinase is a high affinity receptor for brain-derived neurotrophic factor (BDNF). BDNF can act as a survival factor for several neuronal subgroups and its mRNA is distributed widely throughout the central nervous system. However, the functional targets of BDNF are poorly defined. We have used immunochemical and immunohistochemical techniques to determine the regional distribution and cellular localization of trkB tyrosine kinase-like immunoreactivity. The staining pattern indicates that the trkB-like antigen is widely distributed and present within both glia and neurons. Astrocytes were the most intensively labelled but many neuronal populations were also stained. In some regions including brain stem, spinal cord, hippocampus and diagonal band of Broca, neurons were stained at varying intensities. In other areas such as the cortex of the forebrain and amygdaloid nucleus, the stain was intense but diffuse, preventing positive identification of the cell types involved. Immunoblot results indicated two separate protein bands in all brain and spinal cord regions examined, of molecular weights 145 and 85 kDa, respectively. These findings aid the definition of neuronal and glial subpopulations of the central nervous system that may utilize BDNF.