Expression of TrkB subtypes in the adult monkey cerebellar cortex.

BDNF and its specific receptor TrkB are concerned with synaptic plasticity as well as maintenance of the nervous system. TrkB has three subtypes: full-length TrkB (TK+), which has a tyrosine kinase containing intracellular domain, and two truncated TrkBs (TK-; T1 and T2), which lack tyrosine kinases. To understand the molecular interaction among these subtypes, we investigated the expression and distribution of BDNF, TK+, and T1 in the adult monkey cerebellum by single and double immunohistochemistry and Western blot analysis. We observed by single immunohistochemistry that BDNF, TK+, and T1 are distributed in almost all the somata and dendrites of Purkinje and granule cells. In the double-stained sections, three kinds of regions were observed: TK+ >T1; TK+ =T1; TK+ <T1. Moreover, three types of TrkB dimers (TK+/TK+ homodimer, TK+/TK- heterodimer, and TK-/TK- homodimer) were induced by stimulating with exogenous BDNF. These observations suggest that the functions of BDNF may be modified by interaction among subtypes of TrkB in each region of the Purkinje cells.