Upregulation of BDNF mRNA and trkB mRNA in the nigrostriatal system and inthe lesion site following unilateral transection of the medial forebrain bundle

We have performed unilateral transection of the medial forebrain bundle (MF B) and studied BDNF mRNA and trkB mRNA levels at different postlesion times in the nigrostriatal system by means of in situ hybridization. BDNF mRNA l evels were transiently induced in the substantia nigra pars compacta at 1 d ay postaxotomy. The disposition of BDNF mRNA expressing cells at this postl esion time in substantia nigra mimicked that of the dopaminergic neurons ex pressing the mRNA for the dopamine transporter. TrkB mRNA levels remained u naltered in the ventral mesencephalon at the different postlesion times exa mined-1 to 14 days. In contrast, trkB mRNA levels were significantly induce d in the striatum at the longer postlesion time examined-14 days-when all n eurodegenerative events are completed. It is becoming apparent that nigral BDNF mRNA levels are anterogradely transported to its target tissue in stri atum. However, following axotomy, the lesion site represents a second poten tial target for BDNF action. Consequently, we also analyzed the pattern of mRNA expression for BDNF and trkB at the lesion site where dopaminergic axo ns are disconnected. There, we found notable inductions of both BDNF mRNA a nd trkB mRNA levels at 4 days postaxotomy. BDNF mRNA expressing cells were confined at the site of axotomy, which coincided precisely to that showing induction of trkB mRNA. Altogether, our results anticipate promising trophi c roles of BNDF in the injured nigrostriatal system. (C) 2000 Academic Pres s.