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Expression of brain-derived neurotrophic factor (BDNF) in the ventral mesencephalon has been assayed by mRNA in situ hybridization in adult rats with unilateral injections of 6-hydroxydopamine in the substantia nigra. On contralateral control sides, a specific hybridization signal was detected in the substantia nigra pars compacta (A9), ventral tegmental area (A10) and substantia nigra pars lateralis (A8). Cellular levels of BDNF mRNA were lower than those in BDNF expressing cortical and hippocampal neurons. The 6-hydroxydopamine injections completely abolished BDNF mRNA labeling in the pars compacta of the substantia nigra, whereas many labeled neurons remained in the ventral tegmental area and pars lateralis. The results strongly suggest that BDNF is expressed by nigral dopaminergic neurons.

In this study we investigated the splicing pattern of fibronectin (FN) mRNA during development and aging by using Northern blot hybridization with probes that either recognize all forms of FN mRNA or that are specific for the different spliced forms (FN-EIIIA, FN-EIIIB, and FN-V). We find that (1) the FNmRNA in the hippocampus of some but not all old rats showed a pattern of splicing similar to that found in the forebrain of 21 day old rats and (2) the hybridization signal for the alternatively spliced FN mRNA containing the EIIIA, EIIIB, and V95 segments was relatively abundant at early postnatal stages but very few transcripts were detected in adult and old rats. However, the hybridization signal for the juvenile FN-V mRNA was markedly increased in some but not all two-year-old rats suggesting that aging is an individual process.