TNF and Hyperammonemia: In summary, this study shows that sustained (but not short-term) hyperammonemia induces TNF-a expression in Purkinje neurons; this may be due to the activation of TNFR1 by TNF-a produced in glia (and later also by TNF-a produced in Purkinje cells), which induces the nuclear translocation of NF-κB and the induction of TNF-a mRNA transcription.