Marked diversity in the action of growth factors on N-methyl-D-aspartate-induced neuronal degeneration.

Neuronal degeneration was induced in cultured rat hippocampal neurons by a 20-min exposure to the glutamatergic agonist, N-methyl-D-aspartate (NMDA; 100 microM), and the neuroprotective activity of a set growth factors and cytokines was compared. During the early stages of degeneration, NMDA induced changes that were characteristic of neuronal necrosis, including swelling and darkening of the neuronal soma and swelling of neurites, leading to the formation of beaded varicosities ('blebs'). These changes were followed by nuclear pyknosis, formation of double-stranded DNA breaks and loss of membrane integrity. Only transforming growth factor-beta 1 (TGF-beta 1; 1-10 ng/ml) and tumor necrosis factor-alpha (TNF-alpha; 30 ng/ml) protected the hippocampal neurons against NMDA neurotoxicity after short-term (60 min) pre-treatments. Interleukin-1 beta (10-100 ng/ml) and fibroblast growth factor-2 (FGF-2; 50 ng/ml) were clearly effective when administered 24 h prior to the NMDA exposure, but not when given 60 min before the insult. Interestingly, the protective effect of interleukin-1 beta was significantly reduced in the presence of a neutralizing antibody to TGF-beta. Of note, short-term pre-treatment with brain-derived neurotrophic factor (BDNF; 5-50 ng/ml) significantly potentiated NMDA-induced neurodegeneration. These experiments demonstrate marked diversity in the actions of growth factors on NMDA-induced neuronal degeneration.