3 replies to this topic

[henri]

It has been said that the neurons from embryos that one transplants into patients (in Parkinson's disease, for instance) don't form synapses with other neurons once they've been put in place. Still, the condition may improve. One explanation is that the newly transplanted neurons secrete GF:s (growth factors) that affect other neurons. I'm not sure if I'm bying this because it would seem strange that the GF:s would induce growth in the degenerated neurons that were in the brain originally while the new, healthy ones would be unable to respond. Or maybe the connections that already exist can be strengthened, but no new ones formed in the adult brain when the particular growth factors are applied.

Also, there have been studies in which GF:s have been introduced into the brain by more direct means and improvement may have resulted. I think that the lack of GF:s has been conceived to be one thing that causes age-related changes in the nervous system (in general, connections seem to get fewer in at least some parts of the brain).

If the aging brain isn't producing enough growth factors, why doesn't it? One way to explain this would be that the neurons are getting so weak that they can't. In this case, all one would need to do would be to apply rejuvenating treatments to the cells. But it might also be a more complicated issue, in which case the treatments would more complicated be as well. Maybe the GF system is rather independent from other age related changes. I guess one would just have to check it. But neurons can't survive very long on dishes, or can they? If they can't be made, it might be difficult to disentangle this process from the others.

[liorrh]

the big picture
the GF secretion is a result of activity. the beuronal bundles use GF to remodel themselves to better suit current activity.

so generaly if your brain is not active in a certain part, that part will not generate GF.

I think this is the main reason, others being concurrent drop in the efficiency of other systems, like immune and endocrine which regulate GF centrally.

[John Schloendorn]

It is often not just a matter of having growth factors and period. Sometimes they need to be secreted locally to create a so called microenvironment. Some people imagine this to be a complicated 3D-landscape of growth factor concentrations, with tiny gradients and all sorts of patterns down to the micron-scale to properly direct the growth of the complicated microstructures that make up our neuronal network. You could not get this right in all cases with an injection. It's generally something that only cells can do.

As for why does it stop working, this is less than clear. I think it's safe to say that there are both components of decreased growth factor production and growth factor resistance, each possibly ultimately due to age-related cell damage, but it is for the greatest part not known just how this looks like in detail.