Certain types of neuronal tumor cells can grow and replicate in tissue culture.
Also, in the brains of some songbirds, new neurons appear and disappear every year. The nearly complete lack of regenerative sucess in the mammalian CNS seems to result from two factors:
(1) Inhibitory influences from neuroglia
(2) Absence of growth cues that were present during development.
Some developmental cues are electrical in nature. A large research effort is directed at finding a way to promote regrowth of damaged neurons using electrical stimulation. Other developmental cues are chemical in nature, involving both substances that trigger mitosis (mitogenic factors) and those that regulate growth (neurotropins).
In 1992 Canadian researchers published their unexpected finding that cells taken from the brains of adult mammals could be encouraged to proliferate into both neurons and astrocytes.
They cultured small pieces of mouse brain tissue in dishes and added epidermal growth factor (EGF).
Previously epidermal growth factor was known to trigger mitosis in a varitey of nonneuronal cells and promote wound healing and tissue regeneration.
These experiments challenge the dogma that stem (progenitor) cells are not present in adult brains. A tantalizing possibility is that scientists may be able to find ways of stimulating these dormant stem cells to replace neurons lost through damage or disease.
Also, such tissue-cultured neurons might be useful for transplantation purposes.
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