Posted by linkadge on September 7, 2006, at 7:10:20
In reply to CNS nerve regeneration, posted by FredPotter on September 6, 2006, at 23:47:21
I think its really too early to know the extent of what SSRI's are doing.
>As far as I know this has been observed in the >peripheral nervous system but not the CNS.
SSRI's have been shown to enhance hippocampal neurogenesis. Certain parts of the brain are complete at a certain age, while other parts such as the hippocampus and olfactory bulb continue to replace neurons untill death.
>Just as well perhaps as uncontrolled growth of >brain cells would be a form of cancer. As I >understand it there is an enzyme that prevents >new CNS nerves from growing where they shouldn't >grow.
Its not necessarily uncontrolled brain growth in that it seems to be restricted to areas of the brain that normally regenerate. A similar upregulation of neurogenesis is observed with other (natural) antidepressant treatments such as exercise. Excercise enahances hippocampal neurogenesis, but exercise is not linked to cancer.
There have been some links between the antidepressants and cancer, but I don't know how strong they are.
>As the CNS is complete at an early age this >means they won't grow anywhere.The idea that the CNS is complete at a certain age has been challenged. Actual new brain cell growth seems to be restricted to the hippocampus and olfactory systems, but the application of growth factors for instance, can help to restablish connections between existing brain cells. Ie axons, growth cones, etc can extend and network existing brain cells throughout life.
>I also hear loose talk about promoting >interhemispheric connections. Do these reports >refer to just dendritic growth tather than axon >growth? What's the story?
Not exactly sure.
I am skeptical too about the whole matter. There have been a few studies showing that antidepressants simply increase hippocampal turnover, ie they increase neurogenesis and neuronal elimination. The survival of newborn neurons seems to depend on BDNF. Though, contrary to whats been hoped, antidepressants don't always increase BDNF. Sometimes they have no effect on the levels of this protein.
Other studies show that SSRI's increase neurogenesis in certain subfields of of the hippocampus, and supress neurogensis in others. Some studies too suggest that SSRI's only extend the length of mature neurons, and that immature neurons are not effected. Other neurotranasmitters such as dopamine and norepinephrine promote neurogenesis, so perhaps a serotonin selective agent is supressing other forms of neurogenesis dependant on other neurotransmitters. SSRI's tend to decrease exploritory behavior in mice for instance. This could be an explaination for poop-out, ie, they may produce a short term boost by ehancing growth of the most relavant information, at the expense of other brain growth. Ie perhaps the ability to learn completely new concepts is compromised. (This is just speculation on my part though)
Stress is the greatest supressor of hippocampal neurogenesis. This is one pathway by which stress leads to depression.
Linkadge
poster:linkadge
thread:683849
URL: http://www.dr-bob.org/babble/20060901/msgs/683900.html