levy@ttrdc.UUCP (06/14/87)
In article <1349@sigi.Colorado.EDU>, eddy@boulder.Colorado.EDU (Sean Eddy) writes: > ...there are cells that do not > divide after a certain point, yet still age and die. Neurons are the > classic example; not only do they not divide, they cannot even > be replaced (in humans) if damaged. Am I misinformed, then, when I hear about nerves growing back together in people who have an accidentally severed appendage surgically reattached? Also, what about the nerves which grow back into a wounded region of the body, say an area of burned flesh? -- |------------dan levy------------| Path: ..!{akgua,homxb,ihnp4,ltuxa,mvuxa, | an engihacker @ | vax135}!ttrdc!ttrda!levy | at&t data systems division | Disclaimer: try datclaimer. |--------skokie, illinois--------|
eddy@boulder.Colorado.EDU (Sean Eddy) (06/14/87)
In article <1757@ttrdc.UUCP> levy@ttrdc.UUCP (Daniel R. Levy) writes: >In article <1349@sigi.Colorado.EDU>, (Sean Eddy) writes: >> ...there are cells that do not >> divide after a certain point, yet still age and die. Neurons are the >> classic example; not only do they not divide, they cannot even >> be replaced (in humans) if damaged. > >Am I misinformed, then, when I hear about nerves growing back together in >people who have an accidentally severed appendage surgically reattached? >Also, what about the nerves which grow back into a wounded region of the >body, say an area of burned flesh? "Nerves growing back together" is different from neurons being replaced. You can sever an axon and the the part of the axon still attached to the cell body will regrow and form new attachments, usually in the right way. But if you destroy the cell body, end of story. To my knowledge, the cell bodies themselves are not replaceable (yet; it would be nice if we could find a way). - Sean Eddy - MCD Biology; U. of Colorado at Boulder; Boulder CO 80309 - eddy@boulder.colorado.EDU !{hao,nbires}!boulder!eddy - - Go Celtics!o
warren@sniff.UUCP (06/15/87)
In article <1757@ttrdc.UUCP> levy@ttrdc.UUCP (Daniel R. Levy) writes: >In article <1349@sigi.Colorado.EDU>, eddy@boulder.Colorado.EDU (Sean Eddy) writes: >> ...there are cells that do not >> divide after a certain point, yet still age and die. Neurons are the >> classic example; not only do they not divide, they cannot even >> be replaced (in humans) if damaged. > >Am I misinformed, then, when I hear about nerves growing back together in >people who have an accidentally severed appendage surgically reattached? >Also, what about the nerves which grow back into a wounded region of the >body, say an area of burned flesh? >-- No, you are not misinformed. Damaged nerves can heal but only to a very limited extent. So you're both right. In Seans case Neurons do die and are not replaced through normal cell division. However, the brain is so..... redundant that you could kill off billions of Neurons and very possibly never no it. Wars have historically been very beneficial in gaining insights into brain (Neuron) function. Also, in a classic experiment called the Island Experiment a monkey (I think) was taught a particular trick. The monkey underwent a series of operations each one of which removed a piece of the monkeys cortex. To everyones surprise, in the end, when all that was left was a little island of cortex; the monkey could still do the trick. In your case Daniel, you know that there are different degrees of burns. Small amounts of nerve damage from small burns can be tolerated. However, you must also know that severe burns cause irreparable damage to nerves. Think about this the next time you have a beer. The alcohol, it is said, kills Neurons. :-) :-) A good book to read for those interested in the brain is "Mind and Supermind" by Albert Rosenfield, Holt Rinehart Winston. It's easy reading and very interesting. Warren (an amateur doctor at best)
jnp@calmasd.UUCP (06/15/87)
(Daniel R. Levy) writes: > (Sean Eddy) writes: > > ...there are cells that do not > > divide after a certain point, yet still age and die. Neurons are the > > classic example........ > Am I misinformed, then, when I hear about nerves growing back together in > people who have an accidentally severed appendage surgically reattached? No - they can heal - grow back together, under correct circumstances, but they will not divide. Kill them, and they are gone forever. -- These opinions are solely mine and in no way reflect those of my employer. John M. Pantone @ GE/Calma R&D, Data Management Group, San Diego ...{ucbvax|decvax}!sdcsvax!calmasd!jnp jnp@calmasd.GE.COM
ericb@dartvax.UUCP (Eric J. Bivona) (06/16/87)
I seem to recall from some research I did on neural transplants that
most of the neurons of the brain ("gray matter") are not as resilient
as the neurons of the motor/sense system ("white matter"). There has
been interesting experiments done on replacing damaged neural tissue,
but the only replacement for brain tissue is embryonic brain tissue
(big moral/ethical problem). There is an out though, the nervous
is immuneologically exempt, and does probably won't reject tissue
grafts, even cross-species tissue grafts. Experiments along these
lines have been done between cows/dogs/monkeys (I recall). This
technique is closely related to the transplanting of adrenal gland
cells into the brain to treat/cure the lack of dopamine (?).
Maybe some one else has more of grip on this subject, it's been a while
since I looked at it. If so, please post (maybe to one of the med groups?)
Eric J Bivona
"Discretion is the better part of nearly every human endeavor"
ericb@dartmouth.edu
{...}!decvax!dartvax!ericbgagen@bgsuvax.UUCP (kathleen gagen) (06/16/87)
In article <1757@ttrdc.UUCP>, levy@ttrdc.UUCP (Daniel R. Levy) writes: > Am I misinformed, then, when I hear about nerves growing back together in > people who have an accidentally severed appendage surgically reattached? > Also, what about the nerves which grow back into a wounded region of the > body, say an area of burned flesh? When nerves "grow back together" the nerve cells do not undergow mitosis. Rather, the end of the cut axon extends to enervate the region distal to the cut. This process is more likely to occure if the sheth that covers the nerve has been lined up on both sides of the cut region. ___ Kathi Gagen
lyang@scherzo.UUCP (06/16/87)
In article <333@sniff.dec.com> warren@sniff.dec.com (warren sypteras) writes: >In article <1757@ttrdc.UUCP> levy@ttrdc.UUCP (Daniel R. Levy) writes: >>In article <1349@sigi.Colorado.EDU>, eddy@boulder.Colorado.EDU (Sean Eddy) writes: >>> [ statement about neuron death ] >> >> [ statement about nerve regeneration ] > >No, you are not misinformed. Damaged nerves can heal but only to a very >limited extent. As state before, if a nerve is severed and the cell body remains alive, then that nerve can regenerate and grow new connections. However, if the cell body is killed, then that's bye-bye for that neuron. As an aside, there are cells in the brain that do undergo reproduction. These are the cells that mutate into cancerous cells. (aka brain tumors) An interesting area of cancer research involves understanding why neurons don't reproduce; what inhibits the cell division process in these cells? > >So you're both right. In Seans case Neurons do die and are not replaced >through normal cell division. However, the brain is so..... redundant >that you could kill off billions of Neurons and very possibly never no >it. Wars have historically been very beneficial in gaining insights into >brain (Neuron) function. Also, in a classic experiment called the Island >Experiment a monkey (I think) was taught a particular trick. The monkey >underwent a series of operations each one of which removed a piece of >the monkeys cortex. To everyones surprise, in the end, when all that was >left was a little island of cortex; the monkey could still do the trick. > There are two common conclusions that can be drawn from experiments like these. One is "information in the brain is reproduced, and only a small amount of the brain need be retained." This conclusion is the one you cite. The other conclusion is "we didn't actually remove the part of the brain that contains the information on doing learned trick." >Think about this the next time you have a beer. The alcohol, it is said, >kills Neurons. :-) :-) Actually, alcohol kills the 'dumb' cells first; thus, you should always get trashed the night before an exam. :-) ================================================================================ --Larry Yang [lyang@sun.com,{backbone}!sun!lyang]| A REAL _|> /\ | Sun Microsystems, Inc., Mountain View, CA | signature | | | /-\ |-\ /-\ "Muammar Quadaffi is the Father Of My Baby", | <|_/ \_| \_/\| |_\_| Insists Manic Depressive Vetrinarian. | _/ _/
steve@blblbl.UUCP (Steve Gisselbrecht) (06/22/87)
Sorry, folks--I can't cite a source, since it's an article that I read
in a copy of Science News sometime in the misty past, and I no longer
have the magazines to look through. But here's how I remember it:
It seems that they did some work with parrots, and actually got central
nervous system regeneration to occur. (NOT peripheral nervous system,
which, at the time, was the only thing that had ever shown regeneration
after physical trauma of any kind.) The key, apparently, was creating
an enzymatic environment similar to that in the peripheral nervous
channels. Apparently, the work was very promising for a human analogue
someday.
Can anyone clarify or contradict this?
steve