NANFA-- Re: nanfa V1 #1451

Dave McNeely (dlmcneely_at_lunet.edu)
Fri, 15 Nov 2002 10:23:32 -0600

courses I took as part of my
> zoology degree was embryology. Really boring stuff, because basically
nobody
> understands how or why cells "know" how to differentiate, and when. But
at
> SOME point neural tissue "knew" it had to grow. So why can't it be
regrown?
> - ----- Original Message -----
> From: Sajjad Lateef <sajjadlateef_at_yahoo.com>
> To: <nanfa_at_aquaria.net>
> Sent: Thursday, November 14, 2002 10:35 AM
> Subject: Re: NANFA-- Re: nanfa V1 #1449
>
>
> > --- Dave McNeely <dlmcneely_at_lunet.edu> wrote:
> >
> > > that neural tissue cannot regenerate,
> >
> > It can? References, please.
> >
> > Sajjad
> On 15 Nov 2002 at 7:29, Moontanman_at_aol.com wrote:
>
> > Bacteria are more likely to develop resistance to antibiotics than to
> > salt baths or copper sulfate due to the way resistance evolves.
>
> Oh, my!
>
> Well, it appears then that we MUST have that discussion I was referring
to, about which I did not want to make this sort of comment
> because I was not knowlegable enough to substantiate anything I might have
said.
>> Now I'm on pins and needles, waiting to hear the mechanism by which
bacteria develop resistance to antibiotics, and how that differs
> from developing resistance to copper and sodium salts :-)
>
> Those of you wanting to hear about FISH may tune out now...
>
> Prost,
>
> Martin
> Jackson, MS
> - --
> Life's a fish and then you fry.
--
> /"Unless stated otherwise, comments made on this list do not necessarily
> / reflect the beliefs or goals of the North American Native Fishes
> / Association"
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>
> ------------------------------
>
> Date: Fri, 15 Nov 2002 09:07:30 -0500
> From: "Crail, Todd" <tcrail_at_northshores.com>
> Subject: RE: NANFA-- Re: nanfa V1 #1449
>
> Because politicians and a "moral majority" haven't allowed stem cell
research?
> ;)
>
> I liked Developmental, I not only took it once... I took it twice [sigh]
The
> professor decided that on his bell curve 77 was a D+ instead of a C- to
teach
> a brash, arrogant, class skipping, soon to be *not* graduating student a
> lesson.
>
> But then again, where else could one gain pickup phrases like "I love the
way
> your dorsalbalstophoral lip invaginates, baby" or "that's some notochord
> remnant you have there sweet node".   <evil_grin>
>
> - -----Original Message-----
> From: Irate Mormon 
> Sent: Friday, November 15, 2002 1:01 AM
> To: nanfa_at_aquaria.net
> Subject: Re: NANFA-- Re: nanfa V1 #1449
>
>
> Well, it just stands to reason!  One of the courses I took as part of my
> zoology degree was embryology. Really boring stuff, because basically
nobody
> understands how or why cells "know" how to differentiate, and when.  But
at
> SOME point neural tissue "knew" it had to grow.  So why can't it be
regrown?
--
> /"Unless stated otherwise, comments made on this list do not necessarily
> / reflect the beliefs or goals of the North American Native Fishes
> / Association"
> / This is the discussion list of the North American Native Fishes
Association
> / nanfa_at_aquaria.net. To subscribe, unsubscribe, or get help, send the word
> / subscribe, unsubscribe, or help in the body (not subject) of an email to
> / nanfa-request_at_aquaria.net. For a digest version, send the command to
> / nanfa-digest-request_at_aquaria.net instead.
> / For more information about NANFA, visit our web page,
http://www.nanfa.org

Well. Regarding neural tissue regeneration: Not the primary references, but maybe data that have now found there way into a freshman general biology textbook are even more apropos to the current discussion than a reference to the original literature would be: Raven and Johnson, _Biology sixth edition_, pp414-415 provides a discussion of neural tissue repair by tissue specific (adult) neural stem cells. On page 1097 the same book details the results of experiments that demonstrate regeneration of the spinal cord of laboratory rats.

For the person who queried about how antibiotic resistance arises: This is detailed in almost every general biology textbook published. I will summarize it briefly here. (1) Antibiotic exposure kills or prevents reproduction of susceptible individual cells, while other cells that have greater resistance survive and reproduce. Variability in resistance among cells is common to most strains of bacteria and is an example of individual variation that exists in all populations of organisms -- such as differences in eye color or differences in the amount of melanin in the skin in people. (2) The differential susceptibility to antibiotics that naturally occurs among cells is genetic, thus heritable. (3) Therefore, the individual cells that are less susceptible and that reproduce pass along the trait to their progeny, which then represent a greater proportion of the cell population than resistant cells did before selection occured. (4) The process repeats over a series of cell generation, rendering the population of cells on average more resistant than before selection. (5) So increase in antibiotic resistance in a population of bacterial cells is a simple Darwinian process. (6) Since bacterial genes may pass from one cell to another through several mechanisms, and may be expressed in the recipient cell, antibiotic resistance may increase in populations of cells that previously did not possess the trait.

The reason that resistance to such drugs as iodine, malachite green, silver nitrate, formaldehyde has not shown the same kind of response in bacterial cell populations as resistance to antibiotics has may be one or a combination of these (I am speculating): (1) there are no specific genes in nature that convey this resistance on the cells that possess them and so not selection is possible, (2) the treatments are so effective that all cells exposed are killed, whether individual cells have somewhat greater resistance than others or not, (3) the drugs are destroyed so rapidly by organismic metabolism or environmental conditions that they do not remain in sufficient concentration to continue selecting between resistant and non-resistant strains for any effective number of generations, (4) ??? .

The antibiotic resistance phenomenon has great relevance to fishes and to aquariaists because (1) fish diseases are treated with antibiotics, sometimes with rather little attention to whether or not the treatment is effective or to complete eradication of the bacteria responsible for the disease. Note that partial treatment is worse than no treatment, because it increases the likelihood of antibiotic resistance becoming more widespread. (2) Antibiotics have been found to be widespread in the environment, including natural waters that harbor fish. Nothing is known about the degree to which these antibiotics contribute to antibiotic resistance in wild populations of bacteria. (3) Antibiotic resistant bacterial populations have been found to be widespread in rivers in the U.S., and they probably exist in other parts of the world.

I don't think we are dealing with a trivial problem here. BTW, where do the antibiotics that are used to treat fishes in aquaria in the home of the average fish keeper end up? Where do the bacteria that were in the treatment water but did not die end up? Sewer, soil in the back yard, stay in the tank? Hmmmmmmmm ........ . What about non-target bacteria. Can a population of bacteria in the wild "catch" antibiotic resistance from something that was originally not a target of treatment by one of the mechanisms by which bacteria swap genes around (like plasmids)? Why are some bacterial strains that used not to be significant pathogens very dangerous now? Does it matter whether we are talking about pet fish, pet dogs, wildlife, or people?

Dave McNeely /----------------------------------------------------------------------------- /"Unless stated otherwise, comments made on this list do not necessarily / reflect the beliefs or goals of the North American Native Fishes / Association" / This is the discussion list of the North American Native Fishes Association / nanfa_at_aquaria.net. To subscribe, unsubscribe, or get help, send the word / subscribe, unsubscribe, or help in the body (not subject) of an email to / nanfa-request_at_aquaria.net. For a digest version, send the command to / nanfa-digest-request_at_aquaria.net instead. / For more information about NANFA, visit our web page, http://www.nanfa.org