Xref: utzoo sci.bio:816 sci.med:3858
Path: utzoo!mnetor!uunet!husc6!spdcc!dyer
From: dyer@spdcc.COM (Steve Dyer)
Newsgroups: sci.bio,sci.med
Subject: Re: Acetylcholine source needed...
Message-ID: <560@spdcc.COM>
Date: 14 Jan 88 23:11:47 GMT
References: <506@dl901b.engin.umich.edu>
Organization: S.P. Dyer Computer Consulting, Cambridge MA
Lines: 60
Summary: try an electric eel...

In article <506@dl901b.engin.umich.edu>, schonek@caen.engin.umich.edu (Anthony J Schonek) writes:
>     I was curious about "Acetylcholine."  Supposedly it is a chemical in the
> brain that stimulates memory response.  (I'm not a biologis/doctor so please
> excuse the ignorance)  Anyway, does this actually stimulate memory response;
> and in what forms could this chemical be purchased in order to perform the
> desired effects.  I heard fish and liver contain this chemical, but is
> there a drug that would be more efficient?

Acetylcholine (ACh) is a neurotransmitter found both in the central and
peripheral nervous systems and at the neuromuscular junction.  Its effects
vary depending on the particular subsystem you are studying; this is to be
expected.

In a sense, having too much ACh is as bad as having too little.  For example,
the so-called nerve gases and most of the very poisonous insecticides in
common use today act by inhibiting cholinesterase, the enzyme that deactivates
ACh.  ACh is released at the neuromuscular junction in response to a nerve
pulse and is quickly destroyed.  If the enzyme is deactivated, ACh accumulates,
and a single nerve "pulse" becomes a prolonged depolarization, resulting in
paralysis.

It's a little misleading to simply say that ACh stimulates memory response,
although there have been inconsistently successful attempts to increase levels
of acetylcholine activity in the brain to improve functioning in people with
dementia stemming from Alzheimer's Disease and Huntington's Chorea.  This is
postulated from the neurochemical and histological evidence found in such
diseases.  Raising ACh levels might help to eke out whatever activity is
remaining in nerve pathways destroyed in disease, thus helping the person's
condition, but to say that this helps "learning" is like saying that treating
scurvy with Vitamin C helps "walking".  Undoubtedly cholinergic systems are
involved with memory and learning, but one usually has just the right amount
of ACh without any outside help.

There are drugs which increase ACh in the brain.  These are cholinesterase
inhibitors which can pass the blood-brain barrier and have very limited uses;
physostigmine as an antidote to certain anticholinergic drugs, another,
5-aminotetrahydroacridine, is being tested for use in Alzheimer's Disease.
Other approaches in the treatment of HD, AlzD and other nervous disorders
involve the diet, "loading" the person with the precusor of acetylcholine,
choline.  (Note that circulating cholinesterases would inactivate Ach
immediately if it were administered as itself.  It would also not cross
the blood-brain barrier, and would improperly stimulate whatever
nerves and musculature it happened to touch before being hydrolyzed.)

Choline is a quaternary ammonium base; it has the disagreeable side-effect
of being attacked by bacteria in the gut to various methylamines, an extremely
fishy-smelling class of substances.  Choline is also a component of the
phospholipid lecithin.  This is supposed to avoid the cosmetic problem
produced by choline, while still providing choline for conversion to
ACh.  Exactly how "bioavailable" the choline is in lecithin varies a
good deal.  None of these dietary treatments have been a smashing success,
although certain persons with Alzheimers Disease and Huntington's Chorea
have shown some improvement.

Needless to say, if you're studying for an exam, I doubt any of these
would be better than a cup of coffee.
-- 
Steve Dyer
dyer@harvard.harvard.edu
dyer@spdcc.COM aka {ihnp4,harvard,husc6,linus,ima,bbn,m2c}!spdcc!dyer