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The gut has a mind of its own
Operating like the cranial brain and looking uncannily similar to
it, the gut brain is continuously active, whether we're aware of it or no -
writes CHANTAL OUIMET - ( By CHANTAL OUIMET)
Special to The Globe and Mail - Tuesday,
December 31, 2002 - Page R7
Ever
wonder why you get cramps when you're stressed ? Or why you get "butterflies"
in your stomach before a job interview ?
And why your gut tells you not to
trust a certain person ?
Scientists
say it's because the body has two brains -- the familiar one encased in
our skull and another more obscure one in our gut. This "second brain,"
known as the enteric nervous system, is located in our digestive tract and
holds about 100-million nerve cells -- more than in our spinal cord.
Less
complex and smaller than our cranial brain, this "second brain,"
which contains between 70 to 85 per cent of the body's immune cells, is an
independent data-processing centre handling a complicated circuitry of
neurons, neuromodulators and neurotransmitters.
"Every
neurotransmitter that exists in our brain, also exists in the gut without
exception. The brain in the gut is simply the brain gone south," says
Dr. Michael Gershon, author of The Second Brain, and chairman of the
department of anatomy and cell biology at Columbia University College of
Physicians and Surgeons.
In
1899, anatomists and physiologists studying dogs found that, unlike any
other reflex, the continuous push of material through the digestive system
continued after nerves linking the brain to the intestines were severed.
In other words, they discovered the gut had a mind of its own.
Operating
like our brain and looking uncannily similar to it, the gut brain responds
to stimulus and is continuously active whether we're aware of it or not.
But it doesn't think or feel. Feeling is held in the cerebral cortex of
the brain. This "second brain" performs a different role.
"The
brain in the head deals with the finer things in life: religion,
philosophy, appreciation of art and music, creativity, etc.," says
Dr. Gershon. "Whereas the brain in the gut deals with this dirty,
messy and disgusting business of digestion. The brain in the head doesn't
have to get its hands dirty with that kind of thing since it has delegated
the job."
They
may have different roles but our two brains are interconnected. One
thousand to 2,000 nerve fibres connect them and enable the two to talk.
When one gets upset, the other one does too.
"I
don't think we could have made that statement a few years ago. . . . We've
been finding out that the nerves in the gut independently regulate gut
function, but do so in a dialogue with the nerves in our head. It's a
nerve-to-nerve discussion," says Keith Sharkey, physiology and
biophysics professor at the University of Calgary.
Interest
in the gut brain resurfaced in the early 1980s after new technology became
available.
"For
the first time, we were able to see in elegant and exquisite detail the
specific way that nerves went from A to B," explains Prof. Sharkey.
"That gives you a chance to ask questions that could not or had not
been asked before."
There
are approximately 250 research laboratories now studying the enteric
nervous system around the world. T
his new breed of neuroscientists is not
only fuelling the present renaissance in the field of neurogastroenterology (study of the nerves entrenched in the lining of the
esophagus, stomach, small intestine and colon), but offering insights into
malfunctions of both brains.
Scientists
have discovered that the gut brain may be involved in gastrointestinal
disorders like ulcerative colitis, Crohn's disease and irritable bowel
syndrome -- a condition that affects between 15 and 20 per cent of the
population.
"Back
in the days when . . . I was a medical student, I was taught that these
diseases were psychosomatic. . . .
But they're a real thing. Your gut can
literately drive your brain crazy," notes Dr. Gershon. "If you
are walking around with a burning sensation in your upper belly and it
feels terrible, you can get pretty anxious. Likewise, if you've got aches
and you're on the toilet with diarrhea every five minutes, it can change
your personality. But it's more than that."
For
many years, individuals (mostly women) with irritable bowel syndrome, a
functional disorder characterized by abdominal pain, bloating, flatulence,
diarrhea and/or constipation, suffered in silence. Doctors believed the
illness was imagined -- all in the head.
"We
now know IBS is not psychosomatic. There is an element of the brain
controlling the gut which has to be born in the mind.
But we now
understand that there is also an organic and physiological basis for the
functional changes in the little brain," declares Prof. Sharkey.
Dr.
Nicholas Diamant, a gastroenterologist at Toronto Western Hospital and an
emeritus professor of medicine and physiology at the University of
Toronto, agrees that both brains are involved in the disorder.
"The
brain sends signals down to the little brain via the spinal cord which
acts as a gate for the pain signals," Dr. Diamant says. "The
brain may not be closing this gate adequately to modulate and regulate the
signals coming up from the gut. Therefore, the brain is letting more
signals come up than it normally would."
A
study by the Mayo Foundation published this August in Gastroenterology,
the official journal of the American Gastroenterological Association,
suggested there is genetic determinant that predicts the response to
medication of IBS patients with diarrhea-predominant symptoms.
"It
has to do with how the body inactivates the [neuro]transmitter serotonin.
In some patients, the body inactivation is more efficient and the patient
therefore responds better to the medication," explains Dr. Michael
Carmilleri, professor of medicine and physiology at the Mayo Clinic in
Rochester and one of the authors of the report.
"It's
a landmark paper. . . . We are starting to relate changes in the
signalling in the 'second brain' to real diseases based not only on
functional changes but on genetic studies as well," says Prof.
Sharkey.
This
July, a drug came on the Canadian market to treat patients (women only)
with constipation-predominant IBS.
Experts say Tegaserod, known
commercially as Zelnorm, is only effective in 60 to 65 per cent of people.
"IBS
is defined by a series of symptoms," says Prof. Sharkey. "It's a
multiple disease entity. . . . We don't understand it well enough to ever
consider a miracle-type cure because it's too complicated for that."
In
the case of Crohn's disease and ulcerative colitis (both autoimmune
diseases), Dr. Carmilleri says the gut brain may play a role. "There
is some interaction between the immune cells in the intestines and the 'second
brain.' "
The
discovery of the brain-gut connection also allowed scientists to learn
what is at the heart of the most visceral human emotions.
A gut feeling,
for example, isn't just a poetic image used to convey intuition. It arises
from the interplay between our two brains.
"It's
a "body loop" which is activated every time we are being
challenged or stressed. From a lifetime of activating this "body loop"
during good or bad situations, we learn to interpret this preverbal
feedback as good or bad," says Emeran Mayer, professor of medicine
and physiology at the University of California -- Los Angeles.
Butterflies
are minor indicators of pain and another example of this close
relationship. Prof. Mayer says when one is faced with an anxiety-ridden
situation, the brain in our skull sends urgent messages to our "second
brain" and throws it off balance. "The big brain also becomes
more sensitive to signals from the gut and amplifies them to unpleasant
conscious sensations," he wrote.
Therefore, one reads this response
as gurgling or "butterflies" in the belly.
Stomach
cramps, heartburn, diarrhea or constipation due to stress are again an
illustration of the gut rising to the level of conscious perception.
"The dialogue between the brain in our head and the brain in our gut
sometimes goes awry. . . . in such a way that the brain in our gut
responds inappropriately to stimulus," says Prof. Sharkey. In turn,
the nerves tell the muscles to contract more or less or make the glands
secrete more or less fluid.
Not
all of the signals sent from the "second brain" to the cranial
brain are bad news. "Some of the information that is being sent from
the gut to the brain can establish how well the brain in the head works. .
. . Your gut doesn't think for you but if it's behaving well, it can
contribute to your mood being good," says Dr. Gershon. As a result,
this interaction plays a role in dictating behavior and in creating human
joy as well as sadness.
Scientists
affirm the brain constantly communicates and listens to our "second
brain." Its functions are then taken over by the brain with respect
to the activation of major emotions such as fear, anxiety, anger, sadness
or happiness. There is no direct proof but a lot of suggestive evidence.
"Chemicals
released from cells within the 'second brain' . . . can activate vagal
sensory neurons (cells high in the neck) which signal back to the brain.
These vagal sensory neurons play a prominent role in many emotional
processes and it is certainly conceivable that such signals play a role in
generating happiness or a sense of well-being.
The newborn gets its first
sense of well-being from stimulation of the gut and release of chemicals
through milk," wrote Prof. Mayer.
Dr.
Diamant, a specialist in the mind-body connection, says each person's
"second brain" reacts differently. "If you think everybody
feels the same thing when the gut does something, you are in deep trouble.
You have to consider the whole person and all the baggage they carry. The
gut's reaction may be based on many experiences as well as the
individual's genetic makeup."
It's
an exciting time for scientists because research in the field of
neurogastroenterology is still evolving.
Even medical students are
generally shocked by the "second brain's" complexity.
"That
hasn't really made it to the textbooks yet," says Prof. Sharkey.
"It takes a few years for emerging knowledge to become dogma."
Writes CHANTAL OUIMET -
By CHANTAL OUIMET
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