Sleeping Versus Waking

Why do treatments for the symptoms of the common cold make us drowsy? How does coffee work? This
chapter touches briefl y on neurotransmitters whose actions in
the brain affect our sleep–wake cycle and on a few well-known
substances that block these effects.
HISTAMINE AND OREXIN
One such neurotransmitter is histamine, whose neurons infl uence our level of arousal throughout the day. Lying next to these
neurons is another group of neurons that release orexin, which
is a neurotransmitter that infl uences both our level of arousal
and craving for food. Take a moment to appreciate how the
anatomical organization of this system optimizes your daily
existence and survival. The neurons that wake you in the morning and maintain your consciousness also make you crave food.
In contrast, the inactivation of these two brain regions makes
you sleepy and reduces the activity of your food-craving center
in the brain. The failure of the orexin arousal-inducing system
may underlie narcolepsy, a disorder characterized by inappropriate and intense sleepiness.
Over-the-counter anti-histamine medications used to treat
allergies and cold symptoms block histamine receptors and
interfere with the ability of this neurotransmitter to keep one
aroused and awake. The result is drowsiness. Meanwhile, because
GABA neurons induce sleepiness by turning off histamine and
acetylcholine neurons, any drug that enhances the action of
GABA (e.g., alcohol, barbiturates, or Valium) is going to be
synergistic with the over-the-counter anti-histamine drugs.
Thus, if taken together, these two kinds of drugs can bring
about a life-threatening depression in brain activity.
ADENOSINE
This neurotransmitter has diverse functions throughout the
brain that are also related to our sleep–wake cycles. We know a
lot about it because of the ready availability of a very safe, highly
effective adenosine receptor antagonist that is served hot or cold,
with or without cream, throughout the world — caffeinated
coffee! Caffeine is also commonly found with theophylline (a
molecule that is very similar to caffeine) in tea. Indeed, although
caffeine is found in at least 63 plant species, 54% of the world’s
consumption derives from just two different beans, Coffea arabica
and Coffea robusta, and 43% derives from the tea plant Camellia
sinensis
.
Coffee is rich in biologically active substances such as trigonelline, quinolinic acid, tannic acid, and pyrogallic acid. The
vitamin niacin is formed in great amounts from trigonelline
during the coffee bean roasting process. Coffee is also a rich
source of the antioxidants caffeic, chlorogenic, coumaric, ferrulic, and sinapic acids and silverskin. Various ingredients in
coffee beans contribute to aspects of the drink — for example,
its bitterness — that people fi nd either appealing or unpleasant.
Recently, some entrepreneurs have found a way to remove the
bitterness by “fi ltering” coffee beans through the gastrointestinal tract of the Asian Palm Civet, Paradoxurus hermaphroditus. The
civets, nocturnal omnivores that are about the size of a cat, eat
the beans, which then pass through the animals’ gastrointestinal
systems undigested but presumably not unaffected. The beans
are then extracted from the animals’ stool, cleaned up, and sold.
It’s hardly an enticing process, but the claim is that the animal’s
digestive enzymes metabolize the proteins that cause the bitter
taste of the coffee bean. Although this is certainly possible, the
novel fl avor of the beans is just as likely a result of the bean’s
absorption of some of the less appealing contents of the
animals’ gut.
Coffee drinking (or consuming caffeine from non-coffee
sources) has been associated with a signifi cantly lowered risk
of developing Parkinson’s disease. The neuroprotective effect
requires about fi ve to six cups of coffee per day for many years
and appears to be mostly benefi cial only to males. Women benefi t from coffee-drinking in other ways, particularly with regard
to a reduced incidence of type-2 diabetes. Overall, people who
drink substantial amounts of coffee daily tend to live longer
than people who do not. In addition, recent evidence suggests
that moderate coffee-drinking of about two to three cups each
day might reduce your chance of developing Alzheimer’s disease. What is the connection among coffee, diabetes, and diseases of the brain? No one is sure, but elevated insulin levels in
the blood may be a critical link because type-2 diabetes makes
both men and women more likely to develop both Parkinson’s
and Alzheimer’s disease.
Many people drink coffee to reduce drowsiness. How does
caffeine achieve this effect in the brain? The answer begins with
a consideration of the function of the acetylcholine neurons
that control your ability to pay attention. Adenosine negatively
controls the activity of these neurons, meaning that when adenosine binds to its receptor on acetylcholine neurons, their
activity slows. The production and release of adenosine in your
brain is linked to metabolic activity while you are awake.
Therefore, the concentration of adenosine in the neighborhood
of acetylcholine neurons increases constantly while your brain
is active during the day. As the levels of adenosine increase, they
steadily inhibit your acetylcholine neurons, your brain’s activity
gradually slows, and you begin to feel drowsy and ultimately fall
asleep. Caffeine comes to the rescue because it, like theophylline
from tea, is a potent blocker of adenosine receptors and, therefore, of the adenosine-driven drowsiness and sleep. One can
take this too far, however. One of my students decided to test
these caffeine effects by ingesting a packet of instant coffee,
right out of the box. He reported that he enjoyed eating it
so much that he decided to fi nish off the entire container of
32 packets! Three days later, he stopped having explosive diarrhea and fi nally fell asleep completely exhausted.
Given everything that you’ve read about drugs that produce
a rewarding and euphoric feeling, you might suspect that coffee
also somehow affects dopamine neurons. You would be correct.
Caffeine sets free the activity of dopamine neurons to bring
euphoria and bliss to every cup of coffee or every glass of cola.
Most cans of cola contain about 40 milligrams of caffeine;
therefore, most teenagers consume as much caffeine as their
parents — the only thing that differs is the vehicle for the drug.
The widespread availability of foods containing caffeine has led
experts to suggest that 80% of all people in North America
have measureable levels of caffeine in their brains from embryo
to death.
Caffeine and theophylline are not the only drugs we regularly consume to block our adenosine receptors. There is also
theobromine, which is found in chocolate. Chocolate is as
addicting as coffee — if not more so — possibly because it contains an array of other psychoactive compounds that may contribute to the pleasurable sensation of eating it. Chocolate
contains fats that may induce the release of endogenous opiates
(see Chapter 8) and produce a feeling of euphoria. It contains
phenethylamine, a molecule that resembles amphetamine and
some of the other psychoactive stimulants discussed earlier. It
contains a small amount of the marijuana-like neurotransmitter
anandamide. It contains some estrogen-like compounds, a fact
that may explain a recent series of reports showing that men
who eat chocolate live longer than men who do not eat chocolate (the effect was not seen for women who have an ample
supply of their own estrogen until menopause). Chocolate also
contains magnesium salts, the absence of which in elderly
females may be responsible for the common post-menopausal
condition known as chocoholism. And fi nally, a standard bar of
chocolate contains as many anti-oxidants as a glass of red wine.
Clearly, there are many good reasons for men and women to eat
chocolate to obtain its indescribably soothing, mellow, and yet
euphoric effect, with or without the addition of caffeine. My
fear, of course, is that one day the Food and Drug Administration
may take notice of the many psychoactive compounds present
in chocolate and regulate its sale.

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