NOTICE: Posting schedule is irregular. I hope to get back to a regular schedule as the day-job allows.

Friday, August 5, 2011

Ethanol, the Science behind the story... [Full link to blog for email clients.][FT:C44]

In the prior blog I provided an example of alcohol effects on the brain in story form.  Today I present the science behind that story, courtesy of Guest Blogger Karni Mata.  K. Mata takes her name from the Goddess of Rats, or in her case, Goddess (mother) of Lab Rats, due to her position as a laboratory manager.  K. has a doctorate in Psychology and works with me on several matters of interest to the readers of this blog.  She was a bit too shy to come out here and introduce this blog herself, but believe me, she has very thoroughly researched the topic and is Teddy's Rat Lab's resident expert.

And now... the Science Behind The Story:

Alcohol.  Ethanol.

It's a fuel, a disinfectant, an anesthetic, and a foodstuff.

The molecule ethanol - EtOH - consists of two carbon atoms, six hydrogen and one oxygen.  It has the characteristics of both a hydrophilic (water-soluble) and hydrophobic (oil/lipid-soluble) compound and easily penetrates the skin, the mucous membrane lining of nose and mouth, the stomach lining, and distributes widely through the blood and body.  A set of six enzymes - collectively called alcohol dehydrogenase - breaks it down, and the level of ethanol in the blood remains elevated until it is either broken down by this metabolic method (i.e. "metabolized") or it is excreted via sweat, breath and urine.  The primary breakdown product of ethanol is "acetaldehyde" which is responsible for the headaches, upset stomach, and overall discomfort of a hangover.  A further breakdown product of acetaldehyde makes "acetone" and "methyl ketone" which produce a sour taste, and are responsible for the bad breath and body odor of alcoholics and the chronically intoxicated.

The name - acetaldehyde - may seem familiar, especially if you have ever heard of the preservative "formaldehyde."  In fact, acetaldyhyde is a 2-carbon structure, while formaldehyde has only one carbon.  When a person drinks wood alcohol - methanol (ethanol is "grain alcohol") - the same alcohol dehygrogenase breaks down the single-carbon methanol molecule into the single-carbon formadehyde.  There is a large amount of alcohol dehydrogenase in the retina of the eye.  This is one reason why excess ethanol affects vision, and why drinking wood alcohol can cause blindness as the formaldehyde kills and "preserves" the sensitive neurons of the retina. 
Alcohol affects multiple brain systems working overall as a central nervous system depressant. It may seem that alcohol stimulates a person since his or her speech becomes more animated and free, social inhibitions are reduced, and emotional responsivity is increased. However, it actually decreases the brain’s ability to function, resulting in cognitive effects such as hazy thinking and foggy memory, sensory effects such as dulled hearing and impaired vision, and physical effects such as weakened muscles and uncoordinated movement. Depression of self-control and judgment occurs as well, leading to poor reasoning and decision-making.

Within seconds of consumption, it alters the action of neurotransmitter systems. The neurotransmitter dopamine, involved in systems of reward, is initially increased causing euphoria. This feeling of pleasure can be accompanied by increased self-confidence and sociability. These dopamine surges in the brain sends signals that alcohol is important and valuable, and induce the brain to want more. High amounts of GABA neurotransmitters are released, increasing the action of inhibitory neurons, causing many systems to decrease activity, dulling the senses and pain and reaction time. Additionally, glutamate, an excitatory neurotransmitter, is less active, contributing to feelings of relaxation and sluggishness. A fourth neurotransmitter, serotonin, is increased in the presence of alcohol which may increase positive mood. It is also a neurotransmitter that when increased will raise the levels of dopamine and GABA, intensifying their effects.

As the limbic system, a group of several brain structures that work together is affected, emotions become more intense. Hypothalamus dysfunction can increase the intensity of feelings of attraction, or aggression, or sadness depending on the situation one is in. Sexual desire can increase, but the ability to perform sexually is decreased. Additionally, the amygdala is compromised, where emotional control, motivation, and interpretation of nonverbal emotional expression are processed. In the hippocampus, memory processes are also hampered. The thalamus relays information from the sensory organs to the cerebral cortex where they are processed into meaning. When this neural pathway is slowed down, the ability to respond quickly to information from the environment is slower and less accurate, resulting in longer reaction times which seriously hamper the ability to drive.

As blood alcohol rises, the frontal lobes are affected. This is where higher mental processes including thought, reasoning and decision making are largely processed. A dangerous consequence is that an intoxicated person may decide to drive even if he or she knows, when sober, that they should not.

As blood alcohol concentration levels increase in the cerebellum, fine motor coordination is reduced and speech is slurred. The ability to judge distances, and when to stop, is also impaired. The brain stem areas that control movement and balance are also affected resulting in a staggered gait and clumsiness. When blood alcohol levels become very high, the medulla in the brain stem, which regulates life support functions, becomes compromised. The body sends signals that poisoning is occurring, leading to vomiting (poison = toxin; someone drunk is “intoxicated”). Because inhibitory neural pathways are more active, swallowing, breathing and heart rate can also be affected, leading to unconsciousness and even death.

There are benefits from alcohol.  The mild depressant action of just one or two drinks relieves stress and enhances mood.  Many of the alcohol preparations, such as red wine, contain beneficial antioxidants.  Ethanol does have some caloric content - it is produced as a partial breakdown of glucose.  It is also used as a "solvent" to dissolve many medicines that would be poorly absorbed by the stomach and intestines.  It also serves as a considerable "disinfectant" when added to water and food of questionable purity. 

Still, as illustrated in the case of poor Joe from our last blog, it has its dangers as well. In comparison with other intoxicants - such as marijuana - Society as a whole has decided that the dangers of excessive ethanol consumption are acceptable.  Only time will tell if Society makes the same decision about other intoxicants.

In the next blog we'll discuss some long-term consequences of ethanol use, as well as a discussion of problems strictly associated with (and indicative of) alcoholism.

Until then, take care of your brain - and if you take it out for a few drinks after work - do so with caution!
(and again - many thanks to K. Mata for today's blog!).

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