Like how do you get drunk from alcohol?
In: Biology
Perhaps surprisingly, we don’t fully know yet.
So, for starters, alcohol is specifically a molecule called ethanol. When you drink this ethanol, it goes into your blood and from there circulates through your body. Ethanol is poisonous at high levels, so to prevent it accumulating, cells have evolved a way of turning it into something harmless, which is a three-step process. The first step of this process converts ethanol into another molecule called acetaldehyde. Acetaldehyde is actually more poisonous than ethanol, but it’s a necessary first step in the process. The second step converts acetaldehyde into a molecule called acetate, which is a lot less poisonous. Finally, acetate is converted into something called acetyl co-enzyme A which is an energy-dense molecule that cells can use to generate energy in a similar way to carbohydrates. This end product is the reason alcohol has calories.
It is not yet entirely clear how ethanol and its later products affect the body. They don’t have any measurable effect until there’s loads of them, so it’s hard to study like we might other drugs (as this method requires using very small amounts and seeing how cells change in response). What we do know is that ethanol and/or acetaldehyde have some kind of effect on a lot of different things in the brain called neurotransmitters.
The brain works by having lots of different brain cells “talk” to each other. They do this at positions between cells called synapses, where electrical signals in the input cells are converted into chemical signals, and those chemical signals produce a new electrical signal in the output cells. At any given synapse, there are almost always multiple input cells. Each input cell sends its own signal to the output cell, and the output cell must figure out whether or not it should create its own signal to send to the next cell in the line. It does this by basically adding up the “values” of the input cell signals: some input cells say “Do it!” and some input cells say “Don’t do it!”. Each of these signals has a strength associated with it, so you might have one cell creating a weak “do it” signal and another creating a very strong “don’t do it” signal, which can be imagined as “do it” signals being some size of positive value, like +5, and “don’t do it” signals being some size of negative value, like -5. The output cell adds all those numbers up, and if the total is higher than a certain threshold (say, 30), it will continue the signal. If the total is lower, it’ll do nothing and the signal will stop.
What ethanol and/or acetaldehyde do is they stick to the bits of the output cell that detect the input signals, and trick them into thinking certain signals are stronger or weaker than they really are. This happens mostly to a sensor called GABA, which detects “don’t do it” signals. If normally the input “don’t do it” signal was -5, then when drunk, the output cell would perceive that signal as a -10 instead. This makes the output cell less likely to continue the signal than it would be normally. Essentially, a lot of the brain’s functions work less well because it’s harder for them to get a signal down a full chain of brain cells – all brain cells have some cells saying “don’t do it” to them, but alcohol is like giving those “don’t do it” cells megaphones, so the “do it” cells have to shout even louder to make themselves heard. This is where a lot of the perceptions of drunkenness come from, like the sudden inability to do basic things.
The other major effect that ethanol and/or acetaldehyde has in the brain is on the dopamine neurotransmitter, which you may have heard of as something like the happy chemical or the reward chemical or something. This is a neurotransmitter used in the parts of the brain that control reward-motivated behaviour – the more something stimulates these parts of the brain, the more we’ll want to keep doing it. Addictions tend to act upon this part of the brain, making it so effective that we start to become dependent on it just to feel normal. In these circuits, once dopamine (a “do it” signal) has been released, the input cell that sent the dopamine sucks it back up for reuse. Ethanol/acetaldehyde block the sucking up process, which means the dopamine remains between the cells for longer, which the output cells perceive as being a bigger and longer-lasting “do it” signal – this makes it more likely for them to continue the signal down the chain.
There is also evidence that ethanol/acetaldehyde affect a wide range of other neurotransmitters in the brain, but it’s not clear how relevant those effects are to the experience of alcohol.
Finally, a hangover occurs after the body has converted most of the ethanol into acetaldehyde. Basically, when the alcohol is mostly in the body as ethanol with a bit of acetaldehyde, that’s being drunk. When it’s mostly acetaldehyde and acetate, that’s being hungover.
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