Let’s say a soldier is in a firefight and his brain releases norepinephrine. If it isn’t reinforced by continuing to be in that stressful situation or thinking about it, how long will that norepinephrine produce effects in the brain?
If that same soldier stays in a warzone for a few weeks and his adrenaline hormone levels go up. Then he stays away and doesn’t dwell on it, how long until his adrenaline levels are back to normal?
Is it different for dopamine, serotonin or oxytocin?
You’ve heard of selective serotonin reuptake inhibitors? The reuptake means that the neuron “sucks up” unused serotonin, and the SSRI slows that. MRs really only work in the synapse in many cases. While in the neuron, they are stored or broken down.
“How long”, not “how”. I should also have said “active” rather than “in the system” although that was in the body of the text.
The key word you need for this is half-life, the amount of time needed for half the amount to be used up. For example, googling shows that norepinephrine of around 2 or 3 minutes. Dopamine is 2 minutes, serotonin around 90 minutes, oxytocin around 3 to 5 minutes. (I can’t vouch for the accuracy of any of those figures, just going by the University of Google.)
Those numbers are for blood concentrations. Would the half-lives of those neurotransmitters be similar in the brain?
Are norepinephrine and epinephrine the very same thing, just called different things depending on whether they’re in the brain or not?
I’m surprised serotonin sticks around for 30 times longer than the others. What could explain that?
Half life accounts for the lifespan of one individual molecule, but if an event requires an increase in synaptic NT, then more particles are released and/or synthesized and/or not reuptaken and/or not broken down and/or … And the event may modulate the length of that. For example, an elevated fight or flight response for a long period may lead to PTSD, and neurotransmitter activity is semi-permanently affected (there are other factors in PTSD, that’s not the only cause).
They are different. Epinephrine (sometimes called adrenaline) and norepinephrine (noradrenaline) are both catecholamines alongside dopamine. The synthesis route goes Tyrosine (dietary or synthesized from other sources) > L-Dopa > Dopamine > Norepinephrine > Epinephrine.
And it’s not just what NT that determines the effect but where in the nervous system it is released. For example, everyone “knows” that dopamine is associated with euphoria or addiction. That is true, but in other parts of the brain, it also does things like motor control with no euphoric effects.
Different hormones have very different half-lives: Classical neurotransmitters in active synapses have half-lives in the order of milliseconds - they need to be removed from the synapses very fast, both by re-uptake into the pre-synaptic cell and by degradation to enable the rapid firing rates of the neurons. The same neurotransmitters may have significantly longer half-lives in the extracellular fluid and in the blood stream, where they act more like classical hormones and bind to different types of receptors.