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All neuromodulators like dopamine, serotonin, acetylcholine, histamine, and norepinephrine act only on metabotropic receptors?

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closed as off-topic by Bryan Krause, David, Amory, The Last Word, James Feb 20 '18 at 20:02

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Homework questions are off-topic on Biology unless you have shown your attempt at an answer. For more information see our homework policy." – Bryan Krause, David, Amory, The Last Word, James
If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ What research have you done to answer this on your own? The Biology.SE community has agreed that questions that show little or no prior research effort are off-topic on this site unless you have shown your attempt at an answer. Please edit your question and tell us where you've looked, what you do know about the topic, and where exactly you still have questions. Unresearched questions may be subject to down-voting and closure. $\endgroup$ – MattDMo Dec 9 '16 at 3:20
  • $\begingroup$ I have already search about this and I found that the receptors for neuromodulators are typically metabotropic receptors, what I want to know is if this is always the case, or there are cases where neuromodulators like dopamine act directly on ionotropic receptors. Any help will be appreciated $\endgroup$ – Sirius Fuenmayor Dec 9 '16 at 3:58
  • $\begingroup$ No, they don't act only on metabotropic receptors - please look into each of them if you can't find the information with broad search terms. $\endgroup$ – Bryan Krause Dec 9 '16 at 4:30
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    $\begingroup$ Also, do you consider neuropeptides such as endorphins, enkephalins, etc. (opiod peptides), oxytocin, and Substance P as neuromodulators? What about GABA? Are you just wondering about internally-synthesized molecules, or do you include pharmaceuticals and "natural products" like SSRIs, psilocybin, phencyclidine (PCP), opiates (natural and synthetic), etc.? This question can get too broad very quickly... $\endgroup$ – MattDMo Dec 9 '16 at 14:58
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Not all neuromodulators act only on metabotropic receptors. However, you are correct to observe that this is a general rule of thumb.

Of the substances you have listed:

  • Acetylcholine is not primarily a neuromodulator, but rather a "normal" neurotransmitter. As such it acts on both ionotropic and metabotropic receptors.

  • Serotonin - the one exception among the neuromodulators you have listed - acts on numerous classes of metabotropic receptors, but also on the 5-HT3 receptor, which is ionotropic.

  • All other neuromodulators you have listed act on metabotropic receptors only.

This tendency of neuromodulation to be metabotropically mediated is possibly a consequence of the nature of the neuronal function itself. Neuromodulatory systems do not per se relay information, but change how other information relays work. As such there is no need for the most rapid, temporal, coding (best achieved via the more rapid ionotropic signal transduction), and a slower coding may even be more efficient.

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