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Question: How does the firing of dopaminergic neurons affect the dispersal of dopamine?

Evidence of my limited familiarity with dopaminergic neurons and motivation for asking the question: Most of what I know about dopamine and dopaminergic neurons comes from reading papers on reinforcement learning and its possible neuronal implementation. I was surprised to see that (if I've understood correctly) firing of dopamininergic neurons might encode an error signal like the one propagated in simple temporal-difference learning (like in Schultz et al. 1997), while dopamine itself seems not to be involved in such basic aspects of learning but instead in higher levels of hierarchical reinforcement learning, like constructing representations of the environment found in model-based RL to be used in executive functions and generalizing and applying learnt information in novel tasks. I suspect that firing of dopamininergic neurons affects the dispersion of dopamine , but I'm not sure if my suspicion is the result of a misunderstanding.

Hypothetical context for an answer in case the question is too broad: I'm imagining a group of dopaminergic neurons, some with axons extending to some brain region A and others with axons extending to brain region B. Say the neurons with axons extending to brain region A fire more than the others. This means they will produce more dopamine, and I suspect more dopamine will be present in A, but I'm having trouble finding supporting evidence.

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    $\begingroup$ @Christiaan I'm asking specifically about what you identify as the latter half, i.e. "Is DA release related/coupled to DA production?". Additionally, I'm wondering how, if at all, these are related to the firing of dopaminergic neurons (your comment almost makes me think DA release is synomomous with firing of dopaminergic neurons, but that's not the case, is it?). $\endgroup$ – Alex Jun 3 '16 at 20:06
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    $\begingroup$ Firing of DA neurons inherently leads to DA release. Decreased firing to less release, more firing to more. Maybe I am overinterpreting your question. One way or another, try to trim the fluff from the question and leave the question core. Perhaps bold-out the question or something. Even better, as said, split it up. $\endgroup$ – AliceD Jun 3 '16 at 20:08
  • $\begingroup$ A lot better. Still broad imo, but I retracted the close vote. Thanks so much for your efforts. +1 I'll leave the one comment on splitting it up in place for now, but I removed the rest of the comments to prevent clutter. Good work :) I would leave your upvoted comment in place for now. It helps. $\endgroup$ – AliceD Jun 3 '16 at 21:30
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    $\begingroup$ Great to see you editing your question as it becomes more clear! As Chistiaan suggests though, I would focus on the core question first. Most obviously, simply remove the "An elaboration of my above question is ...". You can post follow-up questions once you understand the answer you received to this question later. If you were to find that answer yourself, you can even answer your own question here! Also, edit your question into one coherent post (no need to show the evolution of it, there is version control). Do not expect the reader to retrace your steps, it makes it harder to follow. $\endgroup$ – Steven Jeuris Jun 3 '16 at 23:35
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I've mostly figured it out now, and I've a better idea of the words and phrases I need to search to get the information I was asking for.

The short answer comes from wikipedia: "The neurons' somata produce the enzymes that synthesize dopamine, and they are then transmitted via the projecting axons to their synaptic destinations, where most of the dopamine is produced." The transmission is a direct result of the firing of the neuron, so DA is dispersed, in the areas where dopaminergic axons end, proportional to the firing of the neurons.

A more complete answer would involve an understanding of the difference between tonic and phasic transmission, for which this has proved an informative and accessible source.

The above sources support the suspicion I mentioned in the hypothetical context provided in the question.

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Dopaminergic neurons synthesize dopamine and release it at their synapses with target neurons (see David Sulzer's review article. The activity of a dopaminergic neuron (its instantaneous firing rate) is one of the main determinants of how much dopamine is released per unit time at its many synaptic terminals. The amount of dopamine synthesized is also important.

There are many other factors that influence the extracellular concentration of dopamine in the brain, including, but not limited to, the number and distribution of synaptic vesicles (which sequester the dopamine until it is released into the synaptic clefts), the number and distribution of calcium channels (which control how much calcium enters each synaptic terminal in order to trigger fusion of synaptic vesicles with the plasma membrane), and the amounts and types of dopamine transporters (that traffic dopamine from the synaptic cleft back into the presynaptic terminal and then back into synaptic vesicles).

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  • $\begingroup$ Welcome to CogSci. Could you add sources & references? $\endgroup$ – AliceD Jun 5 '16 at 5:07
  • $\begingroup$ One could start here and look into the referenced papers: ncbi.nlm.nih.gov/pubmed/26248886 $\endgroup$ – BitShrink Jun 22 '16 at 18:53
  • $\begingroup$ That's a modeling paper... The first sentence of your answer seems to target the question specifically. That should, ideally, be followed by (John Doe, Year) and a link to the article. Apologies for being nitpicky here. $\endgroup$ – AliceD Jun 22 '16 at 19:18
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    $\begingroup$ No problem, it's actually helpful guidance. The problem is (not that this is a good excuse) it takes me about 5 times as long to document an answer as to come up with an answer. But I see now that you are trying to create an enduring scholarly resource (rather than just quickly answer questions) and so I'll try to stay mindful of that. $\endgroup$ – BitShrink Jun 22 '16 at 19:21
  • $\begingroup$ Admittedly, many posts here on this site are accompanied only by a link to a wiki page. Personally, I tend to downvote those answers. Wikipedia's content is dynamic/volatile and often unreliable or even outright incorrect. Proper citations are soooo much better :) Thanks for your listening ear and feel more than welcome to hang around here more often. Expert contributions are warmly welcomed. I'll remove that downvote above. I have to make some changes to your answer to be able to remove that downvote. Feel free to roll those edits back. When updated I'm happy to upvote. $\endgroup$ – AliceD Jun 22 '16 at 19:30

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