Basal Ganglia Parkinsons Question Help

[coreytayloris]

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Hey,
having trouble with this basal ganglia and parkinsons stuff and just wondering if anyone can clear it up for me.

ok, so ive come to understand that:


Tonically, both indirect and direct pathways are active, but that the indirect pathway is slightly stronger, and thus movements are essentially inhibited (such as why we aren’t walking, because the action of walking is being inhibited).
Then, when you want to complete an action (eg walk), the motor cortex sends signals down to the neo striatum, exciting the direct pathway and make you walk. While this is also going on, the indirect pathways that are inhibiting actions that conflict with walking (such as running, jumping), these pathways remain inhibiting these actions
.
So, im cool up until thatpoint.

Next is where i get stuck.

When you complete an action that gives you an unexpected reward, The nigrostriatal tract releases dopamine. This dopamine stimualtes the direct pathway for that action, and inhibits the indirect pathway for that action, this makes the pathway for that movement in that context easier to excite in the future.

Now, I assume Dopamine is only released this one time for that action - thus somehow facilitating that action to be compelted easier in the future. I mean obviously, every time you go to complete that action, dopamine isnt going to be released just to facilitate it is it?

But then, why does loss of dopamine cause parkinsons?
If dopamine is released only the first time you complete th action, then it doenst make sense that the action would be inhibited due to loss of dopamine.


I assume Dopamine isnt being released every time you do a simple action like walking, or lifting your arms?? (although i guess at one point in your life dopamine would have been released in response to you doing those actions and getting rewarded for them - eg maybe when you were a 2 year child and you got some sort of reward for being able to walk as a result of your parents joy at seeing you take your first few steps)

Or alternatively, i guess, if isdopamine released every time you go to initiate an action, then that would mean that loss of dopamine would cause parkinsons. (but my lecturer said dopamine isnt released everytime you go to complete an action, just when you complete an action that gives you an unexpected reward)

Anyone know the answer!!????????
Been wrecking my head!!!!

 

[Justforkicks4]

Hey,
having trouble with this basal ganglia and parkinsons stuff and just wondering if anyone can clear it up for me.

ok, so ive come to understand that:


Tonically, both indirect and direct pathways are active, but that the indirect pathway is slightly stronger, and thus movements are essentially inhibited (such as why we aren’t walking, because the action of walking is being inhibited).
Then, when you want to complete an action (eg walk), the motor cortex sends signals down to the neo striatum, exciting the direct pathway and make you walk. While this is also going on, the indirect pathways that are inhibiting actions that conflict with walking (such as running, jumping), these pathways remain inhibiting these actions
.
So, im cool up until thatpoint.

Next is where i get stuck.

When you complete an action that gives you an unexpected reward, The nigrostriatal tract releases dopamine. This dopamine stimualtes the direct pathway for that action, and inhibits the indirect pathway for that action, this makes the pathway for that movement in that context easier to excite in the future.

Now, I assume Dopamine is only released this one time for that action - thus somehow facilitating that action to be compelted easier in the future. I mean obviously, every time you go to complete that action, dopamine isnt going to be released just to facilitate it is it?

But then, why does loss of dopamine cause parkinsons?
If dopamine is released only the first time you complete th action, then it doenst make sense that the action would be inhibited due to loss of dopamine.


I assume Dopamine isnt being released every time you do a simple action like walking, or lifting your arms?? (although i guess at one point in your life dopamine would have been released in response to you doing those actions and getting rewarded for them - eg maybe when you were a 2 year child and you got some sort of reward for being able to walk as a result of your parents joy at seeing you take your first few steps)

Or alternatively, i guess, if isdopamine released every time you go to initiate an action, then that would mean that loss of dopamine would cause parkinsons. (but my lecturer said dopamine isnt released everytime you go to complete an action, just when you complete an action that gives you an unexpected reward)

Anyone know the answer!!????????
Been wrecking my head!!!!

Good question. There are two separate dopamine receptors (D1 STIMULATES Direct Pathway and D2 INHIBITS Indirect Pathway--thus, both facilitate movement). So...when you lose dopamine production from the substantia nigra pars compacta...the overall effect is bradykinesis.

 

[coreytayloris]

Ya, but what has dopamine production got to do with regular normal day to day movements?

Dopamine is only involved when you complete an action that results in an unexpected reward....

How is dopamine involved in regular tasks like walking, lifting a pen etc etc

 

[Dwindlin]

Ya, but what has dopamine production got to do with regular normal day to day movements?

Dopamine is only involved when you complete an action that results in an unexpected reward....

How is dopamine involved in regular tasks like walking, lifting a pen etc etc

It is my understanding that the neurons in nigrostriatal are dopaminergic neurons, so each time they fire they use dopamine as their transmitter as opposed to GABA or glutamate.

 

[coreytayloris]

but they only fire when you complete an action that gets you an unepxected reward, right?

 

[Dwindlin]

but they only fire when you complete an action that gets you an unepxected reward, right?

I don't believe so. I'm fairly certain they fire for all movements.

 

[TexasMDtobe]

but they only fire when you complete an action that gets you an unepxected reward, right?

I think you might be combining the motor loop of the Basal Ganglia and the reward systems associated with the limbic loop of the Basal Ganglia.

Motor Loop - Dopaminergic SNpc neurons to Dorsal Neostriatum
Limbic Loop - Dopaminergic Ventral Tegmental Area to Ventral Neostriatum

From what I understand, only the Limbic loop of the Basal Ganglia is tied to the reward centers.

So SNpc fires for every movement, and loss of it leads to hypokinetic disorders such as Parkinson's and the VTA fires in instances of reward in order to increase likelihood of future behavior.

If someone knows better, please correct me, I'm still trying to keep these loops straight.

 

[Mattchiavelli]

"Now, I assume Dopamine is only released this one time for that action - thus somehow facilitating that action to be compelted easier in the future. I mean obviously, every time you go to complete that action, dopamine isnt going to be released just to facilitate it is it?"
This assumption is incorrect which is why you're confusing yourself 🙂
Dopamine is required for all voluntary modulated movements, which is why a patient with parkinsons that starts Sinemet (levodopa/carbidopa) will "unlock," because now they have more available dopamine. It's also why patients on traditional antipsychotics (strong D2 blockers) can get "extrapyramidal" or parkinsonian sx which are clinically indistinguishable on a physical exam from actual Parkinson's disease.

 

[coreytayloris]

Thanks guys.

Ya that makes more sense.

That was my original thinking, but then when I asked my lecturer just to confirm that I had it right in my head, he told me that dopamine was only released when an unexpected reward was received after completing an action.

However, I also asked a guy in my class who did neuro for undergrad and he also said that dopamine is released every time you go to complete an action,

So i dunno, I think maybe my lecturer maybe misunderstood my question.
I think dopamine being released for every action makes much more sense and explains parkinsons. Dopamine only being released upon being rewarded by an unexpected action then parkinsons doesnt make sense at all!

Thanks!!!