Dopamine causes vomiting because of its peripheral actions? Not CNS? - USMLE Forums
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Old 12-23-2009
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Arrow Dopamine causes vomiting because of its peripheral actions? Not CNS?

I faced this sentence in UWorld, which says that L-Dopa, if not given with Carbidopa, causes you to vomit, because the Dopamine levels in periphery is increased. Hence by giving L-Dopa with Carbidopa, we decrease the vomiting side effect.

But I thought Dopamine causes vomiting because it stimulates the CTZ in the CNS, not in the periphery?

What do you guys think?
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Old 12-23-2009
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CTZ is in area postrema, receives blood from fenestrated capillaries not from blood that passed blood brain barrier, so peripheral dopamine affects it...

Also, dopamine effect on GI is not entirely central, there's a peripheral effect
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Old 12-23-2009
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Ahh, does this mean that CTZ is actually outside of the Blood brain barrier? That makes sense now. Thanks.

My bad, my neuroanat is...floppy.
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Oh, and by the way, if this is so, does this mean that Ondansetron actually acts OUTSIDE of the central nervous system?

Because since it blocks the 5HT on the CTZ, and the CTZ is directly linked to our blood, this means that ondansetron by right don't have to cross the BBB to work is it? Cuz I am a little confuse when First Aid says that ondansetron is a "central-acting anti-emetic". What do they mean by the "central" actually?
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It does act centrally, they all do, CTZ is in th dorsal medulla, but area postrena and OVLT cells (osmoreceptors) are exception from other CNS areas in that they receive blood from fenestrated capillaries, so drugs or substances should not go through the blood brain barrier.. check FA in first pages of neuro..
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