alpha 2 antagonists

[seminoma]

Firecracker says this about Yohimbine (an alpha-2 antagonist)

Is a non-FDA approved drug that blocks presynaptic alpha-2-adrenergic receptors, resulting in increased cholinergic and decreased adrenergic tone, and has also been used in the management of erectile dysfunction.

Why would it decrease adrenergic tone? Don't alpha2 agonists reduce adrenergic tone?

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[EazyE1907]

Firecracker says this about Yohimbine (an alpha-2 antagonist)


Why would it decrease adrenergic tone? Don't alpha2 agonists reduce adrenergic tone?

By decrease adrenergic tone, it means decrease sympathetic Neurotransmitter release from pre-synaptic vesicles. Primarily Norepinephrine. which would then lead to decrease adrenergic tone.

 

[EazyE1907]

By decrease adrenergic tone, it means decrease sympathetic Neurotransmitter release from pre-synaptic vesicles. Primarily Norepinephrine. which would then lead to decrease adrenergic tone.

Edit: NVM you are absolutely right. read the question wrong. step has certainly fried my brain. sorry. Looks like a typo.

 

[SBR249]

By decrease adrenergic tone, it means decrease sympathetic Neurotransmitter release from pre-synaptic vesicles. Primarily Norepinephrine. which would then lead to decrease adrenergic tone.

I don't think presynaptic neurons do release norepinephrine.

 

[EazyE1907]

post-synaptic noradrenergic neurons into the synaptic cleft.

 

[seminoma]

I don't think presynaptic neurons do release norepinephrine.

What? How does norepi get to alpha and beta receptors?

 

[SBR249]

nvm, I read the question stem wrong. I thought based on the cholinergic reference that we are talking about the ganglionic synapse.

As an aside, does "cholinergic" means "parasympathetic" and "adrenergic" means "sympathetic"? If so I find that to be a very imprecise and somewhat confusing.

 

[EazyE1907]

What? How does norepi get to alpha and beta receptors?

Two ways. 1. Pre-synaptic cholinergic fibers release ACh which stimulates the chromaffin cells of the adrenal medulla to release both epinephrine and norepinephrine

2. pre synaptic cholinergic nerve fibers release ach, which stimulate post-synaptic nerve fibers to realse NE into the synaptic cleft which then binds to their respectice alpha and beta receptors.

nvm, I read the question stem wrong. I thought based on the cholinergic reference that we are talking about the ganglionic synapse.

As an aside, does "cholinergic" means "parasympathetic" and "adrenergic" means "sympathetic"? If so I find that to be a very imprecise and somewhat confusing.

Yes. but there are two exceptions. nerve fibers innervating the 1)adrenal medulla and 2) the sweat glands are BOTH innervated by CHOLINERGIC nerve fibers (meaning they release ACh) but are controlled by the SYMPATHETIC nervous system.

hope that helps.

 

[SBR249]

I'm not saying that I'm confused about what innervates what. I'm saying the way the question is phrased is both incorrect and confusing if they used cholinergic to refer to parasympathic and adrenergic to refer to sympathetic precisely because of the exception of the sweat glands. Not to mention all autonomic ganglia synapses are cholinergic to begin with.

As for the adrenal medulla, that is not an exception. The fibers innervating the adrenal medulla is the preganglionic fibers. So in essence, the adrenal medulla neuroeffector junction is the ganglion and the adrenal medulla is the postganglionic neuron. Except instead of transducing a signal to an effector organ, the postganglionic neurons release epi/NE into circulation.

Sweat glands are innervated by cholinergic postganglionic fibers.

 

[EazyE1907]

I'm not saying that I'm confused about what innervates what. I'm saying the way the question is phrased is both incorrect and confusing if they used cholinergic to refer to parasympathic and adrenergic to refer to sympathetic precisely because of the exception of the sweat glands. Not to mention all autonomic ganglia synapses are cholinergic to begin with.

As for the adrenal medulla, that is not an exception. The fibers innervating the adrenal medulla is the preganglionic fibers. So in essence, the adrenal medulla neuroeffector junction is the ganglion and the adrenal medulla is the postganglionic neuron. Except instead of transducing a signal to an effector organ, the postganglionic neurons release epi/NE into circulation.

Sweat glands are innervated by cholinergic postganglionic fibers.

dude. the exception is that they are BOTH under sympathetic control whilst being innervated by cholinergic fibers.

 

[SBR249]

Don't get all worked up. I know exactly what you are saying. However, I'm saying that the adrenal medulla is NOT an exception because it follows the model of every other sympathetic pathway. The difference is that there is no postganglionic fibers because the adrenal medulla is innervated by preganglionic fibers which is cholinergic for ALL sympathetic pathways. The adrenal medulla itself is basically a specialized version of postganglionic neurons. The sweat glands on the other hand is innervated by postganglionic cholinergic neurons which IS an exception because that's not usually the case in the sympathetic nervous system. That's a very important distinction.

 

[seminoma]

Two ways. 1. Pre-synaptic cholinergic fibers release ACh which stimulates the chromaffin cells of the adrenal medulla to release both epinephrine and norepinephrine

2. pre synaptic cholinergic nerve fibers release ach, which stimulate post-synaptic nerve fibers to realse NE into the synaptic cleft which then binds to their respectice alpha and beta receptors.


hope that helps.

I think you're confusing pre/post "synaptic" with pre/post "ganglionic". The postganglionic nerve becomes the presynaptic nerve at the next synapse.