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Old 09-23-2004, 03:45 PM
chorpler chorpler is online now
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Prozac a serotonin agonist?

My wife just took an exam in her psychology class. One of the questions was this:

Quote:
Prozac is an SSRI antidepressant. Which of the following best describes Prozac's mode of action?

a. Prozac is a serotonin agonist.

b. Prozac is a serotonin antagonist.

c. Prozac prevents the reabsorption of serotonin into the axon.

d. Both a and c

e. Both b and c
The correct answer on the test was D. Now, I knew that C was correct, and I knew that Prozac is not a serotonin antagonist, but I also thought that Prozac was not a serotonin agonist. The teacher says that it is. I found one web site that lists Prozac as a serotonin agonist, but frankly it doesn't seem too credible, and it's the only one I could find after a few minutes of Google searches. Is it true?
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Old 09-23-2004, 04:02 PM
Shagnasty Shagnasty is offline
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Agonist would mean that Prozac (fluoxetine) binds to the same receptors that seretonin normally does on the cell. I have a degree in psychopharmacology and I have to admit that doesn't sound too familiar to me either. Here is one article that says it is an antagonist rather than an agonist. I doubt that is conclusive either though.
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Old 09-23-2004, 04:04 PM
Shagnasty Shagnasty is offline
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Sorry, here is the article.

http://www.biopsychiatry.com/fluox5ht2c.htm
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Old 09-23-2004, 10:20 PM
KarlGauss KarlGauss is offline
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Quote:
Originally Posted by Shagnasty
Agonist would mean that Prozac (fluoxetine) binds to the same receptors that seretonin normally does on the cell.
I agree with you. That is the literal definition of an agonist.

Still, in casual parlance we often use the term 'agonist' to denote an agent which potentiates or stimulates the receptor regardless of its mode of action. An example might be any of the acetylcholinesterase inhibitors (i.e. donezepil et al) which while not directly stimulating the acetylcholine receptor, have a net effect to augment cholinergic transmission.
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Old 09-24-2004, 01:43 AM
chorpler chorpler is online now
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Quote:
Originally Posted by KarlGauss
I agree with you. That is the literal definition of an agonist.

Still, in casual parlance we often use the term 'agonist' to denote an agent which potentiates or stimulates the receptor regardless of its mode of action. An example might be any of the acetylcholinesterase inhibitors (i.e. donezepil et al) which while not directly stimulating the acetylcholine receptor, have a net effect to augment cholinergic transmission.
I realize I should have defined my understanding of agonist and antagonist, which is the same as Shagnasty said. An agonist would be something that binds to, and activates, the particular receptor it is an agonist for. And an antagonist would be something that binds to the receptor but does not activate it, thus preventing whatever is supposed to bind to the receptor (and activate it) from doing its job.

So then, Prozac is not an agonist in the technical sense (and, in fact, according to Shagnasty's cite, it may actually be an antagonist) but people often call something an agonist when it has the effect of activating its particular receptor, even if it does so indirectly (by merely increasing synaptic concentration of the endogenous chemical that binds to and activates the receptor, say) like Prozac? I wondered if that might be the case, but it seems pretty imprecise...
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Old 09-24-2004, 04:38 AM
Little Cloud Little Cloud is offline
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Having taught a psychopharmacology class myself, I can say with some assurance that your wife was the victim of a lousy test question. The people I teach really need to know the information I'm teaching. I don't spend my time trying to trip them up with stupid, ambiguous questions. Maybe the professor was just in a bad mood while writing that question and could have used a little Prozac.
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