Posted by fachad on March 22, 2002, at 7:53:22
In reply to ISO: further clarification please! » IsoM, posted by Janelle on March 22, 2002, at 2:36:14
Each of the neurotransmitters has corresponding receptors that they bind to. A drug that has anti-whatever properties binds to the receptor of that neurotransmitter and keeps it from functioning.
An anti-histamine blocks histamine receptors and the things they do like make itching, watery eyes, runny nose and hives.
An SSRI binds to the serotonin uptake pump receptor and keeps serotonin from being drawn back in after it is put into the synapse.
So, an anticholinergic drug binds to cholinergic receptors and keeps acetylcholine from acting there.
As a result you get dry mouth, constipation, urinary retention, etc. Even though you are taking a drug like a TCA for brain cells, your body uses acetylcholine (and serotonin and epehepherine/norepinepherine) all over your body.
Another part of this anticholinergic thing is "binding affinity". Some drugs are weakly anticholinergic and they will bind to receptors that are not already occupied. Others have a strong affinity and they will "bump" acetylcholine right off a receptor where it was working and occupy the receptor.
You can often predict side effects of a drug by knowing its binding affinities at the different receptors. Drugs that block histamine will cause drowsiness. Drugs that block dopamine will relieve psychosis, but may cause movement disorders. Drugs that block NE may lower blood pressure.
Drugs that block the serotonin uptake pump will increase the amount of serotonin in the synapse in the CNS, which may alleviate depression. They will also increase the amount of serotonin in the synapse in intestinal neurons. In the intestines, serotonin modulates motility and pain. So some people on SSRIs get stomach cramps and diarrhea.
So while blocking a receptor in one area may be the theraputic benefit, blocking it in another area causes the side effects, and you can't control where a drug goes once you swallow a pill.
> Okay, I follow that there's cholinergic: its root word is 'choline' which is a type of B vitamin, a fatty acid actually. Choline is needed to make the neurotransmitter acetylcholine.
>
> And I know that anticholinergic refers to those pesky side effects associated with TCA's (I used to be on a TCA so I know first hand about those effects - yuck!)
>
> My question now is does anticholinergic mean that somehow the substance (say a TCA) works against the neurotransmitter acetylcholine? I ask because the prefix "anti" means against or opposing.
>
> Thanks!
poster:fachad
thread:99306
URL: http://www.dr-bob.org/babble/20020322/msgs/99447.html