Posted by scott-d-o on January 30, 2004, at 18:26:06
In reply to DA agonists, posted by Questionmark on January 30, 2004, at 16:33:32
wow, thats lot of questions.. i see where your screen name comes from..
> Questions:
> Why do you think diff DA agonists seem to have such different effects sometimes? (i have no experience with them; just seems to be that way from what i've read/heard). E.g., Mirapex causing such extreme fatigue and some others not doing so, and etc.depends on what types receptors they agonize, what part of the brain the receptors are located in, etc. for example, agonising DA autoreceptors causes a decrease in DA release.. if you don't understand why, look up some of my past postings where I explain this in detail. im oversimplifing this, but basically da agonists cause mixed affects because they agonise both autoreceptors and postsynaptic receptors. therefore they can cause opposite affects just by a change in dosage, for instance, apomorphine will agonise presynaptic autoreceptors at low doses causing hypomotility, and agonise postsynaptic receptors at high doses causing hypermotility.
> Why do DA agonists seem to be so diff than DA reuptake inhibitors (psychostimulants)? i know that most stimulants act strongly upon NE if not 5-HT as well, but still. It seems weird.mostly because they bind to the dopamine transport system and thus have much more widespread activity in the brain. also, dopamine agonists usually only bind to certain types of dopamine receptors, but since blocking reuptake causes greater concentrations of dopamine thruout the brain, and dopamine is much more non-selective for what receptors it binds to than a DA agonist is. for instance, bromocriptine only agonises DA2 receptors, but natural dopamine will agonise any dopamine receptor in the brain, probably ones we don't even have defined yet, it is even a partial agonist at adrenergic receptors. the other reason is, as you mention, psychostimulants usually block reuptake of all the monoamines, in fact, cocaine is actually more selective for the 5-HT transporter, than it is for the DA transporter.. it has been determined that the 5-HT reuptake inhibition of cocaine contributes a good bit to its addictive nature but not as much as DAT blockade does. amineptine is the only truly selective DRI that I know of and it's no longer on the market.
> Is there a crash with DA agonists as there is with stimulants?
i would think not but don't have any personal experience with them.. i don't think they would since they aren't depleting the brain's dopamine levels like a reuptake inhibitor would.
> Are they all good for sexual problems (anorgasmia in particular)? If not, which are?
yes, they all help.. altho some may be better than others. apomorphine (uprima) is one that is marketed specifically for this purpose..
> Do you know all that are available in the U.S.?
too lazy for this one ;-) i mentioned a couple earlier.
> Are they typically only prescribed for Parkinson's or would a psychiatrist be fairly willing to prescribe it for other conditions (depression, ADHD, SP, antidepressant-induced anorgasmia)?
depends on the doctor..
scott
poster:scott-d-o
thread:307418
URL: http://www.dr-bob.org/babble/20040127/msgs/307476.html