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Can/are SSRI's used as "boosting" agents in ADHD??

JohnBoy2000

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Primarily what I'm thinking is, as stated in Stahls book - drugs with very minor NRI properties appear to exert quite noticeable NRI effects when applied in combination with SRI's.

However, NRI's in mono-therapy, require high dose, super high receptor occupancy, to exert clinically notable effects.

It seems that this may be relative to somewhat similar activation patterns in post synaptic protein phosphorylation, common to both serotonin and noradrenaline receptor agonism.

The outcome seemingly, one being considerably more efficacious in the presence of the other.


Relative to the title question - ADHD obviously responding to DA enhancement, or "tuning" of DA neurons, as the theory seems to go.

Obviously it responds to NA enhancement - prefrontal cortex, no DA transporters etc.

I use the example of ADHD, as it can be treated with NRI's - thus it's an easy way of highlighting my query.


Irregardless, the overall question is - if one were taking an NA agent in monotherapy like, Strattera, could one effectively make an SNRI out it, by applying say, Lexapro in combination therapy - thus avail of the "combination" effect on NA we see with SNRI's?

Is that principle sound?

Or are SNRI's entities onto themselves, with their own intrinsic properties can not be replicated by combining SSRI's and NRI's??
 
SSRIs can under some circumstances enhance some NE cell's firing, so in that sense an NRI will have more NE available to block the reuptake of if SSRIs have increased the synaptic NE in certain regions.

But there is also a mutual sensitization of effectors downstream of 5-HT and NE receptors.

You may be interested in this https://www.ncbi.nlm.nih.gov/pubmed/12482470
 
SSRIs can under some circumstances enhance some NE cell's firing, so in that sense an NRI will have more NE available to block the reuptake of if SSRIs have increased the synaptic NE in certain regions.

But there is also a mutual sensitization of effectors downstream of 5-HT and NE receptors.

You may be interested in this https://www.ncbi.nlm.nih.gov/pubmed/12482470

Is that basically the consensus explanation as to why NRI's like effexor yield noticeable NE related activation (mutual CREB or 2nd messenger related phosphorylation, and "mutual sensitization", as you put it), despite the same degree of NE implication in mono therapy yielding an insignificant NE related outcome?


In your opinion - in terms of "making" a combination SNRI - I'm reading a lot of SSRI's carrying CYP2D6 related enzyme inhibition - which means they would alter plasma levels of combination agents.

I'm guessing this is in part at least, a reason why effexor is used with mirtazapine most often - mirtazapine being partly metabolized by CYP 2D6, effexor has no implication on this enzyme - where's most other SSRI's seem to.


I guess I'm looking to determine what may be the most suitable SSRI related drug to add as a combination to pre-existing mianserin and strattera.

I don't like the idea of tampering with their plasma levels via CYP2D6 inhibition - as the therapeutic indices for these drugs are so narrow as it is.

From Stockleys book - it seems effexor is the only real SSRI related drug that doesn't inhibit CYP2D6 - so I'd be looking maybe at a low dose of that, 75 to 150 mg - back with side effects that that entails.

Any idea what serotonin receptor occupancy of effexor at 75 mg would be?
As in, with Lexapro, isn't it 90 % at 10 mg, 95% at 20 or something?


I'm open to suggestions for research.
 
https://ils.unc.edu/bmh/neoref/nrschizophrenia/jsp/review/tmp/352.pdf


Maybe answering my own question a little - this paper seems to delineate receptor occupancies, dose relative, for five primary SSRI's.

The graphs on page 6 of 10 seem to suggest about 80% receptor occupancy occurs for the majority - certainly for venlafaxine.

I guess all I can do it is try and see if the "combination" hypothesis will effectively create the SNRI effect via combining strattera with an SRI.
 
One school of thought is that ultimately 5-HT and NE regulation of glutamatergic signaling at dendritic regions of pyramidal cells in cortex plays a large role in monoaminergic antidepressant's effects. This is a synergistic regulation, as both 5-HT and NE can induce downregulation of AMPAr (via dynamin/p38 MAPK mediated AMPAr endocytosis and an increase in the time between Gi alpha reassociation).

This seems to be largely due to 5-HT1A and a2 activation, as well as 5-HT2A/5-HT2C. The 5-HT and NE mediated Long Term Depression at some excitatory synapses in PFC is interestingly impaired by stress.

There is evidence suggesting that simultaneous 5-HT and NE augmentation can be more effective than either alone
https://www.ncbi.nlm.nih.gov/pubmed/23832963/
https://www.ncbi.nlm.nih.gov/pubmed/12544378/
https://www.ncbi.nlm.nih.gov/pubmed/15960562/

Why decreasing AMPr mediated excitatory post synaptic potentials helps with depression needs more exploring, the role of some areas of the cortex in mood disorders is rather complex.

a2 receptor function is more complicated than one might think at first glance as well (it is more than solely a pre-synaptic regulator of transmitter release), see Yale's paper https://www.ncbi.nlm.nih.gov/pubmed/17448997/
 
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