Amphetamine and TAAR1 question

[Skorpio]

So this Natur1WAe paper just dropped, and it talks about the mechanism of TAAR1 activation by amphetamine, and the modulation of dat endocytosis through g13 dependent signalling.

I have a few questions, that having some trouble wrapping my head around.

1) first, how does this factor into the vmat based dopamine release of amp? Is it driving vmat reversal (or happening in series at least) or are the two processes unrelated.

2) they mention that taar1 knockout mice are hypersensitive to amphetamine. Is this because there are more dats on the cell surface to allow amphetamine to enter the cell? If not what are your ideas?

3) since taar1 is located on interior membrane with the g protein side in the cytosol, amp needs to cross two membranes to get to it. Is it diffusing through the membranes (this doesn't make sense because pretreatment dat inhibitors will block amphetamine effect, which implies a need for tranaporters) or are there specific transporters allowing amp to get to the ligand binding face of taar1?

Also if anybody has any interesting taar1 papers I'd love to read them.

Amphetamines signal through intracellular TAAR1 receptors coupled to Gα13 and GαS in discrete subcellular domains - Molecular Psychiatry

The extensive use of amphetamines to treat attention deficit hyperactivity disorders in children provides a compelling rationale for understanding the mechanisms of action of amphetamines and amphetamine-related drugs. We have previously shown that acute amphetamine (AMPH) regulates the...

www.nature.com

Let me know if you want a scihub link

 

[checktest]

Where's @Seppi for this? Right in his(her?) wheelhouse.

Perhaps amphetamine/meth after uptake through DAT and VMAT, is driving VMAT reversal (see nature comm vs. review paper below), relatively locking a preferential outward flow of DA, but is partially modulated in a feedback loop by TAAR1 in terms of some sensitivity/end rates? Perhaps something akin to L-type Ca2+ channels (compare DAT) linked to VMAT and TAAR (compare IP3R and ryanodine receptors, but sort of a different feedback) releasing more Ca2+ (DA from vacuole instead of Ca2+) from sarcoplasmic reticulum with feedback (say from TAAR) driving SERCA pump (but instead Meth overrides channel preventing previous return). Has to be some kind of feedback cycle there, but I wonder where the balance lies. OCTs like OCT3 could be a secondary valve for DA and such if VMAT was fully inhibited or something?

Maybe the TAAR1 knockout lack that regulation/typical feedback , the tuning down of the DA signal over time rather than overall DAT number. Could be some oligomerization alteration, or that DAT gets 'stuck' in the reversed form more. Could be more DATs on the cell surface, or maybe more DATs don't get internalized over time due to lack of TAAR tuning (via G13 through RhoA). TAAR auto-inhibitory circuit.

I wonder if other transporters are involved to some degree beyond VMAT and DAT. Amphetamine/especially meth do diffuse some (some other papers certainly imply a degree of diffusion even if elements are blocked), especially in the cytosol to more acidic vacuoles. Differences in plasmalemmal vs. vacuole membrane kinetics. Even though it says some effects are blocked by DAT inhibitors like cocaine and methylphenidate, that doesn't seem to match other papers entirely and clinical uses.

Preferential Rho-signaling activity from TAAR1 in non-lipid rafts was interesting compared to epinephrine's PKA activation in lipid rafts. Phosphorylation and internalization targets.

I would be curious to see some sort of sequential experiment, say a BRET-FRET for DAT and VMAT2 in presence of amphetamine as modulated by VMAT2 inhibitors, TAAR1 agents. V-ATPase inhibitor as well. Co-localization, activation of D2, A2A as well.


Various papers that were free or open access

https://www.cell.com/trends/pharmacological-sciences/fulltext/S0165-6147(14)00212-0

General review, transport cycle model

Mechanisms of amphetamine action illuminated through optical monitoring of dopamine synaptic vesicles in Drosophila brain - Nature Communications

Amphetamines are known to enhance extracellular dopamine levels, but the underlying mechanisms are unclear. Utilising a new pH biosensor for synaptic vesicles, the authors show that amphetamines diminish vesicle pH gradients, disrupting dopamine packaging and leading to increased...

www.nature.com

Some mechanisms of amphetamine action - highlights DAT - VMAT tandem, vesicle alkilization by amp in MPP+ model

Brain-Specific Overexpression of Trace Amine-Associated Receptor 1 Alters Monoaminergic Neurotransmission and Decreases Sensitivity to Amphetamine - Neuropsychopharmacology

Trace amines (TAs) such as β-phenylethylamine, p-tyramine, or tryptamine are biogenic amines found in the brain at low concentrations that have been implicated in various neuropsychiatric disorders like schizophrenia, depression, or attention deficit hyperactivity disorder. TAs are ligands for...

www.nature.com

Overexpression of TAAR1 - Decreased sensitivity to amphetamine, negative regulatory interaction

Pharmacology of human trace amine-associated receptors: Therapeutic opportunities and challenges

The discovery in 2001 of a G protein-coupled receptor family, subsequently termed trace amine-associated receptors (TAAR), triggered a resurgence of i…

www.sciencedirect.com

Wider, multi TAAR review

Frontiers | Trace Amine-Associated Receptors as Novel Therapeutic Targets for Immunomodulatory Disorders

Trace amines and their receptors (trace amine-associated receptors; TAARs) are an emerging pharmacological target for the treatment of human disorders. While...

www.frontiersin.org

As above, wider TAAR review, immuno focused but nice developmental history and evo

The Molecular Basis of Species-Specific Ligand Activation of Trace Amine-Associated Receptor 1 (TAAR1)

The trace amine-associated receptor 1 (TAAR[1] ) is an aminergic G protein-coupled receptor (GPCR) potently activated by 3-iodothyronamine (1), an endogenous derivative of thyroid hormone. Structure activity relationship studies on 1 and related agonists ...

www.ncbi.nlm.nih.gov

TAAR1 molecular level inquiry

Methamphetamine-induced impulsivity during chronic methamphetamine treatment in rats: effects of the TAAR 1 agonist RO5263397

Impulsivity is an important personality trait associated with several clinical syndromes including drug abuse. While repeated drug exposure is known to increase certain behavioral responses, such as locomotion, to subsequent drug exposure, few studies ...

www.ncbi.nlm.nih.gov

Meth and TAAR1 agonist, interesting acute vs. chronic

https://www.cell.com/neuron/fulltext/S0896-6273(14)00487-5

AMP-EAAT3 internalization given insight by your posted TAAR paper

Vesicular Monoamine Transporters: Structure-Function, Pharmacology, and Medicinal Chemistry

Vesicular monoamine transporters (VMAT) are responsible for the uptake of cytosolic monoamines into synaptic vesicles in monoaminergic neurons. Two closely related VMATs with distinct pharmacological properties and tissue distributions have been characterized. ...

www.ncbi.nlm.nih.gov

VMAT

An unsuspected role for organic cation transporter 3 in the actions of amphetamine - Neuropsychopharmacology

Amphetamine abuse is a major public health concern for which there is currently no effective treatment. To develop effective treatments, the mechanisms by which amphetamine produces its abuse-related effects need to be fully understood. It is well known that amphetamine exerts its actions by...

www.nature.com

OCT3 and amphetamine

Interrelation of dopamine transporter oligomerization and surface presence as studied with mutant transporter proteins and amphetamine

Our previous work suggested a role for oligomerization in regulating dopamine transporter (DAT) internalization, with d-amphetamine dissociating DAT oligomers and monomers being endocytosed. This model was put to detailed testing in the present work with ...

www.ncbi.nlm.nih.gov

DAT oligomers and amphetamine


Not gonna pretend I actually know the topic, I mostly downloaded the papers today waiting for a corticosterone shot and some people. Interesting stuff though.

 

[Dresden]

Amphetamine acts sterically as a DA/NE receptor substrate.

 

[Skorpio]

Not gonna pretend I actually know the topic, I mostly downloaded the papers today waiting for a corticosterone shot and some people. Interesting stuff though.

That's a real coincidence, they were using corticosterone to block the Oct channels In one experiment on the Oct paper.

I dont think oct is really a major player based on that paper, simply a secondary channel for dopamine to enter the synapse from (as opposed to DAT).

The EAAT3 paper is very cool in the context of the original paper, because it extends the effects of TAAR1 downstream to involve glutamatergic signaling, as well as providing secondary support for the original paper.

The vmat paper in flies is pretty interesting, they are saying da release is due to pH changes in the monoamine vesicles which occurs due to amp transport by vmat.

I'll come back as I read more of these papers, thanks a lot for the references.

 

[Seppi]

Where's @Seppi for this? Right in his(her?) wheelhouse.

I lol'd. Seriously though, I don't check this website all that often.

To answer the OP, as mentioned by checktest, the mechanism by which amphetamine induces the release of vesicular contents is through collapse of the pH gradient (vesicular alkalization). See the refs cited about that in https://en.wikipedia.org/wiki/Amphetamine#Dopamine

As for why TAAR1 KO seems to have unexpected effects (based upon TAAR1's known function), it's because TAAR1 and DRD2 dynamically interact in vivo and even heterodimerize to regulate neuronal function. Removing either receptor from DA neurons completely borks the dynamics of the release/reuptake system they regulate and as a result, you see the unexpected (mostly opposite) effects in TAAR1 KO experiments.

Also, neat paper. Thanks for sharing it.