MDMA and TAAR1‐mediated RhoA Activation in Serotonin Neurons
Suzanne Underhill, Susan Amara
The FASEB Journal April 1, 2020 DOI: 10.1096/fasebj.2020.34.s1.05856 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Preclinical in vitro study Peer reviewed |
|---|---|
| Population | Primary cultures from raphe nuclei of E15 mice, HEK293 cells, noradrenergic neurons from locus coeruleus, and dopamine neurons from midbrain |
| Intervention | MDMA |
| Topics | MDMA Serotonin |
| Key points | MDMA triggers internalization of the serotonin transporter (SERT) via TAAR1 and RhoA signaling in serotonergic neurons, as shown by reduced SERT activity and GFP-tagged SERT internalization that were blocked by a RhoA inhibitor and absent in TAAR1-knockout cells. Higher MDMA doses were required to decrease transporter activity in norepinephrine and dopamine neurons. |
Abstract
We have recently described the biochemical cascade through which the psychostimulant amphetamine leads to internalization of the dopamine and norepinephrine transporters, (DAT and NET). Amphetamine is a relatively high affinity substrate for DAT and NET and they both serve as efficient conduits for amphetamine entry into the cell. Once inside the cell, amphetamine activates the trace amine associated receptor 1 (TAAR1), a GPCR that we have shown couples to both G S and G 13 signaling pathways. TAAR1 signaling through G 13 increases the activity of RhoA, a small GTPase that regulates trafficking of the catecholamine carriers and increases their internalization. We wanted to investigate if similar G‐protein coupled signaling events also occur in serotonergic neurons. Although amphetamine does not have a particularly high affinity for the serotonin transporter (SERT), other TAAR1 ligands do, including 3,4‐methylenedioxymethamphetamine (MDMA). We developed primary cultures from the raphe nuclei of E15 mice. 3 H‐serotonin uptake mediated by these cultures was largely citalopram sensitive, indicating SERT‐mediated serotonin transport. Pre‐treatment of these cultures with MDMA resulted in a decrease of SERT activity that could be blocked by an inhibitor of RhoA. Similarly, by total internal reflection fluorescence microscopy in HEK293 cells we found internalization of GFP‐tagged SERT in response to MDMA was blocked by a RhoA inhibitor. In HEK293 cells in which the TAAR1 gene has been deleted, MDMA did not trigger SERT internalization. In noradrenergic neurons cultured from the locus coeruleus or dopamine neurons from the midbrain, only higher doses of MDMA pretreatment could decrease transporter activity at the cell surface, likely reflecting the differences in affinity of the drug for the different monoamine transporters. These data indicate that pharmacological agents can regulate TAAR1 signaling in serotonergic, as well as catecholaminergic neurons and that the selectivity of TAAR1 agonists depends not only on affinity for the GPCR but also on their transport efficiency. Moreover, these findings suggest that the activation of TAAR1 in serotonin neurons and the subsequent internalization of surface SERT likely contribute to the modulation of serotonin signaling observed in response to MDMA. Support or Funding Information This work was supported by Intramural Research Program at the NIH, NIMH (ZIAMH002946).
Comparable studies
Other preclinical and animal studies on MDMA, most cited first.