Addiction; Amphetamine and congeners; Angelman Syndrome; Cocaine; Neurotransmitter Transporters; Psychopharmacology
Neurotransmitters transporters are located in presynaptic specializations. They inactivate neurotransmitter-mediated neurotransmission following exocytotic release by a simple reuptake mechanism. Recent crystallographic examination of the mammalian serotonin transporter provides a structural scaffold which supports transport by an alternative access mechanism. Monoamine transporters are a target of clinically relevant drugs: (i) antidepressants competitively block the reuptake of monoamines. Thereby, these compounds enhance the extracellular monoamine concentration which is relevant for clinical success. (ii) amphetamines and cathinones, some of which behave as substrates of the transporters, trigger non-exocytotic neurotransmitter release (transporter-mediated efflux). The exact molecular mechanism of the psychostimulant action, however, still remains enigmatic. Neurotransmitter transporters are subject to regulation by constituents of the plasma membrane such as cholesterol and phosphoinositides. In addition, neurotransmitter transporters engage in quaternary complexes, which are also determined by their interaction with lipids.
Understanding the structure-activity relationships of neurotransmitter transporters (especially the monoaminergic, high-affinity and low capacity transporters such as transporters for dopamine, norepinephrine and serotonin - and also the low-affinity, high capacity transporters such as organic cation transporters), the trafficking processes to and at the plasma membrane, the functional impact of the lipids in the plasma membrane - this is the declared goal of my research.
Techniques, methods & infrastructure
We use biochemical and fluorescence spectroscopical methods for the determination of the neurotransmitter transporter function. These include radioactively labeled tracer flux measurements (uptake/efflux experiments), flux measurements of fluorescent tracer and electrophysiological experiments (patch-clamp measurements in the whole cell configuration and two-electrode voltage clamp measurements). We work both with heterologously expressed transporters in cell lines (with/without mutagenesis to examine the structure/function relationship and concomitant quantitative structure activity relationship, QSAR) and native brain tissue (ex vivo) as well as primary neuronal cell culture. We explore the conformational equilibrium and the quaternary structure of transporters and interacting proteins by fluorescence resonance energy transfer (FRET) microscopy. Furthermore, we examine our psychostimulant drugs also in in vivo in behavioral-pharmacological experiments. We also interact with a couple of other research groups and especially with the Stockner group to apply computational approaches, molecular modeling and molecular dynamics simulations to answer our research questions.