Neurons are polarized cells that communicate via synapses with each other. On both sides of the synapse are variable densities of different signaling molecules that participate in the transduction of information from the pre-synaptic to the post-synaptic side and vice versa. In order to allow synaptic transmission, the arrangement, number and density of these specialized molecules seems to be important.

Research in the group focus on the functional impact of a dynamic organization of signaling molecules in the neuronal membrane like voltage gated ion channels, adhesion molecules and transmitter receptors.

1. Surface Dynamic of voltage gated ion channels

Synaptic plasticity is believed to be fundamental for learning and memory. The probability of a successful transmitter release varies by 10-90% and is influenced by many factors. A major factor that we are focusing on is the position of voltage-gated calcium ion channels (VGCC), which, amongst other signaling molecules, play a major role in the triggering of pre-synaptic neurotransmitter release. So far many thinks are known about their functional role in general and their electrophysiology properties. But still little is known about the synaptic targeting, plasticity-related regulation and the dynamics of presynaptic VGCC. To study these aspects of the VGCC our laboratory wants to make live imaging studies on a labeled and functional VGCC.  For that we use molecular biological techniques (cloning of calcium channel constructs by mutagenesis, transfection of channels into cell lines and neurons), protein biochemistry and electrophysiological techniques (patch clamp) to create a VDCC that can be used for live cell imaging.

Using conventional fluorescence microscopy, the spatial resolution is limited by the diffraction of light. This leads to a relatively low resolution of 200-300nm in lateral and 500-700nm in axial direction, which is many factors larger than the sub-cellular structures under investigation. Recently, a number of super-resolution technologies that break the diffraction limit have been developed. These are on the one hand techniques like STED, RESOLFTs and SSIM that sharpen the point-spread function of microscopes and on the other hand PALM, FPALM and STORM that rely on the localization of single fluorescent particles. We are focusing on the second type of techniques employing single particle tracking using a spinning disk and heading to use PALM-like techniques in the near future.

Currently, we are investigating 3D tracking of individual fluorophores in the nanometer scale with video frame rate. In addition we try to monitor synaptic activity by the observation of pHluorin tagged synaptic vesicle proteins.

2. Influence of the molecular dynamic on network activity

One of the main features of neuronal populations is their network activity, which emerges on early developmental stages. Several lines of evidence demonstrate that neuronal network activity is not a by-product, but rather a necessary component or pre-requisite for proper functioning of neuronal ensembles. Being influenced by wide variety of factors, we focus on the influence of network activity by the lateral dynamic of glutamate receptors. Our previous work has shown that the filtering properties of a glutamatergic synapse are changed, if AMPA receptor mobility is altered (Heine et al. 2008, Frischknecht et al. 2009). Here we will develop molecular tools to alter specifically the dynamic of, for example AMPA receptors, to investigate the impact of local changes in the molecular dynamic on the spontaneous and evoked network activity.

These investigations will be done on neuronal cultures and brain slices and activity will be recorded using multi-electrode arrays (MultiChannel Systems, Reutlingen, Germany). As a functional readout, to see how experimentally induced molecular and morphological changes are correlated we will analyze the spatial and temporal network synchronization, as well as other aspects of neuronal network activity.