I am working on the vertebrate retina, with a main focus on the mouse and bird retina. Currently my work is focused on three major topics:
- Functional and molecular analysis of electrical synapses in the retina
- Circuitry and functional role of retinal interneurons: horizontal cells and amacrine cells
- Circuitry for light-dependent magnetoreception in the bird retina
Electrical synapses (gap junctions) permit fast transmission of electrical signals and passage of metabolites by means of channels, which directly connect the cytoplasm of adjoining cells. A functional gap junction channel consists of two hemichannels (one provided by each of the cells), each comprised of a set of six protein subunits, termed connexins. These building blocks exist in a variety of different subtypes, and the connexin composition determines permeability and gating properties of a gap junction channel, thereby enabling electrical synapses to meet a diversity of physiological requirements.
In the retina, various connexins are expressed in different cell types. We study the cellular distribution of different connexins as well as the modulation induced by transmitter action or change of ambient light levels, which leads to altered electrical coupling properties.
Horizontal cells receive excitatory input from photoreceptors and provide feedback inhibition to photoreceptors and feedforward inhibition to bipolar cells. Because of strong electrical coupling horizontal cells integrate the photoreceptor input over a wide area and are thought to contribute to the antagonistic organization of bipolar cell and ganglion cell receptive fields and to tune the photoreceptor–bipolar cell synapse with respect to the ambient light conditions. However, the extent to which this influence shapes retinal output is unclear, and we aim to elucidate the functional importance of horizontal cells for retinal signal processing by studying various transgenic mouse models.
Wide-field amacrine cells
The retina houses a multitude of amacrine cell types, which display the highest diversity in morphology, transmitter repertory and putative function of all retinal neurons. So far, only few of these cell types have been thoroughly investigated, because in many cases a low population density impedes the systematic study. This is notably true for wide-field amacrine cells, which are characterized by their far-reaching cellular processes and are thought to mediate long-range lateral inhibition at the retinal output stage. By using retinas expressing fluorescent markers in only a subset of neurons we target the identification of specific wide-field amacrine cell types for studying their morphology, circuitry and physiology.
Retinal circuitry for light-dependent magnetoreception in the bird
We are studying which neuronal cell types and pathways in the bird retina are involved in the processing of magnetic signals. Likely, magnetic information is detected in cryptochrome-expressing photoreceptors and leaves the retina through ganglion cell axons that project via the thalamofugal pathway to Cluster N, a part of the visual wulst essential for the avian magnetic compass. Thus, we aim to elucidate the synaptic connections and retinal signaling pathways from putatively magnetosensitive photoreceptors to thalamus-projecting ganglion cells in migratory birds using neuroanatomical and electrophysiological techniques.
DFG-funded project (in collaboration with apl. Prof. Dr. Ulrike Janssen-Bienhold): Einfluss von Horizontalzellen auf die Lichtantworten retinaler Ganglienzellen
DFG-funded project (in collaboration with apl. Prof. Dr. Ulrike Janssen-Bienhold): Electrical synapses in rod and cone pathways of the mouse retina
European commission-funded project (within switchBoard - an Innovative Training Network (ITN) funded by the European Commission's Horizon 2020 programme): Role of bipolar cell-to-bipolar cell and bipolar cell-to-amacrine cell coupling in the mouse retina
Principal Investigator in the DFG-funded Research Training Group Molecular Basis of Sensory Biology
Principal Investigator in the DFG-funded Collaborative Research Center SFB1372: Magnetoreception and Navigation in Vertebrates