Research

During my studies of physics at the University of Munich I developed an interest in physiological optics and, therefore joined the Institute of Medical Optics, University of Munich. There I performed experiments in the psychophysics of vision to obtain my Masters degree in Physics (Diplomarbeit). In order to learn more about the neurophysiological basis of vision, I joined the laboratory of Otto D. Creutzfeldt at the Max Planck Institute for Psychiatry in Munich. Under his supervision I studied the different components of the visual system which limit spatial resolution. I measured the modulation transfer function of the cat eye and, by electrophysiological recordings, the grating resolution of individual ganglion cells. Furthermore I simulated in a homogeneous network of neurons how excitation and inhibition influence spatial resolution. Based on this work I obtained a Ph.D. in Physics. At the same time I attended a graduate program in neurobiology sponsored by the Volkswagen Foundation. 

Because visual acuity is limited by the sampling properties of the retina, I wanted to learn more about retinal circuitry. I spent part of 1972 in London, working with Brian Boycott, F.R.S., in the MRC Cell Biophysics Unit, Department of Biophysics, King's College, London. We succeeded in morphologically classifying cat retinal ganglion cells and thus defining the anatomical basis of parallel processing in the ascending visual pathway. In 1973 I went for a postdoctoral training to the John Curtin School of Medical Research in Canberra (Australia). In the lab of Peter Bishop, F.R.S., I worked with Brian Cleland and William R. Levick, F.R.S., on a physiological/morphological identification of retinal ganglion cells. We showed that the physiological brisk-transient (Y) cells corresponds to the morphological alpha cell type.  After returning to Germany I was able to establish my own small lab at the University of Constance. The structure and function of the mammalian retina was in the meantime my major scientific interest. Leo Peichl was my first Ph.D. student and in a continued co-operation with Brian Boycott, F.R.S., we studied the mosaics of retinal neurons, established their regular arrays and the territorial behaviour of their dendritic fields. This type of analysis was performed for horizontal cells and different classes of retinal ganglion cells. The independent mosaics of ON- and OFF-ganglion cells were established. 

In 1977 the Max Planck Society offered me a group leader position (Nachwuchs-gruppenleiter) at the Friedrich-Miescher Laboratory in Tübingen. During the four years in Tübingen we worked on the projection of the different ganglion cell classes to the visual centers of the brain thus elaborating further the idea of parallel pathways in the visual system. We also continued our studies of retinal mosaics and retinal circuits. We started to work on retinal transmitters using iontophoresis and extracellular recordings from the in vivo retina. By these approaches we could show, how inhibitory neurotransmitters such as GABA and glycine influence light responses of retinal ganglion cells. 

In 1980 the Max Planck Society offered me the Directorship of the Department of Neuroanatomy at the Max Planck Institute for Brain Research in Frankfurt. In 1981 we moved the lab to Frankfurt and continued our studies of mammalian retinal organization. Immunocytochemical methods became available for selective labeling of cell types and for the study of retinal circuits. In addition we used electron microscopy to study synaptic interactions in the retina. We also established during the years different in vitro models (dissociated cells, retinal slices and retinal whole mounts) and studied retinal circuits in the rat with the patch clamp method. In parallel we performed an anatomical analysis of the primate retina. The focus of our work was on the rod circuit of the mammalian retina and on parallel pathways through the primate retina. Both in rodents and in primates we were able to identify at least 10 different types of bipolar cells and study their connectivity. In recent years we have become very much involved with transmitter-receptors in the retina and their synaptic localization. In this context most of our studies are now performed on the mouse retina because of the continuously increasing availability of mutant mice which offer the possibility to delete specific transmitter receptors and also to label circuits by the expression of molecular markers such as green fluorescent protein. Although this involved more and more molecular tools, the question of how the eye, the window to the brain, works was always in the center of our interest. In 2008 the Department of Neuroanatomy was closed because of my retirement.