Mark Pottek   Dr.
   Phone: ++49-441-798-3732, Fax: ++49-441-798-3423
   e-mail: mark.pottek@uni-oldenburg.de
   W4 1-177

You all know the following from your all-days experience: the alarm clock rings halfway through the night, your hand fumbles for the light switch, and suddenly a blazing photon beam strikes your visual system. Your eyes, which just before in the twilight were able to sense the clock's face, are now dazzled for several moments; and only step by step the shapes of the sleeping room emerge from the light-flooded scenery. During these moments, the visual system performs adaptation to the altered light conditions - and a large part of this versatility is provided by the retina.

Horizontal cell of the carp retina

The retina does not only meet the requirements for physical perception of light, but is also equipped with circuits for pre-interpretation of the perceived features. These pathways provide for an extraction of a suitable part of information from the visual scenery, even under changing light conditions. By this means, visual perception works over a wide range of background light levels reaching from dim starlight to bright sunlight representing an intensity range of more than 10 log units.

Changes in the horizontal cell's membrane potential (above) evoked by short light flashes (below)

Retinal horizontal cells play an important role in adjusting the photoreceptor's sensitivity with respect to the ambient light conditions. By directly receiving synaptic input from a vast amount of photoreceptors they calculate the mean properties of the global light conditions and feed the calculation result back to the photoreceptors to tune their working range. This feature of horizontal cells is the main topic in my research. I perform intracellular recordings in the everted eyecup preparation of several animals to study the horizontal cell's electrical properties during adaptation to different light levels as well as during treatment with agents supposed to act as endogenous modulators mediating the illumination-correlated changes in retinal activity. This approach allows to elucidate the spatial, spectral, and temporal features of the first retinal synapse and additionally provides for a fascinating possibility of directly observing life in action.