Institute Cell Biology and Neurosciences, FB Biosciences, J. W. Goethe-University, Siesmayerstr. 70, 60054 Frankfurt a. M., Germany
Birds are among the best investigated model systems for the analysis of magnetic field impact on behavior and physiology. Astonishingly small changes of field intensity, direction and inclination obviously suffice to serve as magnetic map and compass factors. But still the neurobiological mechanisms and the magnetophysical principles of the underlying sensory processes are widely unknown. For the first time, we now offer a sound model of iron-mineral based magnetoreception in birds based on histological and physicochemical data from a dendritic system in the avian beak. Two different iron minerals, nanocrystals of magnetite and microsized crystals of maghemite, which are localized in subcellular compartments in nervous terminals (Fig.), enable each dendrite as the smallest sensory unit to sense only one direction of the magnetic field. The entire sensory system of the beak, with dendrites distinctly oriented in the three dimensions, could process this peripheral receptor information in the central nervous system to a magnetic map factor, the local field vector. Our concept of a highly sensitive magnetometer in the beak has been verified by mathematical simulations and matches several electrophysiological and behavioral experiments.