Proprioception in Extraocular Muscles of Mammals

The eyes are the most complex organs of the body and allow us to perceive objects in proper shape, color, and detail. Besides that, individuals know where objects are located in space and this is fundamental to precisely reach out for them or avoid obstacles. For the spatial localization of objects, the brain needs visual information from the retina and additional information in which direction the eyes are pointing. The eyes are moved by three pair of eye muscles. It is supposed that eye position information comes from special sensors (proprioceptors) in eye muscles. Surprisingly, classical proprioceptors are absent in eye muscles of most mammals and instead a specialized nerve ending, the so-called palisade ending is present. With the exception of rodents, palisade endings are regularly found in mammals including man. For many years there has been consensus that palisade endings are sensors providing the brain with eye position information. The sensory role of palisade endings was put into question when we showed that palisade endings exhibit molecular characteristics of motor terminals and originate from the motor nuclei in the brain stem. These novel findings have reopened the discussion about the function of palisade endings and it is still not clear whether they are sensory or motor. The present project will continue our investigations on palisade endings and will be done in international cooperation with the Profs. Angel Pastor and Rosa de la Cruz from the University of Seville. In one part of the project we will test whether the development of palisade endings is genetically programmed or influenced by external (epigenetic) factors. The core of the project is to analyze the function of palisade endings. Based on two hypotheses, we will test whether palisade endings have a sensory or motor function. For analyses we will use techniques which are currently state of the art and include molecular and electrophysiological experiments. Present findings will help to settle a long-lasting discussion about the function of palisade endings. Furthermore, palisade endings are also found in human EOMs and are destroyed in many surgical procedures to treat strabismus. Thus, knowledge of the functional significance of palisade endings would be of particular interest for strabismus surgeons.