Roland Brandt

Institute of Neurobiology, University of Heidelberg, INF 364, 69120 Heidelberg, Germany.

Received 05/21/96; Accepted 07/05/96; On-line 08/01/96

The author thanks Thorsten Maas for providing figure 1, Tommy Jackson for critically reading the manuscript, and Alan Summerfield for excellent photographic assistance. This work was supported by a habilitation fellowship from the Deutsche Forschungsgemeinschaft.