Carl Ludwig and the localization of the medullary vasomotor center: old and new concepts of the generation of sympathetic tone.

In Carl Ludwig's laboratories in Leipzig, P. Owsjannikow (1871) and C. Dittmar (1873) performed precise, histologically controlled lesioning experiments into the question of the location of the vasomotor center in the medulla oblongata. A small area in the ventrolateral parts of the medulla with its caudal border 3 mm cranial to the obex and an extension of 3-4 mm in cranial direction was described as the vasomotor area which has to be left intact for normal vasomotor tone and reflexes. This finding, ignored for more than 100 years, is the most precise description of what is known today as the location of spinally projecting sympatho-excitatory neurones, named the RVML region. Already in these early publications the question of the origin of basic vasomotor tone within these areas was raised and the possibilities of automaticity and reflexogenic input were discussed. Both possibilities are still valid today and under current investigation. A specific chemosensitivity of the RVLM neurones has been demonstrated during the recent decade and its role with regard to the generation of the sympathetic tone and the nervous control of the entire cardiovascular system is being discussed.