DIRECT PROJECTIONS FROM THE PERIAQUEDUCTAL GRAY TO THE PONTINE MICTURITION CENTER (M-REGION) - AN ANTEROGRADE AND RETROGRADE TRACING STUDY IN THE CAT

Micturition is a spino-bulbo-spinal reflex. The bulbospinal part of th is reflex is formed by the projections from the M-region, also called the pontine micturition center or Barrington's nucleus, to the pregang lionic parasympathetic motoneurons in the sacral cord innervating the bladder. In respect to the spine-bulbar part of the micturition reflex , our group recently showed that the sacral cord projections to the br ainstem terminate mainly in the periaqueductal gray (FAG). In this stu dy it was investigated whether the FAG might serve as a link between t he sacral cord and the hi-region, by examining the possible connection s using the tracers wheat germ-agglutin horseradish peroxidase and tri tiated leucine. The results demonstrate that a specific circumscribed rostrocaudally oriented cell group within the ventrolateral FAG and pa rts of the dorsomedial FAG project specifically to the M-region. A con cept is put forward in which specific parts of the FAG are involved in the control of micturition and that information concerning bladder fi lling is conveyed via the FAG to the M-region.