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 this reflex is formed by the projections from the M-region, also called the pontine micturition center or Barrington's nucleus, to the preganglionic 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 brainstem terminate mainly in the periaqueductal gray (FAG). In this study it was investigated whether the FAG might serve as a link between the sacral cord and the hi-region, by examining the possible connections using the tracers wheat germ-agglutin horseradish peroxidase and tritiated leucine. The results demonstrate that a specific circumscribed rostrocaudally oriented cell group within the ventrolateral FAG and parts of the dorsomedial FAG project specifically to the M-region. A concept is put forward in which specific parts of the FAG are involved in the control of micturition and that information concerning bladder filling is conveyed via the FAG to the M-region.