THE PONTINE MICTURITION CENTER PROJECTS TO SACRAL CORD GABA IMMUNOREACTIVE NEURONS IN THE CAT

Stimulation of the pontine micturition center (PMC) results in micturi tion, i.e. an immediate relaxation of the bladder sphincter and a cont raction of the detrusor muscle of the bladder. Earlier studies have sh own that the bladder contraction is brought about by a direct excitato ry pathway from the PMC to the parasympathetic bladder motoneurons in the sacral cord. How the PMC produces the inhibition of the bladder sp hincter is not known. The present study in two adult male cats demonst rates at the ultrastructural level a direct pathway from the PMC to th e dorsal gray commissure of the sacral cord. More than half (55%) of t hese terminals made contact with gamma amino butyric acid (GABA) immun oreactive neurons or somata, the others with non-GABA immunoreactive p rofiles. The PMC terminals contained many round vesicles, some dense c ored vesicles and exclusively asymmetric synaptic clefts, which corres pond with an excitatory pathway. A concept is put forward in which thi s pathway produces the relaxation of the bladder sphincter during mict urition. (C) 1997 Elsevier Science Ireland Ltd.