The Two Pontine Micturition Centers in the Cat are not Interconnected ; Implications for the Central Organization of Micturition

Abstract

In the cat the detrusor muscle of the urinary bladder is innervated by sacral cord parasympathetic preganglionic motoneurons in the intermediolateral cell column and the external urethral sphincter by motoneurons in the ventrolateral part of the nucleus of Onuf. Neurons coordinating the activity of the urinary bladder and the external urethral sphincter during micturition and urinary continence are not located in the sacral spinal cord, but in two pontine regions, the M (=medial)-region or pontine micturition center and the L (=lateral)-region or pontine storage center. The M-region excites the detrusor muscle of the bladder via direct projections to its parasympathetic preganglionic motoneurons, and inhibits the bladder sphincter via direct excitatory projections to the GABA interneurons, that in turn inhibit the bladder sphincter motoneurons. The L-region, via direct projections, excites the bladder sphincter motoneurons. The present study investigated whether there are interconnections between the Mand L-regions. If so, micturition is the result of a coordinated activity of the two pontine regions, if not, they control micturition and continence independently. Ten adult cats were injected with anteroand retrograde tracers. First, WGA-HRP was injected in the segments caudal S1 and S2 in order to delimit the Mand L-regions in the pons. In all cases with M-region injections anterogradely labeled fibers were found to the sacral intermediolateral cell column containing bladder motoneurons, but not to the nucleus of Onuf. In these cases no specific projections were found to either to the ipsilateral Lregion or to the contralateral Mand L-regions. In the cases with L-region injections a distinct projection of labeled fibers was found to the sacral nucleus of Onuf, but not to the sacral intermediolateral cell column. In the cases no specific projections was observed to either the ipsilateral M-region, or to the contralateral Mand L-regions. The results indicate that the M-region produces micturition via direct projections to the sacral cord, but not via an inhibitory projection to the L-region. The L-region has a continuous excitatory effect on the bladder sphincter, but does not influence the M-region. It is concluded that the Mand L-regions are two separate functional systems which act independently. INTRODUCTION Micturition depends on a coordinated action or synergy between the urinary bladder and the external urethral sphincter (EUS). When the bladder contracts, the EUS relaxes and micturition takes place. An opposite action is necessary during continence: the EUS is tonically contracted and the bladder is relaxed while it is slowly filled with urine. The motoneurons innervating the detrusor muscle of the bladder in the cat are the preganglionic parasympathetic neurons in the sacral cord intermediolateral cell column (IML; Morgan et al., 1979). The motoneurons of the EUS are located in the socalled nucleus of Onuf, in the cat located at the level S1-S2 (Sato et al., 1978).

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Cite this paper

@inproceedings{Blok1998TheTP, title={The Two Pontine Micturition Centers in the Cat are not Interconnected ; Implications for the Central Organization of Micturition}, author={Bertil F . M . Blok}, year={1998} }