The sensory outflow from the urethra: complex structural and functional interactions
4 May 2018
Antwerp University Hospital (UZA) - Auditorium Kinsbergen (route 12) - Wilrijkstraat 10 - 2650 Edegem
Prof S. De Wachter, Prof J. Gillespie & Prof Em J.-J. Wyndaele
PhD defence Monica Eggermont - Faculty of Medicine and Health Sciences
During normal storage and micturition the bladder and urethra work together as one functional unit. This coordinated activity of the LUT is regulated by a complex neural control system, which incorporates different spinal and supraspinal reflex pathways. The urethra has long been considered as a simple tube to guide urine outside the body. However, it becomes more and more apparent that urethral function is complex.
Studies have been undertaken to explore on the sensory outflow from the female rat urethra with the use of several functional and structural techniques, in order to provide a greater insight into the overall urethral function and the urethral afferents. A first study elaborates on the functional characteristics of single urethral afferents. In both the pelvic and pudendal nerve responsive single afferent units are identified and their response patterns are described. No association is found between the type of nerve and location of the response. This raises the possibility of different pelvic and pudendal receptor types with different signalling functions. Moreover, these results suggest the presence of regional differences along the urethra.
A re-evaluation and characterization of the structural urethral elements, afferent and efferent, is performed in a second study. These data have been correlated with functional urethral wall compliance data. A highly folded epithelium characterizes the proximal urethra. The mid urethra and distal urethra also show regional specializations with the presence of a luminal protrusion of smooth muscle and a distinct vascular plexus respectively. Measurements of the urethral wall compliance endorse the identified regional complexities. A third study describes the autonomic and sensory nerve distribution in the epithelium and lamina propria of the urethra. Large numbers of peptidergic, nitrergic and cholinergic nerve fibres are found close to the (sub)epithelium, revealing a highly complex and heterogeneous network of putative afferent fibres.
Further, regional differences are present. The immunohistochemical and morphological characteristics of an unknown identified peptidergic cell are explored in a last structural study, suggesting a potential sensory neuronal function. Their specific location further suggests a regional specialisation. Latter studies make it clear that the urethra is not a simple structure with a single function. The sensory urethral outflow is complex and regional sensory specialisations are present, which may be related to urethral function. The presence of a potential sensory neuron in the proximal urethra adds to this complexity. An appreciation of such diversity is critical to fully understand the functions of the urethra.