The innervation of the urethra of the female cat

Abstract

The portion of the urethra of the female cat which lies between the urethralvesical junction and the external sphincter is a centrally coordinated adjunct to the total sphincter mechanism which plays an active role in integrated mictural function. Simultaneous recordings of pressure changes in the isolated bladder, urethra, and external sphincter show that the urethra relaxes in synchrony with the external sphincter when the bladder contracts as the result of an evoked mictural reflex. A physiological analysis of the afferent and efferent components of the innervation of the urethra indicates that the inhibitory nerve supply of the urethra, derived principally from the pelvic nerves, is supplemented by impulses mediated via the hypogastric nerves. In addition, the hypogastric nerves contribute excitatory fibers to the innervation of the urethra. The latter fibers are antagonistic to the pelvic nerves. Central integration of reflexes synergises the parasympathetic and sympathetic impulses which regulate urethral resistance. These data are derived by means of simultaneous recordings of pressure changes in the isolated bladder and urethra which occur in response to electrical stimulation of their afferent and efferent neural supply in high spinal (C2) preparations. A pharmacological analysis indicates that the inhibitory as well as excitatory fibers contributed to the innervation of the urethra by the hypogastric nerves are adrenergic. On the other hand, a question is raised concerning the possibility of the pelvic nerve inhibitory fibers being noncholinergic in nature. The tone of the urethra of the female cat is not dependent upon its parasympathetic and sympathetic innervation.