Neural Control of the Lower Urinary Tract

Abstract

This article summarizes anatomical, neurophysiological, pharmacological, and brain imaging studies in humans and animals that have provided insights into the neural circuitry and neurotransmitter mechanisms controlling the lower urinary tract. The functions of the lower urinary tract to store and periodically eliminate urine are regulated by a complex neural control system in the brain, spinal cord, and peripheral autonomic ganglia that coordinates the activity of smooth and striated muscles of the bladder and urethral outlet. The neural control of micturition is organized as a hierarchical system in which spinal storage mechanisms are in turn regulated by circuitry in the rostral brain stem that initiates reflex voiding. Input from the forebrain triggers voluntary voiding by modulating the brain stem circuitry. Many neural circuits controlling the lower urinary tract exhibit switch-like patterns of activity that turn on and off in an all-or-none manner. The major component of the micturition switching circuit is a spinobulbospinal parasympathetic reflex pathway that has essential connections in the periaqueductal gray and pontine micturition center. A computer model of this circuit that mimics the switching functions of the bladder and urethra at the onset of micturition is described. Micturition occurs involuntarily in infants and young children until the age of 3 to 5 years, after which it is regulated voluntarily. Diseases or injuries of the nervous system in adults can cause the re-emergence of involuntary micturition, leading to urinary incontinence. Neuroplasticity underlying these developmental and pathological changes in voiding function is discussed.

The sacral autonomic outflow: against premature oversimplification

“…The autonomic regulation of the pelvic organs is more complex, as far as the final pathways are concerned, than for other autonomic control systems such as the regulation of arterial blood pressure, body temperature, pupil diameter, etc. The minimal number of final autonomic pathways are two sacral ones and one lumbar one for the lower urinary tract [4], one pathway each of the lumbar and sacral autonomic outflows for the hindgut and one sacral pathway and two lumbar pathways for the reproductive organs [3]. On top of these is the lumbar vasoconstrictor pathway to the blood vessels in the pelvic viscera.…”

Sacral Neuromodulation for the Treatment of Urinary Bladder Dysfunction: Mechanism of Action and Future Directions

“…The afferent information from the bladder neck and urethra is conveyed via the pudendal and hypogastric nerves to the lumbosacral spinal cord [1,2]. These lower urinary tract afferents terminate on interneurons in the lateral aspect of the dorsal horn and in the intermediate zone of the lumbosacral cord.…”

“…These excitatory terminals contain the neurotransmitter glutamate [8]. The cholinergic parasympathetic preganglionic motoneurons send their axons to the postganglionic neurons in the bladder wall [2]. The descending pathway from the PMC makes also direct excitatory glutaminergic contact with inhibitory interneurons in the sacral intermediomedial cell column.…”

“…Urinary continence is controlled by the pontine continence center or L-region [1,2]. The pontine continence center continuously excites the EUS during continence (Figure 1).…”

<b>Noradrenergic effects in rat sacral autonomic nucleus using in vitro slice patch-clamp r</b><b>ecordings </b>

“…These neurons receive input from several brainstem nuclei and spinal interneurons. Retrograde tracers such as fast blue and fast DiI are frequently used to distinguish parasympathetic preganglionic neurons (PGNs) within the SPN, because the SPN also contains interneurons, which show similar membrane properties to the PGNs (6). Induced firing of retrogradely labeled SPN neurons in the rat shows several distinct properties (4,19).…”