Neural Networks, the Brain Pontine Micturition Center and Bladder Control

A significant component of lower urinary tract symptoms (LUTS) is due to failure of nervous control of bladder function, or otherwise failure of neural pathways to compensate for bladder dysfunction. It remains however unclear how the brain controls bladder filling and voiding and how the micturition reflex is inhibited at times when voiding is undesirable. Prior studies have shown that the pontine micturition center (PMC, aka Barrington's nucleus) directly controls voiding. PMC neurons provide innervation of sacral spinal cord nuclei that control bladder contraction and sphincter relaxation. Here we identify the neurochemical identity of PMC neurons that contribute to micturition control and we identify a network of afferent neurons, which directly modulates these PMC neurons to initiate voiding behavior. Micro‐injections of adeno‐associated viruses (AAVs), modified Rabies virus, Cholera Toxin b (CTb) or Diphtheria Toxin a (DTA), were placed into anatomically defined regions of the mouse brain, enabling highly selective expression of proteins in target neuron populations. A novel non‐invasive voidspot assay; micturition video thermography (MVT) was used to track voiding behavior in awake‐behaving mice. MVT was combined with cystometry (CMG) recordings of bladder pressure, chemo‐ and optogenetic stimulation and in vivo fiber photometry. Activating PMC neurons and select nearby populations using Gq DREADDs, changes micturition behaviors. Optogenetically stimulating specific subpopulations of PMC neurons triggered time‐locked void responses. Conversely, selective ablation of neurons in the PMC using diphtheria toxin A resulted in urinary retention, and delayed or eliminated the voiding reflex on CMG. To identify the input connections controlling PMC neurons, we used CTb and modified Rabies virus. To test the functional consequence of afferent neuron activity, we light‐stimulated their axon terminals within the PMC and observed micturition events within seconds (excitatory afferents) or increased inter‐void intervals (inhibitory afferents). Finally, we recorded Ca 2+ ‐dependent fluorescence changes in distinct neuron populations to study the timing of neuronal activity with respect to detrusor contraction and voiding. We found that specific subpopulations have distinct activity patterns that may drive particular aspects of bladder control. Our results taken together, identify a network of neurons that can control urinary voiding and continence by acting on PMC neurons. We demonstrate facilitatory roles of periaqueductal grey (PAG) and hypothalamic afferents, for voiding and modulating continence. We will further explore the heterogeneity of neurons within the PMC. This information helps us with a detailed understanding of how forebrain, brainstem and spinal inputs converge to control bladder filling and voiding, and hence the neurologic mechanisms of LUTS in mice and humans. As we define the brain pathways controlling normal micturition, we will evaluate how they are altered in settings of abnormal micturition, such as brain degeneration and prostatic enlargement. Support or Funding Information NIH/NIDDK: P20 DK119789, R01 DK113030, P20 DK108276 This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .