Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease, characterized by several randomly distributed focal lesions in the central nervous system (CNS) caused by a myelin-destructive auto-immune response, resulting in delayed and interrupted neuronal pathways. Of note, over 80% of MS patients have urinary symptoms as one of their earliest symptoms, which includes hesitancy, urgency, frequency, and incontinence, significantly affecting their quality of life. Studies in animal models of MS such as the EAE (experimental autoimmune encephalomyelitis) and CIE (coronavirus-induced encephalomyelitis) models have shown that inflammatory demyelination in the CNS causes voiding dysfunction (1,2), however, the effect of CNS demyelination independent of inflammation has not been studied. Although inflammation and demyelination in the CNS are two important factors that affect functional output in MS patients,  drugs that target the bladder receptors are the mainstay of oral pharmacotherapy for patients with MS-associated lower urinary tract dysfunction/symptoms (MS-LUTD/S), which are unfortunately not effective. To effectively address this, understanding the precise impact of CNS demyelination on urinary performance is essential since the micturition circuit regulating bladder function involves several regions of the CNS vulnerable to MS-associated demyelination insult. In this study, we seek to elucidate the impact of CNS demyelination on urinary performance using the cuprizone model, a classic mouse model used to study the effects of CNS demyelination and spontaneous remyelination.

C57Bl/6 mice were treated with dietary cuprizone (0.2% w/w) for four weeks to induce demyelination, after which one group was switched to normal diet for the next four weeks to recover from demyelination, while another group continued an additional four weeks of cuprizone treatment. Following this treatment paradigm, voiding spot assay, pressure/flow cystometry and bladder strip myography were performed to assess demyelination-induced differences in urinary performance.

Mice with cuprizone-induced demyelination develop aberrant bladder function characterized by significantly increased micturition frequencies and reduced urine volume per micturition, compared to their control littermates. Recovery from cuprizone diet rescues the phenotype. Interestingly, we did not observe any significant difference in the cystometric parameters between our treatment groups, as evaluated by cystometry under urethane anesthesia.

Cortical demyelination causes increased micturition frequency and reduced volume per micturition in mice, without the need for CNS inflammation. Based on our findings, we conclude that CNS demyelination results in urinary pathophysiology that is reversible upon remyelination. Since the brainstem reflex works similarly in untreated and cuprizone treated mice under urethane, the aberrance seen in the voiding spot assay could be attributed to cortical and corpus callosal demyelination due to cuprizone.

Our data represent a novel compelling connection and strong correlation between CNS myelination particularly cortical and corpus callosal myelination and cortical control of bladder function. Therapeutics aimed at increasing the remyelination potential of the CNS neurons offer the possibility of alleviating urinary dysfunction associated with MS and improving the quality of life in aging MS patients.

Ramasamy R, Smith PP. Animal modeling of lower urinary tract dysfunction associated with multiple sclerosis: Part I: Justification of the mouse model for MS research. Neurourol Urodyn. 2021 Mar 14. doi: 10.1002/nau.24649. Epub ahead of print. PMID: 33719097.
Ramasamy R, Smith PP. Animal modeling of lower urinary tract dysfunction associated with multiple sclerosis: PART 2: Mouse models for multiple sclerosis research. Neurourol Urodyn. 2021 Mar 19. doi: 10.1002/nau.24654. Epub ahead of print. PMID: 33739481.
Vega-Riquer JM, Mendez-Victoriano G, Morales-Luckie RA, Gonzalez-Perez O. Five Decades of Cuprizone, an Updated Model to Replicate Demyelinating Diseases. Curr Neuropharmacol. 2019;17(2):129-141. doi: 10.2174/1570159X15666170717120343. PMID: 28714395; PMCID: PMC6343207.