Investigation of image-guided in vivo irradiation on voiding patterns and bladder contractility in female mice.

Radiotherapy for pelvic malignancies impacts the bladder causing urinary symptoms in many patients. Preclinical models using image-guided irradiation enable investigation of the physiology underlying radiation-response in the bladder. We aimed to characterise voiding patterns and bladder contractility following image-guided irradiation of the mouse bladder. Bladders of adult, female mice were irradiated (IRR) with a single fraction (20 Gy) under cone beam computed tomography. Pre- and post-IRR, void spot assays of urination patterns were performed. Contractility of bladder strips was quantified with myography. At 2-weeks, 1-month and 2-months post-IRR, around 50% of mice exhibited increased void locations. At 2-weeks, 50% had increased void spot counts; moreover, the majority exhibited smaller mean and smaller maximum void spot volumes. In bladder strips, neurogenic-contractions were smaller at 2-weeks, independent of their voiding patterns. Some recovery of contraction-amplitude was noted up to 8-months. At 2-weeks, depolarization-contractions and carbachol-contractions were similar in non-IRR and IRR strips; however, ATP-contractions were smaller. Neurogenic-contractions, carbachol-contractions and ATP-contractions had similar sensitivity to the SK channel blocker, apamin. Neurogenic contractions had similar sensitivity to paxilline (BK) and TEA (pan-K+) in non-IRR and IRR tissue. Targeted bladder irradiation resulted in altered urination patterns in the acute post-IRR phase, coincident with reduced neurogenic-contractions which might limit voiding. The ability of the bladder to contract per se and the contribution of K+-channels to contractility was minimally impacted by irradiation. Whilst the underlying mechanisms of the observations require further investigation, the study demonstrates the application of image-guided irradiation for quantifying radiation-induced changes in mouse bladder.