Modulatory effects of intravesical P2X2/3 purinergic receptor inhibition on lower urinary tract electromyographic properties and voiding function of female rats with moderate or severe spinal cord injury

Abstract

Objectives To evaluate the role that intravesical P2X2/3 purinergic receptors (P2X2/3Rs) play in early and advanced neurogenic lower urinary tract (LUT) dysfunction after contusion spinal cord injury (SCI) in female rats. Materials and Methods Female Sprague‐Dawley rats received a thoracic Th8/Th9 spinal cord contusion with either force of 100 kDy (cN); moderate) or 150 kDy (cN; severe); Sham rats had no injury. Evaluations on urethane‐anesthetised rats were conducted at either 2 or 4 weeks after SCI. LUT electrical signals and changes in bladder pressure were simultaneously recorded using cystometry and a set of custom‐made flexible microelectrodes, before and after intravesical application of the P2X2/3R antagonist AF‐353 (10 μM), to determine the contribution of P2X2/3R‐mediated LUT modulation. Results Severe SCI significantly increased bladder contraction frequency, and reduced both bladder pressure amplitude and intraluminal‐pressure high‐frequency oscillations (IPHFO). Intravesical P2X2/3R inhibition did not modify bladder pressure or IPHFO in the Sham and moderate‐SCI rats, although did increase the intercontractile interval (ICI). At 2 weeks after SCI, the Sham and moderate‐SCI rats had significant LUT electromyographic activity during voiding, with a noticeable reduction in LUT electrical signals seen at 4 weeks after SCI. Intravesical inhibition of P2X2/3R increased the ICI in the Sham and moderate‐SCI rats at both time‐points, but had no effect on rats with severe SCI. The external urethral sphincter (EUS) showed strong and P2X2/3R‐independent electrical signals in the Sham and moderate‐SCI rats in the early SCI stage. At 4 weeks after SCI, the responsiveness of the EUS was significantly attenuated, independently of SCI intensity. Conclusions This study shows that electrophysiological properties of the LUT are progressively impaired depending on SCI intensity and that intravesical P2X2/3R inhibition can attenuate electrical activity in the neurogenic LUT at early, but not at semi‐chronic SCI. This translational study should be useful for planning clinical evaluations.

Choice of cystometric technique impacts detrusor contractile dynamics in wistar rats

“…Second, the closing pressure refers specifically to the pressure value at the moment of sphincter closure (concurrent with the end of bursting in the rat) (Cruz & Downie, 2005; Jin et al, 2014; Vera & Nadelhaft, 2001) which requires simultaneous EMG of the EUS. However, the pressure rise in the third phase of the micturition hits the higher value some seconds after EUS closure (Cheng et al, 1997; Cruz & Downie, 2005; Salazar et al, 2019).…”

Voiding Dysfunction in Old Male Rats Associated With Enlarged Prostate and Irregular Afferent-Triggered Reflex Responses

“…It is important to keep in mind that the sources for the EMG recordings from the bladder dome may include a combination of detrusor, innervation, and mechanical artifacts that may alter electrophysiological recordings. Although the source of the acquired EMG from the bladder dome remains unknown, the signals from the lower urinary tract are highly reproducible and persistently reflect voiding activity [8,13]. In this study, EMG responses were affected by AF-353 in MOR, which can be attributed to the fact that P2X3R play a fundamental role in the activity of sensory neurons [7], in turn attenuating the hyperexcited putative prostate-bladder reflex [23].…”

“…Although neither EMG nor CMG properties were restored to those observed in MYR, the overall number of nonvoiding events, indicative of bladder overactivity, improved in MOR. One reason for these differences may be that the intramuscular injections of AF-353 affected the activation of P2X3R in sensory neurons from dorsal root ganglia or spinal cord sensory neurons, making micturition effects less evident than is the case for intravenous injections or direct intravesical application, as observed in female rats with neurogenic bladder following semichronic spinal cord injury [8,14]. Nonetheless, it is important to keep in mind that P2X3R are also required for the activity of primary and sensory neurons involved in the micturition process [28].…”

“…After reaching the anesthetic plane, a midline abdominal incision was performed and a suprapubic catheter (PE-50) was sutured onto the bladder dome for intravesical infusion of saline solution and pressure sensing. Additionally, 1 custom-made stainless steel spring electrode (internal diameter = 0.457 mm) was placed on the bladder dome [8,13]. Abdominal muscles and skin were sutured in 2 layers after surgery.…”

“…Ionotropic P2X3 and P2X2/3 purinergic receptors (P2X3R) are hetero- or homo-trimer protein complexes that function as nonselective ion channels activated by adenosine triphosphate (ATP), and participate in afferent transmission of sensory stimuli in different tissues, including the lower urinary tract [ 7 , 8 ]. Due to the relevance of these receptors for nociception, various antagonists have been designed for pharmacological use in diseases related to pain, including AF-353, an antagonist able to block P2X3 and P2X2/3 receptors in the periphery and the central nervous system [ 9 ].…”