Characterization of bladder and external urethral activity in mice with or without spinal cord injury—a comparison study with rats

Abstract

To clarify the lower urinary tract function in mice, we compared bladder and urethral activity between rats and mice with or without spinal cord injury (SCI). Female Sprague-Dawley rats and C57BL/6N mice were divided into five groups:1) spinal intact (SI) rats,2) SI mice,3) pudendal nerve transection (PNT) SI mice,4) spinal cord injury (SCI) rats, and 5) SCI mice. Continuous cystometry (CMG) and external urethral sphincter (EUS)-electromyogram (EMG) analyses were conducted under an awake, restrained condition. During voiding bladder contractions, SI animals exhibited EUS bursting with alternating active and silent periods, which, in rats but not mice, coincided with small-amplitude intravesical pressure oscillations in CMG recordings. In SI mice with bursting-like EUS activity, the duration of active periods was significantly shorter by 46% (32 ± 5 ms) compared with SI rats (59 ± 9 ms). In PNT-SI mice, there were no significant differences in any of cystometric parameters compared with SI mice. In SCI rats, fluid elimination from the urethra and the EUS bursting occurred during small-amplitude intravesical pressure oscillations. However, SCI mice did not exhibit clear EUS bursting activity or intravesical pressure oscillations but rather exhibited intermittent voiding with slow large-amplitude reductions in intravesical pressure, which occurred during periods of reduced EUS activity. These results indicate that EUS pumping activity is essential for generating efficient voiding in rats with or without spinal cord injury. However, EUS bursting activity is not required for efficient voiding in SI mice and does not reemerge in SCI mice in which inefficient voiding occurs during periods of reduced tonic EUS activity.

Morphological changes in different populations of bladder afferent neurons detected by herpes simplex virus (HSV) vectors with cell-type-specific promoters in mice with spinal cord injury

“…Thus, it is possible that the contribution of A-fiber bladder afferents to SCI-induced lower urinary tract (LUT) dysfunction might be different between mice and rats. In this regard, we recently reported that the behavior of EUS during the voiding reflex, which is still dependent on capsaicin-insensitive A-fiber afferents after SCI (Cheng and de Groat, 2004), is quite different in rats and mice (Kadekawa et al, 2016) although C-fiber dependent NDO during urine storage is similarly observed between these two species after SCI (McCarthy et al, 2009; Wada et al, 2017). In SCI rats, EUS bursting occurs during voiding bladder contractions, which coincides with small-amplitude IVP oscillations during cystometry.…”

“…In SCI rats, EUS bursting occurs during voiding bladder contractions, which coincides with small-amplitude IVP oscillations during cystometry. Furthermore, α-bungarotoxin, a neuromuscular blocking agent, reduces voiding by suppressing EUS bursting activity, which is also necessary for efficient urine elimination in normal rats (Yoshiyama et al, 2000), indicating that EUS bursting activity recovers after SCI in rats and is able to induce relatively efficient voiding (Kadekawa et al, 2016). However, SCI mice do not exhibit clear EUS bursting or IVP oscillations during voiding, but rather exhibit periods of reduced EUS activity during voiding accompanied by a slowly developing large-amplitude reduction in IVP (Kadekawa et al, 2016).…”

“…Furthermore, α-bungarotoxin, a neuromuscular blocking agent, reduces voiding by suppressing EUS bursting activity, which is also necessary for efficient urine elimination in normal rats (Yoshiyama et al, 2000), indicating that EUS bursting activity recovers after SCI in rats and is able to induce relatively efficient voiding (Kadekawa et al, 2016). However, SCI mice do not exhibit clear EUS bursting or IVP oscillations during voiding, but rather exhibit periods of reduced EUS activity during voiding accompanied by a slowly developing large-amplitude reduction in IVP (Kadekawa et al, 2016). These differences in voiding between SCI mice and rats might be related to a difference in the post-SCI changes of neurofilament-expressing bladder afferent neurons in the L6 DRG between the two species and in turn a difference in A-fiber-dependent reflex activity during voiding although further studies are needed to clarify this point…”

“…A total of 24 8–9 week-old female C57BL/6N mice (Envigo, Frederick, MD) weighing 18–20 g were used, and SCI mice underwent complete transection of Th8/9 spinal cord after induction of anesthesia by intraperitoneal (i.p.) injection of pentobarbital (50 mg/kg), according to the methods described previously (McCarthy et al, 2009; Ikeda et al, 2012; Kadekawa et al, 2016). SCI animals were treated with ampicillin (100 mg/kg, subcutaneously) for 5 days post-SCI and this treatment was continued twice a week afterwards.…”

“…Therefore, this study was performed using a mouse model of SCI (Kadekawa et al, 2016) to examine the morphological and molecular changes across various populations of hypogastric and pelvic bladder afferent neurons following SCI. For this purpose, we utilized a novel tracing and labeling approach utilizing replication-deficient herpes simplex virus (HSV) vectors, which encoded the mCherry reporter gene product driven by a non-specific promoter (cytomegalovirus [CMV]) and three different neuronal cell type-specific promoters, including CGRP, neurofilament-200 (NF200) and TRPV1, which are able to express the mCherry protein in non-selective CGRP- expressing C-fiber, NF200-expressing A-fiber, and TRPV1-expressing bladder afferent neurons, respectively.…”