Impact of prostatic radiation therapy on bladder contractility and innervation

Abstract

Aims: To determine the effect of prostatic radiation therapy (RT) on bladder contractility and morphology, and axon, or neuron profiles within the detrusor and major pelvic ganglia (MPG) in male rats.

Methods: Male Sprague-Dawley rats (8 weeks) received a single dose of prostatic RT (0 or 22 Gy). Bladders and MPG were collected 2- and 10-weeks post-RT. Detrusor contractile responses to carbachol and electrical field stimulation (EFS) were measured. Bladders were stained with Masson's trichrome, and antibodies for nonspecific neuronal marker, cholinergic nerve marker choline acetyltransferase (ChAT), and alpha-smooth muscle actin. MPG gene expression was assessed by quantitative polymerase chain reaction for ubiquitin carboxy-terminal hydrolase L1 (Uchl1) and Chat.

Results: At 2 weeks post-RT, bladder smooth muscle, detrusor cholinergic axon profiles, and MPG Chat gene expression were increased (p < .05), while carbachol and EFS-mediated contractions were decreased (p < .05). In contrast, at 10 weeks post-RT, nerve-mediated contractions were increased compared with control (p < .05), while bladder smooth muscle, detrusor cholinergic axon profiles, MPG Chat expression, and carbachol contractions had normalized. At both 2- and 10-weeks post-RT, there was no change in detrusor nonspecific axon profiles and MPG Uchl1 expression.

Conclusion: In a rat model, RT of the prostate and MPG was associated with early changes in MPG Chat gene expression, and bladder cholinergic axon profiles and smooth muscle content which resolved over time. After RT recovery, bladder contractility decreased early and increased by 10 weeks. Long-term changes to the MPG and increased bladder cholinergic axons may contribute to RT-induced bladder dysfunction in prostate cancer survivors.

Keywords: bladder dysfunction; pelvic ganglia; prostatic radiation; smooth muscle.

Figure 1.

Representative images from each group are shown of bladder cross sections stained with Masson’s trichrome. At 2 weeks post-RT, bladders had (A) increased detrusor smooth muscle area and (C) increased bladder to body weight ratio. At 10 weeks post-RT, (B) detrusor smooth muscle content and (D) bladder to body weight ratio were not different between groups. Data are mean ± SEM; *p<0.05 vs Control; n=10/group for bladder to body weight; n=5/group for histology.

Figure 2.

At 2 weeks post-RT, bladders had decreased contractile responses to (A) increasing concentrations of carbachol and (C) electrical field stimulation. Carbachol contractions (B) were unchanged 10 weeks following prostatic RT. Conversely, EFS-mediated contractions (D) were increased in RT bladders 10 weeks post-RT. Bladders 2 and 10-weeks post RT given atropine to inhibit EFS contractions (E-I) showed no significant difference, when compared to control not given the inhibitor. Data are mean ± SEM; *p<0.05 vs Control; n=10/group.

Figure 3.

Representative images of control and 2 or 10 weeks post-RT bladder tissues stained with beta-3 tubulin (TUJ1, red) to assess non-specific axon profiles, alpha smooth muscle actin (αSMA, green) and DAPI (blue) to identify nuclei. The number of non-specific axon profiles per high powered field were not significantly different at (A) 2 weeks post-RT or (B) 10 weeks post-RT when compared to respective control bladders. There was no change in non-specific nerve marker (Uchl1) gene expression compared to the controls (C,D). Data are mean ± SEM; n=5/group.

Figure 4.

Representative images of control and 2 or 10 weeks post-RT bladder tissues stained with choline acetyltransferase (ChAT, red) to assess non-specific axon profiles, alpha smooth muscle actin (αSMA, green) and DAPI (blue) to identify nuclei. (A) The number of cholinergic axon profiles per high powered field was unchanged 2 weeks post-RT, whereas (B) at 10 weeks post-RT, the number of cholinergic axon profiles were significantly increased. Cholinergic nerve marker (Chat) gene expression in the major pelvic ganglia was (C) increased 2 weeks post-RT and (D) decreased at 10 weeks post-RT. Data are mean ± SEM; *p<0.05 vs Control; n=5/group.