There are not a few patients with urinary urgency, detrusor overactivity (DO), bladder pain and so on associated with cystitis in the world. Some medications and invasive therapies have been established recently because of unmet needs in lower urinary tract dysfunction (LUTD) associated with cystitis. However, therapy for LUTD associated with cystitis has been limited yet because of adverse effect, insufficient effect and so on. Low-level laser therapy (LLLT) has been utilized for clinical practices such as relieving pain and inflammation. LLLT selectively controls the activity of the sensory nervous associated with A-delta and C fibers. In cystitis, hypersensitivity involving not only the afferent A-delta but also C fibers occurs and causes urinary urgency, DO and bladder pain. This study aimed to investigate the effect of LLLT on LUTD in cystitis model rats.

We prepared the rat cystitis model induced by intravesical 0.3% acetic acid infusion. Changes in micturition reflex parameters were compared among three groups: normal saline infusion with sham irradiation, acetic acid infusion with sham irradiation, and acetic acid infusion with laser irradiation. Irradiation was applied to the skin on each side of the L6 lumbosacral intervertebral foramen.

In the rat cystitis model groups, there was a significant decrease in the voiding interval and volume compared to the group receiving normal saline infusion. After sham or laser irradiation, only the group with laser irradiation showed a significant increase in voiding interval (217%, p=0.0002) and voiding volume (192%, p=0.0012) in the parameters of storage dysfunction. The basal pressure, intravesical pressure, and residual urine volume remained unchanged in all groups before and after irradiation.

This study indicates that LLLT may improve decrease in bladder capacity due to DO without impairing voiding function in a rat model of cystitis. The L6 lumbosacral nerve that projects to the bladder contains various nerve fibers, among which C and Ad fibers transmit the abnormal stimulated sensation of the bladder to the center during the storage phase and efferent B fibers control bladder contraction during the voiding phase. We consider that the selective control of the storage disorder resulting from the laser irradiation may be due to the selective inhibition of afferent C and A delta fibers, but not efferent B fibers.

In this study, we investigated the effect of LLLT on storage disorder and voiding function in rats with acetic acid-induced cystitis subjected to transcutaneous laser irradiation of the lumbosacral nerves. Laser irradiation resulted in a significant increase in voiding interval and voiding volume, suggesting that DO during the storage phase was improved by laser irradiation. Laser irradiation did not affect voiding function during the voiding phase. These results indicate that laser irradiation to the skin on each side of the lumbosacral intervertebral foramen improves storage disorder associated with DO without impairing voiding function in cystitis. LLLT may become a new device that improves LUTD associated with cystitis.