Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic bladder inflammation characterized by the main symptoms of urinary frequency, urgency, and pelvic pain. The hypersensitivity of bladder afferent nerves is considered as a significant pathophysiologic mechanism in IC/PBS. It has been shown that serotonin (5-HT, 5-hydroxytryptamine) receptors are involved in the regulation of the micturition reflex, but the effect of 5-HT receptors on cystitis remains unknown. In this study, we utilized a rat model of interstitial cystitis induced by intraperitoneal injection of cyclophosphamide (CYP) to investigate the role of 5-HT receptors on cystitis.

Sprague Dawley female rats, aged 2-3 months, were randomly divided into control and experimental groups. Interstitial cystitis (IC) rat model was induced in the experimental group by intraperitoneal injection of CYP (75 mg/kg) on days 1, 4, and 7, and the normal control (NC) group was injected intraperitoneally with saline at the same time. Histological changes in the bladder of rats with cystitis were observed using hematoxylin-eosin (HE) staining. Western Blot (WB) and immunofluorescence were performed to analyze the expression of 5-HT1A, 5-HT2A, and 5-HT7 receptors in the dorsal root ganglion (DRG) of L6-S1 in two groups. Urodynamic tests were performed to observe the effects of intrathecal injection of different doses of 5-HT2A receptor agonist 25CN-BNOH or 5-HT2A receptor antagonist M100907 on micturition in NC and CYP-treated groups. Calcium influx of bladder sensory neurons induced by capsaicin and 25CN-BNOH were evaluated using calcium imaging. Additionally, differentially expressed genes in DRG were compared between two groups using mRNA sequencing.

Submucosal hemorrhage, edema, and inflammatory cell infiltration were observed in the bladder wall of cystitis rats by HE staining. The urodynamics of rats with CYP-induced cystitis showed decreased threshold pressure (TP), intercontraction interval (ICI) and bladder capacity (BC), and increased maximum voiding pressure (MVP). The 5-HT2A receptor was significantly upregulated in the bladder afferent neurons in CYP-induced cystitis rats among 5-HT1A, 5-HT2A and 5-HT7 receptors. Intrathecal administration of the 5-HT2A receptor agonist 25CN-NBOH decreased TP, ICI and BC in normal rats, but the effects were not observed in cystitis rats. In contrast, intrathecal administration of the 5-HT2A receptor antagonist M100907 increased TP, ICI and BC in cystitis rats. Neuronal calcium imaging of DRG showed increased intracellular calcium concentration induced by capsaicin or 25CN-NBOH in cystitis rats, and neuronal calcium influx was inhibited by M100907. The results of mRNA sequencing indicated that differentially expressed genes were enriched in inflammation-related pathways and cellular calcium homeostasis.

These findings suggest that the 5-HT2A receptor is involved in the hypersensitivity of bladder afferent neurons in CYP-induced cystitis, and M100907 could improve bladder overactivity and afferent neuron hypersensitivity in CYP-induced cystitis by inhibiting calcium influx in the afferent pathway.

The 5-HT2A receptor may be a potential therapeutic target for the treatment of IC/BPS.

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Continence 12S (2024) 101466
DOI: 10.1016/j.cont.2024.101466