Acute urinary tract infection elicits bladder afferent hypersensitivity

Abstract

•We explored the neurophysiology underlying painful bladder sensations during UTI.•UTI induces significant bladder afferent hypersensitivity during distension.•Low-threshold afferents elicit exaggerated responses at normal bladder pressures.•Afferent hypersensitivity correlated with the development of bladder dysfunction.•Bladder afferents are key regulators of sensory and behavioural responses to UTI.

Keywords: Afferent; Bladder; Cystitis; Lower urinary tract symptoms; Urinary tract infection; Uropathogenic E. coli.

Fig. 1

UPEC infection alters bladder voiding patterns and increases bladder afferent mechanosensitivity to distension. (A) Bacteria was detected in the urine (CFU/μl) and bladders (CFU/bladder) of mice 24hrs after UPEC instillation but not 1X PBS (Sham) into the bladder (n = 5–30). Black dash line represents limit of detection. (B) Immune cell phenotyping from bladders of sham (N = 8) and UPEC-treated (N = 5) mice revealed a significant increase in CD45⁺ cells in bladders from UPEC mice compared to Sham. Bladder function in sham and UPEC mice was assessed by void spot assay over 3hrs (C). (Ci) UPEC mice exhibit a significant increase in the total number of void spots compared to Sham (N = 13, ∗p < 0.05, unpaired t-test), a significant increase in small sized urine spots based on pixel density (small; 500-100,000, large; >100,000 pixels (Cii) (N = 13, ∗∗p < 0.01, two-way ANOVA), and (Ciii) an increase in total urine area (N = 13, ∗p < 0.05, unpaired t-test). (Civ-v) Representative examples of filter paper used to collect urine from Sham and UPEC mice following visualisation with a UV transilluminator. (D) Ex vivo bladder nerve recordings were performed during bladder distension (0–50 mmHg) with saline in sham and UPEC mice. (Di) Peak mechanosensitive afferent responses to distension are significantly increased during UPEC infection (N = 4–5, ∗∗∗p < 0.001, unpaired t-test). (Dii) Bladder afferents exhibit significant hypersensitivity to distension during bladder distension (N = 4–5 mice: Sham vs UPEC ∗∗∗P < 0.001, two-way ANOVA. Sidak multiple comparisons at each pressure: ∗P < 0.05, ^$P < 0.01, ^#P < 0.001). ANOVA – analysis of variance. Dash-line in Bii represents peak firing rate of afferents in Sham mice.

Fig. 2

Low- but not high-threshold mechanosensitive bladder afferents are sensitised during UPEC infection. Based on activation threshold during bladder distension, bladder afferents were classified as either low-threshold (LT) or high-threshold (HT). (Ai) UPEC infection significantly enhances low-threshold (LT) mechanosensory responses to distension (Sham (n = 76) vs UTI (n = 51) ∗∗∗P < 0.001, two-way ANOVA. Sidak multiple comparisons at each pressure: ∗P < 0.05, ^#P < 0.01, ^$P < 0.001). Experimental trace of single LT mechanosensory afferents from Sham (Aii) and UPEC (Aiii) mice during bladder distension (0–50 mm Hg). (Aiv) Peak mechanosensory response to distension in LT afferents was significantly enhanced during UPEC infection (Sham (13.70 ± 0.49) vs UPEC (15.90 ± 0.81) ∗P < 0.05). (Av) Total area under the curve (AUC) of LT mechanosensory afferent response to distension was significantly enhanced during UPEC infection (Sham (151.8 ± 7.5) vs UPEC (204 ± 13.2) ∗∗∗P < 0.01). (Bi) UPEC infection had no impact on high-threshold (HT) mechanosensory responses to distension (Sham (n = 6) vs UPEC (n = 6) ^ns P > 0.05, two-way ANOVA. Sidak multiple comparisons at each pressure. Experimental trace of single HT mechanosensory afferents from Sham (Bii) and UPEC (Biii) mice during bladder distension (0–50 mm Hg). (Biv) Peak mechanosensory response to distension in HT afferents was unchanged during UPEC infection (Sham (10.5 ± 1.02) vs UPEC (11.83 ± 1.47) ^nsP > 0.05). (Bv) Total area under the curve (AUC) of HT mechanosensory afferent response to distension was unchanged during UPEC infection (Sham (92 ± 6.11) vs UPEC (107 ± 16.01) ^nsP > 0.05). ANOVA – analysis of variance. Dash-line in Ai represents peak firing rate of LT afferents in Sham mice.