Structural Changes of the Urinary Bladder After Chronic Complete Spinal Cord Injury in Minipigs

PURPOSE The aim of this study was to determine the structural changes of the urinary bladder after chronic spinal cord injury (SCI) in minipigs with the primary focus on the analysis of urinary bladder wall proteins and their quantitative distribution. METHODS Seven Göttingen minipigs (adult, female) underwent a complete spinal cord transection. Follow-up time was 4 months during which the bladder was drained by frequent single catheterisation and data from the bladder diary and daily urine strip test were collected. Samples from the urinary bladder were taken, fixed in 4% paraformaldehyde and stained for histological analyses. Bladder wall thickness, single tissue quantities/distributions, types I and III collagen, and elastin quantifications were performed. Comparisons to healthy urinary bladder tissue of age-matched minipigs were performed for statistical analyses. RESULTS No urinary tract infections were observed in our SCI minipig collective during follow-up. A trend towards a reduction in bladder volumes and an increase in incontinence periods were seen. The bladder wall thickness significantly increased after chronic SCI. Furthermore, bladder wall composition was severely altered by a significant loss of smooth muscle tissue and a significant increase in connective tissue. Elastic fibres were reduced in number and altered in their structural appearance after SCI. Type I collagen was significantly increased, while type III collagen was significantly decreased after SCI. CONCLUSIONS Chronic SCI highlighted that the urinary bladder wall undergoes fibrotic events with reduced contractile and elastic properties due to changes of the bladder wall protein composition. These changes show in detail how SCI severely influences the urinary bladder wall composition and depicts the similarities between minipigs and humans.