Functional deficits and morphological changes in the neurogenic bladder match the severity of spinal cord compression

Abstract

Following spinal cord injury (SCI), loss of spinal and supraspinal control results in desynchronisation of detrusor vesicae (parasympathicus) and external urethral sphincter (sympathicus) activity. Despite recovery of lower urinary tract function being a high priority in patients with SCI, effective treatment options are unavailable largely because mechanisms are poorly understood. We used a clinically relevant model of thoracic SCI compression injury in adult female Wistar rats and confirmed that lesion volumes following severe injuries were significantly greater compared to moderate injuries (p < 0.05). Between 1-9 weeks, we assessed recovery of bladder function as well as return of locomotor function using the Basso, Beattie and Bresnahan (BBB) score. Bladder morphometrics and overall intramural innervation patterns, as assessed with ß-III tubulin immunohistochemistry, were also examined. Despite variability, bladder function was significantly worse following severe compared to moderate compression injury (p < 0.05); furthermore, the degree of bladder and locomotor dysfunction were significantly correlated (r = 0.59; p < 0.05). In addition, at 9 weeks after SCI we saw significantly greater increases in bladder dry weight (p < 0.05) and wall thickness following severe compared to moderate injury as well as increases in intramural axon density (moderate: 3× normal values; severe 5×; both p < 0.05) that also correlated with injury severity (r = 0.89). The moderate and severe compression models show consistent and correlated deficits in bladder and locomotor function, as well as in gross anatomical and histopathological changes. Increased intramural innervation may contribute to neurogenic detrusor overactivity and suggests the use of therapeutic agents which block visceromotoric efferents.