Long-Term Management and Monitoring of the Bladder After Spinal Cord Injury in a Rodent Model

Abstract

Spinal cord injury (SCI) is a complex clinical condition with a wide range of permanent functional and neurological consequences. A prime factor limiting the patient's quality of life (QoL) is difficulties in bladder function. Chronic animal models that help to develop novel therapeutic strategies are highly demanded, but their availability is scarce and frequently accompanied by substantial limitations. We want to provide our detailed protocols that allow full reproducibility of a novel model for investigating both the acute and chronic condition, and give transparency regarding challenges. The preclinical animal model of female rats with mid-thoracic SCI contusion and a permanently implanted urinary catheter allowed the measuring of bladder function repetitively. Over a period of six months, data were collected weekly from the same, conscious individuals. To our knowledge, this is the first study that obtained a clinically relevant urodynamic dataset seamlessly from the acute to the chronic phase in rats with SCI. The ability to generate a complete data set from one single individual, rather than requiring multiple subjects, has the potential to markedly reduce the number of experimental animals, eliminate group differences, and give more flexibility for therapeutic intervention. Future projects could also benefit from the described optimizations in animal care.

Keywords: 3R; animal model; neurogenic bladder; neurogenic lower urinary tract dysfunction (nLUTD); spinal cord injury (SCI).

Figure 1

(A) After contusion spinal cord injury (SCI), the rats experienced a comparable drop-down of locomotion on the BBB to a maximum score of one (mean of both hind limbs) one day post-injury (DPI). A plateau was observed at a maximum score of 11 at 29 DPI. The rats failed to achieve better functionality during the six-month follow-up period. Values shown are means ± standard deviation. (B) µCT scans of the spinal cords were used to visualize and quantify the damage to the spinal cord at the level of injury at Th8/Th9. Top: Volume rendering of the spinal cord. Bottom: Five curved longitudinal slices that were equally distributed relative to the width of the spinal cord to follow the actual geometry of the strongly distorted, injured spinal cord. The magenta lines in the volume rendering indicate the slice position of the single curved longitudinal slices. They are equally spaced along the width of the spinal cord. The clear healthy regions are indicated by green margins, injured tissue by yellow margins, and cyst formations represented in red. Scale bar: 2 mm. (C) Volume rendering of the spinal cord with five representative cross-sections at different locations relative to the lesion site. Scale bar: 1 mm. (D) Quantified values from the µCT images of the thoracic spinal cord revealed consistent and severe defects in all rats. Values are shown as means ± standard deviation.

Figure 2

(A) After contusion spinal cord injury (SCI), the rats lost about 10% of their body weight within the first two weeks post-injury (WPI), which they regained in two weeks’ time. Values shown are means ± standard deviation. (B) Bladder volumes did increase after SCI over the course of 24 WPI. From an average of about 1 mL shortly after the SCI, a volume in excess of 2 mL was noted during the second half of the follow-up period. Values shown are means ± standard deviation.

Figure 3

(A) Weekly urodynamic measurements in the conscious animals were scored based on patterns that resembled specific bladder functionality after contusion spinal cord injury (SCI). During continuous filling of the bladder at a rate of 120 µL/min, intravesical pressure (in mmHg) and voided urine (in grams) were recorded and displayed against time (in seconds). The highest score of four denoted normal micturition and the absence of non-voiding contractions (NVC), whereas a score of three was given in the presence of NVC. For visual purposes, the scale collecting the voided urine was reset to zero after each micturition. When only urine leakage was observable, but the detrusor was still active, this was assigned to a score of two. The lowest score of one denoted the least functionality and only urine leakage, with no visible detrusor activity. Shown measurements are representative and were not recorded in the same individual. (B) The rats showed a drastic drop-down in functionality during the first two weeks post-injury (WPI), but regained some functionality after about three weeks. Values shown are means ± standard deviation.