Preserved Adrenal Function After Lumbar Spinal Cord Transection Augments Low Pressure Bladder Activity in the Rat

Abstract

Spinal cord injury (SCI) disconnects supraspinal micturition centers from the lower urinary tract resulting in immediate and long-term changes in bladder structure and function. While cervical and high thoracic SCI have a greater range of systemic effects, clinical data suggest that those with lower (suprasacral) injuries develop poorer bladder outcomes. Here we assess the impact of SCI level on acute changes in bladder activity. We used two SCI models, T3 and L2 complete transections in male Wistar rats, and compared bladder pressure fluctuations to those of naïve and bladder-denervated animals. By 2 days after L2 transection, but not T3 transection or bladder denervation, small amplitude rhythmic contractions (1 mmHg, 0.06 Hz) were present at low intravesical pressures (<6 mmHg); these were still present 1 month following injury, and at 3 months, bladders from L2 SCI animals were significantly larger than those from T3 SCI or naïve animals. Low-pressure contractions were unaffected by blocking ganglionic signaling or bladder denervation at the time of measurements. L2 (and sham surgery) but not T3 transection preserves supraspinal adrenal control, and by ELISA we show lower plasma adrenal catecholamine concentration in the latter. When an adrenalectomy preceded the L2 transection, the aberrant low-pressure contractions more closely resembled those after T3 transection, indicating that the increased bladder activity after lumbar SCI is mediated by preserved adrenal function. Since ongoing low-pressure contractions may condition the detrusor and exacerbate detrusor-sphincter dyssynergia, moderating bladder catecholamine signaling may be a clinically viable intervention strategy.

Keywords: adrenal gland; bladder; catecholamines; non-voiding contractions; spinal cord injury.

FIGURE 1

Pressure changes during infusions and analysis of minima and amplitude of bladder contractions. (A) Representative pressure recording from a urethane anesthetized rat during bladder filling at a rate of 50 μl/min. (B) Amplitude of NVCs are significantly higher at mid (7–10 mmHg) and high (14–18 mmHg) vs. low (1–4 mmHg) intravesical pressure, mean ± SEM, repeated measures one-way ANOVA, p-values as shown. (C) Peak analysis is used to analyze the relationship between intravesical pressure and NVC amplitude. (D) The measured amplitudes are binned based on the intravesical pressure at their minima, the resulting bar graph for naïve animals is presented as an example.

FIGURE 2

Amplitude of NVCs is increased at low pressures after L2x. (A–C) Representative traces of intravesical bladder pressures after different injury levels in urethane anesthetized rats. (D) Amplitude of NVCs is significantly higher 2 days post-L2 transection (L2x) compared to 2 days post-T3 transection (T3x) and naïve controls; one-way ANOVA, mean ± SEM. (E,G) Representative traces of low intravesical bladder pressures of awake rats that are naïve or 2 days post-L2x. (F) The amplitude of NVCs in awake L2x animals is significantly higher than that in naïve animals, (H) with no difference in baseline intravesical pressures, t-tests, mean ± SEM. Exact p-values shown.

FIGURE 3

Increased amplitude of low-pressure contractions persist to 1-month post-L2x. (A–C) Increased NVC amplitude after L2x is still elevated at least 1 month post-injury compared to sham operated animals; unpaired t-test, mean ± SEM. (D) The baseline intravesical pressure at which the NVCs were measured at was not different between groups, one-way ANOVA (p = 0.5602). (E) Wet bladder weights differed significantly by 3 months post SCI (or sham injury) between all groups, one-way Welch’s ANOVA (p < 0.0001) followed by Games Howell post-test for unequally distributed data.

FIGURE 4

Larger amplitude NVCs at higher pressures are immediately reduced by L2 transection. (A,C) Example bladder pressures traces from one animal during 100 μl/min saline infusion either before (C) or 1 h after (D) L2 transection, ^∗indicates start of bladder voiding in naïve animal. (B) There is no difference in low pressure NVC amplitudes immediately following and up to 2 h after L2x, repeated measures ANOVA, p = 0.1939. Lines connect individual animals over the 2 h timeline. (D) Maximum amplitude of NVCs during infusions decreased upon transection of the L2 cord, Mann–Whitney two tailed test. Exact p-values shown.

FIGURE 5

Eliminating bladder innervation results in decreased large amplitude NVCs but does not eliminate the low pressure NVCs 2-days post-L2x. (A,B) NVCs from animals 2 days post-L2x were recorded before and after treatment with hexamethonium bromide (HexBr, A) or bilateral removal of the pelvic ganglia (B). Neither treatment affected the NVC amplitude at low pressures, paired t-tests, (A) p = 0.6042; (B) p = 0.3285. (C,D) Representative traces of intravesical pressures during bladder filling, 100 μl/min of saline in naïve animals (C) and 2 days post-bilateral pelvic ganglionectomy (PGx, D). (E) NVC amplitudes sorted into 1 mmHg bins based on intravesical pressure at NVC minima (see Figure 1). As pressure increases, NVC amplitude increases in naïve animals (C,E, n = 8) but higher amplitude NVCs are lost when bladder is denervated (D,E, n = 5). (F,G) NVC amplitudes at low pressures are not increased 2 days post-PGx (F) but the maximum NVC amplitude reached was significantly lower 2 days post-PGx (G), unpaired t-tests, exact p-values shown.

FIGURE 6

Relationship between amplitude of contractions and intravesical pressure after L2x is governed by adrenal function. (A–C) Representative traces of intravesical pressures during 100 μl/min[[Au Query: Please cite “Figure 6G” inside the text.]] of saline bladder filling 2-days after (A) L2x, (B) T3x and (C) AdxL2x. (D) The intravesical pressures at which the NVC amplitudes reach 1 mmHg for each injury group are plotted, amplitudes reach 1 mmHg at lower pressures 2 days post-L2x compared to naïve, T3x or AdxL2x; one-way ANOVA, Tukey’s multiple comparisons test, mean ± SEM, exact p-values shown. (E) NVC amplitudes sorted into 1 mmHg bins based on intravesical pressure at NVC minima (see Figure 1C) show elevated amplitudes at low pressures after L2x, but not after T3x or when an adrenalectomy is performed immediately prior to the L2x (AdxL2x). Black line in (E) shows mean naïve values from Figure 5E for reference. (F,G) Plasma concentrations of individual adrenal catecholamines were not significantly different between animals with preserved (pooled L2 sham and L2x), or lost (T3x) descending adrenal control 2 days after surgery. (H) However, overall relative total adrenal catecholamine concentration was significantly higher in animals with preserved adrenal function than in those with lost descending control (mean ± SEM, unpaired t-tests with Welch’s correction, exact p-values shown).