Nerve growth factor‐dependent hyperexcitability of capsaicin‐sensitive bladder afferent neurones in mice with spinal cord injury

Abstract

Nerve growth factor (NGF) has been implicated as an important mediator in the induction of C-fibre bladder afferent hyperexcitability, which contributes to the emergence of neurogenic lower urinary tract dysfunction after spinal cord injury (SCI). In this study, we determined whether NGF immunoneutralization using an anti-NGF antibody (NGF-Ab) normalizes the SCI-induced changes in electrophysiological properties of capsaicin-sensitive C-fibre bladder afferent neurones in female C57BL/6 mice. The spinal cord was transected at the Th8/Th9 level. Two weeks later, continuous administration of NGF-Ab (10 μg kg h , s.c. for 2 weeks) was started. Bladder afferent neurones were labelled with Fast-Blue (FB), a fluorescent retrograde tracer, injected into the bladder wall 3 weeks after SCI. Four weeks after SCI, freshly dissociated L6-S1 dorsal root ganglion neurones were prepared. Whole-cell patch-clamp recordings were then performed in FB-labelled neurones. After recording action potentials or voltage-gated K currents, the sensitivity of each neurone to capsaicin was evaluated. In capsaicin-sensitive FB-labelled neurones, SCI significantly reduced the spike threshold and increased the number of action potentials during membrane depolarization for 800 ms. These SCI-induced changes were reversed by NGF-Ab. Densities of slow-decaying A-type K (K ) and sustained delayed rectifier-type K currents were significantly reduced by SCI. The NGF-Ab treatment reversed the SCI-induced reduction in the K current density. These results indicate that NGF plays an important role in hyperexcitability of mouse capsaicin-sensitive C-fibre bladder afferent neurones attributable to a reduction in K channel activity. Thus, NGF-targeting therapies could be effective for treatment of afferent hyperexcitability and neurogenic lower urinary tract dysfunction after SCI.

Role of p38 MAP kinase signaling pathways in storage and voiding dysfunction in mice with spinal cord injury

“…Vizzard et al showed that the immunoreactivity of TrkA, which is a high‐affinity receptor for NGF, is predominantly expressed in C‐fiber afferent neurons and is increased in rat bladder afferent neurons after SCI . We recently reported that anti‐NGF antibody treatment in SCI mice reduced C‐fiber‐dependent NVCs during bladder filling and reduced hyperexcitability of TRPV1 positive, capsaicin‐sensitive C‐fiber bladder afferent neurons . It has also been reported that NGF‐activation of p38 MAPK increases the expression of TRPV1 receptor in DRG neurons .…”

“…13,14 We recently reported that anti-NGF antibody treatment in SCI mice reduced C-fiber-dependent NVCs during bladder filling and reduced hyperexcitability of TRPV1 positive, capsaicin-sensitive C-fiber bladder afferent neurons. 5,15,16 It has also been reported that NGF-activation of p38 MAPK increases the expression of TRPV1 receptor in DRG neurons. 8 Therefore, it is likely that p38 MAPK activation in bladder afferent pathways after SCI contributes to C-fiber afferent hyperexcitability at least in part via upregulation of TRPV1, leading to NVCs during the storage phase.…”

Effects of nerve growth factor neutralization on TRP channel expression in laser-captured bladder afferent neurons in mice with spinal cord injury

“…These results indicate that NGF plays an important role in the plasticity of TRP channel expression in bladder afferent neurons in SCI mice. We recently reported that anti-NGF Ab treatment, when administered using the same regimen as in this study, improved C-fiber-dependent DO, as indicated by a decrease in non-voiding contractions during bladder filling and the reduced hyperexcitability of capsaicin-sensitive C-fiber bladder afferent neurons in SCI mice [5, 11, 14]. Therefore, NGF-dependent changes in TRP channels, such as the changes in TRPV1, TRPC3, and TRPC6 found in this study, may contribute to the functional alterations of bladder function and bladder afferent activity that underlie SCI-induced DO.…”

“…In addition, because this study showed that anti-NGF Ab treatment normalized the expression of TRPV1, TRPC3, and TRPC6, but not TRPC1 in SCI mice, NGF might be less important for the regulation of TRPC1 expression in SCI. Furthermore, our recent study also demonstrated that NGF plays an important role in the hyperexcitability of capsaicin-sensitive bladder afferent neurons due to the reduction of slow-decaying A-type K + (KA) channel activity in SCI mice [11]. Taken together, these current and previous results provide evidence that NGF-targeting therapies could be effective for the treatment of SCI-induced bladder afferent hyperexcitability and DO via the normalization of ion channels activity, such as that of KA channels [11], and the expression of TRP channels such as TRPV1, TRPC3, and TRPC6.…”

“…Two weeks after SCI, an osmotic pump (#1002, Alzet Osmotic Pumps, Cupertino, CA) was placed subcutaneously under the skin on the back of the animal to continuously administer vehicle to the SI and the SCI groups and 10 μg/kg per hour of anti-NGF antibody (#L148M, Exalpha Biologicals Inc., Shirley, MA) to the SCI+NGF-Ab group for two weeks. The dosage of the antibody was determined according to previous studies [8, 11, 14] as well as our own preliminary experiments. Four weeks after SCI, the L6 DRG were removed fresh and stored at −80°C until use.…”