Myelin-associated neurite growth inhibitors: regulators of plastic changes of neural connections in the central nervous system

Botulinum Toxin Type A for Refractory Neurogenic Detrusor Overactivity in Spinal Cord Injured Patients in Singapore

Introduction: Managing neurogenic detrusor overactivity (NDO) successfully in spinal cord-injured patients is a challenge. The aims of preserving kidney function by achieving safe bladder pressures with anticholinergic medication often leave a significant proportion of patients with side effects. Botulinum toxin type A has been shown to be a promising alternative. Materials and Methods: Spinal cord injury patients who had NDO, on clean intermittent self-catheterisation, and were refractory to oral medications, were recruited. Three hundred units of botulinum toxin type A (Botox) in 30 mL NaCl solution were injected under cystoscopic guidance into the bladder. Results: Fifteen patients were recruited of whom 9 were tetraplegic and 6 were paraplegic. Eleven (73.3%) had complete injuries. There was a significant reduction in the mean number of leakages from 3.75 ± 1.79 pre-injection to 0.67 ± 1.31 and 1.5 ± 1.5 at 6 and 26 weeks post-injection, respectively (P <0.05). Seventy-five per cent, 37.5% and 50% were completely dry at 6, 26 and 39 weeks post-injection, respectively. The mean maximal catheterisable volume increased from 312.3 ± 145.6 mL pre-injection to 484.6 ± 190 mL, 422.3 ± 157.3 mL and 490.0 ± 230.4 mL at 6, 26 and 39 weeks post-injection, respectively (P <0.005). Maximum detrusor pressure decreased significantly from 66.3 ± 22.6 cmH2O to 21.2 ± 23.1 cmH2O and 33.6 ± 30.2 cmH2O at 6 and 26 weeks post-injection, respectively (P <0.05). The volume at which reflex detrusor contractions first occurred increased from 127.8 ± 57.5 mL pre-injury to 305.7 ± 130.8 mL at 6 weeks and 288.3 ± 13.0 mL at 26 weeks post-injection (P <0.05). Mean cysometric bladder capacity increased from 187.8 ± 69.2 mL to 305 ± 136.4 mL and 288.3 ± 13.0 mL at 6 and 26 weeks post- injury, respectively (P <0.05). Sixty per cent of patients were completely off medications at 6 and 26 weeks post-injection. One patient had urinary tract infection and 1 experienced autonomic dysreflexia during cystoscopy. Satisfaction levels increased from 4.3 ± 2.3 pre-injury to 7.2 ± 1.9 and 7.3 ± 2.3 at 6 weeks and 26 weeks, respectively. This also correlated with fewer leakages. Conclusion: Botulinum toxin type A injected into the detrusor is safe and efficacious for spinal cord injured patients with refractory detrusor overactivity. This effect is maintained at 26 weeks post-injection. Key words: Anticholinergics, Spinal cord injury, Urodynamics, Voiding

What is the optimum dose of type A botulinum toxin for treating neurogenic bladder overactivity?

OBJECTIVE

To assess the effects of two doses of botulinum toxin A (Dysport, Ipsen-Biotech, France; 500 and 1000 Speywood units, SU) injected into the bladder for treating incontinence due to a neurogenic overactive bladder.

PATIENTS AND METHODS

In an open-label, prospective study between October 2002 and May 2004, in two centres, we analysed the effects of successive doses of 500 and 1000 SU of Dysport, endoscopically injected into the detrusor muscle. At each step, patients (26 women and 19 men) were re-evaluated at 1 month (clinical evaluation and pressure-flow study). If there was a 'good' clinical response (complete absence of urinary leakage) the patient was observed until incontinence recurred; otherwise a further injection was administered at a higher dose.

RESULTS

The mean (sd, range) follow-up was 22 (0.75, 5-31) months; 11 of the 45 patients (24%) did not respond primarily at 1 month for both doses. The analysis of the two curves of survival with no re-injection of Dysport showed a statistically longer action at 1000 SU (P = 0.016). However, in this group there was one patient with general muscle weakness and asthenia, which could have been related to the injection.

CONCLUSIONS

The optimum dose of Dysport for incontinence secondary to a neurogenic overactive bladder is not yet defined; 1000 SU probably has a more prolonged effect than 500 SU but exposes the patient to major complications. Further studies evaluating the clinical effect of 750 SU of Dysport are necessary.

Lack of ultrastructural detrusor changes following endoscopic injection of botulinum toxin type a in overactive neurogenic bladder

INTRODUCTION

Endoscopical injections of Botulinum toxin type A into the detrusor muscle are gaining clinical acceptance in the treatment of neurogenic detrusor overactivity. Structural effects of Botulinum toxin type A are only known from studies on striated muscles, where a widespread nerve sprouting occurs temporarily. The aim of this study was to evaluate the ultrastructural effects of Botulinum toxin type A injections on the human detrusor.

MATERIAL AND METHODS

30 detrusor biopsies were obtained from 24 patients with neurogenic detrusor overactivity. Patients were divided into two groups: Group I included 13 biopsies from patients before the first Botulinum toxin type A injection. Group II included 6 biopsies from patients within 3 months after the first injection and 11 biopsies at the time of decreasing efficacy of Botulinum toxin type A. The biopsies were processed by standard procedure for detailed electron microscopic study and evaluated by 2 examiners without prior knowledge of clinical/urodynamic data.

RESULTS

No statistically significant detrusor changes have been found concerning muscle cell fascicle structure (p = 0.445), width of intercellular space (p = 0.482) and number/kind of muscle cell junctions (p = 0.443). A median of 70% of intrinsic axon terminals presented with signs of degeneration in group I, a median of 66% in group II (p = 0.840). Out of 309 evaluated axon terminals in both groups, 1 sprouting axon was found in group I, 3 sprouting axons in group II (p = 0.864). Specimen from group I and group II showed only limited collagen deposits within the detrusor. No changes in the ultrastructure of the detrusor have been observed in those biopsies obtained before and after the Botulinum toxin type A injection of the same patient.

CONCLUSION

This study verifies our earlier report of severe intrinsic axon degeneration in the detrusor of patients with neurogenic detrusor overactivity. It also shows nearly no structural differences of the detrusor before and after Botulinum toxin type A injections. Contrary to reports of striated muscle, axonal sprouting within the detrusor was very limited after Botulinum toxin type A injections indicating pathophysiologically different reactions to the toxin either between striated muscle and smooth muscle or between different treated diseases.

Increased lesion-induced sprouting of corticospinal fibres in the myelin-free rat spinal cord

Myelin contains potent inhibitors of neurite growth which have been implicated in the failure of long-distance regeneration of nerve fibres within the CNS. These myelin-associated neurite growth inhibitors may also be involved in the stabilization of neural connections by suppressing sprouting and fibre growth. After lesions of the CNS in neonatal animals, extensive rearrangements of the remaining fibre systems have been observed. In the rat, this plasticity of neuronal connections is severely restricted following the first few weeks of postnatal life, coincident with the progression of myelination of the nervous system. A well-studied example of postnatal plasticity is the sprouting of one corticospinal tract (CST) into the denervated half of the spinal cord after unilateral motor cortex or pyramidal lesions. In the hamster and rat, significant CST sprouting is restricted to the first 10 postnatal days. Here we show that very extensive sprouting of corticospinal fibres occurs after deafferentations as late as P21 if myelination is prevented by neonatal X-irradiation in the rat lumbar spinal cord. Sprouted fibres from the intact CST cross the midline and develop large terminal arbors in the denervated spinal cord, suggesting the establishment of synaptic connections. Our results suggest that myelin and its associated neurite growth inhibitors play an important role in the termination of neurite growth permissive periods during postnatal CNS development. Corticospinal sprouting subsequent to lesions early in life, i.e. in the absence of myelin-associated neurite growth inhibitors may explain the frequent occurrence of mirror movements in patients with hemiplegic cerebral palsy.

Lesion-induced plasticity of central neurons: sprouting of single fibres in the rat hippocampus after unilateral entorhinal cortex lesion

In response to a central nervous system trauma surviving neurons reorganize their connections and form new synapses that replace those lost by the lesion. A well established in vivo system for the analysis of this lesion-induced plasticity is the reorganization of the fascia dentata following unilateral entorhinal cortex lesions in rats. After general considerations of neuronal reorganization following a central nervous system trauma, this review focuses on the sprouting of single fibres in the rat hippocampus after entorhinal lesion and the molecular factors which may regulate this process. First, the connectivity of the fascia dentata in control animals is reviewed and previously unknown commissural fibers to the outer molecular layer and entorhinal fibres to the inner molecular layer are characterized. Second, sprouting of commissural and crossed entorhinal fibres after entorhinal cortex lesion is described. Single fibres sprout by forming additional collaterals, axonal extensions, boutons, and tangle-like axon formations. It is pointed out that the sprouting after entorhinal lesion mainly involves unlesioned fibre systems terminating within the layer of fibre degeneration and is therefore layer-specific. Third, molecular changes associated with axonal growth and synapse formation are considered. In this context, the role of adhesion molecules, glial cells, and neurotrophic factors for the sprouting process are discussed. Finally, an involvement of sprouting processes in the formation of neuritic plaques in Alzheimer's disease is reviewed and discussed with regard to the axonal tangle-like formations observed after entorhinal cortex lesion.