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Keywords:

  • overactive bladder;
  • spinal cord injury;
  • purinergic receptor;
  • afferents;
  • electrophysiology

What's known on the subject? and What does the study add?

It is well known that urinary bladder sensation requires the activation by ATP of ionotropic purinergic P2X3/P2X2/3 receptors located in bladder afferent C-fibres. Furthermore, in rat models of neurogenic bladder hyperactivity the release of ATP from the bladder urothelium is greater than ATP release in neurally intact rats. Therefore, the activation of purinergic receptors in bladder sensory fibres seems to be a sentinel event for the development of bladder hyperactivity after spinal cord injury.

We found that inhibition of P2X3/P2X2/3 purinergic receptors decreased the frequency of sensory field potentials evoked by activation of bladder noxious pathways. At the same time, the pharmacological blockade of these receptors significantly decreased the frequency of non-voiding contractions in rats with neurogenic bladder hyperactivity. The present study uncovers sensory purinergic receptors as potential therapeutic targets to treat neurogenic bladder hyperactivity, especially when the release of ATP from the urothelium is elevated.

OBJECTIVE

  • • 
    To evaluate the role of bladder sensory purinergic P2X3 and P2X2/3 receptors on modulating the activity of lumbosacral neurones and urinary bladder contractions in vivo in normal or spinal cord-injured (SCI) rats with neurogenic bladder overactivity.

MATERIALS AND METHODS

  • • 
    SCI was induced in female rats by complete transection at T8–T9 and experiments were performed 4 weeks later, when bladder overactivity developed. Non-transected rats were used as controls (normal rats).
  • • 
    Neural activity was recorded in the dorsal horn of the spinal cord and field potentials were acquired in response to intravesical pressure steps via a suprapubic catheter. Field potentials were recorded under control conditions, after stimulation of bladder mucosal purinergic receptors with intravesical ATP (1 mm), and after intravenous injection of the P2X3/P2X2/3 antagonist AF-353 (10 mg/kg and 20 mg/kg).
  • • 
    Cystometry was performed in urethane-anaesthetised rats intravesically infused with saline. AF-353 (10 mg/kg) was systemically applied after baseline recordings; the rats also received a second dose of AF-353 (20 mg/kg). Changes in the frequency of voiding (VC) and non-voiding (NVC) contractions were evaluated.

RESULTS

  • • 
    SCI rats had significantly higher frequencies for field potentials and NVC than NL rats. Intravesical ATP increased field potential frequency in control but not SCI rats, while systemic AF-353 significantly reduced this parameter in both groups.
  • • 
    AF-353 also reduced the inter-contractile interval in control but not in SCI rats; however, the frequency of NVC in SCI rats was significantly reduced.

CONCLUSION

  • • 
    The P2X3/P2X2/3 receptors on bladder afferent nerves positively regulate sensory activity and NVCs in overactive bladders.