Bladder filling inhibits somatic spinal motoneurones

Area of Science:

• Neuroscience
• Physiology
• Urology

Background:

• Visceral afferent activation influences spinal motoneurone activity, but the underlying neural circuits are not fully understood.
• Investigating the impact of bladder distension on spinal circuits is crucial for understanding visceral-neuromuscular interactions.

Purpose of the Study:

• To elucidate the neural pathways responsible for modulating spinal motoneurone excitability during bladder filling.
• To compare the effects of bladder filling on spinal motoneurone excitability in healthy subjects and patients with neurological conditions.

Main Methods:

• Assessed spinal motoneurone excitability using H-reflex, F-wave, and motor-evoked potential (MEP) measurements in calf muscles.
• Recorded responses during various bladder filling conditions in healthy individuals, patients with spinal cord lesions, and patients with multi-infarct encephalopathy.

Main Results:

• Maximal bladder filling suppressed H-reflex, F-wave, and MEPs in healthy subjects, with responses normalizing after voiding.
• Bladder filling significantly reduced H-reflex in patients with encephalopathy, similar to healthy controls.
• Patients with spinal cord lesions showed no change in H-reflex during bladder filling, indicating a lesion-dependent effect.

Conclusions:

• Bladder distension induces post-synaptic inhibition of spinal motoneurones through a suprasegmental pathway.
• This pathway is interrupted by rostral spinal cord lesions.
• The findings suggest the propriospinal system mediates this vesical-induced inhibition, rather than diffuse noxious inhibitory control.