Bladder filling inhibits somatic spinal motoneurones.
OBJECTIVE
Despite evidence that the activation of visceral afferents modulates spinal motoneurone activity in humans the responsible circuits remain unclear. We investigated changes in spinal motoneurone excitability during bladder filling in 8 healthy subjects and in 8 patients with spinal cord lesions and 5 patients with multi-infarct encephalopathy.


METHODS
Spinal motoneurone excitability was studied by analysing changes in H-reflex, F-wave and motor-evoked potential (MEP) size recorded from the calf muscles under different bladder filling conditions.


RESULTS
In normal subjects, maximal bladder filling significantly suppressed the H-reflex, F-wave and MEPs; after bladder voiding these responses returned to normal. In patients with encephalopathy maximal bladder filling strongly reduced H-reflex size; similarly to normal subjects H-reflex returned to control value after bladder voiding. In patients with spinal cord lesions, activation of bladder afferents left the H-reflex unchanged.


CONCLUSIONS
These findings indicate that bladder distension induces post-synaptic inhibition of spinal motoneurones through a suprasegmental pathway, which is interrupted by rostral spinal cord lesions. This vesical-induced inhibition is probably mediated by the propriospinal system rather than by the diffuse noxious inhibitory control circuit.
Inghilleri
M
M
Dipartimento di Scienze Neurologiche, Viale dell'Università 30, 00185, Rome, Italy.
Carbone
A
A
Pedace
F
F
Conte
A
A
Frasca
V
V
Berardelli
A
A
Cruccu
G
G
Manfredi
M
M
D000328:Adult; D000368:Aged; D002544:Cerebral Infarction / Q000503:physiopathology; D004576:Electromyography; D019054:Evoked Potentials, Motor; D006181:H-Reflex; D006801:Humans; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology; D012016:Reference Values; D013116:Spinal Cord / Q000166:cytology / Q000502:physiology* / Q000503:physiopathology; D013118:Spinal Cord Diseases / Q000503:physiopathology; D001743:Urinary Bladder / Q000294:innervation / Q000502:physiology* / Q000503:physiopathology; D014554:Urination / Q000502:physiology