Bladder filling inhibits somatic spinal motoneurones M. Inghilleri a,b, * , A. Carbone c , F. Pedace a,b , A. Conte a , V. Frasca a , A. Berardelli a,b , G. Cruccu a,b , M. Manfredi a,b a Dipartimento di Scienze Neurologiche, Viale dell’Universita ` 30, 00185 Rome, Italy b Istituto Neuromed IRCCS, Pozzuoli, Italy c Dipartimento di Urologia, Universita ` di Roma, ‘La Sapienza’, Rome, Italy Accepted 10 September 2001 Abstract Objectives: 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 supraseg- mental 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. q 2001 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Motoneurone excitability; Bladder proprioception; H-reflex; Motor-evoked potential 1. Introduction The neuronal mechanisms activated during the filling and voiding phases of bladder function involve several struc- tures: somatic and autonomic peripheral pathways from and to the bladder, segmental spinal circuits and the supraspinal control centres (de Groat et al., 1981; Mc Mahon, 1986; de Groat, 1998). Urinary bladder control involves a continuous interaction between the central and peripheral nervous systems. Distension of the bladder leads to a gradual increase in pelvic nerve afferent firing, but initially evokes no pelvic nerve efferent firing; subse- quently, when the micturition threshold is reached, the effer- ent pathway is switched on (Habler et al., 1993) in an ‘all- or-nothing’ fashion. The micturition reflex is elicited by the activation of afferent unmyelinated C fibres and the finely myelinated A delta fibres of pelvic nerves connected to the slowly adapting mechano-receptors of the bladder wall (de Groat et al., 1982, 1998; Habler et al., 1993; Sengupta and Gebhart, 1994). Neurones that receive input from the urin- ary bladder (Fields et al., 1970; Milne et al., 1981) can be found in the dorsal horn cells connected to supraspinal structures controlling the micturition reflex (Mc Mahon and Morrison, 1982; de Groat et al., 1998; Blok and Holstege, 2000). The same neurones increase their firing rates as vesical pressure increases to a level that might be considered noxious. Urinary bladder distension in monkeys (Brennan et al., 1989), however, inhibits spino-thalamic tract cells (i.e. wide dynamic range, high threshold and high threshold inhibitory cells). It also depresses the activ- ities of most convergent neurones in rats (Cadden and Morrison, 1991). Other studies have demonstrated that blad- der distension or contraction in animals decreases respira- tory activity, probably by acting on the brainstem (Schondorf and Polosa, 1980; Gdovin et al., 1994). In this study we investigated the effects of urinary bladder filling on spinal motoneurone excitability in humans. In normal subjects, we assessed the soleus H-reflex changes under different bladder filling conditions. We recorded the muscle-evoked potentials after transcranial magnetic stimu- lation in normal subjects to see whether the effects are pre- Clinical Neurophysiology 112 (2001) 2255–2260 1388-2457/01/$ - see front matter q 2001 Elsevier Science Ireland Ltd. All rights reserved. PII: S1388-2457(01)00674-5 www.elsevier.com/locate/clinph * Corresponding author. Tel.: 139-6499-14131; fax: 139-6499-14302. CLINPH 2001574