Modulation of cutaneous and urethral afferent transmission during micturition in the decerebrate cat

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Buss, Robert R.
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This study examined the role of primary afferent depolarization (PAD), a phenomenon closely associated with presynaptic inhibition, of cutaneous and urethral afferent transmission as one mechanism contributing to reduced activity in excitatory pathways to striated urethral sphincter (EUS) motoneurones during micturition in the decerebrate cat. PAD was inferred by measuring changes in the electrical excitability of individual afferents within the dorsal horn of the spinal cord. PAD was observed in 21 of 30 cutaneous afferents (perineal and hindlimb) terminating in the rostral sacral segments of the spinal cord during micturition evoked by bladder distension or electrical stimulation of the pontine micturition centre. Cutaneous afferents terminating in the lower lumbar spinal cord (5 of 5) did not receive PAD during micturition. It is suggested that the PAD observed in sacral cutaneous afferents may be mediated by a previously described population of sacral PAD interneurones that were shown to give PAD to primary afferents entering the sacral spinal cord. The effects of electrical stimulation of urethral afferents in the sensory pudendal nerve were examined in isolation of cutaneous (i.e., dorsal penile) pudendal afferents. Excitability measurements showed that urethral afferents gave PAD to and received PAD from perineal and hindlimb cutaneous afferents. Stimulation of muscle afferents at group II but not group I strength was effective at producing PAD in urethral afferents. Stimulation of urSPud afferents evoked excitatory postsynaptic potentials in 7 of 7 EUS motoneurones. Intracellular recordings from two EUS motoneurones revealed that urethral-evoked excitatory postsynaptic potentials were depressed during micturition when there was no activity in the EUS ENG. (Abstract shortened by UMI.)