Excitability changes in sacral afferents innervating the urethra, perineumand hindlimb skin of the oat during micturition

1. Excitability changes in afferents innervating the urethra, perineum and hindlimb were measured in decerebrated cats during micturition and in respo nse to stimulation of lumbosacral afferents. Increases in excitability were interpreted as primary afferent depolarization (PAD) and decreases as prim ary afferent hyperpolarization. 2. Excitability increases were observed in 11 of 19 urethral. pudendal affe rents during micturition. Four of these 11 afferents showed an excitability increase during voiding. Seven of these showed a biphasic change with a de crease in excitability when sphincter activity resumed at the end of the vo id. Three of 19 afferents showed an excitability decrease during micturitio n and no change was detected in five afferents. 3. During micturition, the peak amplitude of urethral afferent-evoked excit atory postsynaptic potentials in seven of eight sphincter motoneurones was diminished to a mean of 36% of control values. 4. Eighty per cent of hindlimb cutaneous afferents and 50% of dorsal penile /clitoral and superficial perineal nerve afferents in the sacral cord showe d increased excitability during voiding. No excitability increases were mea sured in 13 hindlimb cutaneous fibres examined in the lumbar segments. 5. PAD was observed in sacral urethral, perineal and hindlimb cutaneous aff erents in response to electrical stimulation of other perineal, urethral, h indlimb cutaneous and group II muscle afferents. 6. It is concluded that control of transmission from urethral afferents by the micturition circuitry is different to that by sensory transmission from hindlimb and perineal regions during micturition. We hypothesize that more than one population of sacral PAD-mediating interneurones is involved.