Oscillatory firing of single human sphincteric alpha 2 and alpha 3-motoneurons reflexly activated for the continence of urinary bladder and rectum. Restoration of bladder function in paraplegia.

1. By recording with 2 pairs of wire electrodes from human sacral nerve roots (S3-S5) rhythmic as well as occasional firing was observed in alpha 2 and alpha 3-motoneurons in response to physiologic stimulation of the urinary bladder and the anal canal. The rhythmic firing consisted of periodically occurring impulse trains, most likely produced by true spinal oscillators which drove the motoneurons. 2. Alpha 2-motoneurons, innervating fast fatigue-resistant muscle fibres, were observed to fire with impulse trains of about 2 to 4 action potentials (Ap's). These impulse trains occurred every 110 to 170 msec (5-9 Hz). Alpha 3-motoneurons, innervating slow fatigue-resistant muscle fibres, fired about every 1400 msec (approximately 0.7 Hz) with impulse trains of about 11 to 60 Ap's. Alpha 1-motoneurons, innervating fast fatigue muscle fibres, and gamma-motoneurons were not observed in the continuous oscillatory firing mode. 3. Sphincteric motoneurons were observed most likely in the oscillatory firing mode in response to the sustained stretch (reflex) of the external and sphincter or to retrograde filling of the bladder (urethro-sphincteric guarding reflex), in order to preserve continence. A urethral sphincteric alpha 2-motoneuron increased its mean activity from 0.5 to 18 Ap's/sec during retrograde filling by changing its firing pattern from the occasional spike mode via the transient oscillatory firing mode to the continuous oscillatory mode. Up to a filling of the bladder of 500 ml the mean activity of the stretch receptors, measuring probably mural tension, increased roughly proportionally and the sphincteric motoneuron increased its activity to about 1 Ap/sec in the occasional spike mode. Up to 600 ml, the motoneuron responded in the transient oscillatory mode with mean activities of up to 5 Ap's/sec. With higher bladder fillings, the flow receptors afferents fired additionally, probably according to pressure symptoms, and the motoneuron switched into the continuous oscillatory firing mode and increased its activity up to 18 Ap's/sec at 700 ml. When the bladder was about 800 ml full, the stretch afferent activity decreased, the flow receptor activity increased strongly and the alpha 2-motoneuron activity decreased; the overflow incontinence had probably started. Micturition was not observed, probably because of brain death. 4. It is suggested that one adequate stimulus for an alpha 2-motoneuron of the external anal sphincter to jump into the oscillatory firing mode, was the activity from secondary spindle afferent (SP2) fibres from external anal sphincter muscle spindles.(ABSTRACT TRUNCATED AT 400 WORDS)