Reflex stimulation of continuously oscillatory firing alpha and gamma-motoneurons in patients with spinal cord lesion.
Single nerve-fibre action potentials (APs) were recorded extracellularly from lower human sacral nerve roots, and simultaneous single-fibre impulse patterns of alpha and gamma-motoneurons and secondary muscle spindle afferents were analysed. Identified alpha and gamma-motoneurons fired oscillatory, due to the sustained stretch reflex of the external sphincters induced by an anal catheter (and, possibly, the bladder catheter). The motoneurons and the secondary muscle spindle afferents transiently synchronized their firing upon repetitive touch, pin-prick and dimpling stimulation of the perianal skin inside the anal reflex area, by reducing the duration of their oscillation period until resetting of the oscillation cycle. In one case, the anal reflex area extended approximately 6 cm laterally from the anus. The responses to pin-prick stimulation were different from those to touch stimulation in three aspects. Firstly, the response time till the shortening of the oscillation period was longer than the oscillation period (approximately 100 ms) for pin-prick, and it was shorter for touch. Second, the response to pain stimulus was longer (shortening of several oscillation periods) and stronger than for touch stimulation. Pin-prick stimulation reduced the oscillation period to between 5 and 40 ms (mean = 18 ms), and touch stimulation to between 8 and 28 ms (mean = 15 ms). Third, transient synchronization of afferents and efferents was most pronounced for pin-prick stimulation. The shortest latency following touch was approx. 10 ms when measuring from the afferent volley running in the direction of the spinal cord, and 30 ms when measuring from the beginning of the skin touch. It is discussed that repetitive touch stimulation reinforced the sustained stretch reflex of the anal sphincter which is possible with no network reorganization (variation of the same network state) and therefore fast, whereas repetitive pin-prick stimulation replaced the sustained stretch reflex by the protection reaction of the anal sphincter (change from one network state to a different one) which made time consuming network reorganization necessary. Different sacral reflexes were analysed by studying time-related activation changes of group conduction velocities in velocity distributions. During the reflex response to stretch of the external anal sphincter, the alpha 2-motoneurons (FR) (and the secondary muscle spindle afferents) were strongly activated whereas upon eliciting the bulbocavernosus reflex (squeezing of the glans penis) the alpha 3-motoneurons (S) were mainly activated. Sacral reflexes are discussed with respect to the organization and reorganization of preformated neuronal networks, and the synchronization of oscillatory firing networks is discussed with respect to the overlapping of synfire chains.
Schalow
G
G
Department of Clinical Research, Swiss Paraplegic Centre Nottwil, Switzerland.
Zäch
G A
GA
D000200:Action Potentials; D000344:Afferent Pathways / Q000503:physiopathology; D001003:Anal Canal / Q000294:innervation; D006801:Humans; D008959:Models, Neurological; D009046:Motor Neurons / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation; D009130:Muscle, Smooth / Q000294:innervation; D009412:Nerve Fibers / Q000502:physiology*; D009991:Oscillometry; D012018:Reflex / Q000502:physiology*; D012867:Skin / Q000294:innervation; D013119:Spinal Cord Injuries / Q000503:physiopathology*; D013126:Spinal Nerve Roots / Q000503:physiopathology; D013997:Time Factors; D001743:Urinary Bladder / Q000294:innervation