Classification, oscillatory and alternating oscillatory firing of alpha 1 (FF) and alpha 2-motoneurons (FR) in patients with spinal cord lesion.
Gen Physiol Biophys, (August 1996)Abstract
Single-nerve fibre action potentials (APs) were recorded extracellularly from sacral nerve roots of people with spinal cord lesion (patients with paraplegia). Single-fibre APs of certain fibres were identified by the conduction velocity and the AP waveform, and simultaneous impulse patterns were extracted from the summed impulse traffic and analysed with respect to spacio-temporal relationships. The velocity values of components of compound APs, induced by electrical nerve root stimulation or electrical intravesical stimulation, were similar to the group conduction velocity values obtained from single-nerve fibre APs of natural impulse traffic. When changing the root temperature in one case from 32 degrees C to 35.5 degrees C, the group conduction velocities changed in the following way: secondary muscle spindle afferents (SP2): 40 m/s (32 degrees C) to 50 m/s (35.5 degrees C); bladder stretch afferents (S1): 31.3 to 40 m/s; bladder tension afferents (ST): 25 to 33.8 m/s; mucosal afferents (M): 12.5 to 13.8 m/s; alpha 1:-; alpha 2-motoneurons: 40 to 50 m/s; alpha 3: 33 to 40 m/s. The group conduction velocities showed different temperature dependence apart from SP2 fibres and alpha 2-motoneurons, which were therefore used for calibration. The distance between two Pacinian corpuscle (PC) receptors in a sacral dermatome of one paraplegic patient was calculated to be approximately 20 mm. A similar distance between PC receptors was found in a brain-dead individual. Receptor densities seem therefore to remain unchanged following spinal cord lesion. Motoneurons fired irregularly repeatedly with impulse trains. In paraplegics the oscillation periods and the interspike intervals of the impulse trains varied much more than observed for brain-dead and normal individuals. Motoneurons could therefore not always be identified by their pattern of oscillatory firing. Alternating long and short oscillation periods (T) could be measured in an oscillatory firing alpha 1 (T = 125 ms) and alpha 2-motoneuron (T = 150 ms). In both cases the average difference between the alternating oscillation periods was 5 ms. Tremor, alternating long and short oscillation periods, cellular oscillator properties, and recurrent excitation and inhibition are discussed with respect to the oscillator theory of the functioning of the human central nervous system. Mathematical predictions from populations of interacting biological oscillators are compared to measurements on neuronal network data.