Spinal oscillators in man under normal and pathologic conditions

1. Single-fibre action potentials (APs) were recorded from lower sacral nerve roots of brain-dead humans (HTs) and two paraplegics with thoracical spinal cord lesions. Impulse patterns of single oscillatory firing alpha 2 and alpha 3-motoneurons were identified and analysed. An alpha 2-motoneuron fired typically with 3 AP impulse trains every 160 msec. 2. In stable spinal oscillators of HTs the oscillation period was 70 msec plus 30 msec times the number of APs per impulse train; the respective values in paraplegics were 35 msec plus 40 msec times the number of APs per impulse train. These linear relationships indicate that spinal oscillators consist of at least 2 kinds of nerve cells. 3. Successive interspike intervals (IIs) of the impulse trains increased from about 3.5 msec to over 10 msec in paraplegics similarly as was the case in HTs. 4. The distributions of the first IIs (of impulse trains) and of the oscillation period of unstable continuously oscillatory firing alpha 2-motoneuron showed similar peaks. By relating the peak values of the first II and the oscillation period, a shortest II of 3.5 msec was obtained in a HT and a paraplegic, and a shortest oscillation period of 70 msec was measured in a HT and 40 msec in a paraplegic. The derivation of the shortest II of 3.5 msec from the oscillation itself is taken as an indication for alpha 2-motoneurons being included in the spinal oscillator function, since the shortest soma-dendritic spike intervals of motoneurons is expected to be 3.5 msec. 5. The spinal oscillator of a paraplegic showed more and higher activity changes than that in a HT as if spinal oscillators in paraplegics were insufficiently damped. 6. By interpreting the peaks in oscillation period distributions of unstable oscillators as being different oscillation loop pathways, it is speculated that the oscillators consist of the motoneuron, to which different interneuron pathways are connected. A contrasting of pathways with increasing excitation of the oscillator was observed. 7. The comparison of possible loop pathways of oscillation between paraplegics and HTs (closer to normal) indicates that the loss of descending tracts in paraplegics and the adaptation to it result in an increase of the oscillation pathways for alpha 2-oscillators from 1 to 3 in HTs to up to 6 in paraplegics. 8. Different measured and theoretically predictable spinal alpha 2-oscillators can cover altogether a frequency range between 5 and 10 Hz.(ABSTRACT TRUNCATED AT 400 WORDS)