MONOSYNAPTIC AND POLYSYNAPTIC DRIVE OF OSCILLATORY FIRING ALPHA(1) (FF) AND ALPHA(2)-MOTONEURONS (FR) IN A PATIENT WITH SPINAL-CORD LESION

Single-nerve fibre action potentials (APs) were recorded extracellular ly from lower sacral nerve roots of patients with spinal cord lesions (paraplegics), and simultaneous single-fibre impulse patterns of alpha (1) (FF) and alpha(2)-motoneurons (FR) and primary and secondary muscl e spindle afferents were analyzed. An alpha(1)-motoneuron was activate d in a time-locked manner by a primary spindle afferent fibre to fire oscillatory with an oscillation period of 110 to 140 ms. The distribut ion width for the time-locking (phase) was approx. 3 ms, which is inte rpreted as monosynaptic activation. A phase-correlated firing of a sec ondary muscle spindle afferent fibre gave rise to an additional oscill ation period of the oscillatory firing alpha(1)-motoneuron, when the p rimary fibre ceased firing. The phase distribution width was approx. 8 0 ms, and therefore indicates polysynaptic drive. The drive of the osc illatory firing alpha(1)-motoneuron thus included a monosynaptic from a primary and a polysynaptic activation from a secondary muscle spindl e afferent fibre. An alpha(2)-motoneuron was simultaneously activated to fire oscillatory by a different secondary spindle afferent fibre. T he phase distribution width between them was approx. 120 ms, which ind icates polysynaptic drive. The <alpha(1) and alpha(2)-motoneurons fire d in the occasional firing mode and in the transient and continuous os cillatory firing mode. Upon touch, pin-prick and bladder and anal cath eter pulling, the alpha(1)-motoneuron changed its firing rate more qui ckly than did the alpha(1)-motoneuron. Thus, the alpha(1)-motoneuron f ired more dynamically than did the alpha(2)-motoneuron. Synchronous os cillatory firing of the alpha(1) and alpha(2)-motoneurons occurred tra nsiently during pin-pricking. It is discussed that transient synchroni zation of oscillatory firing motoneurons points to relative coordinati on of self-organized oscillatory firing motoneuronal networks to gener ate Locomotion and other intergrative functions. It is further discuss ed that loss of specific properties of spinal oscillators following sp inal cord lesion may give rise to pathologic synchronization, and in t his way to disorders in movement.