[Comparative characterization of the thermoregulatory activity of motor units in "spinal" and intact cats]

The functional features of motor units (MU) were studied in spinal (n = 26) and intact (n = 18) cats during thermoregulatory muscle activity (TMA). The spinal cats were demonstrated to retain the ability to generate TMA though MU activity was extremely irregular. Thus, the variability of interspike intervals (ISI) was 100 to 400 msec at firing rates of 1-10 imp per sec). Irregular patterns of MU activity were obtained in all the spinal cats while the stable firing of MU was found only in 30% of spinal cats. In contrary, all the intact cats demonstrated steady-state MU impulsing (ISI variability being less than 40-50 msec at firing rates of 5-15 imp per sec). Both in spinal and intact cats, TMA was found only in the flexor muscles, which elucidated the important role of flexor reflex in generating TMA. The investigation showed that the influence of supraspinal structures on the spinal cord is significant in TMA formation. On the other hand, the spinal cord is able to produce abortive TMA forms on the basis of flexor reflex.