Abstract

In 23 unanesthetized spinal cats effects of PMP on spinal motor activities and afferent discharge of Group la fibers from muscle spindles and from a skin nerve were investigated repeatedly. Following low doses of PMP (5-15 mg/kg), polysynaptic reflex was selectively depressed with no change in the monosynaptic reflex. At higher doses (20-40 mg/kg) the monosynaptic reflex also was depressed. No difference in the effects could be observed between flexor and extensor motoneurones. The effects noted were observed both in cats with intact dorsal roots and in those in which both dorsal and ventral roots from L4 caudal had been cut bilaterally.

Random alpha motoneurone discharges decreased in frequency following administration of low doses of PMP (10-30 mg/kg).

Using intracellular microelectrode techniques action potentials of motoneurones as well as of interneurones could be shown to disappear in association with depression of EPSP following doses of PMP of 10-20 mg/kg.

At doses above 35 mg/kg in cats with intact dorsal roots there were decreases in the gumma discharge.

Afferent discharges of Group la fibers from muscle spindles decreased in frequency following doses of 20-40 mg/kg, but no appreciable change was observed in the afferent discharges of the sural nerve.

In 6 unanesthetized cats immobilized with flaxedil, doses of 5-30 mg/kg of PMP altered EEG arousal patterns in neocortex and hippocampus to patterns similar to those of sleep.