Postnatal Excitability Changes of the Ankle Monosynaptic Reflexes in the Cat

The effects of repetitive stimulation on the amplitude of ankle extensor and flexor mono synaptic reflexes were studied under various experimental conditions in high spinal cats during postnatal development. The extensor monosynaptic reflex elicited from a dorsal root at 1/9 sec decreases initially when the stimulus rate is increased to 2/sec. This depression increases with age and is more pronounced in the flexor monosynaptic pathway than in the extensor one in the newborn kitten. This latter observation and the demonstration of a subliminal fringe in the flexor motoneurone pool of the newborn kitten indicate an earlier maturation of the flexor monosynaptic pathway. In young kittens the extensor monosynaptic reflex decreases less with increasing rate of stimulation when elicited from a dorsal root than from a peripheral nerve. In older kittens the reverse is true. Prolonged stimulation reduces the differences between dorsal root and peripheral nerve stimulation. In young kittens prolonged dorsal root stimulation at 2/sec causes a decrease of the extensor monosynaptic response. In adult animals on the other hand it increases. The flexors show a passing increase and subsequent decrease in young kittens during prolonged stimulation and in the adult there is only a decrease. Nembuta® depresses the extensor monosynaptic potential and accentuates frequency‐dependent depression variably with age.