Recurrent and Antidromic Effects on the Monosynaptic Reflex during Postnatal Development in the Cat

The recurrent effects on the amplitude of the ankle extensor and flexor monosynaptic reflexes were studied at different rates of stimulation during postnatal development in high spinal cats. The recurrent + antidromic effects on the ankle extensor monosynaptic reflex were also in vestigated. Recurrent inhibition of extensors was observed in the youngest kittens but disappeared more or less during the first postnatal month to reappear during the first part of the Second month. At that time, recurrent inhibition of flexors also appeared as did recurrent facilitation. All recurrent effects were found to increase with stimulation frequency and, with the exception of the extensors during the first month, they also increased in both magnitude and duration with age, reaching adult values during the second postnatal month. It was concluded that the increased recurrent effects are partly due to a reduction of the excitability in the monosynaptic pathway, although a postnatal change in the recurrent effects per se can not be excluded. Recurrent + antidromic effects on the extensors were also found to increase in magnitude and duration with increasing age.