REFLEXES IN THE HIND LIMBS OF CATS AFTER TRANSECTION OF THE SPINAL CORD AT VARIOUS LEVELS

Abstract

In cats the spinal cord was transected at levels varying from L 6 to T 4. Varying amounts of time up to 23 days were allowed for recovery. De-capitate cats and acute spinal cats were also studied. The animals were studied while supported in a hammock with legs hanging pendent. Later, kymograph records were made of the responses in the isolated gastrocnemius and tibialis anterior muscles to stimulation of the ipsilateral and contralateral tibial nerves at the ankle with rapid faradic make and break shocks. With the animal supported in the hammock there was considerable extensor tonus which showed itself best when pressure was made against the pads of the toes in the position of the positive Stutz reaction. This reaction was as well developed after transections at L 3 as after transections at higher levels. Cats with transections at or above L 3 were able to bear the weight of the posterior part of the body on the hind legs for varying periods up to 3 min. The ipsilateral flexion reflex was obtained with great regularity in all animals with transection at L 5 or above. The crossed response was more variable. Crossed flexion was more often obtained than crossed extension. Sometimes lightly touching a foot would cause crossed extension and forcefully pinching the toes together would cause crossed flexion. Electrical stimulation of the tibial nerve at the ankle more often caused crossed flexion than crossed extension both in The intact leg and when the contractions of the tibialis anterior and gastrocnemius were recorded on the kymograph. In the crossed response there is a dilemma of reaction which makes these reflexes uncertain and difficult to obtain. This dilemma is just as pronounced after high as after low transections. The contraction of the tibialis anterior in response to ipsilateral stimulation of the tibial nerve is often followed by a prolonged rebound contraction of the gastrocnemius. The after discharge in this extensor rebound contraction may last for many seconds. A diagram of a reverberating neurone circuit is given which could be used to explain after discharge.