Absence of hind limb tactile placing in spinal cats and kittens

Tactile placing and associated responses of the fore and hind paws to a light tactile stimulus were studied in normal young-adult cats and kittens and their spinal littermates. All spinal transections were performed at T12 on the 14th postnatal day. In the first study, responses of normal and spinal young-adult cats were compared at 9 to 10 months of age. Frequency of forelimb tactile placing (FL-TP) was similar for both groups, but hind limb tactile placing (HL-TP), seldom elicited in the normal cats, was never elicited in the spinal cats. Due to the absence of HL-TP in the spinal young-adult cats, a second study was conducted. Kittens, 1 to 62 days of age, were tested to determine if tactile placing was present prior to supraspinal maturation. The initial withdrawal response to the light tactile stimulus was equally developed in forelimbs and hind limbs at birth. In normal kittens, development of FL-TP preceded that of HL-TP by 2 weeks. During the first week after transection, forelimb responses of spinal kittens were more frequent than those of their normal littermates, suggesting an enhancement of motor responses proximal to the lesion, the difference decreasing thereafter. Frequency of hind limb withdrawal was not immediately altered after transection, and airstepping was easily triggered within 48 h after cordotomy. During tactile-triggered airstepping, the hind paw occasionally contacted the placing surface, but HL-TP was not observed in spinal kittens during the testing period. The absence of HL-TP in all spinal cats tested suggests that tactile placing is not a spinal reflex.