Noradrenergic agonists and locomotor training affect locomotor recovery after cord transection in adult cats.

In one series of experiments, the effects of noradrenergic, serotonergic, and dopaminergic precursors and agonists on the initiation of locomotion were investigated within the first week after complete spinalization at +13 in five adult cats. In addition, the effects of clonidine and daily locomotor training were investigated during the first week after transection in another cat. The electromyographic (EMG) activity of vastus lateralis (VL) and semitendinosus (St) was recorded bilaterally through percutaneously implanted copper wires in all cats. The movement of the hindlimbs on the treadmill was also simultaneously videorecorded before and after the injection of drugs. Without drug injection, strong and sustained perineal or abdominal stimulation did not induce any prolonged episodes of coordinated stepping on the treadmill during the first week after spinalization. St often had sustained activity, in contrast to VL, in which minimal or no activity was present. Injection of apomorphine (0.3 to 0.5 mg/kg, n = 3), a dopaminergic agonist, or DL-5-HTP (50 mg/kg, n = 2), a serotonergic precursor, failed to induce locomotion at such an early stage after spinalization. In contrast, injection of either L-dopa (50-60 mg/kg, n = 2), a noradrenergic precursor, or clonidine (150 micrograms/kg, n = 2), a noradrenergic agonist, induced locomotion on the treadmill. The animal demonstrated bilateral foot placement on the soles and complete weight support of the hindquarters. The spinal cat could follow the treadmill speed up to 0.80 ms-1. However, these effects disappeared when the NA drugs were tapered off.(ABSTRACT TRUNCATED AT 250 WORDS)