Conduction in descending spinal pathways initiated by somatosympathetic reflexes

In anesthetized, paralyzed cats, the effects of stimulation at the dorsolateral sulcus (DLS) of the spinal cord at the C8 segment were recorded from the T2 white ramus. Stimulation of the DLS at the C8 segment produced evoked responses which had average conduction latencies of 13.3, 25.8, and 43.4 ms and were designated as the early, intermediate, and late response, respectively. Intermediate and late evoked responses were also recorded when the contralateral funiculus, the third or late evoked response was abolished or greatly attenuated, but the intermediate response was still observed although it was diminished in amplitude. The early evoked response was usually observed with stimulation at the ipsilateral C8 segment following placement of the lesion. These data suggest that afferent impulses, which ascend to supraspinal segments of the central nervous system, are transmitted to preganglionic neurons of the sympathetic nervous system through descending pathways in the dorsolateral funiculus of the spinal cord. Stimulation of afferent fibers on the ipsilateral or contralateral side of the spinal cord produces volleys which ascend unilaterally and descend bilaterally to preganglionic neurons. The pathways producing the intermediate evoked response, which was still observed after an ipsilateral lesion was made in the spinal cord, may include both the ascending pathway and other connections with the preganglionic neurons.