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Objective : Morphological studies have demonstrated that the spinocervical tract (SCT) neurons have their target cells not only in the lateral cervical nucleus (LCN) but also within the lumbosacral segments of the spinal cord. The study is aimed at investigating the possibility of collateral segmental actions of SCT neurons upon spinomesencephalic tract (SMT) neurons in the lumbar spinal cord. Methods : Extracellular microelectrode recordings were made from lumbar (L3-L6) spinomesencephalic tract (SMT) neurons on adult male cats antidromically activated by stimulation of midbrain. The effects of stimulating dorsolateral funiculus (DLF) were recorded at cervical cord at C3 and rostral C1 levels, below and above the termination of SCT axons in LCN. Results : Thirty-nine cells responded to the stimulation of cervical DLF stimulation. Among them thirty-four cells that showed excitatory responses, twenty-three cells were more excited by the stimulation at C3 and five cells by the C1 stimulation, and six cells showed similar responses to C3 and C1 stimulations. Inhibitory responses were recorded in five. Four inhibited cells showed their inhibitory responses to both C3 and C1 stimulation, and one cell was inhibited by C3 stimulation. Histologically, the location of recording sites of SMT cells responding to stimulation of upper cervical DLF was widely distributed in the lamina II-VII of gray matter inhibitory responses were found in lamina V-VII Conclusion : These results suggest that there is a functional coupling between the SCT and SMT neurons, and that the linkage might be formed either segmentally between SMT neurons and axon collaterals of SCT neurons or suprasegmentally via cells in the lateral cervical neurons with axons descending to the lumbar cord.