A system of rat spinal cord lamina 1 cells projecting through the contralateral dorsolateral funiculus.

The aim of these experiments was to sample the properties of lamina I neurones with long ascending projections. Recordings have been made from 136 units at the L4/5 level, with ascending axons reaching C2. More than 80% of the units projected via the contralateral dorsolateral white matter and only 10% via the contralateral ventral quadrant. None projected via the dorsal columns. Receptive fields were typically 1-2 cm2 and although a substantial number of units responded to a limited range of intense stimuli, a greater number of units were fired by both low- and high-threshold stimulation. In contrast to cells of deeper laminae, the majority of units were excited following activation of descending pathways in the dorsolateral funiculus. The functional role of these units is not obvious, but the location of the ascending projection and the influence of descending pathways does not support the notion that the output of lamina 1 constitutes a simple "pain pathway."