Somatotopical arrangement of rat spinal dorsal horn cells processing input from deep tissues.

Extracellular recordings were made from 29 dorsal horn neurones which could be driven by mechanical stimulation of deep tissues, in spinal segment L4 of rats. The recording sites were marked by iontophoresis of pontamine sky blue. According to the location of the receptive fields the cells were classified as deep neurones (12 cells), which had input from deep tissues only, and as cutaneo-deep neurones (17 cells), which had receptive fields in both skin and deep tissues. The deep cells showed a correlation between the recording sites in the dorsal horn and the location of the receptive fields on the hind-limb: the more distal a deep receptive field was situated on the hind-limb the more medial was the location of the recording site in the dorsal horn. In cutaneo-deep neurones the correlation was statistically significant for the deep receptive fields but not for the cutaneous ones.