Response behaviour of cat dorsal horn neurones receiving input from skeletal muscle and other deep somatic tissues.

1. In chloralose-anaesthetized cats, lumbosacral dorsal horn neurones driven by receptors in skeletal muscle and other deep tissues (tendon, joint, bone) were studied. 2. Upon mechanical stimulation two main types of neurones were found: units having exclusive input from deep tissues (D cells, 28.8%) and units with input from both cutaneous (C) and deep (D) receptors (C-D cells, 71.2%). In both categories, low-threshold mechanosensitive (LTM) and high-threshold mechanosensitive (HTM) elements were present. 3. Neurones responding exclusively to noxious stimulation of skeletal muscle were not found; the input from muscle nociceptors converged on the dorsal horn cells together with other deep or cutaneous input. D cells with exclusively HTM input were numerous; these could from the anatomical basis for a specific spinal pathway for deep pain. 4. For C-D neurones with input from deep nociceptors the cutaneous receptive field (RF) was usually located distal to the deep one. This arrangement might be of relevance for the occurrence of hyperaesthetic skin distal to painful deep lesions. 5. Cold block of the spinal cord resulted in a marked increase in the neurones' mechanical responsiveness and in the number of RFs per neurone. Simultaneously, the proportion of HTM RFs increased, particularly in cells with input from skeletal muscle. 6. The recording sites in the dorsal horn were located in the superficial dorsal horn and in and around laminae V/VI. Evidence is presented that in dorsal horn cells with deep input not only the mechanical excitability but also the degree of convergence is controlled by descending spinal pathways.