MULTIPLE SPINAL PATHWAYS MEDIATE CUTANEOUS NOCICEPTIVE C-FIBER INPUT TO THE PRIMARY SOMATOSENSORY CORTEX (SI) IN THE RAT

In the present study partial lesions of the lower thoracic spinal cord in Tats anaesthetized with halothane and nitrous oxide were made in o rder to elucidate which of the spinal funiculi mediate a nociceptive C fibre input to SI. Field potentials evoked by noxious CO2-laser stimu lation were recorded in the left SI. Nociceptive C fibre input from th e right hindpaw to SI was propagated by the dorsal funiculi (DF) and t he left and right lateral funiculi (LLF and RLF, respectively). Nocice ptive C fibre input from the left hindpaw was propagated by LLF and RL F, but not DF. Input from the hindpaws mediated by LLF and RLF caused widespread surface positive potentials throughout most of SI, although potentials in the hindlimb area tended to be larger than those in oth er areas of SI. Input from the right hindpaw mediated by DF caused sur face positive potentials mainly in the hindlimb area of SI. Intracorti cally, the field potentials reversed polarity in the superficial lamin ae and had maximal negative amplitudes in laminae III-IV (input transf erred by DF and LLF) and in laminae V-VI (input transferred by LLF and RLF). It is concluded that there are multiple spinal pathways which c an transfer information from cutaneous nociceptive C fibres to SI in t he rat. These ascending pathways seem to activate partly different tha lamo-cortical systems.