Thermo-dependence of noxious mechanical heterotopic stimulation-dependent modulation of the spinal dorsal horn response to somatosensory stimulation

Abstract

Despite frequent clinical hyper-or hypothermia cases, the thermal-dependence of the endogenous pain modulation system at the spinal cord is not well understood. The spinal dorsal horn neuronal network responses during mechanical heterotopic noxious stimuli was evaluated at three different body temperatures (34, 37 or 40 • C) by measurement of lumbar cord dorsum potentials activated by electrical stimulation of the ipsilateral sural nerve in adult thiopental anesthetized rats. A noxious clamp was applied randomly to the tail, right hind paw, right forepaw, muzzle, or left forepaw. Heterotopic noxious stimuli induced a decrease of the negative wave amplitude and duration at 37 • C. This effect was reduced at 40 • C for both amplitude (−18.2% for 37-40 • C; p < 0.0005) and duration (−16.4% for 37-40 • C; p < 0.0001). The P wave showed neither amplitude nor duration changes at either of the three tested temperatures. Clinical range changes of temperature could modify pain sensation, while hyperthermia increased nociceptive sensory input to dorsal horn and exacerbated pain sensation in individuals with fever.