Intrathecally administered endotoxin or cytokines produce allodynia, hyperalgesia and changes in spinal cord neuronal responses to nociceptive stimuli in the rat

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Abstract
Inflammatory processes occurring within the central nervous system (CNS) can produce ‘illness induced behaviours’ which include fever, sleep and the development of allodynia and hyperalgesia. Here we demonstrate the effects of the pro‐inflammatory mediators, bacterial endotoxin, and rat recombinant interleukin 1 β (rrIL‐1β) or tumour necrosis factor‐ α (rrTNF α) on the integration of somatosensory information at the single neuronal level, via recordings from wide‐dynamic range neurones in the dorsal horn of the spinal cord in anaesthetized rats. Intrathecal administration of E. coli lipopolysaccharide (LPS, 10 and 100 μ g, i.t.) enhanced the activity of dorsal horn neurones, including facilitation of neuronal post‐discharge. Intrathecal administration of IL‐1β (5–5000 pg) or TNF‐ α (5–5000 pg) enhanced dorsal horn neuronal responses, including the acute responses to C‐fibre stimulation, wind‐up and post‐discharge, however, the effects of IL‐1 β were more robust than those of TNF α. Intrathecal administration of IL‐1 β (1–1000 pg) also leads to the development of mechanical allodynia and hyperalgesia. On the other hand intrathecal application of TNF α did not produce changes in sensitivity to mechanical stimuli. Changes in the activity of spinal wide‐dynamic range neurones induced by local inflammation may provide a pathomechanism for the clinical pathology of central pain syndrome, which can accompany CNS disease or acute CNS injury.