Articles: hyperalgesia.
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Chronic-constriction injury (CCI) of the sciatic nerve causes mechanical and heat hyperalgesia and mechanical allodynia in the plantar surface of the hindpaw. The underlying mechanism thought to account for these phenomena include central sensitization induced by peripheral nerve injury, ie, the increase in neuronal activity of spinal dorsal horn neurons. As a marker of neuronal activation of the central nervous system, Fos expression has been used widely to monitor the change in neuronal activity evoked by peripheral input. ⋯ The number of noxious stimulus-evoked Fos-labeled neurons in both the superficial and deep laminae of the dorsal horn in the CCI rats was increased significantly compared with those in sham-operated rats, suggesting an increased excitability of dorsal horn neurons to noxious stimuli. Concurrent EA treatment to the Zusanli point with the pinch stimulus suppressed the increase in the number of Fos-labeled cells in the spinal dorsal horn in the CCI rats. The present results show that EA treatment has antinociceptive effects on both pain behavior and neuronal activation of the spinal dorsal horn neurons in CCI rats.
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The generation of transgenic mice that lack or overexpress genes relevant to pain is becoming increasing common. However, only one visceral pain model, the writhing test, is widely used in mice. Here we describe a novel model, chemical stimulation of the colon, which we have developed in mice. ⋯ The peak behavioural responses were evoked by 0.1% capsaicin and by 1% mustard oil respectively. The nociceptive behavioural responses were dose-dependently reversed by morphine (ED50 = 1.9 +/- 1 mg/kg s.c.). We conclude that this model represents a useful tool both for phenotyping mutant mice and for classical pharmacology since information on visceral pain, referred hyperalgesia and colon inflammation can all obtained from the same animal.
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The analgesic properties of the synthetic cannabinoid WIN55,212-2 were investigated in a model of neuropathic pain. In male Wistar rats, bilateral hind limb withdrawal thresholds to cold, mechanical and noxious thermal stimuli were measured. Following this, unilateral L5 spinal nerve ligation was performed. ⋯ This effect was prevented by co-administration of the CB(1) receptor antagonist SR141716a, but not by co-administration of the CB(2) receptor antagonist SR144528, suggesting this action of WIN55,212-2 is mediated via the CB(1) receptor. Administration of SR141716a alone had no affect on the observed allodynia and hyperalgesia, which does not support the concept of an endogenous analgesic tone. These data indicate that cannabinoids may have therapeutic potential in neuropathic pain, and that this effect is mediated through the CB(1) receptor.
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J. Pharmacol. Exp. Ther. · Jun 2001
Propentofylline, a glial modulating agent, exhibits antiallodynic properties in a rat model of neuropathic pain.
The present study was undertaken to determine whether propentofylline, a glial modulating agent, could both prevent the induction of mechanical allodynia and attenuate existing mechanical allodynia in a rodent L5 spinal nerve transection model of neuropathic pain. In a preventative paradigm, propentofylline (1 and 10 mg/kg intraperitoneally) was administered systemically daily, beginning 1 day prior to nerve transection. This regimen produced a dose-dependent decrease in mechanical allodynia (p < 0.01). ⋯ Spinal cords (L4-L6 segments) were removed for immunohistochemical analysis on day 10 or 20 post-transection. Microglial and astrocytic activation was decreased by both peripheral and central administration of propentofylline in both preventative and existing allodynia paradigms. This research supports a growing body of literature highlighting the importance of glial activation in the development of persistent neuropathic pain states, and the potential to therapeutically modulate glial activation in the treatment of neuropathic pain.
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Changes in phenotype or connectivity of primary afferent neurons following peripheral nerve injury may contribute to the hyperalgesia and allodynia associated with neuropathic pain conditions. Although earlier studies using partial nerve injury models have focused on the role of damaged fibres in the generation of ectopic discharges and pain, it is now thought that remaining undamaged fibres may be equally important. We have examined the expression of the sensory neuron-specific cation channel Vanilloid Receptor 1 (VR1), an important transducer of noxious stimuli, in three models of nerve injury in the rat, using anatomical separation or fluorescent retrograde tracers to identify damaged or undamaged sensory neurons. ⋯ Unexpectedly, after L5 spinal nerve ligation, VR1-IR of the A-fibre somata increased approximately 3-fold in the uninjured L4 DRG compared to controls; a much greater increase than seen in the somata with C-fibres. Furthermore, we found that VR1-IR persisted in the transected sciatic nerve proximal to the lesion, despite its down-regulation in the damaged neuronal somata. This persistence in the nerve proximal to the lesion after nerve section, together with increased VR1 in DRG neurons left undamaged after partial nerve injury, may be crucial to the development or maintenance of neuropathic pain.