Sensitization of lamina I spinoparabrachial neurons parallels heat hyperalgesia in the chronic constriction injury model of neuropathic pain.
It has been proposed that spinal lamina I neurons with ascending axons that project to the midbrain play a crucial role in hyperalgesia. To test this hypothesis the quantitative properties of lamina I spinoparabrachial neurons in the chronic constriction injury (CCI) model of neuropathic pain were compared to those of unoperated and sham-operated controls. Behavioural testing showed that animals with a CCI exhibited heat hyperalgesia within 4 days of the injury, and this hyperalgesia persisted throughout the 14-day post-operative testing period. In the CCI, nociceptive lamina I spinoparabrachial neurons had heat thresholds that were significantly lower than controls (43.0 +/- 2.8 degrees C vs. 46.7 +/- 2.6 degrees C; P < 10(-4), ANOVA). Nociceptive lamina I spinoparabrachial neurons were also significantly more responsive to graded heat stimuli in the CCI, compared to controls (P < 0.02, 2-factor repeated-measures ANOVA), and increased after-discharges were also observed. Furthermore, the heat-evoked stimulus-response functions of lamina I spinoparabrachial neurons in CCI animals co-varied significantly (P < 0.03, ANCOVA) with the amplitude of heat hyperalgesia determined behaviourally. Taken together these results are consistent with the hypothesis that lamina I spinoparabrachial neurons have an important mechanistic role in the pathophysiology of neuropathic pain.
Andrew
David
D
Department of Oral and Maxillofacial Surgery, School of Clinical Dentistry, University of Sheffield, Sheffield, UK. d.andrew@sheffield.ac.uk
D000818:Animals; D004195:Disease Models, Animal; D006358:Hot Temperature; D006801:Humans; D006930:Hyperalgesia / Q000209:etiology / Q000503:physiopathology*; D008297:Male; D009437:Neuralgia / Q000209:etiology / Q000503:physiopathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D020426:Sciatic Neuropathy / Q000150:complications / Q000503:physiopathology*; D011984:Sensory Receptor Cells; D013116:Spinal Cord / Q000503:physiopathology*