Extracellular signal-regulated kinase activation in the chronic constriction injury model of neuropathic pain in anaesthetized rats
Granted by ‘Cátedra Externa del Dolor Fundación Grünenthal/Universidad de Cádiz’; Fondo de Investigación Sanitaria (PI10/01221); CIBERSAM G18; Junta de Andalucía (CTS-510, CTS-4303 and CTS-7748); FP7-PEOPLE-2010-RG (268377) and PVGPC2010-057 (First Author Fellowship). We would like to thank also Conselho de Reitores das Universidades Portuguesas (CRUP) that financed the collaboration between the Spanish and Portuguese authors (project Acção Integrada E-42/07).
Conflicts of interest
The authors declare no conflict of interest.
The role of extracellular signal-regulated kinases (ERKs) in nociception has been explored in the last years. While in spinal cord their activation is frequently correlated with pain or acute noxious stimuli, supraspinally, this association is not so evident and remains unclear. This study aims to evaluate ERK1/2 activation in the spinal cord and brainstem nuclei upon neuropathy and/or an additional mechanical stimulus.
Acute noxious mechanical stimulation was applied in the left hindpaw of anaesthetized SHAM-operated and chronic constriction injured (CCI, neuropathic pain model) rats. Other SHAM or CCI rats did not receive any stimulus. Immunohistochemistry against the phosphorylated isoforms of ERK1/2 (pERK1/2) was performed in lumbar spinal cord and brainstem sections to assess ERK1/2 activation.
In the spinal cord, stimulation promoted an increase in pERK1/2 expression in the superficial dorsal horn of SHAM rats. No significant effects were caused by CCI alone. At supraspinal level, changes in ERK1/2 activation induced by CCI were observed in A5, locus coeruleus (LC), raphe obscurus (ROb), raphe magnus, dorsal raphe (DRN), lateral reticular and paragigantocellularis nucleus. CCI increased pERK1/2 expression in all these nuclei, with exception of LC, where a significant decrease was verified. Mechanical noxious stimulation of CCI rats decreased pERK1/2 expression in ROb and DRN, but no further changes were detected in either SHAM- or CCI-stimulated animals.
ERK1/2 are differentially activated in the spinal cord and in selected brainstem nuclei implicated in nociception, in response to an acute noxious stimulus and/or to a neuropathic pain condition.