Sigma-1 receptor (σ1R) is expressed in key CNS areas involved in nociceptive processing but only limited information is available about its functional role. In the present study we investigated the relevance of σ1R in modulating nerve injury-evoked pain. For this purpose, wild-type mice and mice lacking the σ1R gene were exposed to partial sciatic nerve ligation and neuropathic pain-related behaviors were investigated. To explore underlying mechanisms, spinal processing of repetitive nociceptive stimulation and expression of extracellular signal-regulated kinase (ERK) were also investigated. Sensitivity to noxious heat of homozygous σ1R knockout mice did not differ from wild-type mice. Baseline values obtained in σ1R knockout mice before nerve injury in the plantar, cold-plate and von Frey tests were also indistinguishable from those obtained in wild-type mice. However, cold and mechanical allodynia did not develop in σ1R null mice exposed to partial sciatic nerve injury. Using isolated spinal cords we found that mice lacking σ1R showed reduced wind-up responses respect to wild-type mice, as evidenced by a reduced number of action potentials induced by trains of C-fiber intensity stimuli. In addition, in contrast to wild-type mice, σ1R knockout mice did not show increased phosphorylation of ERK in the spinal cord after sciatic nerve injury. Both wind-up and ERK activation have been related to mechanisms of spinal cord sensitization. Our findings identify σ1R as a constituent of the mechanisms modulating activity-induced sensitization in pain pathways and point to σ1R as a new potential target for drugs designed to alleviate neuropathic pain.
aDepartment of Pharmacology, Laboratorios Esteve. Av. Mare de Déu de Montserrat, 221. 08041 Barcelona, Spain
bLaboratory of Neuropharmacology, Facultat de Ciències de la Salut i de la Vida, Universitat Pompeu Fabra. Doctor Aguader, 88. 08003 Barcelona, Spain
cDepartment of Pharmacology and Institute of Neuroscience, Faculty of Medicine, Universidad de Granada, Av. de Madrid 11. 18012 Granada, Spain
dDepartment of Physiology, Faculty of Medicine, Universidad de Alcalá de Henares. Alcalá de Henares, 28871 Madrid, Spain
*Corresponding author. Tel.: +34 93 4466244; fax: +34 93 4466220.
Received March 24, 2009; Received in revised form May 1, 2009; Accepted May 12, 2009.