Simultaneous assessment of the effects of L-type current modulators on sensory and motor pathways of the mouse spinal cord in vitro

Knockdown of L calcium channel subtypes: differential effects in neuropathic pain

The maintenance of chronic pain states requires the regulation of gene expression, which relies on an influx of calcium. Calcium influx through neuronal L-type voltage-gated calcium channels (LTCs) plays a pivotal role in excitation-transcription coupling, but the involvement of LTCs in chronic pain remains unclear. We used a peptide nucleic acid (transportan 10-PNA conjugates)-based antisense strategy to investigate the role of the LTC subtypes Ca(V)1.2 and Ca(V)1.3 in long-term pain sensitization in a rat model of neuropathy (spinal nerve ligation). Our results demonstrate that specific knockdown of Ca(V)1.2 in the spinal dorsal horn reversed the neuropathy-associated mechanical hypersensitivity and the hyperexcitability and increased responsiveness of dorsal horn neurons. Intrathecal application of anti-Ca(V)1.2 siRNAs confirmed the preceding results. We also demonstrated an upregulation of Ca(V)1.2 mRNA and protein in neuropathic animals concomitant to specific Ca(V)1.2-dependent phosphorylation of the cAMP response element (CRE)-binding protein (CREB) transcription factor. Moreover, spinal nerve ligation animals showed enhanced transcription of the CREB/CRE-dependent gene COX-2 (cyclooxygenase 2), which also depends strictly on Ca(V)1.2 activation. We propose that L-type calcium channels in the spinal dorsal horn play an important role in pain processing, and that the maintenance of chronic neuropathic pain depends specifically on channels comprising Ca(V)1.2.

Sigma-1 receptors regulate activity-induced spinal sensitization and neuropathic pain after peripheral nerve injury

Sigma-1 receptor (sigma(1)R) 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 sigma(1)R in modulating nerve injury-evoked pain. For this purpose, wild-type mice and mice lacking the sigma(1)R 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 sigma(1)R knockout mice did not differ from wild-type mice. Baseline values obtained in sigma(1)R 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 sigma(1)R null mice exposed to partial sciatic nerve injury. Using isolated spinal cords we found that mice lacking sigma(1)R 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, sigma(1)R 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 sigma(1)R as a constituent of the mechanisms modulating activity-induced sensitization in pain pathways and point to sigma(1)R as a new potential target for drugs designed to alleviate neuropathic pain.