Sodium Channels and Pain

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 96; no. 14; pp. 7635 - 7639
• Main Authors: Waxman, S. G., Dib-Hajj, S., Cummins, T. R., Black, J. A.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 06.07.1999; National Acad Sciences; National Academy of Sciences; The National Academy of Sciences
• Series: Colloquium Paper
• Subjects: Animals; Axotomy; Cellular biology; Colloquium Paper; Electric current; Ganglia, Spinal - physiology; Ganglia, Spinal - physiopathology; Humans; Inflammation; Messenger RNA; Neurons; Neurons, Afferent - physiology; Neuroscience; Pain; Pain - physiopathology; Physical trauma; Ribonucleic acid; RNA; RNA, Messenger - genetics; Sensory neurons; Sodium; Sodium channels; Sodium Channels - genetics; Sodium Channels - physiology; Transcription, Genetic
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.96.14.7635

Although it is well established that hyperexcitability and/or increased baseline sensitivity of primary sensory neurons can lead to abnormal burst activity associated with pain, the underlying molecular mechanisms are not fully understood. Early studies demonstrated that, after injury to their axons, neurons can display changes in excitability, suggesting increased sodium channel expression, and, in fact, abnormal sodium channel accumulation has been observed at the tips of injured axons. We have used an ensemble of molecular, electrophysiological, and pharmacological techniques to ask: what types of sodium channels underlie hyperexcitability of primary sensory neurons after injury? Our studies demonstrate that multiple sodium channels, with distinct electrophysiological properties, are encoded by distinct mRNAs within small dorsal root ganglion (DRG) neurons, which include nociceptive cells. Moreover, several DRG neuron-specific sodium channels now have been cloned and sequenced. After injury to the axons of DRG neurons, there is a dramatic change in sodium channel expression in these cells, with down-regulation of some sodium channel genes and up-regulation of another, previously silent sodium channel gene. This plasticity in sodium channel gene expression is accompanied by electrophysiological changes that poise these cells to fire spontaneously or at inappropriate high frequencies. Changes in sodium channel gene expression also are observed in experimental models of inflammatory pain. Thus, sodium channel expression in DRG neurons is dynamic, changing significantly after injury. Sodium channels within primary sensory neurons may play in important role in the pathophysiology of pain.