This project concerns the role of CNS peptide-containing neurons in sensory processes especially as they relate to pain and the control of pain. A model of peripheral inflammation has been developed to investigate the relationship between spinal cord opioid-containing neurons (enkephalin and dynorphin) and abnormal primary afferent input. Alterations in opioid gene expression are assessed by measurement of peptide and mRNA levels and in situ hybridization techniques. Molecular mechanisms regulating dynorphin gene transcription are presently being investigated. The time course and stimulus requirements for the increase in spinal cord dynorphin gene expression have been fully characterized. The earliest time reliable changes in preprodynorphin mRNA levels can be measured is 4 hours after inflammation. This now permits us to perform pharmacological experiments on induction and blockade of the response. The inflammation also induces an increase in c-fos proto-oncogene mRNA that is very rapid in onset (within 30 min). These results suggest that c-fos, a nuclear protein, may be involved in transcriptional regulation of the dynorphin gene. A new technique for localizing DNA binding proteins and possible transcription factors has been employed to identify additional proteins that bind to the 5-prime end of the dynorphin gene. It is in this region that most transcriptional regulation occurs. Evidence for a protein specific to neural tissue and certain neural-derived cell lines has been obtained. The significance of these studies is that they reveal which opioid neurons in spinal cord are activated in response to inflammatory pain and, possibly, pain associated with arthritis and cancer. Further elucidation of the pivital role of the spinal dynorphin system in nociceptive processes and mechanisms underlying the increase in gene expression may provide new avenues for the pharmacotherapy of pain and new insights into chronic opioid abuse and tolerance.
