Integrative And Molecular Studies Of Pain And Pain Contr

Dental &Craniofacial Research

Investigators

Linked publications, trials & patents

Abstract

Our research program addresses basic molecular and physiological processes of nociceptive transmission in the central nervous system. The research program is vertically integrated and uses molecular biology, in vitro cell-based models, animal models and human subjects. We concentrate on the primary afferent pain sensing neurons and their connections in the dorsal spinal cord. The dorsal spinal cord is the first site of synaptic processing for nociceptive sensations and a locus of altered neuronal plasticity and gene expression in persistent pain. Questions related to higher CNS pain processing are performed with humans using in vivo functional brain imaging of pain patients and normal volunteers. The Unit also investigates novel treatments for severe intractable pain, one of which uses the basic molecular mechanisms of the vanilloid receptor 1. This molecule is a heat-sensitive calcium/sodium ionophore and converts painful heat into nerve action potentials by depolarizing the pain-sensing nerve terminals in the skin. Ionophore activity also is stimulated by binding of capsaicin, a prototypical vanilloid chemical, and the active ingredient in hot pepper. Activation of this receptor with ultra-potent vanilloids can be so strong that the increase in calcium kills the cell. This in vitro observation has directly led to a bench-to-bedside program in which vanilloid agonists are used to kill pain-sensing neurons and thereby provide long-term pain control. We have also shown that the vanilloid receptor is sensitized in acidic conditions (as are found in inflammation and tissue damage) to molecules released by cells during injury. The importance of this observation is that the pain sensing capacity is maintained and enhanced following injury. We showed that VR1 is phosphorylated by the PKC-alpha isoform suggesting that VR1 is a point of multimodal convergence of pain stimuli. This stimulated us to find blockers of the VR1 ion channel that would be effective across all forms of pain stimuli. The program has yielded new leads for analgesic compounds and new insights into the molecular nature of the ionophore domain of VR1. A second program is centered on gene discovery in spinal cord using subtraction cloning and differential hybridization to identify new genes induced by pain stimuli. We have completed the first subtraction cloning of pain state-baseline and have printed a microarray of these genes. The arrays were probed and re-gridded to segregate highly expressed from low abundance transcripts and the new array differentially hybridized. We are currently examining the families of genes that are activated. In addition to pain these studies fundamentally explore the molecular basis of synaptic plasticity in general, as we hypothesize a modularity in the neuronal response to a new level of synaptic or pharmacological input (e.g. learning, neurological disorders, drug abuse,). In terms of translational research our main activity has centered on deletion of primary afferent pain sensing neurons using the ultra-potent vanilloid resiniferatoxin (RTX). The results indicate that RTX provides a mechanism-based, anatomically directed approach to control of chronic pain. Presently, we are assembling the IND application and the clinical protocol for use of RTX in human subjects suffering from pain associated with advanced metastatic disease.