INTEGRATIVE AND MOLECULAR STUDIES OF PAIN AND PAIN CONTROL

Dental &Craniofacial Research

Investigators

Linked publications & trials

Abstract

Our research program addresses basic molecular and physiological processes of nociceptive transmission in the central nervous system. The molecular research is performed in animal and in vitro cell-based models. We concentrate on the primary affernt pain sensing neurons and the connections in the dorsal spinal cord. The dorsal spinal cord is the first site of synaptic processing for nociceptive information processing and our research has identified it as a locus of neuronal plasticity and altered gene expression in persistent pain states. Questions related to higher CNS pain processing are performed with humans using in vivo functional brain imaging of chronic pain patients and normal volunteers. The Unit also investigates novel methods for controlling nociceptive transmission and has three novel treatments for sever intractable pain under investigation. Two main basic science issues are being addressed. The first centers on the molecular mechanisms of pain transduction through an investigation 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 is stimulated by binding of capsaicin a prototypical vanilloid compound and the active ingredient in hot pepper. Point mutations within a unique region in the carboxy end of the molecule suggest the occurrence of separate molecular motifs for thermal and chemical activation. We refer to these as the "heat domain" and "vanilloid domain". This program has directly led to a bench to bedside application in which vanilloid agonists are used to kill pain neurons via ligand-induced calcium cytotoxicity and thereby provide pain control. The second program is centered on gene discovery in spinal cord. Subtraction cloning, sequencing and differential hybridization has revealed new genes enriched in spinal cord and induced by pain stimuli. We are in the process of characterizing the novel genes and placing into context the known genes. These studies have revealed large amounts of new information. For example, we observe dorsal enrichment for a specific phosphorylated subunit of an important inhibitory transmitter, a dorsal enrichment of selected stimulatory and inhibitory modulators of the Rho/Rac cell shape signal transduction pathway, and the induction of expression of two novel genes during persistent experimental pain. This project is a long term, high-risk endeavor, which is setting new directions for molecular pain research. The translational program uses our basic science findings to create new treatments for chronic pain. Three target areas emerged from our bench research. (1) In vivo gene transfer. We are getting the adenoviral-mediated gene transfer of secreted beta-endorphin ready for clinical trial. This involves a CRADA with GenVec, a local gene therapy company, in which the therapeutic cassette is placed into their adenoviral vector and preclinical toxicology is performed. (2) We developed a recombinant cytotoxic toxin-ligand fusion protein called substance P-Pseudomonas exotoxin-35 (SP-PE) as a means to kill spinal cord neurons involved in pain transmission. Complete pain control is achieved by intrathecal administration of as little as15 picomoles of SP-PE. We are currently preparing a large amount of conjugate for preclinical toxicology and clinical trial. (3) We are testing a ultrapotent vanilloid agonist, resiniferatoxin, as a pain control agent for used in removal of primary afferent pain sensing neurons. We developed an intraganglionic injection method. The results of intraganglionic RTX suggest that it will be a very effective approach to control of certain types of chronic pain.