Doctoral Dissertation Defense

COMMITTEE IN CHARGE: Kelly M. Standifer, Ph.D., Chair, Randle Gallucci, Ph.D., Larry P. Gonzalez, Ph.D., Beverley Greenwood-Van Meerveld, Ph.D., Eric W. Howard, Ph.D.

ABSTRACT: Nociceptin/Orphanin FQ (N/OFQ) and its receptor, the Nociceptin/Orphanin FQ Peptide receptor (NOPr), modulate many important biological processes including cardiovascular, renal and immune function, respiration, anxiety, food intake, nociception, tolerance and reward. They have emerged as important therapeutic targets for treatment of associated disorders. Previous studies revealed NOPr signaling cascades and N/OFQ modulation of these signaling cascades and effects on behavioral outcomes. However, there is a critical gap in our understanding of the molecular mechanisms occurring between agonist stimulation of the receptor and behavioral output. In order to develop effective targetspecific therapies, the molecular mechanisms underlying the biological effect of a drug also must be understood. These experiments aimed to delineate molecular mechanisms that mediate NOPr-induced biological outcomes.

Here, we demonstrate that 1) N/OFQ activates NF?B, a critical transcription factor in immune function, and temporally modulates pro- and anti-inflammatory cytokine mRNA expression. Cytokines are associated with enhanced nociceptive sensitivity in neuropathic and inflammatory pain states. Our data provides an important potential mechanism for N/OFQ regulation of immune factors and NOPr-mediated regulation of pain states. 2) N/OFQ regulates Oct-2 transcription factor activation and expression in vitro and in vivo. N/OFQ and Oct-2 are implicated in several biological processes, including immune system function, development and inflammatory pain, raising the possibility that N/OFQ may regulate these functions in an Oct-2-dependent manner. 3) Supraspinal NOPr activation increases nociceptive sensitivity while spinal NOPr activation reduces it. Sustained activation of supraspinal NOPr by intracerebroventricular infusion of N/OFQ desensitizes and down-regulates NOPr in the PAG, with subsequent loss of N/OFQ-induced hyperalgesia. Chronic NOPr antagonist treatment, in contrast, upregulates spinal dorsal horn NOPr expression, with no effect on PAG NOPr. This suggests that endogenous N/OFQ tone is higher at the level of the spinal cord that at the PAG. These studies demonstrate novel signaling pathways for N/OFQ in vitro, including activation of transcription factors and induction of protein synthesis, as well as receptor regulation. Importantly, NOPrmediated changes also occur in vivo. Our studies expand the understanding of potential molecular mechanisms of NOPr signaling and regulation and may enhance the development of therapeutics targeting the NOPr.