Chronic abdominal pain is a major cause of patient morbidity in inflammatory bowel diseases (IBD). A balance of pro- and anti-nociceptive factors regulating colonic dorsal root ganglion (DRG) neurons, which synapse onto second order dorsal horn neurons, are known to regulate chronic pain but the mechanisms are poorly understood. This thesis examined whether neuroanatomical remodeling of DRG central nerve terminals underlies pro-nociceptive signaling and whether subsets of immune cells source the anti-nociceptive factor, β-endorphin. To examine pro-nociceptive mechanisms, acute and chronic dextran sulfate sodium (DSS) mouse models of colitis were established and substance P (SP; marker of nociceptor terminals) immunohistochemistry used to investigate changes in immunoreactivity of DRG terminals in the thoracic dorsal horn (segments T9-T13). SP immunoreactivity was increased in the dorsal horn (4 fold; P < 0.001) and central canal (P < 0.001) following chronic colitis. In contrast, SP immunoreactivity was unchanged in acute colitis. However, five weeks later SP immunoreactivity was increased both in the dorsal horn (4 fold; P < 0.01) and central canal (P < 0.001). In the cervical spinal cord, SP immunoreactivity was not increased following colitis, suggesting that changes seen in the thoracic level were specific to signaling from colonic DRG neurons. Immunoreactivity for the SP NK1 receptor on second order neurons was also examined and a significant increase in immunoreactivity was observed on post-synaptic second order cell bodies following chronic DSS. This could provide an additional mechanism for enhanced SP neurotransmission centrally. ii The source of the anti-nociceptive mediator, β-endorphin, during chronic DSS colitis was investigated using magnetic cell sorting and flow cytometry. The number of β- endorphin expressing CD4+ (2.4 fold; P < 0.05) and CD11b+ (2.6 fold; P < 0.05) cells in mice increased following chronic colitis. These findings suggest that during colitis there is a time-dependent increase of SP immunoreactivity in thoracic DRG central terminals, which could play a role in pro- nociceptive signaling in chronic inflammation. These actions may be balanced by anti- nociceptive factors such as β-endorphin which are found in subsets of immune cells. / Thesis (Master, Physiology) -- Queen's University, 2012-08-29 16:28:41.166

This study was designed to explore the hormonal regulation of CNS opioid peptide levels in female Sprague Dawley rats. Forty-eight animals were divided into 2 equal groups for acute and chronic studies. Each group was further divided into 4 subgroups, each containing 6 animals. Each rat in the control group received an inert pill (in 0.25 ml corn oil daily by gavage); the second group, 15 μg norethindrone (NE, a potent progestin present in the oral contraceptive Micronor®); the third group, 15 μg NE and 1 μg ethinyl estradiol, EE2 (present in the oral contraceptive Modicon®) and the fourth group, 10 times the dose of the third group. Rats were treated either acutely for 5 days or chronically for 7 weeks. Opioid peptides were estimated by radioimmunoassay. Acute administration of 150 μg NE + 10 μg EE2 decreased the levels of methionine-enkephalin (ME), leucine-enkephalin (LE), dynorphin (DYN) and β-endorphin like immunoreactivity (β-EI) by about 50% in the pituitary. The same dose on chronic administration also decreased DYN, but increased the levels of ME and LE in the pituitary by 331 and 69%, respectively. In the hypothalamus, chronic administration of NE + EE2 increased the level of ME (155%) and LE (87%) as well as of DYN (97%). In the striatum, the levels of LE (33%) and DYN (115%) were elevated during chronic administration. It is concluded that the acute administration of NE + EE2, in general, reduces the levels of ME, LE, DYN and β-EI. The extent of this decrease is about the same in the pituitary, hypothalamus and striatum. Chronic administration of these hormones, however, results in a reversal of this decrease (except for β-EI) and actually can increase the levels of ME, LE and DYN in all three tissues.