Abstract not available

Capsaicin (1.3 mumol/kg, i.v.) and resiniferatoxin (48 nmol/kg, i.v.) failed to induce plasma extravasation in Suncus murinus (P>0.05). But SP (20 nmol/kg, i.v.) was able to induce salivation, and plasma extravasation in the bladder and the trachea significantly (P<0.05). NK1 receptor antagonists CP-99,994, R116301 (ID50 = 1.2 mumol/kg), and R115614 (ID50 = 1.8 mumol/kg) significantly reduced plasma leakage in the bladder (P<0.05), but not the trachea (P>0.05). R116301 (ID50 = 0.7 mumol/kg) and R115614 (ID50 = 1.2 mumol/kg) were able to inhibit the salivation response significantly (P<0.05). / R116301 and R115614 significantly reduced emesis induced by resiniferatoxin, motion, copper sulphate, and cisplatin (P<0.05), in the dose range between 23-70 mumol/kg, s.c. Both antagonists (100-300 nmol, i.c.v.) were also able to reduce cisplatin-induced emesis significantly (P<0.05), but only R116301 (10-300 nmol, i.c.v.) was able to significantly inhibit emesis induced by nicotine and copper sulphate (P<0.05). / The development of tachyldnin NK1 receptor antagonist aprepitant as an effective anti-emetic drug illustrates the importance of NK1 receptors in the emetic reflex. However, the exact anti-emetic mechanism of action is still unknown. The primary aim of the study was to investigate the relative contribution of centrally versus peripherally located NK1 receptors in the emetic reflex in Suncus murinus. The study also investigated the potential contribution of NK2 and NK3 receptors in emesis control. / The present studies demonstrated that R116301 and R115614 exhibited anti-emetic properties against various drugs, motion, and tachykinin receptor agonists. The studies also imply the existence of the classical SP subsite and the septide subsite of the NK1 receptors that are involved in the emetic reflex of Suncus murinus, which suggests that NK1 receptor antagonists that can block both subsites could become effective anti-emetic drugs. The present studies also demonstrated that both NK2 and NK3 receptors maybe involved in emesis control. It is possible that dual NK1/NK2 receptor antagonists or triple NK 1/NK2/NK3 receptor antagonists may have clinical potential as anti-emetic drugs besides the clinically used NK1 receptor antagonists. / The rank order of potency (based on pEC50 values) of tachykinin receptor agonists to contract Suncus murinus ileum was as follow: [Sar9Met(O2)11] substance P (SP) (8.1) > septide (7.9) (both NK1 receptor agonists) > neurokinin A (NKA) (7.7) > SP (7.6) > GR 64349 (NK2 receptor agonist) (7.0). For the NK1 receptor antagonists, the rank order of potency (based on pKB/pA2 values) to inhibit ileal contraction was: R116301 (7.8-8.2) ≈ R115614 (7.7-8.3) > CP-99,994 (6.4-7.3) against various NK1 receptor agonists. Furthermore, NK2 receptor antagonist saredutant (pA2 = 7.3) competitively antagonised GR 64349-induced ileal contraction. / When injected intracerebroventricularly, SP (100 nmol), septide, [Sar 9Met(O2)11] SP, NKA (all at 30 nmol), GR 64349 (10 and 30 nmol), and senktide (NK3 receptor agonist) (3-30 nmol) significantly induced emesis in Suncus murinus (P<0.05). They were also effective in inducing locomotor hyperactivity, ano-genital grooming, circling, face washing, hindlimb licking, scratching, and straub tail (3-30 nmol, P<0.05). R116301 and R115614 (both at 3 and 10 mumol/kg, s.c.) significantly antagonised some of the actions of the agonists including emesis, locomotor hyperactivity, ano-genital grooming, licking, scratching, and straub tail (P<0.05). Saredutant and NK3 receptor antagonist osanetant (both at 30 mumol/kg, s.c.) attenuated emesis induced by GR 64349 and senktide respectively (P<0.05). Saredutant (30 mumol/kg, s.c.) was also able to inhibit GR 64349-induced face washing and scratching, while osanetant (30 mumol/kg, s.c.) also significantly attenuated senktide-induced straub tail (P<0.05). / Cheng, Ho Man Frankie. / "September 2007." / Adviser: John A. Rudd. / Source: Dissertation Abstracts International, Volume: 69-08, Section: B, page: 4691. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (p. 194-223). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract in English and Chinese. / School code: 1307.