Effect of cerebral ventricles perfusion with morphiceptin and Met-enkephalin on trigemino-hypoglossal reflex in rats.
Opioids administered by intracerebroventricular injections produce analgesic responses in rats. The present study was undertaken to investigate the effects of a highly selective mu-opioid receptor ligand morphiceptin on trigemino-hypoglossal reflex in rats. The analgesic effect of morphiceptin was compared with another opioid peptide, Met-enkephalin. With the experimental settings used in this study, we have demonstrated that both morphiceptin and Met-enkephalin show significant dose-dependent analgesic effects after i.c.v. administration in rats as assayed by trigemino-hypoglossal reflex test. The antinociceptive response to Met-enkephalin was short lasting and was observed 10 to 15 min after i.c.v. perfusion. Morphiceptin had a relatively longer duration of antinociceptive action, the effect was observed 20-50 min after i.c.v. perfusion. Neither morphiceptin nor Met-enkephalin produced antinociception after peripheral injections. The results of the present study indicate that both tested peptides act at mu-opioid receptors situated in the central nervous system. They also suggest that mu-opioid receptors present in the central nervous system are an important element of the trigemino-hypoglossal reflex arc. For that reason selective mu-opioid receptor ligands, like morphiceptin, inhibit the reflex more significantly.
Zubrzycka
M
M
Department of Experimental and Clinical Physiology, Institute of Physiology and Biochemistry, Medical University of Lodz, Poland.
Fichna
J
J
Janecka
A
A
D000700:Analgesics / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D003782:Dental Pulp / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D004723:Endorphins / Q000008:administration & dosage / Q000494:pharmacology*; D004744:Enkephalin, Methionine / Q000008:administration & dosage / Q000494:pharmacology*; D007002:Hypoglossal Nerve / Q000187:drug effects* / Q000502:physiology; D007274:Injections, Intraperitoneal; D007275:Injections, Intravenous; D007276:Injections, Intraventricular; D008297:Male; D010147:Pain Measurement / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D017450:Receptors, Opioid, mu / Q000819:agonists; D012018:Reflex / Q000187:drug effects* / Q000502:physiology; D014059:Tongue / Q000187:drug effects / Q000294:innervation / Q000502:physiology; D014276:Trigeminal Nerve / Q000187:drug effects* / Q000502:physiology
D000700:Analgesics; D004723:Endorphins; D017450:Receptors, Opioid, mu; D004744:Enkephalin, Methionine; C028889:morphiceptin