Role of glutamatergic receptors located in the nucleus raphe magnus on antinociceptive effect of morphine microinjected into the nucleus cuneiformis of rat.
Neurons in the nucleus cuneiformis (CnF), located just ventrolateral to the periaqueductal gray, project to medullary nucleus raphe magnus (NRM), which is a key medullary relay for descending pain modulation and is critically involved in opioid-induced analgesia. Previous studies have shown that antinociceptive response of CnF-microinjected morphine can be modulated by the specific subtypes of glutamatergic receptors within the CnF. In this study, we evaluated the role of NMDA and kainate/AMPA receptors that are widely distributed within the NRM on morphine-induced antinociception elicited from the CnF. Hundred and five male Wistar rats weighing 250-300 g were used. Morphine (10, 20 and 40 microg) and NMDA receptor antagonist, MK-801 (10 microg) or kainate/AMPA receptor antagonist, DNQX (0.5 microg) in 0.5 microl saline were stereotaxically microinjected into the CnF and NRM, respectively. The latency of tail-flick response was measured at set intervals (2, 7, 12, 17, 22, 27 min after microinjection) by using an automated tail-flick analgesiometer. The results showed that morphine microinjection into the CnF dose-dependently causes increase in tail-flick latency (TFL). MK-801 microinjected into the NRM, just 1 min before morphine injection into the CnF, significantly attenuated antinociceptive effects of morphine. On the other hand, DNQX microinjected into the NRM, significantly increased TFL after local application of morphine into the CnF. We suggest that morphine related antinociceptive effect elicited from the CnF is mediated, in part, by NMDA receptor at the level of the NRM whereas kainite/AMPA receptor has a net inhibitory influence at the same pathway.
Haghparast
Abbas
A
Neuroscience Research Center, Shaheed Beheshti Medical University, P.O. Box 19615-1178, Tehran, Iran. Haghparast@yahoo.com
Soltani-Hekmat
Ava
A
Khani
Abbas
A
Komaki
Alireza
A
D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism; D008297:Male; D008526:Medulla Oblongata / Q000033:anatomy & histology / Q000378:metabolism*; D008845:Microinjections; D009020:Morphine / Q000494:pharmacology*; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009434:Neural Pathways / Q000033:anatomy & histology / Q000378:metabolism*; D009619:Nociceptors / Q000502:physiology; D010147:Pain Measurement / Q000187:drug effects; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology; D011903:Raphe Nuclei / Q000033:anatomy & histology / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D017470:Receptors, Glutamate / Q000187:drug effects / Q000378:metabolism*; D018092:Kainic Acid Receptors / Q000187:drug effects / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D013681:Tegmentum Mesencephali / Q000033:anatomy & histology / Q000187:drug effects / Q000378:metabolism*
D000701:Analgesics, Opioid; D018691:Excitatory Amino Acid Antagonists; D018698:Glutamic Acid; D009020:Morphine; D017470:Receptors, Glutamate; D018092:Kainic Acid Receptors; D016194:Receptors, N-Methyl-D-Aspartate