Cardiovascular responses to microinjections of nociceptin into a midline area in the commissural subnucleus of the nucleus tractus solitarius of the rat.
Immunoreactivity for nociceptin, an endogenous ligand for the ORL1 opioid receptors, has been reported in the nucleus tractus solitarius (nTS). A midline area in the commissural subnucleus (nCom) of nTS is the site of peripheral chemoreceptor projections. This investigation was carried out in urethane-anesthetized, artificially ventilated, adult male Wistar rats, to study the cardiovascular effects of the activation of ORL1 receptors in a midline area of the nCom. Microinjections (30 nl) of nociceptin (0.15-0.62 mM) into the nCom elicited depressor and bradycardic responses. Prior microinjections of [N-Phe(1)]-nociceptin-(1-13)-NH(2) (4.5 mM), a specific antagonist for ORL1 opioid receptors, into the nCom blocked the effects of nociceptin (0.31 mM, the maximally effective concentration), but not endomorphin-2 (0.6 mM; an endogenous ligand for micro -opioid receptors). On of other hand, naloxone (0.125 mM; an antagonist for classical opioid receptors) did not block the effects of nociceptin, while it did block the effects of endomorphin-2. The blockade of nociceptin effects by [N-Phe(1)]-nociceptin-(1-13)-NH(2) and endomorphin-2 by naloxone, was not due to some nonspecific effects because the responses to L-Glu (5 mM) remained unaltered after the microinjection of these antagonists. These results indicate that activation of ORL1 receptors in the nCom may play a role in the regulation of cardiovascular function.
Shah
Neel
N
Department of Neurological Surgery, MSB H-586, New Jersey Medical School, 185 South Orange Ave., Newark, NJ 07103, USA.
Chitravanshi
Vineet C
VC
Sapru
Hreday N
HN
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D002319:Cardiovascular System / Q000187:drug effects*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D008297:Male; D008845:Microinjections / Q000379:methods*; D009292:Narcotic Antagonists / Q000494:pharmacology; D018847:Opioid Peptides / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D011957:Receptors, Opioid / Q000819:agonists / Q000502:physiology; D017552:Solitary Nucleus / Q000187:drug effects* / Q000502:physiology; D000094942:Nociceptin Receptor; D000097629:Nociceptin
D009292:Narcotic Antagonists; D018847:Opioid Peptides; D011957:Receptors, Opioid; D000094942:Nociceptin Receptor; D000097629:Nociceptin; C000722285:Oprl1 protein, rat