Opioid and antiopioid actions of Tyr-MIF-1, Tyr-W-MIF-1 and hemorphin-4 on rat locus coeruleus neurons: intracellular recording in vitro.
Intracellular recording was used to study the effects of naturally occurring opioid tetrapeptides, including Tyr-Pro-Leu-Gly-NH2 (Tyr-MIF-1), Tyr-Pro-Trp-Gly-NH2 (Tyr-W-MIF-1), and Tyr-Pro-brain slice preparation. These tetrapeptides which, like other opioids, caused inhibitory effects on all LC neurons tested. Tyr-MIF-1 (10-100 microM), Tyr-W-MIF-1 (1-10 microM) and hemorphin-4 (1-30 microM) caused dose-related inhibition of the spontaneous firing. The IC50 were 37.5, 3.8 and 6.7 microM for Tyr-MIF-1, Tyr-W-MIF-1 and hemorphin-4, respectively. In addition, these tetrapeptides were tested for their blocking effects on the Tyr-D-Arg-Phe-sarcosine-OH (TAPS)-induced inhibitory actions. The results showed that Tyr-MIF-1, Tyr-W-MIF-1 and hemorphin-4 significantly decreased the actions of lower concentration of TAPS (30 nM), but did not decrease the actions of higher concentration of TAPS (100 nM). It is concluded that the blood-derived peptide hemorphin-4 and the endogenous peptides Tyr-W-MIF-1 and Tyr-MIF-1 possess opioid and antiopioid actions in the LC neurons.
Yang
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YR
Department of Physiology, National Yang-Ming University, Taipei, Taiwan, ROC.
Chiu
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D000818:Animals; D004594:Electrophysiology; D004723:Endorphins / Q000494:pharmacology*; D006454:Hemoglobins / Q000494:pharmacology*; D066298:In Vitro Techniques; D008125:Locus Coeruleus / Q000166:cytology / Q000187:drug effects*; D009075:MSH Release-Inhibiting Hormone / Q000031:analogs & derivatives* / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009292:Narcotic Antagonists / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D010446:Peptide Fragments / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D004723:Endorphins; D006454:Hemoglobins; D009292:Narcotic Antagonists; D010446:Peptide Fragments; C049857:hemorphin 4; C077532:tyrosyl-prolyl-tryptophyl-glycinamide; C036930:tyrosyl-prolyl-leucyl-glycinamide; D009075:MSH Release-Inhibiting Hormone