Opioid and Antiopioid Actions of Tyr-MIF-1, Tyr-W-MIF-1 and Hemorphin-4 on Rat Locus Coeruleus Neurons: Intracellular Recording in vitro

Yea-Ru Yang；Tsai-Hsien Chiu

intracellular recording ； Tyr-MIF-1 ； Tyr-W-MIF-1 ； hemorphin-4 ； locus coeruleus

The Chinese Journal of Physiology

40卷3期（1997 / 09 / 01）

131 - 135

英文

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-ProTrp-Thr-OH (hemorphin-4), on neurons of the locus coeruleus (LC) in the rat, in a totally submerged brain slice preparation. These tetrapeptides which, like other opioids, caused inhibitory effects on all LC neurons tested. Tyr-MIF-1 (10-100μM), Tyr-W-MIF-1 (1-10μM) and hemorphin-4 (1-30μM) caused dose-related inhibition of the spontaneous firing. The IC50 were 37.5, 3.8 and 6.7μM for TyrMIF-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 (30nM), but did not decrease the actions of higher concentration of TAPS (100nM). It is concluded that the blood-derived peptide hemorphin-4 and the endogenous peptides TyrW-MIF-1 and Tyr-MIF-1 possess opioid and antiopioid actions in the LC neurons.