Endomorphin-1 and -2 induce naloxone-precipitated withdrawal syndromes in rats

In 1997, endomorphin-1 (EM-1) and -2 (EM-2) were identified as the most specific endogenous μ-opioid ligands. These two peptides have shown analgesic effects and many other opioid functions. In the present study, we attempt to investigate the possible ability of endomorphins to induce naloxone-preci...

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Published in:Peptides (New York, N.Y. : 1980) N.Y. : 1980), 2003-03, Vol.24 (3), p.477-481
Main Authors: Chen, J.-C., Tao, P.-L., Li, J.-Y., Wong, C.-H., Huang, E.Y.-K.
Format: Article
Language:English
Subjects:
Analgesics, Opioid - pharmacology
Animals
Behavior
Biological and medical sciences
Endomorphin-1
Endomorphin-2
Fundamental and applied biological sciences. Psychology
Injections, Intraperitoneal
Male
Morphine
Morphine - pharmacology
Naloxone - pharmacology
Neuropeptides
Oligopeptides - pharmacology
Opiate dependence
Rats
Rats, Sprague-Dawley
Substance Withdrawal Syndrome - etiology
Withdrawal syndromes
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Summary:In 1997, endomorphin-1 (EM-1) and -2 (EM-2) were identified as the most specific endogenous μ-opioid ligands. These two peptides have shown analgesic effects and many other opioid functions. In the present study, we attempt to investigate the possible ability of endomorphins to induce naloxone-precipitated withdrawal in comparison with that induced by morphine. Using the previously established scoring system in rats, 12 withdrawal signs (chewing, sniffing, grooming, wet-dog shakes, stretching, yawning, rearing, jumping, teeth grinding, ptosis, diarrhea, and penile erection) were observed and scored following naloxone (4 mg/kg, i.p.) challenge. Compared with the sham control, EM-1 and EM-2 (20 μg, i.c.v., b.i.d. for 5 days) both produced significant naloxone-induced withdrawal syndromes with similar severity to that induced by the same dose of morphine. There was no significant difference between EM-1, EM-2, and morphine-treated group for naloxone-induced withdrawal signs, except for grooming. EM-1 and EM-2 induced more grooming than that caused by morphine. Although EM-1 and EM-2 both led to the withdrawal, they displayed different potency for certain signs and suggest their distinct regulations. The present results indicate EM-1 and EM-2 could initiate certain mechanism involved opiate dependence.
ISSN:0196-9781
1873-5169
DOI:10.1016/S0196-9781(03)00078-0