Effects of chronic morphine treatment on beta-endorphin-related peptides in the caudal medulla and spinal cord.
The effects of chronic morphine treatment on beta-endorphin (beta E)-immunoreactive (beta E-ir) peptide levels were determined in the rat caudal medulla and different areas of the spinal cord. Seven days of morphine pelleting had no effect on total beta E-ir peptides in the caudal medulla. In contrast, it significantly increased beta E-ir peptide concentrations in the cervical and thoracic regions of the spinal cord compared with placebo-pelleted controls, whereas in the lumbosacral region this trend did not reach statistical significance. Injections of the opiate receptor antagonist naloxone 1 h before the rats were killed had no effect on the morphine-induced increases in the cord. Chromatographic analyses revealed that enzymatic processing of beta E-related peptides in the spinal cord seemed unaffected by the morphine and/or naloxone treatments. In light of previous data showing that morphine down-regulates beta E biosynthesis in the hypothalamus, the present results suggest that the regulation of beta E-ir peptides in the spinal cord is distinct from that found in other CNS areas. These data provide support for previous results suggesting that beta E-expressing neurons may be intrinsic to the spinal cord.
Bronstein
D M
DM
Mental Health Research Institute, University of Michigan, Ann Arbor.
Gutstein
H B
HB
Akil
H
H
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D002850:Chromatography, Gel; D004343:Drug Implants; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000378:metabolism*; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology; D011333:Pro-Opiomelanocortin / Q000378:metabolism; D011863:Radioimmunoassay; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism*; D001615:beta-Endorphin / Q000302:isolation & purification / Q000378:metabolism*
D004343:Drug Implants; D009270:Naloxone; D001615:beta-Endorphin; D011333:Pro-Opiomelanocortin; D009020:Morphine