Opioid peptides alleviated while naloxone potentiated methamphetamine-induced striatal dopamine depletion in mice.
Delta opioid peptide [D-Ala2, D-Leu5] enkephalin (DADLE) can partially reverse long-term loss of striatal dopamine transporters induced by multiple doses of methamphetamine via an unknown mechanism. This study was designed to examine the modulating effects of three opioid ligands, DADLE, Leucine enkephalin (L-enk), and naloxone, on the long-lasting dopamine depletion produced by 4 cumulative doses of methamphetamine. Both DADLE (at a dose of 18 mg/kg) and L-enk (100 microg/kg x 2) effectively attenuated methamphetamine-induced dopamine depletion in the striatum while their protective effects were not blocked by coadministration of naloxone. In contrast, naloxone (10 mg/kg x 2) alone potentiated the long-lasting dopamine depletion produced by methamphetamine. Moreover, none of the treatments with DADLE (18 mg/kg), L-enk (100 microg/kg), or naloxone (10 mg/kg) alone affected body temperature. These results suggest that the opioid ligands may, directly or indirectly, modulate this methamphetamine-induced dopamine neurotoxicity in the nigrostriatal system via a temperature-independent mechanism.
Yu
L
L
Institute of Behavioral Medicine, National Cheng Kung University College of Medicine, Tainan, Taiwan. lungyu@mail.ncku.edu.tw
Kuo
Y M
YM
Cherng
C F
CF
D000818:Animals; D001831:Body Temperature / Q000187:drug effects / Q000502:physiology; D003342:Corpus Striatum / Q000187:drug effects* / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism*; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology*; D004338:Drug Combinations; D004357:Drug Synergism; D008297:Male; D008694:Methamphetamine / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009270:Naloxone / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology; D018847:Opioid Peptides / Q000502:physiology*
D018765:Dopamine Uptake Inhibitors; D004338:Drug Combinations; D009292:Narcotic Antagonists; D018847:Opioid Peptides; D009270:Naloxone; D008694:Methamphetamine; D004298:Dopamine