Morphine withdrawal increases glutamate uptake and surface expression of glutamate transporter GLT1 at hippocampal synapses.
Opiate abuse causes adaptive changes in several processes of synaptic transmission in which the glutamatergic system appears a critical element involved in opiate tolerance and dependence, but the underlying mechanisms remain unclear. In the present study, we found that glutamate uptake in hippocampal synaptosomes was significantly increased (by 70% in chronic morphine-treated rats) during the morphine withdrawal period, likely attributable to an increase in the number of functional glutamate transporters. Immunoblot analysis showed that expression of GLT1 (glutamate transporter subtype 1) was identified to be upregulated in synaptosomes but not in total tissues, suggesting a redistribution of glutamate transporter expression. Moreover, the increase in glutamate uptake was reproduced in cultured neurons during morphine withdrawal, and the increase of uptake in neurons could be blocked by dihydrokainate, a specific inhibitor of GLT1. Cell surface biotinylation and immunoblot analysis showed that morphine withdrawal produced an increase in GLT1 expression rather than EAAC1 (excitatory amino acids carrier 1), a neuronal subtype, at the cultured neuronal cell surface, whereas no significant change was observed in that of cultured astrocytes. Electron microscopy also revealed that GLT1 expression was markedly increased in the nerve terminals of hippocampus and associated with the plasma membrane in vivo. These results suggest that GLT1 in hippocampal neurons can be induced to translocate to the nerve terminals and express on the cell surface during morphine withdrawal. The translocation of GLT1 at synapses during morphine withdrawal provides a neuronal mechanism for modulation of excitatory neurotransmission during opiate abuse.
Xu
Nan-Jie
NJ
Laboratory of Molecular Cell Biology, Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, Shanghai 200031, China.
Bao
Lan
L
Fan
Hua-Ping
HP
Bao
Guo-Bin
GB
Pu
Lu
L
Lu
Ying-Jin
YJ
Wu
Chun-Fu
CF
Zhang
Xu
X
Pei
Gang
G
D027322:Amino Acid Transport System X-AG / Q000378:metabolism; D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D027342:Excitatory Amino Acid Transporter 2 / Q000235:genetics / Q000378:metabolism*; D050580:Excitatory Amino Acid Transporter 3; D050491:Glutamate Plasma Membrane Transport Proteins; D018698:Glutamic Acid / Q000493:pharmacokinetics*; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism*; D008297:Male; D009020:Morphine / Q000009:adverse effects*; D009021:Morphine Dependence / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D017729:Presynaptic Terminals / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013375:Substance Withdrawal Syndrome / Q000378:metabolism*; D027981:Symporters / Q000378:metabolism; D013569:Synapses / Q000378:metabolism*; D013574:Synaptosomes / Q000737:chemistry / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects
D027322:Amino Acid Transport System X-AG; D027342:Excitatory Amino Acid Transporter 2; D050580:Excitatory Amino Acid Transporter 3; D050491:Glutamate Plasma Membrane Transport Proteins; D012333:RNA, Messenger; C493398:Slc1a1 protein, rat; D027981:Symporters; D018698:Glutamic Acid; D009020:Morphine