Glial glutamate transporters maintain one-to-one relationship at the climbing fiber-Purkinje cell synapse by preventing glutamate spillover.
A glial glutamate transporter, GLAST, is expressed abundantly in Bergmann glia and plays a major role in glutamate uptake at the excitatory synapses in cerebellar Purkinje cells (PCs). It has been reported that a higher percentage of PCs in GLAST-deficient mice are multiply innervated by climbing fibers (CFs) than in the wild-type (WT) mice, and that CF-mediated EPSCs with small amplitude and slow rise time, designated as atypical slow CF-EPSCs, are observed in these mice. To clarify the mechanism(s) underlying the generation of these atypical CF-EPSCs, we used (2S,3S)-3-[3-(4-methoxybenzoylamino)benzyloxy]aspartate (PMB-TBOA), an inhibitor of glial glutamate transporters. After the application of PMB-TBOA, slow-rising CF-EPSCs were newly detected in WT mice, and their rise and decay kinetics were different from those of conventional fast-rising CF-EPSCs but similar to those of atypical CF-EPSCs in GLAST-deficient mice. Furthermore, both slow-rising CF-EPSCs in the presence of PMB-TBOA in WT mice and atypical CF-EPSCs in GLAST-deficient mice showed much greater paired-pulse depression compared with fast-rising CF-EPSCs. In addition, both of them were more markedly inhibited by gamma-d-glutamyl-glycine, a low-affinity competitive antagonist of AMPA receptors. These results indicated that both of these types of EPSCs were mediated by a low concentration of glutamate released from neighboring CFs. Based on all of these findings, we suggest that glial transporters prevent glutamate released from a single CF from spilling over to neighboring PCs other than the synaptically connected PC, and play an essential role in the maintenance of the functional one-to-one relationship between CFs and PCs.
Takayasu
Yukihiro
Y
Department of Neurophysiology, Gunma University Graduate School of Medicine, Maebashi, Gunma, 371-8511, Japan. takayasu@showa.gunma-u.ac.jp
Iino
Masae
M
Shimamoto
Keiko
K
Tanaka
Kohichi
K
Ozawa
Seiji
S
D000818:Animals; D000831:Animals, Newborn; D001224:Aspartic Acid / Q000494:pharmacology; D001581:Benzothiadiazines / Q000494:pharmacology; D002531:Cerebellum / Q000166:cytology; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D027341:Excitatory Amino Acid Transporter 1 / Q000172:deficiency / Q000502:physiology*; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D018698:Glutamic Acid / Q000378:metabolism*; D066298:In Vitro Techniques; D008689:Methacrylates / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009412:Nerve Fibers / Q000502:physiology*; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D010767:Phosphorylcholine / Q000031:analogs & derivatives / Q000494:pharmacology; D011689:Purkinje Cells / Q000502:physiology*; D013569:Synapses / Q000502:physiology*
D001581:Benzothiadiazines; D018690:Excitatory Amino Acid Agonists; D027341:Excitatory Amino Acid Transporter 1; D008689:Methacrylates; C120673:benzyloxyaspartate; D010767:Phosphorylcholine; C079200:poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate); D001224:Aspartic Acid; D018698:Glutamic Acid; C004639:cyclothiazide