The Journal of Neuroscience, April 1, 1999, 19(7):2580-2588
Optical Detection of Synaptically Induced Glutamate Transport in
Hippocampal Slices
Satoshi
Kojima1,
Takeshi
Nakamura1,
Takahisa
Nidaira3,
Kyoko
Nakamura2,
Noriko
Ooashi2,
Etsuro
Ito1,
Kei
Watase4,
Kohichi
Tanaka4,
Keiji
Wada4,
Yoshihisa
Kudo2, and
Hiroyoshi
Miyakawa2
1 Division of Biological Sciences, Graduate School of
Science, Hokkaido University, Sapporo 060-0810, Japan,
2 Laboratory of Cellular Neurobiology, Tokyo University of
Pharmacy and Life Science, Tokyo 192-03, Japan, 3 Hamamatsu
Photonics K.K., Hamamatsu 812, Japan, and
4 Department of Degenerative Neurological Diseases,
National Institute of Neuroscience, National Center of Neurology and
Psychiatry, Kodaira, Tokyo 187-8502, Japan
Although it has long been believed that glial cells play a major
role in transmitter uptake at synapses in the CNS, the relative contribution of glial and neuronal cells to reuptake of synaptically released glutamate has been unclear. Recent identification of the
diverse glutamate transporter subtypes provides an opportunity to
examine this issue. To monitor glutamate transporter activity, we
optically detected synaptically induced changes of membrane potential
from hippocampal CA1 field in slice preparations using a
voltage-sensitive dye, RH155. In the presence of ionotropic glutamate-receptor blockers, synaptic inputs gave rise to a slow depolarizing response (SDR) in the dendritic field. The amplitude of
SDR correlated well with presynaptic activities, suggesting that it was
related to transmitter release. The SDR was found to be caused by the
activities of glutamate transporters because it was not affected by
blockers for GABAA, nACh,
5-HT3, P2X, or metabotropic glutamate receptors but was greatly reduced by
dihydrokainate (DHK), a specific blocker for GLT-1 transporter,
and by D,L-threo-
-hydroxyaspartate (THA), a blocker for
EAAC, GLAST, and GLT-1 transporters. When SDR was
detected with RH482 dye, which stains both glial and neuronal cells, 1 mM DHK and 1 mM THA were equally effective in
suppressing SDR. The SDR was very small in GLT-1 knockout mice but was
maintained in gerbil hippocampi in which postsynaptic neurons were
absent because of ischemia. Because GLT-1 transporters are exclusively expressed in astrocytes, our results provide direct evidence that astrocytes play the dominant role in sequestering synaptically released glutamate.
Key words:
glutamate transporter; glutamate uptake; voltage-sensitive dye; astrocytes; hippocampus; brain slice
Copyright © 1999 Society for Neuroscience 0270-6474/99/1972580-09$05.00/0
Previous Article | Next Article
